Enhanced adsorption of MCPA pesticide using a novel sand/graphene oxide composite

Abstract

Developing graphene-based composites for mitigating water pollutants is crucial, as current composites often have limitations, including their specific adsorption behavior towards only one type of contaminant.Additionally, these existing composites are associated with high costs, challenging recovery processes, and potential toxicity to both the environment and human health. Multiple coated sand/graphene oxide composites (M-GO/S) present a promising solution to these challenges. In this study, we focused on investigating the adsorptive removal of the pesticide 2-methyl-4-chlorophenoxyacetic acid (MCPA) using M-GO/S composites. Additionally, we aimed to elucidate the underlying adsorption mechanism and develop an HPLC method for analyzing MCPA. The retention time for MCPA was determined to be 1.538 minutes. The optimal parameters for MCPA adsorption onto M-GO/S were established as a 75 mg/L MCPA concentration, a dosage of 0.05 g, and a contact period of 105 minutes at neutral pH. The isotherm studies indicate that it is challenging to distinctly classify the adsorption process using the Langmuir and Freundlich models, as they show similar R² values. This may be attributed to the likely occurrence of multilayered attachment of MCPA following an initial monolayer adsorption. The adsorption intensity (n) value of 0.625 further suggests that complex interactions are involved in MCPA adsorption, likely due to the surface complexity of the M-GO/S composite. Apart from that, the kinetics studies revealed that the rate-controlling step involves chemical adsorption between the surface of M-GO/S and MCPA. Chemical interactions arise through hydrogen bonding and critical interactions between the hydroxyl groups on M- GO/S and the aromatic rings of MCPA. M-GO/S is a promising candidate for the adsorptive removal of negatively charged pesticide molecules like MCPA. It outperforms activated carbon and sand in effectiveness, and it is more advantageous than graphene oxide due to its simple recovery process.