Synthesis and application of modified Litchi peel for removal of hexavalent chromium from aqueous solutions

In this study, the removal of Cr(VI) from aqueous solutions by modified Litchi peel (MLP) has been investigated. Fourier-transform infrared spectrophotometer (FTIR) and scanning electron microscopic analysis (SEM) were used to characterize the biosorbents. The main results are as follow: 1) the optimal pH condition and optimum dosage for the adsorption of Cr(VI) were found to be 1-4 and 8.0 g L− 1, respectively; 2) the adsorption process on Cr(VI) increased rapidly in 80 min and almost reached adsorption equilibrium in 100 min; 3) the adsorption of Cr(VI) increased with the increase of temperature. Furthermore, the Langmuir and Freudlich models were used to study the equilibrium process. It was found that the Langmuir model provided better correlation for the adsorption of Cr(VI) on MLP and Litchi peel (LP). The maximum adsorption at equilibrium for MLP is 9.55 mg g− 1 at 303 K, while for LP it is only 7.05 mg g− 1 at 303 K. Different kinetic models were used to analyze the kinetics of the adsorption. The pseudo-second-order model could better reflect the MLP adsorption kinetic process of Cr(VI). The thermodynamic parameters showed that the biosorption was endothermic, and there was an energy barrier for the adsorption of Cr(VI) on MLP. The present study demonstrated that MLP is an effective adsorbent for removing Cr(VI) from aqueous solutions.