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2015 Volume 31 Issue 12
2015, 31(12): 2229-2250
doi: 10.3866/PKU.WHXB201510301
Abstract:
A correlation between the electronic circular dichroism (ECD) spectra and the absolute configurations of a serials' chiral salen-Ni(Ⅱ) complexes was investigated. The solid-state structures, absolute configurations, and preferential conformations in solution of quasi-planar chiral [Ni(salen)] complexes were studied using their crystal structures, solid-state and solution ECD spectra in combination with theoretical ECD calculations. Furthermore, two different nomenclatures for the absolute configurations of square-planar [M(salen)] complexes were inspected carefully, and suggestions for proper use of them are discussed. The calculated ECD spectra of [Ni(sal-R,R-chxn)] [sal-R,R-chxn = (R,R)-1,2-cyclohexylene bis(salicylicdeneiminate)] in dichloromethane solution revealed that the first ECD band in the visible region was dominated by the ligandto-metal charge transfer transition (LMCT), which was incorrectly assigned to a d-d transition in the literature. When the absolute configuration of [Ni(sal-R,R-chxn)] was Λ, the first ECD absorption band in the visible region was positive. This ECD fingerprint is universally applicable for assigning the absolute configurations of other square-planar chiral [Ni(salen)] and six-coordinate trans-[CoⅢ(salen)L2] complexes with a "closed-shell" electronic structure. This work provides some insight into the coordination stereochemistry and chiroptical properties of chiral [M(salen)] complexes. Additionally, this work is significant for the understanding of chiral recognition and asymmetric catalytic mechanisms.
A correlation between the electronic circular dichroism (ECD) spectra and the absolute configurations of a serials' chiral salen-Ni(Ⅱ) complexes was investigated. The solid-state structures, absolute configurations, and preferential conformations in solution of quasi-planar chiral [Ni(salen)] complexes were studied using their crystal structures, solid-state and solution ECD spectra in combination with theoretical ECD calculations. Furthermore, two different nomenclatures for the absolute configurations of square-planar [M(salen)] complexes were inspected carefully, and suggestions for proper use of them are discussed. The calculated ECD spectra of [Ni(sal-R,R-chxn)] [sal-R,R-chxn = (R,R)-1,2-cyclohexylene bis(salicylicdeneiminate)] in dichloromethane solution revealed that the first ECD band in the visible region was dominated by the ligandto-metal charge transfer transition (LMCT), which was incorrectly assigned to a d-d transition in the literature. When the absolute configuration of [Ni(sal-R,R-chxn)] was Λ, the first ECD absorption band in the visible region was positive. This ECD fingerprint is universally applicable for assigning the absolute configurations of other square-planar chiral [Ni(salen)] and six-coordinate trans-[CoⅢ(salen)L2] complexes with a "closed-shell" electronic structure. This work provides some insight into the coordination stereochemistry and chiroptical properties of chiral [M(salen)] complexes. Additionally, this work is significant for the understanding of chiral recognition and asymmetric catalytic mechanisms.
2015, 31(12): 2251-2258
doi: 10.3866/PKU.WHXB201510232
Abstract:
The hydrolyzation reaction and thermal transformation of UF4/KBr in air at ambient temperatures were studied by in-situ transmission Fourier transform infrared (FT-IR) spectroscopy. The infrared spectra for a series of different compounds containing uranium before and after reaction were obtained. Following hydrolysis of UF4/KBr in air, the primary products were UO2F2 and their hydrolysates. Other products, including U3O8, UO2, and UO3, appeared with increased reaction time. During the heating process, the hydrolysates of UF4/KBr reacted with each other, finally yielding only uranium oxides.
The hydrolyzation reaction and thermal transformation of UF4/KBr in air at ambient temperatures were studied by in-situ transmission Fourier transform infrared (FT-IR) spectroscopy. The infrared spectra for a series of different compounds containing uranium before and after reaction were obtained. Following hydrolysis of UF4/KBr in air, the primary products were UO2F2 and their hydrolysates. Other products, including U3O8, UO2, and UO3, appeared with increased reaction time. During the heating process, the hydrolysates of UF4/KBr reacted with each other, finally yielding only uranium oxides.
2015, 31(12): 2259-2268
doi: 10.3866/PKU.WHXB201510152
Abstract:
The atmospheric oxidation mechanism of o-xylene (oX) initiated by hydroxyl (OH) radicals has been investigated by using quantum chemistry, transition state theory, and unimolecular theory (RRKMME) calculations. Molecular structures of reactants, transition states, and products are optimized at M06- 2X/6-311++G(2df, 2p) level, and the electronic energies are calculated at the ROCBS-QB3 level. The classical transition state theory is employed to predict the rates or rate constants for all the reaction steps as well as the branching ratios of the reaction pathways. RRKM-ME calculations are employed to explore the pressure-dependence of the reaction kinetics. Under atmospheric conditions, the oxidation of o-Xylene is dominated by OH addition to the C1 and C3 positions, forming adducts oX-1-OH (R1) and oX-3-OH (R3), which will readily react with atmospheric oxygen. The reactions of R1 and R3 with O2 can proceed by irreversible H-abstraction to dimethylphenols (R3 only), or by reversible addition to form bicyclic radicals,which recombine with atmospheric oxygen to form bicyclic peroxy radicals (BPRs). BPRs will react with NO and/or HO2 in the atmosphere, forming organonitrate, hydroperoxides (ROOH), and bicyclic alkoxy radicals (BARs), of which the BARs eventually transfer to the final products, including biacetyl, butenedial, methylglyoxal, 4-oxo-2-pentenal, epoxy-2,3-butenedial, and a small amount of glyoxal. The products ROOH and methylglyoxal are considered to contribute to the formation of secondary organic aerosols. A new oxidation mechanism of oX in the atmosphere is proposed, based on the current theoretical predictions and previous experimental measurements, and the predicted product yields under high NO conditions are compared with previous experimental measurements. The effect of temperature on the oxidation mechanism is also discussed.
