Study the Influence of Drying Control Chemical Additives on the Physical and Optical Properties of Nanocrystalline Cadmium Sulfide–Doped Tetraethylorthosilicate Silica Xerogels

The experimental results of the influence of drying control chemical additives (DCCAs)—such as formamide (FA), N-methyl formamide (NMF), N-N-dimethyl formamide (DMF), acetamide (AA), glycerol (GLY), and oxalic acid (OXA)—on the physical and optical properties of nanocrystalline cadmium sulfide (CdS)–doped silica xerogels were reported in this paper. Tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] was used as a precursor for the three-dimensional silica network in which the CdS nanocrystallites were trapped. Silica alcosol was prepared by taking the mixture of ethanolic (EtOH) TEOS, water (H₂O), hydrochloric acid (HCI), and ammonium hydroxide (NH₄OH). Ethanolic cadmium acetate [Cd(CH₃COO)₂ 2H₂O] and thiourea [CS(NH₂)₂] were added to the alcosol for the formation of CdS crystallites. To study the effect of DCCAs on the physical and optical properties of nanocrystalline CdS-doped silica xerogels, the molar ratio of TEOS:EtOH:H₂O:HCl:NH₄OH:Cd(CH₃COO₂)₂ 2H₂O:CS(NH₂)₂ was kept constant at 1:5:7:0.01:0.0027:0.001:0.002, respectively, and the molar ratio of DCCA/TEOS was varied from 0.001 to 1. The addition of DCCAs (e.g., formamide) resulted in decreased gelation time (tg) from 240 to <20 hrs. Transparent CdS-doped alcogels and xerogels were obtained for the DCCA/TEOS molar ratios of <0.5, whereas turbid alcogels and translucent nanocrystalline CdS-doped silica xerogels were obtained for higher DCCA/TEOS molar ratios (>0.5). It has been found that the percentage of volume shrinkage of the samples, when heated at 300°C for 3 hr, was more (>15%) for OXA, GLY, and DMF and the shrinkage was less (<15%) for AA, NMF, and FA. The density of the CdS-doped silica xerogels with DCCAs was less than that without DCCAs. Red shift was observed in the optical absorption spectra of the samples with addition of the DCCAs. An increase in CdS crystallite size in the silica matrix with the incorporation of DCCAs was observed in the X-ray diffraction patterns in the order: OXA < GLY < DMF < AA < NMF < FA. From XRD studies, the structure of the CdS crystallites in the silica matrix was found to be hexagonal wurtzite.     

Effect of pH,Aging, and Drying on the Size of CdS Nanocrystallites,Monolithicity, and Transparency of Nanocrystalline CdS-Doped Silica Xerogels

CdS semiconductor nanocrystals are prepared in SiO₂ matrix xerogels by a sol–gel method using ethanolic tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄], catalyst (HCl or NH₄OH), cadmium acetate [Cd (CH₃COO)₂ 2 H₂O], and thiourea [SC (NH₂)₂] and drying the alcogels at room temperature and heating up to 250°C. The effect of alcosol pH on the CdS crystallite size in silica matrix, color, monolithicity, and transparency of the xerogels is studied by varying the pH from 1 to 10, and maintaining the CdS/SiO₂ molar ratio constant at 0.0025. It was found that the color of samples varied from light yellow to orange and transparency decreased from 85 to 15% with the variation of alcosol pH from 1 to 10, respectively. The cracked sample were found for pH < 3, opaque, powdery samples for the pH > 8, and transparent monolithic yellow-colored samples in the pH range 3–7. The quantum size effect was observed in the optical absorption spectra of the samples. The threshold peak decreased from 520 to 250 nm, energy increased from 2.4 to 4.9 eV, and the CdS crystallite size decreased from 6 to 1 nm with the variation of pH of the alcosol from 10 to 1, respectively. In the case of the effect of aging, a minimum of 5 days aging is required for monolithic samples and the CdS crystallite to increase in size with and remain constant, even when the aging period is increased for 10 days. Monolithic samples were obtained with drying and heating rates of <0.4 wt.% loss/h and 30–50°C/h range and cracked samples with >0.4 wt.% loss/h and >50°C/h drying and heating rates, respectively. The density of the CdS crystallites doped-silica xerogels decreased from 1.57 to 1.30 gm/cm³ with an increase in pH from 1 to 10, respectively. From XRD spectra, the CdS crystallite structure was found to be a hexagonal wurtzite structure. The intensity of the peaks increased and the breadth decreased with the variation of pH of the alcosol from 1 to 10 because of an increase in CdS crystallite size.     

