Surface modification of nano-silica is an important way to solve nanometer powder agglomeration, it can not only improve the dispersibility of nano-silica in aqueous phase medium, but also improve its compatibility with organic phase. Therefore, surface modification of nano-silica has important theoretical significance and application value. At present, the theoretical basis of powder modification mainly focuses on physical adsorption theory, chemical bond theory and coordination theory, etc. The commonly used nano-silica modifiers are ionic polymers (polyethylenimine, maleimide propyltrimethylammonium chloride, polysodium methacrylate, etc. ), non-ionic polymers (polyurethane, etc. ), and coupling agents (titanate coupling agent, silane coupling agent, etc. ), and the modification methods include molecular self-assembly, grafting, chemical deposition, dry modification and wet modification, etc. Poly(amide-amine) (PAMAM) has been extensively studied and utilized in many fields such as the preparation of nanoparticles, molecular carrier, catalyst and separation and purification of heavy metal ions because of its regular dendrimer structure, controllable molecular weight and multi-functional group, and high reactivity. Most of the modification strategies are conducted indirectly, that is, the -NH2 group is firstly introduced onto the surface of SiO2 powder, then PAMAM molecules are synthesized by means of polymerization. However, as silane fragments bonded by hydroxyl may break under the effect of stirring and heating (such as -CH2-CH2-), it is difficult to avoid the occurrence of side reactions in the synthesis process, and the molecular weight and length of the molecular chain of the synthetic products are difficult to control. As a result, the efficiency of this method is not high. Our group proposed to adopt PAMAM macromolecular to modify silica directly through dry modification method, which can avoid the participation of moisture, and the surface of silica retain more active points. The aim of modification can be achieved by directly coupling the modifier molecular PAMAM (central nuclear nitrogen atom, amide center, chain terminated amine group, etc. ) with these active points on the surface of silicon dioxide to form ligand structure, at the same time, the modification process is simplified and the operating cost is reduced. In this paper, the modification methods of PAMAM for silicon dioxide are introduced firstly, then the application of PAMAM modified silicon dio-xide is introduced emphatically from four aspects, including adsorption and separation of heavy metal ions, biotechnology, dispersibility in medium and coatings, and catalytic carriers in order to provide reference for the preparation of modified nano-silica with better performance and stability. © 2019, Materials Review Magazine. All right reserved.
