Chemical modification of silica-gel with hydroxyl- or amino-terminated polyamine for adsorption of Au(III)

Silica-gel chemically modified by γ-aminopropyltrimethoxysilane (APTS) reacted with methyl acrylate (MA) to form esterified silica-gel SiO2–MA, and then SiO2–MA reacted with ethanolamine (EA), diethanolamine (DEA), ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) respectively to obtain five novel adsorbents, hydroxyl-terminated polyamine functionalized silica-gels (SiO2–EA and SiO2–DEA) and amino-terminated ones (SiO2–EDA, SiO2–DETA, and SiO2–TETA). Their structures were characterized by FTIR, WAXD, thermal analysis, and elemental analysis. The investigation of adsorption kinetics of the five adsorbents for Au(III) under different temperatures showed that all the adsorption processes were endothermic in nature. The amino-terminated polyamine grafted silica-gels exhibited higher adsorption rates than the hydroxyl-terminated ones. The Langmuir model was better than Freundlich model to fit the adsorption isotherms of the five products for Au(III).