Studies on the effect of organic additives on the monolithicity and optical properties of the rhodamine 6G doped silica xerogels

Rhodamine 6G (R6G) laser dye doped silica xerogels were prepared by sol–gel processing using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] precursor, citric acid (CTA) catalyst and ethanolic R6G in the presence of various organic additives such as formamide (FA), N′methylformamide (N′MF), dimethylformamide (DMF), acetamide (AA), glycerol (GLY), oxalicacid (OXA), ethyleneglycol (EG) and diethyleneglycol (DEG). The organic additive/TEOS molar ratio was varied from 0.001 to 0.1 by keeping the TEOS/EtOH/H₂O/CTA/R6G molar ratio constant at 1:5:7:1.2×10⁻³:9.2×10⁻⁶. It was found from the spectral studies of the additive modified R6G doped silica xerogels that the absorption maxima at 530 nm and emission maxima at 565 nm were increased with the addition of organic additive and with the increase of the additive/TEOS molar ratio. The transparency of the R6G doped silica xerogels was increased with the increase of additive/TEOS molar ratio from 0.001 to 0.1 with OXA, DEG and EG and in the case of DMF, N′MF, FA, AA and GLY, the transparency of the samples increased up to 0.014 of additive/TEOS molar ratio and then decreased for >0.014 of additive/TEOS molar ratio. Monolithic samples were obtained with all the organic additives. The percentage volume shrinkage of the samples was less EG and DEG and more with OXA additives.     

Luminiscent dye Rhodamine 6G doped monolithic and transparent TEOS silica xerogels and spectral properties

Sol–gel process was used for the preparation of Rhodamine 6G (R6G) doped silica xerogels, using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] as the precursor for the silica network. Silica alcosol was prepared by hydrolysis and polycondensation of ethanol (EtOH) diluted TEOS in the presence of citric acid (CTA) catalyst. The ethanolic R6G was added to the alcosol to trap R6G molecules inside the SiO₂ gel network during the gelation of the TEOS alcosol. The effect of CTA/TEOS molar ratio on the gelation time of the R6G doped TEOS alcosol, transparency and monolithicity of the R6G doped silica xerogel was studied by varying the CTA/TEOS molar ratio from 1.2×10⁻⁴ to 180×10⁻⁴ by keeping the molar ratios of TEOS:EtOH:H₂O:R6G constant at 1:5:7:9.2×10⁻⁶, respectively. It was found that the minimum (<70 h) gelation time was observed at higher and lower CTA/TEOS molar ratios of 72×10⁻⁴ where as maximum (>180 h) gelation time was observed for CTA/TEOS molar ratio of 72×10⁻⁴. While opaque and monolithic R6G doped SiO₂ xerogels were obtained for <4.8×10⁻⁴ CTA/TEOS molar ratios, whereas cracked and transparent xerogels were obtained for >120×10⁻⁴ molar ratios of CTA/TEOS. Transparent, homogeneous and monolithic samples were obtained between 4.8×10⁻⁴ and 120×10⁻⁴ of CTA/TEOS molar ratios. Leaching out property was studied by using water, methanol and ethanol solvents for the R6G doped SiO₂ xerogels of 9.2×10⁻⁶ and 12×10⁻⁴ of R6G/TEOS and CTA/TEOS molar ratios, respectively, and found that R6G molecules were trapped in the pores of the SiO₂ network.Bleaching out phenomena of the R6G doped SiO₂ xerogels was studied by focusing the high intensity light on some part of the samples for a period of 1 h and found that the pores were continuous in SiO₂ network. Visible spectra of R6G in water, ethanol, SiO₂ alcosol and xerogel were taken for 1.6×10⁻⁴ M R6G and observed that there were two absorption peaks at 499 and 525 nm in the spectrum of R6G in water due to dimerization of R6G molecules and only one absorption peak at 530 nm in the spectra of ethanol, SiO₂ alcosol and xerogel because of monomerization of R6G molecules. Visible spectra of the R6G doped silica xerogels for varying R6G/TEOS molar ratios from 9.2×10⁻⁸ to 9.2×10⁻⁵ were taken and found the red shift (5–10 nm) with increasing the R6G/TEOS molar ratio from 9.2×10⁻⁸ to 9.2×10⁻⁵. The effect of temperature on these sample was studied by varying the temperature from 50 to 300 °C and found that the R6G doped silica samples were stable up to 200 °C. IR spectra were taken for pure R6G powder and R6G doped silica xerogels of 9.2×10⁻⁸ and 9.2×10⁻⁵ R6G/TEOS molar ratios and found that most of the peaks present in pure R6G powder spectrum were absent in the spectra of trapped R6G SiO₂ xerogels. This shows that, the SiO₂ network hinders the rotational and vibrational transitions of R6G when it is caged in the SiO₂ network. The peaks related to bending motion in R6G molecules were not disturbed by the SiO₂ network     

