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2012 Volume 28 Issue 2
2012, 28(02):
Abstract:
2012, 28(02): 257-264
doi: 10.3866/PKU.WHXB201112091
Abstract:
In order to explore the chiral origin of cis-[Ni(NCS)2tren] [tren: tris(2-aminoethyl) amine], a pair of chiral crystals of cis-[Ni(NCS)2tren] was characterized by X-ray single crystal structural analysis, solution UV-Vis-near infrared (NIR) spectroscopy, solid state UV-circular dichiroism (CD), and powder X-ray diffraction (XRD) spectra. The results indicated that the chiral crystals of cis-[Ni(NCS)2tren] were obtained by mirror symmetry-breaking crystallization, and the special chiral ring conformations (δδλ, λλδ) of the coordinated tripod-type tren ligands are responsible for the chiral origin of cis-[Ni(NCS)2tren]. The Cotton effects of Ni(II) complexes in the solid-state UV-CD spectra are presumably attributed to the π-π* and charge-transfer chromophores of the NCS- ligands by the chiral perturbation of the helical ring conformations and metal-centered chirality. According to the statistical results of solid-state CD spectra of cis-[Ni(NCS)2tren] for twenty batch syntheses, their enantiomeric excess (ee) values are between 39% and 100%.
In order to explore the chiral origin of cis-[Ni(NCS)2tren] [tren: tris(2-aminoethyl) amine], a pair of chiral crystals of cis-[Ni(NCS)2tren] was characterized by X-ray single crystal structural analysis, solution UV-Vis-near infrared (NIR) spectroscopy, solid state UV-circular dichiroism (CD), and powder X-ray diffraction (XRD) spectra. The results indicated that the chiral crystals of cis-[Ni(NCS)2tren] were obtained by mirror symmetry-breaking crystallization, and the special chiral ring conformations (δδλ, λλδ) of the coordinated tripod-type tren ligands are responsible for the chiral origin of cis-[Ni(NCS)2tren]. The Cotton effects of Ni(II) complexes in the solid-state UV-CD spectra are presumably attributed to the π-π* and charge-transfer chromophores of the NCS- ligands by the chiral perturbation of the helical ring conformations and metal-centered chirality. According to the statistical results of solid-state CD spectra of cis-[Ni(NCS)2tren] for twenty batch syntheses, their enantiomeric excess (ee) values are between 39% and 100%.
2012, 28(02): 265-272
doi: 10.3866/PKU.WHXB201111251
Abstract:
Two new Salen ligands H2L1 (N,N'-bis(3-dimethoxy-salicylidene)-4,5-dimethoxy-1,2- phenylenediamine) and H2L2 (N,N'-bis(3-dimethoxy-salicylidene)-4,5-dinitryl-1,2-phenylenediamine), and their nickel, copper, and zinc complexes ML1, and ML2 (M=Ni, Cu, Zn) were synthesized. The compounds synthesized were characterized by 1H-nuclear magnetic resonance (1H NMR), ultraviolet-visible absorption spectrometry (UV-Vis), infrared (IR) spectrometry, mass spectroscopy (MS), and elemental analysis. The fluorescence properties of the complexes were also studied. The fluorescence intensity of ligand H2L2 was lower than that of ligand H2L1, because of the introduction of the strong electron-withdrawing group, ―NO2. Moreover, the fluorescence intensities of the zinc complexes are greater than those of the ligands; however the fluorescence is quenched upon complexing of nickel or copper ions. In addition, the cyclic voltammetry shows that the redox process in CuL1 was a one-electron quasi-reversible charge-transfer. Because of the introduction of the electron-donating group ―OCH3, the solution conductivity of ligand H2L1 was lower than that of H2L2.
Two new Salen ligands H2L1 (N,N'-bis(3-dimethoxy-salicylidene)-4,5-dimethoxy-1,2- phenylenediamine) and H2L2 (N,N'-bis(3-dimethoxy-salicylidene)-4,5-dinitryl-1,2-phenylenediamine), and their nickel, copper, and zinc complexes ML1, and ML2 (M=Ni, Cu, Zn) were synthesized. The compounds synthesized were characterized by 1H-nuclear magnetic resonance (1H NMR), ultraviolet-visible absorption spectrometry (UV-Vis), infrared (IR) spectrometry, mass spectroscopy (MS), and elemental analysis. The fluorescence properties of the complexes were also studied. The fluorescence intensity of ligand H2L2 was lower than that of ligand H2L1, because of the introduction of the strong electron-withdrawing group, ―NO2. Moreover, the fluorescence intensities of the zinc complexes are greater than those of the ligands; however the fluorescence is quenched upon complexing of nickel or copper ions. In addition, the cyclic voltammetry shows that the redox process in CuL1 was a one-electron quasi-reversible charge-transfer. Because of the introduction of the electron-donating group ―OCH3, the solution conductivity of ligand H2L1 was lower than that of H2L2.
2012, 28(02): 273-282
doi: 10.3866/PKU.WHXB201111243
Abstract:
The thiosulfate anion (S2O32-) was intercalated into a ZnAl layered double hydroxide (LDH), and its oxidation reaction with hexacyanoferrate(III) (Fe(CN)63-) in the confined region between the layers of LDH has been discussed. Based measurements of the intermediate state and final product using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, the oxidation product tetrathionate (S4O62-) dissolved in solution, while the reduction product hexacyanoferrate (II) existed in the interlayer of the LDH. Furthermore, the kinetics of this reaction were investigated in batch mode. The influences of the initial Fe(CN)63- concentration, ZnAl-S2O3 LDH quantity, and reaction temperature on the oxidation reaction were studied. The reaction follows a diffusion-controlled process represented by Crank-Ginstling and Brounstein model with the apparent activation energy of 24.6 kJ·mol-1, which was about 13.7 kJ·mol-1 less than that of the solution reaction under the same conditions. The influence of water content on interlayer spacing was simulated by molecular dynamics. The simulation result shows that the size of this microreactor can be regulated in a certain orientation in the solution environment. From the experimental results and theoretical calculation, we propose a mechanism for the interlayer reaction. This layered material can be used as a novel nano-reactor to regulate the rate of chemical reactions.
The thiosulfate anion (S2O32-) was intercalated into a ZnAl layered double hydroxide (LDH), and its oxidation reaction with hexacyanoferrate(III) (Fe(CN)63-) in the confined region between the layers of LDH has been discussed. Based measurements of the intermediate state and final product using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, the oxidation product tetrathionate (S4O62-) dissolved in solution, while the reduction product hexacyanoferrate (II) existed in the interlayer of the LDH. Furthermore, the kinetics of this reaction were investigated in batch mode. The influences of the initial Fe(CN)63- concentration, ZnAl-S2O3 LDH quantity, and reaction temperature on the oxidation reaction were studied. The reaction follows a diffusion-controlled process represented by Crank-Ginstling and Brounstein model with the apparent activation energy of 24.6 kJ·mol-1, which was about 13.7 kJ·mol-1 less than that of the solution reaction under the same conditions. The influence of water content on interlayer spacing was simulated by molecular dynamics. The simulation result shows that the size of this microreactor can be regulated in a certain orientation in the solution environment. From the experimental results and theoretical calculation, we propose a mechanism for the interlayer reaction. This layered material can be used as a novel nano-reactor to regulate the rate of chemical reactions.
2012, 28(02): 283-289
doi: 10.3866/PKU.WHXB201111292
Abstract:
We report the conditions required for the formation of perylene oli mers, which are closely related to the crystal nuclei for the formation of perylene nanocrystal. The effects of water content and perylene concentration on aggregation were studied using fluorescence and absorption spectra. The spectra indicated that fluorescent J-type perylene oli mers were formed. An aggregation number of 9, and large equilibrium constant were obtained for the reaction.
We report the conditions required for the formation of perylene oli mers, which are closely related to the crystal nuclei for the formation of perylene nanocrystal. The effects of water content and perylene concentration on aggregation were studied using fluorescence and absorption spectra. The spectra indicated that fluorescent J-type perylene oli mers were formed. An aggregation number of 9, and large equilibrium constant were obtained for the reaction.
2012, 28(02): 290-296
doi: 10.3866/PKU.WHXB201112121
Abstract:
Three rare earth complexes of [Ln(5-Cl-2MOBA)3phen]2 (Ln=Nd(1), Eu(2), Ho(3); 5-Cl- 2MOBA: 5-chloro-2-methoxybenzoate; phen: 1,10-phenanthroline) were synthesized and characterized by elemental analysis, thermogravimetry-differential thermogravimetry-differential scanning calorimetry (TG-DTG-DSC), infrared (IR) spectra, ultraviolet (UV) spectra, and molar conductance techniques. The fluorescence spectra showed that complex (2) emitted a characteristic fluorescence of the Eu3+ ions. The thermal properties are discussed by thermogravimetry - differential scanning calorimetry / Fourier transform infrared (TG-DSC/FTIR) techniques. And the three-dimensional IR accumulation spectra for the three complexes were also analyzed.
