This paper aims to review the recent works on the photocatalytic degradation of organic pollutants in the presence of nanophotocatalyst. In this regard the effects of operation parameters which could influence the photocatalytic degradation of organic pollutants (such as catalyst preparation method, initial concentration of organic pollutants, presence of doping, catalyst loading, calcinations temperature, pH, presence of oxidants, UV intensity, temperature, and presence of supports) are discussed. Recent research suggests that the parameters mentioned above have great influence on the photocatalytic activity of prepared nanocatalyst. Also, the general mechanism of photocatalytic degradation and some recent synthesis methods are discussed here.

Cost of biodiesel produced from virgin vegetable oil through transesterification is higher than that of fossil fuel, because of high raw material cost. To minimize the biofuel cost, in recent days waste cooking oil was used as feedstock. Catalysts used in this process are usually acids, base, and lipase. Since lipase catalysts are much expensive, the usage of lipase in biodiesel production is limited. In most cases, NaOH is used as alkaline catalyst, because of its low cost and higher reaction rate. In the case of waste cooking oil containing high percentage of free fatty acid, alkaline catalyst reacts with free fatty acid and forms soap by saponification reaction. Also, it reduces the biodiesel conversions. In order to reduce the level of fatty acid content, waste cooking oil is pretreated with acid catalyst to undergo esterification reaction, which also requires high operating conditions. In this review paper, various parameters influencing the process of biofuel production such as reaction rate, catalyst concentration, temperature, stirrer speed, catalyst type, alcohol used, alcohol to oil ratio, free fatty acid content, and water content have been summarized.

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Novel polyvinyl pyrrolidone capped pure, Ag (1-3%) and Cu doped (1-3%) zinc oxide (ZnO) nanoparticles (NPs) were successfully synthesized via the co-precipitation method. The synthesized NPs were characterized by UV-visible spectrophotometry, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and field emission scanning electron microscopy (FE-SEM). Compared to pure ZnO, the absorption bands of Ag and Cu doped ZnO NPs were shifted and, further, the band gap energy was also decreased which confirms the incorporation of Ag and Cu into the ZnO lattice. The XRD diffraction peak confirms that all the synthesized compounds are found to be of highly crystalline hexagonal wurtzite structure. In addition, the presence of Ag and Cu in the ZnO NPs was further evidenced from EDS analysis. FE-SEM images established the morphology of the doped ZnO NPs which was not affected by the addition of Ag and Cu. The photocatalytic activity of undoped, Ag doped (1-3%) and Cu doped (1-3%) ZnO NPs were tested with brilliant green dye under UV irradiation. Degradation study reveals that doping has a distinct effect on the photocatalytic behavior of ZnO NPs. In addition to that, kinetic, thermodynamic and reusability studies have been performed for the 2% Ag doped ZnO NPs.