Luminiscent dye Rhodamine 6G doped monolithic and transparent TEOS silica xerogels and spectral properties

Sol–gel process was used for the preparation of Rhodamine 6G (R6G) doped silica xerogels, using tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄] as the precursor for the silica network. Silica alcosol was prepared by hydrolysis and polycondensation of ethanol (EtOH) diluted TEOS in the presence of citric acid (CTA) catalyst. The ethanolic R6G was added to the alcosol to trap R6G molecules inside the SiO₂ gel network during the gelation of the TEOS alcosol. The effect of CTA/TEOS molar ratio on the gelation time of the R6G doped TEOS alcosol, transparency and monolithicity of the R6G doped silica xerogel was studied by varying the CTA/TEOS molar ratio from 1.2 × 10^-4 to 180 × 10^-4 by keeping the molar ratios of TEOS:EtOH:H₂O:R6G constant at 1:5:7:9.2× 10^-6, respectively. It was found that the minimum (<70 h) gelation time was observed at higher and lower CTA/TEOS molar ratios of 72 × 10^-4 where as maximum (>180 h) gelation time was observed for CTA/TEOS molar ratio of 72 × 10²⁴. While opaque and monolithic R6G doped SiO₂ xerogels were obtained for <4.8 × 10^-4 CTA/TEOS molar ratios, whereas cracked and transparent xerogels were obtained for >120 × 10^-4 molar ratios of CTA/TEOS. Transparent, homogeneous and monolithic samples were obtained between 4.8 × 10^-4 and 120 × 10^-4 of CTA/TEOS molar ratios. Leaching out property was studied by using water, methanol and ethanol solvents for the R6G doped SiO₂ xerogels of 9.2 × 10^-6 and 12 × 10^-4 of R6G/TEOS and CTA/TEOS molar ratios, respectively, and found that R6G molecules were trapped in the pores of the SiO₂ network.

Bleaching out phenomena of the R6G doped SiO₂ xerogels was studied by focusing the high intensity light on some part of the samples for a period of 1 h and found that the pores were continuous in SiO₂ network. Visible spectra of R6G in water, ethanol, SiO₂ alcosol and xerogel were taken for 1.6 × 10^-4 M R6G andobserved that there were two absorption peaks at 499 and 525 nm in the spectrum of R6G in water due to dimerization of R6G molecules and only one absorption peak at 530 nm in the spectra of ethanol, SiO₂ alcosol and xerogel because of monomerization of R6G molecules. Visible spectra of the R6G doped silica xerogels for varying R6G/TEOS molar ratios from 9.2 × 10^-8 to 9.2 × 10^-5 were taken and found the red shift (5–10 nm) with increasing the R6G/TEOS molar ratio from 9.2 × 10²⁸ to 9.2 × 10^-5. The effect of temperature on these sample was studied by varying the temperature from 50 to 300 8C and found that the R6G doped silica samples were stable up to 200 8C. IR spectra were taken for pure R6G powder and R6G doped silica xerogels of 9.2 × 10^-8 and 9.2 × 10^-5 R6G/TEOS molar ratios and found that most of the peaks present in pure R6G powder spectrum were absent in the spectra of trapped R6G SiO₂ xerogels. This shows that, the SiO₂ network hinders the rotational and vibrational transitions of R6G when it is caged in the SiO₂ network. The peaks related to bending motion in R6G molecules were not disturbed by the SiO₂ network     

