Using Rice Bran Hydrogel Beads to Remove Dye from Aqueous Solutions

Appropriately disposing of and reusing waste is a major step in promoting environmentally sustainable development. Following the rise in environmental awareness, agricultural waste has been applied as a reusable organic resource and as a cost-efficient material for preparing hydrogel adsorbents. The present study combined rice bran with sodium alginate and chitosan to prepare two new types of hydrogel beads. The beads were then modified using simple methods, and their material characteristics were analyzed using a Fourier transform infrared spectroscope, a scanning electron microscope, and thermogravimetric analysis. Specifically, the effects of pH, adsorbent dosage, adsorption time, and adsorption temperature on the performance of the hydrogel beads in the adsorption of dyes with various properties were examined. The results revealed that the optimal conditions for the rice bran/alginate hydrogel beads to adsorb crystal violet were pH 5, a dosage of 30 mg, at 30 °C, for 6 h of adsorption; furthermore, the kinetic and isothermal adsorption data were found to be consistent with the pseudo-second-order model and the Freundlich isotherm model, respectively. The optimal conditions for the rice bran/chitosan hydrogel beads to adsorb reactive blue 4 were pH 3, a dosage of 40 mg, at 50 °C, for 7 h of adsorption, and the kinetic and isothermal adsorption data were consistent with the pseudo-first-order model and the Langmuir isotherm model, respectively. This study applied natural polymers and agricultural waste to prepare cost-efficient and environmentally friendly adsorbents, which satisfy today’s environmental protection trends and economic values because of their low environmental impact and favorable adsorptive and regenerative properties. They can be prepared without high-temperature and high-pressure processing, and can be recycled through the separation of water bodies using simple filter methods, thus substantially reducing energy and monetary costs.