In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl gro...In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl groups, including 2-(2-methoxyphenoxy)-1-phenylethanone, 2-(2-methoxyphenoxy)-1-phenylethanol, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanol, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanol have been selected and their electrochemical properties have been studied experimentally by cyclic voltammetry, and FT-IR spectroelectrochemistry. Combining with electrolysis products distribution analysis and density functional theory calculations, oxidation mechanisms of all six model dimers have been explored. In particular, a total effect from substituents of both para-methoxy(on the aryl ring closing to Cα) and Cα-OH on the oxidation mechanisms has been clearly observed, showing a significant selectivity on the Cα-Cβbond cleavage induced by electrochemical oxidations.展开更多
Solvent effects are important for the solution preparation of nanoscale metal materials, in which the sizes and properties of the nanomaterials are greatly influenced by the solvents. In this study, a series of Pd/XC-...Solvent effects are important for the solution preparation of nanoscale metal materials, in which the sizes and properties of the nanomaterials are greatly influenced by the solvents. In this study, a series of Pd/XC-72 catalysts were synthesized by a facile solvothermal method in solvents with different numbers of hydroxyl groups, including ethanol, ethylene glycol, and glycerine. The as-prepared catalysts Pd/XC-72(EA), Pd/XC-72(EG) and Pd/XC-72(GI) were characterized by XRD, TEM, TGA, ICP-MS and multipoint nitrogen adsorption-desorption experiments. It was found that Pd/XC-72(GI) had the highest metallic dispersion and the smallest particle size (4.9 nm). Furthermore, Pd/XC-72(GI) exhibited the best catalytic performance for solvent-free selective oxidation of benzyl alcohol while the catalytic activities of Pd/XC-72 catalysts decreased in the order: Pd/XC-72(GI) > Pd/XC-72(EG) > Pd/XC-72(EA).展开更多
The co-oxidation of a mixture of phenylsulfinylacetic acid (PSAA) and oxalic acid (OxH2) by Cr(VI) in 20% acetonitrile-80% water (v/v) medium follows third order kinetics, first order, each with respect to PSAA, OxH2 ...The co-oxidation of a mixture of phenylsulfinylacetic acid (PSAA) and oxalic acid (OxH2) by Cr(VI) in 20% acetonitrile-80% water (v/v) medium follows third order kinetics, first order, each with respect to PSAA, OxH2 and Cr(VI). The reaction involves nucleophilic attack of sulfur atom of PSAA on chromium of the oxidizing species, Cr(VI)-OxH2 to form a ternary complex, Cr(VI)-OxH2-PSAA followed by a one-step three-electron reduction of Cr(VI) to Cr(III) and simultaneous oxidation of both the substrates. The reaction is catalysed by Mn2+ ion while retarded by Al3+ ion. Electron releasing substituents in the meta- and para-positions of the phenyl ring of PSAA enhance the rate of co-oxidation while electron withdrawing substituents retards the reaction. The Hammett plots at different temperatures exhibit excellent correlation with negative ρ values. The reaction series obey isokinetic relationship and the observed isokinetic temperature is lying below the experimental range of temperature.展开更多
Substituent effect of metal porphyrin molecular catalysts plays a crucial role in determining the catalytic activity of oxygen electrocatalysis.Herein,substituent position effect of Co porphyrins on oxygen electrocata...Substituent effect of metal porphyrin molecular catalysts plays a crucial role in determining the catalytic activity of oxygen electrocatalysis.Herein,substituent position effect of Co porphyrins on oxygen electrocatalysis,including the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER),was investigated.Two Co porphyrins,namely 2,4,6-OMe-CoP and 3,4,5-OMe-CoP,were selected as the research objects.The ORR and OER performance was evaluated by drop-coating molecular catalysts on carbon nanotubes(CNTs).The resulted 3,4,5-OMe-CoP/CNT exhibited high bifunctional electrocatalytic activities and better long-term stability for both ORR and OER than 2,4,6-OMe-CoP/CNT.Furthermore,when applied in the Zn-air battery,3,4,5-OMe-CoP/CNT exhibited comparable performance to that with precious metal-based materials.The enhanced catalytic activity may be attributed to the improved charge transfer rate,mass transfer and hydrophilicity.This work provides an effective strategy to further enhance catalytic activity by introducing substituent position effect,which is of great importance for developing more efficient energy-related electrocatalysts.展开更多