Ethyl group as matrix modifier and inducer of ordered domains in hybrid xerogels synthesised in acidic media using ethyltriethoxysilane (ETEOS) and tetraethoxysilane (TEOS) as precursors

Hybrid silica xerogels favourably combine the properties of organic and inorganic components in one material; consequently these materials are useful for multiple applications. The versatility and mild synthetic conditions provided by the sol-gel process are ideal for the synthesis of hybrid materials. The specific aims of this study were to synthesise hybrid xerogels in acidic media using tetraethoxysilane (TEOS) and ethyltriethoxysilane (ETEOS) as silica precursors, and to assess the role of the ethyl group as a matrix modifier and inducer of ordered domains in xerogels. All xerogels were synthesised at pH 4.5, at 60 °C, with 1:4.75:5.5 TEOS:EtOH:H₂O molar ratio. Gelation time exponentially increased with the ETEOS molar ratio. Incorporation of the ethyl groups into the structure of xerogels reduced cross-linking, increased the average siloxane bond length, and promoted the formation of ordered domains. As a result, a transition from Qⁿ to Tⁿ signals detected in the ²⁹Si NMR spectra, the Si–O structural band in the FTIR spectra shifted to lower wavelength, and a new peak in the XRD pattern at 2θ < 10° appeared in the XRD patterns. Mass spectroscopy detected fragments with high numbers of silicon atoms and a polymeric distribution.     

A hydrothermal method to prepare the spherical ZnS and flower-like CdS microcrystallites

The spherical ZnS and flower-like CdS microcrystallites are prepared by a convenient hydrothermal process through the reactions of Zn(CH₃COO)₂·2H₂O or Cd(CH₃COO)₂·2H₂O with S and NaH₂PO₂·H₂O in aqueous solution at 180 °C for 12 h. Powder X-ray diffraction (XRD) is used to confirm the cubic phases of the ZnS and CdS microcrystallites. Their chemical compositions are characterized by X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images show the morphologies of the as-synthesized ZnS and CdS. The photoluminescence spectra (PL) exhibit their optical properties.     

Effect of preparation conditions on the physical and hydrophobic properties of two step processed ambient pressure dried silica aerogels

The experimental results on the physical and hydrophobic properties of the ambient pressure dried silica aerogels as a function of sol-gel and drying conditions, are reported.The aerogels have been produced by a two stage (acidic and basic) catalytic sol-gel process using tetraethylorthosilicate (TEOS) precursor, oxalic acid (OXA) and ammonium hydroxide (NH₄OH) catalysts, ethanol (EtOH) solvent and hexamethyldisilazane (HMDZ) silylating agent at 200^∘C.The molar ratios of HMDZ/TEOS (M), OXA/TEOS (A) NH₄OH/TEOS (B), acidic H₂O/TEOS (Wa) basic H₂O/TEOS (Wb), EtOH/TEOS (S) were varied from 0.09 to 0.9, 3.115 × 10^{− 5} to 3.115 × 10⁻³, 4 × 10^{− 3} to 8 × 10^{− 2}, 2 to 9, 1.25 to 5 and 1 to 16 respectively. The physical properties such as the percentage (%) of volume shrinkage, density, thermal conductivity, percentage of porosity, the percentage of optical transmission and contact angle have been found to be strongly dependent on the sol-gel parameters. It was found from the FTIR spectra of the aerogels that with the increase of M, the bands at 3500 and 1600 cm^{− 1} corresponding to H-OH and Si-OH respectively decreased and the bands at 840 and 1250 cm^{− 1} due to Si-C and 2900 and 1450 cm⁻¹ due to C-H increased. The best quality silica aerogels in terms of low density, low volume shrinkage, low thermal conductivity, high hydrophobicity and high optical transmission have been obtained with the molar ratio of TEOS:EtOH:acidicH₂O:basicH₂O:OXA:NH₄OH:HMDZ at 1:8:3.75:2.25:6.23 × 10^{− 5}: 4 × 10^{− 2}:0.36 respectively, by ambient pressure dried method.     

