Photocatalytic degradation of hazardous Rhodamine B dye using sol-gel mediated ultrasonic hydrothermal synthesized of ZnO nanoparticles

The present study is focused on the sol-gel ultrasonic hydrothermal synthesis of zinc oxide (ZnO) nanoparticles and its application in the degradation of Rhodamine B (RhB) dye. ZnO nanoparticles were synthesized with varying temperatures at 90 °C, 190 °C and 550 °C. Zinc nitrate hexahydrate [Zn(NO3)2·6H2O] and potassium hydroxide were used to prepare ZnO nanoparticles and investigated using the X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and diffuse reflectance spectroscopy (DRS) for crystallinity, surface morphology, and band gap, respectively. Results obtained from XRD analysis shows that the synthesized ZnO nanoparticles are of hexagonal structure and crystalline in size ranged from the 21.1–32.41 nm. The effects of temperature show that the crystalline size of ZnO increased with increasing temperature and surface morphology investigated by FESEM. DRS used to calculate the band gap of nanoparticles shows that 3.26 eV at 90 °C, 3.25 eV at 190 °C and 3.23 eV at 550 °C. The optimal condition was determined using the response surface methodology (RSM) based Box Behnken design (BBD) method. We found that the ZnO material synthesized at 90 °C exhibits a smaller size, providing a larger surface area for photocatalytic degradation of the RhB dye. Energy is saved as it was synthesized at low temperatures. The maximum removal efficiency of Rohdamine B (RhB) dye (25 mg/L) obtained were 95% at optimized conditions i.e. pH 7, 2 g/L catalyst dose after 70 min of ultraviolet photocatalytic treatment. •Synthesis of ZnO nanoparticles by sol-gel ultrasonic hydrothermal method at various temperatures.•Photocatalytic degradation of Rhodamine B dye using ZnO nanoparticles was studied.•Influence of different parameter (pH, dose of catalyst, dye concentration, irradiation time) on degradation activity.•The degradation of Rhodamine B dye followed kinetics first order model.