Functionalization of biosourced silica and surface reactions with mercury in aqueous solutions.

From left to right: TES anchored on SiO 2 , Ag0 nanoparticle (TEM), calomel-amalgam coexistence (XRD) and Ag 1.1 Hg 0.9 nanoparticle (TEM) [Display omitted] • Biosourced silica functionalized with triethoxysilane and silver nanoparticles. • Rapid Hg2+ removal from high concentration chloride-containing aqueous solutions. • Competitive capacity levels achieved (21–101 mg/g). • Co-existence of calomel and amalgam on silica observed for first time. • Evidence of hyperstoichiometric interaction with Hg:Ag molar ratio higher than 3. This study presents the production of pure silica from rice husk and its stepwise functionalization with triethoxysilane (TES) and silver nanoparticles. The derived TES-SiO 2 (0.97 mmol TES per g of SiO 2) and Ag0@SiO 2 (3.70–21.60 mg Ag per g of SiO 2) materials were used for the removal of Hg2+ from aqueous solutions in the presence of chloride ions. The removal of Hg2+ was rapid and the equilibrium solid phase loading was between 21 and 101 mg/g. TES-SiO 2 was more effective than Ag0@SiO 2 in removing mercury due to the highly reactive hydride groups. In the case of Ag0@SiO 2 samples the removal of Hg2+ is proportional to the amount of Ag0. The materials were characterized before and after the removal of Hg2+ to allow insights into the interaction mechanism. The reaction products for TES-SiO 2 sample were calomel (Hg 2 Cl 2) and AgCl. On the surface of Ag0@SiO 2 samples besides these products the silver amalgams Ag 1.1 Hg 0.9 and possibly Ag 2 Hg 3 were identified. These results show that redox reactions between silicon-hydride group, Ag0 and Hg2+ take place on the surface of the materials. The coexistence of calomel and silver amalgams on amorphous silica is observed for the first time while the calomel formation in heterogeneous Hg2+ redox systems is a rare observation. Also, the samples showed extraordinary efficiency in terms of Hg:Ag molar ratio (2.28–3.02), considerably higher than those reported before. Besides the beneficial effect of the Cl- presence on the removal of Hg2+ from the solution there is evidence of a hyperstoichiometric interaction between Ag0 and Hg2+ at the nanoscale. [ABSTRACT FROM AUTHOR]