A theoretical study of the XP and NEXAFS spectra of alanine: gas phase molecule, crystal, and adsorbate at the ZnO(10 ̅10) surface

The adsorption of alanine on the mixed-terminated ZnO(10 ?10) surface is studied by means of quantum-chemical ab initio calculations. Using a finite cluster model and the adsorption geometry as obtained both by periodic CPMD and embedded cluster calculations, the C1s, N1s and O1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra are calculated for single alanine molecules on ZnO(10 ?10). These spectra are compared with the spectra calculated for alanine in the gas phase and in its crystalline form and with experimental XPS and NEXAFS data for the isolated alanine molecule and for alanine adsorbed on ZnO(10 ?10) at multilayer and monolayer coverage. The excellent agreement between the experimental and calculated XP and NEXAFS spectra confirms the calculated adsorption geometry: A single alanine molecule is bound to ZnO(10 ?10) in a dissociated bidentate form with the two O atoms of the acid group bound to two Zn atoms of the surface and the proton transferred to one O atom of the surface. Other possible structures, such as adsorption of alanine in one of its neutral or zwitterionic forms in which the proton of the -COOH group remains at this group or is transferred to the amino group, can be excluded since they would give rise to quite different XP spectra. In the multilayer coverage regime, on the other hand, alanine is in its crystalline form as is also shown by the analysis of the XP spectra.     

银纳米粒子表面油酸盐吸附的分子模拟

采用分子力学方法模拟了油酸盐分子在银纳米粒子(111)表面的两种主要吸附形态: 双键吸附和羧基吸附, 计算了不同溶剂环境中油酸盐分子的吸附能和振动频率. 结果表明: 作为银纳米粒子保护剂的油酸盐能够稳定地存在于极性和非极性溶剂环境中, 与银表面的作用方式随溶剂极性的改变而改变, 水相中以双键吸附为主, 而在有机相中主要是羧基吸附. 这与红外光谱实验的推论基本吻合. 从而在分子水平上为实验结果提供了有价值的理论支持和微观信息.     

Affinity of hydroxyapatite (001) and (010) surfaces to formic and alendronic acids: a quantum-mechanical and infrared study

The affinity of the (001) and of the water reacted (010)WR hydroxyapatite surfaces towards formic and alendronic acids is studied with density functional theory (PBE functional) using periodic boundary conditions based on Gaussian basis set. Structures, energetic of the adsorption and vibrational features of the adsorbates are computed in order to understand at the atomic level both the cariogenic processes (for the formic acid) and the features of anti-osteoporosis drugs (for the alendronic acid). For both molecules the interaction energy is very high on an absolute scale, and for all examined cases, it is higher on the (010)WR HA surface than on the (001) one. For the latter, a number of cases by which the acidic proton of the adsorbate is transferred to the HA surface are also characterized. For the formic acid case, experimental infrared spectra are also measured and the position and nature of the C=O stretching bands have been found to be in excellent agreement with the quantum mechanical simulations. For alendronic acid IR experiments are still not available and the present predicted infrared spectra will be useful as a guide to interpret future experimental studies.     

Mechanism study of reduction of CO_2 into formic acid by in-situ hydrogen produced from water splitting with Zn: Zn/ZnO interface autocatalytic role

We have previously developed a new process of highly efficient conversion of CO_2 and water into formic acid with metallic Zn without the addition of catalyst, however, its mechanism is not clear, particularly in the catalytic role of Zn/ZnO interface. Herein, the autocatalytic role of Zn/ZnO interface formed in situ during the reduction of CO_2 into formic acid with Zn in water was studied by combining high resolution transmission electron microscopy(HRTEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) techniques and experimental data. The electron microscope results show that possible defects or dislocations formed on Zn/ZnO interface, in which plays a key role for Zn H-formation. Further XPS analyses indicate that oxygen vacancies on Zn/ZnO interface increased at short reaction times(less than 10 min). These analyses and experimental results suggest that a highly efficient and rapid conversion of CO_2 and water into formic acid should involve an autocatalytic role of the Zn/ZnO interface formed in situ, particularly at the beginning of the reaction.     

