Synthesis, structural and photocatalytic studies of Mn-doped CdS nanoparticles

Mn-doped CdS nanoparticles (Cd_1?x Mn _x S; where x = 0.00–0.10) were synthesized by a chemical precipitation method. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope (TEM), and UV–Vis spectrometer. The XRD and TEM measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge upon Mn doping. The direct allowed band gaps of undoped and Mn-doped CdS nanoparticles measured by UV–Vis spectrometer were 2.3 and 2.4 eV at 400 °C, respectively. Photocatalytic activities of CdS and Mn-doped CdS were evaluated by irradiating the solution to ultraviolet light and taking methyl orange (MO) as organic dye. It was found that 5 mol% Mn-doped CdS bleaches MO much faster than undoped CdS upon its exposure to the ultraviolet light. The experiment demonstrated that the photo-degradation efficiency of 5 mol% Mn-doped CdS was significantly higher than that of undoped CdS.     

Enhanced photocatalytic activity in composites of TiO2 nanotubes and CdS nanoparticles

A new composite consisting of TiO(2) nanotubes and CdS nanoparticles, where CdS particles bind covalently to the titania surface through a bifunctional organic linker, was successfully fabricated; this titania nanotube-based composite shows enhanced photocatalytic activity under visible-light irradiation.     

Chemical effects of size quantization of CdS nanoparticles

The behaviour of photoreaction occurring on the superfine duster interface of semiconductor CdS has been studied. The results indicated that the size quantization effect of semiconductor nanoparticles was obviously reflected not only in their physical properties, but also in the interfacial photocatalysis reactions initiated by superfine nanopartides. This means that the direction and mechanisms in photoreactions of the compounds adsorbed on the surface of nanopartides could vary with the alteration of particle size because the redox potential values of semiconductor particles could be changed with the variation of particle size. Doubtlessly, this effect could play an important role in controlling the interfacial reaction mechanisms and raising the selectivity to photoreaction paths.     

Preparation,morphology, size quantization effect and photocatalytic properties of CdS Q-nanocrystals

Intercommunity of lots of molecules and perturbation of few molecules have been shown in bulk materials because the intermolecular force is very much smaller than that of intramolecules. So, macroscopic solid theories have been applied to investigating their properties. On the other hand, microscopic quantum mechanical theory (or molecular orbital theory) has enabled the study of single molecule. However, it becomes much more complicated to the study on the small-parti- cle species representin…     

Photoinduced variations in the size of nanoparticles of CdS in colloidal solutions

The possibility of decreasing the size of colloidal nanoparticles of CdS in the oxidative photocorrosion reaction in the presence of methylviologen and of increasing their size during photocatalytic reduction of sulfur in ethanol in the presence of cadmium acetate. A dependence of the quantum yield of the latter reaction on the initial size of CdS nanoparticles was observed, which was interpreted as a result of quantum size effects. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 170–175, May–June, 2007.     

Parameters affecting carbofuran photocatalytic degradation in water using ZnO nanoparticles

Carbofuran photodegradation in water using zinc oxide nanoparticles as a catalyst was examined as well as some parameters influencing its percentage degradation rate such as zinc oxide load, initial concentration of carbofuran, the temperature of the reaction, the initial pH of the solution, and doping of zinc oxide nanoparticles with 5% (w:w) silver. Zinc oxide and Ag-doped zinc oxide nanoparticles were produced using solvothermal and photoreduction methods, respectively, and silver doping effects on the structural, optical, and photocatalytic properties of zinc oxide nanoparticles were investigated using XRD, UV-VIS spectrophotometer, TEM, SEM, SEM/EDX, and FTIR. The average diameter of the synthesized samples was 26.6, 30.55 nm for undoped zinc oxide and Ag-doped zinc oxide, respectively. Zinc oxide doping with silver did not change the shape of the zinc oxide crystal, but decreased the reflection in the visible region, as well as the energy of the bandgap, and increased the zinc oxide photocatalytic activity.     

Immobilization of CdS nanoparticles formed in reverse micelles onto aluminosilicate supports and their photocatalytic properties

CdS nanoparticles, prepared in reverse micellar system, were immobilized onto thiol-modified aluminosilicate particles (ASSH) by a simple operation: addition of ASSH in the micellar solution and mild stirring. The resulting CdS nanoparticles-aluminosilicate composites (ASCdS) were used as photocatalysts for H2 generation from 2-propanol aqueous solution. The chemical properties of the aluminosilicate, such as affinity for water and other reactants, were found to affect the photocatalytic property of the CdS nanoparticles immobilized. Zeolite particles, having affinity for water and 2-propanol, gave a good ASCdS photocatalyst with respect to H2 generation.     

