Methylparaben Removal using Microwave Assisted Activated Carbon: a Comparative Study

Abstract

The presence of methylparaben (MP) in water sources raises concerns due to its persistence and potential adverse effects on human health and aquatic ecosystems. This study evaluates the potential of microwave (MW) energy for the sustainable production of activated carbons (ACs) specifically designed for MP removal from water. KOH activation of sawdust from an invasive wood was employed to obtain an AC under pre-established conditions. For comparison, ACs previously developed by our team using the same precursor and solutions of KOH or H3PO4, as activating agents, with conventional and MW heating, along with a commercial sample, were analyzed. Adsorption kinetics was determined and properly described by the pseudo-second order rate model. Equilibrium adsorption tests revealed that the MW-assisted KOH-derived AC achieved the highest MP removal efficiency (>92%) despite having a lower BET surface area (1110 m² g-1) than those obtained by H3PO4 activation with MW heating (1297 m² g-1) and the commercial sample (1424 m² g-1). This superior performance was attributed to the higher content of surface basic functionalities (1.3 meq g-1), which are expected to enhance π–π interactions between MP molecules and the adsorbent surface. MP adsorption isotherms for all the ACs were represented by the Langmuir, Freundlich, Langmuir-Freundlich, and Khan models, with the latter one offering the best fit. It predicted the highest adsorption capacity (1.3 mmol g-1) and affinity (303.0 mmol L-1) for the AC developed in the present study. Additionally, competitive adsorption tests using a binary equimolar solution of MP and sodium diclofenac highlighted the selectivity and efficiency of the MW-assisted KOH derived AC. Despite the presence of competitive effects, it maintained a superior removal efficiency for MP. These findings emphasize the feasibility of MW-assisted KOH activation as a promising and sustainable process for developing ACs with high adsorption capacities, particularly for MP removal from water.