Ever-increasing environmental pollutions and water scarcity are highly challenging issues that pose formidable obstacles to human beings on all fronts. Hetero-photocatalytic methods which utilized semiconductors as photocatalysts are highly promising and green technologies for the degradation of recalcitrant organic pollutants which cannot be completely removed by conventional treatment processes. In the view of the current scenario, zinc oxide nanostructures have been demonstrated to be predominant photocatalyst candidates for photodegradation because of their cost-effectiveness, non-toxicity, strong oxidation capability, flexibility in synthesizing, earth-abundance nature, easy crystallization, and high performance in the absorption over an extensive fraction of solar spectrum in comparison with titanium dioxide. Nevertheless, bare zinc oxide possesses several intrinsic limitations, like high recombination rate of the photogenerated charge carriers, limited solar light application, photo corrosion, broad bandgap and limited visible light absorption. Moreover, photocatalysts separation from remediated solutions restricts their large-scale applications. In this review paper, the authors briefly discussed basic principles of the zinc oxide photocatalytic process besides various modifications such as coupling with low bandgap semiconductors like metal and non-metal doping, synthesizing with graphene oxide, or reduced graphene oxide and their integration in magnetic materials to successfully addressing aforesaid disconcerting challenges. Moreover, hybridized photocatalytic and membrane systems are explored. Finally, challenges and future research directions are proposed for giving profound and well-defined insights toward reaching fully exploited zinc oxide-based nanoparticles in the field of water and wastewater treatments. Manuscript profile

In this study, through the application of TiO2/ZnS as a novel nano photocatalyst, the degradation of AR18 in synthetic wastewater was explored. The nano photocatalyst was synthesized by the co-precipitation method and characterized by Scanning electron microscopy (SEM), Fourier transfer infrared (FTIR), and X-ray powder diffraction (XRD) techniques. The average size of ZnS/TiO2 nano photocatalyst was 79nm. For experimental design and statistical analysis of each factor including AR18 concentration, pH, catalyst dosage, and treatment time on the degradation rate of AR18 (response) by Central Composite Design (CCD) was used. The analysis of variance (ANOVA) demonstrates a second-order regression model with R2 = 0.9995, adjusted R2=0.9991, and predicted R2=0.9982) for the removal of AR18. The optimum conditions for each operating factor were as the following: AR18 concentration at 30 mg.L-1, catalyst dosage at 1.2 g.L-1, pH at 5, and treatment time at 120 min. In this condition, the actual and predicted AR18 removal was 94% and, 93.07%, respectively. Manuscript profile

The wastewater containing Tert- Butyl alcohol (TBA) contains water-soluble polymer discharged from different chemical and textile industries. In this study, through the application of the UV/ZnFe2O4 approach in a batch photoreactor, the decomposition of synthetic wastewater including TBA was investigated. The co-precipitation method was utilized for synthesizing the ZnFe2O4 nano photocatalyst. Using FTIR spectroscopy, XRD, and SEM images, the characterization of catalyst was ascertained. For evaluation and exploration of the stability of nano photocatalyst particles, the Zeta potential was utilized. The influence of different crucial factors including the concentration of catalyst, the initial dosage of contaminants, and pH, on the mineralization of TBA was studied. At optimal situations (pH at 6, 25 mg/l of TBA, and 0.9 g/l of catalyst) and after 120 min of remediation time, around 58% of Chemical Oxygen Demand (COD) and 93.5% of TBA was eliminated. The main reason for the generation of active radicals in the photocatalytic method is the electron-hole mechanism. According to the Langmuir Hinshelwood model, the kinetic of the TBA decomposition was elucidated hence, the half-life of the reaction and the apparent rate of the pseudo-first-order reaction, (t_(1/2)=35 min) and (K_app=1.98×10^(-2) min^(-1)) was obtained, respectively. Manuscript profile