# Tailoring plasmonic size in Au/WO3 photonic crystals for photoelectrochemical water splitting and pharmaceutical degradation

## TL;DR

This paper shows how adjusting the size of gold nanoparticles in a structured WO3 material improves both water splitting and pollution cleanup.

## Contribution

The novel integration of plasmonic size effects with photonic crystal structures enhances photoelectrochemical performance.

## Key findings

- 20 nm Au NPs optimize photocurrent generation through near-field enhancement and carrier generation.
- 5 nm Au NPs show highest activity in ibuprofen degradation due to efficient electron transfer and Fermi level shift.

## Abstract

Integrating plasmonic nanoparticles (NPs) into semiconductor metal oxides and structuring them as photonic crystals have been two effective strategies to develop robust photo(electro)catalysts with improved light harvesting and suppressed electron–hole recombination. In this work, Au-decorated WO3 inverse opal photoanodes were engineered to synergistically exploit plasmonic, photonic, and charge transfer effects for enhanced photoelectrochemical water splitting and the degradation of pharmaceutical pollutants. The WO3 inverse opal scaffolds, fabricated via colloidal co-assembly, functioned as visible light photonic crystals, enabling slow photon effects by aligning their photonic band gap with the absorption edge of WO3 and the localized surface plasmon resonance (LSPR) of Au NPs. Au NPs of varying sizes (5–80 nm) were incorporated post-synthetically to tailor plasmonic behavior and band alignment at the Au–WO3 metal–semiconductor heterojunction. Photoelectrochemical measurements revealed optimal photocurrent generation for 20 nm Au NPs, driven by near-field enhancement and improved carrier generation, while 5 nm Au NPs exhibited the highest photoelectrocatalytic activity in ibuprofen degradation, facilitated by a favorable Fermi level shift and efficient interfacial electron transfer. This work highlights the importance of size-engineered plasmonic particles integrated into photonic crystal frameworks for the rational design of multifunctional photoelectrodes in solar energy conversion and environmental remediation.

Combination of plasmonic size-dependent near-field enhancement and electron transfer with slow photon effects in Au/WO3 inverse opal photoanodes boosts PEC and photoelectrocatalytic performance.