Recently, semiconducting metal oxide (SMO) gas sensors have attracted the attention of researchers for high conductivity, labile features by environment, low cost, easy preparation, etc. However, traditional SMOs have some defects such as higher operating temperature and lower response value, which greatly limit their application in the field of gas sensor. In this work, the carbon nitride decorated ball-flower like Co₃O₄ composite was successfully synthesized via a facile hydrothermal method, the composition and morphology of the as-synthesized samples were studied by the techniques of X-ray powder diffraction (XRD), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR) and N₂-sorption. As a consequence, the pure Co₃O₄ and the carbon nitride decorated Co₃O₄ both possess ball-flower like structure, and the as-synthesized carbon nitride decorated Co₃O₄ composite exhibits significant sensing properties to ethanol which is 1.6 times higher than that of pure Co₃O₄, furthermore, the composite possesses high selectivity and stability towards ethanol detection.

A novel ultrathin g-C₃N₄ nanosheet-modified BiOCl hierarchical flower-like plate heterostructure (abbreviated as BC/CN) was constructed via a thermal polymerization of urea precursor followed with hydrolysis route. The as-prepared samples were well characterized by various analytical techniques. The morphological observation showed that hierarchical flower-like BiOCl nanoplates were discretely anchored on the surface of ultra-thin C₃N₄ nanosheets. The photocatalytic performance of the as-prepared photocatalysts was evaluated by degradation of methylene blue (MB) under visible-light irradiation. The results showed that BC/CN photocatalyst exhibited enhanced photostability and photocatalytic performance in the degradation process. On the basis of experimental results and the analysis of band energy structure, it could be inferred that the enhanced photocatalytic performance of BC/CN photocatalyst was intimately related with the hybridization of hierarchical flower-like BiOCl nanoplates with ultrathin g-C₃N₄ nanosheets, which provided good adsorptive capacity, extended light absorption, suppressed the recombination of photo-generated electron–hole pairs, and facilitated charge transfer efficiently.

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.

Regardless of its good electron-transfer ability and chemical stability, pure Zn₂SnO₄ (ZSO) still has intrinsic deficiencies of a narrow spectral response region, poor absorption ability, and high photo-activated carrier recombination rate. Aiming to overcome the deficiencies above-mentioned, we designed a facile hydrothermal route for etching ZSO nanoparticles in a dilute acetic acid solution, through which efficient oxygen vacancy defect engineering was accomplished and SnO_2−x nanocrystals were obtained with an ultrafine particle size. In comparison with the untreated ZSO nanoparticles, the specific surface area of SnO_2−x nanocrystals was substantially enlarged, subsequently leading to the notable augmentation of active sites for the photo-degradation reaction. Aside from the above, it is worth noting that SnO_2−x nanocrystals were endowed with a broad spectral response, enhancing light absorption capacity and the photo-activated carrier transfer rate with the aid of oxygen vacancy defect engineering. Accordingly, SnO_2−x nanocrystals exhibited significantly enhanced photoactivity toward the degradation of the organic dye rhodamine B (RhB), which could be imputed to the synergistic effect of increasing active sites, intensified visible-light harvesting, and the separation rate of the photo-activated charge carrier caused by the oxygen vacancy defect engineering. In addition, these findings will inspire us to open up a novel pathway to design and prepare oxide compound photocatalysts modified by oxygen vacancy defects in pursuing excellent visible-light photoactivity.