Selective capture of silver ions from aqueous solution by series of azole derivatives-functionalized silica nanosheets

Abstract

The introduction of bifunctional groups into low-cost adsorbents for selective adsorption of Ag(I) through synergistic effect will have a profound impact on the recovery of precious metals. Organo silica nanosheets (organo-SiNSs) functionalized by series of azole derivatives (2-mercaptoimidazole (MI), 2-mercaptobenzimidazole (MBT) and 1H-1,2,4-triazole-3-thiol (MTT)), are fabricated and employed for selective removal of Ag(I). The structures of the organo-SiNSs are investigated using several characterization methods. The results of batch adsorption experiments display that the maximum adsorption amounts are 70.3, 103.2 and 139.5 mg·g−1 on MI-SiNSs, MBI-SiNSs and MTT-SiNSs for Ag(I) ions, and reach rapid equilibrium within 10–30 min. The adsorption processes are chemisorption and fit pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Notably, MTT-SiNSs is greatly selective for Ag(I) in multicomponent system, and the distribution coefficient value of Ag(I) ions reaches 2331.26 ml·g−1. The reusability of organo-SiNSs is verified by four cycles of regeneration tests with 0.1 mol·L–1 HNO3 as the eluent. A combination of experimental, structural along with theoretical analysis is conducted to proclaim the structure-adsorptivity relationship: (i) The adsorption mechanisms are attributed to complexation. (ii) The amino group and sulfhydryl group of MTT-SiNSs as well as MBI-SiNSs may have synergistic impacts on Ag(I) capture. (iii) The differences in adsorption behavior and selectivity of the three organo-SiNSs are mainly related to the form of function groups, charge density and steric hindrance of adsorbent. This work not only sheds light on the promise of functionalized organo-SiNSs for the rapid and selective removal/enrichment of Ag(I) ions in complex water systems, but also provides new insights for designing cost-effective SiNSs-based adsorbents.