Utilization of rice husk wastes in synthesis of graphene oxide-based carbonaceous nanocomposites

Rice husk is an agricultural waste-based biomass that can provide an alternative renewable source of bioenergy. Rice husk carbon and rice husk ash are major solid residues obtained after converting rice husk to bioenergy. This paper reports the synthesis of two graphene oxide-based activated carbons using rice husk carbon through H₃PO₄ and ZnCl₂ activation, respectively. By contrast, mesoporous silica was produced using recycled rice husk ash. Graphene oxide/ordered mesoporous carbon was prepared using mesoporous silica as a template source. These composites were inspected using a Raman spectrometer, Fourier transform infrared spectrometer, transmission electron microscope, field-emission scanning electron microscope, X-ray diffractometer, and surface area analyzer. Experimental results indicated that graphene oxide-based H₃PO₄ activated carbon, ZnCl₂ activated carbon, and ordered mesoporous carbon had a surface area of 361, 732, and 936 m²/g, respectively; a pore volume of 0.299, 0.581, and 1.077 cm³/g, respectively; and an average pore size of 2.31, 3.17, and 4.35 nm, respectively. The carbonaceous composites with graphene oxide exhibited a higher adsorption ability than did pure carbon materials without graphene oxide. The maximum adsorption capacities using methylene blue as adsorbate followed the order of ordered mesoporous carbon (1591 mg/g) > ZnCl₂ activated carbon (899 mg/g) > H₃PO₄ activated carbon (747 mg/g). The isothermal adsorption and kinetics study for graphene oxide/ordered mesoporous carbon indicated that adsorption followed the Langmuir isotherm model and pseudo-second order kinetic model. Rice husk waste has excellent prospective potential for producing highly valuable nanoproducts and for reducing environmental pollution.