Simultaneous Synthesis of Silica Polymorphs and Activated Carbon from Rice Husk

Rice husk is an agricultural waste rich in carbon and silica contents. So far, no studies have been reported that simultaneously transform it into polymorph silica and activated carbon. This study aims to analyze the thermal event and identify the phase, functional groups, and microstructure of the silica and activated carbon derived from a rice husk. Silica precursor was prepared by the sol-gel route followed by calcining at temperatures of 500–1100 °C with a rise of 200 °C. The residue from the silica preparation was transformed into activated carbon through impregnation, followed by carbonation at 650 °C. Thermal analysis results expose that crystallization of silica occurs at around 900 °C, while the formation of active carbon occurs at lower than 832 °C. XRD analysis revealed that silica calcined at 500 and 700 °C is amorphous, while samples calcined at 900 and 1100 °C are crystalline, with the major and minor phases being cristobalite and tridymite, respectively. The FTIR analysis strengthened this analysis, which detected the presence of Si–O–Si bending vibrations in the sample calcined at 900 °C or more, indicating a phase transition from amorphous to crystalline. A morphological change to a denser structure accompanies this phase transformation. On the other hand, processing the rice husk residue resulted in activated carbon with an amorphous structure and highly porous. The formation of activated carbon was confirmed by the FTIR analysis, which detected the appearance of the C = C group, a characteristic of this substance.