Adsorption behavior of Ag(I) onto elemental sulfur-encapsulated silica nanocapsules for industrial applications

Abstract

Pure silica nanocapsules (SiNC-P) and elemental sulfur-encapsulated silica nanocapsules (SiNC-ES) as Ag(I) adsorbents were successfully synthesized by a one-step water-in-oil microemulsion polymerization process. The characterization of the synthesized materials, such as surface morphology, surface area, porosity, functional groups and thermal characteristics, was carried out using various analytical techniques. The SiNC-P and SiNC-ES have nearly similar morphology, but the surface area and pore size of the SiNC-ES are higher than SiNC-P. The Ag(I) adsorption study showed that it increased with increasing elemental sulfur (ES) amount in the SiNC-ES. The SiNC-ES shows high adsorption capacity, independent of pH, and higher adsorption rate as compared to SiNC-P. The maximum Ag(I) adsorption capacity of SiNC-P and SiNC-ES was 50.49 mg g−1 and 98.51 mg g−1, respectively. The adsorption isotherm data were best described by the Langmuir model. The diffusion modeling analysis of the kinetic data indicated that film diffusion is the controlling step, while chemical reaction modeling obeys the pseudo-second-order kinetic model. The SiNC-ES was reusable and good adsorption performance up to four adsorption cycles was observed. The practical capability of the SiNC-ES to adsorb Ag(I) was successfully demonstrated using an industrial waste solution in which a high removal efficiency was observed (η>90%). This demonstrates that the SiNC-ES can be a potential adsorbent for Ag(I) recovery from industrial wastes.