Photophysical properties of a porphyrin-phthalocyanine heterodimer covalently linked with a dipentoxy chain have been studied. Absorption spectra show that there is weak exciton coupling between the two chromophores i...Photophysical properties of a porphyrin-phthalocyanine heterodimer covalently linked with a dipentoxy chain have been studied. Absorption spectra show that there is weak exciton coupling between the two chromophores in the ground state. Fluorescence spectra show that intramolecular energy transfer from porphyrin to phthalocyanine moiety occurs in competition with electron transfer. The efficiency of these two processes depends upon the mutual orientation of the two chromophores. The effect of solvent, polarity on the intramolecular processes is also discussed.展开更多
Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent（s） used in the preparation process can affect the particle size and alloying de...Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent（s） used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction （XRD） and Transmission electron microscopy （TEM）. The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry （CV） and Chronoamperometry （CA）. Pt-Ru/C catalyst prepared in H2O or binary solvents of H2O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.展开更多
Density functional theory (DFT) calculations have been carried out in order to compare the molecular structures, atomic charges, molecular orbitals, electronic absorption spectra, and infrared (IR) spectra of the meta...Density functional theory (DFT) calculations have been carried out in order to compare the molecular structures, atomic charges, molecular orbitals, electronic absorption spectra, and infrared (IR) spectra of the metal-free 5,15 -di[4-(5-acetylsul-fanylpentyloxy)phenyl]porphyrin H2[DPP(OC5H10SCOCH3)2] (1) (DPP = 5,15-diphenylporphyrin) and its zinc complex Zn[DPP(OC5H10SCOCH3)2] (2), which exhibit novel structures with two 5-acetylsulfanylpentyloxy side chains at the para-positions of opposite meso-attached phenyl groups. The calculated molecular structure and electronic absorption and IR spectra of 1 and 2 are consistent with the experimental results. The influences of meso-substitution, polar solvents, and central metal substitution on the structure and properties of porphyrin derivatives have been investigated by comparing the corresponding data for 1 and 2 with the help of data for the unsubstituted porphyrin derivatives, namely the metal-free porphyrin H2Por (3) and the porphyrinato-zinc compound (4). The identities of the main transitions in the electronic absorption spectra of 1 and 2 are assigned and the vibrational modes in their IR spectra are identified with the assistance of animated pictures produced based on normal coordinates. The theoretical work presented here will be helpful in increasing our understanding of the structure and spectroscopic properties, as well as substituent and solvent effects, for these novel porphyrin compounds.展开更多
The influence of solvent and the rate of addition of water on the characteristics of alumina-zirconia powders obtained by sol-gel method were investigated. The Al2O3-ZrO2 powders (1:1 molar ratio) were prepared using ...The influence of solvent and the rate of addition of water on the characteristics of alumina-zirconia powders obtained by sol-gel method were investigated. The Al2O3-ZrO2 powders (1:1 molar ratio) were prepared using aluminum tri-sec-butoxide and zirconium n-propoxide as precursors. Ethanol (EtOH), isopropanol (iPrOH) and isobutanol (iBuOH) were used as solvents. The Al2O3-ZrO2 powders were characterized by nitrogen physisorption (SBET), Fourier transformed infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Prepared oxides calcined at 700℃ showed high specific surface area (200 - 240 m2/g). Obtained results suggest that the homogeneity of the mixed oxides is favored by using a water addition rate of 0.06 and 0.10 mL/min with ethanol as solvent.展开更多
基金The authors gratefully acknowledge the financial support of the Natural Science Foundation of China,China(Grant No.21975082 and 21736003)the Guangdong Basic and Applied Basic Research Foundation(Grant Number:2019A1515011472 and 2022A1515011341)the Science and Technology Program of Guangzhou(Grant Number:202102080479).
