Impurity element doping is extensively taken as one of the most efficient strategies to regulate the electronic structure as well as the rate of photogenerated charge separation of photocatalysts. Herein, a one-pot hydrothermal synthesis process was exploited to obtain La-doped ZnIn₂S₄ microspheres, aiming at gaining insight into the role that doping ions played in the improvement of pollutant photodegradation. Systematical characterization means, comprising of X–ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and Raman spectra, combination with high-resolution transmission electron microscopy (HRTEM), were employed to in depth reveal the concomitancy of La ions and ZnIn₂S₄ crystal lattice. The results showed that the La-doped ZnIn₂S₄ samples exhibited a slightly wider and stronger spectral absorption than pristine ZnIn₂S₄; and the specific surface area of doped ZnIn₂S₄ samples was a bit larger. The La-doped ZnIn₂S₄ electrodes showed improved photocurrent response, and the photocurrent density reached a maximum value at La content of 1.5 wt%. As expected, La-doped ZnIn₂S₄ samples exhibited a remarkable enhancement of photocatalytic behaviour toward the photodegradation of tetracycline hydrochloride (TCH) and methyl orange (MO). The prominently enhanced photoactivity of doped ZnIn₂S₄ samples was due to the synergistic effect of the elevated visible-light absorption ability and effective photogenerated charge carriers’ separation.

In this study, a novel Zn₂SnO₄/BiOBr hybrid photocatalyst was prepared via a mild hydrothermal synthesis combined with a chemical deposition method. The morphological structure, chemical composition, crystal structure, and optical properties were comprehensively characterized by a series of measurement techniques. Morphological observation showed that fine Zn₂SnO₄ nanoparticles were anchored on the nanoplate surface of a flower-like BiOBr 3D hierarchical structure. The experimental results of UV-vis diffuse reflection spectroscopy revealed that the visible-light absorptive capacity of the Zn₂SnO₄/BiOBr hybrid photocatalyst was promoted, as compared to that of pure Zn₂SnO₄. Evidenced by electro-negativity theoretical calculation, Zn₂SnO₄ and BiOBr possessed matched band edges for accelerating photogenerated charge separation at the interface. The Zn₂SnO₄/BiOBr hybrid photocatalyst exhibited enhanced photocatalytic performance in the degradation of Rhodamine B (RhB) under visible light irradiation. According to the band energy structure and the experimental results, the enhanced photocatalytic performance was ascribed to the improved visible-light absorptive capacity and the contact interface between Zn₂SnO₄ nanoparticles and BiOBr nanoplates, being able to favor the prompt charge migration and suppress the recombination of photogenerated carriers in the hybrid system.

Improving the photocatalytic performance of multi-component photocatalysts through structural modulation and band alignment engineering has attracted great interest in the context of solar energy utilization and conversion. In our work, Zn₂SnO₄/SnO₂ hierarchical architectures comprising nanorod building block assemblies were first achieved via a facile solvothermal synthesis route with lysine and ethylenediamine (EDA) as directing agents, and then chemically etched in NaOH solution to enlarge the surface area and augment active sites. The etched Zn₂SnO₄/SnO₂ hierarchical architectures were further decorated by Cu₂O nanoparticles though an in situ chemical deposition method based on band alignment engineering. In comparison with unetched Zn₂SnO₄/SnO₂, the specific surface area of Zn₂SnO₄/SnO₂/Cu₂O hierarchical architectures became larger, and the responsive region and absorbance intensity became wider and higher in the whole visible-light range. Zn₂SnO₄/SnO₂/Cu₂O hybrid photocatalysts presented enormously improved visible-light photocatalytic behaviour for Rhodamine B (RhB) decomposition. The enhancement of photocatalytic behaviour was dominantly attributed to the synergy effect of the larger specific surface area, higher light absorption capacity, and more effective photo-induced charge carrier separation and migration. A proposed mechanism for the enormously promoted photocatalytic behaviour is brought forth on the basis of the energy-band structure combined with experimental results.