Selective oxidation of alcohols over nickel zirconium phosphate

Nickel zirconium phosphate nanoparticles were found to function as efficient catalysts for the selec-tive oxidation of a wide range of alcohols to their corresponding ketones and aldehydes using H2O2 as an oxidizing agent and without any organic solvents, phase transfer catalysts, or additives. The steric and electronic properties of various substrates had significant influence on the reaction con-ditions required to achieve acetylation. The results showed that this method can be applied for the chemoselective oxidation of benzyl alcohols in the presence of aliphatic alcohols. The catalyst used in the current study was characterized by ICP-OES, XRD, NH3-TPD, Py-FTIR, N2 adsorp-tion-desorption, SEM and TEM. These analyses revealed that the interlayer distance in the catalyst increased from 0.75 to 0.98 nm when Ni2+ was intercalated between the layers, whereas the crystal-linity of the material was reduced. The nanocatalyst could also be recovered and reused at least seven times without any discernible decrease in its catalytic activity. This new method for the oxi-dation of alcohols has several key advantages, including mild and environmentally friendly reaction conditions, short reaction time, excellent yields and a facile work-up.     

New insight into the effect of interface supercapacitance on the performance of titanium dioxide/carbon nanowire array for photoelectrochemical water oxidation

The electrode/electrlyte interface is of great signifance to photoelectrochemical (PEC) water oxidation as the reaction mainly occur here. Herein, we focus on the effect of supercapactance of the electrode/electrlyte interface on the performance of PEC. It is discovered that the supercapacitor on the interface is crucial because it links the charge transport and solution ion adsorption on its two sides. In this study, we demonstrate an approach to promote the performance of TiO₂ nanowire array (TiO₂ NWs) photoanode in photoelectrochemical cells (PECs) by increasing its supercapacitance. A 2−5 nm carbon layer was coated and the interface supercapacitance increases by about 150 times. This enhances the separation rate of electron-hole pairs by collecting more holes. Meanwhile, it also promotes the water oxidation rate by adsorbing more OH⁻ on its surface. As a result, the photocurrent density of C-TiO₂ NWs was about 8 times higher than that of its carbon-free counterpart. This approach of increasing the supercapacitance of photoanodes would be attractive for enhancement of the efficiency of PECs and this work demonstrate the importance of supercapacitance of the interface for PECs.     

Rationally designed/constructed MnOx/WO3 anode for photoelectrochemical water oxidation

The activity of WO₃ photoanode could be improved efficiently after loading MnO_x by photodeposition. The maximum photocurrent density of composite photoanode is achieved with a deposition time of 3 min, which is higher than that of pristine WO₃ photoanode around 40%.     

A co-activation strategy for enhancing the performance of hematite in photoelectrochemical water oxidation

Hematite(α-Fe_2O_3) is a promising photoanode for photoelectrochemical(PEC) water splitting.However,the severe charge recombination and sluggish water oxidation kinetics extremely limit its use in photohydrogen conversion.Herein,a co-activation strategy is proposed,namely through phosphorus(P)doping and the loading of CoAl-layered double hydroxides(CoAl-LDHs) cocatalysts.Unexpectedly,the integrated system,CoAl-LDHs/P-Fe_2O_3 photoanode,exhibits an outstanding photocurrent density of 1.56 mA/cm~2 at 1.23 V(vs.reversible hydrogen electrode,RHE),under AM 1.5 G,which is 2.6 times of pureα-Fe_2O_3.Systematic studies reveal that the remarkable PEC performance is attributed to accelerated surface OER kinetics and enhanced carrier separation efficiency.This work provides a feasible strategy to enhance the PEC performance of hematite photoanodes.     

Explicit study on the oxidation mechanism of nickel in molten Li2CO3-K2CO3

The oxidation behavior of nickel in Li+K carbonate melt is followed by measuring the open-circuit potential and by electrochemical impedance spectroscopy under an O₂+CO₂ gas mixture in the ratio 90/10 at a total pressure of 1 atm at 650 °C. X-ray diffraction (XRD) and energy-dispersive spectroscopy are employed for qualitative and quantitative analyses of the different compounds involved during the oxidation of nickel. Atomic force microscopy is used for both imaging the evolution of the oxide layer and determining its surface roughness. The in situ oxidation process of nickel demonstrates three stages: rapid formation of a compact surface oxide (first stage), thicker oxide layer (second stage), and a porous oxide structure (third stage). The lithiation reaction has been identified to occur during the second stage. Formation of an intermediate and unstable compound, namely NiCO₃, has been confirmed by XRD. Electronic Publication     

