Photochemical synthesis of ZnO/Ag nanocomposites

Composite ZnO/Ag nanoparticles have been formed via the photocatalytic reduction of silver nitrate over the ZnO nanocrystals, their optical, electrophysical and photochemical properties have been investigated. Mie theory has been applied to analyze the structure of the absorption spectra of ZnO/Ag nanocomposite. The irradiation effects upon the optical properties of ZnO/Ag nanostructure have been investigated. It has been found that the irradiation of ZnO/Ag nanoparticles results in electrons accumulation by both the semiconductor and the metallic components of the nanocomposite. It has been found that silver nitrate can be photochemically deposited onto the surface of ZnO nanoparticles under the illumination with the visible light in the presence of the sensitizer – methylene blue. Kinetics of the sensitized Ag(I) photoredution has been studied. It has been concluded that the key stage of this process is the electron injection from singlet-excited methylene blue molecule into ZnO nanoparticle.     

太阳能光催化制氢的科学机遇和挑战

面对人类对能源的需求持续增长,以及化石能源的日益枯竭和其带来的环境污染问题,太阳能成为主要的可再生清洁能源的来源。讨论了利用太阳能催化生氢或消耗二氧化碳,探索在半导体基光催化剂表面的光催化反应和光化学反应。半导体材料被认为是最有前景的光催化剂,其材料合成是发展先进催化剂的核心。减少电荷重新复合,是提高太阳能转化为化学能的关键,关系到太阳能的转换效率。研究结果发现了提高光催化制氢的关键因素,通过Pt-PdS/CdS催化体系使其量子效率提高到93%,提供了发展高效催化剂体系的方法。     

双金属/TiO2纳米管复合结构中增强的光电流

将传统半导体材料与金属微纳结构相结合,利用其表面等离激元共振效应,可有效地增强复合结构的光电转换效率,使其广泛地被用于光电化学和光电探测等领域.本文以氧化铝纳米管为模板,采用原子层沉积技术制备出高有序的TiO2纳米管,并通过电子束热蒸发技术在大孔径的纳米管薄膜中分别负载金、铝和双金属金/铝纳米颗粒,形成金属纳米颗粒/TiO2纳米管复合结构.研究结果表明,相对于纯TiO2纳米管,Au/TiO2复合纳米管在568 nm的可见光照射下,其光电流密度约有400%的提高;在365 nm紫外光照射下,Al/TiO2复合纳米管的光电流提高约50%;同时负载双金属Au和Al纳米颗粒的TiO2纳米管在整个紫外-可见光区域光电流均显著增强.     

Synthesis and structural characterisation of CdS nanoparticles prepared in a four-components "water-in-oil" microemulsion

Nanostructured semiconductor particles are currently under intense investigation because of their enhanced photoreactivity and photocatalytic properties due to the quantum-size effect and the dependence of the photophysical and photochemical properties on their size as it approaches the exciton diameter. This increasing interest has led to the development of several synthetic procedures to prepare and stabilise uniform crystallites. In this paper, we report a novel synthetic pathway to obtain cadmium sulphide (CdS) nanoparticles in a quaternary "water-in-oil" microemulsion formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB), pentanol, n-hexane and water. The synthesis of CdS in this system is achieved by mixing two microemulsions containing Cd(NO3)2 and Na2S, respectively. The nanocrystals have been characterised by using UV--visible spectroscopy and Transmission Electron Microscopy to investigate the influence of various parameters of the particles' formation and stability in solution. Capping of nanoparticles with suitable organic molecules has been performed in order to increase their stability and afford solubility in a wide range of solvents.     

Photocatalytic disinfection of water with Ag–TiO2 nanocrystalline composite

A method of solution impregnation and calcination has been demonstrated for synthesizing nanoparticles of Ag–TiO₂ composite photocatalysts for use in the disinfection of water. Only a small proportion of the TiO₂ surface is covered by nano-islands of Ag corresponding to a loading of 4 wt.% of Ag; thus, most of the TiO₂ surface is available for photocatalytic function. Although the primary particles of both Ag and TiO₂ are in the 10- to 20-nm range, microscopic studies indicate that the primary particles of Ag are deposited on nano-agglomerates of 30- to 70-nm-sized TiO₂. It is seen that the relatively small loading of Ag has not caused any UV–vis spectral shift but has enhanced the rate of photocatalytic antibacterial action of TiO₂, presumably by electron trapping.     

