Macro-Silica Spheres: Preparation And Applications For Heavy Metal Ion Adsorption

Nowadays the most popular methods used for macro-silica sphere preparation are sol-gel process, spray drying process and the hydrolysis of organic silane agents. However, the common disadvantage of the first two methods consist in the weak binding capacity of silica nano-particles which results in the formation of nonspherical and fragmentation of silica spheres. The application of hydrolysis of organic silane agents is limited in the large-scale production of silica spheres because of the exorbitant price of silane agents, complex reaction steps and the long aging time. So the key point of macro-silica sphere preparation is to increase the binding capacity of silica nano-particles.In this study, we introduced adhesive into the silica particles'preparation, explored the different kinds of adhesives'effects on the nano-particles'spherulization, such as gelatin, starch, urea-formaldehyde (UF) resin, hydroxyethyl cellulose (HEC) and PEG10000, and then developed three novel methods with the adhesive of urea-formaldehyde resin. The sol-gel process was fit for the preparation of macro-silica spheres with diameters ranging from 10μm to 100μm in the solvent of benzyl alcohol. The productivity was up to 95%. The macro-silica spheres'properties, such as morphology, dispersion and rigidity, indicated that they were completely propitious to use in chromatography. We could acquire the desirable particle diameter by controlling stirring speed in the course of reaction and realized large-scale production successfully. Spray drying process could produce the 10μm-20μm spheres with a very narrow particle distribution. Compared with other methods, spray drying process was more economic and environmental, and suitable for large-scale continuous production. The pH-induced rapid colloid aggregation technics was simple and convenient, and the primary experiment showed the possibility of preparation macro-silica spheres with diameters higher than 150μm.The macro-silica spheres modified with mercaptopropyl alkoxysilane (MPTMS) or iminodiacetic acid (IDA) could adsorb heavy metal ions such as Pd²⁺ completely in a certain concentration. Through spray drying process, the agglutination of nano-particles constitute of macro-silica spheres was more incompact, so they could adsorb Pd²⁺ in aqueous solution more effectively and quickly than the spheres prepared with sol-gel transformation process. As to the three kind of macro-silica spheres prepared with sol-gel method, the adsorb capacity for Pd²⁺ of spheres with the hydroxyethylcellulose adhesive was better than spheres prepared with adhesives of PEG10000 and urea-formaldehyde (UF) resin. However, the four kinds of spheres all could adsorb the Pd²⁺ effectively.