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2011 Volume 27 Issue 10
2011, 27(10):
Abstract:
2011, 27(10): 2251-2254
doi: 10.3866/PKU.WHXB20111015
Abstract:
In this communication, we report a novel CoPy/C catalyst for the oxygen reduction reaction (ORR) in alkaline electrolyte using cobalt sulfate heptahydrate (CoSO4·7H2O) and pyridine (Py) as the Co and N precursors supported on Vulcan XC-72R, followed by heat treatment in an inert atmosphere. Electrochemical performances were evaluated using cyclic voltammograms (CVs) and rotating disk electrode (RDE) technique in terms of its ORR activity as a function of Co content in the catalyst synthesis. Results show that the presence of Co in the CoPy/C catalyst greatly affects the formation of ORR catalytic active sites and that the best performing catalyst is 10%Co%30Py/C, which was synthesized at 800°C. In 3.0 mol·L-1 KOH, 10%Co30%Py/C (in O2) produces an obvious ORR current with an on-set potential at 0.014 V. Compared with the 40% Py/C the on-set potential of the 10% Co30% Py/C for oxygen reduction shifted positively by 71 mV (versus RHE (reversible hydrogen electrode)) and a well-defined limiting current plateau was achieved. Therefore, a maximum current density of 1.0 mA·cm-2 was obtained at -0.16 V with a half-wave potential of -0.07 V. Transmission electron microscopy (TEM) measurements show that the nanoparticles with a diameter of 20 nm are uniformly dispersed on Vulcan carbon (Vulcan XC-72R).
In this communication, we report a novel CoPy/C catalyst for the oxygen reduction reaction (ORR) in alkaline electrolyte using cobalt sulfate heptahydrate (CoSO4·7H2O) and pyridine (Py) as the Co and N precursors supported on Vulcan XC-72R, followed by heat treatment in an inert atmosphere. Electrochemical performances were evaluated using cyclic voltammograms (CVs) and rotating disk electrode (RDE) technique in terms of its ORR activity as a function of Co content in the catalyst synthesis. Results show that the presence of Co in the CoPy/C catalyst greatly affects the formation of ORR catalytic active sites and that the best performing catalyst is 10%Co%30Py/C, which was synthesized at 800°C. In 3.0 mol·L-1 KOH, 10%Co30%Py/C (in O2) produces an obvious ORR current with an on-set potential at 0.014 V. Compared with the 40% Py/C the on-set potential of the 10% Co30% Py/C for oxygen reduction shifted positively by 71 mV (versus RHE (reversible hydrogen electrode)) and a well-defined limiting current plateau was achieved. Therefore, a maximum current density of 1.0 mA·cm-2 was obtained at -0.16 V with a half-wave potential of -0.07 V. Transmission electron microscopy (TEM) measurements show that the nanoparticles with a diameter of 20 nm are uniformly dispersed on Vulcan carbon (Vulcan XC-72R).
2011, 27(10): 2255-2268
doi: 10.3866/PKU.WHXB20110901
Abstract:
Counter electrode is one of the important parts of dye-sensitized solar cells (DSSC). Improving the performance of a counter electrode is an effective approach to enhance the energy conversion efficiency and reduce the cost of DSSC. In this paper, recent progresses in the study of various counter electrodes for use in DSSC are reviewed. We present researches about different counter electrodes including metals such as platinum, ld and nickel, various nanostructured carbon materials, and conductive polymers. Platinum counter electrodes give the best performance but their high cost restricts the industrialization of DSSC. More attention is being paid to novel materials such as different nanostructured carbon materials, conductive polymers and their composite counter electrodes because of their low cost and high activity.
Counter electrode is one of the important parts of dye-sensitized solar cells (DSSC). Improving the performance of a counter electrode is an effective approach to enhance the energy conversion efficiency and reduce the cost of DSSC. In this paper, recent progresses in the study of various counter electrodes for use in DSSC are reviewed. We present researches about different counter electrodes including metals such as platinum, ld and nickel, various nanostructured carbon materials, and conductive polymers. Platinum counter electrodes give the best performance but their high cost restricts the industrialization of DSSC. More attention is being paid to novel materials such as different nanostructured carbon materials, conductive polymers and their composite counter electrodes because of their low cost and high activity.
2011, 27(10): 2269-2274
doi: 10.3866/PKU.WHXB20110908
Abstract:
The solvothermal reactions of Sr(NO3)2 with 1,4-benzenedicarboxylic acid (BDC) in a mixture of H2O/N,N'-dimethylformamide (DMF) resulted in a novel coordination polymer, [Sr(BDC) (H2O)] (1), which was characterized by single crystal and variable temperature powder X-ray diffraction (VTPXRD), elemental analysis, infra-red (IR) spectroscopy, and thermogravimetric-mass spectrometric (TG-MS) analysis. Compound 1 crystallizes in the orthorhombic space group Pbca with a=1.1854(2) nm, b=0.7122 (1) nm, and c=2.0031(4) nm. It is a three-dimensional (3D) framework consisting of zigzag chains that are formed by face-shared SrO8 square antiprisms and bridging BDC ligands. TG-MS and VTPXRD studies revealed that the framework of compound 1 exhibited a high thermal stability.
The solvothermal reactions of Sr(NO3)2 with 1,4-benzenedicarboxylic acid (BDC) in a mixture of H2O/N,N'-dimethylformamide (DMF) resulted in a novel coordination polymer, [Sr(BDC) (H2O)] (1), which was characterized by single crystal and variable temperature powder X-ray diffraction (VTPXRD), elemental analysis, infra-red (IR) spectroscopy, and thermogravimetric-mass spectrometric (TG-MS) analysis. Compound 1 crystallizes in the orthorhombic space group Pbca with a=1.1854(2) nm, b=0.7122 (1) nm, and c=2.0031(4) nm. It is a three-dimensional (3D) framework consisting of zigzag chains that are formed by face-shared SrO8 square antiprisms and bridging BDC ligands. TG-MS and VTPXRD studies revealed that the framework of compound 1 exhibited a high thermal stability.
2011, 27(10): 2275-2281
doi: 10.3866/PKU.WHXB20110912
Abstract:
The heterogeneous reaction of carbonyl sulfide (COS) on hematite particles in the presence of nitrate was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). For sodium nitrate-containing samples, the hematite sample containing NaNO3 with mass fraction of 4% gave the highest reaction rate, which was about 5 times higher than that of hematite. For the particles containing nitrate at the same mass fraction (24%) the reactivity in descending order was α-Fe2O3/KNO3, α-Fe2O3/NaNO3, α-Fe2O3/NH4NO3 and α-Fe2O3. No uptake of COS was observed for the pure NaNO3, KNO3 and NH4NO3 samples. These results indicate that the added nitrate increased the COS conversion ability of α-Fe2O3 particles.
The heterogeneous reaction of carbonyl sulfide (COS) on hematite particles in the presence of nitrate was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). For sodium nitrate-containing samples, the hematite sample containing NaNO3 with mass fraction of 4% gave the highest reaction rate, which was about 5 times higher than that of hematite. For the particles containing nitrate at the same mass fraction (24%) the reactivity in descending order was α-Fe2O3/KNO3, α-Fe2O3/NaNO3, α-Fe2O3/NH4NO3 and α-Fe2O3. No uptake of COS was observed for the pure NaNO3, KNO3 and NH4NO3 samples. These results indicate that the added nitrate increased the COS conversion ability of α-Fe2O3 particles.
2011, 27(10): 2282-2290
doi: 10.3866/PKU.WHXB20111012
Abstract:
The equilibrium geometries, binding energies and aromaticities of (1,3,5-C3P3H3)M and (1,3, 5-C3P3H3)2M (M=Ti, V, Cr) were calculated by density function theory. The results indicate that the ground states of (1,3,5-C3P3H3)M and (1,3,5-C3P3H3)2M have C3v and D3h symmetries, respectively. The main interactions between the ligands and metal are covalent interactions featuring three types of interactions represented as σ, π and δ between the ligands and the metal. The dissociation method of the ligands and the metal in sandwich V complexes is different from that of Ti and Cr complexes, i.e., the former consists of two steps and the latter consists of one step. The first dissociation energy of (1,3,5-C3P3H3)2Cr is the largest and so it is the most stable one. These complexes have central, inner and outer aromaticities and the central-aromaticities of the complexes are stronger than that of (1,3,5-C3P3H3). The contributions of aromaticities is dominated by π bonds and the lone pair electronics of the metal atom. The inner-aromaticities of the complexes increase in the following order: Ti, V, Cr, and they are evidently stronger than the outer-aromaticities. Compared with (1,3,5-C3P3H3)Ti (C3v, 1A1) the distortion of the ligands for the high spin multiplicity of half-sandwich (1,3,5-C3P3H3)Ti (C3, 5A1) is larger and more stable. The central and inner aromaticities in the C plane of the high spin multiplicity half-sandwich (1,3,5-C3P3H3)Ti (C3, 5A1) are stronger than that of (1,3,5-C3P3H3)Ti (C3v, 1A1), but the central aromaticity in the P plane is weaker.