Novel approach to control CdS morphology by simple microwave-solvothermal method

Nanosize CdS powders with different microstructures are prepared in different solvents by using rapid microwave irradiation. Effect of solvents and Cd²⁺ precursors are to be able to control the particle size, and microstructures of CdS have been investigated by X-ray diffraction and TEM. The different particle size and morphologies are observed using different Cd²⁺ precursors in different solvents. TEM micrographs clearly show multiarmed nanorods and spherical shape morphologies of CdS powders are obtained in polar solvent like water (H₂O), whereas non-polar polyol solvent like ethylene glycol (EG), prickle and cluster like morphologies of CdS are achieved with different Cd²⁺ precursors such as CdSO₄ and Cd (CH₃COO)₂. The spectroscopy studies of nanosize CdS are examined by photo-luminescence spectra. Band gap and the absorption co-efficient for nano CdS is also evaluated from optical absorption studies.     

Growth of thin CdS films on glass substrates via reaction of thiourea with cadmium acetate in aqueous solution

Thin CdS films have been produced by chemical surface deposition from aqueous solutions of cadmium acetate, Cd(CH₃COO)₂. We have studied the morphology and optical properties of the CdS films and calculated the mechanical stress induced by the difference in linear thermal expansion coefficient between the film and substrate materials.     

Comparative studies of the physical and hydrophobic properties of TEOS based silica aerogels using different co-precursors

In the present paper, the experimental results on the physical and hydrophobic properties of tetraethoxysilane (TEOS) based silica aerogels using six different organosilane co-precursors (C.P) of the type R_nSiX_4-n as synthesis components, are reported and discussed. The aerogels have been produced by sol-gel processing followed by supercritical drying using methanol solvent extraction. The molar ratio of TEOS, ethanol (EtOH), water (0.001M oxalic acid (H₂C₂O₄) catalyst) was kept constant at 1:5:7, respectively, and the molar ratio of C.P/TEOS (A) was varied from 0.1 to 0.6 and compared the aerogel properties. The hydrophobicity of the aerogels has been tested by the contact angle measurements. The contact angle (θ) has been found to be the highest (θ=136°) for the trimethylethoxysilane (TMES) co-precursor, while for the other co-precursors it is in between 120° and 130°. The surface chemical modification of the hydrophobic aerogels has been studied using Fourier Transform Infrared Spectroscopy (FTIR). As the C.P/TEOS molar ratio increased, the intensity of the C–H and Si–C peaks in the FTIR spectra increased, clearly indicating the organic modification of the aerogels. The aerogels based on mono-alkyl (CH₃) trialkoxysilane co-precursor have shown higher optical transmission (≈65%) compared to the phenyl, di or tri alkyl alkoxysilanes (5–50%). The trialkyl modified aerogels showed the lowest bulk density (118.3 kg/m³) and volume shrinkage (<2%). The alkyl alkoxy/chloro–silane modified aerogels have been found to be thermally stable up to a maximum temperature of 573 K, whereas the phenyl trialkoxysilane modified aerogels are stable up to a temperature as high as 823 K. The aerogels have been characterized by scanning electron microscopy, thermogravimetric and differential thermal analyses.     

Comparative studies of the physical and hydrophobic properties of TEOS based silica aerogels using different co-precursors

