Optimization of diclofenac sodium adsorption onto graphene nanosheets: capacity, kinetics, isotherms and removal

Recently, emerging contaminants have been studied with greater attention due to their growing presence in aquatic environments, medications being one of the major pollutants owing to their global consumption. Among the main pharmaceuticals detected, the anti-inflammatory diclofenac sodium (DS) is considered the most ecotoxic and features on the European list of priority substances for monitoring as part of Water Framework Directive 39/2013. Among the water treatment processes available, adsorption is a highly effective technical and economic alternative. As such, this study aimed to assess DS removal efficiency using graphene oxide (GO) as an adsorbent. DS was ana-lyzed using a central composite design, with four factors: diclofenac sodium concentration (DSC of 50 to 450 mg L-1), adsorbent concentration (ADSC of 0.2 to 5 g L-1), contact time (Ct of 5 to 45 min) and pH (5 to 9). The results confirmed the modeling of adsorption capacity, adsorbate removal, pseudo-first-order and pseudo-second-order kinetics, intraparticle diffusion, and Langmuir and Freundlich isotherms. DS demonstrated an affinity for adsorption onto GO nanosheets. Maximum adsorption capacity for GO was 669.50 mg g-1 (DSC of 450 mg L-1, ADSC of 0.2 g L-1, Ct of 34.3 min and pH 5) obtained by duplicate identification batches. The data also supported the creation of an equation that indicates the adsorbent dose needed for total DS removal (100%) from a solution.