The equilibrium geometries, binding energies and aromaticities of (1,3,5-C3P3H3)M and (1,3, 5-C3P3H3)2M (M=Ti, V, Cr) were calculated by density function theory. The results indicate that the ground states of (1,3,5-C3P3H3)M and (1,3,5-C3P3H3)2M have C3v and D3h symmetries, respectively. The main interactions between the ligands and metal are covalent interactions featuring three types of interactions represented as σ, π and δ between the ligands and the metal. The dissociation method of the ligands and the metal in sandwich V complexes is different from that of Ti and Cr complexes, i.e., the former consists of two steps and the latter consists of one step. The first dissociation energy of (1,3,5-C3P3H3)2Cr is the largest and so it is the most stable one. These complexes have central, inner and outer aromaticities and the central-aromaticities of the complexes are stronger than that of (1,3,5-C3P3H3). The contributions of aromaticities is dominated by π bonds and the lone pair electronics of the metal atom. The inner-aromaticities of the complexes increase in the following order: Ti, V, Cr, and they are evidently stronger than the outer-aromaticities. Compared with (1,3,5-C3P3H3)Ti (C3v, 1A1) the distortion of the ligands for the high spin multiplicity of half-sandwich (1,3,5-C3P3H3)Ti (C3, 5A1) is larger and more stable. The central and inner aromaticities in the C plane of the high spin multiplicity half-sandwich (1,3,5-C3P3H3)Ti (C3, 5A1) are stronger than that of (1,3,5-C3P3H3)Ti (C3v, 1A1), but the central aromaticity in the P plane is weaker.
2011, 27(10): 2291-2296
doi: 10.3866/PKU.WHXB20111005
Abstract:
The interaction between the tea polyphenols derivative (-)-epigallocatechin-3-gallate (EGCG) and Zn(II) was investigated by ultraviolet visible (UV-Vis) spectroscopy and liquid-state 1H nuclear magnetic resonance (NMR). In addition, density functional theory (DFT)-based UV and chemical shifts were calculated to view insight into the complex structure and property. The main conformer of EGCG is an aromatic B-ring in an e-bond (equatorial bond) and an aromatic D-ring in an a-bond (axial bond) and these are linked to the C-ring. In addition, the Zn(II) ion can coordinate with the phenolic hydroxyl groups in the D-ring and form a steady tetrahedral Zn(II)-EGCG complex in a 1:1 molar ratio.
The interaction between the tea polyphenols derivative (-)-epigallocatechin-3-gallate (EGCG) and Zn(II) was investigated by ultraviolet visible (UV-Vis) spectroscopy and liquid-state 1H nuclear magnetic resonance (NMR). In addition, density functional theory (DFT)-based UV and chemical shifts were calculated to view insight into the complex structure and property. The main conformer of EGCG is an aromatic B-ring in an e-bond (equatorial bond) and an aromatic D-ring in an a-bond (axial bond) and these are linked to the C-ring. In addition, the Zn(II) ion can coordinate with the phenolic hydroxyl groups in the D-ring and form a steady tetrahedral Zn(II)-EGCG complex in a 1:1 molar ratio.
2011, 27(10): 2297-2302
doi: 10.3866/PKU.WHXB20110938
Abstract:
The geometrical structures, electronic spectra, and second-order nonlinear optical (NLO) properties of eight bis(imino)pyridine complexes were calculated and analyzed using density functional theory (DFT) B3LYP method. The results indicate that both the ancillary ligands and the central metal ions affect the polarizabilities of the complexes slightly and the ancillary ligands also influence the second-order NLO coefficients slightly. With an increase in the number of d-orbital electrons, a slight decrease in second-order NLO coefficients (β) was observed. An increase in the metal ion radius within the same family led to an increase in the βtot value of these complexes. When the central metal ion acts as an electronic donor, the transition energy relative to the maximal oscillator strength is smaller and its corresponding βtot value is larger.
The geometrical structures, electronic spectra, and second-order nonlinear optical (NLO) properties of eight bis(imino)pyridine complexes were calculated and analyzed using density functional theory (DFT) B3LYP method. The results indicate that both the ancillary ligands and the central metal ions affect the polarizabilities of the complexes slightly and the ancillary ligands also influence the second-order NLO coefficients slightly. With an increase in the number of d-orbital electrons, a slight decrease in second-order NLO coefficients (β) was observed. An increase in the metal ion radius within the same family led to an increase in the βtot value of these complexes. When the central metal ion acts as an electronic donor, the transition energy relative to the maximal oscillator strength is smaller and its corresponding βtot value is larger.
2011, 27(10): 2303-2310
doi: 10.3866/PKU.WHXB20111013
Abstract:
An extensive series of pyrazole aluminum compounds containing an Al2N4 center as a pseudoconjugated system were theoretically investigated for their one-photon absorption and two-photon absorption (OPA and TPA) properties by density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods. The results indicate that pyrazole aluminum compounds are od TPA materials and that the TPA maximal absorption cross-section (δmax) can reach 2860.1 GM (1 GM=10-50 cm4·s·photon-1). By incorporating electron-acceptors in the central core, a π-conjugated bridge and terminal groups, the OPA and TPA properties can be modulated. This research provides strategies for the enhancement of molecular TPA in the target region. The origin of the large δmax of some of the studied molecules was determined using a three-level energy model. We conclude that an increase in the intramolecular charge transfer can enhance δmax. Moreover, the pyrazole aluminum compounds behave in a similar manner to pyrazabole chromophores in terms of linear optical, and TPA properties and they possess an increased δmax to some extent.
An extensive series of pyrazole aluminum compounds containing an Al2N4 center as a pseudoconjugated system were theoretically investigated for their one-photon absorption and two-photon absorption (OPA and TPA) properties by density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods. The results indicate that pyrazole aluminum compounds are od TPA materials and that the TPA maximal absorption cross-section (δmax) can reach 2860.1 GM (1 GM=10-50 cm4·s·photon-1). By incorporating electron-acceptors in the central core, a π-conjugated bridge and terminal groups, the OPA and TPA properties can be modulated. This research provides strategies for the enhancement of molecular TPA in the target region. The origin of the large δmax of some of the studied molecules was determined using a three-level energy model. We conclude that an increase in the intramolecular charge transfer can enhance δmax. Moreover, the pyrazole aluminum compounds behave in a similar manner to pyrazabole chromophores in terms of linear optical, and TPA properties and they possess an increased δmax to some extent.
2011, 27(10): 2311-2318
doi: 10.3866/PKU.WHXB20110920
Abstract:
Periodic density functional theory calculations using pseudopotential plane-waves were performed systematically to investigate the surface relaxation of different Al2O3 surfaces including α-Al2O3 (0001) and γ-Al2O3 (110), (110C), and (110D) surfaces, as well as the adsorption of CO molecules on these surfaces. Our calculated results indicate that the CO molecules tend to adsorb perpendicularly on the Al atoms at the surface through carbon atoms and interactions were observed between the CO 5σ state and the substrate. After adsorption, some electrons transferred from the CO molecules to the surface and accordingly the surface work functions of the different Al2O3 surfaces decreased. The adsorption results in small perturbations of the C ― O bond length and the corresponding C ― O stretching frequency was blue-shifted in all the adsorption structures. By examining the results of the CO adsorption on the different surfaces, it is clear that CO can be used as an effective probe molecule to distinguish the active adsorption sites on the different Al2O3 surfaces.
Periodic density functional theory calculations using pseudopotential plane-waves were performed systematically to investigate the surface relaxation of different Al2O3 surfaces including α-Al2O3 (0001) and γ-Al2O3 (110), (110C), and (110D) surfaces, as well as the adsorption of CO molecules on these surfaces. Our calculated results indicate that the CO molecules tend to adsorb perpendicularly on the Al atoms at the surface through carbon atoms and interactions were observed between the CO 5σ state and the substrate. After adsorption, some electrons transferred from the CO molecules to the surface and accordingly the surface work functions of the different Al2O3 surfaces decreased. The adsorption results in small perturbations of the C ― O bond length and the corresponding C ― O stretching frequency was blue-shifted in all the adsorption structures. By examining the results of the CO adsorption on the different surfaces, it is clear that CO can be used as an effective probe molecule to distinguish the active adsorption sites on the different Al2O3 surfaces.
2011, 27(10): 2319-2325
doi: 10.3866/PKU.WHXB20110936
Abstract:
The adsorption and dissociation of CO2 on the α-U(001) surface at 0.25 monolayer (ML) coverage was studied using density functional theory (DFT) within the generalized gradient approximation (GGA). Stable structures and corresponding energies of CO2 adsorbed on the α-U(001) surface were obtained while the transition state and corresponding energy barrier for CO2 dissociation was determined. We discussed the interaction mechanism between CO2 and the α-U(001) surface. We found that CO2 strongly chemisorbed onto the α-U(001) surface in a multi-bonding manner with adsorption energies of 1.24-1.67 eV and the degree of C―O bond activation depended on the degree of electron transfer from surface to the adsorbed CO. The interaction between the U atoms and the CO2 molecules mainly comes from the population of the CO2 2πu lowest unoccupied molecular orbital (LUMO) by U electrons with CO2 2πu/1πg/3σu-U 6d orbital hybridization. The dissociative adsorption energies for the CO2 adsorbed on the hollow1 and hollow2 sites with three C―U bonds and six O―U bonds (H1-C3O6 and H2-C3O6 ) are 3.15 and 3.13 eV, respectively. The corresponding dissociation barriers are 0.26 and 0.36 eV, which indicates that the dissociation of adsorbed CO2 into CO and O occurs easily.
