Experimental and theoretical investigations on Hg(II) removal by recyclable composite sorbents comprised of polymers bearing thiourea or amidoxime functional groups and mesoporous silica

Abstract

It is extremely desirable but still challenging to skilfully manufacture highly efficient sorbents to remmediate, in a reversible manner, the water pollution with mercury. Herein, new sorbents for Hg(II) ions have been designed by the initial synthesis of polyacrylonitrile networks inside mesoporous SiO2 microparticles, followed by the chemical modification of acrylonitrile groups with thiourea or amidoxime moieties. The Hg(II) ions sorption properties of the new composites were compared with respect of initial solution pH, contact time, equilibrium concentration and impact of interfering metal ions. It was demonstrated that the sorbents containing thiourea groups exhibited superior sorption capacities (1.76 mmol Hg(II) g−1) compared to the ones containing amidoxime groups (1.68 mmol Hg(II) g−1), and also higher selectivity for Hg(II) ions separation from binary mixtures with Cu(II), Cd(II) or Pb(II) ions. Kinetic study and DFT results supported a combined sorption mechanism, both physical sorption and chem-isorption being possible. Following the elution of Hg(II) ions with 1 M HNO3 and the regeneration with 0.1 M NaOH, all sorbents exhibited around 90 % sorption capacity recovery after 4 reuse cycles.