Utilisation of pH stacking in conjunction with a highly absorbing chromophore, 5-aminofluorescein, to improve the sensitivity of capillary electrophoresis for carbohydrate analysis

This study explores the use of pH stacking in conjunction with 5-aminofluorescein as a derivatization agent for the sensitive analysis of simple sugars such as glucose, lactose and maltotriose by capillary electrophoresis (CE). The derivatization agent was selected on the basis of its extremely high molar absorptivity, its compatibility with a 488nm light-emitting diode (LED) and the fact that it has two ionizable groups making it compatible with on-line stacking using a dynamic pH junction. The influence of both acetic and formic acids at concentrations of 0.19, 0.019 and 0.0019molL(-1) were investigated with regard to both derivatization efficiency and the ability to stack using a dynamic pH junction. Superior sensitivity and resolution was obtained in formic acid over acetic acid. Substantially lower peaks were obtained with 0.19molL(-1) formic acid when compared to 0.019 and 0.0019molL(-1) concentrations, which was confirmed by computer simulation studies to be due to the inadequate movement of the pH boundary for stacking. Further simulation studies combined with experimental data showed the separation with the best resolution and greatest sensitivity when the carbohydrates were derivatized with the 0.095molL(-1) formic acid. Utilisation of stacking via dynamic pH junction mode in conjunction with LED detection enabled efficiencies of 150,000 plates and detection limits in the order of 8.5x10(-8)molL(-1) for simple sugars such as glucose, lactose and maltotriose hydrate. The current system also demonstrates a 515 times improvement in sensitivity when compared to using a normal deuterium lamp, and 16 times improvement over other systems using LEDs.     

ZnO/C纳米球的亚甲基蓝单吸附特性:平衡、动力学及机理

采用电弧放电法制备了ZnO/C纳米球,利用FESEM、XRD和N₂吸附/脱附测试进行了表征。在避光条件下研究了复合材料对亚甲基蓝的吸附性能。研究结果表明,随着亚甲基蓝的浓度及接触时间的增长吸附量明显上升,在吸附时间为150 min时达到吸附平衡。采用Langmuir、Freundlich及Temkin等温吸附模式对吸附平衡进行了研究。结果表明,吸附等温线符合Langmuir等温吸附模式,单层吸附饱和容量可达188.68 mg·g^-1。利用动力学模型、内扩散模型和外扩散速率控制模型拟合实验数据,拟合数据表明其动力学符合伪二级动力学模型;内扩散机理不是吸附速率的唯一限制机理,亚甲基蓝的总吸附速率受膜扩散控制。     

ZnO/C纳米球的亚甲基蓝单吸附特性:平衡、动力学及机理

采用电弧放电法制备了ZnO/C纳米球,利用FESEM、XRD和N₂吸附/脱附测试进行了表征。在避光条件下研究了复合材料对亚甲基蓝的吸附性能。研究结果表明,随着亚甲基蓝的浓度及接触时间的增长吸附量明显上升,在吸附时间为150 min时达到吸附平衡。采用Langmuir、Freundlich及Temkin等温吸附模式对吸附平衡进行了研究。结果表明,吸附等温线符合Langmuir等温吸附模式,单层吸附饱和容量可达188.68 mg·g^-1。利用动力学模型、内扩散模型和外扩散速率控制模型拟合实验数据,拟合数据表明其动力学符合伪二级动力学模型;内扩散机理不是吸附速率的唯一限制机理,亚甲基蓝的总吸附速率受膜扩散控制。     

Photo-induced oxidation of some organic carbonyl compounds by vanadium(V)

The oxidation of pyruvic acid, levulinic acid, acetaldehyde, isobutyraldehyde and acetylacetone by vanadium(V) in aqueous solution on illumination with visible light is described. Pyruvic acid undergoes oxidation much more rapidly than does levulinic acid ; both give acetic acid. Acetaldehyde is more rapidly oxidized than is isobutyraldehyde, the former giving formic acid, and the latter, formic acid and acetone. Acetylacetone is converted into acetic acid. The oxidations are rapid and quantitative and may be used for the estimation of these carbonyl compounds.     