The atmospheric oxidation mechanism of o-xylene (oX) initiated by hydroxyl (OH) radicals has been investigated by using quantum chemistry, transition state theory, and unimolecular theory (RRKMME) calculations. Molecular structures of reactants, transition states, and products are optimized at M06- 2X/6-311++G(2df, 2p) level, and the electronic energies are calculated at the ROCBS-QB3 level. The classical transition state theory is employed to predict the rates or rate constants for all the reaction steps as well as the branching ratios of the reaction pathways. RRKM-ME calculations are employed to explore the pressure-dependence of the reaction kinetics. Under atmospheric conditions, the oxidation of o-Xylene is dominated by OH addition to the C1 and C3 positions, forming adducts oX-1-OH (R1) and oX-3-OH (R3), which will readily react with atmospheric oxygen. The reactions of R1 and R3 with O2 can proceed by irreversible H-abstraction to dimethylphenols (R3 only), or by reversible addition to form bicyclic radicals,which recombine with atmospheric oxygen to form bicyclic peroxy radicals (BPRs). BPRs will react with NO and/or HO2 in the atmosphere, forming organonitrate, hydroperoxides (ROOH), and bicyclic alkoxy radicals (BARs), of which the BARs eventually transfer to the final products, including biacetyl, butenedial, methylglyoxal, 4-oxo-2-pentenal, epoxy-2,3-butenedial, and a small amount of glyoxal. The products ROOH and methylglyoxal are considered to contribute to the formation of secondary organic aerosols. A new oxidation mechanism of oX in the atmosphere is proposed, based on the current theoretical predictions and previous experimental measurements, and the predicted product yields under high NO conditions are compared with previous experimental measurements. The effect of temperature on the oxidation mechanism is also discussed.
2015, 31(12): 2269-2277
doi: 10.3866/PKU.WHXB201510082
Abstract:
Dual-fuel combustion is a promising method for achieving high-efficiency clean combustion in internal combustion engines. Most current research focuses on the effects of dual-fuel injection on engine performance and emissions. Our understanding of dual-fuel in-cylinder combustion processes needs further investigation. In this study, an optical diagnostic system was established to determine the intermediate products during in-cylinder combustion; the system enabled simultaneously qualitative two-dimensional measurements of formaldehyde and OH radicals. To confirm the feasibility of using this laser diagnostic system, laser-induced fluorescence (LIF) spectra and images of formaldehyde and OH radicals in a laminar premixed methane flame were acquired; the excitation laser wavelengths for formaldehyde and OH radicals were verified to be 355 and 292.85 nm, respectively. Non-simultaneous determination of formaldehyde and OH radicals in the combustion chamber was performed to analyze the two-stage heat release process and distribution regions of formaldehyde and OH radicals during dual-fuel combustion. In this investigation, the engine speed was kept at 1200 r·min-1 and the total equivalent fuel quality was 30 mg of n-heptane. Isooctane was injected in intake manifold at the beginning of the intake stroke and n-heptane (9 mg) was directly injected into the cylinder at 10° crank angle before compression top dead center. The results indicate that formaldehyde is formed in the low-temperature heat-release stage and is mainly located in the region near the spray jet; formaldehyde then fills most of the combustion chamber. When the high-temperature heat-release stage is initiated, formaldehyde located at the edge of the combustion chamber is consumed first, followed by consumption of formaldehyde in the center region. Accompanied with the disappearance of formaldehyde during the high-temperature heat-release stage, OH radicals first emerge at the edge of the combustion chamber and later fill the whole combustion chamber. Finally, simultaneous measurements of formaldehyde and OH radicals were conducted. Formaldehyde consumption is spatially accompanied by the formation of OH radicals. In general, the distributions of formaldehyde and OH radicals are separate spatially, but there are some regions where formaldehyde and OH radicals exist simultaneously.
Dual-fuel combustion is a promising method for achieving high-efficiency clean combustion in internal combustion engines. Most current research focuses on the effects of dual-fuel injection on engine performance and emissions. Our understanding of dual-fuel in-cylinder combustion processes needs further investigation. In this study, an optical diagnostic system was established to determine the intermediate products during in-cylinder combustion; the system enabled simultaneously qualitative two-dimensional measurements of formaldehyde and OH radicals. To confirm the feasibility of using this laser diagnostic system, laser-induced fluorescence (LIF) spectra and images of formaldehyde and OH radicals in a laminar premixed methane flame were acquired; the excitation laser wavelengths for formaldehyde and OH radicals were verified to be 355 and 292.85 nm, respectively. Non-simultaneous determination of formaldehyde and OH radicals in the combustion chamber was performed to analyze the two-stage heat release process and distribution regions of formaldehyde and OH radicals during dual-fuel combustion. In this investigation, the engine speed was kept at 1200 r·min-1 and the total equivalent fuel quality was 30 mg of n-heptane. Isooctane was injected in intake manifold at the beginning of the intake stroke and n-heptane (9 mg) was directly injected into the cylinder at 10° crank angle before compression top dead center. The results indicate that formaldehyde is formed in the low-temperature heat-release stage and is mainly located in the region near the spray jet; formaldehyde then fills most of the combustion chamber. When the high-temperature heat-release stage is initiated, formaldehyde located at the edge of the combustion chamber is consumed first, followed by consumption of formaldehyde in the center region. Accompanied with the disappearance of formaldehyde during the high-temperature heat-release stage, OH radicals first emerge at the edge of the combustion chamber and later fill the whole combustion chamber. Finally, simultaneous measurements of formaldehyde and OH radicals were conducted. Formaldehyde consumption is spatially accompanied by the formation of OH radicals. In general, the distributions of formaldehyde and OH radicals are separate spatially, but there are some regions where formaldehyde and OH radicals exist simultaneously.
