Novel aluminium (hydr) oxide-functionalized activated carbon derived from Raffia palm (Raphia hookeri) shells: Augmentation of its adsorptive properties for efficient fluoride uptake in aqueous media

In this study a novel activated carbon derived from Raffia palm shells was synthesized firstly by activating the precursor with phosphoric acid to produce Raffia Palm Shell Activated Carbon (RPSAC) and further functionalized by coating its surface with aluminium hydroxide to produce a composite called Aluminium Oxide-coated Raffia Palm Shell Activated Carbon (ACRPSAC). These adsorbents were extensively characterized and tested for fluoride adsorption in aqueous media using batch adsorption experiment in comparison with a commercially available activated carbon (CAC). ACRPSAC demonstrated excellent qualities and fluoride adsorption capacity as compared to RPSAC. SEM/EDX revealed that ACRPSAC developed both micro and meso-pores on its surface with BET-surface area and pore volume of 715.80 m²/g and 0.47 cm³/g respectively. FTIR and XRD proved that ACRPSAC was largely amorphous and had sufficient functionality for fluoride uptake in solution. Batch adsorption studies showed that the fluoride removal abilities were in the order of ACRPSAC > RPSAC > CAC with maximum Langmuir adsorption capacity of 4.10 > 2.26 > 2.24 mg/g. respectively. The experimental data was well described by the Langmuir (R² = 0.8802–0.9751) and the pseudo-second order kinetic (R² = 0.9974–0.9999) models, signifying that fluoride uptake by the adsorbents was a chemisorption process. Thermodynamic studies revealed that the process was spontaneous, endothermic and feasible for ACRPSAC and RPSAC but was non-spontaneous for CAC. It was concluded that ACRPSAC is an excellent activated carbon for eliminating fluoride from groundwater and can be further studied for its commercialization.