Boosting visible-light photocatalytic degradation of polystyrene nanoplastics with immobilized CuxO obtained by anodization

Abstract

Plastics composed mainly of polystyrene polymer have become widely used materials in different industries. The poor disposition of these products and their interaction with the environment has caused their fragmentation into particles that reach a nanometric scale (≤1 µm), called nanoplastics (NPs), considered pollutants due to their effects on human health and capacity to absorb toxic-bioaccumulative substances. Currently, advanced oxidation processes have shown efficiency in removing emerging pollutants, making them promising alternatives to treat NPs. This study proposes photocatalytic degradation with visible light irradiation to mitigate the contamination produced by polystyrene nanoplastics (PS-NPs). Therefore, PS particles of ~ 350 nm were degraded using immobilized copper oxide semiconductors grown by the anodizing process for the first time. The anodization process considered two growth media (NH4F and NaOH), obtaining immobilized Cu2O/CuO semiconductors with different morphologies and a bandgap between 1.6 and 2 eV. The degradation of the nanoplastics was examined using several analytical methods such as TOC, ATR-FTIR, turbidity, and gas chromatography showing the presence of intermediates compounds with the carbonyl group, confirming the degradation of PS-NPs. The results showed that photocatalysis in visible light with copper oxide semiconductors promotes polymer chain scissions and reduces the concentration of PS-NPs up to 23%, representing six times more than the reductions achieved by photolysis. In addition, mineralization of up to 15% was achieved. Although contamination by nanoplastics involves many challenges, this study provides the basis for an alternative process that allows the mitigation of these nanoplastics using visible light.