Upcycling of easy separated Casuarina equisetifolia fruit waste as a biosorbent: tailoring the surface modification to enhance selective removal of cationic dye or simultaneously removal of cationic and anionic dyes

This study aimed at the valorization of the abundant and underutilized Casuarina equisetifolia fruit waste (CEFW) biomass as an intact easily separable biosorbent for the treatment of dye-polluted water. The intact CEFW was chemically modified to improve its selective biosorption of MB, or to simultaneously remove MB and MO. H2O2 treatment increased the surface functional groups, created pores, and enhanced the selective biosorption of MB. CTAB treatment introduced quaternary ammonium groups and enabled the simultaneously removal of MB and MO. The biosorption of MB by H2O2-treated CEFW was optimum at pH 6 and increased with the mass of the biosorbent. The pH can be adjusted to enhance the biosorption efficiency of the CTAB-treated CEFW toward MB or MO. pH 6 achieves balanced simultaneous removal of MB and MO. The kinetic and isotherm studies revealed that electrostatic interactions and chemisorption dominate the biosorption process which has multilayer character. The single and binary isotherm studies demonstrated that the co-existence of MB and MO enhances their removal. Overall, the modification of the CEFW can be tuned to remove anionic, cationic dyes or both simultaneously and synergistically. The low-cost and easy separation nominate the application of the intact CEFW for dyes removal from polluted water.