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2017 Volume 33 Issue 10
2017, 33(10):
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2017, 33(10): 1923-1924
doi: 10.3866/PKU.WHXB201705023
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2017, 33(10): 1925-1926
doi: 10.3866/PKU.WHXB201706025
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2017, 33(10): 1927-1928
doi: 10.3866/PKU.WHXB201706144
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2017, 33(10): 1929-1929
doi: 10.3866/PKU.WHXB201706022
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2017, 33(10): 1930-1931
doi: 10.3866/PKU.WHXB201706026
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2017, 33(10): 1932-1933
doi: 10.3866/PKU.WHXB201706024
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2017, 33(10): 1934-1943
doi: 10.3866/PKU.WHXB201715185
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Understanding the energy band alignment across multiple layers in thin-film optoelectronic devices is extremely important because it governs elementary optoelectronic processes, such as charge carrier generation, separation, transport, recombination and collection. This monograph summarizes recent progress in visualization of energy band alignment in thin-film optoelectronic devices, such as organic solar cells (OSCs) and organic-inorganic perovskite photodetectors from our group by using scanning Kelvin probe microscopy (SKPM). Since active layers are enclosed by the top and bottom electrodes in vertically stacked devices, it is highly challenging to study the energy band alignment under operando conditions. Thus, cross-sectional SKPM has been developed to resolve this challenge. The results demonstrated that the interlayer was one of the most important factors for adjusting energy band alignment, determining device polarity and improving device performance. The characterization methods described in this monograph are poised to be widely applied to research in various thin-film optoelectronic devices, such as photovoltaic devices, photodetectors and light-emitting diodes (LEDs), especially those devices with tandem structures.
Understanding the energy band alignment across multiple layers in thin-film optoelectronic devices is extremely important because it governs elementary optoelectronic processes, such as charge carrier generation, separation, transport, recombination and collection. This monograph summarizes recent progress in visualization of energy band alignment in thin-film optoelectronic devices, such as organic solar cells (OSCs) and organic-inorganic perovskite photodetectors from our group by using scanning Kelvin probe microscopy (SKPM). Since active layers are enclosed by the top and bottom electrodes in vertically stacked devices, it is highly challenging to study the energy band alignment under operando conditions. Thus, cross-sectional SKPM has been developed to resolve this challenge. The results demonstrated that the interlayer was one of the most important factors for adjusting energy band alignment, determining device polarity and improving device performance. The characterization methods described in this monograph are poised to be widely applied to research in various thin-film optoelectronic devices, such as photovoltaic devices, photodetectors and light-emitting diodes (LEDs), especially those devices with tandem structures.
2017, 33(10): 1944-1959
doi: 10.3866/PKU.WHXB201705177
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Anodized TiO2 nanotube arrays are one of the key electrode materials for supercapacitors, because of their easy synthesis, controllable morphology, and environmentally friendly characteristics. In this paper, the multi-modification of TiO2 nanotube arrays is presented. These modifications include the introduction of oxygen vacancies, and the modification of the arrays by metals, nonmetals, metal oxides and conductive polymers; these modifications provide scope to increase the electrochemical performance of the TiO2 nanotube arrays. Recent advances of anodized TiO2 nanotube arrays in supercapacitors are systematically summarized, providing guidance for the practical application of these arrays.
Anodized TiO2 nanotube arrays are one of the key electrode materials for supercapacitors, because of their easy synthesis, controllable morphology, and environmentally friendly characteristics. In this paper, the multi-modification of TiO2 nanotube arrays is presented. These modifications include the introduction of oxygen vacancies, and the modification of the arrays by metals, nonmetals, metal oxides and conductive polymers; these modifications provide scope to increase the electrochemical performance of the TiO2 nanotube arrays. Recent advances of anodized TiO2 nanotube arrays in supercapacitors are systematically summarized, providing guidance for the practical application of these arrays.
2017, 33(10): 1960-1977
doi: 10.3866/PKU.WHXB201705191
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Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers, constructed with lightweight elements by covalent bonds. Owing to their low density, high thermal stability, and inherent porosity, COFs have many potential applications in gas adsorption, heterogeneous catalysis, energy storage, etc. This article reviews the latest progress in COFs, including their structural design, synthesis, purification, characterization methods, and applications in gas adsorption, catalysis, and photoelectricity. Finally, the prospects of COFs are also discussed.
Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers, constructed with lightweight elements by covalent bonds. Owing to their low density, high thermal stability, and inherent porosity, COFs have many potential applications in gas adsorption, heterogeneous catalysis, energy storage, etc. This article reviews the latest progress in COFs, including their structural design, synthesis, purification, characterization methods, and applications in gas adsorption, catalysis, and photoelectricity. Finally, the prospects of COFs are also discussed.
2017, 33(10): 1978-1988
doi: 10.3866/PKU.WHXB201705124
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In this study, 1H nuclear magnetic resonance (NMR) measurements and quantum chemistry (QC) studies of ethanol (ET)-water mixtures and ethylene glycol (EG)-water mixtures are carried out at different temperatures to discuss the interactions between water and the alcohols present in the mixtures. From 1H NMR spectra, it is observed that the chemical shift of the water proton shows two different trends in the ET-water mixtures and the EG-water mixtures. With increasing water concentration, the water proton chemical shift decreases dramatically for ET-water mixtures, while the chemical shift increases slowly for EG-water mixtures. The alcohol hydroxyl proton resonance peaks of both ET and EG shift to lower field with decreasing water concentration. It is found that the resonance peaks of all alkyl protons shift monotonically to low field with increasing alcohol concentration at different temperatures. The geometry optimization results indicate the formation of H-bonds between the water molecules and the hydroxyl groups of the alcohols alongside the weakening of O-H bonds in the alcohols, which results in an O-H bond length decrease. It is interesting to note that the bond length values computed for C-C, C-H and O-H bond in both ET and EG are larger when calculated at the density functional theory (DFT) (B3LYP) level than when calculated using Hartree-Fock (HF) level of theory with the same polarization function and diffusion function. However, the O-H…O H-bond computed at HF level of theory is stronger than that calculated at DFT level of theory. The theoretical results are in good agreement with the experimental ones. In the calculation of NMR chemical shift, DFT(B3LYP) is better than HF, which implies that for the same method, the larger the basis sets are, the more accurate are the calculated values.
