Water pollution poses a significant threat to both human health and ecosystem integrity. Chemical pollutants such as dyes and pesticides affect the water quality and endanger aquatic life. Among the methods for water purification from organic pollutants, photodegradation is certainly a valid technique to decrease such contaminants. In this work, pristine NiO, ZnO, and NiO-ZnO photocatalysts were synthesized by the homogeneous co-precipitation method. X-ray diffraction confirms the formation of a photocatalyst consisting of ZnO (Hexagonal) and NiO (Cubic) structures. The crystalline size was calculated by the Scherrer formula, which is 19 nm for the NiO-ZnO photocatalyst. The band gap measurements of the prepared samples were obtained using the Tauc Plot, equation which is 2.93 eV, 3.35 eV and 2.63 eV for NiO, ZnO, and NiO-ZnO photocatalysts, respectively. The photocatalytic performance of NiO-ZnO nanocomposite was evaluated through the degradation of Methylene Blue and Nile Blue dyes under sunlight, and Bentazon herbicide under a UV light. Photocatalyst degradation efficiency was 95% and 97% for Methylene Blue and Nile Blue in 220 min under sunlight while a degradation of 70% for Bentazon after 100 min under UV light source was found.

The removal of organic pollutants from water is significantly important as they have harmful effects on the ecosystem. Heterogeneous photocatalysis is a potential technique for the removal of organic pollutants from the wastewater. In this article, zinc oxide (ZnO) and samarium oxide (Sm₂O₃) nanoparticles and ZnO-Sm₂O₃ nanocomposite (ZS) were synthesized by the co-precipitation method. We report the bandgap engineering of zinc oxide (ZnO) by making a composite with samarium oxide (Sm₂O₃) to enhance the photocatalytic activity. The smaller optical energy bandgap of the ZS nanocomposite as compared to the individual oxide nanoparticles shows that it has a light absorption range from UV to natural light. The photodegradation of bentazon herbicide as a model pollutant has been investigated by using the prepared samples. The photocatalytic activity of the prepared sample against bentazon herbicide was carried out under UV light for 140 min. The degradation efficiency against bentazon of the prepared samples was ZS > ZnO > Sm₂O₃, respectively. The ZnO-Sm₂O₃ nanocomposite showed a higher photocatalytic performance against bentazon and achieved a 90% degradation efficiency under a UV light source in 140 min. The pseudo-first-order degradation kinetic was studied under different operational conditions, such as catalyst loading, initial pH and bentazon concentration, showing that the degradation rate of bentazon was strongly influenced by these operational parameters. The obtained optimization conditions for practical application were a catalyst loading of 20 mg, pH of solution equal to 7 and bentazon concentration of 5 ppm for ZS nanocomposite in 60 mL of contaminated water. Furthermore, based on the scavenger study, hydroxyl and superoxide radicals play major role in the degradation experiment. The obtained results show that ZS nanocomposite can be a good potential candidate for wastewater treatment.

Herbicides and dyes in wastewater are considered serious water pollutants. These water pollutants have harmful effects on the ecosystem and due to this, the degradation of these pollutants is very important. In this article, titanium dioxide (TiO₂) nanoparticles were synthesized by the sol–gel method and used as photocatalysts. TiO₂ powder was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and UV-Visible (UV-Vis) spectroscopy. The XRD analysis revealed the anatase phase for TiO₂. The SEM investigation showed that TiO₂ nanoparticles exhibit highly irregular block-shaped morphology. TiO₂ nanoparticles degrade the organic pollutants under UV as well as sunlight. The photocatalytic activity of such prepared catalyst was carried out in solutions of bentazon herbicide (BZ) and Nile blue dye (NB) and in the mixture of these pollutants, under UV and sunlight. The degradation rate of both BZ and NB was very high in individual solutions as well as in the combination of them. The obtained results show that TiO₂ photocatalyst is a potential candidate for the photocatalytic degradation of dyes and herbicides under UV and sunlight.