Sand coated with graphene oxide-PVA matrix for aqueous Pb2+ adsorption: Insights from optimization and modeling of batch and continuous flow studies

Abstract

In the present study, a composite of graphene oxide-polyvinyl alcohol coated sand (GO-PVA@sand) was prepared and examined for adsorption of aqueous Lead ion (Pb2+) in batch and fixed-bed columns. The characterization of GO-PVA@sand revealed that GO-sheets were randomly immobilized into the PVA-matrix and formed a stable complex surrounding sands particles. And hence, preventing leaching of GO from the GO-PVA@sand and avoiding agglomeration of GO-PVA@sand inside the column that leads to no column chocking. The adsorption of Pb2+ onto GO-PVA@sand was endothermic in nature, attained equilibrium in ≤ 45 min, followed the pseudo-second-order kinetics, and the Langmuir adsorption isotherm with the maximum adsorption capacity of 8.25 mg/g. Moreover, the fixed-bed column study revealed that the adsorption capacity (qeq) decreased from 7.4 to 7.0 mg/g by increasing inlet flow rate from 5 to 15 mL/min because of drop in the contact time between Pb2+ and GO-PVA@sand. In contrast, the qeq increased from 7.2 to 7.6 mg/g, with an increase of bed-height from 2 to 6 cm, due to greater contact time and surface exposure. Besides increasing inlet concentration from 20 to 40 mg/L, the qeq increased from 7.2 to 8.0 mg/g, apparently because of the presence of a higher mass driving force. To understand the potential for process scale-up, breakthrough modeling was performed and found that the Thomas and Yoon-Nelson model best described the adsorption behavior. The post-adsorption characterization of GO-PVA@sand showed Pb2+ adsorbed through ion-exchange, cation-π, electrostatic interaction, and hydrogen bonding. The regeneration and reuse potential of the GO-PVA@sand up-to five adsorption-desorption cycles, signify its relevance in low-cost continuous water treatment.