Effectiveness of gold nanoparticle-coated silica in the removal of inorganic mercury in aqueous systems: Equilibrium and kinetic studies

The adsorption of inorganic mercury, Hg (II), in aqueous solution has been investigated to evaluate the effectiveness of synthesized gold (Au) nanoparticle-coated silica as sorbent in comparison with activated carbon and Au-coated sand. The synthesis of the Au-coated silica was confirmed by x-ray diffraction (Bragg reflections at 38.2°, 44.4°, 64.6°, and 77.5°) and the Au loading on silica surface was 6.91±1.14 mg/g. The synthesized Au-coated silica performed an average Hg adsorption efficiency of ~96 (±2.61) % with KD value of 9.96 (±0.32) L/g. The adsorption kinetics of Hg(II) on to Au-coated silica closely follows a pseudo-second order reaction where it is found out to have an initial adsorption rate of 4.73 g/μg/min/ and overall rate constant of 4.73 × 10−4 g/μg/min/. Au-coated silica particles are effective in removing Hg (II) in aqueous solutions due to their relatively high KD values, rapid adsorption rate, and high overall efficiency that can even decrease mercury levels below the recommended concentrations in drinking water.