A highly efficient calix[4]arene based resin for the removal of azo dyes

The present study presents the adsorption behavior of p-tert-butyl-calix[4]arene based silica resin (4) for reactive black-5 (RB-5) and reactive red-45 (RR-45) azo dyes. The batchwise adsorption study was carried out to optimize various experimental parameters such as the effect of adsorbent dosage, pH, electrolyte, contact time, temperature and dye concentration. The maximum adsorption of RB-5 and RR-45 was achieved at pH 9 and pH 3, respectively. The kinetic studies revealed that the adsorption process followed the pseudo-second-order kinetic model. The positive and negative values of ∆H and ∆G demonstrated that the nature of adsorption process was endothermic and spontaneous. The adsorption behavior was analyzed by Langmuir and Freundlich isotherms. The values of correlation coefficients (R2) showed that the Freundlich isotherm model found to be best fit. Results of study showed that resin 4 proved to be highly effective for the removal of selected azo dyes.

Research Highlights
► Adsorption behavior of p-tert-butyl-calix[4]arene based silica resin for azo dyes.
► Azo dyes (i.e., RB-5 and RR-45) were used as adsorbate.
► Different parameters were optimized to evaluate adsorption performance of resin 4.
► Adsorption efficiency of resin 4 for selected azo dyes is highly pH dependent.
► The adsorption data were evaluated by adsorption isotherms.