Development of an analytical method for beryllium in airborne dust by micellar electrokinetic chromatography

The separation of diacetylacetonato–beryllium [Be(acac)₂] from acetylacetone was achieved with micellar electrokinetic chromatography (MEKC) followed by subsequent beryllium analysis carried out using capillary electrophoresis. Analysis using a separation and absorption detector, with a 50 μm capillary cell, could detect approximately 1000 ppb of beryllium in the final sample. Be(acac)₂ is a promising reagent for absorption spectrophotometry, because its molar absorption coefficient, (32 000 l mol⁻¹ cm⁻¹) is very large. As the complex and acetylacetone have a similar absorption wavelength, the excess free ligand must removed from the sample to be measured. Acetylacetone is a weak acid with keto–enol tautomerism in aqueous solution. Acetylacetone and neutral Be(acac)₂ should be separated with capillary zone electrophoresis (CZE) using a neutral or basic buffer solution as the mobile phase. Although the pH and temperature of the mobile phase were optimized, separation with CZE was interfered with by a portion of acetylacetone. This interfering portion seems to be a neutral keto-form with the same migration time as Be(acac)₂. As a neutral species separation method, MEKC with sodium dodecyl sulfate was tried and the separation was completed. The optimum pH value and buffer temperature are pH 7.8 and 15°C, respectively.     

Ab initio calculations of the O1s XPS spectra of ZnO and Zn oxo compounds

O1s core level binding energies of oxygen atoms in bulk ZnO, at different ZnO surfaces, and in some Zn oxo compounds were calculated by means of wave function based quantum chemical ab initio methods. Initial and final state effects were obtained by Koopmans' theorem and at the DeltaSCF level, respectively. After correction for scalar relativistic effects and electron correlation, the calculated XPS peak positions are in excellent agreement with the available experimental data for all systems included in the present study. The O1s core level shifts between an isolated H2O molecule and the Zn oxo compounds or ZnO, as well as between oxygen atoms in bulk ZnO and at various ZnO surfaces, can be understood by means of Madelung potentials and electronic relaxation or screening. XPS spectra were calculated for various cluster models which are designed to describe different possibilities of stabilizing the polar O-terminated ZnO(0001) surface by the adsorption of H atoms. The experimental spectra are only compatible with the theoretical results for the fully hydroxylated H-ZnO(0001) surface exhibiting a (1x1) surface structure.     

Density functional theory study of formic acid adsorption on anatase TiO2(001): geometries, energetics, and effects of coverage, hydration, and reconstruction

We present density functional theory calculations and first-principles molecular dynamics simulations of formic acid adsorption on anatase TiO(2)(001), the minority surface exposed by anatase TiO(2) nanoparticles. A wide range of factors that may affect formic acid adsorption, such as coverage, surface hydration, and reconstruction, are considered. It is found that (i) formic acid dissociates spontaneously on unreconstructed clean TiO(2)(001)-1 x 1, as well as on the highly reactive ridge of the reconstructed TiO(2)(001)-1 x 4 surface; (ii) on both the 1 x 1 and 1 x 4 surfaces, various configurations of dissociated formic acid exist with adsorption energies of about 1.5 eV, which very weakly depend on the coverage; (iii) bidentate adsorption configurations, in which the formate moiety binds to the surface through two Ti-O bonds, are energetically more favored than monodentate ones; (iv) partial hydration of TiO(2)(001)-1 x 1 tends to favor the bidentate chelating configuration with respect to the bridging one but has otherwise little effect on the adsorption energetics; and (v) physical adsorption of formic acid on fully hydrated TiO(2)(001)-1 x 1 is also fairly strong. Comparison of the present results for formic acid adsorption with those for water and methanol under similar conditions provides valuable insights to the understanding of recent experimental results concerning the coadsorption of these molecules.     