In this study, 1H nuclear magnetic resonance (NMR) measurements and quantum chemistry (QC) studies of ethanol (ET)-water mixtures and ethylene glycol (EG)-water mixtures are carried out at different temperatures to discuss the interactions between water and the alcohols present in the mixtures. From 1H NMR spectra, it is observed that the chemical shift of the water proton shows two different trends in the ET-water mixtures and the EG-water mixtures. With increasing water concentration, the water proton chemical shift decreases dramatically for ET-water mixtures, while the chemical shift increases slowly for EG-water mixtures. The alcohol hydroxyl proton resonance peaks of both ET and EG shift to lower field with decreasing water concentration. It is found that the resonance peaks of all alkyl protons shift monotonically to low field with increasing alcohol concentration at different temperatures. The geometry optimization results indicate the formation of H-bonds between the water molecules and the hydroxyl groups of the alcohols alongside the weakening of O-H bonds in the alcohols, which results in an O-H bond length decrease. It is interesting to note that the bond length values computed for C-C, C-H and O-H bond in both ET and EG are larger when calculated at the density functional theory (DFT) (B3LYP) level than when calculated using Hartree-Fock (HF) level of theory with the same polarization function and diffusion function. However, the O-H…O H-bond computed at HF level of theory is stronger than that calculated at DFT level of theory. The theoretical results are in good agreement with the experimental ones. In the calculation of NMR chemical shift, DFT(B3LYP) is better than HF, which implies that for the same method, the larger the basis sets are, the more accurate are the calculated values.
2017, 33(10): 1989-1997
doi: 10.3866/PKU.WHXB201705175
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2,4-Dithiouracil is potentially an important photosensitizer for use in photodynamic therapy. Its photophysics when populated in the lowest excited state has been studied extensively. However, its higher light absorbing excited states and the corresponding reaction dynamics have not been investigated sufficiently. Herein, the resonance Raman spectroscopy and density functional theory were adopted to clarify the electronic transitions associated with the UV absorptions in the far-UV region and the short-time structural dynamics corresponding to the higher light absorbing excited states. The UV absorption spectrum in acetonitrile was deconvoluted into four bands:the moderate intense absorption band at 358 nm (f=0.0336) (A band), the intense broad absorption bands at 338 nm (f=0.1491), 301 nm (f=0.1795), and 278 nm (f=0.3532) (B, C, and D bands) respectively, on the basis of the relationship between the resonance Raman intensities and the oscillator strength f. The result was consistent with the predictions made using the time-dependent density functional theory calculations and the resonance Raman intensity patterns. Thus, the four bands resulted from the deconvolution are assigned as the S0→S2, S0→S6, S0→S7 and S0→S8 transitions, respectively. The resonance Raman spectra of the corresponding B, C, and D bands are assigned and the qualitative short-time structural dynamics are obtained. The major character in the short-time structural dynamics of 2,4-dithiouracil in the S8 excited state is that a non-adiabatic process via S8(ππ*)/S(nπ*) curve-crossing, accompanied with ultrafast structural distortion, takes place in or near the Franck-Condon region, while the major character in the short-time structural dynamics in the S7 and S6 excited state appears in the multidimensional reaction coordinates, which are mostly along the C5C6/C2S8/C4S10/N2C3 bond lengths + C4N3H9/N1C2N3/C2N1C6/C6N1H7/C5C6H12 bond angles for the S7 excited state and the C5C6/N3C2/C4S10/C2S8 bond lengths + C6N1H7/C5C6H12/C5C6N1/C5C6H12/C2N1C6/N1C2N3/C4N3H9/N1C2N3 bond angles for the S6 excited state.
2,4-Dithiouracil is potentially an important photosensitizer for use in photodynamic therapy. Its photophysics when populated in the lowest excited state has been studied extensively. However, its higher light absorbing excited states and the corresponding reaction dynamics have not been investigated sufficiently. Herein, the resonance Raman spectroscopy and density functional theory were adopted to clarify the electronic transitions associated with the UV absorptions in the far-UV region and the short-time structural dynamics corresponding to the higher light absorbing excited states. The UV absorption spectrum in acetonitrile was deconvoluted into four bands:the moderate intense absorption band at 358 nm (f=0.0336) (A band), the intense broad absorption bands at 338 nm (f=0.1491), 301 nm (f=0.1795), and 278 nm (f=0.3532) (B, C, and D bands) respectively, on the basis of the relationship between the resonance Raman intensities and the oscillator strength f. The result was consistent with the predictions made using the time-dependent density functional theory calculations and the resonance Raman intensity patterns. Thus, the four bands resulted from the deconvolution are assigned as the S0→S2, S0→S6, S0→S7 and S0→S8 transitions, respectively. The resonance Raman spectra of the corresponding B, C, and D bands are assigned and the qualitative short-time structural dynamics are obtained. The major character in the short-time structural dynamics of 2,4-dithiouracil in the S8 excited state is that a non-adiabatic process via S8(ππ*)/S(nπ*) curve-crossing, accompanied with ultrafast structural distortion, takes place in or near the Franck-Condon region, while the major character in the short-time structural dynamics in the S7 and S6 excited state appears in the multidimensional reaction coordinates, which are mostly along the C5C6/C2S8/C4S10/N2C3 bond lengths + C4N3H9/N1C2N3/C2N1C6/C6N1H7/C5C6H12 bond angles for the S7 excited state and the C5C6/N3C2/C4S10/C2S8 bond lengths + C6N1H7/C5C6H12/C5C6N1/C5C6H12/C2N1C6/N1C2N3/C4N3H9/N1C2N3 bond angles for the S6 excited state.
