Heteroatom doped biochar-aluminosilicate composite as a green alternative for the removal of hazardous dyes: Functional characterization and modeling studies

Abstract

In this work, a novel nitrogen-doped biochar bentonite composite was synthesized by a single-pot co-pyrolysis method. Batch studies were conducted to evaluate the performance of the developed composite in eliminating synthetic dyes from the aqueous matrix. Energy dispersive X-ray spectroscopy analysis and field emission scanning electron microscopy imaging confirmed the N doping and bentonite impregnation into biochar. X-ray photoelectron spectroscopy analysis revealed that the N atoms were doped interstitially into the carbon matrix of biochar in the form of pyridinic and pyrrolic nitrogen. Simultaneous heteroatom doping and bentonite impregnation reduced the specific surface area to 41.721 m2 g−1 but improved the adsorption capacity of biochar for dye adsorption. Further experimental studies depicted that simultaneous bentonite impregnation and N doping into the biochar matrix is beneficial for direct blue-6 (DB-6) and methylene blue (MB) removal and maximum adsorption capacities of 53.17 mg. g−1 and 41.33 mg. g−1 were obtained for MB and DB-6, respectively, at varying conditions. Adsorption energetics of the dyes with the developed composite portrayed the spontaneity of the process through negative ΔG values. The Langmuir and Freundlich isotherm models fitted the best for MB and DB-6 adsorption. The monolayer adsorption capacity and favourability factor for MB and DB-6 adsorption were calculated to be 54.15 mg. g−1 and 0.217, respectively from the best-fitted isotherms. Based on density functional theory calculations and spectroscopic studies, major interactions governing the adsorption were predicted to be charge-based interactions, π-π interactions, H-bonding, and Lewis acid-base interactions.