Ceramic ultrafiltration membrane with low palladium loading via atomic layer deposition for micropollutant degradation

Abstract

Catalytic ceramic membranes are regarded as a promising technology for removal of organic micropollutants (OMPs). However, excessive catalyst loading will decrease membrane flux and increase deposition costs, thus hindering practical application. In this work, ceramic ultrafiltration membranes were modified by atomic layer deposition to achieve a low loading of palladium (Pd) for OMP degradation. The Pd deposited on the membrane surface and within the pores was used to activate peroxymonosulfate (PMS) to induce reactive species (RS) for the degradation of four OMPs (benzotriazole, diclofenac, sotalol, and trimethoprim). The Pd-deposited membranes exhibited an almost complete degradation of the four OMPs at a high flux of 100 L/(m2 h). Notably, Pd confined within membrane nanopores induced a pronounced nano-confinement effect, enhancing degradation kinetics by up to three orders of magnitude compared to surface-deposited Pd, revealing a distinct catalytic mechanism governed by confined reaction environments. Varying RS can be generated from PMS activation by Pd-modified alumina membranes, but the dominant RS pathways were found to depend on the type of OMPs, providing new mechanistic insight into PMS activation in heterogeneous catalytic membrane systems. A high degradation efficacy was achieved at a pH of 7, while the PMS dosage (20–80 μM), anion (1 mM Cl¯, SO42¯, HCO3¯, or ClO¯), and natural substances in river water had a minor impact on the OMPs' degradation. However, considerably high salinity, e.g., as present in brine water, exhibited a negative impact on the degradation of certain OMPs. This study demonstrates that a robust and effective strategy for OMPs' degradation can be achieved by ceramic membranes with a low loading of catalysts, which shows strong potential for cost-effective and scalable application in water treatment.