The effect of nanoparticle growth on rheological properties of silica and silicate dispersions

CdS and ZnS nanoparticles were prepared in the solid–liquid interfacial adsorption layer as a nanophase reactor. The substrates were hydrophilic and hydrophobic aerosils and hydrophilic layer silicates dispersed in ethanol–cyclohexane mixtures. The growth of particles at various surface concentration of precursor ions was monitored by absorption spectroscopy, band-gap-energy measurements and particle diameter measurements. Also, the rheological properties of nanoparticle–support composites in organic and aqueous dispersions were measured. The energy of separation between the nanoparticles depended on the particle diameter. The intercalation of nanoparticles in the layered silicates yielded a nanostructured two-phase system. The presence of semiconductive subcolloids was proven by transmission electron microscopy measurements, which offer an excellent possibility for the determination of the particle size distribution. Received: 20 July 1999/Accepted in revised form: 22 September 1999     

Structure and spectral-optical characteristics of Se,Se/CdS,and Se/Cd<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>S nanoparticles,stabilized in polymer-containing media

A method was proposed for the production of colloidal nanoparticles of selenium stabilized by polymers and surfactants, and their structural and optical characteristics were studied. It was shown that during the deposition of CdS and Cd_0.5Zn_0.5S on the surface of the Se nanoparticles followed by dissolution of the selenium with sodium sulfite it is possible to obtain network “nanoframeworks” with size 30–50 nm, formed by CdS or Cd_0.5Zn_0.5S particles measuring 3–5 nm. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 24–29, January–February, 2007.     

Construction of inorganic nanoparticles by micro-nano-porous structure of cellulose matrix

In our previous work, the CdS nanoparticles/cellulose films exhibited significantly high photocatalytic H₂ production efficiency under visible light irradiation than the ordinary CdS photocatalyst. In present paper, the CdS nanoparticles were synthesized in situ in pores of the regenerated cellulose substrate and the porous structure of cellulose, formation of the CdS nanoparticles and interactions between CdS and cellulose matrix in the composite films were investigated deeply. The experimental results indicated that the micro-nano-porous structure of the cellulose matrix could be used easily to create inorganic nanoparticles, which supplied not only cavities for the formation of nanoparticles, but also a shell (semi-stiff cellulose molecules support the pore wall) to protect their nano-structure. When the cellulose films with porous structure at wet state were immersed into inorganic ions solution, the ions interacted immediately with the –OH groups of cellulose, and then transformed into inorganic composite via another treatment, finally inorganic nanoparticles formed during the dry. The pore size of the cellulose matrix decreased from 180 nm (at wet state) to about 18 nm (at dry state), leading to the formation of nanoparticles. The results revealed that the CdS nanoparticles with a mean particle diameter about 6 nm were dispersed well, and were immobilized tightly in the cellulose matrix, resulting in a portable photocatalyst with high efficiency for photocatalytic for H₂ evolution. This is simple and “green” pathway to prepare the organic–inorganic hybrid materials.     

Studies on optical absorption and structural properties of Fe doped CdS quantum dots

Fe doped CdS quantum dots have been prepared using simple precursors by chemical precipitation technique. Fe doped CdS quantum dots have been synthesized by mixing cadmium nitrate, sodium sulfide and adding Fe under suitable conditions. X-ray diffraction analysis reveals that undoped and Fe doped CdS crystallizes in hexagonal structure. The lattice constants of Fe doped CdS nanoparticles decreased slightly with incorporation of Fe and no secondary phase was observed. The average grain size of the nanoparticles is found to lie in the range of 2.8–4.2 nm. HRTEM results show that undoped and 3.75% Fe doped CdS nanoparticles exhibit a uniform size distribution and average size of the nanoparticles is about 2–3 nm. Raman spectra show that 1LO and 2LO peaks of the Fe doped CdS samples are slightly red shifted compared with those of undoped CdS. Optical absorption spectra of Fe doped CdS nanoparticles exhibited red shift.     

Simple and low temperature preparation and characterization of CdS nanoparticles as a highly efficient photocatalyst in presence of a low-cost ionic liquid

A simple and low temperature method is proposed for preparation of CdS nanoparticles in presence of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM] [EtSO₄], a room-temperature ionic liquid (RTIL). The powder X-ray diffraction (XRD) studies display that the products are excellently crystallized in the form of cubic structure and size of the nanparticles prepared in presence of the RTIL is smaller than that prepared in water. Energy dispersive X-ray spectroscopy (EDX) investigations reveal that the products are very pure and nearly stoichiometric. The results obtained by scanning electron microscopy (SEM) demonstrate that the CdS nanoparticles prepared in presence of the RTIL have lower tendency for aggregation relative to the prepared sample in water. Diffuse reflectance spectra (DRS) of the product prepared in the neat RTIL, shows 1.52 eV blue shift relative to bulk CdS, which can be attributed to quantum confinement effect of the CdS nanoparticles. A possible formation mechanism for CdS nanoparticles in presence of the RTIL is presented. Photocatalytic activity of the CdS nanoparticles towards photodegradation of methylene blue (MB) using UV and visible lights was performed. The results demonstrate that observed firstorder rate constant for photodegradation of MB on CdS nanoparticles prepared in the neat RTIL are about 20 and 6 times greater than the prepared sample in water using visible and UV lights, respectively.     