2017, 33(10): 1998-2003
doi: 10.3866/PKU.WHXB201705181
Abstract:
Ion exchange adsorption is an important physicochemical process at solid/liquid interfaces. In this study, an approach was established to estimate the activation energy of cation exchange reaction on the charged surface, considering Hofmeister effects. The experimental results showed that Hofmeister effects strongly affect the ionic adsorption equilibrium on the charged particle surface. The position of the adsorbed counterion in the diffuse layer was predicted according to the established model, and the ion exchange activation energies for different bivalent cations were estimated via the cation exchange experiments. The activation energy decreases with increasing ion concentration, and the adsorption saturation of cations is a function of the activation energy at different concentrations. The established model of cation exchange adsorption in the present study has universal applicability in solid/liquid interface reactions.
Ion exchange adsorption is an important physicochemical process at solid/liquid interfaces. In this study, an approach was established to estimate the activation energy of cation exchange reaction on the charged surface, considering Hofmeister effects. The experimental results showed that Hofmeister effects strongly affect the ionic adsorption equilibrium on the charged particle surface. The position of the adsorbed counterion in the diffuse layer was predicted according to the established model, and the ion exchange activation energies for different bivalent cations were estimated via the cation exchange experiments. The activation energy decreases with increasing ion concentration, and the adsorption saturation of cations is a function of the activation energy at different concentrations. The established model of cation exchange adsorption in the present study has universal applicability in solid/liquid interface reactions.
2017, 33(10): 2004-2012
doi: 10.3866/PKU.WHXB201705183
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Carbonyl sulfide (OCS) was photoexcited at 230 nm so that it dissociated into a vibrationally cold but rotationally hot CO (X1Σg+, v = 0, J = 42–69) fragment, which was eventually subjected to resonance enhanced multiphoton ionization. The kinetic energy release distribution and angular distribution of the CO fragment were obtained by detecting the time-sliced velocity map images of CO+ in various rotational states (J = 55–69), wherein both the singlet dissociation channel of S(1D) + CO and the triplet pathway of S(3PJ) + CO were involved. For the triplet fragment channel, the total quantum yield of OCS dissociation at 230 nm was estimated to be 4.16%, based on the measured branching ratioin every rotational state. High-level quantum chemical calculations on the potential energy surface and the absorption cross section of OCS revealed the dissociation mechanism along the triplet channel of OCS, with photolysis at 230 nm. The ground state OCS (X1A') is photoexcited to the bent A1A' state at 230 nm, which then decays back to X1A' in a bent structure via internal conversion and subsequently couples to the 23A"(c3A") state by spin-orbit coupling, followed by direct dissociation along its potential energy surface.
Carbonyl sulfide (OCS) was photoexcited at 230 nm so that it dissociated into a vibrationally cold but rotationally hot CO (X1Σg+, v = 0, J = 42–69) fragment, which was eventually subjected to resonance enhanced multiphoton ionization. The kinetic energy release distribution and angular distribution of the CO fragment were obtained by detecting the time-sliced velocity map images of CO+ in various rotational states (J = 55–69), wherein both the singlet dissociation channel of S(1D) + CO and the triplet pathway of S(3PJ) + CO were involved. For the triplet fragment channel, the total quantum yield of OCS dissociation at 230 nm was estimated to be 4.16%, based on the measured branching ratioin every rotational state. High-level quantum chemical calculations on the potential energy surface and the absorption cross section of OCS revealed the dissociation mechanism along the triplet channel of OCS, with photolysis at 230 nm. The ground state OCS (X1A') is photoexcited to the bent A1A' state at 230 nm, which then decays back to X1A' in a bent structure via internal conversion and subsequently couples to the 23A"(c3A") state by spin-orbit coupling, followed by direct dissociation along its potential energy surface.
2017, 33(10): 2013-2021
doi: 10.3866/PKU.WHXB201705113
Abstract:
In this study, molecular dynamics simulations were performed to gain insight into the adsorption and diffusion behavior of uranyl carbonate species on pyrophyllite basal surface at various temperatures (298.15, 313.15, and 333.15 K). At these temperatures, four kinds of uranium species, i.e. UO22+, UO2CO3, UO2(CO3) 22-, UO2(CO3) 34-, and uranyl oligomers were obtained. According to the atomic density profile of each uranyl species, only UO22+ and UO2CO3 were adsorbed on the pyrophyllite surface. Therefore, due to the strong coordination interaction between carbonate ion and uranyl, the pyrophyllite surface exhibited weak adsorption capacity for uranium after prolonged simulations. Self-diffusion coefficients of water molecules and uranyl species in both the adsorbed layer and the diffuse layer were calculated. With increasing temperature, the diffusion coefficients for all species increased; however, in the adsorbed layer, the diffusion coefficients for UO2(CO3) 22- and UO2(CO3) 34- increased faster than those for UO22+ and UO2CO3. Nonetheless, the diffuse order remained unchanged in both the layers: UO22+ > UO2CO3 > UO2(CO3) 22- > UO2(CO3) 34-. This indicates that UO22+ is the main diffusing species.
