Insightful performance analysis of fluoride ion adsorption onto graphene-zinc oxide composite beads and its prediction by Artificial Neural Network (ANN) modeling

In this present study, a facile, sustainable, eco-friendly, and low-cost material was developed using synthesized graphene-oxide (SGO) incorporated with zinc oxide (SGO/ZnO) and its adsorptive performance was compared with commercial graphene oxide (CGO) and synthesized graphene-oxide (SGO) for the removal of fluoride ion from aqueous environment. The materials were characterized using techniques such as Fourier transform spectroscopy (FTIR), Scanning electron microscopy coupled with energy dispersive X-Ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Zeta potentiometer, Brunauer–Emmett–Teller (BET) measurement, Transmission Electron Microscopy (TEM). The SEM analysis confirmed the existence of a spherical structure, smooth and agglomerated white particle in between the wrinkled GO sheet, demonstrating a successful synthesis of SGO/ZnO composite. The EDX analysis revealed the presence of carbon, zinc, and oxygen with no impurities. The successful incorporation of ZnO on SGO yielded a BET surface of 123 m²/g for SGO/ZnO, which is far greater than that of the separate SGO and ZnO with surface areas of 19 m²/g and 76 m²/g respectively. The batch studies revealed that the removal of fluoride ion by CGO, SGO, and SGO/ZnO was 89.4 %, 94.8 %, and 99.2 %. Also, the jovanovic isotherm model fitted well to the fluoride ion adsorption onto CGO, SGO, and SGO/ZnO suggesting a monolayer adsorption with mechanical contact possibility. The estimated adsorption capacities (Q_max) were 105.64, 116.37, and 188.60 mg/g for CGO, SGO, and SGO/ZnO, respectively. In addition, the adsorption kinetics study showed that the pseudo-second-order kinetic model suits the adsorption model, indicating the presence of an ionic interaction between the adsorbent functional groups and the fluoride ion. The adsorption thermodynamic analysis indicates that the adsorption process was spontaneous, endothermic, with strong affinity between the adsorbate and adsorbents. Furthermore, the regenerability and reusability analysis showed that about 39.5 %, 49.9 %, and 70.6 % of fluoride ion on CGO, SGO, and SGO/ZnO was removed after fifth desorption-adsorption cycles, suggesting that the SGO/ZnO was more stable. The interaction mechanism between SGO/ZnO and fluoride ion was governed primarily by pore-filling, hydrogen bonding, electrostatic attraction, and physical adsorption.