The adsorption and dissociation of CO2 on the α-U(001) surface at 0.25 monolayer (ML) coverage was studied using density functional theory (DFT) within the generalized gradient approximation (GGA). Stable structures and corresponding energies of CO2 adsorbed on the α-U(001) surface were obtained while the transition state and corresponding energy barrier for CO2 dissociation was determined. We discussed the interaction mechanism between CO2 and the α-U(001) surface. We found that CO2 strongly chemisorbed onto the α-U(001) surface in a multi-bonding manner with adsorption energies of 1.24-1.67 eV and the degree of C―O bond activation depended on the degree of electron transfer from surface to the adsorbed CO. The interaction between the U atoms and the CO2 molecules mainly comes from the population of the CO2 2πu lowest unoccupied molecular orbital (LUMO) by U electrons with CO2 2πu/1πg/3σu-U 6d orbital hybridization. The dissociative adsorption energies for the CO2 adsorbed on the hollow1 and hollow2 sites with three C―U bonds and six O―U bonds (H1-C3O6 and H2-C3O6 ) are 3.15 and 3.13 eV, respectively. The corresponding dissociation barriers are 0.26 and 0.36 eV, which indicates that the dissociation of adsorbed CO2 into CO and O occurs easily.
2011, 27(10): 2326-2332
doi: 10.3866/PKU.WHXB20111016
Abstract:
Based on spin-polarized density functional theory we studied the electronic structures, magnetic and optical properties of Ni-doped ZnO nanowires. The magnetic results show that three magnetic coupling states are present: ferromagnetic (FM), antiferromagnetic (AFM), and paramagnetic (PM) states for the six kinds of Ni-doped configurations. The calculated energy results indicate that antiferromagnetic coupling is more stable when Ni atoms substitute for Zn atoms in the ZnO nanowires on the outside surface along the [0001] direction. AFM coupling has a metallic nature. The FM results from the density of states show that the spin polarization phenomenon appears near the Fermi level and causes strong hybridization between Ni 3d and O 2p. Moreover, the magnetic moments mainly originate from the unpaired electrons of the Ni 3d orbitals and the electrons of the O 2p orbitals contribute a little to the magnetic moments. The coupling of FM has a half-metal nature. In addition, the optical properties indicate that the absorption peaks show a significant red shift and od emission in the far UV band while a blue shift is apparent for the near UV band (380 nm). These results indicate that the Ni-doped ZnO nanowires are promising magneto-optical electronic materials and they can be used for nanoscale spintronics device materials.
Based on spin-polarized density functional theory we studied the electronic structures, magnetic and optical properties of Ni-doped ZnO nanowires. The magnetic results show that three magnetic coupling states are present: ferromagnetic (FM), antiferromagnetic (AFM), and paramagnetic (PM) states for the six kinds of Ni-doped configurations. The calculated energy results indicate that antiferromagnetic coupling is more stable when Ni atoms substitute for Zn atoms in the ZnO nanowires on the outside surface along the [0001] direction. AFM coupling has a metallic nature. The FM results from the density of states show that the spin polarization phenomenon appears near the Fermi level and causes strong hybridization between Ni 3d and O 2p. Moreover, the magnetic moments mainly originate from the unpaired electrons of the Ni 3d orbitals and the electrons of the O 2p orbitals contribute a little to the magnetic moments. The coupling of FM has a half-metal nature. In addition, the optical properties indicate that the absorption peaks show a significant red shift and od emission in the far UV band while a blue shift is apparent for the near UV band (380 nm). These results indicate that the Ni-doped ZnO nanowires are promising magneto-optical electronic materials and they can be used for nanoscale spintronics device materials.
2011, 27(10): 2333-2339
doi: 10.3866/PKU.WHXB20111022
Abstract:
A freestanding film composed of graphene (GN) sheets and polyaniline (PANI) nanofibres was fabricated by reducing a graphite oxide ( )/PANI precursor that was prepared by flow-directed assembly from a complex dispersion of and PANI. This was followed by reoxidation and redoping of the reduced PANI in the composite to restore the conducting PANI structure. A scanning electron microscope (SEM) image indicates that the GN/PANI film is a layered structure with PANI nanofibres uniformly sandwiched between the GN sheets. In the composite film, the PANI nanofibres can increase the basal spacing between GN sheets. Therefore, electrolyte ions have better accessibility to the GN surfaces. The GN sheets can act as current collector to decrease the inner resistance of the electrode, which is convenient for electronic and ionic transportation during the redox process of PANI. The electrochemical properties of the freestanding GN/PANI film were estimated by cyclic voltammetry and galvanostatic charge-discharge in 1 mol·L-1 HCl electrolyte. Electrochemical analysis demonstrates that the as-prepared GN/PANI film has od capacitive behavior. The specific capacitance was 495 F·g-1 at a current density of 0.1 A·g-1 and the capacitance was 313 F·g-1 even at a current density of 3 A·g-1. After 2000 cycles, the capacitance of the GN/PANI film decreases 10% of its initial capacitance, which demonstrates that the GN/PANI electrode has od cycle stability.
A freestanding film composed of graphene (GN) sheets and polyaniline (PANI) nanofibres was fabricated by reducing a graphite oxide ( )/PANI precursor that was prepared by flow-directed assembly from a complex dispersion of and PANI. This was followed by reoxidation and redoping of the reduced PANI in the composite to restore the conducting PANI structure. A scanning electron microscope (SEM) image indicates that the GN/PANI film is a layered structure with PANI nanofibres uniformly sandwiched between the GN sheets. In the composite film, the PANI nanofibres can increase the basal spacing between GN sheets. Therefore, electrolyte ions have better accessibility to the GN surfaces. The GN sheets can act as current collector to decrease the inner resistance of the electrode, which is convenient for electronic and ionic transportation during the redox process of PANI. The electrochemical properties of the freestanding GN/PANI film were estimated by cyclic voltammetry and galvanostatic charge-discharge in 1 mol·L-1 HCl electrolyte. Electrochemical analysis demonstrates that the as-prepared GN/PANI film has od capacitive behavior. The specific capacitance was 495 F·g-1 at a current density of 0.1 A·g-1 and the capacitance was 313 F·g-1 even at a current density of 3 A·g-1. After 2000 cycles, the capacitance of the GN/PANI film decreases 10% of its initial capacitance, which demonstrates that the GN/PANI electrode has od cycle stability.
2011, 27(10): 2340-2346
doi: 10.3866/PKU.WHXB20111002
Abstract:
Although higher specific capacitances have been achieved for manganese dioxide/multi-walled carbon nanotubes (MnO2/MWCNTs), the low conductivity of MnO2 is still the main obstacle in increasing its loading or film thickness. Another problem is that the cycling stability of MnO2/MWCNTs is much lower than that of activated carbon electrodes. Therefore, this new type of electrode material is still limited in application until now. In this paper, lanthanum doped MnO2/MWCNTs composites were prepared by an in situ redox method. The surface morphology and phase structure of the as-prepared samples were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectrometry. The electrochemical properties were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS). The La-doped MnO2 could be formed on the MWCNTs by the reduction of MnO4-. The resistance of the composite electrodes decreased because La doping increases the number of imperfections in the MnO2 lattice, which improves the electrical conductivity and the electrochemical activity of the electrode. La doping is, therefore, an effective way to overcome the intrinsic low electric conductivity of MnO2, which facilitates an increase in the loading or the film thickness of MnO2 without increasing electrode resistance. The major effect of La doping is a significant improvement in the charge/discharge cycling performance of a symmetric electrochemical supercapacitor with electrodes composed of MnO2/ MWCNTs. The specific capacitance of the composite electrodes was improved by La doping.
Although higher specific capacitances have been achieved for manganese dioxide/multi-walled carbon nanotubes (MnO2/MWCNTs), the low conductivity of MnO2 is still the main obstacle in increasing its loading or film thickness. Another problem is that the cycling stability of MnO2/MWCNTs is much lower than that of activated carbon electrodes. Therefore, this new type of electrode material is still limited in application until now. In this paper, lanthanum doped MnO2/MWCNTs composites were prepared by an in situ redox method. The surface morphology and phase structure of the as-prepared samples were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectrometry. The electrochemical properties were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS). The La-doped MnO2 could be formed on the MWCNTs by the reduction of MnO4-. The resistance of the composite electrodes decreased because La doping increases the number of imperfections in the MnO2 lattice, which improves the electrical conductivity and the electrochemical activity of the electrode. La doping is, therefore, an effective way to overcome the intrinsic low electric conductivity of MnO2, which facilitates an increase in the loading or the film thickness of MnO2 without increasing electrode resistance. The major effect of La doping is a significant improvement in the charge/discharge cycling performance of a symmetric electrochemical supercapacitor with electrodes composed of MnO2/ MWCNTs. The specific capacitance of the composite electrodes was improved by La doping.