Improved photoelectrochemical performance of bismuth vanadate by partial O/F-substitution

Fluorine-containing bismuth vanadate (F:BiVO₄) powder was synthesized using a new, clean, and simple solid-vapor reaction. Incorporation of fluorine mainly leads to the formation of cation vacancies. Electrodes were fabricated from the pre-synthesized powder samples by electrophoretic deposition onto fluorine-doped tin oxide coated glass slides and subsequent calcination. The photoelectrochemical performance concerning the water oxidation reaction was investigated and compared to pristine BiVO₄ revealing strongly enhanced photoelectrochemical behavior for the F-containing BiVO₄.     

Electrochemical water oxidation by photo-deposited cobalt-based catalyst on a nano-structured TiO2 electrode

A cobalt-based catalyst was directly photo-deposited on the surface of a widely used n-type nano-structured semiconductor(TiO 2).Different thicknesses of the TiO 2 films as well as different time of photo-deposition of the Co-based catalyst on TiO 2 films have been optimized.It was found that the electrode with 3 layers of TiO 2 film(in 8 m thickness) and 1 hour photo-deposition of the cobalt-based catalyst by light irradiation from a 500 W Xenon lamp gave the highest current density(～5 mA/cm 2).Using this cobalt-modified TiO 2 film as a working electrode in an electrochemical device,highly efficient water oxidation has been demonstrated in a pH 7.0 aqueous solution with low overpotential.     

TiO2 nanotubes： A novel solid phase extraction adsorbent for the sensitive determination of nickel in environmental water samples

A novel method was developed for the sensitive determination of nickel in environmental water samples by using TiO2 nanotubes, a new nanomaterial, as solid phase extraction absorbent. In general, TiO2 nanomaterials were often used for catalytic degradation of pollutants in environmental field, and only a very few application in environmental analytic chemistry. In present work, TiO2 nanotubes was firstly used for the enrichment of nickel and the factors would influence the preconcentration performance were optimized. Under the optimal conditions, TiO2 nanotubes exhibited its good enrichment capacity for nickel and the detection limit of the proposed method was 1 ng· mL^-1. The proposed method was validated with real water samples, and excellent results were obtained with the spiked recoveries in the range of 94.4-99.2%, respectively.     

NiFe双氢纳米粒子有效提高BiVO4光阳极光电化学水分解性能

近年来, 太阳能驱动的光电化学水分解作为一种高效、环保、可持续的技术, 已经引起了广泛的关注. 为了更好地使用光电化学技术将太阳能转化为化学能, 至关重要的是提高光电极材料的光吸收和光转化效率. BiVO4禁带宽度(Eg=2.4-2.5 eV)小, 具有很好的可见光响应能力, 因此BiVO4光电极材料引起了广泛关注. 但是, 当单独BiVO4作为光电阳极材料时, 电子-空穴对分离弱、载流子传输慢, 从而使BiVO4不能很好地在光电化学水分解中发挥作用. 为了缓解或解决此类限制性因素, 本课题组通过水热法合成了NiFe双氢纳米粒子, 并将其负载于BiVO4电极表面, 光电催化分解水实验表明其产氢效率得到大幅度提高. 同时制备了Ni(OH)2/BiVO4和Fe(OH)2/BiVO4电极并用于研究NiFe/BiVO4电极的反应机理. 在上文基础上, 本文采用电子扫描电镜(SEM)、高分辨投射电镜(HRTEM)、X射线衍射(XRD)、紫外可见漫反射(UV-Vis DRS)等表征手段和线性扫描伏安法(LSV)和电流时间(I-t)等对其光电化学活性进行了测试, 研究了NiFe/BiVO4电极在发生水氧化时的反应机理. SEM结果表明, Ni(OH)2是以纳米片组成的纳米球负载于多孔BiVO4表面; 而当Fe(OH)2负载于BiVO4表面时, BiVO4的纳米尺寸减小; NiFe-LDH纳米粒子负载于BiVO4表面时, 可以明显看见BiVO4纳米颗粒表面包裹着一层更小的纳米粒子.这证明了Ni(OH)2, Fe(OH)2和NiFe-LDH纳米粒子均成功负载于BiVO4表面. 这也得到HRTEM结果的确认. UV-Vis DRS结果表明NiFe-LDH纳米粒子能有效拓宽BiVO4的吸收边, 从而增加对可见光的吸收, 增加了对光的利用率. LSV测试结果表明, 暗反应条件下Ni(OH)2/BiVO4比NiFe/BiVO4和Fe(OH)2/BiVO4电极的起始电位更低, 说明Ni(OH)2有更好的传输电子性能; 而在光照条件下, 在同一电位时NiFe/BiVO4比Ni(OH)2/BiVO4和Fe(OH)2/BiVO4电极的光电流值更高. 值得注意的是, 此时Ni(OH)2/BiVO4比Fe(OH)2/BiVO4电极的光电流值低, 这又说明Fe(OH)2比Ni(OH)2对光更敏感. 因此当NiFe-LDH纳米粒子负载于BiVO4表面时, 不仅提高了BiVO4光电极的光吸收效率, 而且加速了载流子的传输从而抑制了光生电子-空穴的复合, 使反应过程中的量子效率得到提高.     

