Photodegradation of toxic malachite green dye by ZnO and ZnO/SiO2 nanocomposites under solar radiation: a green practice

ZnO/SiO2 nanocomposites (NCs) were synthesized and assessed for their ability to degrade the carcinogenic compound malachite green (MG) under collected sunlight, employing a parabolic solar collector for enhanced energy collection. The ZnO/SiO2 NCs and ZnO nanoparticles (NPs) underwent characterization through X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FT-IR), and UV-Visible spectroscopy. The XRD analysis confirmed the hexagonal wurtzite structure of ZnO NPs, with particle diameters ranging from 14 to 18 nm, while the nanocomposites exhibited sizes in the range of 14-19 nm. TEM images yielded an average particle size of 17 nm for ZnO NPs and 21 nm for NCs. The band gap energy of the NCs was measured at 3.30 eV, indicating a slight red shift compared to bulk ZnO (3.37 eV).Furthermore, BET surface area measurements unveiled a microporous structure in the nanocomposites, accompanied by an increased surface area. Kinetic studies revealed a pseudo-first-order reaction kinetics, demonstrating faster photodecomposition for the nanocomposites at an optimal catalyst concentration of 0.5 g per 100 ml under neutral pH conditions. Remarkably, the maximum photodegradation efficiency re ached an impressive 98.8% for ZnO/SiO2 NCs and 96.8% for ZnO NPs within a mere 40 minute exposure to collected sunlight. The utilization of a solar collector contributed to a significant 40% enhancement in photodegradation efficiency compared to natural sunlight. This study underscores the substantial improvement in the photodegradation efficiency of ZnO/SiO2 nanocomposites, highlighting their potential as heterogeneous photocatalysts that harness solar energy as a renewable and cost-effective resource.