Photocatalytic membranes for pharmaceutical removal: advancements and future directions

Abstract

Abstract Photocatalytic membrane reactors (PMRs) synergistically integrate photocatalysis and membrane filtration, offering a promising solution for the efficient degradation of pharmaceutical pollutants in water. This review explores the two primary PMR configurations suspended and immobilized photocatalyst systems highlighting their unique advantages and limitations. Suspended PMRs offer flexibility in catalyst loading and easy recovery but are prone to membrane fouling, catalyst aggregation, and higher operational costs. In contrast, immobilized PMRs reduce fouling and eliminate the need for catalyst recycling; however, they may face challenges such as catalyst leaching, reduced active surface exposure, and potential loss of photocatalytic efficiency over time. Key operational parameters-including light intensity, residence time, pH, photocatalyst loading, and initial contaminant concentration are critically examined for their influence on degradation efficiency achieving a stable flux of approximately 25 L·m⁻²·h⁻¹ during the removal of venlafaxine using Polyvinylidene Fluoride/g-C₃N₄ membranes. Recent advances in photocatalyst design, particularly doping strategies to extend visible-light absorption, are also highlighted; for example, N-Cu-doped TiO₂ achieved complete sulfamethoxazole removal with 89% TOC reduction. Mechanistic pathways for pharmaceutical degradation are critically reviewed, providing insights into photocatlytic oxidation. Finally, the review identifies current limitations and future research directions, including cost-effective membrane fabrication, reactor optimization, enhanced light harvesting, improved mineralization efficiency, and long-term stability. These developments are vital for practical implementation of PMRs in decentralized hospital wastewater treatment and solar-powered units in off-grid or resource-limited settings. Graphical Abstract