Synthesis of starch-g-poly (acrylic acid)/ZnSe quantum dot nanocomposite hydrogel, for effective dye adsorption and photocatalytic degradation: thermodynamic and kinetic studies

Quantum dot nanocomposite hydrogels have received much attention for designing highly efficient photocatalyst due to the stability of the quantum dots in the hydrogel network. In this study, ZnSe quantum dot nanocomposite hydrogel (ZnSe QD-NCH) was prepared based on starch and acrylic acid as an effective dye adsorbent and photocatalyst by free radical polymerization and subsequent loading of zinc and selenide ions. The structure of ZnSe QD-NCH was confirmed by various techniques, such as, Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and fluorescence analysis. The effects of various parameters on crystal violet (CV) adsorption were examined, including temperature, contact time, pH, initial dye concentration, and the amount of adsorbent. The best adsorption was obtained at 65 °C, 30 min, pH = 6, C 0 = 10 ppm, and 0.05 g dose of adsorbent. The photocatalytic activity of ZnSe QD-NCH was investigated in the presence of visible and ultraviolet light. The results demonstrated that removal of dye by ZnSe QD-NCH is 94.5%, 95.5%, and 98.5% in dark, visible, and UV light, respectively. The kinetic studies showed that dye adsorption follows the pseudo second-order kinetic model. The isotherm models of dye adsorption demonstrated that the adsorption behavior follows the Freundlich isotherm model. The negative Gibbs free energy also indicated that removal of CV is spontaneous. The reusability experiments showed that the adsorption of CV is more than 89% after 4 cycles. Graphic abstract