2015, 31(12): 2278-2284
doi: 10.3866/PKU.WHXB201510136
Abstract:
MXenes are a new series of two-dimensional (2D) carbides or nitrides. Lithium storage properties and lithiated structures of three MXenes phases, Ti2C, V2C, and Nb2C, are studied by density functional theory. Additionally, the influence of fluorine functional groups on the lithiated structures and properties are also investigated. By calculating the adsorption energy, density of state, and charge population, we observe that double Li atom layers can be adsorbed on the surfaces of MXenes. For Ti2C, V2C, and Nb2C, the calculated maximum Li capacities reach values up to 995.04, 941.31, and 541.93 mAh·g-1, respectively. Fluorine functional groups are observed to effectively enhance the stability and conductivity of the lithiated structures of these three 2D crystals.
MXenes are a new series of two-dimensional (2D) carbides or nitrides. Lithium storage properties and lithiated structures of three MXenes phases, Ti2C, V2C, and Nb2C, are studied by density functional theory. Additionally, the influence of fluorine functional groups on the lithiated structures and properties are also investigated. By calculating the adsorption energy, density of state, and charge population, we observe that double Li atom layers can be adsorbed on the surfaces of MXenes. For Ti2C, V2C, and Nb2C, the calculated maximum Li capacities reach values up to 995.04, 941.31, and 541.93 mAh·g-1, respectively. Fluorine functional groups are observed to effectively enhance the stability and conductivity of the lithiated structures of these three 2D crystals.
2015, 31(12): 2285-2293
doi: 10.3866/PKU.WHXB201510191
Abstract:
The total interaction energies and two-, three-, and four-body interaction energies of water clusters (H2O)n (n = 8, 10, 16, 20, 22, 24) are obtained from MP2/aug-cc-pVTZ calculations including the basis set superposition error (BSSE) correction. The calculation results show that the two-body interaction energies contribute more than 70% to the total interaction energy, the three-body interaction energies contribute up to 25%, the four-body interaction energies sometimes contribute up to 3%, and other many-body interaction energies always contribute less than 0.5%. It is also found that about 99.4% of the total interaction energies can be reproduced when some special two-, three-, and four-body interactions are considered. These interactions are the two-body interactions where the distance between two water molecules is less than 0.68 nm, the three-body interactions where the nearest water-water distance among three water molecules is less than 0.31 nm, and the four-body interactions where the nearest water-water distance among four water molecules is less than 0.31 nm. Our investigation results suggest that a reliable method, aimed at modeling biosystems, should possess the ability to correctly simulate these special two-, three-, and four-body interactions.
The total interaction energies and two-, three-, and four-body interaction energies of water clusters (H2O)n (n = 8, 10, 16, 20, 22, 24) are obtained from MP2/aug-cc-pVTZ calculations including the basis set superposition error (BSSE) correction. The calculation results show that the two-body interaction energies contribute more than 70% to the total interaction energy, the three-body interaction energies contribute up to 25%, the four-body interaction energies sometimes contribute up to 3%, and other many-body interaction energies always contribute less than 0.5%. It is also found that about 99.4% of the total interaction energies can be reproduced when some special two-, three-, and four-body interactions are considered. These interactions are the two-body interactions where the distance between two water molecules is less than 0.68 nm, the three-body interactions where the nearest water-water distance among three water molecules is less than 0.31 nm, and the four-body interactions where the nearest water-water distance among four water molecules is less than 0.31 nm. Our investigation results suggest that a reliable method, aimed at modeling biosystems, should possess the ability to correctly simulate these special two-, three-, and four-body interactions.
2015, 31(12): 2294-2302
doi: 10.3866/PKU.WHXB201510161
Abstract:
The adsorption properties of amino methylene phosphonic acid (A), hydroxyethylenediphosphonic acid (B), sodium phosphonobutanetricarboxylic acid (C) and their inclusions with cationic modified betacyclodextrin (HPTEA-β-CD) for mild steel are evaluated by a combination of quantum chemistry and molecular dynamics simulations. The theoretical conclusions are experimentally verified by the weight loss method. The theoretical results indicate that reaction activity sites of A, B, and C are mainly concentrated at the N, O, P atoms, and the C molecule exhibited the highest reaction activity. Molecular dynamics method presents the equilibrium adsorption behavior of three HPTEA-β-CD inclusion complexes with molecules A, B, and C on an Fe(001) surface, and molecular C-HPTEA-β-CD exhibits the best inhibition performance, according to the adsorption energy. Experimental results of the weight loss show that the three inhibitors exert an excellent corrosion inhibition performance to q235 steel, and C-HPTEA-β-CD exhibits the highest corrosion efficiency of 91.50%, which is in good accordance with theoretical results.
The adsorption properties of amino methylene phosphonic acid (A), hydroxyethylenediphosphonic acid (B), sodium phosphonobutanetricarboxylic acid (C) and their inclusions with cationic modified betacyclodextrin (HPTEA-β-CD) for mild steel are evaluated by a combination of quantum chemistry and molecular dynamics simulations. The theoretical conclusions are experimentally verified by the weight loss method. The theoretical results indicate that reaction activity sites of A, B, and C are mainly concentrated at the N, O, P atoms, and the C molecule exhibited the highest reaction activity. Molecular dynamics method presents the equilibrium adsorption behavior of three HPTEA-β-CD inclusion complexes with molecules A, B, and C on an Fe(001) surface, and molecular C-HPTEA-β-CD exhibits the best inhibition performance, according to the adsorption energy. Experimental results of the weight loss show that the three inhibitors exert an excellent corrosion inhibition performance to q235 steel, and C-HPTEA-β-CD exhibits the highest corrosion efficiency of 91.50%, which is in good accordance with theoretical results.
