Bandgap engineering of tetragonal phase CuFeS2 quantum dots via mixed-valence single-atomic Ag decoration for synergistic Cr(VI) reduction and RhB degradation

Bandgap engineering through single-atom site binding on semiconducting photocatalyst can boost the intrinsic activity, selectivity, carrier separation, and electron transport. Here, we report a mixed-valence Ag(0) and Ag(I) single atoms co-decorated semiconducting chalcopyrite quantum dots (Ag/CuFeS QDs) photocatalyst. It demonstrates efficient photocatalytic performances for specific organic dye (rhodamine B, denoted as RhB) as well as inorganic dye (Cr(VI)) removal in water under natural sunlight irradiation. The RhB degradation and Cr(VI) removal efficiencies by Ag/CuFeS QDs were 3.55 and 6.75 times higher than those of the naked CuFeS QDs at their optimal pH conditions, respectively. Besides, in a mixture of RhB and Cr(VI) solution under neutral condition, the removal ratio has been elevated from 30.2% to 79.4% for Cr(VI), and from 95.2% to 97.3% for RhB degradation by using Ag/CuFeS QDs after 2 h sunlight illumination. The intrinsic mechanism for the photocatalytic performance improvement is attributed to the narrow bandgap of the single-atomic Ag(I) anchored CuFeS QDs, which engineers the electronic structure as well as expands the optical light response range. Significantly, the highly active Ag(0)/CuFeS and Ag(I)/CuFeS effectively improve the separation efficiency of the carriers, thus enhancing the photocatalytic performances. This work presents a highly efficient single atom/QDs photocatalyst, constructed through bandgap engineering via mixed-valence single noble metal atoms binding on semiconducting QDs. It paves the way for developing high-efficiency single-atom photocatalysts for complex pollutions removal in dyeing wastewater environment.