In this study, molecular dynamics simulations were performed to gain insight into the adsorption and diffusion behavior of uranyl carbonate species on pyrophyllite basal surface at various temperatures (298.15, 313.15, and 333.15 K). At these temperatures, four kinds of uranium species, i.e. UO22+, UO2CO3, UO2(CO3) 22-, UO2(CO3) 34-, and uranyl oligomers were obtained. According to the atomic density profile of each uranyl species, only UO22+ and UO2CO3 were adsorbed on the pyrophyllite surface. Therefore, due to the strong coordination interaction between carbonate ion and uranyl, the pyrophyllite surface exhibited weak adsorption capacity for uranium after prolonged simulations. Self-diffusion coefficients of water molecules and uranyl species in both the adsorbed layer and the diffuse layer were calculated. With increasing temperature, the diffusion coefficients for all species increased; however, in the adsorbed layer, the diffusion coefficients for UO2(CO3) 22- and UO2(CO3) 34- increased faster than those for UO22+ and UO2CO3. Nonetheless, the diffuse order remained unchanged in both the layers: UO22+ > UO2CO3 > UO2(CO3) 22- > UO2(CO3) 34-. This indicates that UO22+ is the main diffusing species.
2017, 33(10): 2022-2028
doi: 10.3866/PKU.WHXB201705174
Abstract:
MXene is a new group of electrocatalysts for two-dimensional hydrogen evolution reaction (HER). Its surfaces are often covered by hydrophilic O and OH mixed groups. To find the effect of the O and OH mixed groups on HER, we studied the HER activity for M2XO2-2x(OH)2x (M=Ti, V; X=C, N) by first-principle calculations. Results indicate that HER activity is closely related to OH-occupied coverage (x). For Ti2CO2-2x(OH)2x, excellent HER activity could be maintained when the OH-occupied coverage was not larger than 1/3. For Ti2NO2-2x(OH)2x, V2CO2-2x(OH)2x, and V2NO2-2x(OH)2x, high HER activity was obtained when OH-occupied coverage reached 4/9, 1/3, and 5/9, respectively. Next, we analyzed the charge-transfer density and found that the charges on the oxygen groups were strongly affected by the OH-occupied coverage. Finally, we revealed the variation of HER activity that oxidizability of O groups is weakened with increasing OH-occupied coverage. In this paper, we propose a new method to obtain the optimal HER activity for M2XO2-2x(OH)2x by adjusting the OH-occupied coverage of the surfaces, which is useful in industrial hydrogen production.
MXene is a new group of electrocatalysts for two-dimensional hydrogen evolution reaction (HER). Its surfaces are often covered by hydrophilic O and OH mixed groups. To find the effect of the O and OH mixed groups on HER, we studied the HER activity for M2XO2-2x(OH)2x (M=Ti, V; X=C, N) by first-principle calculations. Results indicate that HER activity is closely related to OH-occupied coverage (x). For Ti2CO2-2x(OH)2x, excellent HER activity could be maintained when the OH-occupied coverage was not larger than 1/3. For Ti2NO2-2x(OH)2x, V2CO2-2x(OH)2x, and V2NO2-2x(OH)2x, high HER activity was obtained when OH-occupied coverage reached 4/9, 1/3, and 5/9, respectively. Next, we analyzed the charge-transfer density and found that the charges on the oxygen groups were strongly affected by the OH-occupied coverage. Finally, we revealed the variation of HER activity that oxidizability of O groups is weakened with increasing OH-occupied coverage. In this paper, we propose a new method to obtain the optimal HER activity for M2XO2-2x(OH)2x by adjusting the OH-occupied coverage of the surfaces, which is useful in industrial hydrogen production.
2017, 33(10): 2029-2034
doi: 10.3866/PKU.WHXB201705121
Abstract:
A compact PbS quantum-dot thin film was prepared using the combination of TiO2 nanorod arrays and 1,2-ethanedithiol following the spin-coating assisted successive ionic layer absorption and reaction procedure. Solar cells with the novel structure of FTO/compact PbS quantum-dot thin film sensitized TiO2 nanorod arrays/spiro-OMeTAD/Au were assembled. Subsequently, the influence of the length of TiO2 nanorod arrays on the photovoltaic performance of all-solid-state compact PbS quantum-dot thin film sensitized solar cells was evaluated. The corresponding solar cells having TiO2 nanorod array lengths of 290, 540, and 1040 nm achieved photoelectric conversion efficiencies (PCE) of 2.02%, 4.81%, and 1.95%, respectively. These results reveal that in order to achieve high PCE values with the all-solid-state quantum dot sensitized solar cells, it is very important to balance the hole diffusion length with the loading amount of quantum-dots.
A compact PbS quantum-dot thin film was prepared using the combination of TiO2 nanorod arrays and 1,2-ethanedithiol following the spin-coating assisted successive ionic layer absorption and reaction procedure. Solar cells with the novel structure of FTO/compact PbS quantum-dot thin film sensitized TiO2 nanorod arrays/spiro-OMeTAD/Au were assembled. Subsequently, the influence of the length of TiO2 nanorod arrays on the photovoltaic performance of all-solid-state compact PbS quantum-dot thin film sensitized solar cells was evaluated. The corresponding solar cells having TiO2 nanorod array lengths of 290, 540, and 1040 nm achieved photoelectric conversion efficiencies (PCE) of 2.02%, 4.81%, and 1.95%, respectively. These results reveal that in order to achieve high PCE values with the all-solid-state quantum dot sensitized solar cells, it is very important to balance the hole diffusion length with the loading amount of quantum-dots.
