Bisphenol A Adsorption from Aqueous Solution Using Graphene Oxide-Alginate Beads

In this study, the potential of graphene oxide-alginate beads (GO-AB) as an adsorbent for bisphenol A (BPA) removal from aqueous solution was investigated. GO was first prepared via modified Hummers' techniques and an aerogel alginate bead with embedded GO was prepared using an extrusion dripping method, where calcium chloride was utilized as a curing agent. The physicochemical characteristics of GO-AB were investigated using XRD, FTIR, BET, TGA. The results revealed that crystal structure and the surface groups of GO and alginate were retained upon the formation of GO-AB. A batch adsorption testing was carried out as a function of pH (3, 7, and 9), contact time (up to 420 min) and initial concentration of BPA (50-200 mg center dot L-1). The adsorption rate was typically faster at the beginning of the adsorption process and started to level off after 180 min. AB and GO-AB had better adsorption performances at neutral condition (pH 7) than alkaline and acidic environments due to repulsive electrostatic interaction between BPA and the adsorbent surface's charge. The sorption kinetic data was observed fitted to the pseudo-second-order kinetics model (R-2 > 0.98) and obeyed the Freundlich isotherm model adsorption behaviour compared to Langmuir. However, the R-L value of Langmuir model is between 0 and 1, which implies a favourable adsorption process. The maximum BPA adsorption capacity for AB and GO-AB was found to be 250.00 and 384.62 mg center dot g(-1), respectively, indicating that GO-AB is a promising adsorbent for BPA removal from aqueous solution. In addition, the adsorption efficiency of GO-AB exhibited more than 80% in the six-consecutive adsorption-desorption cycles of experiments, further confirming the excellent reusability of GO-AB.