Amino-terminated SiO2-Al2O3 composite aerogels from fly ash for improved removal of Cu2+ and Pb2+ ions in wastewater: one-pot synthesis, excellent adsorption capacity and mechanism

Abstract

In this study, by using a sol-gel grafting-atmospheric drying method, amino-terminated SiO2-Al2O3 composite aerogels, namely 3-aminopropyltriethoxysilane (APTES) or 3-(2-amino-ethoxy) propylmethyldimethoxysilane (AEAPMDS) modified SiO2-Al2O3 aerogels (AMSAAs), were synthesized from the fly ash, and verified as excellent sorbents for removing heavy metal ions (Cu2+ and Pb2+ ions) from wastewater. The effects of modification conditions and testing parameters including pH value, adsorbent dose, initial ions concentration and adsorption time on the micro-structure of AMSAAs and the removal of heavy metal ions were systematically investigated. And the adsorption mechanism was revealed. Results demonstrated that 0.2 mol/L APTES modified aerogels possessed (0.2APTES-SAAs) the best adsorption properties. Under the optimal pH value of 4.0–6.0 and the adsorbent dose of 0.4–0.6 g/L, the equilibrium adsorption capacities of Cu2+ and Pb2+ ions were as high as 195 mg/g and 500 mg/g within 20–30 min, respectively. The adsorption processes were agreed fairly well with Freundlich isotherm adsorption model and the pseudo-second-order kinetic model, which indicated that the adsorption processes were heterogeneous multilayer adsorption and controlled by the chemical reaction between AMSAAs and heavy metal ions.