CTAB-modified alkali-activated binder derived from Favia corals and glass waste: A novel bio-based adsorbent for effective removal of Mn(VII) ions from aqueous solutions

A combination of Favia corals (FC) and glass waste (GW) was alkali-activated and modified with cetyltrimethylammonium bromide (CTAB) to fabricate a novel (CTAB-FC/GW) bio-based adsorbent material. This adsorbent was successfully employed for the removal of Mn(VII) ions from aqueous solutions. The chemical composition of CTAB-FC/GW presented large quantities of calcium, oxygen, and silicon in the form of oxides which supports its application for being functionalized by CTAB that occurred through a chemical reaction between the surface oxygen groups of oxides with the silanol groups present on FC/GW structure. The physicochemical characterization technique data suggested that CTAB successfully modified the adsorbent structure. The CTAB-functionalization proved to be an excellent strategy for yielding a material with better adsorptive properties. At the optimum pH 3.0, the efficiency of CTAB-FC/GW in removing Mn(VII) ions was increased to 94 % by CTAB supporting as compared to 73 % of the untreated FC/GW binder. Conventional models were employed to fit the adsorption data in the 25–55 °C range, and the maximum capacities, according to the Langmuir equation, ranged from 171.95 to 225.1 mg/g. Furthermore, the number of Mn(VII) adsorbed per functional group, the density of CTAB-FC/GW active sites, the removal capacities at saturation, and the interaction energies were clarified using the steric and energetic parameters of the statistical double-layer adsorption model. The theoretical treatment revealed that different manganese states [e.g., Mn(II) and Mn(VII)] provided a multi-docking adsorption mechanism, which was mainly regulated by the silanol and hydroxyl functional groups of CTAB-FC/GW. The adsorption of Mn(VII) was endothermic and directed by physical electrostatic interactions and surface complexation. The macroscopic examination of the Mn(VII) adsorption system via three thermodynamic functions indicated that the adsorption process followed a spontaneous mechanism. The CTAB-FC/GW was found to be highly stable and suitable for reuse in wastewater treatment based on the regeneration results. Overall, the results suggested a novel technique for producing positively charged binders using coral limestone and solid wastes to be used as promising biosorbents in eliminating anionic contaminants, which further promotes environmental sustainability.