Three rare earth complexes of [Ln(5-Cl-2MOBA)3phen]2 (Ln=Nd(1), Eu(2), Ho(3); 5-Cl- 2MOBA: 5-chloro-2-methoxybenzoate; phen: 1,10-phenanthroline) were synthesized and characterized by elemental analysis, thermogravimetry-differential thermogravimetry-differential scanning calorimetry (TG-DTG-DSC), infrared (IR) spectra, ultraviolet (UV) spectra, and molar conductance techniques. The fluorescence spectra showed that complex (2) emitted a characteristic fluorescence of the Eu3+ ions. The thermal properties are discussed by thermogravimetry - differential scanning calorimetry / Fourier transform infrared (TG-DSC/FTIR) techniques. And the three-dimensional IR accumulation spectra for the three complexes were also analyzed.
2012, 28(02): 297-302
doi: 10.3866/PKU.WHXB201112012
Abstract:
Cu2O micro-spheres were fabricated by a solvothermal method using poly vinylpyrrolidone (PVP) as an additive. The influences of PVP dosage and reaction temperature on the morphologies of the products were investigated. Cu2O micro-spheres with diameters of 100-200 nm and about 1 μm were synthesized with reaction time of 2.5 and 4.5 h, respectively. Meanwhile, differential thermal analysis (DTA) was used to determine the catalytic performance of these Cu2O micro-spheres with different diameters for thermal decomposition of ammonium perchlorate (AP). Adding 2% (w) Cu2O micro-spheres with diameters of 100-200 nm and about 1 μm into AP decreased the maximum temperature of AP decomposition by 116 and 118 °C, respectively, and increased the amount of AP decomposed at lower temperature.
Cu2O micro-spheres were fabricated by a solvothermal method using poly vinylpyrrolidone (PVP) as an additive. The influences of PVP dosage and reaction temperature on the morphologies of the products were investigated. Cu2O micro-spheres with diameters of 100-200 nm and about 1 μm were synthesized with reaction time of 2.5 and 4.5 h, respectively. Meanwhile, differential thermal analysis (DTA) was used to determine the catalytic performance of these Cu2O micro-spheres with different diameters for thermal decomposition of ammonium perchlorate (AP). Adding 2% (w) Cu2O micro-spheres with diameters of 100-200 nm and about 1 μm into AP decreased the maximum temperature of AP decomposition by 116 and 118 °C, respectively, and increased the amount of AP decomposed at lower temperature.
2012, 28(02): 303-308
doi: 10.3866/PKU.WHXB201112013
Abstract:
Bond shortening of NH/CH due to improper hydrogen bonding is always thought to be accompanied by a blue shift in its corresponding frequency. However, results here show that owing to anharmonic effects, especially the contribution of mode-mode coupling, the blue shift could be greatly decreased. The strong interaction may even, in some cases, cause the previously predicted blue-shifting frequencies by harmonic methods to be red-shifted instead in the gas phase. Though these results need to be clearly verified by further infrared (IR) spectrum experiments in the gas phase for the selected systems, comparisons with previous IR results obtained from matrix isolation experiments strongly support the results of the calculations.
Bond shortening of NH/CH due to improper hydrogen bonding is always thought to be accompanied by a blue shift in its corresponding frequency. However, results here show that owing to anharmonic effects, especially the contribution of mode-mode coupling, the blue shift could be greatly decreased. The strong interaction may even, in some cases, cause the previously predicted blue-shifting frequencies by harmonic methods to be red-shifted instead in the gas phase. Though these results need to be clearly verified by further infrared (IR) spectrum experiments in the gas phase for the selected systems, comparisons with previous IR results obtained from matrix isolation experiments strongly support the results of the calculations.
2012, 28(02): 309-314
doi: 10.3866/PKU.WHXB201111211
Abstract:
The structures of a nanoparticle/copolymer mixed system were studied using lattice dynamic Monte Carlo simulations. Each copolymer chain consisted of one A bead and three B beads, and the amphiphilic property of the A1B3 chains was represented by an attraction between B-B beads. Nanoparticles were hydrophobic with an attraction amongst themselves. By properly choosing the attraction between the nanoparticle and the B beads, we observe two interesting structures: a nanoparticle/ A1B3 chain core-shell structure and an A1B3 vesicle with nanoparticles dispersed in the hydrophobic shell. The evolutions of these two structures were investigated. Our results show that the A1B3 vesicle acts as a template for the formation of the nanoparticle-dispersed vesicle.
The structures of a nanoparticle/copolymer mixed system were studied using lattice dynamic Monte Carlo simulations. Each copolymer chain consisted of one A bead and three B beads, and the amphiphilic property of the A1B3 chains was represented by an attraction between B-B beads. Nanoparticles were hydrophobic with an attraction amongst themselves. By properly choosing the attraction between the nanoparticle and the B beads, we observe two interesting structures: a nanoparticle/ A1B3 chain core-shell structure and an A1B3 vesicle with nanoparticles dispersed in the hydrophobic shell. The evolutions of these two structures were investigated. Our results show that the A1B3 vesicle acts as a template for the formation of the nanoparticle-dispersed vesicle.
2012, 28(02): 315-323
doi: 10.3866/PKU.WHXB201111232
Abstract:
The performance of different exchange-correlation functionals for the description of the interaction of pyridine with different cluster models of ZSM-5 zeolite has been assessed. Theoretical calculations show that upon increasing the cluster model from 8T to 128T, the adsorption energy of pyridine in ZSM-5 zeolite increases gradually and reaches convergence by the 72T cluster model. On the basis of the 72T cluster model, the pyridine adsorption energy calculated with different functionals is further examined. Compared to the conventional functionals (B3LYP and M06-2X), the B97D functional which takes into account the dispersion correction provides calculated results that agree well with experimental data. The present results indicate that the B97D functional is suitable for studying long-range interactions in weakly interacting systems.
The performance of different exchange-correlation functionals for the description of the interaction of pyridine with different cluster models of ZSM-5 zeolite has been assessed. Theoretical calculations show that upon increasing the cluster model from 8T to 128T, the adsorption energy of pyridine in ZSM-5 zeolite increases gradually and reaches convergence by the 72T cluster model. On the basis of the 72T cluster model, the pyridine adsorption energy calculated with different functionals is further examined. Compared to the conventional functionals (B3LYP and M06-2X), the B97D functional which takes into account the dispersion correction provides calculated results that agree well with experimental data. The present results indicate that the B97D functional is suitable for studying long-range interactions in weakly interacting systems.
2012, 28(02): 324-330
doi: 10.3866/PKU.WHXB201112061
Abstract:
Based on the density functional pseudopotential method, the geometries, electronic structures, and optical properties of MgF2 with different atomic fractions of Cu doping (2.08%, 4.16%, and 6.24%) are compared in detail. Cu substitution of the Mg sites induces an effective reduction of the band gap of MgF2; and the band gap is continuously reduced with increasing Cu doping level. Also, the calculations show that the refractive index and absorption increase with increasing Cu doping. More importantly, an absorption around 4 eV is found. The mechanisms of this transition in the doped and undoped materials are discussed. The Cu doped MgF2 system could be a potential candidate for photoelectrochemical applications.
Based on the density functional pseudopotential method, the geometries, electronic structures, and optical properties of MgF2 with different atomic fractions of Cu doping (2.08%, 4.16%, and 6.24%) are compared in detail. Cu substitution of the Mg sites induces an effective reduction of the band gap of MgF2; and the band gap is continuously reduced with increasing Cu doping level. Also, the calculations show that the refractive index and absorption increase with increasing Cu doping. More importantly, an absorption around 4 eV is found. The mechanisms of this transition in the doped and undoped materials are discussed. The Cu doped MgF2 system could be a potential candidate for photoelectrochemical applications.
2012, 28(02): 331-337
doi: 10.3866/PKU.WHXB201111021
Abstract:
The adhesion of Ag, Au, and Pt adatoms on pristine graphene and that containing point defects including N-substitution, B-substitution, and a single vacancy, as well as the interfacial properties of these systems, were investigated using density functional theory. The calculations show that Ag and Au cannot bind to pristine graphene. In contrast, B and N-doping increase the interaction between Ag, Au, or Pt metal adatoms and graphene, while a vacancy defect leads to the strong chemisorption of metal adatoms on graphene. Based on electronic structural analysis, N-doping strengthens the covalent bond between Au or Pt and carbon atoms, while B-doping leads to the formation of a chemical bond between Au or Ag and B. The vacancy defect acts as an anchoring site for metal adatoms and increases the bonding between metal adatoms and carbon atoms. Therefore, three types of point defect can effectively enhance the interaction between noble metal adatoms and graphene in the sequence: vacancy defect>>B-doping>N-doping.