2015, 31(12): 2303-2309
doi: 10.3866/PKU.WHXB201510233
Abstract:
Response theory was used to investigate one-photon absorption (OPA) and emission, and twophoton absorption (TPA) of two novel truncated two-photon fluorescent probes AcHS-1,2 in the presence and absence of H2S using density functional theory in combination with the polarizable continuum model . Changes in the optical properties, including large redshifts of the OPA, TPA, and emission peak positions were observed when the probes reacted with H2S, indicating that AcHS-1,2 make effective and selective chemosensors for H2S. We have also demonstrated that the terminal group on the probes influenced their nonlinear optical properties (AcHS-1: n-butyl group and AcHS-2: hydroxyethyl group). The responsive mechanism of AcHS-1,2 for sensing H2S was analyzed by studying the charge variations between the charge transfer and ground states of the free molecules and their reaction products using Mulliken population analysis. Importantly, this mechanism was attributed to an intramolecular charge transfer.
Response theory was used to investigate one-photon absorption (OPA) and emission, and twophoton absorption (TPA) of two novel truncated two-photon fluorescent probes AcHS-1,2 in the presence and absence of H2S using density functional theory in combination with the polarizable continuum model . Changes in the optical properties, including large redshifts of the OPA, TPA, and emission peak positions were observed when the probes reacted with H2S, indicating that AcHS-1,2 make effective and selective chemosensors for H2S. We have also demonstrated that the terminal group on the probes influenced their nonlinear optical properties (AcHS-1: n-butyl group and AcHS-2: hydroxyethyl group). The responsive mechanism of AcHS-1,2 for sensing H2S was analyzed by studying the charge variations between the charge transfer and ground states of the free molecules and their reaction products using Mulliken population analysis. Importantly, this mechanism was attributed to an intramolecular charge transfer.
2015, 31(12): 2310-2315
doi: 10.3866/PKU.WHXB201510162
Abstract:
The precursor powder of CaVO3 was prepared by sol-gel method using vanadium pentoxide, calcium nitrate, citric acid, and oxalic acid as raw materials. The target product CaVO3 was obtained by calcining the precursor powder in argon atmosphere at 1000 ℃. In order to determine the appropriate calcination temperature, thermal stability of the precursor powder was tested. The target product CaVO3 was characterized by Fourier transform infrared (FTIR) spectrometry, thermogravimetry (TG), X-ray diffraction (XRD), and conductivity. In addition, the properties for oxygen reduction reaction (ORR) were also investigated, and the results showed that the electron transfer number of ORR on the modified electrode was 1.5-1.7, which indicating that ORR was a two-electron process.
The precursor powder of CaVO3 was prepared by sol-gel method using vanadium pentoxide, calcium nitrate, citric acid, and oxalic acid as raw materials. The target product CaVO3 was obtained by calcining the precursor powder in argon atmosphere at 1000 ℃. In order to determine the appropriate calcination temperature, thermal stability of the precursor powder was tested. The target product CaVO3 was characterized by Fourier transform infrared (FTIR) spectrometry, thermogravimetry (TG), X-ray diffraction (XRD), and conductivity. In addition, the properties for oxygen reduction reaction (ORR) were also investigated, and the results showed that the electron transfer number of ORR on the modified electrode was 1.5-1.7, which indicating that ORR was a two-electron process.
2015, 31(12): 2316-2323
doi: 10.3866/PKU.WHXB201510221
Abstract:
The orientated cathode in a proton exchange membrane fuel cell was simulated and compared with a random cathode using a microstructure lattice model. The differences between catalyst utilization and electrode performance were studied. Transport and electrochemical reactions in the model catalyst layer were calculated. The orientated cathode performed better than the traditional random cathode and was explained by variations of the oxygen levels, the over potential and the reaction rate across the catalyst layer with cell current density. Additionally, we examined the electrode performance at different thicknesses. Unlike the traditional random cathode, a thinner orientated cathode performed better.
The orientated cathode in a proton exchange membrane fuel cell was simulated and compared with a random cathode using a microstructure lattice model. The differences between catalyst utilization and electrode performance were studied. Transport and electrochemical reactions in the model catalyst layer were calculated. The orientated cathode performed better than the traditional random cathode and was explained by variations of the oxygen levels, the over potential and the reaction rate across the catalyst layer with cell current density. Additionally, we examined the electrode performance at different thicknesses. Unlike the traditional random cathode, a thinner orientated cathode performed better.
2015, 31(12): 2324-2331
doi: 10.3866/PKU.WHXB201510231
Abstract:
The mixed adsorption of a cationic gemini surfactant, ethanediyl-1,2-bis(dodecyldimethylammonium bromide) 12-2-12), and a nonionic surfactant, polyoxyethylene mono-dodecyl ether (C12En, where n = 4, 10, 23) at the air/water interface was studied using surface tension measurements. The dilational viscoelastic properties of the films that formed at the air/water interface were examined using an interfacial rheology technique that was described using the Lucassen-van den Tempel (LVT) model. The values of the limit elasticity were fitted accordingly. Foams were generated by the mixed surfactant aqueous solutions and the stability of foams determined using the half-life. C12En exhibited attractive interactions towards 12-2-12 within the adsorption films. The average minimum area (Amin) of the adsorbed molecules decreased in the order: 12-2-12/C12E23 > 12-2-12/C12E10 > 12-2-12/C12E4, while the limit elasticity decreased in the reverse order: ε0,fit(12-2-12/C12E4) > ε0,fit(12-2-12/C12E10) > ε0,fit(12-2-12/C12E23) at a comparable concentration of the surfactant in the bulk. Compared with the film adsorbed by 12-2-12 alone, only 12-2-12/C12E4 form had denser structure. Thus, by adding the nonionic component C12E4, which contained a small hydrophilic head group, the interfacial elasticity of the 12-2-12 film increased significantly and the stability of the corresponding foams was effectively enhanced.