In the present paper, the experimental results on the physical and hydrophobic properties of tetraethoxysilane (TEOS) based silica aerogels using six different organosilane co-precursors (C.P) of the type R_nSiX_4-n as synthesis components, are reported and discussed. The aerogels have been produced by sol-gel processing followed by supercritical drying using methanol solvent extraction. The molar ratio of TEOS, ethanol (EtOH), water (0.001M oxalic acid (H₂C₂O₄) catalyst) was kept constant at 1:5:7, respectively, and the molar ratio of C.P/TEOS (A) was varied from 0.1 to 0.6 and compared the aerogel properties. The hydrophobicity of the aerogels has been tested by the contact angle measurements. The contact angle (θ) has been found to be the highest (θ =136?) for the trimethylethoxysilane (TMES) co-precursor, while for the other co-precursors it is in between 12?8 and 13?8. The surface chemical modification of the hydrophobic aerogels has been studied using Fourier Transform Infrared Spectroscopy (FTIR). As the C.P/TEOS molar ratio increased, the intensity of the C–H and Si–C peaks in the FTIR spectra increased, clearly indicating the organic modification of the aerogels. The aerogels based on mono-alkyl (CH₃) trialkoxysilane co-precursor have shown higher optical transmission (≈65%) compared to the phenyl, di or tri alkyl alkoxysilanes (5–50%). The trialkyl modified aerogels showed the lowest bulk density (118.3 kg/m³) and volume shrinkage (<2%). The alkyl alkoxy/chloro–silane modified aerogels have been found to be thermally stable up to a maximum temperature of 573 K, whereas the phenyl trialkoxysilane modified aerogels are stable up to a temperature as high as 823 K. The aerogels have been characterized by scanning electron microscopy, thermogravimetric and differential thermal analyses.     

Chemical deposition of CdS films: structure,RBS, PIXE,optical and photoelectrochemical solar cell studies

CdS semiconductor films have been chemically prepared from a basic solution containing CdSO₄, thiourea and NH₄OH. X-ray diffraction studies have revealed the presence of polycrystalline mixed cubic and hexagonal phases of CdS in the deposit. The surface topography has been identified by SEM analysis and found to be non-uniform and spongy. Rutherford Backscattering Spectrometry (RBS) analysis gave the Cd to S ratio as 1.016 whereas that of Proton Induced X-ray Emission (PIXE) analysis gave the Cd to S ratio as 0.905. The band gap of the CdS film has been estimated from optical absorption studies and found to be 2.46 eV. The CdS/S^2–, S₂ ^2– interface has been characterized in order to identify the charge transfer process. Finally, Photoelectrochemical Solar Cells (PESCs) have been fabricated with cell configuration Ti/CdS/S^2–, S₂ ^2–/Pt and the results have been discussed.     

Preparation of ear-like, hexapod and dendritic PbS using cyclic microwave-assisted synthesis

Different morphologies of PbS were prepared using microwave-assisted synthesis of 1:4, 1:1 and 4:1 molar ratios of Pb(CH₃COO)₂ to NH₂CSNH₂ in propylene glycol. Cubic PbS was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED). Raman spectrometry revealed the presence of vibrations at 134, 274 and 430 cm^− 1. The product morphologies for different molar ratios of Pb(CH₃COO)₂ to NH₂CSNH₂ were also characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The obtained morphologies changed with molar ratios used for the starting agents. The simulated diffraction pattern was also in accordance with the interpretation of the experimental results.     

Effect of gel parameters on monolithicity and density of silica aerogels

As part of continuing investigation of the preparation and characterization of silica aerogels, detailed experimental results on monolithicity and density of the aerogels as a function of catalysts and their concentrations, molar ratios of tetraethylorthosilicate (TEOS), ethanol (EtOH) and H₂O, gel pH and gel ageing, are reported. With large concentrations of catalysts, lower and higher aged alcogels have been found to produce opaque, cracked and highdensity silica aerogels; however, good-quality monolithic, transparent and low-density aerogels have been obtained at lower catalyst concentration (0. 01n HCl) with alcogel ageing periods between 9 and 30 days. The best quality silica aerogels, in terms of transparency and monolithicity, have been obtained using TEOSEtOHH₂O in the molar ratio of 158.     

Synthesis of nanometer-sized hematite single crystals through NAC-FAS method

Nanometer-sized spherical hematite single crystals were prepared by heating the precipitate which was synthesized from Fe(OH)(CH₃COO)₂ and NaOH in alkaline ethanol-water solutions without the deliberate addition of surfactants or adsorbing ligands. Hematite nanocrystals (5–10 nm in diameter) and ferrihydrite (<5 nm) were obtained from the mixture of H₂O/EtOH (Rs) = 100 ml/100 ml as a initial medium, whereas goethite, hematite (20–40 nm), and ferrihydrite were precipitated at Rs = 200/0. Adsorbing ligands such as acetoxy groups and ethanol on particles retarded the hematite growth and goethite formation. TEM observation of the particles prepared at Rs = 100/100 with heat treatment at 400°C for 2 hours showed them consisting of single spherical hematite crystals 22 nm in mean diameter with narrow size distribution. Various individual effects were investigated for their contributions to crystal structure and size of precipitates; they included NaOH to Fe(OH)(CH₃COO)₂ ratio, solvent, dropping rate of alkaline solution, and aging time.     

