Heterogeneous Photocatalysis and Photocatalytic Membrane Reactors for Microplastic Removal, Degradation and Valorization

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Abstract
Microplastic (MP) pollution represents a major environmental challenge because of its persistence and widespread accumulation in aquatic and terrestrial ecosystems. This review critically examines current technologies for MP removal and degradation, with particular emphasis on heterogeneous photocatalysis and its integration into photocatalytic membrane reactors (PMRs). Biological, physicochemical and advanced oxidation processes—including adsorption, membrane bioreactors, electrocoagulation, flotation, advanced filtration, sol–gel technologies and photocatalytic systems—are analyzed in terms of mechanisms, advantages, limitations and remediation potential. The literature identifies heterogeneous photocatalysis as one of the most promising approaches for degrading recalcitrant polymers through the generation of reactive oxygen species. Recent advances in photocatalyst engineering have significantly enhanced the performance of TiO2-, ZnO-, WO3-, graphene-, CdS- and MOF-based materials. Particular attention is devoted to PMRs, which combine photocatalytic degradation with membrane separation, enabling continuous operation, efficient photocatalyst recovery, improved removal efficiency and reduced membrane fouling. The review also highlights plastic photoreforming as an emerging strategy for simultaneously converting plastic waste into hydrogen and other value-added chemicals. Overall, integrated photocatalytic membrane systems offer a promising and sustainable platform for large-scale MP remediation, although further research is needed to improve long-term stability, energy efficiency and industrial-scale implementation.

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