Achieving complete remediation of tetracycline contaminated water using a PVDF/δ-MnO2 photocatalytic membrane reactor

Abstract

This study presents the development and evaluation of a novel photocatalytic membrane reactor (PMR) engineered for the efficient removal of tetracycline (TC) from water. δ-Manganese dioxide (δ-MnO₂) nanoparticles with a distinctive flower-like morphology were synthesized and thoroughly characterized to confirm their structure and surface properties. Following this, poly(vinylidene difluoride) (PVDF) membranes were manufactured via wet immersion process and then modified by coating them with the δ-MnO₂ catalyst to impart photocatalytic functionality. Testing the modified membranes revealed improved performance in TC rejection, albeit with a trade-off in flux, which decreased due to increased frictional resistance with higher δ-MnO₂ loading. Notably, the membrane with the highest coating concentration (M5) achieved a rejection rate of 96.1 %. This study further explored the degradation mechanism of TC by δ-MnO₂ under UV light, revealing the generation of reactive oxygen species such as hydroxyl radicals (•OH) and singlet oxygen (¹O₂), as well as valence band holes, all of which played pivotal roles in the decomposition of TC. Liquid Chromatography-Mass Spectrometry (LC/MS) analysis of the retentates and permeates confirmed effective TC degradation, showing a proportional decrease in TC concentration and an increase in intermediate formation with higher δ-MnO₂ content. Moreover, LC/MS analysis of permeates from the M5 membrane indicated complete TC removal, achieving 100 % elimination from wastewater in the PMR system. This approach shows strong potential for water purification and removing pharmaceutical contaminants by combining membrane separation and photocatalytic degradation within the PMR system.