2011, 27(10): 2347-2352
doi: 10.3866/PKU.WHXB20110905
Abstract:
We investigated LiFePO4 particles that were prepared by a hydrothermal reaction at different ingredient temperatures. The precursors and final LiFePO4 products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and elemental analysis. The results show that ingredient temperature had a significant effect on the color and characteristics of the LiFePO4 precursors. High purity Li3PO4 was obtained and the formation of Fe(OH)3 in the precursors was inhibited by controlling the ingredient temperature carefully. In addition well-crystalline and free Fe3+ LiFePO4 samples were synthesized, which greatly increased the discharge capacity of the LiFePO4 cathode materials. At an ingredient temperature of 30 °C the discharge specific capacity of the as-prepared sample was found to be 156 mAh·g-1 at 0.1C rate, 151 mAh·g-1 at 0.5C rate and it remained 127 mAh·g-1 even at a rate of 10C while the cycling retention rate was 99% after 20 cycles.
We investigated LiFePO4 particles that were prepared by a hydrothermal reaction at different ingredient temperatures. The precursors and final LiFePO4 products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and elemental analysis. The results show that ingredient temperature had a significant effect on the color and characteristics of the LiFePO4 precursors. High purity Li3PO4 was obtained and the formation of Fe(OH)3 in the precursors was inhibited by controlling the ingredient temperature carefully. In addition well-crystalline and free Fe3+ LiFePO4 samples were synthesized, which greatly increased the discharge capacity of the LiFePO4 cathode materials. At an ingredient temperature of 30 °C the discharge specific capacity of the as-prepared sample was found to be 156 mAh·g-1 at 0.1C rate, 151 mAh·g-1 at 0.5C rate and it remained 127 mAh·g-1 even at a rate of 10C while the cycling retention rate was 99% after 20 cycles.
2011, 27(10): 2353-2359
doi: 10.3866/PKU.WHXB20111004
Abstract:
Single intercalation particles, mixed particles, homogeneous porous electrodes and nonhomogeneous, multilayered porous electrode models are proposed in this paper. Some peculiar features of impedance spectra were simulated using the above-mentioned models. The results reveal that the features of impedance spectra of the single intercalation particle and the mixed particles are the same and the features consist of lithium ion migration through the solid electrolyte interphase (SEI) film (RSEI‖CSEI semicircle), an electron and ion transfer process (Rct‖Cdl semicircle), and a finite-diffusion Warburg element. For the nonhomogeneous, multilayered porous electrodes model, a peculiar feature of impedance spectra is that a new arc appears in the Nyquist plot. A detailed analysis revealed that a different particle size distribution could lead to the appearance of a new arc and a different layer distribution (a thicker layer and a thinner layer), which could lead to a well-developed semicircle.
Single intercalation particles, mixed particles, homogeneous porous electrodes and nonhomogeneous, multilayered porous electrode models are proposed in this paper. Some peculiar features of impedance spectra were simulated using the above-mentioned models. The results reveal that the features of impedance spectra of the single intercalation particle and the mixed particles are the same and the features consist of lithium ion migration through the solid electrolyte interphase (SEI) film (RSEI‖CSEI semicircle), an electron and ion transfer process (Rct‖Cdl semicircle), and a finite-diffusion Warburg element. For the nonhomogeneous, multilayered porous electrodes model, a peculiar feature of impedance spectra is that a new arc appears in the Nyquist plot. A detailed analysis revealed that a different particle size distribution could lead to the appearance of a new arc and a different layer distribution (a thicker layer and a thinner layer), which could lead to a well-developed semicircle.
2011, 27(10): 2360-2366
doi: 10.3866/PKU.WHXB20111023
Abstract:
We studied the influence of temperature on the conductivity of a polysulfide electrolyte and the photovoltaic performance of quantum dot sensitized solar cells by electrochemical methods. The results indicate that the conductivity of the electrolyte increases and the diffusion impedance of the polysulfide ions in the electrolyte decreases with an increase in the temperature. Moreover, the photoelectric conversion efficiency of the quantum dot sensitized solar cells decreases when the temperature increases. This phenomenon is mainly caused by a more serious back reaction and the desorption of quantum dots at higher temperatures.
We studied the influence of temperature on the conductivity of a polysulfide electrolyte and the photovoltaic performance of quantum dot sensitized solar cells by electrochemical methods. The results indicate that the conductivity of the electrolyte increases and the diffusion impedance of the polysulfide ions in the electrolyte decreases with an increase in the temperature. Moreover, the photoelectric conversion efficiency of the quantum dot sensitized solar cells decreases when the temperature increases. This phenomenon is mainly caused by a more serious back reaction and the desorption of quantum dots at higher temperatures.
2011, 27(10): 2367-2372
doi: 10.3866/PKU.WHXB20111011
Abstract:
The deposition of a thin insulating layer around the TiO2 film to form a"core-shell"structure is a promising approach for the modification of electrodes. This is currently one of the focuses in the dye sensitized solar cell (DSC), which has received much attention for development of low-cost and simple assembly technology. In this paper, yttrium oxide (Y2O3), as a shell material, was coated onto the TiO2 film by a dipping method. The Y2O3/TiO2"core-shell"electrode was then used to fabricate the DSC. The composition and structure of the Y2O3/TiO2 film were measured. The effects of the Y2O3 layer on the flat-band potential, electron recombination, and the characteristics of DSC were investigated in detail. Results suggest that the flat-band potential of the film shifted negatively when TiO2 was coated with Y2O3 while electron recombination loss at the TiO2/electrolyte/dye interface was effectively reduced. As a result, the"core-shell"electrode provided a longer electron lifetime value compared with the uncoated TiO2 electrode and ultimately the open-circuit voltage increased dramatically. Studies show that the cell performance can be improved by the introduction of a proper amount of Y2O3 to the DSC.
The deposition of a thin insulating layer around the TiO2 film to form a"core-shell"structure is a promising approach for the modification of electrodes. This is currently one of the focuses in the dye sensitized solar cell (DSC), which has received much attention for development of low-cost and simple assembly technology. In this paper, yttrium oxide (Y2O3), as a shell material, was coated onto the TiO2 film by a dipping method. The Y2O3/TiO2"core-shell"electrode was then used to fabricate the DSC. The composition and structure of the Y2O3/TiO2 film were measured. The effects of the Y2O3 layer on the flat-band potential, electron recombination, and the characteristics of DSC were investigated in detail. Results suggest that the flat-band potential of the film shifted negatively when TiO2 was coated with Y2O3 while electron recombination loss at the TiO2/electrolyte/dye interface was effectively reduced. As a result, the"core-shell"electrode provided a longer electron lifetime value compared with the uncoated TiO2 electrode and ultimately the open-circuit voltage increased dramatically. Studies show that the cell performance can be improved by the introduction of a proper amount of Y2O3 to the DSC.
2011, 27(10): 2373-2378
doi: 10.3866/PKU.WHXB20111008
Abstract:
Pt hollow nanospheres with a particle diameter of 110 nm and a shell thickness of about 5 nm were synthesized in bulk using selenium colloids with a particle diameter of 100 nm as a template. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), energy dispersive X-ray spectrocopy (EDX), and scanning electron microscopy (SEM) were used to determine their morphologies and structures. The electrocatalytic activity of the Pt hollow nanospheres modifying glassy carbon electrode toward methanol oxidation was measured by using methanol as the probe molecule. We show that the multiporous Pt hollow nanospheres composited of atomic clusters have a uniform particle size, od dispersity, a stable structure, a big surface area and od mass transfer performance. Cyclic voltammetry (CV) showed that when the current density of methanol oxidation was 0.10 mA·cm-2 and upon positive scanning the methanol oxidation potential of the Pt hollow nanospheres was around 110 and 64 mV negative than that of the Pt solid nanoparticles and Pt black, respectively. Upon negative scanning the former species was about 51 and 13 mV negative than that of the latter two species, respectively. After 800 segments cyclic voltammetry scanning, upon positive scanning the peak current density of methanol oxidation on the Pt hollow nanospheres was found to be 13 and 15 times as high as that of the Pt solid nanoparticles and Pt black, respectively. Upon negative scanning the former species was about 19 and 38 times as high as that of the two latter species. Our experimental results show that the Pt hollow nanospheres have od electrocatalytic activity and stability toward methanol oxidation.
Pt hollow nanospheres with a particle diameter of 110 nm and a shell thickness of about 5 nm were synthesized in bulk using selenium colloids with a particle diameter of 100 nm as a template. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), energy dispersive X-ray spectrocopy (EDX), and scanning electron microscopy (SEM) were used to determine their morphologies and structures. The electrocatalytic activity of the Pt hollow nanospheres modifying glassy carbon electrode toward methanol oxidation was measured by using methanol as the probe molecule. We show that the multiporous Pt hollow nanospheres composited of atomic clusters have a uniform particle size, od dispersity, a stable structure, a big surface area and od mass transfer performance. Cyclic voltammetry (CV) showed that when the current density of methanol oxidation was 0.10 mA·cm-2 and upon positive scanning the methanol oxidation potential of the Pt hollow nanospheres was around 110 and 64 mV negative than that of the Pt solid nanoparticles and Pt black, respectively. Upon negative scanning the former species was about 51 and 13 mV negative than that of the latter two species, respectively. After 800 segments cyclic voltammetry scanning, upon positive scanning the peak current density of methanol oxidation on the Pt hollow nanospheres was found to be 13 and 15 times as high as that of the Pt solid nanoparticles and Pt black, respectively. Upon negative scanning the former species was about 19 and 38 times as high as that of the two latter species. Our experimental results show that the Pt hollow nanospheres have od electrocatalytic activity and stability toward methanol oxidation.