Microstructure and photocatalytic activity of titanium dioxide nanoparticles

Titanium dioxide nanoparticles with an average diameter of about 10 nm are fabricated using a sintering method. The degradation of methyl orange indicates that the photocatalytic efficiency is greatly enhanced, which is measured to be 62.81%. Transmission electron microscopy is used to investigate the microstructure of TiO 2 nanoparticles in order to correlate their photocatalytic properties. High-resolution transmission electron microscopy examinations show that all the nanoparticles belong to the anatase phase, and pure edge dislocations exist in some nanoparticles. The great enhancement of photocatalytic efficiency is attributed to two factors, the quantum size effect and the surface defects in the nanoparticles.     

Development of photocatalyst coated fluoropolymer based microreactor using ultrasound for water remediation

Formation of thin layers of photocatalyst in photo-microreactor is a challenging work considering the properties of both catalyst and the microchannel material. The deposition of semiconductor materials on fluoropolymer based microcapillary requires the use of economical methods which are also less energy dependent. The current work introduces a new method for depositing nanoparticles of TiO₂ on the inner walls of a hexafluoropropylene tetrafluoroethylene microtube under mild conditions using ultrasound technique. During the ultrasonication process, changes in the polymer surface were observed and characterized using Attenuated Total Reflectance spectroscopy, Scanning Electron Microscopy and Confocal Microscopy. The rough patches form sites for catalyst deposition resulting in the formation of thin layer of TiO₂ nanoparticles in the inner walls of the microtube. The photocatalytic activity of the TiO₂ coated fluoropolymer based microcapillary was evaluated for removal of phenol present in water.     

Photocatalytic degradation of ciprofloxacin drug in water using ZnO nanoparticles

We report the synthesis of nanostructure ZnO semiconductor with ～2.1 nm diameter using a chemical precipitation method. The resulting nanoparticles were characterized by X-ray diffraction analysis (XRD), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties were investigated by UV–vis and fluorescence techniques. The absorption spectra exhibit a sharp absorption edge at ～334 nm corresponding to band gap of ～3.7 eV. The fluorescence spectra displayed a near-band-edge ultraviolet excitonic emission at ～410 nm and a green emission peak at ～525 nm, due to a transition of a photo-generated electron from the conduction band to a deeply trapped hole. The photocatalytic activity of the prepared ZnO nanoparticles has been investigated for the degradation of ciprofloxacin drug under UV light irradiation in aqueous solutions of different pH values. The results showed that the photocatalytic degradation process is effective at pH 7 and 10, but it is rather slow at pH 4. Higher degradation efficiency (～50%) of the drug was observed at pH 10 after 60 min. Photodegradation of the drug follows a pseudo-first-order kinetics.     

A simple and versatile mini-arc plasma source for nanocrystal synthesis

Nanocrystals in the lower-nanometer-size range are attracting growing interest due to their unique properties. A simple and versatile atmospheric direct current mini-arc plasma source has been developed to produce nanoparticles as small as a few nanometers. The nanoparticles are formed by direct vaporization of solid precursors followed by a rapid quenching. Both semiconductor tin oxide and metallic silver nanoparticles have been produced at rates of 1–10 mg/h using the mini-arc source. Transmission electron microscopy and X-ray diffraction analyses indicate that most nanoparticles as produced are nonagglomerated and crystalline. Size distributions of nanoparticles measured with an online scanning electrical mobility spectrometer are broader than the self-preserving distribution, suggesting that the nanoparticle growth is coagulation-dominated, and that the particles experience a range of residence times. The electrical charges carried by as-produced aerosol nanoparticles facilitate the manipulation of nanoparticles. The new mini-arc plasma source hence shows promise to accelerate the exploration of nanostructured materials.     

表面结构对SnO2半导体纳米粒子荧光性质的影响

本文利用荧光光谱对ＳｎＯ２纳米粒子水溶胶及其有机溶胶的光学性质进行了研究。发现粒子的表面结构对其光学性质具有极大的影响。水溶胶的荧光发射是由氧空位控制的,其发射强度工;有机溶胶由于表面活性剂的作用,改变粒子的表面结构,得到较强的荧光发射。     

Preparation of MgTi2O5 nanoparticles for sonophotocatalytic degradation of triphenylmethane dyes

MgTi₂O₅ (magnesium dititanate) nanoparticles were prepared by a simple hydrothermal assisted post-annealing method and characterized with various analytical techniques. The catalytic properties (sonocatalytic, photocatalytic and sonophotocatalytic activity) were evaluated using the degradation of triphenylmethane dyes (crystal violet, basic fuchsin, and acid fuchsin). The sonophotocatalytic activity of MgTi₂O₅ nanoparticles towards crystal violet was found to be ~2.9 times higher than the photocatalytic activity and ~20 times higher than that of the sonocatalytic processes. In addition, the sonophotocatalytic efficiency of MgTi₂O₅ nanoparticles was found to be remarkable for the degradation of basic fuchsin (cationic dye) and acid fuchsin (anionic dye). The mechanism of these catalytic activities has been discussed in detail.     