Selective photocatalytic oxidation of alcohols to aldehydes in water by TiO2 partially coated with WO3

Semiconductor TiO₂ particles loaded with WO₃ (WO₃/TiO₂), synthesized by impregnation of tungstic acid followed by calcination, were used for photocatalytic oxidation of alcohols in water with molecular oxygen under irradiation at λ>350 nm. The WO₃/TiO₂ catalysts promote selective oxidation of alcohols to aldehydes and show higher catalytic activity than pure TiO₂. In particular, a catalyst loading 7.6 wt % WO₃ led to higher aldehyde selectivity than previously reported photocatalytic systems. The high aldehyde selectivity arises because subsequent photocatalytic decomposition of the formed aldehyde is suppressed on the catalyst. The TiO₂ surface of the catalyst, which is active for oxidation, is partially coated by the WO₃ layer, which leads to a decrease in the amount of formed aldehyde adsorbed on the TiO₂ surface. This suppresses subsequent decomposition of the aldehyde on the TiO₂ surface and results in high aldehyde selectivity. The WO₃/TiO₂ catalyst can selectively oxidize various aromatic alcohols and is reusable without loss of catalytic activity or selectivity.     

A photoelectrochemical study on the features of carbonate-catalyzed water oxidation at illuminated TiO2/Solution interface

Photoelectrochemical (PEC) measurements were performed to investigate the catalytic effect of carbonate on water splitting over TiO₂ nanotube photoanode at low applied potentials. The photocurrent measured with the presence of carbonate with a low concentration of 5?×?10^?3?M in 0.5 M NaClO₄ solution of pH?=?6–13 was ca. two to seven times of that measured in the absence of carbonate in solution. By adding a small amount of formate as a precursor of in situ generated carbonate in solution, the significant catalytic effect of carbonate was further evidenced. The features of the photocurrents measured under both potential dynamic and potentiostatic conditions indicated that the existence of carbonate in solution can effectively prevent the surface recombination of the photogenerated electron–hole pairs occurring at the TiO₂/solution interface, which was regarded as the main reason for the catalytic effect of carbonate on the PEC water splitting in this work. The related charge transfer processes during water photooxidation at the TiO₂/solution interface were discussed.     

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

The effect of hydrothermal growth temperature on preparation and photoelectrochemical performance of ZnO nanorod array films

Highly oriented ZnO nanorod arrays with controlled diameter and length, narrow size distribution and high orientation consistency have been successfully prepared on ITO substrates at different growth temperatures by using a simple hydrothermal method. XRD results indicate that the nanorods are high-quality single crystals growing along [001] direction with a high consistent orientation perpendicular to the substrate. SEM images show that the nanorods have average diameters of about 30-70 nm by changing growth temperature. The thin films consisting of ZnO nanorods with controlled orientation onto ITO substrates allow a more efficient transport and collection of photogenerated electrons through a designed path. For a sandwich-type cell, the relatively high overall solar energy conversion efficiency reaches about 2.4% when the growth temperature is at 95 °C.     

Electrocatalytic oxidation of NADH at carbon paste electrodes modified with meldola blue adsorbed on zirconium phosphate: effect of Ca2+ and polyethyleneimine

The basic electrochemistry of carbon paste electrodes modified with Meldola Blue adsorbed on zirconium phosphate (MB-ZP-CPEs) and their ability to oxidize NADH have been investigated. Three types of carbon powder (graphite and glassy carbon-type Sigradur K and G) were used to obtain MB-ZP-CPEs. On comparing cyclic voltammograms recorded at MB-ZP-CPEs, similarly prepared from the three different carbon powders, those made with Sigradur K exhibited the lowest background current, and the best MB electrochemistry, seen as the highest peak intensities and smallest peak separation. Using MB-ZP-CPEs based on Sigradur K a study on NADH oxidation was done focusing on the effect of the Ca²⁺ concentration in the contacting solution and on the addition of polyethyleneimine (PEI) into the paste. It can be stated that MB-ZP-CPEs based on Sigradur K and containing 1.23% (w/w) PEI exhibited the best behavior for NADH oxidation, measured by the highest electrocatalytic rate constant (8.2×10³ M^–1 s^–1).     

