Green synthesis of zinc oxide nanoparticles using cottonseed cake extract: Effect of different synthesis conditions on structural, optical and biological properties

Green synthesis of nanoparticles using plant resources has gained increasing research attention, as it is eco-friendly and more advantageous than conventional synthesis processes, and it also enables sustainable biomass valorization. This research explores the use of cottonseed cake, a byproduct of cotton oil industries rich in biopolymers and bioactive compounds, for the green synthesis of ZnO nanoparticles. The properties of nanoparticles synthesized at different CSCE concentrations (45, 60, and 75% v/v), under room temperature, high temperature (65 °C), and ultrasound treatment conditions (50% amplitude, 30 min) were also investigated. The synthesized nanoparticles were characterized by various techniques, such as UV–visible spectroscopy, FTIR, XRD, FESEM, TEM, EDAX, Raman spectroscopy, photoluminescence spectroscopy, DLS, zeta potential, and BET analysis to analyze their structural and optical properties. UV absorbance in the 250–300 nm range and XRD phase analysis confirmed the formation of ZnO nanoparticles with a crystalline wurtzite structure. FESEM revealed that the nanoparticles were spherical to irregular in shape with an average size of 60 nm. Raman and photoluminescence spectra have shown the defect states and photocatalytic properties of ZnO nanoparticles, which varied according to the synthesis conditions. The nanoparticles also exhibited antioxidant activity and significant antimicrobial potential against both Gram-positive and Gram-negative bacteria. The cottonseed cake extract potentially acted as a capping, reducing, and stabilizing agent during nanoparticle synthesis. The findings demonstrate that synthesis conditions significantly affect the properties of ZnO nanoparticles, making it possible to tailor their properties for applications in diverse fields such as environmental, medicinal, and electronic applications.