Amino-terminated SiO2 aerogel towards highly-effective lead (II) adsorbent via the ambient drying process

This work demonstrated a low-cost sol-gel and ambient drying process towards amino-modified SiO2 (SiO2-NH2) aerogels powders possessing high potential in recovering lead (II) ions from waste water, using industrial waterglass and 3-aminopropyl triethoxysilane (APTES) as the starting materials. Effects of the APTES/SiO2 molar ratio on the chemical composition and pore structure of SiO2-NH2 aerogel were investigated, and the Pb2+ adsorption properties were examined using the batch method. Results showed that the SiO2-NH2 aerogels via the ambient drying route possessed the BET surface area of 400-470 m(2)/g, pore volume of 1.4-1.8 ml/g, and average pore diameter of 12-16 nm. FTIR and chemical composition analysis confirmed the successful anchoring of the NH2 groups on the surface of SiO2 nanoparticles and the optimal APTES/SiO2 molar ratio was 0.21. The adsorption test showed that, at pH range of 4.0-6.0 and room temperature, the samples with the optimal APTES/SiO2 molar ratio of 0.21 exhibited relatively high adsorption capacity compared with the pure SiO2 aerogel and SiO2-NH2 aerogels with lower APTES/SiO2 molar ratio. An equilibrium adsorption time of 7 h was observed, fitting well with the pseudo second-order kinetic model, indicating that the chelating reaction between Pb2+ and anchored NH2 group was the rate-limiting step. The adsorption isotherm was well fitted by the Langmuir adsorption model, with the maximum adsorption capacity of 407.04 mg/g. The rapid adsorption test simulating the filter membrane with SiO2-NH2 aerogel adsorbent indicated the removal percentage of higher than 80% after 5 cycles. (C) 2016 Elsevier B.V. All rights reserved.