The mixed adsorption of a cationic gemini surfactant, ethanediyl-1,2-bis(dodecyldimethylammonium bromide) 12-2-12), and a nonionic surfactant, polyoxyethylene mono-dodecyl ether (C12En, where n = 4, 10, 23) at the air/water interface was studied using surface tension measurements. The dilational viscoelastic properties of the films that formed at the air/water interface were examined using an interfacial rheology technique that was described using the Lucassen-van den Tempel (LVT) model. The values of the limit elasticity were fitted accordingly. Foams were generated by the mixed surfactant aqueous solutions and the stability of foams determined using the half-life. C12En exhibited attractive interactions towards 12-2-12 within the adsorption films. The average minimum area (Amin) of the adsorbed molecules decreased in the order: 12-2-12/C12E23 > 12-2-12/C12E10 > 12-2-12/C12E4, while the limit elasticity decreased in the reverse order: ε0,fit(12-2-12/C12E4) > ε0,fit(12-2-12/C12E10) > ε0,fit(12-2-12/C12E23) at a comparable concentration of the surfactant in the bulk. Compared with the film adsorbed by 12-2-12 alone, only 12-2-12/C12E4 form had denser structure. Thus, by adding the nonionic component C12E4, which contained a small hydrophilic head group, the interfacial elasticity of the 12-2-12 film increased significantly and the stability of the corresponding foams was effectively enhanced.
2015, 31(12): 2332-2340
doi: 10.3866/PKU.WHXB201510202
Abstract:
P25-reduced graphene oxide nanocomposites (RGO-P25) are prepared by using a facile one-step hydrothermal method. Their structure and photoelectrical properties are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The degradation effect of different addition ratios of the RGO-P25 nanocomposite on the photocatalytic degradation of methylene blue (MB) is investigated under UV and visible illumination. Results show that graphene oxide can be reduced during the hydrothermal reaction and thus, a mixed high defect P25 particles and RGO sheet composite is formed by electrostatic attraction. Band gaps of nanocomposites decreased from 3.00 to 2.27 eV with an increase in the amount of the RGO content. The electrical conductivities of the nanocomposites enhanced with an increased RGO amount. Over 80% of the initial methylene blue dye is decomposed by 1% (w, mass fraction) RGO-P25 after 30 min under either visible light or ultraviolet light. Under UV light illumination, 63% (molar fraction) of the N3 dye, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy = 4,4'- dicarboxy-2,2'-bipyridyl), is decomposed by the 1% RGO-P25 nanocomposite. Compared with the bare P25 (75% anatase; 25% rutile), the continual addition of RGO enhances the photocatalytic activity and gives rise to the more effective separation of photogenerated electron-hole pairs.
P25-reduced graphene oxide nanocomposites (RGO-P25) are prepared by using a facile one-step hydrothermal method. Their structure and photoelectrical properties are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The degradation effect of different addition ratios of the RGO-P25 nanocomposite on the photocatalytic degradation of methylene blue (MB) is investigated under UV and visible illumination. Results show that graphene oxide can be reduced during the hydrothermal reaction and thus, a mixed high defect P25 particles and RGO sheet composite is formed by electrostatic attraction. Band gaps of nanocomposites decreased from 3.00 to 2.27 eV with an increase in the amount of the RGO content. The electrical conductivities of the nanocomposites enhanced with an increased RGO amount. Over 80% of the initial methylene blue dye is decomposed by 1% (w, mass fraction) RGO-P25 after 30 min under either visible light or ultraviolet light. Under UV light illumination, 63% (molar fraction) of the N3 dye, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy = 4,4'- dicarboxy-2,2'-bipyridyl), is decomposed by the 1% RGO-P25 nanocomposite. Compared with the bare P25 (75% anatase; 25% rutile), the continual addition of RGO enhances the photocatalytic activity and gives rise to the more effective separation of photogenerated electron-hole pairs.
2015, 31(12): 2341-2348
doi: 10.3866/PKU.WHXB201510151
Abstract:
The conversion of CO2 into organic compounds is a promising method to mitigate global warming and assist in sustaining energy resources. A series of plasmonic photocatalysts, comprised of Ag supported on Ag2WO4 (Ag/Ag2WO4) with different crystalline phases, are fabricated by a facile ion-exchange method and subsequent reduction with hydrazine hydrate. The catalysts are characterized using X-ray diffraction (XRD) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), UV-Vis absorption spectroscopy, and Brunauer-Emmett-Teller analyses. Compared with Ag2WO4, the Ag/Ag2WO4 exhibits a markedly improved quantum yield (QY), energy returned on energy invested (EROEI), and turnover number (TON) for CO2 reduction to CH4 under visible-light irradiation. Among Ag/α-Ag2WO4, Ag/β-Ag2WO4, and Ag/γ-Ag2WO4 catalysts, the highest activity for CO2 photoreduction to CH4 is obtained for Ag/β-Ag2WO4 with an actual molar composition of 4% Ag and 96% Ag2WO4. Correspondingly the QY, EROEI, TON, and pseudo first-order rate constant are 0.145%, 0.067%, 9.61, and 1.96×10-6 min-1, respectively. Moreover, the plasmonic Ag/Ag2WO4 photocatalysts are stable after repeated reaction cycles under visible-light irradiation. It is proposed that the localized surface plasma resonance effect of surfacedeposited Ag contributed to the enhanced activities and stabilities of the Ag/Ag2WO4 photocatalysts.