The adhesion of Ag, Au, and Pt adatoms on pristine graphene and that containing point defects including N-substitution, B-substitution, and a single vacancy, as well as the interfacial properties of these systems, were investigated using density functional theory. The calculations show that Ag and Au cannot bind to pristine graphene. In contrast, B and N-doping increase the interaction between Ag, Au, or Pt metal adatoms and graphene, while a vacancy defect leads to the strong chemisorption of metal adatoms on graphene. Based on electronic structural analysis, N-doping strengthens the covalent bond between Au or Pt and carbon atoms, while B-doping leads to the formation of a chemical bond between Au or Ag and B. The vacancy defect acts as an anchoring site for metal adatoms and increases the bonding between metal adatoms and carbon atoms. Therefore, three types of point defect can effectively enhance the interaction between noble metal adatoms and graphene in the sequence: vacancy defect>>B-doping>N-doping.
2012, 28(02): 338-342
doi: 10.3866/PKU.WHXB201111242
Abstract:
Ti-doped LiFe0.6Mn0.4PO4/C materials were synthesized by a solid-state method. The structures, morphologies, and electrochemical performance of the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge experiments. The results indicate that Ti4+ doping does not change the structure of the materials, but remarkably improves their electrochemical performance. Li(Fe0.6Mn0.4)0.96Ti0.02PO4/C shows excellent rate performance, with initial specific discharge capacities of 160.3 and 134.7 mAh·g-1 at 0.1C and 10C rates. Even at the higher rate of 20C, it shows a discharge capacity of 124.4 mAh·g-1. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses show that the resistance and the polarization of the LiFe0.6Mn0.4PO4/C composite electrode could be effectively decreased by Ti4+ doping, which would account for the improved electrode performance.
Ti-doped LiFe0.6Mn0.4PO4/C materials were synthesized by a solid-state method. The structures, morphologies, and electrochemical performance of the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge experiments. The results indicate that Ti4+ doping does not change the structure of the materials, but remarkably improves their electrochemical performance. Li(Fe0.6Mn0.4)0.96Ti0.02PO4/C shows excellent rate performance, with initial specific discharge capacities of 160.3 and 134.7 mAh·g-1 at 0.1C and 10C rates. Even at the higher rate of 20C, it shows a discharge capacity of 124.4 mAh·g-1. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses show that the resistance and the polarization of the LiFe0.6Mn0.4PO4/C composite electrode could be effectively decreased by Ti4+ doping, which would account for the improved electrode performance.
2012, 28(02): 343-348
doi: 10.3866/PKU.WHXB201111031
Abstract:
High potential cathode material LiCoPO4 was synthesized by sol-gel method. The effects of different sintering conditions on the crystal structure, surface morphology and electrochemical performance of LiCoPO4 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge-discharge tests. The results show that the sample synthesized at 650 ° C for 12 h has a od crystalline orthorhombic olivine-type structure and a uniform particle distribution (0.2-0.4 μm), which delivers the best electrochemical performance. The discharge capacity of the sample at 1C rate can reach 122.7 mAh·g-1. Moreover, from the charge and discharge profiles, two charge/discharge plateaus are presented and they become more obvious with the increase of charge/discharge rate. This phenomenon can be interpreted by considering the two-step extraction/insertion behavior of Li+ in LiCoPO4.
High potential cathode material LiCoPO4 was synthesized by sol-gel method. The effects of different sintering conditions on the crystal structure, surface morphology and electrochemical performance of LiCoPO4 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge-discharge tests. The results show that the sample synthesized at 650 ° C for 12 h has a od crystalline orthorhombic olivine-type structure and a uniform particle distribution (0.2-0.4 μm), which delivers the best electrochemical performance. The discharge capacity of the sample at 1C rate can reach 122.7 mAh·g-1. Moreover, from the charge and discharge profiles, two charge/discharge plateaus are presented and they become more obvious with the increase of charge/discharge rate. This phenomenon can be interpreted by considering the two-step extraction/insertion behavior of Li+ in LiCoPO4.
2012, 28(02): 349-354
doi: 10.3866/PKU.WHXB201112052
Abstract:
Li1.07Mn1.93O4 nanoflakes were synthesized by a gel-combustion method using polyvinylpyrrolidone (PVP) as the polymer chelating agent and fuel. Thermogravimetric and differential thermal analyses (TG/DTA) were used to investigate the combustion process of the gel precursor. X-ray diffraction (XRD) analysis indicated that the as-prepared Li1.07Mn1.93O4 was a pure, highly crystalline phase. Scanning electron microscopy (SEM) results showed that most of the secondary particles were nanoflakes, about 100 nm in thickness, and the primary particle of the nanoflakes was about 100 nm in size. Charge and discharge tests suggested that the Li1.07Mn1.93O4 nanoflakes had excellent rate capability and od cycling stability. The initial discharge capacity was 115.4 mAh·g-1 at a rate of 0.5C (1C=120 mAh·g-1) and the capacity was maintained at 105.3 mAh·g-1 at the high discharge rate of 40C. When cycling at 10C, the material retained 81% of its initial capacity after 850 cycles. Electrochemical impedance spectroscopy (EIS) tests indicated that the charge-transfer resistance (Rct) of the Li1.07Mn1.93O4 nanoflakes was much less than that of commercial Li1.07Mn1.93O4.
Li1.07Mn1.93O4 nanoflakes were synthesized by a gel-combustion method using polyvinylpyrrolidone (PVP) as the polymer chelating agent and fuel. Thermogravimetric and differential thermal analyses (TG/DTA) were used to investigate the combustion process of the gel precursor. X-ray diffraction (XRD) analysis indicated that the as-prepared Li1.07Mn1.93O4 was a pure, highly crystalline phase. Scanning electron microscopy (SEM) results showed that most of the secondary particles were nanoflakes, about 100 nm in thickness, and the primary particle of the nanoflakes was about 100 nm in size. Charge and discharge tests suggested that the Li1.07Mn1.93O4 nanoflakes had excellent rate capability and od cycling stability. The initial discharge capacity was 115.4 mAh·g-1 at a rate of 0.5C (1C=120 mAh·g-1) and the capacity was maintained at 105.3 mAh·g-1 at the high discharge rate of 40C. When cycling at 10C, the material retained 81% of its initial capacity after 850 cycles. Electrochemical impedance spectroscopy (EIS) tests indicated that the charge-transfer resistance (Rct) of the Li1.07Mn1.93O4 nanoflakes was much less than that of commercial Li1.07Mn1.93O4.
2012, 28(02): 355-360
doi: 10.3866/PKU.WHXB201111293
Abstract:
Perovskite-type series of compounds La1-xCaxCoO3 (x=0.2, 0.4, 0.5) were synthesized by a modified amorphous citrate precursor method. Their catalytic activities for hydrogen peroxide electroreduction in 3.0 mol·dm-3 KOH at room temperature were evaluated by cyclic voltammetry and galvanostatic measurements. The influences of annealing temperature and the molar ratio of La to Ca of La1-xCaxCoO3 on catalytic performance were investigated. Among the series of compounds, La0.6Ca0.4CoO3 calcined at 650 °C exhibited the highest catalytic activity. An aluminum-hydrogen peroxide semi fuel cell using La0.6Ca0.4CoO3 as cathode catalyst achieved a peak power density of 201 mW·cm-2 at 150 mA·cm-2 and 1.34 V running in 0.4 mol·dm-3 H2O2.
Perovskite-type series of compounds La1-xCaxCoO3 (x=0.2, 0.4, 0.5) were synthesized by a modified amorphous citrate precursor method. Their catalytic activities for hydrogen peroxide electroreduction in 3.0 mol·dm-3 KOH at room temperature were evaluated by cyclic voltammetry and galvanostatic measurements. The influences of annealing temperature and the molar ratio of La to Ca of La1-xCaxCoO3 on catalytic performance were investigated. Among the series of compounds, La0.6Ca0.4CoO3 calcined at 650 °C exhibited the highest catalytic activity. An aluminum-hydrogen peroxide semi fuel cell using La0.6Ca0.4CoO3 as cathode catalyst achieved a peak power density of 201 mW·cm-2 at 150 mA·cm-2 and 1.34 V running in 0.4 mol·dm-3 H2O2.
2012, 28(02): 361-366
doi: 10.3866/PKU.WHXB201112063
Abstract:
Restructured carbon aerogels (RCAs) were obtained by annealing carbon aerogels (CAs) in sodium melt at 800 °C for 3 h and the differences in electrochemical performance between the resultant CAs and RCAs were studied. X-ray diffraction (XRD), Raman scattering spectra, gas physisorption (BET), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS) were used to probe the structures of CAs and RCAs. The studies indicated that the amorphous carbon particles were rearranged in sodium melt, in which the surface area of the resultant RCAs was 48% larger than that of CAs. Two concentrated pore distributions were observed at the apertures of 2 and 4 nm in RCAs. The pore volume at apertures below 10 nm is 30% of the total volume in RCAs, which is 3 times as many as that in CAs. Electrochemical performances of both CAs and RCAs were investigated and the results indicate that the inner resistance of RCAs is only 45% of that in the sample of CAs. The results also indicate that RCAs display od performance in capacitance characteristics.
