Photocatalytic activity of nanoparticles of metal sulfides in the degradation of organic dyes

The photocatalytic degradation of dyes at the nanosized sulfides of transition metals in aqueous solutions was investigated. The rate of degradation increases with decrease in the synthesis temperature of the nanoparticles and with the addition of alcohol. The substitution of Cd²⁺ cations by Ag⁺ or Cu²⁺ leads to a decrease in the photoactivity of the CdS, while substitution by In³⁺ leads to an increase. The substitution of Ni²⁺ and Co²⁺ cations in the corresponding sulfides by Cd²⁺ leads to an increase in the rate of degradation. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 276–280, September–October, 2006.     

AgBr/Ag_3PO_4光催化降解染料的性能及其降解产物的生态毒性(英文)

通过调节Na_3PO_4溶液中H_3PO_4的含量制得沉淀剂,AgNO_3与此沉淀剂反应制得Ag_3PO_4粉末.当沉淀剂pH=6时,所制得的Ag_3PO_4粉末表现出最高的光催化降解甲基蓝和罗丹明B活性.进一步添加KBr溶液修饰Ag_3PO_4可制得AgBr/Ag_3PO_4粉末.该光催化剂可使阴离子染料(如活性橙和甲基橙)脱色.采用适当的捕获剂考察了参与光催化降解过程的活性物种的抑制活性.光催化反应之后,质谱检测证实染料降解为更小的分子.以Chlorella vulgaris为生物指示剂考察了处理前后染料的生态毒性.     

W18O49 nanorods decorated with Ag/AgCl nanoparticles as highly-sensitive gas-sensing material and visible-light-driven photocatalyst

A novel gas-sensing material and photocatalyst was successfully obtained by decorating Ag/AgCl nanoparticles on the W₁₈O₄₉ nanorods through a clean photochemical route. The as-prepared samples were characterized using combined techniques of X-ray diffractometry, electron microscopy, energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. Gas-sensing measurements indicate that the Ag/AgCl/W₁₈O₄₉ NRs sensors exhibit superior reducing gas-sensing properties to those of bare W₁₈O₄₉ NRs, and they are highly selective and sensitive to NH₃, acetone, and H₂S with short response and recovery times. The Ag/AgCl/W₁₈O₄₉ NRs photocatlysts also possess higher photocatalytic performance than bare W₁₈O₄₉ NRs for degradation of methyl orange under simulated sunlight irradiation. Possible mechanisms concerning the enhancement of gas-sensing and photocatalytic activities of the Ag/AgCl/W₁₈O₄₉ NRs composite were proposed.     

Photocatalytic degradation of azo dyes catalyzed by Ag doped TiO2 photocatalyst

In this paper, photocatalytic degradation of commercial textile azo dyes catalyzed by titanium dioxide and modified titanium dioxide with Ag metal (1% w/w) in aqueous solution under irradiation with a 400 W high-pressure mercury lamp is reported. The effect of various parameters such as irradiation time of UV light, amount of photocatalyst, flow rate of oxygen, pH and temperature for the Ag-TiO₂ photocatalyst were investigated. Kinetic investigations of photodegradation indicated that reactions obey improved Langmuir-Hinshelwood model and pseudo-first-order law. The rate constant studies of photocatalytic degradation reactions for Ag-TiO₂ and TiO₂ photocatalysts indicated that in all cases the rate constant of the reaction for Ag-TiO₂ was higher than that of TiO₂.     

Photocatalytic degradation of organic dyes on visible-light responsive photocatalyst PbBiO2Br

The layered compound of lead bismuth oxybromide PbBiO₂Br, prepared by conventional solid-state reaction method, has an optical band gap of 2.3 eV, and possesses a good visible-light-response ability. The references, PbBi₂Nb₂O₉, TiO_2−xN_x, BiOBr and BiOI_0.8Cl_0.2, which are excellent visible-light-response photocatalysts, were applied to comparatively understand the activity of PbBiO₂Br. Degradation of methyl orange and methylene blue was used to evaluate photocatalytic activity. The results show that PbBiO₂Br is more photocatalytically active than PbBi₂Nb₂O₉, TiO_2−xN_x and BiOBr under visible light.     