文摘In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl groups, including 2-(2-methoxyphenoxy)-1-phenylethanone, 2-(2-methoxyphenoxy)-1-phenylethanol, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanol, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanol have been selected and their electrochemical properties have been studied experimentally by cyclic voltammetry, and FT-IR spectroelectrochemistry. Combining with electrolysis products distribution analysis and density functional theory calculations, oxidation mechanisms of all six model dimers have been explored. In particular, a total effect from substituents of both para-methoxy(on the aryl ring closing to Cα) and Cα-OH on the oxidation mechanisms has been clearly observed, showing a significant selectivity on the Cα-Cβbond cleavage induced by electrochemical oxidations.
文摘Solvent effects are important for the solution preparation of nanoscale metal materials, in which the sizes and properties of the nanomaterials are greatly influenced by the solvents. In this study, a series of Pd/XC-72 catalysts were synthesized by a facile solvothermal method in solvents with different numbers of hydroxyl groups, including ethanol, ethylene glycol, and glycerine. The as-prepared catalysts Pd/XC-72(EA), Pd/XC-72(EG) and Pd/XC-72(GI) were characterized by XRD, TEM, TGA, ICP-MS and multipoint nitrogen adsorption-desorption experiments. It was found that Pd/XC-72(GI) had the highest metallic dispersion and the smallest particle size (4.9 nm). Furthermore, Pd/XC-72(GI) exhibited the best catalytic performance for solvent-free selective oxidation of benzyl alcohol while the catalytic activities of Pd/XC-72 catalysts decreased in the order: Pd/XC-72(GI) > Pd/XC-72(EG) > Pd/XC-72(EA).
文摘The co-oxidation of a mixture of phenylsulfinylacetic acid (PSAA) and oxalic acid (OxH2) by Cr(VI) in 20% acetonitrile-80% water (v/v) medium follows third order kinetics, first order, each with respect to PSAA, OxH2 and Cr(VI). The reaction involves nucleophilic attack of sulfur atom of PSAA on chromium of the oxidizing species, Cr(VI)-OxH2 to form a ternary complex, Cr(VI)-OxH2-PSAA followed by a one-step three-electron reduction of Cr(VI) to Cr(III) and simultaneous oxidation of both the substrates. The reaction is catalysed by Mn2+ ion while retarded by Al3+ ion. Electron releasing substituents in the meta- and para-positions of the phenyl ring of PSAA enhance the rate of co-oxidation while electron withdrawing substituents retards the reaction. The Hammett plots at different temperatures exhibit excellent correlation with negative ρ values. The reaction series obey isokinetic relationship and the observed isokinetic temperature is lying below the experimental range of temperature.
基金support from the National Natural Science Foundation of China(Nos.21808138 and 21773146)Fok Ying-Tong Education Foundation for Outstanding Young Teachers in University,Fundamental Research Funds for the Central Universities(Nos.GK202103029 and GK202103045)+2 种基金Young Talent fund of University Association for Science and Technology in Shaanxi,ChinaChina Postdoctoral Science Foundation(No.2019T120877)Research Funds of Shaanxi Normal University。
文摘Substituent effect of metal porphyrin molecular catalysts plays a crucial role in determining the catalytic activity of oxygen electrocatalysis.Herein,substituent position effect of Co porphyrins on oxygen electrocatalysis,including the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER),was investigated.Two Co porphyrins,namely 2,4,6-OMe-CoP and 3,4,5-OMe-CoP,were selected as the research objects.The ORR and OER performance was evaluated by drop-coating molecular catalysts on carbon nanotubes(CNTs).The resulted 3,4,5-OMe-CoP/CNT exhibited high bifunctional electrocatalytic activities and better long-term stability for both ORR and OER than 2,4,6-OMe-CoP/CNT.Furthermore,when applied in the Zn-air battery,3,4,5-OMe-CoP/CNT exhibited comparable performance to that with precious metal-based materials.The enhanced catalytic activity may be attributed to the improved charge transfer rate,mass transfer and hydrophilicity.This work provides an effective strategy to further enhance catalytic activity by introducing substituent position effect,which is of great importance for developing more efficient energy-related electrocatalysts.