Restructured carbon aerogels (RCAs) were obtained by annealing carbon aerogels (CAs) in sodium melt at 800 °C for 3 h and the differences in electrochemical performance between the resultant CAs and RCAs were studied. X-ray diffraction (XRD), Raman scattering spectra, gas physisorption (BET), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS) were used to probe the structures of CAs and RCAs. The studies indicated that the amorphous carbon particles were rearranged in sodium melt, in which the surface area of the resultant RCAs was 48% larger than that of CAs. Two concentrated pore distributions were observed at the apertures of 2 and 4 nm in RCAs. The pore volume at apertures below 10 nm is 30% of the total volume in RCAs, which is 3 times as many as that in CAs. Electrochemical performances of both CAs and RCAs were investigated and the results indicate that the inner resistance of RCAs is only 45% of that in the sample of CAs. The results also indicate that RCAs display od performance in capacitance characteristics.
2012, 28(02): 367-372
doi: 10.3866/PKU.WHXB201112131
Abstract:
In this work, we prepared activated carbon-based symmetric supercapacitors using Li2SO4 aqueous electrolyte instead of H2SO4 and KOH, and obtained devices with an improved working voltage of 1.6 V from 1.0 V. Cyclic voltammetry and galvanostatic charging/discharging measurements were used to study the electrochemical properties. The results showed that the electrode specific capacitance can reach 129 F·g-1, and the energy density can be as high as 10 Wh·kg-1 at a power density of 160 Wh·kg-1. Electrochemical impedance analysis measurements showed that the charge-transfer resistance of the capacitors decreased markedly with the increase of the concentration of Li2SO4, and the rate capability improved accordingly. The leakage current of the supercapacitor was 0.22 mA after constant-voltage charging at 1.6 V for 1 h, and the columbic efficiency was nearly 100%. The capacitance of the supercapacitor remained above 90% after 5000 charge-discharge cycles. Activated carbon-based supercapacitors using Li2SO4 aqueous electrolyte have many advantages, such as high working voltage, high energy density, and environmental compatibility, and therefore have od industrialization prospects.
In this work, we prepared activated carbon-based symmetric supercapacitors using Li2SO4 aqueous electrolyte instead of H2SO4 and KOH, and obtained devices with an improved working voltage of 1.6 V from 1.0 V. Cyclic voltammetry and galvanostatic charging/discharging measurements were used to study the electrochemical properties. The results showed that the electrode specific capacitance can reach 129 F·g-1, and the energy density can be as high as 10 Wh·kg-1 at a power density of 160 Wh·kg-1. Electrochemical impedance analysis measurements showed that the charge-transfer resistance of the capacitors decreased markedly with the increase of the concentration of Li2SO4, and the rate capability improved accordingly. The leakage current of the supercapacitor was 0.22 mA after constant-voltage charging at 1.6 V for 1 h, and the columbic efficiency was nearly 100%. The capacitance of the supercapacitor remained above 90% after 5000 charge-discharge cycles. Activated carbon-based supercapacitors using Li2SO4 aqueous electrolyte have many advantages, such as high working voltage, high energy density, and environmental compatibility, and therefore have od industrialization prospects.
2012, 28(02): 373-380
doi: 10.3866/PKU.WHXB201112021
Abstract:
Fast charge-discharge composite materials of conducting polypyrrole and functionalized single-walled carbon nanotubes doped with p-toluenesulfonate (PPy-TOS/F-SWNTs) were prepared by galvanostatic electrochemical polymerization. Scanning Electron Microscope (SEM) images showed that the composite had a nano-rod structure with a diameter of about 70 nm. Nitrogen adsorption-desorption experinents were used to characterize the specific surface area (BET) (up to 12.64 m2·g-1) and pore sizes of the composite. Electrochemical properties of the composites were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GC) measurements. The specific capacitance of this composite is about 211 F·g-1 (energy density: 18.7 Wh·kg-1) at a current density of 2.5 A·g-1, and 141.8 F·g-1 (energy density: 12.6 Wh·kg-1) at large current density of 80 A·g-1. The composite had excellent cyclability with a capacity retention of about 95.2% after 10000 cycles at a current density of 10 A·g-1. All these results indicate that this new composite material has a very rapidly charge-discharge ability
Fast charge-discharge composite materials of conducting polypyrrole and functionalized single-walled carbon nanotubes doped with p-toluenesulfonate (PPy-TOS/F-SWNTs) were prepared by galvanostatic electrochemical polymerization. Scanning Electron Microscope (SEM) images showed that the composite had a nano-rod structure with a diameter of about 70 nm. Nitrogen adsorption-desorption experinents were used to characterize the specific surface area (BET) (up to 12.64 m2·g-1) and pore sizes of the composite. Electrochemical properties of the composites were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GC) measurements. The specific capacitance of this composite is about 211 F·g-1 (energy density: 18.7 Wh·kg-1) at a current density of 2.5 A·g-1, and 141.8 F·g-1 (energy density: 12.6 Wh·kg-1) at large current density of 80 A·g-1. The composite had excellent cyclability with a capacity retention of about 95.2% after 10000 cycles at a current density of 10 A·g-1. All these results indicate that this new composite material has a very rapidly charge-discharge ability
2012, 28(02): 381-386
doi: 10.3866/PKU.WHXB201112123
Abstract:
Nanocrystalline TiO2 thin films doped with different concentrations of Mo were deposited by direct current (DC) reactive magnetron sputtering. The influence of Mo on surfaces, crystal structures, the valence states of elements and the absorption band of Mo doped TiO2 films were characterized by means of atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Ultraviolet-visible spectroscopy (UV-Vis). To investigate the photoelectric characteristic of ITO (indium tin oxide)/Mo-TiO2 electrodes, a series of cyclic voltammetry experiments were conducted. The results indicate that an appropriate amount of Mo atoms, observed as Mo6+ and Mo5+ by XPS, could inhibit the crystal growth of particles, enhance the surface roughness of the Mo doped TiO2 thin film, and bring about a remarkable red shift of the absorption spectra. As the concentration of Mo increased, the energy gap declined at first until the amount of doped Mo eventually reached 3.6% (n(Mo)/n(Ti)), when a blue shift of spectra resulted and the energy gap grew wider. The sample doped with 0.9% Mo was irradiated with a Xe lamp and showed the highest photocurrent, which continued to increase with increasing voltage exerted on the anode. An increase in Mo concentration resulted in a decrease in photocurrent. Compared to the pure TiO2 film, the sample with 3.6% Mo had a much lower photocurrent. Our experiments demonstrate that Mo doping, when the concentration was controlled under a relatively low limit, brought about a significant improvement of the photoelectric properties of the TiO2 films. The highest photocurrent observed is 2.4 times that of the sample with no Mo doping.
Nanocrystalline TiO2 thin films doped with different concentrations of Mo were deposited by direct current (DC) reactive magnetron sputtering. The influence of Mo on surfaces, crystal structures, the valence states of elements and the absorption band of Mo doped TiO2 films were characterized by means of atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Ultraviolet-visible spectroscopy (UV-Vis). To investigate the photoelectric characteristic of ITO (indium tin oxide)/Mo-TiO2 electrodes, a series of cyclic voltammetry experiments were conducted. The results indicate that an appropriate amount of Mo atoms, observed as Mo6+ and Mo5+ by XPS, could inhibit the crystal growth of particles, enhance the surface roughness of the Mo doped TiO2 thin film, and bring about a remarkable red shift of the absorption spectra. As the concentration of Mo increased, the energy gap declined at first until the amount of doped Mo eventually reached 3.6% (n(Mo)/n(Ti)), when a blue shift of spectra resulted and the energy gap grew wider. The sample doped with 0.9% Mo was irradiated with a Xe lamp and showed the highest photocurrent, which continued to increase with increasing voltage exerted on the anode. An increase in Mo concentration resulted in a decrease in photocurrent. Compared to the pure TiO2 film, the sample with 3.6% Mo had a much lower photocurrent. Our experiments demonstrate that Mo doping, when the concentration was controlled under a relatively low limit, brought about a significant improvement of the photoelectric properties of the TiO2 films. The highest photocurrent observed is 2.4 times that of the sample with no Mo doping.