2011, 27(10): 2379-2384
doi: 10.3866/PKU.WHXB20110922
Abstract:
We prepared a low Pt loading core-shell structured catalyst PdRu@Pt/CNT (carbon nanotube) with a PdRu alloy as the core and platinum as the shell in addition to carbon nanotubes as supports in a two-stage precipitation-reduction approach. For the anodic oxidation of methanol the activity in terms of Pt loading increased by 70% compared with the lab-made Pt/CNT catalyst and the ratio of the forward current density (If) to the backward current density (Ib) was as high as 2, which is two times of that of Pt/ CNT, indicating that the dispersion and use of platinum effectively improves by covering the surface of the PdRu cores with platinum. Excellent tolerance towards the intermediates of the anodic oxidation of methanol may result from the interaction between the Pt shell and the PdRu core. The core-shell structure of the catalysts was revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM image showed that the active components are highly dispersed on the CNT with a particle size of 4.0 nm. The high platinum utilization and high performance as well as od tolerance toward poisons make the PdRu@Pt/CNT catalyst a promising low-Pt catalyst for low temperature fuel cell applications.
We prepared a low Pt loading core-shell structured catalyst PdRu@Pt/CNT (carbon nanotube) with a PdRu alloy as the core and platinum as the shell in addition to carbon nanotubes as supports in a two-stage precipitation-reduction approach. For the anodic oxidation of methanol the activity in terms of Pt loading increased by 70% compared with the lab-made Pt/CNT catalyst and the ratio of the forward current density (If) to the backward current density (Ib) was as high as 2, which is two times of that of Pt/ CNT, indicating that the dispersion and use of platinum effectively improves by covering the surface of the PdRu cores with platinum. Excellent tolerance towards the intermediates of the anodic oxidation of methanol may result from the interaction between the Pt shell and the PdRu core. The core-shell structure of the catalysts was revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM image showed that the active components are highly dispersed on the CNT with a particle size of 4.0 nm. The high platinum utilization and high performance as well as od tolerance toward poisons make the PdRu@Pt/CNT catalyst a promising low-Pt catalyst for low temperature fuel cell applications.
2011, 27(10): 2385-2392
doi: 10.3866/PKU.WHXB20110931
Abstract:
Anodizing a AZ91D magnesium alloy in environmentally friendly borate-terephthalic acid (TPA) electrolyte was studied. The effect of TPA on the anodizing process and the properties of the resultant anodized film were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the anodizing process, the surface morphology, thickness, phase structure, and corrosion resistance of the anodized film were strongly dependent on the concentration of TPA. In the presence of adequate TPA, a moderate anodizing process was obtained. The current density of the anodizing process was reduced and excessive sparking in the anodizing process was obviously inhibited. In the presence of TPA, the quality of the anodized film improved. The film became more compact and smooth in structure. The thickness of the film decreased slightly. The interface between the anodized film and the magnesium substrate became indistinct indicating a better adhesion between them. The corrosion resistance of the anodized film was obviously enhanced. From these highly positive results, TPA can be used as an effective additive for the anodizing treatment of magnesium alloy. The proposed anodizing process is of importance to make the existing anodizing process 'greener' and to improve the quality of the anodized film.
Anodizing a AZ91D magnesium alloy in environmentally friendly borate-terephthalic acid (TPA) electrolyte was studied. The effect of TPA on the anodizing process and the properties of the resultant anodized film were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the anodizing process, the surface morphology, thickness, phase structure, and corrosion resistance of the anodized film were strongly dependent on the concentration of TPA. In the presence of adequate TPA, a moderate anodizing process was obtained. The current density of the anodizing process was reduced and excessive sparking in the anodizing process was obviously inhibited. In the presence of TPA, the quality of the anodized film improved. The film became more compact and smooth in structure. The thickness of the film decreased slightly. The interface between the anodized film and the magnesium substrate became indistinct indicating a better adhesion between them. The corrosion resistance of the anodized film was obviously enhanced. From these highly positive results, TPA can be used as an effective additive for the anodizing treatment of magnesium alloy. The proposed anodizing process is of importance to make the existing anodizing process 'greener' and to improve the quality of the anodized film.
2011, 27(10): 2393-2399
doi: 10.3866/PKU.WHXB20110926
Abstract:
The photoelectrochemical properties of a SrTiO3 film coated on an indium-tin oxide (ITO) conducting glass were investigated for the anticorrosion of 304 stainless steel (304SS) under solar light illumination. The SrTiO3 nanocrystal powders were synthesized using a sol-gel process in the absence and presence of the cetyltrimethyl ammonium bromide (CTAB) surfactant and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was showed that the as-synthesized SrTiO3 materials exhibit a single perovskite structure and the presence of CTAB leads to uniform particles with an average size of 90 nm. The UV-Vis diffuse reflectance analysis shows that both SrTiO3 films that were prepared in the absence and presence of CTAB surfactant absorbs strongly in the UV region with an absorption threshold edge near 380 nm while the SiTiO3 prepared in the presence of CTAB exhibited a stronger absorption in the UV region than those in the absence of CTAB. The photo-electrochemical anticorrosion effects of SrTiO3 on 304 stainless steel substrates in a 0.5 mol·L-1 NaCl solution were investigated using a 0.1 mol·L-1 NaOH and 0.2 mol·L-1 Na2S hole sacrifice electrolyte solution. Metallographic images of the 304 stainless steel before and after immersion in a 0.5 mol·L-1 NaCl+0.05 mol·L-1 HCl solution for 6 h demonstrates that the SrTiO3 film coated photoelectrode exhibits excellent photoelectrochemical anticorrosion performance on 304 stainless steel.
The photoelectrochemical properties of a SrTiO3 film coated on an indium-tin oxide (ITO) conducting glass were investigated for the anticorrosion of 304 stainless steel (304SS) under solar light illumination. The SrTiO3 nanocrystal powders were synthesized using a sol-gel process in the absence and presence of the cetyltrimethyl ammonium bromide (CTAB) surfactant and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was showed that the as-synthesized SrTiO3 materials exhibit a single perovskite structure and the presence of CTAB leads to uniform particles with an average size of 90 nm. The UV-Vis diffuse reflectance analysis shows that both SrTiO3 films that were prepared in the absence and presence of CTAB surfactant absorbs strongly in the UV region with an absorption threshold edge near 380 nm while the SiTiO3 prepared in the presence of CTAB exhibited a stronger absorption in the UV region than those in the absence of CTAB. The photo-electrochemical anticorrosion effects of SrTiO3 on 304 stainless steel substrates in a 0.5 mol·L-1 NaCl solution were investigated using a 0.1 mol·L-1 NaOH and 0.2 mol·L-1 Na2S hole sacrifice electrolyte solution. Metallographic images of the 304 stainless steel before and after immersion in a 0.5 mol·L-1 NaCl+0.05 mol·L-1 HCl solution for 6 h demonstrates that the SrTiO3 film coated photoelectrode exhibits excellent photoelectrochemical anticorrosion performance on 304 stainless steel.
2011, 27(10): 2400-2405
doi: 10.3866/PKU.WHXB20111003
Abstract:
The depletion potential between two colloid particles immersed in a hard-core Yukawa fluid was investigated by density functional theory for the depletion potential proposed by Roth, Evans, and Dietrich. An attempt was made to study the effects of several factors concerning the colloid particles and the solvent molecules on the depletion potential, which are the size ratio of the colloid particle to the solvent, the interaction between solvent molecules, the packing fraction of the solvent, and the interaction between the colloid particle and the solvent. By means of the depletion potential presented under various conditions, it is shown that the effects of these factors on the depletion potential are significant and this can provide some useful clues on regulating the interaction between colloid particles in related experiments.
The depletion potential between two colloid particles immersed in a hard-core Yukawa fluid was investigated by density functional theory for the depletion potential proposed by Roth, Evans, and Dietrich. An attempt was made to study the effects of several factors concerning the colloid particles and the solvent molecules on the depletion potential, which are the size ratio of the colloid particle to the solvent, the interaction between solvent molecules, the packing fraction of the solvent, and the interaction between the colloid particle and the solvent. By means of the depletion potential presented under various conditions, it is shown that the effects of these factors on the depletion potential are significant and this can provide some useful clues on regulating the interaction between colloid particles in related experiments.
