Morphology Control Of Cdco₃ And Preparation Of Cds/cdco₃ Composite Materials

Uniform monodispersed CdCO₃ fine particles were prepared through simply precipitation method. Good wettability of CdCO₃ was obtained by surface modification using coupling agent. Using modified CdCO₃ particles as stabilizer, paraffin or styrene as oil phase, a oil-in-water (W/O) Pickering emulsion was prepared. Sulfuration reaction was carried out on exposed CdCO₃ particles in cured Picking emulsion, then CdS/CdCO₃ sub-region complex were prepared. CdS/CdO composite can be prepared by using the obtained CdS/CdCO₃ through high temperature calcination under nitrogen atmosphere. CdS and CdO both are important semiconductor materials, thus this study provide basic information for further investigation of the performances of CdS/CdO composites.Firstly, using Na₂CO₃ and CdCl₂ as reagents, a serious of CdCO₃ particles with various morphologies were prepared through direct precipitation method. Good dispersion CdCO₃ can be reached by using different surfactants in the reaction. When cetyltrimethylammonium bromide (CTAB) was added, the prepared CdCO₃ particles were the most uniform with basically cubic shape. Also there can be no surfactants or crystal control agent during the reaction. When the concentration of CdCl₂ and Na₂CO₃ were 2 mmol/L and 4 mmol/L respectivly, polysynthetic twinning CdCO₃ particles were get. While, with excess Na₂CO₃ in 2 mmol/L CdCl₂, peanut-like-twinning of CdCO₃ was obtained. With the increase of concentration of the reagents, uniformly dispersed cubic CdCO₃ was obtained. But further increased reagents concentration led to ununiform particle size and aggregation.Then, Using urea and CdCl₂ as reagents, another serious of CdCO₃ particles with various morphology were preparaed through homogeneous precipitation method. High temperature aging of urea before reaction was beneficial to synthesize monodispersed particles. In water bath, stirred 3 mmol/L CdCl₂ with excess urea produced cubic CdCO₃ particles with approximately 1.5μm diameter. Increasing the concentration of CdCl₂ resulted in near spherical CdCO₃ particle with layered structure. When the concentration rose up to 0.05 mol/L, the obtained CdCO₃ existed in spherical-twinning. Whereas reaction system under ultrasonic produced obviously layered structure of CdCO₃. And twinning CdCO₃ was synthesized by slowly adding urea in drops into the ultrasonic reaction system.Furthermore, CdCO₃ particles were surface modified by A-151. The wetting contact angle of the modified CdCO₃ was measured by using height-width method. The results of FTIR analysis indicated that silanol monomers had already polymerized on the surface of CdCO₃ particles and formed a thin film around, therefore, gave good wettability to the CdCO₃ particles. The wetting contact angle of the modified CdCO₃ increased with the content of A-151. But it did not increase obviously when the weight ratio of A-151 to CdCO₃ exceeded 1.26.The stability of the Pickering emulsion stabilized by modified CdCO₃ particles affected by the degree of wetting of the particle, oil phase, and oil to water ratio. CdCO₃ particles with 79o contact angle embedded in styrene emulsion droplets to prepare stable Pickering emulsion. CdCO₃/PS composite sphere were prepared through polymerization of styrene. Sulfuration reaction was carried out on exposed CdCO₃ particles on the obtained CdCO₃/PS composite surface. Then sub-region complex of monodispersed CdS/CdCO₃ was gained. The thickness of CdS layer increased with reaction time. For the hindrance of CdS to further sulfuration, the CdS layer finally stabilized in semicircle shell.