Pyrite (FeS2)-decorated 1D TiO2 nanotubes in a bilayer as a sustainable photoanode for photoelectrochemical water splitting activity

Herein, FeS₂@TiO₂ nanotubes photocatalyst was prepared by electrochemical anodization method followed by successive ionic layer adsorption and reaction method, and then finally annealed in a tube furnace for homogenous crystallization. The surface morphology, elemental composition, optical properties, and crystalline structure of the prepared FeS₂@TiO₂ nanocomposite were found out by performing scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, and fluorescence spectroscopy, respectively, while bonds vibrations and various functional groups' presence were analyzed using Raman and Fourier transform infrared spectroscopy. A higher photocurrent density of 1.59 mA/cm² at 0.3 V versus reference electrode of Ag/AgCl (1.23 V versus reversible hydrogen electrode) using 100 mW/cm² intensive light source was shown by 15-FeS₂@TiO₂ nanotubes (uniformly loaded photoanode) while donor density (N_D) of 3.68 × 10⁻¹³ cm⁻³ as compared to pure TiO₂ NTs (0.09 mA/cm²), 05-FeS₂@TiO₂ NTs (0.19 mA/cm²), 10-FeS₂@TiO₂ NTs (0.53 mA/cm²) and 20-FeS₂@TiO₂ NTs (0.61 mA/cm²), respectively. The exceptional photoelectrochemical activity results were attributed to the homogenous integration of FeS₂ that not only increase the charge separation but also, intensively interacted with the substrate (TiO₂ nanotubes), which results in an excellent photoelectrochemical activity.     

Flow-injection analysis of glucose without enzyme based on electrocatalytic oxidation of glucose at a nickel electrode

This paper reports a flow-injection analysis (FIA) of glucose not using enzyme based on the electrocatalytic oxidation of glucose at a nickel electrode. The electrocatalytic mechanism and quantificational method of glucose have been investigated. The current intensity of the electrocatalytic oxidation to glucose at the potential of 550 mV is proportional to the concentration of glucose over the range of 0.10-2.50 mmol l⁻¹, with a 0.04 mmol l⁻¹ detection limit (S/N = 3) and a correlation coefficient of 0.9991. The relative standard deviation (R.S.D.) is less than 4.3% (n = 5) for the determination of practical serum samples. The biologic compounds probably existed in the sample, such as ascorbic acid, uric acid, dopamine and epinephrine, do not disturb the determination of glucose. The result is satisfactory for the determination of glucose in human serum sample as comparison to that from the routine hexokinase method.     

Boosting the photoelectrochemical water oxidation performance of bismuth vanadate by ZnCo2O4 nanoparticles

Due to the involvement of four-electron transfer process at photoanode,water oxidation is the ratelimiting step in water splitting reaction.To settle this dilemma,ZnCo₂ O₄ nanoparticles are combined with BiVO₄ to form a p-n ZnCo₂ O₄/BiVO₄ heterojunction photoanode,which is proved by an input voltage-output current test.The built-in electric field formed within the heterojunction structure promotes the effective separation of elect...     

Effect of tellurium promoter on vanadium phosphate catalyst for partial oxidation of n-butane

Te-promoted (1%) vanadium phosphate catalyst (VPDTe) was prepared via VOPO4·2H2O by calcining its precursor VOHPO4·0.5H2O in a flow of n-butane/air.VPDTe catalyst has resulted a higher existence of V5+ phase with V5+/V4+ ratio of 0.23.SEM micrographs show that Te addition altered the arrangement of the platelets from "rose-like" clusters to layer with irregular shape.Te addition has also markedly lowered the reduction activation energies of the vanadium phosphate catalyst as revealed by TPR profile.The amount of active oxygen species associated with V4+ phase of the Te promoted catalyst was significantly higher than those of the unpromoted catalyst.These observations suggest that high mobility and availability of reactive oxygen species contributed to the enhancement of n-butane conversion up to 80% at 673 K,while only 47% over unpromoted catalyst (2400 h-1,1.7% n-butane in air).