Shallow donors in semiconductor nanoparticles: limit of the effective mass approximation

The spatial distribution of the electronic wave function of a shallow, interstitial Li donor in a ZnO semiconductor nanocrystal has been determined in the regime of quantum confinement by using the nuclear spins as probes. Hyperfine interactions as monitored by electron nuclear double resonance spectroscopy quantitatively reveal the transition from semiconductor to molecular properties upon reduction of the size of the nanoparticles.     

Polymer photodegradation initiated by ZnO nanoparticles

The photodegradation initiated by semiconductor nanoparticles in an acrylic photocurable polymer doped with p-ZnO nanoparticles has been investigated. A mechanism and formula of the photoinduced chemical reaction stimulated by primary photochemical processes of water photolysis on the surface of semiconductor ZnO nanoparticles are proposed. The mass loss in this reaction reaches 12%, which confirms the validity of photodegradation for polymer waste disposal.     

Photocatalytic degradation of methylene blue solution by diphenylanthrazoline compounds

The photocatalytic degradation of methylene blue solution by 8 photocatalytic diphenylanthrazoline compounds was investigated. All diphenylanthrazoline compounds exhibited a good photocatalytic activity towards the methylene blue solution. The removal rate for chemical oxygen demand (COD_Cr) in the methylene blue solution at 12 hours was ~54.1% to 96.3%. 2,8‐Bis(4‐triphenylamino)‐4,6‐diphenyl‐1,9‐anthrazoline ( TM‐2‐d ) was selected for further investigation because of its better photocatalytic activity. To study the optimal reaction conditions for the photocatalytic degradation of dye wastewater, photocatalyst was applied to degrade methylene blue solution. The decolorization rate for simulated dye solutions can exceed 99% in 10 hours, and the COD_Cr removal rate exceeded 91%. These organic semiconductor materials, diphenylanthrazoline compounds, displayed comparative photocatalytic properties to the inorganic semiconductor materials, which can be used in the photocatalytic degradation of organic pollutants.     

Experimental cathodoluminescence studies of exciton transport in gallium nitride

The use of time-of-flight cathodoluminescence measurements in the studies of semiconductor samples partially covered with a light-absorbing mask of special geometry in order to obtain new quantitative information about the properties of materials is shown. The values of the exciton diffusion coefficient are determined from the results obtained in an experimental study of gallium nitride.     

Compare the photocatalytic properties of nanocomposites with tandem n (AgBr)-n (Ag2CO3) and p (AgCl)-n (Ag2CO3) heterojunctions

In this work, Ag₂CO₃ nanoparticles (NPs) (as a n-type semiconductor) incorporated in mordenite zeolite (MOR) by a facile precipitation method. Silver halides, AgCl (as a p-type semiconductor) and AgBr (as a n-type semiconductor), with different weight percentage (20%, 40% and 50%) were coupled into Ag₂CO₃-MOR nanocomposite (NC) and producing a series of novel AgCl/Ag₂CO₃ (p-n heterojunction)-MOR and AgBr/Ag₂CO₃ (n-n heterojunction)-MOR NCs. The effects of silver halides on the Ag₂CO₃–MOR catalyst for the photocatalytic degradation of methyl blue (MB) under visible light irradiation have been investigated. The structure, composition and optical properties of NCs were investigated by UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). The prepared AgX/Ag₂CO₃-MOR NCs with the optimal content of AgX (50 wt%) indicated higher photocatalytic activity than that of the Ag₂CO₃-MOR and Ag₂CO₃. The cycle experiments on the heterojuctions NCs indicated that photocatalytic stability of AgBr/Ag₂CO₃-MOR NC was more than AgCl/Ag₂CO₃-MOR NC in all cycles. On the basis of the experimental results, a possible mechanism for the enhanced photocatalytic activity and photoinduced stability of silver compounds was proposed.     

