Entropy-engineered 2D layered double hydroxides as efficient single-component visible-light photocatalysts for selective NOx removal

Abstract

Nitrogen oxides (NOx) remain critical urban pollutants, requiring efficient visible-light-driven photocatalysts for sustainable air purification. Herein, we propose a novel design strategy that integrates two-dimensional (2D) morphology and configurational entropy engineering in layered double hydroxides (LDHs), thereby enabling highly efficient visible-light photocatalysis without the need for heterojunctions or rare-earth elements. A series of multimetallic 2D LDHs was synthesised via a scalable co-precipitation–AMOST approach, incorporating Ni, Fe, and Zn into a MgAl-CO3 host lattice to generate medium- and high-entropy systems. Increasing compositional complexity induces electronic structure modulation, leading to significant band-gap narrowing (from 3.94 to ∼ 2.4–2.8 eV) and enhanced visible-light absorption. Under continuous-flow conditions (150 ppb NO, 40% RH), multimetallic LDHs outperform the parent material, with the medium-entropy MgNiAlFe LDH achieving optimal performance (∼ 48% NO removal with 100% selectivity). Mechanistic investigations combining PL, EPR, scavenger tests, XPS/UPS band alignment, and in situ DRIFTS reveal that entropy-driven electronic tuning enables cooperative generation of •OH and •O2− radicals, suppressing charge recombination and promoting selective NO oxidation. This work establishes entropy engineering in 2D LDHs as an effective and simple strategy for designing single-component visible-light photocatalysts, offering new opportunities for solar-driven air purification.