The conversion of CO2 into organic compounds is a promising method to mitigate global warming and assist in sustaining energy resources. A series of plasmonic photocatalysts, comprised of Ag supported on Ag2WO4 (Ag/Ag2WO4) with different crystalline phases, are fabricated by a facile ion-exchange method and subsequent reduction with hydrazine hydrate. The catalysts are characterized using X-ray diffraction (XRD) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), UV-Vis absorption spectroscopy, and Brunauer-Emmett-Teller analyses. Compared with Ag2WO4, the Ag/Ag2WO4 exhibits a markedly improved quantum yield (QY), energy returned on energy invested (EROEI), and turnover number (TON) for CO2 reduction to CH4 under visible-light irradiation. Among Ag/α-Ag2WO4, Ag/β-Ag2WO4, and Ag/γ-Ag2WO4 catalysts, the highest activity for CO2 photoreduction to CH4 is obtained for Ag/β-Ag2WO4 with an actual molar composition of 4% Ag and 96% Ag2WO4. Correspondingly the QY, EROEI, TON, and pseudo first-order rate constant are 0.145%, 0.067%, 9.61, and 1.96×10-6 min-1, respectively. Moreover, the plasmonic Ag/Ag2WO4 photocatalysts are stable after repeated reaction cycles under visible-light irradiation. It is proposed that the localized surface plasma resonance effect of surfacedeposited Ag contributed to the enhanced activities and stabilities of the Ag/Ag2WO4 photocatalysts.
2015, 31(12): 2349-2357
doi: 10.3866/PKU.WHXB201510281
Abstract:
Porous ZnO nanorods that displayed excellent photocatalytic degradation of organic pollutants (RhB and phenol) were prepared via a solvent thermal method followed by surface modification with carbon dots (C-dots) using a deposition method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-Vis) spectroscopy. The degradation of the organic pollutants using the nanorods was tested under Xe-light illumination and was enhanced following C-dot modification. Nanorods that were modified by the C-dots at a mass fraction of 1.2% (CZn1.2) exhibited the highest photocatalytic activity for the degradation of RhB, which was 2.5 times of the pure porous ZnO nanorods. Additionally, the modified nanorods with strangely oxidation ability could catalyze the degradation of phenol by open-rings reaction under Xe-light illumination. The improved photocatalytic activity was attributed to the effective separation of the photogenerated electrons and holes, in which the C-dots served as the receptor of the photogenerated electrons.
Porous ZnO nanorods that displayed excellent photocatalytic degradation of organic pollutants (RhB and phenol) were prepared via a solvent thermal method followed by surface modification with carbon dots (C-dots) using a deposition method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-Vis) spectroscopy. The degradation of the organic pollutants using the nanorods was tested under Xe-light illumination and was enhanced following C-dot modification. Nanorods that were modified by the C-dots at a mass fraction of 1.2% (CZn1.2) exhibited the highest photocatalytic activity for the degradation of RhB, which was 2.5 times of the pure porous ZnO nanorods. Additionally, the modified nanorods with strangely oxidation ability could catalyze the degradation of phenol by open-rings reaction under Xe-light illumination. The improved photocatalytic activity was attributed to the effective separation of the photogenerated electrons and holes, in which the C-dots served as the receptor of the photogenerated electrons.
2015, 31(12): 2358-2365
doi: 10.3866/PKU.WHXB201510135
Abstract:
CeO2-ZrO2 and CeO2-ZrO2-La2O3 catalysts with mass ratios of 60:40 and 60:30:10 were prepared by co-precipitation method, respectively. The catalytic activity in oxidation of the soluble organic fraction (SOF) in diesel exhausts was studied using thermogravimetric-differential thermal analysis (TGDTA). The results indicate that the catalytic activity of the La-modified CeO2-ZrO2 catalyst is better than that of the CeO2-ZrO2 catalyst; the light-off temperature of SOF is 164 ℃, and the weightlessness fastest point temperature is 212 ℃, whereas for CeO2-ZrO2, these temperatures are 168 and 221 ℃, respectively. X-ray diffraction (XRD) shows that modification with La is beneficial to decrease the growth rate of the crystallite size relative to that of CeO2-ZrO2 after high-temperature ageing. N2 adsorption-desorption results suggest that the addition of La enlarges the surface area. O2-temperature-programmed desorption (O2- TPD) and X-ray photoelectron spectroscopy (XPS) show that modification with La increases the amount of chemisorbed oxygen on the CeO2-ZrO2 catalyst. The CeO2-ZrO2-La2O3 catalyst shows better activity and ageing resistance than the CeO2-ZrO2 catalyst.
CeO2-ZrO2 and CeO2-ZrO2-La2O3 catalysts with mass ratios of 60:40 and 60:30:10 were prepared by co-precipitation method, respectively. The catalytic activity in oxidation of the soluble organic fraction (SOF) in diesel exhausts was studied using thermogravimetric-differential thermal analysis (TGDTA). The results indicate that the catalytic activity of the La-modified CeO2-ZrO2 catalyst is better than that of the CeO2-ZrO2 catalyst; the light-off temperature of SOF is 164 ℃, and the weightlessness fastest point temperature is 212 ℃, whereas for CeO2-ZrO2, these temperatures are 168 and 221 ℃, respectively. X-ray diffraction (XRD) shows that modification with La is beneficial to decrease the growth rate of the crystallite size relative to that of CeO2-ZrO2 after high-temperature ageing. N2 adsorption-desorption results suggest that the addition of La enlarges the surface area. O2-temperature-programmed desorption (O2- TPD) and X-ray photoelectron spectroscopy (XPS) show that modification with La increases the amount of chemisorbed oxygen on the CeO2-ZrO2 catalyst. The CeO2-ZrO2-La2O3 catalyst shows better activity and ageing resistance than the CeO2-ZrO2 catalyst.
