Fabrication of ZnO–Al2O3 inverse opals with atomic layer deposited Amorphous-Al2O3 for enhanced photocatalysis

Zinc oxide inverse opal (IO) has excellent photocatalytic properties, while Al2O3 has high chemical stability and negligible photocatalytic activity. However, combining these materials creates a crystalline ZnO-amorphous Al2O3 composite IO photonic crystal material with improved photocatalytic performance. In this study, ZnO IO and ZnO–Al2O3 combined structures were grown on self-assembled polystyrene (PS) nanosphere templates. ZnO layer was coated by thermal atomic layer deposition (TALD) in the pores of the template, and the template was then removed by annealing to yield a self-standing ZnO IO nanostructure. An ultra-thin film of Al2O3 was coated on the top of ZnO IO by TALD or plasma-enhanced ALD (PEALD). SEM imaging, Raman spectroscopy, and XRD analysis confirmed the presence of a periodically arranged, and wurtzite ZnO IO structure, with an amorphous Al2O3 layer on top. The UV–Vis results demonstrated distinctive absorption bands in both regions, with a notable increase in visible light absorption attributed to the slow photon effect within the near-bandgap region of the photonic materials. The ZnO/Al2O3-TALD photocatalyst exhibited enhanced photocatalytic performance in degrading various pollutants including methylene blue, rhodamine 6G, and 4-nitrophenol under visible light illumination compared to its pristine IO and PEALD composite counterparts. This is attributed to its periodic arrangement of the IO structure that acts as a photonic crystal, precisely controlling light interaction through photonic band gap manipulation and the slow photon effect. This tailored light manipulation within the visible spectrum significantly enhances photodegradation efficiency.