Ag/AgCl/BiOIO3三元复合物光催化剂的性能增强机制

半导体光催化技术是一种环境友好技术,它既能在温和条件下应用于环境领域——利用光能降解有机和无机污染物,又可应用于能源领域——将低密度的太阳能转化为高密度的洁净能源,因而在解决环境污染和能源匮乏问题方面展现出巨大的应用潜力.最近,一种新型Bi基光催化剂, BiOIO3,表现出优异的紫外光催化性能.它由层状[Bi2O2]2+和[IO3]?组装而成,带隙为3.1 eV左右.然而,其较大的带隙限制了其对太阳光的利用.近年来,多种方法如金属掺杂、非金属掺杂、半导体复合、光敏化改性和加氢处理被用来提高半导体的光催化效率.其中,以Ag/AgX (X=Cl, I和Br)作为助催化剂可提高体系的可见光吸收和载流子的分离能力,从而增强光催化性能.基于此,我们设计并合成了一种新型的三元光催化剂.首先采用水热法合成了BiOIO3纳米片,然后在室温条件下原位引进Ag/AgCl,制备了Ag/AgCl/BiOIO3三元异质结构.与Ag/AgCl和纯的BiOIO3相比,该三元Ag/AgCl/BiOIO3复合物光催化剂对NO表现出优异的可见光光催化去除性能.本文采用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描式电子显微镜(SEM)、电化学测试(光电流和阻抗谱)和紫外-可见漫反射光谱(UV-Vis)等表征手段研究了Ag/AgCl/BiOIO3光催化性能增强的机制. SEM结果表明,制备的Ag/AgCl/BiOIO3三元复合物为纳米颗粒和纳米片形貌, Ag/AgCl的引入对BiOIO3形貌影响不大. XRD和XPS测试结果表明,与纯的BiOIO3相比,随着Ag/AgCl 的加入,复合物的峰位置发生了明显位移,表明Ag, AgCl和BiOIO3三组分间存在强的相互作用.光电流响应图谱表明,随着Ag/AgCl的加入, Ag/AgCl/BiOIO3的光电流强度明显增强,同时阻抗谱的圆弧直径明显减小,表明电子和空穴的分离能力增强. UV-Vis图谱中, BiOIO3在可见光区几乎没有吸收,而三元复合物表现出明显的可见光吸收,且随着Ag/AgCl量的增加,复合物的可见光吸收增强,该吸收归结于复合物中Ag的表面等离子体吸收.结合之前报道的光催化剂体系如Ag/AgCl和Ag/AgCl/TiO2,我们提出了Ag/AgCl/BiOIO3复合物光催化剂性能增强的机制.在可见光照射下, Ag0因其表面等离子体吸收而产生电子空穴对.由于功函数不同, Ag和BiOIO3之间形成肖特基势垒.电子从Ag0表面转移到BiOIO3的导带上, BiOIO3导带上电子的电势不足以把O2氧化成?O2?,但电子能以多电子的形式与O2和H+生成水.同时, Ag0表面的空穴能将AgCl表面的Cl?氧化成Cl0.光照诱导AgCl表面的部分Ag+离子被还原,所以AgCl粒子的表面带负电荷. Cl0是活性自由基,能够氧化去除NO,反应之后自身被还原成Cl?.由此可见,在三元复合光催化剂中, Ag0在可见光照射下因其表面等离子体效应产生电子空穴对,随后BiOIO3有效地分离了光生载流子,使得复合材料能有效地利用光生电子和空穴.故三元Ag/AgCl/BiOIO3复合物光催化剂增强的光催化性能可归结于Ag的表面等离子体吸收和BiOIO3的载流子分离能力.该结果有助于设计和制备具有优异的光催化性能的BiOIO3基材料.     

