Optimization of photooxidative removal of p-nitrophenol in a spinning disc photoreactor using response surface methodology

Development of a new rotating photocatalytic reactor for the degradation of hazardous pollutants

The aim of this study was to develop a new rotating photocatalytic reactor operating in recirculation mode with light sources placed outside the photoreactor vessel. The photoreactor with cylindrical geometry was equipped with four artificial lamps used to simulate solar irradiation (2.4% UVB and 12% UVA; 300–700 nm). The photocatalyst was immobilized on abrasive material used as a support and placed on the central (inner) photoreactor tube, which was connected to a power-driven shaft that allowed rotation at a desired speed. A suitable modification of the commercial TiO2 P25 photocatalyst was carried out to reduce its band gap energy and electron-hole recombination and to extend the visible light response range of TiO2. The main task of this research was to apply the basic principles of process intensification methodology, i.e. to explore the influence of rotational hydrodynamics, which allows good access of reactants to the photocatalyst surface, good irradiation of the photocatalytic surface and reduction of mass transfer resistance, leading to increased process efficiency. The homemade photoreactor was used for the photocatalytic degradation of one of the major types of neonicotinoid insecticides, acetamiprid. The influence of various working conditions, such as initial solution pH, rotation speed, recirculation flow rate and initial concentration of acetamiprid on the photocatalytic degradation process was investigated. The optimum degradation conditions were found at a recirculation flow rate of 200 cm3 min−1 and a rotation speed of 200 rpm, indicating that the mass transfer process strongly contributes to the photocatalytic degradation rate at the conditions used in this study. The results obtained during the photocatalytic degradation of acetamiprid in a rotating photoreactor were compared with those obtained under similar operating conditions in a flat-plate photoreactor, and the corresponding conclusions were drawn based on the performed kinetic analysis.

Ecofriendly Green Synthesis of the ZnO-Doped CuO@Alg Bionanocomposite for Efficient Oxidative Degradation of p-Nitrophenol

In the present study, ecofriendly green synthesized ZnO/CuO nanorods were prepared by using the stabilizing and reducing characteristics of the alginate biopolymer. The bionanocomposite (BNC) material was characterized by various sophisticated analytical tools such as Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, transmission electron microscopy, UV-visible spectroscopy, differential scanning calorimetry, and the Brunauer-Emmett-Teller (BET) method. The composition of ZnO/CuO@Alg BNC was found to be C (16.16 ± 0.42%), O (42.26 ± 1.87%), Cu (31.96 ± 1.05%), and Zn (9.62 ± 0.48%), which also supports the approximate 3:1 ratio of Cu2+ and Zn2+ taken as the precursor. The nanocrystalline spinel ferrite was found to have a BET specific surface area of 19.24 m2 g-1 with a total pore volume of 0.075 cm3 g-1 and 1.45 eV as the band gap energy (E g). Further, the material was applied for the photodegradation of p-nitrophenol (PNP) under the advanced oxidative process (AOP) under visible sunlight irradiation. The visible light radiation was used for the degradation of PNP under pH 2 conditions and resulted in 98.38% of the photocatalytic efficiency of the ZnO/CuO@Alg catalyst within 137 min of irradiation time. The photocatalytic reaction was best defined by the pseudo-first-order kinetics which involves the adsorption of the PNP molecule on the surface of the catalyst, thereby demineralizing it in the presence of advanced active •OH radicals. The values of rate constant for the pseudo-first-order model (k 1) were calculated as 0.013, 0.016, 0.019, 0.021, and 0.023 min-1 with half-life periods of 53.31, 43.31, 36.47, 33.00, and 30.13 min for 10-50 mg L-1 PNP concentrations. The presence of t-butyl alcohol decreases the photocatalytic efficiency, which suggests that the degradation of PNP was accomplished by the •OH oxidative radical.