2017, 33(10): 2035-2041
doi: 10.3866/PKU.WHXB201705182
Abstract:
Flaky polyaniline-reduced graphene oxide (PANI-rGO) composites have larger specific capacitance due to the improved redox charge of PANI in the composites, fabricated by simultaneous reduction of PANI-GO. The structural and morphological analyses were carried out using scanning electron microscopy, UV-Vis spectroscopy, and thermogravimetry. The results showed that the composites are flaky in shape. PANI is uniformly coated on GO, and PANI-rGO has specific capacitance as high as 1069 F·g-1 (1.71 F·cm-2) at a current density of 20 A·g-1, 5 times higher than PANI-GO; this is caused by the large surface and conductivity of the rGO in the composite.
Flaky polyaniline-reduced graphene oxide (PANI-rGO) composites have larger specific capacitance due to the improved redox charge of PANI in the composites, fabricated by simultaneous reduction of PANI-GO. The structural and morphological analyses were carried out using scanning electron microscopy, UV-Vis spectroscopy, and thermogravimetry. The results showed that the composites are flaky in shape. PANI is uniformly coated on GO, and PANI-rGO has specific capacitance as high as 1069 F·g-1 (1.71 F·cm-2) at a current density of 20 A·g-1, 5 times higher than PANI-GO; this is caused by the large surface and conductivity of the rGO in the composite.
2017, 33(10): 2042-2051
doi: 10.3866/PKU.WHXB201705125
Abstract:
A photoinduced confined etching system was used for the unstressed chemical planarization of Cu. Cu deposits were found on the surface of TiO2 nanotubes of the tool during the photoinduced confined etching of the Cu workpiece. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the morphology and composition of the Cu deposits, and the mechanism of the photodeposition of Cu in the micro/nanoscale liquid layer between the tool and the workpiece was investigated. Moreover, a simulated cupric solution was used to study the effect of the Cu deposits during the photoinduced confined etching. Several routes including stirring and complexing agent were used to investigate the inhibition of Cu deposition on the surface of TiO2 nanotubes and the simultaneous effect on the etching of Cu workpiece. The results showed that the Cu deposits enhanced the photocatalytic performance of TiO2 nanotubes, but the mechanism of enhancement changed with the increase in Cu deposits. Inhibition of Cu deposition by improving mass transfer can lead to the increase in the etching of Cu; addition of complexing agent combined with enhanced mass-transfer can inhibit Cu deposition, while improving the planing effect. Thus, the choice of inhibition methods and conditions should balance the effect of the micro/nano liquid layer between the tool and workpiece on multiple chemical reactions and mass transfer processes. The results provide an important guiding significance for further regulation and optimization of the photoinduced confined etching system.
A photoinduced confined etching system was used for the unstressed chemical planarization of Cu. Cu deposits were found on the surface of TiO2 nanotubes of the tool during the photoinduced confined etching of the Cu workpiece. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the morphology and composition of the Cu deposits, and the mechanism of the photodeposition of Cu in the micro/nanoscale liquid layer between the tool and the workpiece was investigated. Moreover, a simulated cupric solution was used to study the effect of the Cu deposits during the photoinduced confined etching. Several routes including stirring and complexing agent were used to investigate the inhibition of Cu deposition on the surface of TiO2 nanotubes and the simultaneous effect on the etching of Cu workpiece. The results showed that the Cu deposits enhanced the photocatalytic performance of TiO2 nanotubes, but the mechanism of enhancement changed with the increase in Cu deposits. Inhibition of Cu deposition by improving mass transfer can lead to the increase in the etching of Cu; addition of complexing agent combined with enhanced mass-transfer can inhibit Cu deposition, while improving the planing effect. Thus, the choice of inhibition methods and conditions should balance the effect of the micro/nano liquid layer between the tool and workpiece on multiple chemical reactions and mass transfer processes. The results provide an important guiding significance for further regulation and optimization of the photoinduced confined etching system.
2017, 33(10): 2052-2057
doi: 10.3866/PKU.WHXB201750105
Abstract:
Rolling circle amplification (RCA) is a simple and efficient isothermal enzymatic reaction, which has developed as a novel technology in the field of nucleic acid amplification. Its product has a wide range of applications in the assembly and preparation of multi-functional materials. Here, we report the effects of reaction time and the concentrations of deoxyribonucleoside triphosphates (dNTPs), polymerase, and primer on the product of RCA. The RCA product was characterized by methods including agarose gel electrophoresis, ultraviolet spectroscopy, and transmission electron microscopy (TEM). The results showed that the length of the RCA product was significantly affected by the reaction time, especially when the reaction time was less than 30 min. With an increase of dNTPs concentrations, the concentration and chain length of the RCA product increased. However, while the concentrations of enzyme and primer had little effect on the length of the RCA product, they had a large effect on its concentration. It is worth noting that the content of the RCA product decreased significantly in the presence of excess enzyme concentration.
