Enhanced capacity of thiol-functionalized sugarcane bagasse and rice husk biochars for arsenite sorption in aqueous solutions

Abstract Utilization of biowastes to produce biochars as sorbents to remove toxic elements from water represents an important pathway for aquatic ecosystem decontamination. Here we explored the significance of thiol-functionalization on sugarcane bagasse biochar (Th/SCB-BC) and rice husk biochar (Th/RH-BC) to enhance arsenite (As(III)) removal capacity from water and compared their efficiency with pristine biochars (SCB–BC and RH–BC). The maximum As(III) sorption was found on Th/SCB-BC and Th/RH-BC (2.88 and 2.51 mg g−1, respectively) compared to the SCB–BC and RH–BC (1.51 and 1.40 mg g−1). Relatively, greater percentage As(III) removal was observed with the Th/SCB–BC and Th/RH–BC (92% and 83%, respectively) at pH 7 compared to pristine SCB–BC and RH–BC (65% and 55%). Langmuir (R2 = 0.99) isotherm and pseudo–second order (R2 = 0.99) kinetic models provided the best fits to As(III) sorption data. Desorption experiments indicated that the regeneration ability of biochars was in the order of: Th/SCB–BC (88%) > Th/RH–BC (82%) > SCB–BC (77%) > RH–BC (69%) up to three sorption-desorption cycles. The FTIR spectroscopy and XPS results demonstrated that the thiol (S–H) surface functional groups were successfully grafted on the surface of biochars and enhanced As removal from water. Spectroscopic data indicated that functional groups, such as S–H, –OH, –COOH, C=O were involved in slightly enhanced As(III) sorption on thiol-engineered biochars. This study highlights that thiol-grafting on biochars, notably on SCB-BC, enhanced their ability to remove As from water, which can be used as an effective technique for the treatment of As from drinking water.