2012, 28(02): 387-392
doi: 10.3866/PKU.WHXB201111241
Abstract:
Cobalt oxide (Co3O4) nanowires were controllably synthesized using glycerol and Co(NO3)2 as reagents and adjustment of the experimental parameters. The morphology and structure of the asprepared products were characterized by a series of techniques such as X-ray podwer diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical performance of the nanowires was studied by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. It was found that two pairs of redox peaks appeared in the CV curves of Co3O4 nanowire electrodes at low scan rates. The specific capacitance of the Co3O4 nanowire electrodes was 163 F·g-1 at a current density of 1 A·g-1, according to the galvanostatic charge-discharge measurements. Cycle stability tests showed that the specific capacitance increased over the first tens of cycles and then reduced slowly. After 1000 cycles, the capacitance retention was over 98% at 1 A·g-1 and 80% at 4 A·g-1; it then decreased obviously with further increase in cycle number. In Li-ion battery measurements, Co3O4 nanowire electrodes showed a discharge capacitance of 1124 mAh·g-1 which decreased rapidly during the cycle test. The formation mechanism and the relationship between the structure and electrochemical properties of Co3O4 nanowires were discussed based on the experimental results.
Cobalt oxide (Co3O4) nanowires were controllably synthesized using glycerol and Co(NO3)2 as reagents and adjustment of the experimental parameters. The morphology and structure of the asprepared products were characterized by a series of techniques such as X-ray podwer diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical performance of the nanowires was studied by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. It was found that two pairs of redox peaks appeared in the CV curves of Co3O4 nanowire electrodes at low scan rates. The specific capacitance of the Co3O4 nanowire electrodes was 163 F·g-1 at a current density of 1 A·g-1, according to the galvanostatic charge-discharge measurements. Cycle stability tests showed that the specific capacitance increased over the first tens of cycles and then reduced slowly. After 1000 cycles, the capacitance retention was over 98% at 1 A·g-1 and 80% at 4 A·g-1; it then decreased obviously with further increase in cycle number. In Li-ion battery measurements, Co3O4 nanowire electrodes showed a discharge capacitance of 1124 mAh·g-1 which decreased rapidly during the cycle test. The formation mechanism and the relationship between the structure and electrochemical properties of Co3O4 nanowires were discussed based on the experimental results.
2012, 28(02): 393-398
doi: 10.3866/PKU.WHXB201112163
Abstract:
TiO2 and B-Fe-Ce-modified TiO2 films were synthesized on the surfaces of 316L stainless steel (316L SS) substrates using a sol-gel and dip-coating method. The properties of the films were characterized by field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy and energy dispersive spectrometry. The corrosion resistance of the films and their ability to protect stainless steel were investigated by electrochemical impedance spectroscopy and potentiodynamic polarization curves. Both TiO2 and B-Fe-Ce-modified TiO2 films were composed of anatase nanoparticles about 15 and 10 nm in diameter, respectively. Impedance spectra of the stainless steel substrates coated TiO2 films contained semicircles for capacitive reactance in 0.5 mol·L-1 NaCl solution, but the charge transfer resistance of the B-Fe-Ce-TiO2/316L SS electrode was higher than that of the TiO2/316L SS electrode. The potentiodynamic anodic polarization curve of the B-Fe-Ce-TiO2/316L SS electrode showed a larger stable passive region and a higher breakdown potential than the TiO2/316L SS electrode, indicating that the modified film had better corrosion resistance and protective properties for 316L SS.
TiO2 and B-Fe-Ce-modified TiO2 films were synthesized on the surfaces of 316L stainless steel (316L SS) substrates using a sol-gel and dip-coating method. The properties of the films were characterized by field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy and energy dispersive spectrometry. The corrosion resistance of the films and their ability to protect stainless steel were investigated by electrochemical impedance spectroscopy and potentiodynamic polarization curves. Both TiO2 and B-Fe-Ce-modified TiO2 films were composed of anatase nanoparticles about 15 and 10 nm in diameter, respectively. Impedance spectra of the stainless steel substrates coated TiO2 films contained semicircles for capacitive reactance in 0.5 mol·L-1 NaCl solution, but the charge transfer resistance of the B-Fe-Ce-TiO2/316L SS electrode was higher than that of the TiO2/316L SS electrode. The potentiodynamic anodic polarization curve of the B-Fe-Ce-TiO2/316L SS electrode showed a larger stable passive region and a higher breakdown potential than the TiO2/316L SS electrode, indicating that the modified film had better corrosion resistance and protective properties for 316L SS.
2012, 28(02): 399-406
doi: 10.3866/PKU.WHXB201112142
Abstract:
Three synthesized piperidin-4-one oximes, 3-ethyl-2,6-diphenyl-piperidin-4-one oxime (A), 1- methyl-3-isopropyl-2,6-diphenyl-piperidin-4-one oxime (B), and 3-isopropyl-2,6-diphenyl-piperidin-4-one oxime (C), were tested at different concentrations to determine their ability to inhibit corrosion of mild steel in 1 mol·L-1 H2SO4 and measured by a mass loss method (at various temperatures), polarization and impedance measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energydispersive X-ray spectroscopy (EDS), and a quantum chemical method. The synergistic influence of compounds A, B and C with iodides has also been evaluated. All three compounds show od inhibition efficiency in the following order: A>B>C. Compounds A, B and C were found to physically adsorb on the surface of mild steel while obeying the Temkin isotherm. Polarization measurements indicated that these compounds behave as a mixed mode inhibitor. XRD and SEM with EDS studies revealed the formation of a protective barrier on the mild steel surface by these oximes. The electron donating ability of the studied molecules was tested using semi empirical methods. The studies revealed that the oxime nitrogen, the piperidine moiety, and the phenyl ring assist largely in corrosion control. The studies also showed that the steric crowding by the alkyl group in the piperidine ring affects the inhibitor efficiency. Further, it is interesting to note that all of the studied compounds exhibit synergism with iodide ions.
Three synthesized piperidin-4-one oximes, 3-ethyl-2,6-diphenyl-piperidin-4-one oxime (A), 1- methyl-3-isopropyl-2,6-diphenyl-piperidin-4-one oxime (B), and 3-isopropyl-2,6-diphenyl-piperidin-4-one oxime (C), were tested at different concentrations to determine their ability to inhibit corrosion of mild steel in 1 mol·L-1 H2SO4 and measured by a mass loss method (at various temperatures), polarization and impedance measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energydispersive X-ray spectroscopy (EDS), and a quantum chemical method. The synergistic influence of compounds A, B and C with iodides has also been evaluated. All three compounds show od inhibition efficiency in the following order: A>B>C. Compounds A, B and C were found to physically adsorb on the surface of mild steel while obeying the Temkin isotherm. Polarization measurements indicated that these compounds behave as a mixed mode inhibitor. XRD and SEM with EDS studies revealed the formation of a protective barrier on the mild steel surface by these oximes. The electron donating ability of the studied molecules was tested using semi empirical methods. The studies revealed that the oxime nitrogen, the piperidine moiety, and the phenyl ring assist largely in corrosion control. The studies also showed that the steric crowding by the alkyl group in the piperidine ring affects the inhibitor efficiency. Further, it is interesting to note that all of the studied compounds exhibit synergism with iodide ions.
2012, 28(02): 407-413
doi: 10.3866/PKU.WHXB201112164
Abstract:
The effect of ceria particles on the corrosion resistance of Mg-rich primer on AZ91D magnesium alloy was studied using the Machu test, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that addition of a small amount of cerium oxide (0.1% , mass fraction) had no effect on the corrosion resistance of the coating, and the addition of excessive particles (3%) reduces the corrosion resistance of the coating. However, addition of 0.5% ceria particles to the Mg-rich primer can significantly improve the protection performance of the primer on AZ91D magnesium alloy. The coating resistance increases and coating capacitance decreases after the addition of ceria particles. Although the addition of ceria does not change the protection mechanisms of the magnesium-rich primer on AZ91D magnesium alloy, the electrochemical activity of the magnesium particles in the primer decreases and the service life of the Mg-rich primer is obviously prolonged. The ceria particles also result in an improved barrier effect. In addition, the presence of ceria particles on the AZ91D alloy surface can increase the corrosion potential and decrease the current density of the alloy, which is beneficial for cathode protection of the pure magnesium particles on the alloy substrate.
The effect of ceria particles on the corrosion resistance of Mg-rich primer on AZ91D magnesium alloy was studied using the Machu test, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that addition of a small amount of cerium oxide (0.1% , mass fraction) had no effect on the corrosion resistance of the coating, and the addition of excessive particles (3%) reduces the corrosion resistance of the coating. However, addition of 0.5% ceria particles to the Mg-rich primer can significantly improve the protection performance of the primer on AZ91D magnesium alloy. The coating resistance increases and coating capacitance decreases after the addition of ceria particles. Although the addition of ceria does not change the protection mechanisms of the magnesium-rich primer on AZ91D magnesium alloy, the electrochemical activity of the magnesium particles in the primer decreases and the service life of the Mg-rich primer is obviously prolonged. The ceria particles also result in an improved barrier effect. In addition, the presence of ceria particles on the AZ91D alloy surface can increase the corrosion potential and decrease the current density of the alloy, which is beneficial for cathode protection of the pure magnesium particles on the alloy substrate.
