Chitosan-functionalized natural magnetic particle@silica modified with (3-chloropropyl)trimethoxysilane as a highly stable magnetic adsorbent for gold(III) ion

It is keenly desired to develop an environmentally benign and highly stable magnetic adsorbent for efficient recovery of Au(III) ion from an acidic solution. In the present study, we investigated the synthesis of magnetic adsorbents that the magnetic particles, which was prepared from natural iron sand, were modified with silica layer on which chitosan was fixed through 3-chloropropyltrymethoxysilane (CPTMS) by a sol-gel process. Since the magnetic particles were almost completely covered with the silica layer and chitosan was tightly fixed on it through CPTMS, the adsorbent was highly stable in an acidic solution with pH 3 or lower. Excess CPTMS significantly lowered the adsorption capacity for Au(III) ion, while lead to little improvement in the stability. Thus, 1 mmol of CPTMS against 4 mmol of chitosan gave the best magnetic adsorbent in terms of stability and adsorption capacity, of which the maximum was 112 mg g⁻¹ for Au(III) ion at pH 5. The adsorbent showed high selectivity of Au(III) adsorption in the solution containing Cu(II) and Zn(II), and was reusable for two times keeping high selectivity without fatal decline in the adsorption performance. The magnetic adsorbent was separable from the solution simply with an external magnet, while the modification caused a slight decrease of the saturated magnetization.