Simultaneous removal of Basic Blue41 and Basic Red46 dyes in binary aqueous systems via activated carbon from palm bio-waste: Optimization by central composite design, equilibrium, kinetic, and thermodynamic studies

In this work, palm Bio-waste derived activated carbon (AC) was synthesized by chemical activation method and characterized via Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), Field Emission-Scanning Electron microscopy(FE-SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area and zeta potential measurement. The impact of variables such as adsorbing mass value, contact time, and initial concentration of 2-[N-ethyl-4-[(6-methoxy-3-methyl-1,3-benzothiazol-3-ium-2-yl)diazenyl]anilino]ethanol methyl sulfate (Basic Blue 41), and N-benzyl-4-[(1,4-dimethyl-1,5-dihydro-1,2,4-triazol-1-ium-5-yl)diazenyl]-N-methyl aniline bromide (Basic Red 46) on the removal percentages of Basic Blue 41 and Basic Red 46 dyes were simultaneously studied using central composite design (CCD) and response surface methodology (RSM). In individual solutions, the adsorption process fitted well with Langmuir isotherm and pseudo-second-order kinetic models with the maximum adsorption capacities (qm) of 344.83 and 263.16 mg g⁻¹ for Basic Blue 41 and Basic Red 46, respectively. Extended Langmuir isotherm was used for the binary systems to calculate qm for Basic Blue 41 and Basic Red 46 as 271.81 and 127.23 mg g⁻¹, respectively. Therefore, it could be concluded that the mechanism of the adsorption procedure is monolayer, physical, spontaneous, endothermic, and more desirable at higher temperatures. Furthermore, Density functional theory (DFT) calculations revealed that Basic blue 41 has more electrophilicity, higher softness, and less HOMO–LUMO energy gap rather than Basic Red 46, which show a good agreement with the experimental result that proved the Basic Blue 41 has fast and more favored adsorption than Basic red 46 in binary solutions.