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.