Novel petal-like ZnO crystal synthesized by organic solution method

ZnO crystals with different morphologies have been synthesized by an organic solution method using Zn(CH₃COO)₂ · 2H₂O and polyvinylpyrrolidone as precursors. X-ray powder diffraction, field emission scanning electron microscopy and transition electron microscopy were used to characterize the obtained samples. The results showed that novel petal-like ZnO particles could be obtained when the molar ratio of Zn²⁺/C = O was 1 : 4. The particle had uniform diameter in 200–300 nm and with good dispersibility. Otherwise, octahedron shaped particles with sub-crystalline were achieved when the molar ratio of Zn²⁺ to the carbonyl group of polyvinylpyrrolidone was 1 : 2 or 1 : 8.     

Preparation of a transparent alumina film doped with CdS and its nonlinear optical properties

We have examined the preparation of transparent alumina film and CdS-doped alumina film prepared by the sol-gel process using aqueous sol starting from AlCl₃. The resulting alumina films obtained by sol-gel transformation are transparent in the visible and near infrared up to 1000 °C. Homogeneous solution of alumina sol and Cd(CH₃COO)₂ was converted into gel film by dehydration. Then, on exposure to H₂S stream at 250–600 °C, a CdS-doped film was obtained. It shows relatively sharp blue-shifted visible absorption that is attributed to size quantization effect. Large nonlinear absorption and refractive index have been obtained, because high concentration of CdS particles can be achieved by using this method.     

Photocatalytic performance of CdS nanomaterials for photodegradation of organic azo dyes under artificial visible light and natural solar light irradiation

The CdS semiconductors have been prepared at low temperature via catalyst-free chemical precipitation method without using any surfactant or capping agent. Either water or ethylene glycol, as a solvent, provides spherical CdS nanostructures with a comparable size of 117–121 nm. The molar ratio of Cd/S plays an important role in determining phase structure, morphology and photocatalytic performance of the prepared CdS nanostructures. Increasing molar ratio of S^2? results in not only mixed cubic-hexagonal phases but also low photocatalytic performance. CdS nanoparticles with good dispersibility prepared at Cd/S molar ratio of 1:1 shows high photocatytic efficiency of 95% toward photodegradation of reactive red azo dye (RR141) under visible light irradiation up to 240 min. The degradation efficiency of CdS nanoparticles also reaches 48% under natural solar light irradiation for 80 min. This work demonstrates the promising potential of CdS nanomaterials as photocatalysts for environmental remediation.     

Optimization of CdSe layer on modified ZnO hierarchical spheres by spin-SILAR for efficient CdS/CdSe co-sensitized solar cells

In this study, after CdS quantum dots sensitized ZnO hierarchical spheres (ZnO HS), we used a simple process to deposit CdSe QDs on ZnO by spin-coating-based SILAR, and applied to photoanodes of quantum dots-sensitized solar cells. Before CdS and CdSe QDs deposition, the ZnO HS photoanodes were modified by Zn(CH₃COO)₂·2H₂O methanol solution to further enhance the open-circuit voltage and power conversion efficiency (PCE). The program of modifying photoanodes and the number of CdSe spin-SILAR cycles are evaluated on the optical and electrochemical properties of the cells. As a result, a high energy conversion efficiency of 2.49 % was obtained by using modified ZnO HS/CdS photoanode under AM 1.5 illumination of 100 mW cm^?2. And further decorated by the CdSe QDs, the ZnO HS/CdS/CdSe cell achieved a PCE of 5.36 % due to the modification of ZnO HS nanostructure, the enhanced absorption in the visible region, the lower recombination reaction and higher electron lifetime.