Electrocatalytic oxidation of nitrophenols in aqueous solution using modified PbO2 electrodes

Various kinds of modified lead dioxide (PbO₂) electrodes, doped with bismuth oxides and cobalt oxides, were prepared by electrodeposition in acid solution, and were characterized in terms of their morphological (SEM) and structural (XRD) features. Mineralization experiments on o-nitrophenol (ONP) in an electrocatalytic oxidation system showed that the electrocatalytic activity of Ti/Bi–PbO₂ was superior to the traditional dimensionally stable anodes (DSAs) Ti/β-PbO₂ and other modified PbO₂ electrodes. The mineralization, reaction kinetics and nitro-group transformation of nitrophenols (ONP, p-nitrophenol (PNP) and m-nitrophenol (MNP)) on Ti/Bi–PbO₂ electrodes were studied and compared. NPs were degraded completely under the present experimental conditions by applying a 30 mA cm⁻² current density at pH 4.3 in 0.1 M Na₂SO₄ and 0.01 M NaCl. The degradation of NPs lay in the order: ONP > MNP > PNP. A simple degradation mechanism model is proposed.     

Electrocatalytic degradation of aspen lignin over Pb/PbO2 electrode in alkali solution

A novel procedure about electrochemical catalysis degradation of aspen lignin with Pb/PbO₂ anode in the three-dimensional electrode (TDE) reactor was investigated. SEM, XRD and cyclic voltammogram tests were employed to study the surface morphology, composition and the electrochemical redox performance of the fabricated Pb/PbO₂ electrode. The lignin was cracked by OH and hydrogenated by [H] atom generated from alkaline water electrolysis, leading to the production of 4-methylanisole and other products. Raw material lignin concentration, current density, temperature and time were optimized. The pathway of electrocatalytic degradation and hydrogenation process of lignin in alkaline solution was also discussed.     

Catalytic wet air oxidation of aqueous solution of 2-chlorophenol over Ru/zirconia catalysts

Ru loaded zirconia catalysts (Ru/ZrO₂) were found to be active in the catalytic wet air oxidation (CWAO) of 2-chlorophenol (2-CP) at relatively mild temperature. To optimize the reaction conditions, the effects of different operating parameters, such as the rotation speed, the reaction temperature, the total pressure, the initial concentration and the pH of the initial 2-CP solution on the catalytic activity of 3 wt.% Ru/ZrO₂ were evaluated. The activation energy for the CWAO of 2-CP over Ru/ZrO₂ was calculated to be 36 kJ mol⁻¹. The 2-CP removal rate is zero order with respect to the initial 2-CP concentration. The CWAO of 2-CP changes from first order (oxygen diffusion control) to zero order (kinetic control) with respect to the oxygen partial pressure when the total pressure is higher than 4 MPa. The conversion of 2-CP increases with the pH of the initial 2-CP solution. The dechlorination reaction is promoted at higher pH. However, too high pH limits the total mineralization of 2-CP because the adsorption of the reaction intermediates is hindered. It was also confirmed that Ru(NO)(NO₃)₃ is better than RuCl₃ to act as a ruthenium precursor.     

Electrocatalytic oxidation of hydrazine at overoxidized polypyrrole film modified glassy carbon electrode

Electrocatalytic oxidation of hydrazine (HZ) was studied on an overoxidized polypyrrole (OPPy) modified glassy carbon electrode using cyclic voltammetry and chronoamperometry techniques. The OPPy-modified glassy carbon electrode has very high catalytic ability for electrooxidation of HZ, which appeared as a reduced overpotential in a wide operational pH range of 5-10. The overall numbers of electrons involved in the catalytic oxidation of HZ, the number of electrons involved in the rate-determining and diffusion coefficient of HZ were estimated using cyclic voltammetry and chronoamperometry. It has been shown that using the OPPy-modified electrode, HZ can be determined by cyclic voltammetry and amperometry with limit of detection 36 and 3.7 μM, respectively. The results of the analysis suggest that the proposed method promises accurate results and could be employed for the routine determination of HZ.     

