Effective sequestration of Cr (VI) from wastewater using nanocomposite of ZnO with cotton stalks biochar: modeling, kinetics, and reusability.

The disposal of chromium (Cr) containing wastewater in surface water bodies without prior treatment is a serious threat to humans, animals, and plants. A novel nanocomposite (CSB/ZnO) of cotton stalks biochar (CSB) with ZnO nanoparticles was synthesized for the removal of Cr (VI) ions from contaminated water at batch scale. The impact of adsorbent dosage (1-4 g/L), initial Cr (VI) levels (25-200 mg/L), pH (2-8), and interaction time (0-180 min) was assessed for the removal of Cr (VI) from contaminated water. The Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), and point of zero charge (PZC) characterization showed successful impregnation of ZnO particles on CSB with improved surface characteristics. The maximum adsorption (qmax) of CSB and CSB/ZnO was 54.95 and 107.53 mg Cr/g, respectively that is relatively higher than various previously studied adsorbents. The experimental isothermal data better fitted with the Freundlich model in comparison with other isotherm models while adsorption kinetics well corroborated with the pseudo-second-order model. The results revealed that doping of biochar with metallic nanoparticles (CSB/ZnO) proved very effective (99.6% at 50 mg/L) with high reusability (91%) after five adsorption/desorption cycles and seems a suitable strategy for the decontamination of Cr (VI) contaminated waters.