Homogeneously distributed CdS nanoparticles in nafion membranes: preparation, characterization, and photocatalytic properties

Stable crystalline CdS nanoparticles were synthesized in Nafion ionomer membranes by using thioacetamide (TAA) as a nonionic precursor. Unlike the ionic precursors such as Na(2)S, TAA could diffuse into the cationic-exchangeable ionomer membranes much more uniformly. This led to the formation of homogeneously distributed CdS nanoparticles in the Nafion membranes, which was confirmed by elemental mapping with energy-dispersive X-ray (EDAX) analysis. Results from the characterizations on the physical properties, the chemical stability, and the photocatalytic properties of these CdS nanoparticles embedded in Nafion membranes are presented and discussed. The parallel data from the CdS nanoparticles in Nafion membranes prepared from the ionic Na(2)S precursor are also shown for comparison.     

Size dependent interaction of biofunctionalized CdS nanoparticles with tyrosine at different pH

Enhancement of fluorescence of CdS nanoparticles by tyrosine at pH 10 in contrast to Stern-Volmer quenching at pH 7 was observed and both the effects were found to depend on the size of the nanoparticles.     

一步温和水热法制备具有改善光催化活性和稳定性的碳包覆CdS纳米粒子

首次报道在130oC低温条件下,以乙酸镉和葡萄糖分别作为镉源和碳源,硫脲同时充当硫源和葡萄糖水热碳化的催化剂,通过一步水热碳化法制备了碳包覆的CdS (CdS@C)纳米材料。与相同条件下制备的纯CdS相比,合成的CdS@C粒子具有更小的粒子尺寸、良好的分散性以及更均匀的粒子分布。而且,葡萄糖在水热碳化过程中能够促使CdS优先形成立方晶相。此外,粒子表面的碳物种能拓宽CdS的可见光吸收范围,稍微降低它的带隙能,减缓CdS的光生电子-空穴对的复合和光腐蚀。因此,它能改善CdS在可见光辐射下催化氧化降解甲基橙的活性和稳定性。     

Core-shell structure CdS/TiO2 for enhanced visible-light-driven photocatalytic organic pollutants degradation

CdS modified mesoporous titania core-shell spheres (CdS/CS-TiO₂) with enhanced visible-light activity were synthesized by an in situ method. This method included two steps: planting CdO into the framework of anatase TiO₂ core-shell spheres and then converting it to CdS by ion-exchange. The physicochemical properties of the obtained samples were investigated by X-ray diffraction, scanning electron microscopy, transmission electronic micrograph, UV–vis diffuse reflectance spectra and nitrogen sorption. The in situ strategy resulted in CdS quantum dots highly dispersed in CS-TiO₂ without destroying the mesoporous core-shell structure. Compared with CS-TiO₂, the as-synthesized samples exhibited stronger visible-light absorption capability and greatly enhanced photocatalytic activity toward the degradation of Rhodamine B and 4-chlorophenol aqueous solution under visible light irradiation (λ > 420 nm).     

Biosynthesis of silver nanoparticles and their role in photocatalytic degradation of methylene blue dye

Research on Chemical Intermediates - Nowadays, synthesis of nanoparticles, particularly silver nanoparticles (Ag-NPs), has become a research priority due to their wide application in medicine and...     

Facile synthesis of ZnO nanoparticles for the photocatalytic degradation of methylene blue

Journal of Sol-Gel Science and Technology - ZnO nanoparticle photocatalysts with a grain size range of 20–100?nm were prepared via a simple sol–gel method and characterized by...     

Universal relation for size dependent thermodynamic properties of metallic nanoparticles

The previous model on surface free energy has been extended to calculate size dependent thermodynamic properties (i.e., melting temperature, melting enthalpy, melting entropy, evaporation temperature, Curie temperature, Debye temperature and specific heat capacity) of nanoparticles. According to the quantitative calculation of size effects on the calculated thermodynamic properties, it is found that most thermodynamic properties of nanoparticles vary linearly with 1/D as a first approximation. In other words, the size dependent thermodynamic properties P(n) have the form of P(n) = P(b)(1 -K/D), in which P(b) is the corresponding bulk value and K is the material constant. This may be regarded as a scaling law for most of the size dependent thermodynamic properties for different materials. The present predictions are consistent literature values.     

Temperature dependent spectral properties of type-I and quasi type-II CdSe/CdS dot-in-rod nanocrystals

We investigated systematically the temperature dependence of the spectral properties such as the band gap, bandwidth and fluorescence intensity of CdSe/CdS dot-in-rod nanocrystals. These asymmetry nanoparticles were synthesized by seeded growth techniques with band alignment of the type-I and quasi type-II with initial core sizes of 3.3 and 2.3 nm, respectively. With increasing temperature the band gap decreases and bandwidth increases, largely due to exciton-phonon scattering. Anomalous variations of the band gap and bandwidth were observed at 200-240 K, and the variations are attributed to the anisotropic strain in the CdSe/CdS interface due to temperature dependent lattice mismatch. The integrated intensity of fluorescence shows two variation regimes. In the low temperature regime, the intensity remained roughly constant due to the temperature dependent carrier mobility and trapping by the defect states in the CdS shell. However, in the higher temperature regime, the intensity decreased quickly due to thermal/phonon assisted escape from the CdSe dot. The barrier depths are estimated to be about 557 and 285 meV for type-I and quasi type-II samples, respectively.     