Rolling circle amplification (RCA) is a simple and efficient isothermal enzymatic reaction, which has developed as a novel technology in the field of nucleic acid amplification. Its product has a wide range of applications in the assembly and preparation of multi-functional materials. Here, we report the effects of reaction time and the concentrations of deoxyribonucleoside triphosphates (dNTPs), polymerase, and primer on the product of RCA. The RCA product was characterized by methods including agarose gel electrophoresis, ultraviolet spectroscopy, and transmission electron microscopy (TEM). The results showed that the length of the RCA product was significantly affected by the reaction time, especially when the reaction time was less than 30 min. With an increase of dNTPs concentrations, the concentration and chain length of the RCA product increased. However, while the concentrations of enzyme and primer had little effect on the length of the RCA product, they had a large effect on its concentration. It is worth noting that the content of the RCA product decreased significantly in the presence of excess enzyme concentration.
2017, 33(10): 2058-2063
doi: 10.3866/PKU.WHXB201705101
Abstract:
Melamine phthalaldehyde porous polymer (MA)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared using the solution casting method. The morphology of the membranes was examined using a scanning electron microscope (SEM). The gas separation performance of the prepared MA/PDMS MMMs with different MA contents was investigated. The results indicate that the incorporation of MA could improve the permeability/selectivity combinations of the PDMS membrane. On increasing the MA content, the permeability of the membranes increased, whereas, the separation selectivity increased at first and then decreased. The binary gas permeation test results showed that separation selectivities of 19.2 and 6.0 for CO2/N2 and CO2/CH4, respectively, were achieved on the MA/PDMS (1.2% (w, mass fraction)) membrane. Additionally, the CO2 permeability reached up to 8100 Barrer, much higher than that of the pure PDMS membrane. The MA/PDMS (1.2% (w)) MMM surpasses the Roberson upper bound for CO2/N2 separation.
Melamine phthalaldehyde porous polymer (MA)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared using the solution casting method. The morphology of the membranes was examined using a scanning electron microscope (SEM). The gas separation performance of the prepared MA/PDMS MMMs with different MA contents was investigated. The results indicate that the incorporation of MA could improve the permeability/selectivity combinations of the PDMS membrane. On increasing the MA content, the permeability of the membranes increased, whereas, the separation selectivity increased at first and then decreased. The binary gas permeation test results showed that separation selectivities of 19.2 and 6.0 for CO2/N2 and CO2/CH4, respectively, were achieved on the MA/PDMS (1.2% (w, mass fraction)) membrane. Additionally, the CO2 permeability reached up to 8100 Barrer, much higher than that of the pure PDMS membrane. The MA/PDMS (1.2% (w)) MMM surpasses the Roberson upper bound for CO2/N2 separation.
2017, 33(10): 2064-2071
doi: 10.3866/PKU.WHXB201705103
Abstract:
Three Nd2O3 samples with cubic phase being the main component phase, denoted as Nd2O3-H, Nd2O3-HT, and Nd2O3-C, were synthesized by hydrolysis, hydrothermal, and combustion methods, respectively. A comparative study of the photo-induced formation of peroxide species on the three Nd2O3 samples was carried out using Raman spectroscopy with a 325 nm laser as the excitation source. After irradiation with the laser of the Raman spectrometer at room temperature in air, peroxide species was detected in all Nd2O3 samples. However, the rate of peroxide formation over Nd2O3-C was much greater than that over the other two samples. This observation can be explained by the differences in the structure and basicity of the surface lattice oxygen (O2-) species of the samples. As evidenced by the results of O2- and CO2-temperature-programmed desorption (TPD) characterizations, the Nd2O3-C sample contains greater number of surface lattice oxygen (O2-) species with low coordination numbers than the other two samples. Moreover, the basicity of the surface O2- species in Nd2O3-C is stronger than that in the Nd2O3-H and Nd2O3-HT samples. Both these factors are in favor of the reaction of lattice oxygen with molecular oxygen to generate peroxide species under photo irradiation.
Three Nd2O3 samples with cubic phase being the main component phase, denoted as Nd2O3-H, Nd2O3-HT, and Nd2O3-C, were synthesized by hydrolysis, hydrothermal, and combustion methods, respectively. A comparative study of the photo-induced formation of peroxide species on the three Nd2O3 samples was carried out using Raman spectroscopy with a 325 nm laser as the excitation source. After irradiation with the laser of the Raman spectrometer at room temperature in air, peroxide species was detected in all Nd2O3 samples. However, the rate of peroxide formation over Nd2O3-C was much greater than that over the other two samples. This observation can be explained by the differences in the structure and basicity of the surface lattice oxygen (O2-) species of the samples. As evidenced by the results of O2- and CO2-temperature-programmed desorption (TPD) characterizations, the Nd2O3-C sample contains greater number of surface lattice oxygen (O2-) species with low coordination numbers than the other two samples. Moreover, the basicity of the surface O2- species in Nd2O3-C is stronger than that in the Nd2O3-H and Nd2O3-HT samples. Both these factors are in favor of the reaction of lattice oxygen with molecular oxygen to generate peroxide species under photo irradiation.