Synthesis and photocatalytic performance of Ag/AgCl/ZnO tetrapod composites

Ag/AgCl is a visible-light plasmonic photocatalyst that has attracted considerable attention because of its high visible-light absorption and activity owing to the surface plasmon resonance of noble-metal nanoparticles. In this study, Ag/AgCl/ZnO tetrapod composite was prepared by introducing ZnO tetrapods into Ag/AgCl prepared by a polydopamine reduction route. Ag/AgCl was densely deposited on the three-dimensional support framework provided by the ZnO tetrapods. The framework possessed a certain degree of porosity, thereby improving the specific surface area of the Ag/AgCl/ZnO composite. The interaction of ZnO with Ag/AgCl further increased the separation and transfer of electron–hole pairs. The Ag/AgCl/ZnO composite showed excellent photocatalytic activity and good stability. Under xenon lamp irradiation for 20 min, degradation of rhodamine B reached 90%. After four recycling tests, degradation remained stable without any sign of reduction. Ag/AgCl/ZnO tetrapod composite is shown to be a kind of green photocatalyst offering high activity, good stability, and recyclability.

     

Ag/AgCl/ZIF-8复合材料的制备及其对NO光催化氧化性能的研究

采用室温沉淀法合成菱形十二面体晶体结构ZIF-8(一种Zn金属有机框架材料), 然后通过光还原沉积法将Ag/AgCl纳米颗粒沉积于ZIF-8表面, 得到Ag/AgCl/ZIF-8复合光催化剂, 通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、比表面积测试法(BET)、紫外-可见漫反射吸收光谱(UV-Vis DRS)等一系列表征手段对其晶体结构、形貌、比表面积及吸光性能等进行了表征. 以低浓度NO作为目标去除污染物, 系统研究了Ag/AgCl/ZIF-8复合材料对NO的可见光催化氧化性能, 并对其反应机理进行了深入分析. 结果表明: (1) Ag/AgCl/ZIF-8复合材料中Ag⁰表面等离子体共振(SPR)效应增强了可见光的吸收; (2) ZIF-8具有大的比表面积, 使其能富集更多的氧分子和NO分子, 促进生成超氧自由基和NO光催化氧化; (3) 复合材料中光生空穴能够转移到AgCl的表面氧化Cl^-为Cl⁰, Cl⁰具有强氧化性, 一方面促进了NO光催化氧化, 另一方面有效抑制了光生电子-空穴的复合, 提高了催化剂的稳定性.     

Environmentally benign chitosan as precursor and reductant for synthesis of Ag/AgCl/N-doped carbon composite photocatalysts and their photocatalytic degradation performance

In this study, we reported a novel Ag/AgCl loaded N-doped carbon composite photocatalyst (Ag/AgCl/NC) which was fabricated by a facile and green method. The composite was prepared only by two simple steps. Firstly, the Ag/N-doped carbon (Ag/NC) was prepared by one-step hydrothermal treatment; during this progress the environmentally benign and renewable natural chitosan was used as not only reducer and stabilizer, but also as a nitrogen source and carbon source. Secondly, Ag/AgCl/NC composite was synthesized via in situ oxidation reaction by adding FeCl₃. The Ag/AgCl/NC composite was characterized using X-ray diffraction, transmission electronic microscopy, energy dispersive X-ray spectra, UV-visible diffused reflectance spectra, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption measurements, respectively. The obtained Ag/AgCl/NC composite exhibited a superior photocatalytic activity and stability for the degradation of rhodamine B (RhB) under visible light irradiation.     