基金Project supported by the National Natural Science Foundation of China.
文摘Photophysical properties of a porphyrin-phthalocyanine heterodimer covalently linked with a dipentoxy chain have been studied. Absorption spectra show that there is weak exciton coupling between the two chromophores in the ground state. Fluorescence spectra show that intramolecular energy transfer from porphyrin to phthalocyanine moiety occurs in competition with electron transfer. The efficiency of these two processes depends upon the mutual orientation of the two chromophores. The effect of solvent, polarity on the intramolecular processes is also discussed.
基金supported by 863 Project(No.2006AA05Z102)the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of China (No.707050)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education (No.20060610023)Chengdu Natural Science Foundation (Nos.06GGYB449GX-030,and 07GGZD139GX)
文摘Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent（s） used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction （XRD） and Transmission electron microscopy （TEM）. The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry （CV） and Chronoamperometry （CA）. Pt-Ru/C catalyst prepared in H2O or binary solvents of H2O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.
基金supported by the Na-tional Natural Science Foundation of China (20931001)Beijing Municipal Commission of Education,and China Postdoctoral Science Foundation (20090460210)
文摘Density functional theory (DFT) calculations have been carried out in order to compare the molecular structures, atomic charges, molecular orbitals, electronic absorption spectra, and infrared (IR) spectra of the metal-free 5,15 -di[4-(5-acetylsul-fanylpentyloxy)phenyl]porphyrin H2[DPP(OC5H10SCOCH3)2] (1) (DPP = 5,15-diphenylporphyrin) and its zinc complex Zn[DPP(OC5H10SCOCH3)2] (2), which exhibit novel structures with two 5-acetylsulfanylpentyloxy side chains at the para-positions of opposite meso-attached phenyl groups. The calculated molecular structure and electronic absorption and IR spectra of 1 and 2 are consistent with the experimental results. The influences of meso-substitution, polar solvents, and central metal substitution on the structure and properties of porphyrin derivatives have been investigated by comparing the corresponding data for 1 and 2 with the help of data for the unsubstituted porphyrin derivatives, namely the metal-free porphyrin H2Por (3) and the porphyrinato-zinc compound (4). The identities of the main transitions in the electronic absorption spectra of 1 and 2 are assigned and the vibrational modes in their IR spectra are identified with the assistance of animated pictures produced based on normal coordinates. The theoretical work presented here will be helpful in increasing our understanding of the structure and spectroscopic properties, as well as substituent and solvent effects, for these novel porphyrin compounds.
文摘The influence of solvent and the rate of addition of water on the characteristics of alumina-zirconia powders obtained by sol-gel method were investigated. The Al2O3-ZrO2 powders (1:1 molar ratio) were prepared using aluminum tri-sec-butoxide and zirconium n-propoxide as precursors. Ethanol (EtOH), isopropanol (iPrOH) and isobutanol (iBuOH) were used as solvents. The Al2O3-ZrO2 powders were characterized by nitrogen physisorption (SBET), Fourier transformed infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Prepared oxides calcined at 700℃ showed high specific surface area (200 - 240 m2/g). Obtained results suggest that the homogeneity of the mixed oxides is favored by using a water addition rate of 0.06 and 0.10 mL/min with ethanol as solvent.