Quantum chemical prediction of the adsorption conformations and dynamics at HCOOH‐covered ZnO(1010) surfaces

Results from ab initio Hartree–Fock and gradient‐corrected density functional theory calculations of formic acid interactions with ZnO (101 0) surfaces are reported. Surface relaxation is found to affect equilibrium geometries and adsorption energies significantly. Large variations in adsorption energy with coverage and ordering of the adsorbates are revealed and explained in terms of strong and highly anisotropic electrostatic adsorbate–adsorbate interactions. The results are compared to published experimental and theoretical results, and differences in suggested binding geometries from the different studies are discussed. Dynamic properties of the adsorption, surface mobility, and surface reactivity are inferred from key elements of the potential energy surface obtained from the quantum chemical computations and supported by ab initio molecular dynamics simulations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

PdCu合金纳米晶体的制备和电催化活性研究

改变表面活性剂1-十八烯（ODE）和油胺（OLA）或油酸（OA）的配比,以1,2-二羟基十六烷二醇作还原剂同时还原乙酰丙酮铜Cu(acac)2和乙酰丙酮钯Pd(acac)2一步法制备了单分散的球形和米花形的PdCu纳米粒子.透射电子显微镜和XRD等结构表征表明,两种形状的PdCu纳米粒子均为（111）面占优的合金纳米晶体,其平均粒径分别为12.7 ± 0.18 和 20.4 ± 0.31 nm.电化学循环伏安法（CV）测定了两种PdCu合金纳米粒子对甲酸氧化的电催化活性.结果表明,在球形PdCu纳米粒子上得到的甲酸氧化峰电流密度约为米花状纳米粒子（PdCu-B）上的5.6倍.同时,前者显示出了更好的抗CO毒化能力.计时电流测量也表明,球状PdCu纳米粒子比米花状纳米粒子有更好的电催化稳定性能.     

Adsorption of Methanol,Formaldehyde and Formic Acid on the Si(100)-2×1 Surface:A Theoretical Study

Small organic molecules on Si surface serve model systems in studies of the process of SiC, SiO and thin diamond films formation on the surfaces. We have applied the hybrid density functional B3LYP method in conjunction with cluster model approach and the ONIOM method1 to the study of methanol, formaldehyde and formic acid adsorption on the Si(100)-2×l surface.     

In situ FTIR studies on the effect of temperature on the electro-oxidation of small organic molecules at the Ru(0001) electrode

The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(000 1) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials < 900 mV vs. Ag/AgCl, and at all three temperatures employed, 10, 25 and 50 degrees C. However, both formaldehyde and formic acid did undergo dissociative adsorption, even at -200 mV, to form linear (CO(L)) and 3-fold-hollow (COH) binding CO adsorbates. In contrast to the adsorption of CO, it was found that increasing the temperature to 50 degrees C markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of both formaldehyde and formic acid. On increasing the potential, the electro-oxidation of the CO adsorbates to CO2 took place via reaction with the active (1 x 1)-O oxide. Formic acid was detected as a partial oxidation product during formaldehyde electro-oxidation. At all three temperatures employed, it was found that adsorbed CO species were formed from the adsorption of both formic acid and formaldehyde, and were oxidised to CO2 faster than was observed in the experiments involving CO adsorbed from CO(g), suggesting a higher mobility of the CO adsorbates formed from the adsorption of the HCOOH and HCHO. At potentials > 1000 mV, both the oxidation of formic acid to CO2 and the oxidation of formaldehyde to both CO2 and formic acid were significantly increased, and the oxidation of methanol to CO2 and methyl formate was observed, all of which were attributed to the formation of an active RuO2 phase on the Ru(0001) surface.     