Photocatalytic performance of Ag doped SnO2 nanoparticles modified with curcumin

Visible light active Ag doped SnO₂ nanoparticles modified with curcumin (Cur–Ag–SnO₂) have been prepared by a combined precipitation and chemical impregnation route. The optical properties, phase structures and morphologies of the as-prepared nanoparticles were characterized using UV–visible diffuse reflectance spectra (UV–vis-DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The surface area was measured by Brunauer. Emmett. Teller (B.E.T) analysis. Compared to bare SnO₂, the surface modified photocatalysts (Ag–SnO₂ and Cur–Ag–SnO₂) showed a red shift in the visible region. The photocatalytic activity was monitored via the degradation of rose bengal (RB) dye and the results revealed that Cur–Ag–SnO₂ shows better photocatalytic activity than that of Ag–SnO₂ and SnO₂. The superior photocatalytic activity of Cur–Ag–SnO₂ could be attributed to the effective electron-hole separation by surface modification. The effect of photocatalyst concentration, initial dye concentration and electron scavenger on the photocatalytic activity was examined in detail. Furthermore, the antifungal activity of the photocatalysts and the reusability of Cur–Ag–SnO₂ were tested.     

Sonochemical synthesis of Ag/AgCl nanocubes and their efficient visible-light-driven photocatalytic performance

A novel one-step sonochemical approach to synthesize a plasmonic photocatalyst of AgCl nanocubes (ca. 115 nm in edge length) with a small amount of Ag metal species is presented. The nanoscale Ag/AgCl hybrid photocatalysts with cubic morphology are readily formed under ambient ultrasonic conditions and neither external heat treatment nor reducing agents are required. The size of the Ag/AgCl photocatalysts could be controlled by changing the concentrations of Ag(+) ions and polyvinylpyrrolidone molecules in precursor solutions. The compositions, microstructures, influencing factors, and possible growth mechanism of the Ag/AgCl hybrid nanocubes were systematically investigated. The Ag/AgCl photocatalysts show excellent photocatalytic performance for degradation of various dye molecules under visible light.     

Short time deposition of TiO2 nanoparticles on SiC as photocatalysts for the degradation of organic dyes

The deposition of TiO₂ nanoparticles on SiC was carried out by mechanical milling under different conditions. SiC–TiO₂ samples were used as photocatalysts for the degradation of organic dyes such as methylene blue and rhodamine B. A short time deposition of TiO₂ nanoparticles was observed during mechanical milling (2 min at 200 rpm) to cover the SiC particles. The presence of SiC and TiO₂ (anatase and rutile) was confirmed by means of X-ray diffraction after thermal treatment at 450 °C. The deposition of TiO₂ on SiC was corroborated by scanning electron microscopy analysis; the thickness of the thin layer of TiO₂ deposited on SiC increases as the proportion of TiO₂ increases. The energy band gap values obtained for these compounds were around 3.0 eV. SiC–TiO₂ photocatalysts prepared by mechanical milling exhibited better activity under UV-light irradiation for the degradation of methylene blue and rhodamine B than commercial TiO₂ powder (titania P25).     

Bifunctional AgCl/Ag composites for SERS monitoring and low temperature visible light photocatalysis degradation of pollutant

With the assistance of Polyvinylpyrrolidone (PVP), AgCl/Ag composites were fabricated in N, N-Dimethylformamide (DMF) solvent via a photoactivated route. The size of AgCl particles was in the range of 500 nm to 1 μm and the Ag particle's diameter was about 10–20 nm. Different from those core–shell structures reported before, the Ag nanoparticles were dispersed uniformly both on the surface and in the body of AgCl particles. The generation of such kind of composites was resulted from the reducing ability of DMF and light irradiation during the formation of AgCl particles. The as-obtained AgCl/Ag composites presented great activity for both surface-enhanced Raman scattering (SERS) detection and visible light photocatalytic degradation of organic dyes. Additionally, the AgCl/Ag composites could maintain high photocatalytic activity even though the ambient temperature was as low as 15 °C and recycle photocatalysis experiments indicated that the photocatalyst exhibited higher stability. Such kind of AgCl/Ag composites holds great potential for environmental monitoring devices and pollutant treatments.     

