Synthesis and performance evaluation of diphenylcarbazide functionalized mesoporous silica for selective removal of Cr(VI)

Abstract

We have successfully synthesized diphenylcarbazide functionalized mesoporous silica (DPC-SBA-15) for the selective removal of chromium (Cr(VI)) from aqueous solution. The structural characteristics and the surface modification of DPC-SBA-15 were investigated by small-angle XRD, SEM, HR-TEM, FTIR, and CHNS elemental analysis techniques. Results showed that the mesoporosity and long-range structural ordering of SBA-15 were well-maintained before and after the functionalization. Adsorption parameters such as pH, contact time, adsorbent dose, and initial concentrations were optimized under given conditions. DPC-SBA-15 revealed fast initial kinetics for Cr(VI) ions. Maximum removal up to 0.85 mmol/g was achieved in a short time of 20 min at pH range 1–3, S: L ratio of 4 g/L at 25 ᵒ C. Adsorption kinetics followed the pseudo-second-order and the adsorption process is mainly driven by chemisorption. Thermodynamic parameters showed the spontaneous and exothermic nature of the adsorption process. DPC-SBA-15 is capable to selectively remove Cr(VI) up to 86.3% from the aqueous system in the presence of alkali, alkaline, transition metal ions. Moreover, only a 5.6% decrease in removal efficiency was observed in a mixture of anionic species like phosphates and sulfates. • Pristine SBA-15 is successfully synthesized and functionalized with diphenylcarbazide (DPC) for the selective removal of Cr(VI). • DPC-SBA-15 showed faster initial and equilibrium adsorption kinetics (20 min) and good adsorption capacity even at low Cr(VI) concentrations. • Thermodynamic parameters showed the spontaneous and exothermic nature of the adsorption process. • DPC-SBA-15 is capable to selectively remove Cr(VI) up to 86.3% from the aqueous system in the presence of alkali, alkaline, and transition metal ions.