2017, 33(10): 2072-2081
doi: 10.3866/PKU.WHXB201705127
Abstract:
以钛酸丁酯为钛源，氢氟酸为氟源，采用溶剂热法制备了一系列钛基半导体纳米晶，考察了氢氟酸加入量对纳米晶结构演变的影响，并通过光催化产氢、光降解罗丹明B及瞬态光电流响应测试了所得纳米晶的光催化性能。当不加氢氟酸时，所得纳米晶为TiO2纳米颗粒，主要暴露{101}面。加入少量氢氟酸时，所得纳米晶为主要暴露{001}面的TiO2纳米片，这是由于氟离子吸附于纳米晶表面，降低{001}面表面能所致。由于{001}面与{101}面间的晶面异质结促进了载流子分离，该样品表现出了最高的光催化性能。继续增加氢氟酸加入量，氟离子开始进入晶格构成新晶相，所得纳米晶的表面与体相均形成TiO2与TiOF2混合相，形貌呈现片层堆叠结构，光催化性能下降。当进一步增加氢氟酸加入量后，氟离子全部进入晶格形成大颗粒（NH4）0.3TiO1.1F2.1。因其具有不适宜光催化反应的能带结构，该物质表现出了较差的光催化活性，但其可作为制备氮、氟掺杂钛基半导体材料的前驱体使用。
以钛酸丁酯为钛源，氢氟酸为氟源，采用溶剂热法制备了一系列钛基半导体纳米晶，考察了氢氟酸加入量对纳米晶结构演变的影响，并通过光催化产氢、光降解罗丹明B及瞬态光电流响应测试了所得纳米晶的光催化性能。当不加氢氟酸时，所得纳米晶为TiO2纳米颗粒，主要暴露{101}面。加入少量氢氟酸时，所得纳米晶为主要暴露{001}面的TiO2纳米片，这是由于氟离子吸附于纳米晶表面，降低{001}面表面能所致。由于{001}面与{101}面间的晶面异质结促进了载流子分离，该样品表现出了最高的光催化性能。继续增加氢氟酸加入量，氟离子开始进入晶格构成新晶相，所得纳米晶的表面与体相均形成TiO2与TiOF2混合相，形貌呈现片层堆叠结构，光催化性能下降。当进一步增加氢氟酸加入量后，氟离子全部进入晶格形成大颗粒（NH4）0.3TiO1.1F2.1。因其具有不适宜光催化反应的能带结构，该物质表现出了较差的光催化活性，但其可作为制备氮、氟掺杂钛基半导体材料的前驱体使用。
2017, 33(10): 2082-2091
doi: 10.3866/PKU.WHXB201705176
Abstract:
In the present work, we successfully synthesized ZnO nanorods under hydrothermal conditions, which have been utilized as the matrix to fabricate various noble metal (Pt, Pd, and Ru)-supported ZnO photocatalysts by subsequent reduction with ethylene glycol. In terms of systematic characterization, it was found that the Pt particles in the Pt/ZnO composite have small size with narrow size distribution, while the Pd particles in the Pd/ZnO composite have a larger size distribution due to aggregation. On the other hand, no Ru particles were practically observed in the Ru/ZnO composite. In the photodegradation of a methylene blue solution under UV light irradiation, both Pt/ZnO and Pd/ZnO exhibited significantly enhanced photocatalytic activity compared with the ZnO nanorods, whereas no noticeable increase of catalytic activity could be observed in the case of Ru/ZnO. Furthermore, the photocatalytic activity of the Pt/ZnO catalyst was higher than that of Pd/ZnO, due to its small-sized and uniform Pt particles. Therefore, noble metal particles with small size and high dispersion contribute to the enhancement of the photocatalytic performance of ZnO materials. After detailed investigation of various Pt/ZnO composites with different Pt loadings, it was demonstrated that the optimal Pt loading required to maximally improve the photocatalytic performance of ZnO nanorods corresponds to 3.2%.
In the present work, we successfully synthesized ZnO nanorods under hydrothermal conditions, which have been utilized as the matrix to fabricate various noble metal (Pt, Pd, and Ru)-supported ZnO photocatalysts by subsequent reduction with ethylene glycol. In terms of systematic characterization, it was found that the Pt particles in the Pt/ZnO composite have small size with narrow size distribution, while the Pd particles in the Pd/ZnO composite have a larger size distribution due to aggregation. On the other hand, no Ru particles were practically observed in the Ru/ZnO composite. In the photodegradation of a methylene blue solution under UV light irradiation, both Pt/ZnO and Pd/ZnO exhibited significantly enhanced photocatalytic activity compared with the ZnO nanorods, whereas no noticeable increase of catalytic activity could be observed in the case of Ru/ZnO. Furthermore, the photocatalytic activity of the Pt/ZnO catalyst was higher than that of Pd/ZnO, due to its small-sized and uniform Pt particles. Therefore, noble metal particles with small size and high dispersion contribute to the enhancement of the photocatalytic performance of ZnO materials. After detailed investigation of various Pt/ZnO composites with different Pt loadings, it was demonstrated that the optimal Pt loading required to maximally improve the photocatalytic performance of ZnO nanorods corresponds to 3.2%.
2017, 33(10): 2092-2098
doi: 10.3866/PKU.WHXB201705114
Abstract:
The sintering condition was studied how to influence the performance of indium-zinc-oxide (IZO) target and thin film transistor (TFT) in this paper. IZO targets was prepared by hot-pressing sintering using mixed power (20% (w, mass fraction) In2O3), then fabricated TFT with above sintering targets. X-ray diffraction (XRD) patterns & scanning electron microscopy (SEM) images showed targets had good crystallinity and elements were uniformly distributed. The target was typical densification process with sintering temperature of 850 ℃. The volatilization of In2O3 undermined the densification of the target, with condition of 900 ℃-60 min. It can be seen that increase of sintering temperature and elongation of preserving time could inhibit the In2O3 volatilization, facilitated the sintering densification of IZO target and formed the InZnOx crystal phase, thereby increased the density of the target. IZO TFTs′ performance showed the sputtering deteriorates the film quality with low-density target, and the grain of the high-density target was slightly abnormal, which resulted in deterioration of the film uniformity, all reduced the performance of TFT. Therefore, an appropriate high-density target was essential for the preparation of IZO-TFT."
