Enhancing Near-Infrared Absorption by Modulation the Intermediate Band of Cu–Fe–S Semiconductors for Boosting Photocatalytic Hydrogenation of Nitroarenes

Abstract

The trade-off between maximizing light harvesting efficiency and maintaining high photoredox potentials is still a persistent and fundamental challenge in the field of photocatalysis. Intermediate band semiconductors (IBSCs) offer a promising approach to address the challenge by introducing an additional energy level within the bandgap, enabling simultaneous absorption of low- and high-energy photons while preserving strong redox capabilities. Herein, three kinds of Cu–Fe–S IBSC nanocrystals, i.e., Cu₅FeS₄ nanodisks (NDs), CuFeS₂ NDs, and CuFeS₂ octahedrons (Octas), have been controllably synthesized and they exhibit full spectral absorption capability, especially in the near-infrared (NIR) region extending to a wavelength of over 2500 nm. Notably, the Fe content-dependent NIR absorption enhancement has been revealed, originating from the modulation of the IB position within the band, as confirmed by theoretical calculation. These IBSCs can achieve NIR and full-spectrum photocatalytic transformation of 3-nitrostyrene to 3-vinylaniline with excellent conversion and selectivity and also possess broad applicability for various nitrobenzene derivatives. Under full-spectrum irradiation, CuFeS₂ Octas exhibit a turnover frequency of up to 13.0 h^–1, surpassing most reported nonprecious metal-based photo- and thermocatalysts. This study provides insights into the design of the IBSCs with optimal absorption capability and photoredox potentials, further enhancing the performance of the IBSC-based photocatalysts.