Advanced TiO₂-based catalysts for polypropylene degradation in aquatic media

Plastics are polluting our environment and oceans with a large number and variety of organic and inorganic compounds that arise as a consequence of the current industrial development. Every year we release to the environment millions of tons of plastics whose total elimination may take centuries. The exponential increase in the production of this material is causing a serious environmental problem, resulting in the generation of a large amount of this waste. Microplastics (MPs) are released into the environment in different ways, but one of the most important is through effluents from wastewater treatment plants, since no specific method is used to eliminate or degrade these MPs before they are discharged into the environment. Polypropylene (PP), together with low-density polyethylene (PE), are the most common MPs found in the environment, being released in an amount of approximately 112 million tons per year. Three catalysts, ZnO/TiO₂, CeO₂/TiO₂ and ZnO-CeO₂/TiO₂, were synthesized using the incipient wetness impregnation technique and tested under UV-A and UV-B irradiation for the degradation of polypropylene (PP) particles. A degradation of 6.6 ± 1.6 % of MP area in wastewater was obtained, slightly lower than the 8.4 ± 1.0 % observed with ultrapure water, likely due to the presence of organic matter and other compounds in the Waste Water Treatment Plant (WWTP) outlet. Additionally, toxicity assays using Phaeodactylum tricornutum revealed significant differences among treatments. The ZnO-CeO₂/TiO₂ catalyst resulted in lower growth inhibition compared to ZnO/TiO₂, which showed toxicity levels similar to those of UV-aged PP-MPs without catalyst, highlighting the role of catalyst composition in modulating the environmental toxicity of degraded microplastics.