2012, 28(02): 414-420
doi: 10.3866/PKU.WHXB201112011
Abstract:
The initial behavior of electroless nickel deposition on aluminum pretreated by nickel immersion and electroless nickel pre-plating processes was studied measuring the open circuit potential (OCP) as a function of time (EOCP-t). Scanning electron microscopy (SEM) was used to observe the surface morphology of the pretreated specimens. During the initial stages of the electroless nickel deposition, all pretreated and un-pretreated aluminum substrates experienced removal of the oxide film, activation, mixed control and electroless nickel deposition. After nickel immersion and electroless nickel pre-plating, fine nickel particles were attached to the surface of the aluminum. Our experimental results, including EOCP-t and SEM, indicate that electroless nickel plating in a weak acidic bath was successfully accomplished on the aluminum pretreated with a double treatment of electroless nickel pre-plating in an alkaline nickel solution containing a complexing agent and a reductant. The nickel coating obtained adhered to the aluminum substrate, had a granular appearance and an amorphous structure.
The initial behavior of electroless nickel deposition on aluminum pretreated by nickel immersion and electroless nickel pre-plating processes was studied measuring the open circuit potential (OCP) as a function of time (EOCP-t). Scanning electron microscopy (SEM) was used to observe the surface morphology of the pretreated specimens. During the initial stages of the electroless nickel deposition, all pretreated and un-pretreated aluminum substrates experienced removal of the oxide film, activation, mixed control and electroless nickel deposition. After nickel immersion and electroless nickel pre-plating, fine nickel particles were attached to the surface of the aluminum. Our experimental results, including EOCP-t and SEM, indicate that electroless nickel plating in a weak acidic bath was successfully accomplished on the aluminum pretreated with a double treatment of electroless nickel pre-plating in an alkaline nickel solution containing a complexing agent and a reductant. The nickel coating obtained adhered to the aluminum substrate, had a granular appearance and an amorphous structure.
2012, 28(02): 421-426
doi: 10.3866/PKU.WHXB201112122
Abstract:
The electrochemical oxidation behavior of p-methoxy toluene was studied in an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) on platinum electrode by cyclic voltammetry (CV), chronoamperometry (CP), and in situ Fourier transform infrared spectroscopy (in-situ FTIRS). The results showed that the electrochemical oxidation of p-methoxy toluene in BMIMBF4 was irreversible. The four-electron process was controlled by diffusion, and the diffusion coefficient D was 3.4×10-7 cm2·s-1. The main oxidation product was anisaldehyde. A proper amount of water and a suitable temperature were favorable for the anisaldehyde.
The electrochemical oxidation behavior of p-methoxy toluene was studied in an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) on platinum electrode by cyclic voltammetry (CV), chronoamperometry (CP), and in situ Fourier transform infrared spectroscopy (in-situ FTIRS). The results showed that the electrochemical oxidation of p-methoxy toluene in BMIMBF4 was irreversible. The four-electron process was controlled by diffusion, and the diffusion coefficient D was 3.4×10-7 cm2·s-1. The main oxidation product was anisaldehyde. A proper amount of water and a suitable temperature were favorable for the anisaldehyde.
2012, 28(02): 427-432
doi: 10.3866/PKU.WHXB201111213
Abstract:
A series of dually mixed self-assembled monolayers were prepared by a simple step-by-step method. Four carbonyl chlorides with different chain lengths were selected and assembled onto a N-[3- (trimethoxylsilyl)propyl] ethylene diamine self-assembled monolayer. Different mixed films were obtained by controlling the ratio of co-deposited carbonyl chlorides. The structures of the films were characterized by measuring their contact angles, ellipsometric thickness, and atomic force microscopy. No phase separation was observed in the mixed films. Micro-tribological studies were also carried out on the films. It was found that frictional coefficients decreased as the ratio of the longer component was increased.
A series of dually mixed self-assembled monolayers were prepared by a simple step-by-step method. Four carbonyl chlorides with different chain lengths were selected and assembled onto a N-[3- (trimethoxylsilyl)propyl] ethylene diamine self-assembled monolayer. Different mixed films were obtained by controlling the ratio of co-deposited carbonyl chlorides. The structures of the films were characterized by measuring their contact angles, ellipsometric thickness, and atomic force microscopy. No phase separation was observed in the mixed films. Micro-tribological studies were also carried out on the films. It was found that frictional coefficients decreased as the ratio of the longer component was increased.
2012, 28(02): 433-436
doi: 10.3866/PKU.WHXB201112062
Abstract:
The adsorption and reaction of methanol on Cu and ZrO2/Cu were investigated using in situ infrared diffuse reflectance spectroscopy, in which the catalysts were reduced at different temperatures in order to change the content of surface oxygen species and investigate the change trends of methanol adsorption and reaction over the catalysts with the oxygen species content. The results show that methanol is adsorbed on the surface of Cu to produce CO2 via the intermediate of adsorbed formaldehyde, while the intermediate of formate is formed on the surface of ZrO2/Cu. The production rate of CO2 via the intermediate becomes slower with the rise of the reduction temperature of the catalysts, illustrating that the content of oxygen species on the surface of the catalysts determines the formation of the intermediate and the reaction rate.
The adsorption and reaction of methanol on Cu and ZrO2/Cu were investigated using in situ infrared diffuse reflectance spectroscopy, in which the catalysts were reduced at different temperatures in order to change the content of surface oxygen species and investigate the change trends of methanol adsorption and reaction over the catalysts with the oxygen species content. The results show that methanol is adsorbed on the surface of Cu to produce CO2 via the intermediate of adsorbed formaldehyde, while the intermediate of formate is formed on the surface of ZrO2/Cu. The production rate of CO2 via the intermediate becomes slower with the rise of the reduction temperature of the catalysts, illustrating that the content of oxygen species on the surface of the catalysts determines the formation of the intermediate and the reaction rate.
2012, 28(02): 437-444
doi: 10.3866/PKU.WHXB201112082
Abstract:
Pure-phase α-MnO2 and δ-MnO2 nanorods were synthesized through an easy solution-based hydrothermal method. Platinum nanoparticles supported by the obtained MnO2 nanorods were prepared by the colloid deposition process. The microstructure and adsorption activity of the obtained catalysts were researched by different techniques such as transmission electron microscopy (TEM), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption measurements, and H2 temperature-programmed reduction (H2-TPR). The cataluminescence (CTL) properties of CO and volatile organic compounds (VOCs), such as benzene and toluene, on the resultant catalysts were explored. The results showed that the platinum nanoparticles were well distributed in α-MnO2 and δ-MnO2. In addition, the Pt load process does not affect the crystal phase structure of the α-MnO2 nanorods, but can generate structural changes in the δ-MnO2 nanorods. The phase transformation did not the result of the reaction between the δ-MnO2 nanorods and Pt as shown in the XPS study. The α-MnO2 and δ-MnO2 nanorods showed a high catalytic oxidative activity toward CO, benzene, and toluene, and δ-MnO2 showed a higher activity than the α-MnO2 phase. Although, the Pt load led to a decrease in the surface area of the MnO2 nanorods which was confirmed by the N2 adsorption-desorption measurements, but the H2-TPR results showed that the interaction between Pt and MnO2 was intense, which significantly enhanced its catalytic activity. The Pt/δ-MnO2 nanorods exhibited a higher activity than Pt/α-MnO2. CTL research showed that the activities of the four catalysts increased in the order of α-MnO2≤ δ-MnO2 < Pt/α-MnO2 < Pt/δ-MnO2, and the H2-TPR results were consistent. Pt loading significantly enhanced the catalytic oxidative activity of α-MnO2 and δ-MnO2 nanorods to CO, benzene, and toluene.
Pure-phase α-MnO2 and δ-MnO2 nanorods were synthesized through an easy solution-based hydrothermal method. Platinum nanoparticles supported by the obtained MnO2 nanorods were prepared by the colloid deposition process. The microstructure and adsorption activity of the obtained catalysts were researched by different techniques such as transmission electron microscopy (TEM), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption measurements, and H2 temperature-programmed reduction (H2-TPR). The cataluminescence (CTL) properties of CO and volatile organic compounds (VOCs), such as benzene and toluene, on the resultant catalysts were explored. The results showed that the platinum nanoparticles were well distributed in α-MnO2 and δ-MnO2. In addition, the Pt load process does not affect the crystal phase structure of the α-MnO2 nanorods, but can generate structural changes in the δ-MnO2 nanorods. The phase transformation did not the result of the reaction between the δ-MnO2 nanorods and Pt as shown in the XPS study. The α-MnO2 and δ-MnO2 nanorods showed a high catalytic oxidative activity toward CO, benzene, and toluene, and δ-MnO2 showed a higher activity than the α-MnO2 phase. Although, the Pt load led to a decrease in the surface area of the MnO2 nanorods which was confirmed by the N2 adsorption-desorption measurements, but the H2-TPR results showed that the interaction between Pt and MnO2 was intense, which significantly enhanced its catalytic activity. The Pt/δ-MnO2 nanorods exhibited a higher activity than Pt/α-MnO2. CTL research showed that the activities of the four catalysts increased in the order of α-MnO2≤ δ-MnO2 < Pt/α-MnO2 < Pt/δ-MnO2, and the H2-TPR results were consistent. Pt loading significantly enhanced the catalytic oxidative activity of α-MnO2 and δ-MnO2 nanorods to CO, benzene, and toluene.