2011, 27(10): 2406-2410
doi: 10.3866/PKU.WHXB20110929
Abstract:
Cobalt-doped titania (Co/TiO2) photocatalysts were synthesized by the polymerized complex method (PCM). The materials were characterized by thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), nitrogen adsorption-desorption, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the samples was evaluated by hydrogen evolution. The results show that anatase type titania exists in the materials and cobalt is evenly dispersed. The activity of the cobalt doped titania was found to be superior to that of pure titania. The maximum activity obtained at 0.3% Co/Ti molar ratio was nearly 6 times as high as that of pure titania. The amount of hydrogen produced was up to 2499 μmol. The doping mechanism of cobalt is discussed.
Cobalt-doped titania (Co/TiO2) photocatalysts were synthesized by the polymerized complex method (PCM). The materials were characterized by thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), nitrogen adsorption-desorption, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the samples was evaluated by hydrogen evolution. The results show that anatase type titania exists in the materials and cobalt is evenly dispersed. The activity of the cobalt doped titania was found to be superior to that of pure titania. The maximum activity obtained at 0.3% Co/Ti molar ratio was nearly 6 times as high as that of pure titania. The amount of hydrogen produced was up to 2499 μmol. The doping mechanism of cobalt is discussed.
2011, 27(10): 2411-2415
doi: 10.3866/PKU.WHXB20110937
Abstract:
ZnCo2O4 nanoparticles were synthesized by a co-precipitation decomposition method and their optical and photocatalytic properties were investigated. Their crystal structure and microstructures were characterized using X-ray diffraction (XRD), thermogravimetry (TG)/differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The ZnCo2O4 nanocrystallites obtained were single-phase with an average size of 10-20 nm. The optical bandgap energies of the nanoparticles were estimated to be 3.39 and 2.09 eV from the UV-Vis absorption spectrum. The ZnCo2O4 nanoparticles exhibited high photocatalytic activity for the degradation of methylene blue dye solution under visible light irradiation (λ>420 nm). The photocatalytic activity of the ZnCo2O4 nanoparticles is attributed to their ability to absorb bandgap photons under UV and visible light as well as their nanoscale particle size. Based on these experimental results, a possible band structure of ZnCo2O4 is proposed.
ZnCo2O4 nanoparticles were synthesized by a co-precipitation decomposition method and their optical and photocatalytic properties were investigated. Their crystal structure and microstructures were characterized using X-ray diffraction (XRD), thermogravimetry (TG)/differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The ZnCo2O4 nanocrystallites obtained were single-phase with an average size of 10-20 nm. The optical bandgap energies of the nanoparticles were estimated to be 3.39 and 2.09 eV from the UV-Vis absorption spectrum. The ZnCo2O4 nanoparticles exhibited high photocatalytic activity for the degradation of methylene blue dye solution under visible light irradiation (λ>420 nm). The photocatalytic activity of the ZnCo2O4 nanoparticles is attributed to their ability to absorb bandgap photons under UV and visible light as well as their nanoscale particle size. Based on these experimental results, a possible band structure of ZnCo2O4 is proposed.
2011, 27(10): 2416-2420
doi: 10.3866/PKU.WHXB20110934
Abstract:
Nb2O5/t-ZrO2 catalysts with different loadings were prepared by aqueous solution impregnation using niobium oxalate as a precursor on tetra nal ZrO2 (t-ZrO2). The dispersion states with respect to niobia species on t-ZrO2 were characterized by powder X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and UV visible diffuse reflectance spectroscopy (UV-Vis DRS). The catalytic activity was evaluated by the condensation reaction of iso-butene (IB) and iso-butyraldehyde (IBA) to 2,5-dimethyl-2,4-hexadiene (DMHD) and the Brønsted acidity was evaluated by the Fourier-transform infrared spectroscopy of pyridine adsorption (Py-IR). The results reveal that the dispersion capacity ΓNb of Nb2O5 on t-ZrO2, which was determined by XRD quantitative phase analysis, is almost identical to the value predicted by the "incorporated model". The results also show that the Brønsted acid sites are strongly related to the states of Nb2O5 on Nb2O5/t-ZrO2.
Nb2O5/t-ZrO2 catalysts with different loadings were prepared by aqueous solution impregnation using niobium oxalate as a precursor on tetra nal ZrO2 (t-ZrO2). The dispersion states with respect to niobia species on t-ZrO2 were characterized by powder X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and UV visible diffuse reflectance spectroscopy (UV-Vis DRS). The catalytic activity was evaluated by the condensation reaction of iso-butene (IB) and iso-butyraldehyde (IBA) to 2,5-dimethyl-2,4-hexadiene (DMHD) and the Brønsted acidity was evaluated by the Fourier-transform infrared spectroscopy of pyridine adsorption (Py-IR). The results reveal that the dispersion capacity ΓNb of Nb2O5 on t-ZrO2, which was determined by XRD quantitative phase analysis, is almost identical to the value predicted by the "incorporated model". The results also show that the Brønsted acid sites are strongly related to the states of Nb2O5 on Nb2O5/t-ZrO2.
2011, 27(10): 2421-2426
doi: 10.3866/PKU.WHXB20110932
Abstract:
Mesoporous NiO and CeNiO catalysts were prepared by homogeneous precipitation using sodium dodecyl sulfate (SDS) mixed with triblock copolymer P123 as a template and urea as a hydrolysiscontrolling agent. The prepared catalysts were evaluated for the oxidative dehydrogenation of propane (ODP) to propene and the structure and properties of the catalysts were characterized by N2 adsorptiondesorption, transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and H2 temperatureprogrammed reduction (H2-TPR). The results showed that between 400 and 450°C, the NiO and CeNiO catalysts exhibited similar catalytic behavior for the ODP reaction but at low temperatures (<400°C) the catalysts doped with Ce had higher catalytic activity. On NiO only a 3.1% propene yield was obtained at 325°C while the yield on 5CeNiO (nCe/nNi=5%) was as high as 12.2% at the same temperature. The results of N2 adsorption-desorption and TEM indicated that both the prepared NiO and CeNiO catalysts possessed a high surface area and a wormhole-like mesostructure. The H2-TPR results revealed that part of the oxygen species became more reducible because of the presence of Ce in CeNiO, which may be the main reason for the higher activities of the catalysts.
Mesoporous NiO and CeNiO catalysts were prepared by homogeneous precipitation using sodium dodecyl sulfate (SDS) mixed with triblock copolymer P123 as a template and urea as a hydrolysiscontrolling agent. The prepared catalysts were evaluated for the oxidative dehydrogenation of propane (ODP) to propene and the structure and properties of the catalysts were characterized by N2 adsorptiondesorption, transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and H2 temperatureprogrammed reduction (H2-TPR). The results showed that between 400 and 450°C, the NiO and CeNiO catalysts exhibited similar catalytic behavior for the ODP reaction but at low temperatures (<400°C) the catalysts doped with Ce had higher catalytic activity. On NiO only a 3.1% propene yield was obtained at 325°C while the yield on 5CeNiO (nCe/nNi=5%) was as high as 12.2% at the same temperature. The results of N2 adsorption-desorption and TEM indicated that both the prepared NiO and CeNiO catalysts possessed a high surface area and a wormhole-like mesostructure. The H2-TPR results revealed that part of the oxygen species became more reducible because of the presence of Ce in CeNiO, which may be the main reason for the higher activities of the catalysts.
2011, 27(10): 2427-2431
doi: 10.3866/PKU.WHXB20110928
Abstract:
The near-infrared (NIR) luminescence phosphor Yb3+,Bi3+ co-doped YVO4 was prepared by a conventional solid state method and the sensitization of Yb3+ near-infrared luminescence by Bi3+ was investigated. By co-doping with Bi3+ from 0 to 0.05 the characteristic NIR luminescence of Yb3+ in the YVO4 matrix was greatly enhanced and the strongest site of the excitation wavelength red-shifted from 335 to 352 nm while the wavelength range of the excitation spectrum broadened from 300-360 to 300-430 nm. The optimized Bi3+ content is 0.03. The possible energy transfer mechanism among VO43-, Bi3+ , and Yb3+ was discussed. We conclude that the NIR luminescence of YVO4:Yb3+ can be remarkably improved by co-doping with Bi3+ and its absorbance matches better with the solar energy spectrum. YVO4:Yb3+, Bi3+ is a promising spectral converter for silicon solar cells and it is expected to improve the photoelectric conversion efficiency.
The near-infrared (NIR) luminescence phosphor Yb3+,Bi3+ co-doped YVO4 was prepared by a conventional solid state method and the sensitization of Yb3+ near-infrared luminescence by Bi3+ was investigated. By co-doping with Bi3+ from 0 to 0.05 the characteristic NIR luminescence of Yb3+ in the YVO4 matrix was greatly enhanced and the strongest site of the excitation wavelength red-shifted from 335 to 352 nm while the wavelength range of the excitation spectrum broadened from 300-360 to 300-430 nm. The optimized Bi3+ content is 0.03. The possible energy transfer mechanism among VO43-, Bi3+ , and Yb3+ was discussed. We conclude that the NIR luminescence of YVO4:Yb3+ can be remarkably improved by co-doping with Bi3+ and its absorbance matches better with the solar energy spectrum. YVO4:Yb3+, Bi3+ is a promising spectral converter for silicon solar cells and it is expected to improve the photoelectric conversion efficiency.