The sintering condition was studied how to influence the performance of indium-zinc-oxide (IZO) target and thin film transistor (TFT) in this paper. IZO targets was prepared by hot-pressing sintering using mixed power (20% (w, mass fraction) In2O3), then fabricated TFT with above sintering targets. X-ray diffraction (XRD) patterns & scanning electron microscopy (SEM) images showed targets had good crystallinity and elements were uniformly distributed. The target was typical densification process with sintering temperature of 850 ℃. The volatilization of In2O3 undermined the densification of the target, with condition of 900 ℃-60 min. It can be seen that increase of sintering temperature and elongation of preserving time could inhibit the In2O3 volatilization, facilitated the sintering densification of IZO target and formed the InZnOx crystal phase, thereby increased the density of the target. IZO TFTs′ performance showed the sputtering deteriorates the film quality with low-density target, and the grain of the high-density target was slightly abnormal, which resulted in deterioration of the film uniformity, all reduced the performance of TFT. Therefore, an appropriate high-density target was essential for the preparation of IZO-TFT."
2017, 33(10): 2099-2105
doi: 10.3866/PKU.WHXB201705115
Abstract:
Lead acetate, which is highly soluble in dimethylformamide, was used to synthesize mixed halide perovskite CH3NH3PbBr3-xClx (MA = CH3NH3, 0 ≤ x ≤ 3) nanocrystals (NCs). This method provides an approach to address the low solubility of lead halides, especially lead chloride. Different Br/Cl ratios in MAPbBr3-xClx lead to various optical properties. The photoluminescence emission peak can be tuned from 399 to 527 nm. Their full-widths at half-maxima (FWHM) are about 20 nm. MAPbBr3-xClx NCs have an average diameter of ~(11 ± 3) nm and have uniform dispersion in toluene. The MAPbBr3 NCs have a long average recombination lifetime (τave = 97.4 ns) and a photoluminescence quantum yield (PLQY) of up to 73%.
Lead acetate, which is highly soluble in dimethylformamide, was used to synthesize mixed halide perovskite CH3NH3PbBr3-xClx (MA = CH3NH3, 0 ≤ x ≤ 3) nanocrystals (NCs). This method provides an approach to address the low solubility of lead halides, especially lead chloride. Different Br/Cl ratios in MAPbBr3-xClx lead to various optical properties. The photoluminescence emission peak can be tuned from 399 to 527 nm. Their full-widths at half-maxima (FWHM) are about 20 nm. MAPbBr3-xClx NCs have an average diameter of ~(11 ± 3) nm and have uniform dispersion in toluene. The MAPbBr3 NCs have a long average recombination lifetime (τave = 97.4 ns) and a photoluminescence quantum yield (PLQY) of up to 73%.
2017, 33(10): 2106-2112
doi: 10.3866/PKU.WHXB201705186
Abstract:
Understanding the growth mechanism of nanocrystals is crucial for the synthesis of high-quality monodispersed nanoparticles. In contrast to the widely studied growth mechanism of metal nanocrystals, the growth mechanism of metal oxide nanoparticles is still poorly understood. Exemplified by cobalt/manganese ferrite nanoparticles prepared by thermal decomposition, we reveal the growth mechanism and associated compositional segregations of bimetallic metal oxide nanoparticles by using transmission electron microscopy combined with electron energy loss spectroscopy (EELS). We found that a two-stage heating protocol, involving a first-stage heating at a relatively lower temperature followed by a second-stage heating at a relatively higher temperature, is crucial to synthesize monodispersed ferrite nanoparticles. Controlling the reaction time of the first-stage heating can effectively decouple the nucleation stage and growth stage of ferrite nanoparticles, leading to monodispersed nanoparticles with a narrow size distribution. EELS spectrum imaging further reveals previously unreported compositional segregations in the as-prepared ferrite nanoparticles, suggesting that an Fe-rich core formed at the nucleation stage and a Co-/Mn-rich shell formed at the growth stage. Our results provide useful insight into the synthesis of high-quality monodispersed metal oxide nanoparticles as well as a correct understanding of the surface chemistry and related physiochemical properties of spinel oxide nanocrystals prepared by thermal decomposition.
Understanding the growth mechanism of nanocrystals is crucial for the synthesis of high-quality monodispersed nanoparticles. In contrast to the widely studied growth mechanism of metal nanocrystals, the growth mechanism of metal oxide nanoparticles is still poorly understood. Exemplified by cobalt/manganese ferrite nanoparticles prepared by thermal decomposition, we reveal the growth mechanism and associated compositional segregations of bimetallic metal oxide nanoparticles by using transmission electron microscopy combined with electron energy loss spectroscopy (EELS). We found that a two-stage heating protocol, involving a first-stage heating at a relatively lower temperature followed by a second-stage heating at a relatively higher temperature, is crucial to synthesize monodispersed ferrite nanoparticles. Controlling the reaction time of the first-stage heating can effectively decouple the nucleation stage and growth stage of ferrite nanoparticles, leading to monodispersed nanoparticles with a narrow size distribution. EELS spectrum imaging further reveals previously unreported compositional segregations in the as-prepared ferrite nanoparticles, suggesting that an Fe-rich core formed at the nucleation stage and a Co-/Mn-rich shell formed at the growth stage. Our results provide useful insight into the synthesis of high-quality monodispersed metal oxide nanoparticles as well as a correct understanding of the surface chemistry and related physiochemical properties of spinel oxide nanocrystals prepared by thermal decomposition.
