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

Abstract

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 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.