Electrochemical synthesis of free-standing CdS nanoparticles in ethylene glycol

A novel one-step electrochemical method for the preparation of capping-free cadmium sulfide nanoparticles is described. With gold as the working electrode, capping-free CdS nanoparticles are synthesized very conveniently at 70°C in the ethylene glycol (EG) solution of elementary sulfur, cadmium salt, and supporting electrolyte at −0.1 V. By carefully selecting the reductive potential, elementary sulfur is reduced while the reduction of Cd²⁺ is blocked by the formation of a sulfur monolayer on the gold electrode surface. The produced S²⁻ reacts with cadmium cations in the solution to produce CdS. In this method, magnetic stirring can effectively prevent the deposition of CdS on the electrode surface. XRD analysis indicates that the product is pure cubic-phase CdS. The size and morphology of the particles are studied by TEM. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 9, pp. 1060–1064. The text was submitted by the authors in English.     

Temperature tunability of size in CdS nanoparticles and size dependent photocatalytic degradation of nitroaromatics

Size tunability of thiophenol capped CdS nanoparticles (NPs) has been achieved by controlling the temperatures in situ. Synthesis at 5 degrees C produced stable particles of smallest size having narrow size distribution and high photoluminescence quantum yield. The photoluminescence of thiophenol capped CdS NPs was quenched by the nitroaromatic compounds. The Stern-Volmer constant of dinitrobenzene was about 15-fold higher than nitrobenzene, which indicates that introduction of nitro groups in the benzene ring increases the quenching efficiency. Further, the as-prepared CdS NPs were found to display size dependent photocatalytic activity towards degradation of nitroaromatics. The catalytic efficiency of CdS quantum particles was quintupled with decrease in particle size from 5.8 to 3.8 nm. An empirical equation has been derived to correlate the catalytic efficiency of the nanoparticles with the twin factors operating in the quantum confinement regime: (i) change in surface to volume ratio and (ii) shift in conduction band edge.     

Luminescence of polymer composite materials with cadmium sulfide nanoparticles

The structure and optical characteristics of CdS nanoparticles synthesized in low-density polyethylene were studied. The particles have a hexagonal structure of the greenockite type; the presence of the cubic phase is also possible. The position of the absorption edge slightly depends on the average size of particles because of their polydispersity. It has been shown that the luminescence spectra of nanoparticles are strongly distorted by scattering and self-adsorption in the samples. To correct the spectra, a program for Monte-Carlo simulation of luminescence propagation in the samples was developed. It was shown that the luminescence band at 500–550 nm in the experimental spectra might be spurious because of luminescence absorption in the edge region.     

明胶溶液中笤帚状纳米CdS的合成及其光谱特性研究

以明胶为稳定剂, 制备出CdS纳米棒, 并实现其向笤帚状纳米CdS的形貌转化. 扫描电镜(SEM)图像表明, 生长时间为2 d, 样品为棒状结构, 直径为50～140 nm, 长度为150～710 nm; 生长15 d的CdS微晶为笤帚状, 结节点直径340～620 nm, 长度2.7～8.4 μm. 探讨了其形貌转化的原因. 结合红外吸收(IR)和荧光光谱的测试结果, 提出了可能的离子络合转化和定位生长机理. 合成的CdS微晶具有一定的荧光性质, 并在紫外和荧光光谱上均表现出明显的量子尺寸效应.     

Preparation of colloidal CdSe and CdS/CdSe nanoparticles from sodium selenosulfate in aqueous polymers solutions

Cadmium selenide nanoparticles formation at the interaction between CdCl2 and Na2SeSO3 in aqueous solutions of sodium polyphosphate and gelatin has been studied. Structural and optical properties of CdSe nanoparticles have been characterized. It has been shown that the temperature and the ratio of reagents concentrations are the basic parameters, controlling the size of CdSe nanoparticles. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found and investigated; structural and optical properties of binary CdS/CdSe nanoparticles have been characterized. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles. It has been shown that slow interaction of adsorbed selenosulfate with surface-trapped CdS conduction band electrons is the limiting stage of the photocatalytic reaction.     

