The development of a heterostructured semiconductor photocatalyst makes a significant advancement in catalytic technologies. Highly crystalline Bi₂S₃–ZnO nanosheets with a hierarchical structure have been successfully synthesized by a facile sonochemical process and characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and Brunauer–Emmett–Teller (BET) surface area measurements. X-ray powder diffraction (XRD) analysis reveals that the as synthesized product has an orthorhombic phase of Bi₂S₃ and a hexagonal wurtzite phase of ZnO. XPS analysis shows the presence of the elements Zn, O, Bi and S and their oxidation states. Bi₂S₃–ZnO has increased absorption in the UV region as well as in the visible region. This heterostructured nano catalyst has a higher photocatalytic activity for the degradation of Acid Black 1 (AB 1) under UV-A light than pure ZnO, Bi₂S₃ and commercial Degussa P25. The heterojunction in the Bi₂S₃–ZnO photocatalyst has led to low recombination rates of photoinduced electron–hole pairs and an enhanced photocatalytic activity. Bi₂S₃–ZnO is advantageous in AB 1 degradation because of its reusability and higher efficiency at neutral pH 7.

A metal doped coupled semiconductor oxide, Ag–ZnO–CdO was fabricated by a simple co-precipitation method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental mapping, high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). XRD and EDS reveal the presence of CdO and metallic Ag in the catalyst. FESEM shows a mixture of hexagonal nanosheets, nanoclusters and nanoparticles with a large number of cavities. HR-SEM and TEM images of the catalyst show that ZnO particles have pentagonal or hexagonal plate-like structure. Cadmium oxide and silver clusters are formed on the clear smooth surface of ZnO. Ag–ZnO–CdO has increased absorption in the UV and Visible region when compared to ZnO. This three component nanojunction system exhibited enhanced photocatalytic activity for the degradation of acid black 1 (AB 1) and acid violet 7 (AV 7) under sunlight far exceeding those of the single and two component systems. Ag–ZnO–CdO was found to be stable and reusable without appreciable loss of catalytic activity up to five runs. This metal doped coupled oxide shows increased hydrophobicity, when compared to CdO or ZnO. Our results provide new insights of the performance of a solar active photocatalyst with self-cleaning properties.

This article reports on recent developments in heterogeneous AOP processes such as photo-catalysis, Fenton-like process and catalytic ozonation. The principle, mechanism, and influence of experimental conditions on the degradation of pollutants in heterogeneous catalytic ozonation and the photocatalytic process were discussed. Introducing solid catalysts substantially increased the efficiency of the ozonation process by producing hydroxyl radicals in the degradation process. The different types of catalyst, catalyst dosage, solution pH, ozone flow rate, water matrix and catalytic reusability and stability are reported on here. The list of various semiconductor materials used as photocatalysts, their light absorption properties, various light sources and surface properties such as surface area, pore size and pore volume as a factor in the photocatalytic degradation of various pollutants are discussed. The review article also discussed the pollutants degraded using these three processes.