Visible light-driven photocatalytic activity of ZnO-MnO₂/exfoliated vermiculite composite for cadmium removal

The present study delves into the efficient photocatalytic activity of ZnO-MnO₂/EV composite for cadmium removal under visible light exposure, addressing the significant threat posed by high cadmium concentrations in water. An eco-friendly approach for synthesizing ZnO-MnO₂ and ZnO-MnO₂/exfoliated vermiculite (ZnO-MnO₂/EV) composite is also discussed. Adjusting the band gap of ZnO nanomaterials is crucial in refining their optical properties. Utilizing aqueous floral extract as a reducing agent in synthesizing ZnO-MnO₂ nanoparticles enhances their photocatalytic efficiency under visible light. The composite material, ZnO-MnO₂/EV, is thoroughly characterized using various spectroscopic and microscopic techniques like scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Investigating different ratios of ZnO-MnO₂ and exfoliated vermiculite reveals an optimal ratio of 1:2 for maximal cadmium removal. Key factors such as initial pH, contact duration, cadmium (II) ion concentration, light intensity, temperature, and photocatalyst dose are analyzed to enhance removal efficiency. Based on the collected data, a plausible mechanism for removing cadmium by ZnO-MnO₂/EV is proposed. The study attains a remarkable cadmium removal efficiency of 94.5% for real wastewater under optimized conditions using visible light irradiation.