Diethyl sulfide modified silica and calix[4]pyrrole chelating resin: Synthesis and mercury(ii) cation retention properties

Abstract

Diethyl sulfide was chemically immobilized on the surface of silica gel (0.2–0.5 and 0.06 mm) for the formation of two newly synthesized silica gel phases (S1 and S2). A new chelating resin containing meso-tetramethyl-tetrakis-(thiophene)calix[4]pyrrole, CP(I), was also synthesized via the condensation of CP(I) with formaldehyde. The selection of this receptor is based on fundamental studies. Among the cations and anions considered, CP(I) interacts only with mercury(II). The functionalized silicas and the calixpyrrole resin were characterized by elemental analysis and mass spectrometry. The batch removal of metal cations (Hg2+, Pb2+ and Cd2+) by these materials from aqueous solutions was investigated. The uptake capacities of the silica based materials (S1 and S2) and calixpyrrole polymers (R1) for the Hg2+ cation were determined. The Hg(II) cation uptake data have been found to fit both, the Langmuir and Freundlich isotherms, and the coefficients indicated favorable uptake of this cation by these materials. Parameters such as the kinetics of the uptake process, pH, temperature, silica particle size and metal-ion concentration effects were evaluated. The data obtained clearly indicate that S1 has the higher uptake capability and faster retention rate for Hg(II) ions relative to S2 and R1. In a column operation, it was observed that the Hg2+ cation was effectively removed from aqueous solution by the calixpyrrole resin, R1. The percentage of recovery of this resin for the Hg2+ cation was found to be higher than 95%. The results obtained are compared with previously reported materials for mercury removal from aqueous solutions.