Abstract:
In recent years, biochar has gained popularity as green adsorbent when dealing with
hexavalent chromium ions in the water environment. Herein, we prepared biochar at
distinct pyrolysis temperatures, i.e., 300, 400, and 500 0C (denoted as CSB300, CSB400,
and CSB500, respectively), using cotton stalks as biomass, and we investigated its impact
on Cr (VI) removal. The characterization results based on SEM-EDS, BET, CHN, XRD,
and FTIR analysis showed that the surface area, surface morphology, and elemental and
functional group composition of CSB were considerably influenced by pyrolysis
temperature. Despite having the lowest surface area, CSB500 presented superior
adsorption performance. Batch sorption experiments with Cr (VI) solutions (20 mg/L)
showed the optimal removal conditions to be pH (2), contact time (2 hours), and biochar
dosage (3 g/L). Adsorption kinetics and isotherms were well defined by the Pseudo second
order and Freundlich model. The thermodynamic studies showed the spontaneous and
endothermic nature of the sorption process. The potential Cr (VI) removal mechanism
mainly involved electrostatic attraction followed by Cr (VI) reduction to Cr (III) and
complexation. Regeneration studies showed that the reusability aspect of the biochar could
be improved, while the selected interfering ions had an insignificant effect on CSB500
adsorption capacity.
