A Hybrid Photo-Catalytic Approach Utilizing Oleic Acid-Capped ZnO Nanoparticles for the Treatment of Wastewater Containing Reactive Dyes

In pursuit of overcoming Fenton’s oxidation limitations in wastewater treatment, an introduction of heterogeneous photocatalyst is developed. In this regard, the current work is introducing ZnO nanocrystals that were successfully prepared by thermal decomposition technique and then capped with oleic acid (OA). The synthesized ZnO-OA and the pristine ZnO were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM). Then, the study introduces the application of such materials in advanced oxidation processes, i.e. Fenton's reaction to treat dye-containing wastewater. Synthetic wastewater that prepared using Reactive Blue 4 (RB4) is used as a simulated textile wastewater effluent. Fenton’s oxidation is applied, and the system parameters were assessed using the modified Fenton’s system. The synthesized samples of ZnO are characterized by a recognized wurtzite hexagonal structure. Modifying the surface of ZnO with oleic acid (OA) led to an increase in crystallite size, lattice parameters, and cell volume. These modifications are linked to the efficient capping of ZnO nanoparticles by OA, which further improved the dispersion of the nanoparticles, as demonstrated by SEM imaging. The optimum conditions of ZnO and ZnO-OA synthesized modified Fenton composites showed 400, 40 mg/L for H2O2 and catalyst respectively, at pH 3.0 within 90 min under UV irradiation for maximal dye oxidation reached 93%. The catalytic performance at its optimal circumstances was in accordance with a pseudo-second-order kinetics model for both ZnO-OA and the pristine ZnO based Fenton’s systems. Also, the thermodynamic parameters were also checked and the values settled that both Fenton systems are spontaneous in nature, proceeds at a low energy barrier condition (10.38 and 31.38 kJ/mol for ZnO-OA and the pristine ZnO based Fenton reaction, respectively).