掺氮二氧化钛可见光照射降解微囊藻毒素-LR

采用溶胶凝胶法制备了N掺杂TiO2(N-TiO2)纳米粉体光催化剂,利用X射线光电子能谱(XPS)、X射线衍射(XRD)、紫外可见反射光谱及透射电镜(TEM)分析测定,对光催化剂N/TiO2进行了结构表征.发现N掺杂TiO2相对纯TiO2禁带宽度变窄,可见光区有明显吸收.在可见光照射下,利用纳米N/TiO2作为光催化剂降解微囊藻毒素(Microcystin-LR,MC-LR),通过高效液相色谱仪(HPLC)跟踪检测降解过程MC-LR浓度变化,液质联用仪(LC-MS)检测MC-LR降解中间产物变化.利用电子自旋共振法(ESR)及过氧化物酶催化氧化方法跟踪定性定量测定光催化过程中氧化物种的种类变化.采用总有机碳(TOC)测定仪测定了MC-LR光催化深度氧化矿化效果.结果表明,可见光(λ420nm)照射可有效激发光催化剂N-TiO2活化分子氧降解MC-LR,在反应条件下,光催化反应14h,MC-LR降解率达到100%,20h矿化率达到59%.其光催化反应体系中氧化物种主要为羟基自由基(·OH).质谱检测到13种降解产物,主要反应机理为光催化反应产生·OH进攻MC-LR结构四个易氧化部位,以及一些氨基酸之间的肽键的水解.     

Preparation of aqueous CdS colloids in the presence of cadmium complexonates: effect of complexonates on the size of CdS nanoparticles

The results of a systematic study of the preparation of CdS colloids in aqueous solutions containing different Cd²⁺ complexonates are presented. The effects of the ratio of the reagents and the nature and concentration of various stabilizing surfactants and Cd²⁺ complexonates, including those of some sulfur-containing compounds, on the size of the colloidal particles have been studied. Thermodynamic calculation of the expected equilibrium size of the colloidal particles as a function of the solvent composition, taking into account the increase in the solubility of the CdS phase as the particle size decreases, has been performed. Comparison of the calculated results with the experimental data shows that the size of colloidal particles is determined to a great extent by kinetic factors of their growth rather than by thermodynamic factors. It has been established that when the size of colloidal particles is less than a critical value, their dissolution by adding strong compexing agents to the system does not result in a change in the observed mean-volume size of the particles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1739–1746, September, 1995.The authors are grateful to A. L. Chuvilin (G. K. Boreskov Institute of Catalysis, SB of the RAS) for help in preparing the electron photomicrographs.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4816).     

Preparation and characterization of Pd modified CeO2 nanoparticles for photocatalytic degradation of dye

The aim of this work was to investigate the structural and optical properties of bare cerium dioxide (CeO₂) and Pd-doped CeO₂ (0.5, 1.0, 1.5 and 2.0 wt%) photocatalysts prepared by a combination of homogeneous precipitation and the impregnation method. X–ray diffraction analysis indicated that all samples were composed of the cubic fluorite phase of CeO₂. Scanning electron micrographs revealed that all samples provided mostly spherical morphology with high agglomeration and estimated particle sizes ranging from 10 to 20 nm in diameter. The XPS core-level spectra of Pd species after incorporating 2.0 wt% Pd–doped CeO₂ showed double peaks with binding energies of Pd3d_5/2 and Pd3d_3/2 corresponding to the Pd²⁺ oxidation state. The results from diffuse reflectance UV–visible spectroscopy showed that doping with Pd increased the absorbance onset of CeO₂ to a longer wavelength, while the band gap decreased from 3.0 eV to 2.8 eV with 2.0% Pd doping concentration. This was likely due to the creation of impurity levels of Pd²⁺ inside the conduction and valence bands of CeO₂. The photoluminescence spectra (PL) indicated that the emission peak intensity of CeO₂ decreased in the presence of Pd²⁺ dopant in CeO₂. This was associated with a decrease in the electron–hole recombination rate for electronically-excited. Photocatalytic activity for methyl orange dye degradation under visible light irradiation of 1.0 wt% Pd–doped CeO₂ was determined as the optimal doping level with photocatalytic activity 5 times higher than that of bare CeO₂ photocatalyst.