Advances in metal-organic frameworks for microplastic removal from aquatic environments: Mechanisms and performance insights

Metal-organic frameworks (MOFs) are highly effective materials for mitigating microplastic (MP) pollution in aquatic environments, owing to their exceptional porosity, large surface area, and selective affinity for pollutants. This study evaluates the performance of MOFs in MP removal by analyzing findings from over 65 studies, with a detailed focus on 20 key papers. Approximately 32 % of the studies investigated polystyrene (PS) MPs, and a similar percentage examined MP concentrations ranging from 10 to 1000 mg/L. Notably, 47 % of the studies reported that contact times exceeding 200 min significantly enhanced MP removal, while 36 % indicated optimal removal efficiencies at pH levels between 3 and 6. Furthermore, smaller MPs (<1 mu m) had higher removal efficiency due to increased surface interactions. Among MOFs, ZIF-67 achieved a 92.1 % removal efficiency for micrometer-sized PS MPs, while PSF/MIL-100(Fe) demonstrated a 98 % removal efficiency even after six reuse cycles. Cr-MOF had a remarkable adsorption capacity of 665 mg/g for PS MPs. Adsorption behaviors predominantly followed pseudo-first-order kinetics and Freundlich isotherms. Mechanistic analyses identified electrostatic attraction, pi-pi interactions, and acid-base interactions as the primary adsorption pathways of MPs onto MOFs. This study highlights the high efficiency and reusability of MOFs in microplastic removal. Future research should focus on scaling up MOF applications, optimizing synthesis methods to increase efficiency and reduce cost, and addressing the potential environmental impacts of large-scale MOF deployment.