Experimental and DFT insights into the adsorption competition of two cationic dyes on activated carbon derived from walnut shells in aqueous solutions

The adsorption of cationic dyes is more significant in the binary system compared to the simple system, making it a crucial element in the study of complex matrices. Experimental and theoretical investigations were conducted on the adsorption of two cationic dyes, Malachite Green (MG) and Safranin (SAF), on activated carbon derived from walnut shells (AC-Ws) in both simple and binary systems. The impact of pH and the volume of adsorbent in the two systems were exclusively examined. The electrophilic potency of the dyes influenced elimination efficiency. According to the theoretical analysis, MG proves to be more electrophilic than SAF, and therefore displays greater interaction with surface sites in both simple and binary systems, resulting in removal rates of 93.12% and 78.41%, correspondingly. Best removal results were achieved at pH 7 for both systems. The Langmuir model is the most fitting method to explain the removal of dyes, both in simple and binary systems. According to the results of the kinetic study, the phenomenon obeys the pseudo-second order. The theoretical and experimental studies are in alignment, and it can be deduced that the decrease in the elimination efficiency of SAF in the binary system is due to the decreased acceptance of electrons when SAF is present.