# Reusable BiOI-Modified CuWO4 Heterojunction Films and Their Excellent Photocatalytic Oxidation Activity of Nanoplastics and Methylene Blue

## TL;DR

This paper presents a new photocatalytic material that efficiently degrades dyes and nanoplastics using a CuWO4 film modified with BiOI.

## Contribution

The novel contribution is the creation of a BiOI/CuWO4 heterojunction with enhanced photocatalytic activity for degrading nanoplastics and dyes.

## Key findings

- The BiOI/CuWO4 heterojunction increases light absorption and improves carrier separation, enhancing photocatalytic efficiency.
- The material degrades methylene blue 1.17 times faster than CuWO4 alone.
- It reduces the average size of polystyrene nanoplastics from 425 nm to 325 nm over 80 hours.

## Abstract

CuWO4 films were prepared on FTO glass substrates by the hydrothermal method. To improve their photocatalytic activity, the CuWO4 films were further modified with BiOI using the successive ionic layer adsorption and reaction (SILAR) method. Characterization results indicate that BiOI and CuWO4 achieved nanoscale mixing and formed a Type II p-n heterojunction. The heterojunction formation not only extends the light absorption threshold of CuWO4 from 530 nm to 660 nm but also enhances the light absorption capacity across the entire solar spectrum. More importantly, the heterojunction formation facilitates the separation and transfer of photogenerated carriers and inhibits the recombination of photogenerated electrons and holes, which is evidenced by the results of PL spectra, photocurrent density, and EIS spectra. Compared with individual CuWO4 films, the photocatalytic activity of BiOI/CuWO4 heterojunction films in degrading the organic dye MB is increased by up to 1.17 times. Additionally, BiOI/CuWO4 heterojunction films exhibit certain activity in the photocatalytic degradation of polystyrene (PS) nanoplastics and are capable of reducing the average particle size of nanoplastics from 425 nm to 325 nm within 80 h.