2012, 28(02): 445-449
doi: 10.3866/PKU.WHXB201111244
Abstract:
The optimum reaction parameters for CO oxidation in the presence and absence of H2 have been investigated by photoreduction method to enhance the catalytic activity and selectivity of CO2 for CO preferential oxidation (PROX) in H2-rich stream in detail. X-ray photoelectron spectroscoopy (XPS) results showed that part oxygen vacancies produced on the surface of photoreduced catalysts, which maybe the activity site for the chemisorbed H. Therefore, a possible bi-function reaction mechanism for CO preferential oxidation over the photoreduced Pt/TiO2 catalyst has been proposed.
The optimum reaction parameters for CO oxidation in the presence and absence of H2 have been investigated by photoreduction method to enhance the catalytic activity and selectivity of CO2 for CO preferential oxidation (PROX) in H2-rich stream in detail. X-ray photoelectron spectroscoopy (XPS) results showed that part oxygen vacancies produced on the surface of photoreduced catalysts, which maybe the activity site for the chemisorbed H. Therefore, a possible bi-function reaction mechanism for CO preferential oxidation over the photoreduced Pt/TiO2 catalyst has been proposed.
2012, 28(02): 450-456
doi: 10.3866/PKU.WHXB201112141
Abstract:
Photocatalytic reaction of CH4 gas with H2O vapor over Pt/TiO2 at around room temperature (ca 323 K) was examined in a flow reactor. H2 and CO2 were the main products, and only trace amounts of C2H6, C2H4, and CO were observed. After an induction period, the molar ratio of H2 to CO2 in the outlet gas became close to 1.7. Thus, the main reaction is suggested to be: CH4+2H2O(g)→4H2+CO2, which can be referred to as photocatalytic steam reforming of methane (PSRM). The reaction would be promoted by photoexcited electrons and holes, which were generated by band gap photoexcitation of the TiO2 photocatalyst. In addition, the effects of reaction parameters, such as molar ratio of CH4 to H2O, total flow rate, noble-metal cocatalysts, wavelength of irradiating light, amounts of catalysts, and recycling efficiency of the p-Pt/TiO2 photocatalyst via light deposition of preformed Pt nanoparticles on P25, on the hydrogen evolution were investigated.
Photocatalytic reaction of CH4 gas with H2O vapor over Pt/TiO2 at around room temperature (ca 323 K) was examined in a flow reactor. H2 and CO2 were the main products, and only trace amounts of C2H6, C2H4, and CO were observed. After an induction period, the molar ratio of H2 to CO2 in the outlet gas became close to 1.7. Thus, the main reaction is suggested to be: CH4+2H2O(g)→4H2+CO2, which can be referred to as photocatalytic steam reforming of methane (PSRM). The reaction would be promoted by photoexcited electrons and holes, which were generated by band gap photoexcitation of the TiO2 photocatalyst. In addition, the effects of reaction parameters, such as molar ratio of CH4 to H2O, total flow rate, noble-metal cocatalysts, wavelength of irradiating light, amounts of catalysts, and recycling efficiency of the p-Pt/TiO2 photocatalyst via light deposition of preformed Pt nanoparticles on P25, on the hydrogen evolution were investigated.
Photocatalytic Property and Reaction Mechanism of (Ni-Mo)/TiO2 Nano Thin Film Evaluated with Con Red
2012, 28(02): 457-464
doi: 10.3866/PKU.WHXB201112081
Abstract:
(Ni-Mo)/TiO2 composite thin films were prepared by composite electroplating at a constant current. The surface morphology, phase structure, and optical characteristics of the thin films were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectrum, and ultravioletvisible diffuse reflectance spectroscopy (UV-Vis DRS), respectively. The photocatalytic properties of the (Ni-Mo)/TiO2 composite thin films were evaluated with Con red as a model compound. The effects of pH of the Con red aqueous solution on the photocatalytic activity of the (Ni-Mo)/TiO2 thin films were investigated. Using cyclic voltammetry technique and a method of adding active species scavengers to the solution, the mechanisms of photocatalytic degradation of the films were explored. The results show that the (Ni-Mo)/TiO2 films consist of crystalline grains of TiO2 in the size range of 50-100 nm and nanocrystalline grains of Ni-Mo in solid solution. The (Ni-Mo)/TiO2 films are photocatalytically more active than a TiO2/ITO (indium tin oxide) reference film. Under halogen light irradiation, the photocatalytic degradation rate of the (Ni-Mo)/TiO2 films is 2.43 times as much as that of a porous TiO2 (Degussa P25)/ ITO film. The improvement in photocatalytic activity for the composite films could be mainly attributed to the heterojunction of (Ni-Mo)/TiO2, the electronic passageway of Ni-Mo in the composite films, and the catalysis of Ni-Mo in the composite film for the reaction of excited electrons with dissolved oxygen. The photocatalytic reaction mechanisms of the (Ni-Mo)/TiO2 films evaluated with Con red are given under visible and UV light irradiation, respectively.
(Ni-Mo)/TiO2 composite thin films were prepared by composite electroplating at a constant current. The surface morphology, phase structure, and optical characteristics of the thin films were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectrum, and ultravioletvisible diffuse reflectance spectroscopy (UV-Vis DRS), respectively. The photocatalytic properties of the (Ni-Mo)/TiO2 composite thin films were evaluated with Con red as a model compound. The effects of pH of the Con red aqueous solution on the photocatalytic activity of the (Ni-Mo)/TiO2 thin films were investigated. Using cyclic voltammetry technique and a method of adding active species scavengers to the solution, the mechanisms of photocatalytic degradation of the films were explored. The results show that the (Ni-Mo)/TiO2 films consist of crystalline grains of TiO2 in the size range of 50-100 nm and nanocrystalline grains of Ni-Mo in solid solution. The (Ni-Mo)/TiO2 films are photocatalytically more active than a TiO2/ITO (indium tin oxide) reference film. Under halogen light irradiation, the photocatalytic degradation rate of the (Ni-Mo)/TiO2 films is 2.43 times as much as that of a porous TiO2 (Degussa P25)/ ITO film. The improvement in photocatalytic activity for the composite films could be mainly attributed to the heterojunction of (Ni-Mo)/TiO2, the electronic passageway of Ni-Mo in the composite films, and the catalysis of Ni-Mo in the composite film for the reaction of excited electrons with dissolved oxygen. The photocatalytic reaction mechanisms of the (Ni-Mo)/TiO2 films evaluated with Con red are given under visible and UV light irradiation, respectively.
2012, 28(02): 465-469
doi: 10.3866/PKU.WHXB201111291
Abstract:
Phenothiazine (PTZ)-corrole dyads 1-3 and their gallium(III) complexes 4-6 have been synthesized and characterized. The steady-state absorption and emission spectra and the time-resolved fluorescence decay profiles have been measured in toluene. The radiative and nonradiative rate constants have been obtained from the fluorescence quantum yields and monoexponential fluorescence lifetimes. The absorption spectra revealed that the gallium(III) corrole dyads exhibit stronger Soret bands and Q bands than free base corrole dyads. The fluorescence quantum yields of 1-3 are 0.156, 0.134, and 0.139, and the radiative rate constants are 4.02×107, 3.47×107, and 2.89×107 s-1, respectively. The fluorescence quantum yields of 4-6 are 0.502, 0.443, and 0.494, and the radiative rate constants are 20.9×107, 16.78×107, and 21.11×107 s-1, which are obviously higher than those of the corresponding free base corroles. The lifetimes of 4-6 are 2.40, 2.64, and 2.34 ns, respectively, which are somewhat shorter than those of the corresponding free base corroles. Agarose gel electrophoresis shows that these gallium(III) corrole dyads could cleave supercoiled DNA (form I) to give nicked-circular DNA (form II) under irradiation.
Phenothiazine (PTZ)-corrole dyads 1-3 and their gallium(III) complexes 4-6 have been synthesized and characterized. The steady-state absorption and emission spectra and the time-resolved fluorescence decay profiles have been measured in toluene. The radiative and nonradiative rate constants have been obtained from the fluorescence quantum yields and monoexponential fluorescence lifetimes. The absorption spectra revealed that the gallium(III) corrole dyads exhibit stronger Soret bands and Q bands than free base corrole dyads. The fluorescence quantum yields of 1-3 are 0.156, 0.134, and 0.139, and the radiative rate constants are 4.02×107, 3.47×107, and 2.89×107 s-1, respectively. The fluorescence quantum yields of 4-6 are 0.502, 0.443, and 0.494, and the radiative rate constants are 20.9×107, 16.78×107, and 21.11×107 s-1, which are obviously higher than those of the corresponding free base corroles. The lifetimes of 4-6 are 2.40, 2.64, and 2.34 ns, respectively, which are somewhat shorter than those of the corresponding free base corroles. Agarose gel electrophoresis shows that these gallium(III) corrole dyads could cleave supercoiled DNA (form I) to give nicked-circular DNA (form II) under irradiation.
