The development of coupled semiconductor photocatalysts makes a significant advancement in catalytic functional materials. A new heterostructured Bi 2 O 3 −ZnO, synthesized by a simple hydrothermal−thermal decomposition method, exhibited higher photocatalytic activity for the degradation of Acid Black 1 (AB 1) under UV light than pure ZnO, Bi 2 O 3 , and commercial Degussa P25. X-ray powder diffraction analysis reveals that the as-synthesized product has the monoclinic lattice phase of Bi 2 O 3 and the hexagonal wurtzite phase of ZnO. HR-SEM images show that Bi 2 O 3 −ZnO has an ordered mixture of nanofiber and nanochain structures. This heterostructured Bi 2 O 3 −ZnO has increased UV absorption when compared with ZnO. The enhanced photocatalytic activity of Bi 2 O 3 −ZnO is attributed to the low recombination rates of photoinduced electron−hole pairs, caused by the vectorial transfer of electrons and holes between ZnO and Bi 2 O 3 . Higher efficiency at neutral pH 7 and reusability in the degradation of AB 1 makes Bi 2 O 3 −ZnO, a promising candidate for the photocatalytic treatment of dye effluent.

Development of coupled semiconductor oxides makes a significant advancement in catalytic functional materials. In this article, we report the preparation of nanobundle-shaped BiVO4–ZnO photocatalyst by a simple hydrothermal process followed by thermal decomposition. The photocatalyst was characterized by X-ray powder diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), and UV–vis diffuse reflectance spectroscopy (DRS). The XRD pattern confirmed formation of monoclinic scheelite BiVO4 and the hexagonal wurtzite structure of ZnO. HR-SEM images show nanobundle-like structure, and the size of the nanospheres ranges from 20 to 40 nm. BiVO4–ZnO has increased absorption in the UV and visible region when compared to ZnO. The catalytic activity of BiVO4–ZnO was evaluated by the photodegradation of Acid Violet 7 (AV 7), Evens Blue (EB), and Reactive Red 120 (RR 120). The results revealed that the photocatalytic activity of BiVO4–ZnO was much higher than that of ZnO, BiVO4, and TiO2–P25 under natural sunlight. BiVO4–ZnO is more advantageous than ZnO and BiVO4 in the degradation of AV 7, EB, and RR 120 because it has maximum efficiency at neutral pH 7. BiVO4–ZnO was found to be stable and reusable without appreciable loss of catalytic activity up to four consecutive cycles. The self-cleaning property of BiVO4–ZnO has been evaluated using contact angle measurements. Our results provide some new insights on the performance of solar active photocatalysts on environmental remediation.

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.

This article reports on recent developments in heterogeneous AOP processes such as photocatalysis, 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.

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