2011, 27(10): 2432-2446
doi: 10.3866/PKU.WHXB20111001
Abstract:
The dopamine 3-subtype receptor (D3R) is a promising therapeutic target for the development of new drugs. Using rhodopsin as a template protein, we report homology modeling of a complete D3R structure including dopamine (Dop) in an environment of a 1-palmitoyl-2-oleoylsn-glycero-3-phospha-tidylcholine (POPC) explicit lipid bilayer and water. A 300 ns molecular dynamics (MD) simulation was performed to obtain a stable three-dimensional structure for D3R (2B08-D3R) based on five residues (Asp117, His272, Phe269, Ser208, and Thr276), and these were validated as active sites for the binding of dopamine to the D3R protein by the binding energies (Eb) calculated using MP2/6-31G(d,p) between Dop and each of the residues within 0.6 nm of Dop. The five key residues are locating on TM3, TM5, and TM6 within the D3R helical regions, respectively, forming an active pocket for the binding of Dop to the D3R protein. The phenyl plane of Dop is parallel to the cylinder space formed by the TM2-TM7 helical regions when it bonds non-covalently to the D3R protein. The value of Eb between the Dop and D3R protein is -97.8 kJ·mol-1, which explains why dopamine is easily assimilated into the D3R protein and departs from it as a nerve material and a signal transducer. Using the crystal protein structure of mutated D3R (code: 3PBL) we built another D3R protein structure including dopamine (designated Dop-3PBL-D3R) and identified five residues (Asp83, His272, Phe269, Phe268, and Trp265) as the active sites for the binding of Dop. The phenyl plane of Dop is also parallel to the cylinder space that is formed by the TM2-TM7 helical regions when it binds non-covalently to the Dop-3PBL-D3R protein with an Eb of -80.5 kJ·mol-1 between them.
The dopamine 3-subtype receptor (D3R) is a promising therapeutic target for the development of new drugs. Using rhodopsin as a template protein, we report homology modeling of a complete D3R structure including dopamine (Dop) in an environment of a 1-palmitoyl-2-oleoylsn-glycero-3-phospha-tidylcholine (POPC) explicit lipid bilayer and water. A 300 ns molecular dynamics (MD) simulation was performed to obtain a stable three-dimensional structure for D3R (2B08-D3R) based on five residues (Asp117, His272, Phe269, Ser208, and Thr276), and these were validated as active sites for the binding of dopamine to the D3R protein by the binding energies (Eb) calculated using MP2/6-31G(d,p) between Dop and each of the residues within 0.6 nm of Dop. The five key residues are locating on TM3, TM5, and TM6 within the D3R helical regions, respectively, forming an active pocket for the binding of Dop to the D3R protein. The phenyl plane of Dop is parallel to the cylinder space formed by the TM2-TM7 helical regions when it bonds non-covalently to the D3R protein. The value of Eb between the Dop and D3R protein is -97.8 kJ·mol-1, which explains why dopamine is easily assimilated into the D3R protein and departs from it as a nerve material and a signal transducer. Using the crystal protein structure of mutated D3R (code: 3PBL) we built another D3R protein structure including dopamine (designated Dop-3PBL-D3R) and identified five residues (Asp83, His272, Phe269, Phe268, and Trp265) as the active sites for the binding of Dop. The phenyl plane of Dop is also parallel to the cylinder space that is formed by the TM2-TM7 helical regions when it binds non-covalently to the Dop-3PBL-D3R protein with an Eb of -80.5 kJ·mol-1 between them.
2011, 27(10): 2447-2456
doi: 10.3866/PKU.WHXB20111009
Abstract:
Given the long range correlation characteristics of information about protein foldability and thermostability the multiple sequence alignment of a SH3 domain was analyzed using the modified statistical coupling analysis (SCA) method. Results show that the statistically conserved energy from the SCA method could be used to evaluate the site conservation of the SH3 sequence set properly. Sites with a high average coupling energy correspond to structurally and functionally important positions. Perturbing analysis on several sites revealed local and nonlocal perturbing modes in the SH3 domain. By combining the SCA and the clustering reorder method the structural core and the non-structural core sites of the SH3 domain, and detailed differences between several functional sites could be distinguished. Different perturbing modes that involve different sites exist in the SH3 domain. By sharing the common perturbing sites and the responding sites, different perturbing modes can interact. The coupling responding mode of all the sites in the structure was thus determined. Coupling information about the SH3 domain can improve our understanding about the relationship between the protein sequence and its structure as well as its function. It is also valuable in new protein design.
Given the long range correlation characteristics of information about protein foldability and thermostability the multiple sequence alignment of a SH3 domain was analyzed using the modified statistical coupling analysis (SCA) method. Results show that the statistically conserved energy from the SCA method could be used to evaluate the site conservation of the SH3 sequence set properly. Sites with a high average coupling energy correspond to structurally and functionally important positions. Perturbing analysis on several sites revealed local and nonlocal perturbing modes in the SH3 domain. By combining the SCA and the clustering reorder method the structural core and the non-structural core sites of the SH3 domain, and detailed differences between several functional sites could be distinguished. Different perturbing modes that involve different sites exist in the SH3 domain. By sharing the common perturbing sites and the responding sites, different perturbing modes can interact. The coupling responding mode of all the sites in the structure was thus determined. Coupling information about the SH3 domain can improve our understanding about the relationship between the protein sequence and its structure as well as its function. It is also valuable in new protein design.
2011, 27(10): 2457-2461
doi: 10.3866/PKU.WHXB20111010
Abstract:
C60 layer by layer films without clusters were obtained on Si(111)-7×7 reconstructed surface by controlling parameters such as the evaporation speed and the temperature of substrate during the growth process. The experiments were carried out under ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). These films were observed by ultra-high vacuum scanning tunneling microscopy (UHV-STM) and the mechanism of this phenomenon was analyzed. The adhesion and frictional force curves of these C60 films with different layers were measured. Their frictional properties were found to be affected by the number of layers. The frictional force decreased obviously with the increase in layers and the frictional coefficient also showed a downward tendency. Our simulation showed that adhesion was not the main effect that led to a decrease in the frictional force. Since the increase of layers leads to a higher level of rotation for C60 molecules, we conclude that the decrease in the frictional force is caused by the rotation of the C60 molecules. C60 molecule acts as"nano rolling bearing"here. That is, the rotation of the C60 molecules provides a channel for energy dissipation in the microstructure. These kinds of multilayer films make it possible for us to study the relationship between the rotation of C60 molecule and its other properties.
C60 layer by layer films without clusters were obtained on Si(111)-7×7 reconstructed surface by controlling parameters such as the evaporation speed and the temperature of substrate during the growth process. The experiments were carried out under ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). These films were observed by ultra-high vacuum scanning tunneling microscopy (UHV-STM) and the mechanism of this phenomenon was analyzed. The adhesion and frictional force curves of these C60 films with different layers were measured. Their frictional properties were found to be affected by the number of layers. The frictional force decreased obviously with the increase in layers and the frictional coefficient also showed a downward tendency. Our simulation showed that adhesion was not the main effect that led to a decrease in the frictional force. Since the increase of layers leads to a higher level of rotation for C60 molecules, we conclude that the decrease in the frictional force is caused by the rotation of the C60 molecules. C60 molecule acts as"nano rolling bearing"here. That is, the rotation of the C60 molecules provides a channel for energy dissipation in the microstructure. These kinds of multilayer films make it possible for us to study the relationship between the rotation of C60 molecule and its other properties.
2011, 27(10): 2462-2468
doi: 10.3866/PKU.WHXB20111007
Abstract:
We studied the growth of carbon nanotubes (CNTs) over a Co/Mo/Al2O3 catalyst by decomposing ethylene with or without the assistance of water. The optimal amount of water was determined to be 0.6% (φ) since excess water removed the amorphous carbon around the catalysts and also directly etched the CNTs at high temperature. Under this condition, the yield of CNTs can be increased from 3.7 g·g-1, based on the mass of catalyst, to 70 g·g-1 within 1 h. The time-dependent online conversion of ethylene and the ratio of effective catalysts suggested that the effect of water is insignificant in the final growth period of the CNTs compared to that at the beginning. The correlation between the relative activity of the catalyst and the relative density of the CNT agglomerate suggests that the lack of growth volume inside the CNT agglomerate results in a gradual deactivation of the catalyst in the final CNT growth period. Raman characterization suggests that the degree of CNT defects increases with the bulk density of the CNT agglomerates since the mechanical resistance that is exposed on CNTs inside the agglomerate increases with reaction time. Thermal-gravimetric analysis indicates that the purity of CNTs ranges from 95.0% to 99.9% for a product with average purity of 99.2%. The non-uniform purity of the CNTs is due to the difference in mechanical resistance inside and outside the CNT agglomerate. The growth of CNTs outside the agglomerate is nearly free of mechanical resistance compared to that inside the agglomerate and, consequently, results in a high yield and high purity for the CNTs. These results suggest that it is necessary to control the agglomerate size and the structure, and to use a reactor with a large reactor volume for the growth of CNTs with low resistance and with high yield.
