Synthesis of chemically modified silica gel for preconcentration of heavy metals

Abstract

Three types of novel chemically modified silica with amidoamidoxime (phase A), ethyl 2-benzothiazoly acetate (phase B) and aminothioamido anthraquinone (phase Q) were synthesized for selective extraction and preconcentration heavy metals from water sample. The modified silica’s were characterized by ¹³C-NMR, elemental analysis, FT-IR, N₂-Adsorption and TGA. The extraction studied towards Pb(II), Ni(II), Cd(II), Cu(II) and Co(II) were carried out in batch extraction as function of pH and extraction time. The optimum pH ranges 4-7 with fast extraction equilibrium. The metal adsorption behaviors well agreed with Langmuir’s adsorption model. Phase A showed highly selective towards Cu(II) while phase B preferred both Cu(II) and Pb(II). Phase Q, on the other hand, can be applied for all metal ion extraction. In flow system, the modified silica were packed by lab-made mini-columns. The solution flow rates were optimized. Nitric acid (1%, 5 mL) was used as an eluent from the initial sample volume of 100 mL. No interferences from Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl- and SO₄²¯ was observed. Spiked pond water, tap water and drinking water were chosen as real samples. The proposed method provided high accuracy and precision. The method detection limits were 22, 3.0, 1.2, 1.0, 0.95 ng mL¯¹ for Pb(II), Ni(II), Cd(II), Cu(II) and Co(II), respectively.