High-entropy oxides and alloys as emerging multifunctional nano-sized materials for photocatalytic degradation of organic pollutants

High-entropy materials (HEMs) including oxide versions like (CeGdHfPrZr)O₂ are emerging multifunctional materials with alluring properties and versatile applications across various fields, including environmental science. This review aims to pragmatically present a critical analysis of the latest findings on the photocatalytic application of HEMs for the degradation of different harmful organic pollutants in aqueous media. Notably, with over 70% photocatalytic degradation efficiency in the majority of published research, it can be inferred that HEMs are revolutionary in pollutant remediation. Furthermore, it was shown that spent HEMs may be readily recycled and retain over 70% efficiency while maintaining the original structural integrity for up to 2–20 cycles. Our analysis suggests that the synergy between the multi-metallic components that make up the HEMs, higher oxygen vacancies (OV), and lower e−/h⁺ recombination may be the reason for the exceptional efficiency and cyclic stability. Additionally, the study of the effect of co-existing ions demonstrated the great potential of HEMs for practical applications. Also, the electron trapping/radical-scavenging studies revealed that •O₂⁻ (which can facilitate demethylation/de-ethylation) is the biggest player in the photocatalytic degradation of various organic pollutants using HEMs, followed by •OH radicals and then h⁺.