Electrocatalytic oxidation of organic compounds on noble metals in aqueous solution

The oxidatioin of organic compounds on noble metal electrodes in aqueous solution is a complex reaction due to the occurrence of several adsorbed intermediates and reaction products or by-products. This leads to a lot of electrocatalytic problems, such as the elucidation of the nature of reaction products and the structure of adsorbed species, the role of the electrode material, the effect of the structure of the organic compound, and the role of the composition of the electrolytic solution. These topics are illustrated with the help of various organic compounds (formic acid, methanol, ethanol, ethylene-glycol, C—2 compounds derived from ethylene—glycol, butanol isomers) using principally two experimental approaches: cyclic voltammetry at the macroscopic level and infrared spectroscopy (either FTIRS or EMIRS) at the microscopic level.     

PbO_2/SPE复合膜电极电解发生臭氧的性能

采用化学镀法在Nafion膜上直接沉积制备了PbO2/SPE复合膜电极,结合XRD、SEM分析了复合膜电极上沉积层的晶相结构和形貌特征。结果表明,膜上沉积层为单一的四方结构β型PbO2,且其在Nafion膜上沉积致密,颗粒均匀,尺寸范围为300～500nm。通过恒电流电解实验研究了β-PbO2/SPE复合膜电极电解发生臭氧的性能。结果表明,β-PbO2/SPE复合膜电极相比于其它两种膜电极更适合作为电解发生臭氧的阳极材料,在所测试的电流密度范围内,当i=1.5A/cm2时,臭氧产量达到最高为49.64mg/h,电流效率14.1%,槽压4.33V,能耗102.7W·h/(gO3)。     

Electrocatalytic activity of amorphous RuO2 electrode for oxygen evolution in an aqueous solution

The electrocatalytic activity of amorphous and crystalline RuO₂ thin films for oxygen evolution in an aqueous solution was investigated. The RuO₂ films were prepared on FTO substrates by electrodeposition or RF magnetron sputtering technique. The obtained films were annealed at various temperatures. In both cases, the as-prepared films or the 200 °C annealed film had an amorphous structure, whereas the films annealed at 300 °C and over were crystallized to rutile structure. The analysis of the Tafel slope indicated that the rate-determining step in the oxygen evolution reaction on the amorphous RuO₂ was the combination of the adjacent Ru–OH groups, whereas that on crystalline RuO₂ was the dissociation of O–H bond in Ru–OH group. The onset potentials of the amorphous RuO₂ films for oxygen evolution were shifted toward the negative side by 0.06–0.03 V from those for the rutile crystalline samples. The shift of the onset potential is probably attributed to the structural flexibility which is characteristic of the amorphous surface. This result suggested that the electrocatalytic activity of amorphous RuO₂ for oxygen evolution was higher than that of rutile crystalline RuO₂.     

纳米TiO_2-Pt复合膜电极间接电催化氧化甘油为甘油醛的研究

运用电沉积法在纳米TiO2膜上电沉积分散的Pt微粒制成钛基纳米TiO2-Pt复合膜(nano TiO2-Pt)修饰电极,采用循环伏安法和电解氧化法,研究了复合膜电极的电催化活性以及氧化甘油为甘油醛的过程。结果表明,纳米TiO2为锐钛矿型,Pt纳米粒子均匀分散在TiO2多孔膜的表面和内部。复合膜电极在常温常压下对甘油的电化学氧化具有高催化活性和稳定性,在25~30℃下,电流密度为25 m A/cm2时,电流效率达84%,电解产率达89.6%。     