2015, 31(12): 2366-2374
doi: 10.3866/PKU.WHXB201510141
Abstract:
A Cu3(BTC)2 (copper(Ⅱ) benzene 1,3,5-tricarboxylate) metal organic framework (MOF) catalyst was successfully prepared through an electrochemical route and used for selective catalytic reduction of nitrogen oxide (NOx) with NH3 for the first time. After systematically optimizing the reaction conditions such as solvents, voltage, electrolyte concentration, and reaction time, pure Cu3(BTC)2 with high crystallinity was obtained in 97.2% yield. The physicochemical properties of the catalyst were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, in situ Fourier transform infrared (FTIR) spectroscopy, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). TGA results indicated that the framework was stable up to 310 ℃. The catalytic activity of Cu3(BTC)2 was evaluated using NO conversion as a model reaction. The Cu3(BTC)2 activation temperature significantly affected the catalytic activity. The Cu3(BTC)2 sample activated at 240 ℃ had the best catalytic activity and gave NO conversion of 90% at 220-280 ℃. A reaction mechanism was proposed based on the in situ FTIR spectroscopy results.
A Cu3(BTC)2 (copper(Ⅱ) benzene 1,3,5-tricarboxylate) metal organic framework (MOF) catalyst was successfully prepared through an electrochemical route and used for selective catalytic reduction of nitrogen oxide (NOx) with NH3 for the first time. After systematically optimizing the reaction conditions such as solvents, voltage, electrolyte concentration, and reaction time, pure Cu3(BTC)2 with high crystallinity was obtained in 97.2% yield. The physicochemical properties of the catalyst were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, in situ Fourier transform infrared (FTIR) spectroscopy, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). TGA results indicated that the framework was stable up to 310 ℃. The catalytic activity of Cu3(BTC)2 was evaluated using NO conversion as a model reaction. The Cu3(BTC)2 activation temperature significantly affected the catalytic activity. The Cu3(BTC)2 sample activated at 240 ℃ had the best catalytic activity and gave NO conversion of 90% at 220-280 ℃. A reaction mechanism was proposed based on the in situ FTIR spectroscopy results.
2015, 31(12): 2375-2385
doi: 10.3866/PKU.WHXB201510201
Abstract:
A series of MnSAPO-34 molecular sieves were synthesized by a hydrothermal method for selective catalytic reduction (SCR) of NO with NH3 and characterized using X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). Three factors were studied, including Mn-loading, calcination temperature, and synthesis time. The MnSAPO-34, which was synthesized in 6 h and calcined at 550 ℃ with the Mn-loading (n(MnO)/n(P2O5)= 0.1), exhibits the highest activity among all the samples, with NOx conversion of almost 100% and N2 selectivity higher than 80%. The results show that the porous and crystalline structures of MnSAPO-34 are greatly affected by addition of manganese, and excessive Mn-loading could result in lower crystallinity and the generation of nonframework manganese oxides. Meanwhile, a decrease in specific surface area and pore volume are observed in MnSAPO-34 with higher Mn-loading; however, the opposite characteristics are observed with a decreasing calcination temperature and shorter synthesis time. Manganese species of high oxidation state, mostly Mn4+, are shown to be on the catalysts surface after high temperature calcination, and the increase ratio of Mn3+ could help to improve the catalytic activity. Under proper synthesis conditions, the incorporation of manganese could improve the adsorption of nitric oxide and ammonia, and the interaction between the strongly adsorbed NO and strongly adsorbed NH3 might be the reason for the enhancement in their catalytic efficiency.
A series of MnSAPO-34 molecular sieves were synthesized by a hydrothermal method for selective catalytic reduction (SCR) of NO with NH3 and characterized using X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). Three factors were studied, including Mn-loading, calcination temperature, and synthesis time. The MnSAPO-34, which was synthesized in 6 h and calcined at 550 ℃ with the Mn-loading (n(MnO)/n(P2O5)= 0.1), exhibits the highest activity among all the samples, with NOx conversion of almost 100% and N2 selectivity higher than 80%. The results show that the porous and crystalline structures of MnSAPO-34 are greatly affected by addition of manganese, and excessive Mn-loading could result in lower crystallinity and the generation of nonframework manganese oxides. Meanwhile, a decrease in specific surface area and pore volume are observed in MnSAPO-34 with higher Mn-loading; however, the opposite characteristics are observed with a decreasing calcination temperature and shorter synthesis time. Manganese species of high oxidation state, mostly Mn4+, are shown to be on the catalysts surface after high temperature calcination, and the increase ratio of Mn3+ could help to improve the catalytic activity. Under proper synthesis conditions, the incorporation of manganese could improve the adsorption of nitric oxide and ammonia, and the interaction between the strongly adsorbed NO and strongly adsorbed NH3 might be the reason for the enhancement in their catalytic efficiency.
2015, 31(12): 2386-2394
doi: 10.3866/PKU.WHXB201510137
Abstract:
Three alkynylplatinum(Ⅱ)-2,6-bis(N-ethylbenzimidazol-2'-yl)pyridine complexes 2-4 were synthesized and characterized. The alkynyl ligand in complex 2 is the anticancer drug erlotinib. The interactions between the Pt(Ⅱ) complexes and G-quadruplexes, including human telomeric (Hetelo) and cmyc oncogene (c-myc) quadruplexes, were investigated using UV-Vis spectroscopy, circular dichroism (CD), and fluorescence resonance energy transfer (FRET) melting assays. These studies show that the Pt(Ⅱ) complexes 2-4 have high affinities for G-quadruplexes (Ka > 106 L·mol-1), and can promote the formation of G-quadruplexes even in the absence of alkali cations. The Pt(Ⅱ) complexes 2 and 3, containing a phenylacetylene moiety, induce a high degree of stabilization of the c-myc G-quadruplex, with a melting temperature increase (ΔTm) of more than 24 ℃, but complex 4, containing a propyne moiety, only induces ΔTm of 9.0 ℃. These results indicate that the structure of the alkynyl ligand is important in the interactions between Pt(Ⅱ) complexes and G-quadruplexes. The cytotoxicity of complex 2 to the human adenocarcinoma A549 cell line is higher than those of complexes 3, 4, and erlotinib.
