Accelerated ageing method for the determination of photostability of polymer-based photocatalytic membranes

Photocatalytic membranes (PM) are promising for the removal of micropollutants from water. Limited photo stability of polymeric PM systems is an obstacle to widespread application where a lifetime of years is required, maintaining good filtration and photodegradation efficiencies during exposure to both ultraviolet light and reactive oxygen species. The monitoring of physicochemical properties with commonly available tools, combined with a proposed method to evaluate PM stability using accelerated ageing is reported. Three PMs based on combinations of support membranes (polyethersulphone - PES, polyvinylidene fluoride - PVDF) and photo catalysts (TiO2, palladium porphyrin). Accelerated ageing was implemented through intense UV-violet illumination (2223 W m � 2 of combined 365 nm and 405 nm) for 250 h. The PM photostability was evaluated by i) morphology and surface characteristics, ii) chemical composition, iii) optical properties, and iv) photo degradation of methylene blue (MB) dye. The three PMs exhibited distinct differences in photostability. The PVDF support membrane was stable, however, the degradation of hydrophilic additives led to TiO2 leaching and porphyrin exhibited limited stability due to photobleaching. TiO2-PVDF retained its initial MB removal performance after ageing, while TiO2-PES and porphyrin-PVDF had lower or completely depleted photocatalytic activity. The proposed experimental method realises photostability screening of PMs in a laboratory environment within a short period of time, allowing for early-stage weaknesses to be identified.

Automated summary

Photocatalytic membranes (PM) have potential for water pollutant removal, but limited photo stability of polymeric PM systems poses a challenge. A proposed method combining common tools and accelerated ageing was used to evaluate PM stability. Three PMs based on different support membranes (PES, PVDF) and photo catalysts (TiO2, Pd porphyrin) were tested under intense UV-violet illumination for 250 hours.