Temperature based adsorption studies of Cr(vi) using p-toluidine formaldehyde resin coated silica material

Abstract

In the present investigation, a new adsorbent has been developed by coating p-toluidine formaldehyde resin (PTFR) on silica gel (mass ratio of PTFR/silica 1 : 10). It was characterized using FT-IR, NMR, SEM, TGA and BET instruments to represent the functionality of the material. A detailed investigation on adsorption of Cr(VI) with the prepared adsorbent was performed at different temperatures. The adsorption process was evaluated on the basis of various parameters, such as pH, adsorbent dose, concentration of Cr(VI) and contact time. The Cr(VI) concentration was measured by UV-Vis spectrophotometer and ion chromatograph. It was observed that the HCrO₄⁻ gets adsorbed on the ammonium ions (–NH₃⁺) of PTFR due to electrostatic interaction. The methyl group presenting at the para-position of the benzene ring exerts an inductive effect on the nitrogen atom of the amine group that in turn enhances protonation in the acidic medium. The maximum adsorption capacities of Cr(VI) achieved were 40.0, 41.67 and 43.47 mg g⁻¹ at 303, 313 and 323 K, respectively. The adsorption followed both Langmuir and Freundlich isotherm models. The kinetics was pseudo second order and the thermodynamic parameters, such as ΔH°, ΔS° and ΔG°, analyzed at different temperatures, indicate that the adsorption process was spontaneous and endothermic at high temperature. The desorption of Cr(VI) from the adsorbent was carried out using 0.2 N NaOH at room temperature, and the complete recovery of Cr(VI) was confirmed by ion chromatograph.