Photocatalytic oxidation of organic dyes with visible-light-driven codoped TiO2 photocatalysts

A novel copper (II) and zinc (II) codoped TiO₂ photocatalyst was synthesized by a modified sol-gel method using titanium (IV) isopropoxide, Zn(NO₃)₂ · 6H₂O and copper(Il) nitrate as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and photo-luminescence spectra (PL). The XRD results showed undoped and Zn, Cu-codoped TiO₂ nanoparticles mainly including anatase phase and a tiny amount of Zn- and Cu-oxides exist in the mixed system, which is attributed to the decomposition of copper and zinc nitrates in the TiO₂ gel to form CuO and ZnO and randomly dispersed on the TiO₂ surface. On the basis of the optical characterization results, we found that the codoping of copper (II) and zinc (II) resulted a red shift of adsorption and lower recombination probability between electrons and holes, which were the reasons for high photocatalytic activity of Zn, Cu-codoped TiO₂ nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of samples was tested for degradation of methyl orange (MO) in solutions. The results indicated that the visible-light driven capability of the codoped catalyst were much higher than that of the pure TiO₂ catalyst under visible irradiation. Because of the synergetic effect of copper (II) and zinc (II) element, the Zn, Cu-codoped TiO₂ catalyst will show higher quantum yield and enhance absorption of visible light. In the end, a key mechanism was proposed in order to account for the enhanced activity.     

Properties of Ag/AgCl electrodes fabricated with IC-compatible technologies

The purpose of this work is to fabricate and characterize Ag/AgCl electrodes made on a silicon chip at the wafer level with integrated circuit-compatible fabrication techniques. Such electrodes are useful as reference electrodes in several kinds of chemical sensors. Two types of electrode were investigated. The first type uses an evaporated AgCl layer that is patterned with lift-off photolithography. The second type is formed by exposing a selected part of the silver substrate to a KCrO₃Cl solution. Both types of electrode give the thermodynamically expected potential response to variations of Cl⁻ ion concentration. The potential generated by the KCrO₃Cl-formed electrodes was more stable, however. Auger electron spectroscopy depth profiles indicate that immersion in a KCrO₃Cl solution produces a thin layer of AgCl on top of a layer of AgO. The low electronic resistance of AgO then reduces the measured series resistance of the KCrO₃Cl-formed electrodes. Impedance plane plots and the impedance as a function of frequency were measured for both types of electrode, and the impedance of the evaporated AgCl electrodes was indeed considerably higher. The impedance measurements could be successfully modelled by assuming a Randles equivalent circuit for the AgCl/electrolyte interface. For the KCrO₃Cl-formed electrodes, the impedance was modified by the porosity these electrodes manifested.     

Ultrasonic assisted synthesis of nanocrystalline cellulose as support and reducing agent for Ag nanoparticles: green synthesis and novel effective nanocatalyst for degradation of organic dyes

In this study, nanocrystalline cellulose (NCC) prepared from microcrystalline cellulose using high‐intensity ultrasonication as mechanical method without any chemical treatment. The obtained NCC with around 30–50 nm diameters, utilized as support, reducing and stabilizing agent for in‐situ green and eco‐friendly synthesis of silver nanoparticles (Ag NPs). The catalytic activity of composite was examined for degradation of environmental pollutants. The structure of as‐synthesized composite (Ag@NCC) was characterized by ultraviolet–visible spectroscopy (UV–vis), field emission scanning electron microscopy (FE‐SEM); Transmission electron microscopy (TEM); Energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). The results of the catalytic reaction experiments showed that spherically shaped silver nanoparticles of around 20 nm distributed on the surface of nanocellulose demonstrated high catalytic efficiency towards the removal of methyl orange (MO) and 4‐nitrophenol (4‐NP).     