Study of the effect of formamide and N,N-dimethylformamide on the synthesis of CdS nanoparticles in a SiO2 matrix by sol-gel method

The influence of formamide (F) and N,N-dimethylformamide (DMF) in drying and firing of CdS nanocrystals in SiO₂ glasses by a sol-gel method has been studied. It has been established that pore size distribution and surface area are different with the use of DMF and that influences the quality of the final product. The presence of CdS semiconductor nanoparticles has been demonstrated by transmission electronic microscopy (TEM), and the quantum confinement effect due to the size of nanoparticles is denoted by a blue shift in the visible absorption spectra. From the results obtained in this paper, it is clear that DMF has an influence on final material microstructure.     

水溶性CdSe/CdS量子点的合成及其与牛血清蛋白的共轭作用

用巯基乙酸(TGA)作为稳定剂，合成了水溶性的CdSe和核壳结构的CdSe/CdS半导体量子点。吸收光谱和荧光光谱研究表明，核壳结构的CdSe/CdS半导体量子点比单一的CdSe量子点具有更优异的发光特性。用TEM、电子衍射(ED)和XPS分别表征了CdSe和CdSe/CdS纳米微粒的结构、形貌及分散性。红外光谱和核磁共振谱证实了巯基乙酸分子中的硫原子和氧原子与纳米微粒表面的金属离子发生了配位作用。在pH值为7.4的条件下，将合成的CdSe和CdSe/CdS量子点直接与牛血清白蛋白(BSA)相互作用。实验发现，两种量子点均对BSA的荧光产生较强的静态猝灭作用；而BSA对两种量子点的荧光则具有显著的荧光增敏作用，存在BSA时CdSe/CdS量子点的荧光增强是不存在BSA时体系荧光强度的3倍。     

Synthesis and characterization of CdS nanoparticles prepared by precipitation in the presence of span 20 as surfactant

Cadmium sulfide nanoparticles with average size of ≈16 nm have been synthesized using chemical precipitation reaction of CdCl₂ and Na₂S in the presence of nonionic surfactant stabilized reverse emulsions. Sorbian monolaurate (Span 20) is used for the stabilization of emulsions. The influence of Span 20 on controlling the size and properties of CdS nanoparticles were studied. The obtained CdS nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Energy-dispersive x-ray (EDX), and X-ray diffraction (XRD). The optical properties of CdS nanoparticles are investigated systematically by UV-visible absorption spectroscopy. The blue shift in the absorption region and increase in the bandgap to the larger value (2.77 eV) are attributed to the nanosize of the obtained particles.     

CdSe/CdS/SiO2复合纳米球的制备及发光性能

采用两相法合成了CdSe/CdS核-壳结构的量子点, 用氨水催化水解正硅酸乙酯制得复合结构的CdSe/CdS/SiO₂发光纳米球. 通过对量子点用量、氨水用量、反应时间及溶剂比例等实验条件的调节, 得到了单分散性较好, 尺寸在23~145 nm的复合发光纳米球. 利用紫外-可见吸收光谱和荧光发射光谱对其发光性能进行了研究, 同时利用透射电镜(TEM)观察复合纳米球的形貌. 结果表明, 复合发光纳米球样品的最高荧光量子产率可达8%.     

Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots

Nanoparticles of CdS were prepared at 303 K by aqueous precipitation method using CdSO4 and (NH4)2S in presence of the stabilizing agent thioglycerol. Adjustment of the thioglycerol (T) to ammonium sulphide (A) ratio (T:A) from 1:25 to 1:3.3 was done during synthesis and nanoparticles of different size were obtained. The prepared colloids were characterized by UV-vis and photoluminescence (PL) spectroscopic studies. Prominent first and second excitonic transitions are observed in the UV-vis spectrum of the colloid prepared with a T:A ratio of 1:3.3. Particle size analysis was done using XRD, high resolution TEM and dynamic light scattering and found to be approximately 3 nm. UV-vis and PL spectral features also agree with this particle size in colloid with T:A of 1:3.3. The band gap of CdS quantum dots has increased from the bulk value 2.4-2.9 eV. PL spectra show quantum size effect and the peak is shifted from 628 to 556 nm when the ratio of T:A was changed from 1:25 to 1:3.3. Doping of CdS with Zn2+ and Cu2+ is found to enhance the PL intensity. PL band shows blue-shift and red-shift on doping with Zn2+ and Cu2+, respectively. UV and PL spectral features of the CdS/Au hybrid nanoparticles obtained by a physical mixing of CdS and Au nanoclusters in various volume ratios is also discussed. Au red-shifts and rapidly quenches the PL of CdS. An additional low energy band approximately 650 nm is observed in the UV visible spectrum of the hybrid nanoparticles.     