Three alkynylplatinum(Ⅱ)-2,6-bis(N-ethylbenzimidazol-2'-yl)pyridine complexes 2-4 were synthesized and characterized. The alkynyl ligand in complex 2 is the anticancer drug erlotinib. The interactions between the Pt(Ⅱ) complexes and G-quadruplexes, including human telomeric (Hetelo) and cmyc oncogene (c-myc) quadruplexes, were investigated using UV-Vis spectroscopy, circular dichroism (CD), and fluorescence resonance energy transfer (FRET) melting assays. These studies show that the Pt(Ⅱ) complexes 2-4 have high affinities for G-quadruplexes (Ka > 106 L·mol-1), and can promote the formation of G-quadruplexes even in the absence of alkali cations. The Pt(Ⅱ) complexes 2 and 3, containing a phenylacetylene moiety, induce a high degree of stabilization of the c-myc G-quadruplex, with a melting temperature increase (ΔTm) of more than 24 ℃, but complex 4, containing a propyne moiety, only induces ΔTm of 9.0 ℃. These results indicate that the structure of the alkynyl ligand is important in the interactions between Pt(Ⅱ) complexes and G-quadruplexes. The cytotoxicity of complex 2 to the human adenocarcinoma A549 cell line is higher than those of complexes 3, 4, and erlotinib.
2015, 31(12): 2395-2404
doi: 10.3866/PKU.WHXB201510142
Abstract:
Aromatic thiazine derivatives were proved to be potent aldose reductase inhibitors (ARIs) with high selectivity for aldose reductase (ALr2) over aldehyde reductase (ALR1). Molecular docking and three-dimensional quantitative structure-activity relationship (3D-QSAR) studies are conducted on a dataset of 44 molecules to explore the interactions between aromatic thiazine derivatives and ALr2. The superposition of ALr2 and ALR1 active sites indicate that residues Leu 300 and Cys 298 from ALr2 may explain the good selectivity of the most active compound 1m. The comparative molecular field analysis (CoMFA) model (q2 = 0.649, r2 = 0.934; q2: cross-validated correlation coefficient, r2: non-cross-validated correlation coefficient) and comparative molecular similarity indices analysis (CoMSIA) model (q2 = 0.746, r2 = 0.971), based on the docking conformations of these compounds, are obtained to identify the key structures impacting their inhibitory potencies. The predictive power of the developed models is further validated by a test set of seven compounds, resulting in predictive rPred2 values of 0.748 for CoMFA and 0.828 for CoMSIA. 3D contour maps, drawn from 3D-QSAR models, reveal that future modifications of substituents at the C3 and C4 positions of the benzyl ring and the C5 and C7 positions of the benzothiazine-1,1-dioxide core might be favorable for improving the biological activity, which are in good accordance with the C7 modification results reported in our earlier work. The information rendered by 3DQSAR models could be helpful in the rational design of novel ARIs with good inhibitory activity to treat diabetic complications in the future.
Aromatic thiazine derivatives were proved to be potent aldose reductase inhibitors (ARIs) with high selectivity for aldose reductase (ALr2) over aldehyde reductase (ALR1). Molecular docking and three-dimensional quantitative structure-activity relationship (3D-QSAR) studies are conducted on a dataset of 44 molecules to explore the interactions between aromatic thiazine derivatives and ALr2. The superposition of ALr2 and ALR1 active sites indicate that residues Leu 300 and Cys 298 from ALr2 may explain the good selectivity of the most active compound 1m. The comparative molecular field analysis (CoMFA) model (q2 = 0.649, r2 = 0.934; q2: cross-validated correlation coefficient, r2: non-cross-validated correlation coefficient) and comparative molecular similarity indices analysis (CoMSIA) model (q2 = 0.746, r2 = 0.971), based on the docking conformations of these compounds, are obtained to identify the key structures impacting their inhibitory potencies. The predictive power of the developed models is further validated by a test set of seven compounds, resulting in predictive rPred2 values of 0.748 for CoMFA and 0.828 for CoMSIA. 3D contour maps, drawn from 3D-QSAR models, reveal that future modifications of substituents at the C3 and C4 positions of the benzyl ring and the C5 and C7 positions of the benzothiazine-1,1-dioxide core might be favorable for improving the biological activity, which are in good accordance with the C7 modification results reported in our earlier work. The information rendered by 3DQSAR models could be helpful in the rational design of novel ARIs with good inhibitory activity to treat diabetic complications in the future.
2015, 31(12): 2405-2412
doi: 10.3866/PKU.WHXB201510261
Abstract:
Y-doped ZnO nanofibers were synthesized by an electrospinning method. The structure and morphology of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and thermogravimetric/differential thermal analysis (TG-DTA). The sensitivity of the pure and Y-doped ZnO nanofibers towards acetone from 1×10-6 to 200×10-6 (volume fraction) was investigated. Fine tuning of the sensing ability of the ZnO nanofibres was possible by controlling the amount of Y loaded in the nanofibers. The ZnO nanofibers doped with Y exhibited very high responses towards acetone. Both the pure and Y-doped ZnO sensors showed selectivity towards several potential interferent gases, including ammonia, benzene, formaldehyde, toluene, and methanol. The sensing mechanism is discussed.
Y-doped ZnO nanofibers were synthesized by an electrospinning method. The structure and morphology of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and thermogravimetric/differential thermal analysis (TG-DTA). The sensitivity of the pure and Y-doped ZnO nanofibers towards acetone from 1×10-6 to 200×10-6 (volume fraction) was investigated. Fine tuning of the sensing ability of the ZnO nanofibres was possible by controlling the amount of Y loaded in the nanofibers. The ZnO nanofibers doped with Y exhibited very high responses towards acetone. Both the pure and Y-doped ZnO sensors showed selectivity towards several potential interferent gases, including ammonia, benzene, formaldehyde, toluene, and methanol. The sensing mechanism is discussed.