三氧化钨/氧化银复合材料的水热法合成及其光催化降解性能研究

染料污染是水污染中最严重的问题之一,吸引了很多科学家的关注.人们尝试了很多方法去解决该问题,如化学氧化法、物理吸附法、光催化降解法和生物降解法等.与其他几种方法相比,光催化法有着低能耗、环保以及高效等优势.三氧化钨是常见的半导体材料,具有独特的光学性能,近年来受到了广泛的研究.本文以钨酸钠和硫脲为前驱体,通过水热法制备了三氧化钨/氧化银(WO_3/Ag_2O)复合材料,并用光催化降解亚甲基蓝来分析其光催化性能.通过X射线光电子能谱、X射线衍射、透射电子显微镜、扫描电子显微镜、紫外可见吸收光谱等表征手段对样品的形貌、晶格结构和光催化的性能进行表征.氧化银的带宽为1.2 e V,对可见光很敏感,三氧化钨和氧化银的复合使材料在可见光下的光催化活性显著增强,在可见光下对亚甲基蓝染料的光降解率可以达到98%.实验结果表明,复合材料中的三氧化钨纳米棒为六方相,其平均直径约为200 nm,平均长度约为4μm.而复合材料中的氧化银纳米颗粒为六方相,附着在氧化钨纳米棒的表面,平均晶粒尺寸为20 nm.氧化银的存在为复合材料提供了更多的反应活性位点.相较于单一组分,复合材料在可见光下的光吸收度更高,这说明三氧化钨和氧化银的复合改变了材料的能带结构.研究发现,三氧化钨和氧化银之间形成的异质结构是其优良光催化性能的来源.此外,三氧化钨和氧化银复合材料还具有良好的催化稳定性和化学稳定性.本文结果表明,可以通过给宽带隙的半导体材料复合一些带隙合适的金属氧化物以提升其光催化活性.     

Core–Shell Structured Nanocomposites for Photocatalytic Selective Organic Transformations

Core–shell structured nanocomposites, a type of talented functional materials with unique microstructure and properties, have shown great promise as photocatalysts for various applications, including photocatalytic degradation of pollutants, water splitting for hydrogen production, and selective organic transformations. The synthesis and utilization of efficient core–shell nanoarchitectured photocatalysts for selective organic synthesis are at the center of our research efforts and the focus of this minireview. Specifically, semiconductor‐based core–shell nanocomposites, including metal–semiconductor, semiconductor–semiconductor, semiconductor–shell (graphene and SiO₂) as photocatalysts/cocatalysts for selective oxidation of alcohols, reduction of nitro organics and carbon dioxide for synthesis of fine chemicals, and redox‐combined selective synthesis of pipecolinic acid are summarized. It is hoped that this minireview can make a contribution to catalyzing the development of smart core–shell nanostructures in the field of photocatalytic selective organic transformations for solar energy conversion.     

Size and surface effects on the magnetism of magnetite and maghemite nanoparticles

The size effects of magnetite and maghemite nanoparticles on their magnetic properties (magnetic moment, Curie temperature, blocking temperature, etc.) have been investigated. Magnetic separation and centrifugation of an aqueous solution of nanoparticles were used for their separation into fractions; their sizes were measured by atomic force microscopy, dynamic light scattering, and electron microscopy. A change in the size leads to a change in the Curie temperature and magnetic moment per formula unit. Both native nanoparticles and those covered with a bioresorbable layer have been considered. The magnetic properties have been calculated by the Monte Carlo method for the classical Heisenberg model with various bulk and surface magnetic moments.     

Temperature dependence of photoluminescence of semiconductor quantum dots upon indirect excitation in a SiO2 dielectric matrix

The processes of excitation and relaxation of confined excitons in semiconductor quantum dots upon indirect high-energy excitation have been considered. The temperature behavior of photoluminescence of quantum dots in a SiO₂ dielectric matrix has been described using a model accounting for the process of population of quantum-dot triplet states upon excitation transfer through mobile excitons of the matrix. Analytical expressions that take into account the two-stage and three-stage schemes of relaxation transitions have been obtained. The applicability of these expressions for analyzing fluorescence properties of semiconductor quantum dots has been demonstrated using the example of silicon and carbon nanoparticles in the thin-film SiO₂ matrix. It has been shown that the complex character of the temperature dependences of the photoluminescence upon indirect excitation can be an indication of a multistage relaxation of excited states of the matrix and quantum dots. The model concepts developed in this study allow one to predict the form of temperature dependences of the photoluminescence for different schemes of indirect excitation of quantum dots.