We studied the growth of carbon nanotubes (CNTs) over a Co/Mo/Al2O3 catalyst by decomposing ethylene with or without the assistance of water. The optimal amount of water was determined to be 0.6% (φ) since excess water removed the amorphous carbon around the catalysts and also directly etched the CNTs at high temperature. Under this condition, the yield of CNTs can be increased from 3.7 g·g-1, based on the mass of catalyst, to 70 g·g-1 within 1 h. The time-dependent online conversion of ethylene and the ratio of effective catalysts suggested that the effect of water is insignificant in the final growth period of the CNTs compared to that at the beginning. The correlation between the relative activity of the catalyst and the relative density of the CNT agglomerate suggests that the lack of growth volume inside the CNT agglomerate results in a gradual deactivation of the catalyst in the final CNT growth period. Raman characterization suggests that the degree of CNT defects increases with the bulk density of the CNT agglomerates since the mechanical resistance that is exposed on CNTs inside the agglomerate increases with reaction time. Thermal-gravimetric analysis indicates that the purity of CNTs ranges from 95.0% to 99.9% for a product with average purity of 99.2%. The non-uniform purity of the CNTs is due to the difference in mechanical resistance inside and outside the CNT agglomerate. The growth of CNTs outside the agglomerate is nearly free of mechanical resistance compared to that inside the agglomerate and, consequently, results in a high yield and high purity for the CNTs. These results suggest that it is necessary to control the agglomerate size and the structure, and to use a reactor with a large reactor volume for the growth of CNTs with low resistance and with high yield.
2011, 27(10): 2469-2477
doi: 10.3866/PKU.WHXB20110939
Abstract:
Fe3O4 magnetic nanoparticles were prepared by co-precipitation and supported on the surface of aminopyridine-grafted multiwalled carbon nanotubes (MWCNT-AP), affording a superparamagnetic Fe3O4/MWCNT-AP composite with od dispersity. The Fe3O4/MWCNT-AP composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and hysteresis curve measurements. Transmission electron microscopy (TEM) experimental results suggest that the Fe3O4 nanoparticles are mainly adsorbed on the tips of the MWCNT-AP. UV-Vis absorption and fluorescence results demonstrate that horseradish peroxidase (HRP) can be physically adsorbed onto the surfaces of the Fe3O4/MWCNT-AP composite. Under acidic conditions (pH 4.0), the maximum reaction rate (vmax) value of the HRP increases 3-fold after interaction with Fe3O4/MWCNT-AP.
Fe3O4 magnetic nanoparticles were prepared by co-precipitation and supported on the surface of aminopyridine-grafted multiwalled carbon nanotubes (MWCNT-AP), affording a superparamagnetic Fe3O4/MWCNT-AP composite with od dispersity. The Fe3O4/MWCNT-AP composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and hysteresis curve measurements. Transmission electron microscopy (TEM) experimental results suggest that the Fe3O4 nanoparticles are mainly adsorbed on the tips of the MWCNT-AP. UV-Vis absorption and fluorescence results demonstrate that horseradish peroxidase (HRP) can be physically adsorbed onto the surfaces of the Fe3O4/MWCNT-AP composite. Under acidic conditions (pH 4.0), the maximum reaction rate (vmax) value of the HRP increases 3-fold after interaction with Fe3O4/MWCNT-AP.
2011, 27(10): 2478-2484
doi: 10.3866/PKU.WHXB20110925
Abstract:
ZrO2 aerogels were successfully synthesized by the sol-gel process and ambient pressure drying using ZrO(NO3)2·5H2O as a precursor, 1,2-propylene oxide (PO) as a gelation agent, and formamide (FA) as a drying control chemical additive (DCCA). The prepared zirconia aerogel samples were characterized using differential thermal analysis (DTA), scanning electron microscopy (SEM), and nitrogen adsorption/desorption analysis. The results showed that the zirconia aerogels prepared by the propylene oxide addition method had a nanoscale porous network structure, as well as supercritical dried ones, with a low bulk density (202.08 kg·m-3) and a high surface area (645.0 m2·g-1). Propylene oxide can induce gelation through its nucleophilic property and its irreversible ring-opening reaction, and thus the sol-gel process and the state of gel can be controlled.
ZrO2 aerogels were successfully synthesized by the sol-gel process and ambient pressure drying using ZrO(NO3)2·5H2O as a precursor, 1,2-propylene oxide (PO) as a gelation agent, and formamide (FA) as a drying control chemical additive (DCCA). The prepared zirconia aerogel samples were characterized using differential thermal analysis (DTA), scanning electron microscopy (SEM), and nitrogen adsorption/desorption analysis. The results showed that the zirconia aerogels prepared by the propylene oxide addition method had a nanoscale porous network structure, as well as supercritical dried ones, with a low bulk density (202.08 kg·m-3) and a high surface area (645.0 m2·g-1). Propylene oxide can induce gelation through its nucleophilic property and its irreversible ring-opening reaction, and thus the sol-gel process and the state of gel can be controlled.
2011, 27(10): 2485-2492
doi: 10.3866/PKU.WHXB20111020
Abstract:
Ag3PO4-P(AM-co-MAA) composite microspheres were prepared by the combination of a polymeric microgel method and a reverse micelle technique. Novel silver-poly(acrylamide-co-methacrylic acid) [Ag-P(AM-co-MAA)] composite microspheres with sizes ranging in the tens of micrometers and containing a patterned surface as well as core/shell structures were prepared by the chemical reduction of Ag3PO4-P(AM-co-MAA) composite microspheres in ethanol. Energy dispersive X-ray (EDX) analysis revealed that the chemical composition of the"shell"is dominated by Ag, but the"core"is dominated by the template, P(AM-co-MAA). Scanning electron microscopy (SEM) results demonstrate that the surface morphology of the Ag-polymer composite microspheres is similar to that of their precursors and can be controlled to a certain extent by varying the composition of the template copolymer, the approaches and the amount of Ag3PO4 deposited. X-ray diffraction (XRD) indicated that the salt had been completely converted to Ag. Biological antimicrobial experiments showed that this kind of composites exhibit distinctive antibacterial activity toward Escherichia coli and Staphylococcus aureus.
Ag3PO4-P(AM-co-MAA) composite microspheres were prepared by the combination of a polymeric microgel method and a reverse micelle technique. Novel silver-poly(acrylamide-co-methacrylic acid) [Ag-P(AM-co-MAA)] composite microspheres with sizes ranging in the tens of micrometers and containing a patterned surface as well as core/shell structures were prepared by the chemical reduction of Ag3PO4-P(AM-co-MAA) composite microspheres in ethanol. Energy dispersive X-ray (EDX) analysis revealed that the chemical composition of the"shell"is dominated by Ag, but the"core"is dominated by the template, P(AM-co-MAA). Scanning electron microscopy (SEM) results demonstrate that the surface morphology of the Ag-polymer composite microspheres is similar to that of their precursors and can be controlled to a certain extent by varying the composition of the template copolymer, the approaches and the amount of Ag3PO4 deposited. X-ray diffraction (XRD) indicated that the salt had been completely converted to Ag. Biological antimicrobial experiments showed that this kind of composites exhibit distinctive antibacterial activity toward Escherichia coli and Staphylococcus aureus.
2011, 27(10): 2493-2498
doi: 10.3866/PKU.WHXB20110917
Abstract:
PHI zeolite membrane was prepared by the secondary growth method on the surface of a porous α-Al2O3 disk support. The effects of the zeolite seed preparation method, secondary growth time, and temperature on membrane synthesis were investigated. The as-synthesized PHI zeolite membranes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results show that PHI zeolite emerges on the support. The SEM results show that the support surface is fully covered by uniform and compact PHI zeolite membrane synthesized by the secondary growth method and the thicknesses of the membrane layer was found to be about 20 μm. The as-synthesized PHI zeolite membranes were used for dehydration of methanol (MeOH), ethanol (EtOH), isopropanol (IPA), and tert-butanol (TBA) solutions with different kinetic diameters. The influence of feed concentration on the separation performance was investigated by pervaporation tests. The results show that the PHI membranes exhibited excellent performance of the dehydration of alcohol/water mixtures. It was found that the flux and the separation factors of isopropanol and tert-butanol increased with the increment of the water amount in the feed and the separation factors of methanol and ethanol decreased slightly.
PHI zeolite membrane was prepared by the secondary growth method on the surface of a porous α-Al2O3 disk support. The effects of the zeolite seed preparation method, secondary growth time, and temperature on membrane synthesis were investigated. The as-synthesized PHI zeolite membranes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results show that PHI zeolite emerges on the support. The SEM results show that the support surface is fully covered by uniform and compact PHI zeolite membrane synthesized by the secondary growth method and the thicknesses of the membrane layer was found to be about 20 μm. The as-synthesized PHI zeolite membranes were used for dehydration of methanol (MeOH), ethanol (EtOH), isopropanol (IPA), and tert-butanol (TBA) solutions with different kinetic diameters. The influence of feed concentration on the separation performance was investigated by pervaporation tests. The results show that the PHI membranes exhibited excellent performance of the dehydration of alcohol/water mixtures. It was found that the flux and the separation factors of isopropanol and tert-butanol increased with the increment of the water amount in the feed and the separation factors of methanol and ethanol decreased slightly.