不锈钢基二氧化铅-碳化钨-氧化铈复合电极的制备

研究了不锈钢基体上PbO2-WC-CeO2复合电极材料的电沉积工艺,通过分析其在由65g/LZn2+和150g/LH2SO4组成的电解锌液中的析氧动力学参数、Tafel曲线以及扫描电镜观察,考察了温度、电流密度和WC、CeO2固体颗粒质量浓度对该电极催化活性和耐蚀性的影响,确定了复合电沉积的较佳工艺:CeO240g/L和WC20g/L,电流密度25mA/cm2,温度60°C。在此工艺条件下可以获得致密、均匀的不锈钢基PbO2-WC-CeO2复合电极材料,其交换电流密度为0.732A/cm2,腐蚀电流密度为3.924×105A/cm2。     

乙二醛在纳米TiO2-Pt电极上的电催化氧化

通过电沉积修饰铂微粒制备Ti基纳米TiO₂-Pt（Ti/nano-TiO₂-Pt）修饰电极,采用循环伏安法研究了乙二醛在Ti/nano-TiO₂-Pt上的电催化氧化。结果表明：Ti/nano-TiO₂-Pt修饰电极对乙二醛的氧化呈现较高的电催化活性,可作为乙二醛电氧化合成乙醛酸的高活性催化电极。     

Electrocatalytic oxidation of methanol on platinum microparticles in polypyrrole

The oxidation of methanol on gold electrodes modified with polypyrrole and platinum is reported. These electrodes were characterized by cyclic voltammetry and by 12h polarizations in methanol solutions. They were found to give higher currents and lower rates of drift than electrodes of platinum and platinized gold. The effect of varying the amount of platinum deposited is also discussed.     

陶粒改性及其对海水养殖系统中硫化物的控制

通过沉积焙烧法,在陶粒表面涂覆铁氧化物制备一种硫化物控制材料覆铁陶粒,经X射线衍射测定,覆铁陶粒表面主要成分为α-Fe_2O_3。以硫化物去除率为指标,确定最佳制备方法为:FeCl_3浸泡溶液浓度0.5 mol/L,pH值3.0,450℃焙烧3 h,涂覆3次。获得的覆铁陶粒含铁量提高128.79 mg/g,比表面积是原始陶粒的1.72倍,具有良好的耐腐蚀及抗机械磨损能力,对硫化物的去除量为3.59 mgS/g,是未改性陶粒的11倍以上,对海水养殖系统中产生的硫化物具有较好的控制效果。     

Electrocatalytic reduction of oxygen at glassy carbon electrode modified by polypyrrole/anthraquinones composite film in various pH media

The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. The electrochemical behaviour of the modified electrodes was examined in various pH media and both the formal potential of anthraquinones and reduction potential of dioxygen exhibited pH dependence. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O₂ to H₂O₂. pH 6.0 was chosen as the most suitable medium to study the electrocatalysis by comparing the peak potential of oxygen reduction and enhancement in peak current for oxygen reduction. The diffusion coefficient values of AQ at the modified electrodes and the number of electrons involved in AQ reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, hydrodynamic voltammetric studies showed the involvement of two electrons in O₂ reduction. The mass specific activity of AQ used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry.     

Pd–Ni双金属复合物修饰泡沫镍电极对水中4-氯酚的电化学脱氯

以Pd–Ni双金属复合物修饰泡沫镍电极（Pd–Ni/Ni）为阴极,对水中4–氯酚（4–CP）进行了电催化脱氯。Pd–Ni双金属颗粒直径大约为50–100nm且均匀地分散在泡沫镍基体上。高效液相色谱（HPLC）分析结果表明Pd–Ni/Ni电极比Pd/Ni或Ni/Ni电极具有更高的催化效率,而苯酚是主要的脱氯产物。增大4–CP初始浓度和升高溶液温度均能使电流效率增大,而还原电流的增大则使电流效率减小。在表观电流密度2.500 mA•cm-2、溶液温度15 °C、4–CP初始浓度1 mmol·L^-1时,4–CP脱氯效率可达82%。另外,根据Pd–Ni/Ni,Pd/Ni和Ni/Ni三种电极的电化学阻抗谱的差异以及它们在不同电流条件下的脱氯效率,推断得到不同极化条件下的速率控制步骤。     

Understanding of electrochemical and structural changes of polypyrrole/polyethylene glycol composite films in aqueous solution