Fabrication of dual Z-scheme photocatalyst via coupling of BiOBr/Ag/AgCl heterojunction with P and S co-doped g-C3N4 for efficient phenol degradation

Advances in noble metal mediated Z-scheme photocatalytic system have ushered in a climax on environmental remediation. Herein, graphitic carbon nitride (GCN) and phosphorus sulphur co-doped graphitic carbon nitride (PSCN) were synthesized via calcination process. GCN, PSCN and Z-scheme visible light driven (VLD) ternary BiOBr/PSCN/Ag/AgCl nanophotocatalyst were characterized by X-ray diffraction pattern (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–visible diffuse reflectance spectra (UV–vis DRS). BiOBr/PSCN/Ag/AgCl nanocomposite exhibited superior visible light driven photocatalytic ability as compared to pristine PSCN, AgCl and BiOBr towards degradation of phenol. The results explicated promising photocatalytic activity along with space separation of photocarriers caused via formation of BiOBr/PSCN/Ag/AgCl Z-scheme heterojunction. The visible light absorption efficacy of BiOBr/PSCN/Ag/AgCl photocatalyst was confirmed by photoluminescence (PL) spectra. Finally, recycling experiments were explored for the mechanistic detailing of phenol photodegradation employing BiOBr/PSCN/Ag/AgCl photocatalyst. After seven successive cycles photodegradation efficacy of photocatalyst was reduced to 90% from 98%. Proposed mechanism of BiOBr/PSCN/Ag/AgCl nanophotocatalyst for degradation of phenol was discussed. OH and O₂⁻ radicals were main reactive species responsible for photocatalytic phenol degradation.     

The fabrication and performance of an Ag/AgCl reference electrode in human serum

A simple set of electric circuits was used to assemble a pulse generator. With pulse potentials and under galvanostatical control, a clean silver wire was anodized electrochemically for 0.2–0.5 min in 1.0 mol l⁻¹ HCl with a pulse current density of 20 mA cm⁻², and the pulse wave parameters of t_a/t_c = 1 and a cycle of 4 s forming an Ag/AgCl reference electrode. Even though the AgCl layer was consumed during the working period when the Ag/AgCl electrode was used as a cathode, the AgCl layer could be in situ recovered electrochemically in serum used when a reversed potential was applied to the electrode system immediately after the measuring program was finished. The current response curve of the anode indicated that an AgCl layer in high density was basically accomplished during the first 6 pulse cycles in human serum. In order to keep a stable and uniform AgCl layer on the reference electrode after each measuring cycle, the ratio of the recovery time (t_r) to the working time (t_w) was measured and the smallest value was obtained at 0.03. The open-circuit potential of the Ag/AgCl electrode with respect to a SCE in 0.1 mol l⁻¹ KCl was monitored over a period of 14 days and the mean value was 40.09 mV vs SCE with a standard deviation of 2.55 mV. The potential of the Ag/AgCl reference electrode did remain constant when the measurements were repeated more than 600 times in undiluted human serum with a standard deviation of 1.89 mV. This study indicated that the Ag/AgCl reference electrode could been rapidly fabricated with a pulse potential and could be used as a reference electrode with long-term stable properties in human serum samples.     

Photocatalytic properties of PbMoO4 synthesized by co-precipitation method: organic dyes degradation under UV irradiation

PbMoO₄ molybdate with scheelite structure was synthesized by a simple co-precipitation method. The material was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and adsorption?Cdesorption N₂ isotherms (BET). The photocatalytic activity of PbMoO₄ molybdate was evaluated with the degradation reactions of rhodamine B (rhB), indigo carmine (IC), orange G (OG), and methyl orange (MO) under UV irradiation. In order to elucidate aspects of the degradation mechanism of the organic dyes, some experimental variables were modified such as pH and O₂ level in solution. The total organic carbon (TOC) analysis of samples irradiated revealed that mineralization of organic dyes by the action of PbMoO₄ was feasible in rhB (60%), IC (80%), and OG (65%) after 96?h of irradiation. For the same time of irradiation, a recalcitrant behavior to the mineralization was observed in MO reaching only a 10% of mineralization degree.