Functionalized 2D Clay Derivative: Hybrid Nanosheets with Unique Lead Sorption Behaviors and Interface Structure

Clay mineral and its derivatives can play an important role in stabilizing functional-groups and nanostructures. Here, a TP-SiNSs (TiSi2O5(OH)(2)center dot(OH2)(2)) nanocomposite, with highly dispersed and stabilized TiO2 precursor (TP, Ti(OH)(4) gel) on template-free 2D silica nanosheets (SiNSs, Si2O3(OH)(2)), is presented, which is derived from kaolinite, a natural 2D layer mineral. Unique lead sorption behaviors are observed for balanced hydrophobicity-hydrophilicity, short sorption equilibrium time (within 5 min), large applied sorption capacities (approximate to 38 000 kg polluted drinking water per kg TP-SiNSs, effluent Pb(II) contents <10 mu g L-1), and excellent renewability. The highly dispersed surface titanium hydroxyl groups, together with 2D hierarchical porous nanostructure of TP-SiNSs effectively facilitate the selective adsorption of Pb(II) ions, inhibit the pore blockage after Pb(II) adsorption, and prolong the service life. The detailed adsorption mechanism as a function of pH value and ion concentration is clarified by density functional theory (DFT) calculations, and the higher adsorption selectivity of TP-SiNSs for Pb(II) over Ca(II) and Mg(II) is attributed to surface complex on TP-SiNSs, which induces strong bonding between Pb(II) and titanium hydroxyl groups. The interface geometry and electronic structure calculations demonstrate that the stabilized and spatially distributed titanium hydroxyl group on TP-SiNSs can greatly enhance the surface adsorption ability.