Adsorption of gaseous formaldehyde and carboxylic acids by ammonium-ion-exchanged alpha-zirconium phosphate

Ammonium-ion-exchanged alpha-Zr(HPO(4))(2)H(2)O (alpha-ZrP) was obtained as a single phase with the interlayer distance of 9.4 A by the ion-exchange of proton with ammonium ion. The ammonium ion-exchanged alpha-ZrP could adsorb ill-smelling gases, such as formaldehyde and carboxylic acids (formic acid, acetic acid, propionic acid, and butyric acid). The adsorption amounts of carboxylic acids increased in the order, butyric acid相似文献   

A Critical Assessment of the Specific Role of Microwave Irradiation in the Synthesis of ZnO Micro‐ and Nanostructured Materials

A rapid, microwave‐assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3–4 μm in length and 200–300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single‐mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol–gel process at 200 °C from a Zn(acac)₂ (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.     

Formic acid electrooxidation on Pd in acidic solutions studied by surface-enhanced infrared absorption spectroscopy

A mechanistic study of electrocatalytic oxidation of formic acid on Pd in sulfuric and perchloric acids is reported. Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS) shows the adsorption of CO, bridge-bonded formate, bicarbonate, and supporting anions on the electrode surface. Poisoning of the Pd surface by CO, formed by dehydration of formic acid, is very slow and scarcely affects formic acid oxidation. The anions are adsorbed more strongly in the order of (bi)sulfate > bicarbonate > perchlorate, among which the most strongly adsorbed (bi)sulfate considerably suppresses formic acid oxidation in the double layer region. The oxidation is suppressed also at higher potentials in both acids by the oxidation of the Pd surface. Adsorbed formate is detected only when formic acid oxidation is suppressed. The results show that formate is a short-lived reactive intermediate in formic acid oxidation and is hence detected when its decomposition yielding CO(2) is suppressed. The high electrocatalytic activity of Pd can be ascribed to the high tolerance to CO contamination and also high catalytic activity toward formate decomposition.     

Hydrogen bond formations between pyrazine and formic acid and between pyrazine and trichloroacetic acid

The hydrogen bond formations between pyrazine and formic acids and between pyrazine and trichloroacetic acids were studied through observation of the Raman and infrared spectra for mixture of pyrazine and formic acid and also mixture of pyrazine and trichloroacetic acid at 77 K. It was observed that the mutual exclusion principle held for the Raman and infrared spectra of both mixtures, even for the spectra of the samples whose mixing mole ratio of acids was very low. This fact clearly indicates that the hydrogen bonded molecule does not exist in the form of formic acid-pyrazine or trichloroacetic acid-pyrazine whose geometry belongs to the Cs point group, but exists in the form of formic acid-pyrazine-formic acid or trichloroacetic acid-pyrazine-trichloroacetic acid belonging to the C(i) point group.     

Dye-sensitized solar cells based on functionalized truxene structure

Three new metal-free organic dyes(TX1, TX2 and TX3) based on truxene core structure, with triphenylamine as the electron donor, thiophene as the p spacers, and cyanoacetic acid or rhodanine-3-acetic acid as the electron acceptor are designed and synthesized. Their UV–vis absorption spectra,electrochemical and photovoltaic properties were investigated. The cyanoacrylic acid is verified to be a better acceptor unit(meanwhile the anchoring group) compared to the rhodanine-3-acetic acid. And also, two anchoring groups in TX2 could provide stronger adsorption ability on the Ti O2 surface. In addition, the EIS results indicate a slower charge recombination processes for TX2. As a result, dye TX2 bearing two cyanoacetic acid outperforms the other two dyes, exhibiting the photo-conversion efficiency of 2.64%, with Jsc= 5.09 m A cm–2, Voc= 729 m V, FF = 71.1.