Adsorption of metal and metalloid ions onto nanoporous microparticles functionalized by atomic layer deposition

A novel material was prepared by depositing ultrathin TiO₂ films on nanoporous micron-sized silica gel particles by atomic layer deposition (ALD). Silica gel particles were coated with 20 and 40 cycles of TiO₂ films by ALD. Half samples were heated at 500 °C to change the crystal structure of TiO₂. Their adsorption ability for a mixture of 19 trace elements of heavy metals and other toxic elements, including As(V), Se(IV), Be(II), Al(III), V(V), Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Ba(II), Tl(I), Sb(III), Cd(II), Ag(I), Sr(II), Mo(VI), and Pb(II), from aqueous solutions was investigated. The removal efficiencies of As(V), Se(IV), V(V), Mo(VI), and Pb(II) were higher than 75% simultaneously in the mixed solution at pH 3 for 20 and 40 cycles of TiO₂ coated silica gel particles without heat treatment. In contrast, the uncoated silica gel particles did not adsorb any ions under this pH condition. At pH 5, the 20 cycles of TiO₂ coated samples without heat treatment removed 95% As(V), 95% Se(IV), 86% V(V), 94% Mo(VI), 60% Pb(II), 40% Sb(III), 73% Ag(I), 72% Cu(II), and 49% Ba(II) simultaneously. Before heat treatment, the TiO₂ coated samples showed better adsorption performance than the samples with heat treatment due to the fact that the TiO₂ surface area decreased and thereby the amount of adsorption sites reduced after heat treatment. The micron-sized adsorbent particles were separated easily from water due to their large particle size, making it practically suitable for trace contaminant remediation in water.