Zinc oxide (ZnO) hexagonal prisms with unique nanostructures are successfully synthesized via a simple hydrothermal method with the assistance of polyethylene glycol (PEG). Further studies demonstrated that dissolved PEG played a critical role in adjusting the exposed proportion of {0001} facets and high-index facets. By increasing the amount of PEG, we successfully reduced the exposed proportion of {0001} facets and increased the exposed proportion of high-index facets. The morphology and the properties of ZnO hexagonal prisms were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller N₂ gas adsorption–desorption isotherms, and photoluminescence (PL) spectra. The photocatalytic activity of the ZnO hexagonal prisms was investigated by photocatalytic degradation of methylene blue (MB) aqueous solution under UV-vis light irradiation. Results showed that the ZnO hexagonal prism samples with a high percentage of exposed high-index facets exhibited superior photocatalytic activity. The idea that adjusting the proportion of different facets to enhance the photocatalytic activity of ZnO samples is a meaningful study.

The construction of heterojunctions can effectively inhibit the rapid recombination of photogenerated electrons and holes in photocatalysts and offers great potential for pollutant degradation. In this study, a Z-scheme heterojunction g-C₃N₄/WO₃ photocatalyst was synthesized using a combination of hydrothermal and calcination methods. The photocatalytic degradation performance was tested under visible light; the degradation efficiency of Rh B reached 97.9% within 15 min and that of TC-HCl reached 93.3% within 180 min. The excellent photocatalytic performance of g-C₃N₄/WO₃ composites can be attributed to the improved absorption of visible light, the increase in surface area, and the effective separation of photogenerated electron–hole pairs. In addition, after four cycles of experiments, the photocatalytic performance of g-C₃N₄/WO₃ did not decrease obviously, remaining at 97.8%, which proved that the g-C₃N₄/WO₃ heterojunction had high stability and reusability. The active radical capture experiment confirmed that h⁺ and ·O₂⁻ played a leading role in the photocatalytic degradation. The Z-scheme heterojunction g-C₃N₄/WO₃ designed and synthesized in this study is expected to become an efficient photocatalyst suitable for environmental pollution control.

ZnS is a promising photocatalyst in water purification, whereas its low photon efficiency and poor visible-light response restrict its application. Constructing composites may help solve these problems. In this work, Ag₂O was introduced to ZnS for the first time based on their energy band characteristics to form a novel ZnS/Ag₂O composite photocatalyst. In the model reaction of degrading methylene blue, the as-designed catalyst exhibited high catalytic activity among a series of ZnS-based composite photocatalysts under similar conditions. The catalytic rate constant was up to 0.138 min⁻¹, which is 27.4- and 15.6-times higher than those of ZnS and Ag₂O. This composite degraded 92.4% methylene blue in 50 min, while the ratios were 31.9% and 68.8% for ZnS and Ag₂O. Catalytic mechanism study based on photoluminescence and radical-scavenging experiments revealed that the enhanced photocatalytic activity was attributed to the composite structure of ZnS/Ag₂O. The structure not only facilitated the separation and transmission of photogenerated carriers but also extended the light response range of the catalyst. The as-designed ZnS/Ag₂O composite is promising in degrading organic pollutants in water.