2012, 28(02): 470-478
doi: 10.3866/PKU.WHXB201112051
Abstract:
The effects of rare earth ions (La3+ , Gd3+ , Yb3+ ) on the interactions between nano TiO2 and bovine serum albumin (BSA) were investigated in the presence of ultrasound. A combination of ultraviolet (UV) spectroscopy, fluorescence spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used to characterize the interactions under simulated human physiological conditions. The endogenous fluorescence of BSA was quenched by nano TiO2 in different systems. The mechanism of fluorescence quenching was static quenching with non-radiative energy transfer. SDS-PAGE revealed that the structure of BSA was not obviously destroyed upon binding with nano TiO2 in different systems. Hydrogen bond and van der Waals interaction were deduced, on the basis of the thermodynamic parameters, to be the major driving forces. The binding distance of nano TiO2 to BSA and the thermodynamic parameters were changed in the presence of rare earth ions. However, the number of binding sites and the type of intermolecular force remained essentially unchanged. This indicated that the interaction between nano TiO2 and BSA was influenced by the rare earth ions, and that a lanthanide tetrad effect was observed. It is conjectured that rare earth ions participate in the nano TiO2-BSA interaction process by means of“ionic bridge”formation or“appositional substitution”.
The effects of rare earth ions (La3+ , Gd3+ , Yb3+ ) on the interactions between nano TiO2 and bovine serum albumin (BSA) were investigated in the presence of ultrasound. A combination of ultraviolet (UV) spectroscopy, fluorescence spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used to characterize the interactions under simulated human physiological conditions. The endogenous fluorescence of BSA was quenched by nano TiO2 in different systems. The mechanism of fluorescence quenching was static quenching with non-radiative energy transfer. SDS-PAGE revealed that the structure of BSA was not obviously destroyed upon binding with nano TiO2 in different systems. Hydrogen bond and van der Waals interaction were deduced, on the basis of the thermodynamic parameters, to be the major driving forces. The binding distance of nano TiO2 to BSA and the thermodynamic parameters were changed in the presence of rare earth ions. However, the number of binding sites and the type of intermolecular force remained essentially unchanged. This indicated that the interaction between nano TiO2 and BSA was influenced by the rare earth ions, and that a lanthanide tetrad effect was observed. It is conjectured that rare earth ions participate in the nano TiO2-BSA interaction process by means of“ionic bridge”formation or“appositional substitution”.
2012, 28(02): 479-488
doi: 10.3866/PKU.WHXB201111231
Abstract:
The Cu2+-bound and metal-free α-synuclein (1-17) peptides were simulated with the GROMOS 43A1 force field in the GROMACS package. There were six groups and each group was run for 500 ns in the physiological environment, giving a total of 3 μs. It was found that the Cu2+-bound α-synuclein (1-17) peptide contained more unfluctuating secondary structure samples and more β-conformations than the metal-free α-synuclein (1-17) peptide. Simulations indicate that the Cu2+-bound α-synuclein (1-17) peptide prefers conformations that allow larger solvent exposure of hydrophobic residues than the metal-free α-synuclein (1-17) peptide, which provides underlying evidence for why Cu2+ promotes the aggregation of α-synuclein. By mapping the free energy surface landscape, we found that conformations of Cu2+-bound α-synuclein (1-17) peptide distribute more compactly than the metal-free α-synuclein (1-17) peptide. The results are almost the same as the central conformation obtained by conformational clustering analysis. These new findings indicate that Cu2+ modulates the conformation of α-synuclein from intrinsic disorder to order, which is central to the conformational dynamic and thermodynamic properties of the Cu2+-bound and metal-free α-synuclein (1-17) peptides at the molecular level. This work is propitious to understanding the mechanisms of Cu2+ participation in the fibrillization of α-synuclein.
The Cu2+-bound and metal-free α-synuclein (1-17) peptides were simulated with the GROMOS 43A1 force field in the GROMACS package. There were six groups and each group was run for 500 ns in the physiological environment, giving a total of 3 μs. It was found that the Cu2+-bound α-synuclein (1-17) peptide contained more unfluctuating secondary structure samples and more β-conformations than the metal-free α-synuclein (1-17) peptide. Simulations indicate that the Cu2+-bound α-synuclein (1-17) peptide prefers conformations that allow larger solvent exposure of hydrophobic residues than the metal-free α-synuclein (1-17) peptide, which provides underlying evidence for why Cu2+ promotes the aggregation of α-synuclein. By mapping the free energy surface landscape, we found that conformations of Cu2+-bound α-synuclein (1-17) peptide distribute more compactly than the metal-free α-synuclein (1-17) peptide. The results are almost the same as the central conformation obtained by conformational clustering analysis. These new findings indicate that Cu2+ modulates the conformation of α-synuclein from intrinsic disorder to order, which is central to the conformational dynamic and thermodynamic properties of the Cu2+-bound and metal-free α-synuclein (1-17) peptides at the molecular level. This work is propitious to understanding the mechanisms of Cu2+ participation in the fibrillization of α-synuclein.
2012, 28(02): 489-493
doi: 10.3866/PKU.WHXB201111212
Abstract:
Two different kinds of porous silicon (PS) were grown by electrochemical corrosion in a double-tank cell on the surface of single-crystalline P-type silicon. According to their pore sizes, they were denoted as meso-porous silicon (meso-PS) and macro-porous silicon (macro-PS). The surface and cross-section morphologies of the PS were observed by scanning electron microscope (SEM). The surface chemical bonds of the meso-PS and macro-PS were investigated by Fourier transform infrared (FTIR) spectroscopy. The electrical properties of the PS were studied by measuring the I-V characteristics. The gas sensing properties of meso-PS and macro-PS were thoroughly measured at room temperature. Meso-PS has much higher sensitivity, while macro-PS has better response-recovery characteristics. Meso-PS shows better selectivity for NO2, while macro-PS shows better selectivity for NH3.
Two different kinds of porous silicon (PS) were grown by electrochemical corrosion in a double-tank cell on the surface of single-crystalline P-type silicon. According to their pore sizes, they were denoted as meso-porous silicon (meso-PS) and macro-porous silicon (macro-PS). The surface and cross-section morphologies of the PS were observed by scanning electron microscope (SEM). The surface chemical bonds of the meso-PS and macro-PS were investigated by Fourier transform infrared (FTIR) spectroscopy. The electrical properties of the PS were studied by measuring the I-V characteristics. The gas sensing properties of meso-PS and macro-PS were thoroughly measured at room temperature. Meso-PS has much higher sensitivity, while macro-PS has better response-recovery characteristics. Meso-PS shows better selectivity for NO2, while macro-PS shows better selectivity for NH3.
2012, 28(02): 494-498
doi: 10.3866/PKU.WHXB201111233
Abstract:
Spherulites of rigid chain ladder polyphenylsilsesquioxane (PPSQ) were produced through solvent-induced crystallization. The influences of solution concentration, solvent evaporation time, and temperature on the spherulitic morphology of PPSQ were studied by optical microscopy. Diluting the solution was found to have the same effect as elevating the crystallization temperature. The size of the spherulites increases with either decreasing concentration or increasing temperature. This is caused by the enhanced solubility of PPSQ in xylene under such conditions. Extending the solvent evaporation time while leaving the other conditions unchanged also leads to the formation of larger spherulites. The invariance of spherulitic structure upon sample rotation suggests that the spherulites possess a uniform crystallographic orientation. The negative optical characteristics of spherulites indicates that the PPSQ molecular chains are oriented in the tangential direction of the spherulite. Considering the high rigidity of the molecules, an organization model of PPSQ spherulite is proposed.
Spherulites of rigid chain ladder polyphenylsilsesquioxane (PPSQ) were produced through solvent-induced crystallization. The influences of solution concentration, solvent evaporation time, and temperature on the spherulitic morphology of PPSQ were studied by optical microscopy. Diluting the solution was found to have the same effect as elevating the crystallization temperature. The size of the spherulites increases with either decreasing concentration or increasing temperature. This is caused by the enhanced solubility of PPSQ in xylene under such conditions. Extending the solvent evaporation time while leaving the other conditions unchanged also leads to the formation of larger spherulites. The invariance of spherulitic structure upon sample rotation suggests that the spherulites possess a uniform crystallographic orientation. The negative optical characteristics of spherulites indicates that the PPSQ molecular chains are oriented in the tangential direction of the spherulite. Considering the high rigidity of the molecules, an organization model of PPSQ spherulite is proposed.