Electrochemical monitoring of electrical and structural changes of both PPy and PPy–PEG films electrochemical deposited, in order to highlight if the structural stability offered by PEG has an influence on electrical properties and stability in aqueous solution over immersion time was investigated.Electrochemical analysis suggests that PPy–PEG film inserts cations easier than PPy film for a short immersion time probably due to ability of PEG to form complexes with metal cations.The FTIR spectra showed that the PEG incorporation decreases the rate of PPy overoxidation probably by restraining the electron release and by rendering O₂ inaccessible to PPy.Mott–Schottky analysis based on capacitance measurement reveal p-type conductance for both films.The in situ AFM analysis sustains electrochemical behaviour and has permitted elaboration of a model of PPy and PPy–PEG films behaviour during immersion in testing solution.     

Ti/nanoTiO2-ZrO2修饰电极电催化氧化葡萄糖

在无水乙醇和乙酰丙酮混合溶液中,电解Ti金属制得前驱体Ti（OCH₂CH₃）_（4-y）（acac）_y,再加入ZrCl₄,将上述溶液直接水解、干燥后在450℃煅烧2 h,粉体通过X射线衍射（XRD）分析表明：纳米TiO₂-ZrO₂粉体呈单分散结构。通过凝胶涂抹、煅烧得到高活性的     

Electrocatalytic degradation of 4-chlorophenol on F-doped PbO2 anodes

PbO₂ and F-doped PbO₂ (F-PbO₂) anodes have been prepared by a standard thermal decomposition-electrodeposition technique. The electrochemical stability of these anodes has been investigated by the accelerated life tests in sulphuric acid solution. The results show that the service life of the F-PbO₂ anodes is almost three times longer than that of the PbO₂ anodes. Furthermore, in the degradation of 4-chlorophenol (4-CP), the F-PbO₂ anodes give a higher degradation rate than that observed for the PbO₂ anodes. The influence of F⁻ anion doping on the stability and activity of PbO₂ anodes has been discussed. With the F-PbO₂ anodes, the degradation of 4-CP is investigated according to the results of high-performance liquid chromatograph (HPLC), ionic chromatograph (IC) and cyclic voltammetry (CV). In addition, the electron spin resonance (ESR) technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trap reagent has been applied to detect free radical intermediates generated during in situ the electrocatalytic degradation of aqueous 4-CP on the F-PbO₂ anodes. ESR measurements give the direct evidence that the active species (OH) are responsible for the decomposition of 4-CP over F-PbO₂ under anodic bias potential, strongly suggesting that the electrocatalytic degradation of most organic compounds on F-PbO₂ anodes proceed via surface intermediates of water oxidation, not via direct oxidation at electrode surface. The formation mechanism of surface intermediates is also discussed.     

Mechanism of formation of polypyrrole on a Pt electrode from aqueous solutions

A coherent explanation for the polypyrrole tridimensional growth on a Pt surface has been found. Two different potential ranges were studied on which the reaction mechanism changes. The results are not in disagreement with an instantaneous tridimensional nucleation [see, S. Asavapiriyanont, G. K. Chandler, G. A. Gunawardena and D. Pletcher, J. electronal. Chem.177, 229 (1984)] but do not show any pH dependence, from which a loss of H⁺ by the pyrrole monomers could be deduced.     

Electrodeposition of polypyrrole on aluminium in aqueous tartaric solution

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of tartaric acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by energy spectroscopy dispersion (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al₂O₃ layer.A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium.Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, EDS reveals a good homogeneity and compactness of the film achieved in galvanostatic method. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al₂O₃/PPy shows a capacitor with future applications.     

一种新型二氧化铅电极的研制

用二氧化铅作为电极材料，研究了用铂为基体二氧化铅电极的研制，对在不同反应条件下电镀制成的电极进行了性能测试，并用XRD，XPS，SEM等分析手段进行了表征，得到了电极制作的最佳条件，此电极具有好的应用前景。