Valorization of rice husk through the production of a hybrid nanocomposite (AC/NS/ZV-Cu) and its application as a zero-waste adsorbent

Abstract

Rice husk (RH) is a serious environmental pollutant due to the presence of carbon and silicon in its composition. Rice husk was converted into activated carbon (AC), nano silica (NS) as a byproduct of agricultural waste. The valorization of RH comes from turning the main source of pollution into a useful product. A novel hybrid composite made of activated carbon (AC), nano silica (NS), and zero valent copper (ZV-Cu) was synthesized. Green synthesis was employed to form zero-copper metal, which was subsequently incorporated into the composite matrix. Different techniques have been employed to characterize the new composite materials, including SEM-EDX, TEM, BET surface area measurement, XRD, and FTIR. Also, zeta potential analyses revealed that the net charge of (AC/NS/ZV-Cu) nanocomposite was −1.9 mV. An AC/NS/ZV-Cu nanocomposite was applied to remove methylene blue (MB) dye from wastewater, and the variables influencing the adsorption process were thoroughly examined. The results indicated that several operating variables significantly affect the adsorption efficiency, including the dye concentration in the solution, the pH of the medium, the duration of interaction, and the temperature. Under the optimized experimental conditions, the most suitable pH value was found to be 11, while equilibrium between the adsorbent and the dye was achieved after approximately 2 h. Under these conditions, the highest adsorption capacity reached about 110.45 mg/g. The results obtained were utilized to assess the kinetics and thermodynamics of the adsorption process. The sorption of dye was found to be a pseudo-first-order kinetic process, and the equilibrium data were fitted with the Langmuir isotherm. Additionally, the evidence suggests that an endothermic mechanism governs the adsorption process. Different chemical agents, such as acids (such as HCl) and organic solvents (such as acetone, ethanol, and methanol), have been used as eluents to regenerate the dye-covered adsorbent. The results show that acetone has the greatest efficiency for the regeneration of the nanocomposite. Evaluation of the equilibrium and kinetic data revealed that the adsorption behavior is most accurately described by the Langmuir isotherm model and follows pseudo-first-order kinetic behavior. These results suggest that the synthesized (AC/NS/ZV-Cu) nanocomposite has strong potential to be utilized as an environmentally sustainable and efficient material for the removal of MB dye from wastewater. Finally, the adsorbent waste was utilized as a part of the production of geopolymer to perform zero-waste discharge.