Synthesis of L-glutamic acid containing silica gel for the adsorption and immobilization of Zn²⁺ in water

A porous silica gel with both COOH and NH₂ groups was synthesized in one pot by the addition of L-glutamic acid (L-GA) into a synthesis medium consisting of tetraethyl orthosilicate, water, ethanol, and 1-butylamine. The inclusion of L-GA in the as-synthesized product (L-GA-SiO₂) was evidenced by FT-IR and TG measurements. The L-GA was chemically bonded with silica as indicated by the shift of FT-IR bands at 1510 and 1400 cm⁻¹ in the spectrum of L-GA to higher wavenumbers of 1540 and 1460 cm⁻¹ in the one of L-GA-SiO₂. The TG analysis showed that the L-GA-SiO₂ had an increase of weight loss by 5.6% due to the decomposition of the included L-GA which was centered at around 313 °C, suggested by a new peak in the DTG curve. Compared with the one synthesized without L-GA, the L-GA-SiO₂ was more aggregated with smaller surface area. However, the latter showed a higher removal efficiency by 17.1% toward zinc ions in water than the former and the adsorbed ions were hardly released again into water from the used adsorbent. Graphical abstract:

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