Scalable Graphene Oxide Composite for Cadmium Adsorption in Batch and Fixed-Bed Column Studies

Graphene-oxide (GO) based nanomaterials have been of tremendous interest for water pollutant removal in the past few decades. However, the high colloidal stability of GO limited its application potential to batch adsorption only because of its high pore-clogging nature and difficulty in post-treatment recovery when used as packing material in fixed-bed columns in continuous flow treatment. This work focuses on a facile approach for coating GO onto silica sand (SiS) by employing Polyvinyl-Alcohol (PVA) as adjoining material to form a stable SiS/PVA-GO composite. The spectroscopic and microscopic characterization revealed a randomly intercalated PVA-GO sheets matrix, uniformly wrapped onto the sand surface and forming interconnected pores. The batch adsorption of Cd2+ by SiS/PVA-GO followed the Pseudo-second-order kinetics and Freundlich isotherm. The maximum batch and fixed-bed-column adsorption capacities were 3.70 and 5.80 mg/g, respectively. Additionally, Cd2+ removal efficacy in the column at a varying initial concentration (Co), flow rate (Q), and bed height (h) demonstrated that the Number of Bed Volumes (NBV) treated decreased from 114 to 38 and 229 to 25, with increasing Q from 5-15 mL/min and Co from 10-30 mg/L, respectively. Further, non-linear fitting of breakthrough curves using the Thomas, Yoon–Nelson, Bed-Depth-Service-Time, and Dose-Response models revealed a good correlation. The BSDT model fitting raises the scope for upscaling. The post-adsorption composite characterization using XPS, EDS, and SEM, revealed the predominant adsorption forces were electrostatic, cation-π, and ionic interaction. Overall, this study demonstrates the SiS/PVA-GO as a promising material in the direction of GO-based adsorbent for wastewater treatment.