巯萘剂表面修饰的CdS纳米微粒的合成及发光特性

用疏萘剂(TN)作为表面修饰剂,在甲醇溶液中合成了CdS/TN纳米微粒,用TEM测得纳米微粒呈球形,其粒径约10nm,吸收光谱和荧光光谱研究表明,[S^2-]/[TN]浓度比、TN和镉离子的浓度对CdS/TN纳米微粒的粒径及发光特性具有显著影响,且随着条件的改变,CdS/TN纳米微粒的发射波长红移100nm,表现出明显的量子尺寸特性.XPS显示所制得表面修饰纳米微粒的核为CdS.     

Photocatalytic formation of porous CdS/ZnO nanospheres and CdS nanotubes

It was found that ZnO nanocrystals have photocatalytic activity in the formation of CdS during the reduction of sulfur in the presence of cadmium acetate. It was shown that mesoporous spheres measuring 150–170 nm and consisting of CdS/ZnO particles measuring 5–8 nm are formed during the irradiation of ZnO particles measuring 5.5 nm. During the photodeposition of CdS by the action of light on nanorods produced by ultrasonic treatment of microcrystalline zinc oxide nanotubes of CdS 0.5–0.8 μm in length and 15–110 nm in internal diameter are formed. A mechanism, in which they appear at the ends of the ZnO nanorods and grow on the surface of the CdS/ZnO heterojunction, is proposed for the formation of the CdS nanotubes. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 215–219, July–August, 2007.     

Spectral characteristics of CdS quantum dots and their associates with dye molecules dispersed in gelatin

A sol–gel method for the production of open quantum dots of CdS measuring 2-5 nm and their associates with dye molecules [methylene blue and the pyridinium salt of 3,3′-di(γ-sulfopropyl)-9-ethyl-4,5,4′,5′-dibenzothiacarbocyaninebetaine] dispersed in gelatin is described. Their spectral characteristics are analyzed. Evidence is obtained for the formation of hybrid associates of CdS quantum dots with monomers of the first and J-aggregates of the second dye.     

Size and Spectroscopy of Silicon Nanoparticles Prepared via Reduction of SiCl4

Synthesis of silicon nanoparticles of various sizes from 3 to 9 nm in diameter was accomplished via a low temperature solution route. These nanoparticles are prepared via reduction of SiCl₄ with Na naphthalide in dimethoxyethane and capped with octasiloxane. The resulting nanoparticles were characterized by transmission electron microscopy (TEM), high resolution (HR) TEM, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction, UV–vis, photoluminescence, and their quantum yields were determined. TEM micrographs show that the nanoparticles are well dispersed and SAED and lattice fringes are consistent with diamond structured silicon. X-ray powder diffraction provides no diffraction peaks. UV–vis and photoluminescence show characteristic shifts corresponding to size, consistent with quantum confinement. The smallest sized nanoparticles show the largest quantum yield, consistent with an indirect bandgap nanoparticles.     

Continuous tuning of cadmium sulfide and zinc sulfide nanoparticle size in a water-in-supercritical carbon dioxide microemulsion

The size and size dispersion of cadmium sulfide and zinc sulfide semiconductor nanoparticles can be continuously tuned over a wide range of values by adjusting the density of the fluid phase in water-in-supercritical CO2 microemulsions. The average size of the ZnS nanoparticles decreases linearly from approximately 9.1 to 1.9 nm with increasing fluid density from 0.86 to 0.99 g cm(-3) at a water-to-surfactant ratio (W value) of 10. At a W value of 6, the particle size can be tuned from 7.0 to 1.5 nm in the same density range. In the case of CdS nanocrystals, the size varied from 7.1 to 2.0 nm when the W value was 10 and from 4.0 to 1.3 nm when the W value employed was 6, in the same density range. Monodispersive CdS and ZnS nanoparticles were synthesized by chemical reaction of cadmium or zinc nitrate with sodium sulfide, using two water-in-supercritical CO2 microemulsions as nanoreactors followed by protection with a fluorinated-thiol stabilizer. The stabilizer is introduced at 6 and 16 minutes after the mixing of the two microemulsions where the intensity of the characteristic absorption peak due to the quantum confinement properties of the CdS and ZnS nanoparticles (280 and 360 nm) reaches a maximum, respectively. The supercritical CO2 microemulsion method represents a simple approach to use a density-tunable solvent for synthesizing size-controlled semiconductor nanoparticles over a broad range of values.