An integrated experimental and computational study of modified biochar using biomass waste for the effective extraction of hazardous Cr(VI) from aqueous solutions

Using rice husk as a biomass waste, three adsorbents, rice husk ash (RHA), activated biochar (ABC), and sulfonated biochar (SBC), were synthesized and characterized to enhance the removal of hazardous chromium from aqueous solution. SEM, EDX, BET, FTIR, XRD, and XPS methods were used to analyze the surface characteristics of three adsorbents. To identify the ideal circumstances and examine the kinetics and isotherm behaviors, batch adsorption experiments were carried out. Pseudo second order illustrates the best description for the adsorption process, and the film diffusion or chemisorption is the rate-limiting step. The Freundlich isotherm model fits the adsorption process well with maximum adsorption capacities for RHA, ABC, and SBC are 50.51 mg/g, 146.1 mg/ g, and 104.17 mg/g, respectively. XPS and DFT calculations are used to understand and analyze their adsorption and interactions mechanism. According to XPS, the majority of the Cr that was attached to the adsorbents was Cr (III). The key mechanisms that drive Cr (VI) adsorption onto biochar include electrostatic attraction, reduction of Cr (VI) ions to Cr (III), and surface complexation. MEP analysis and adsorption locator analysis indicated that the protonated system is the main factor that enhances surface interaction through physical close contacts and Hbond formation where the calculated adsorption energies ranged from -8.169 to -6.419 KJ/mol. FMOs perturbation predicted higher stability in the adsorption system than separate modified graphene. The high adsorption capacity and regeneration performance for multiple cycles signify favorable and valuable adsorbents that would have a practical impact on wastewater treatment applications.