In this work, we have reported about the synthesis of zeolite RA and RX, using hydrothermal method and the silicon source used for the synthesis has been extracted from rice husk ash. The prepared samples (Rice husk ash) RHA and extracted (Sodium silicate) SS from RHA are observed to be amorphous in nature. The FESEM micrographs revealed the presence of “wave-like” morphology and “flakes” like structure for the RHA and SS. The elemental composition results indicate that the samples are of pure nature. The synthesized zeolite RA and RX samples are found to exhibit good crystallinity. In the FTIR spectra, the bands present at 522 cm^-1 and 554 cm^-1 for the synthesized zeolite RA and RX indicate the D4R and D6R respectively. The thermal properties of the synthesized samples show that the maximum weight loss recorded are 15% and 5% for the prepared zeolite RA and RX. The zeolite RX as a high Si/Al ratio compared to the zeolite RA which shows the high thermal stability of zeolite RX. From, the FESEM and HRTEM micrographs, RA and RX samples are observed to exhibit “Ice cube” and “octahedral” morphology. From the N₂ adsorption-desorption studies, it is found that typical type IV and type I adsorption isotherms correspond to zeolite RA and RX respectively.  The BET surface areas of the prepared samples are found to be 106.25 m²/g and 512.79 m²/g. By using the BJH equation the average pore sizes have been calculated and are found to be 32 and 38 nm for the zeolite RA and RX accordingly.

The experimental CO₂ sorption studies for the zeolite RA and RX are found to be in accordance with type I adsorption according to the IUPAC classification criterion. The maximum experimental CO₂ adsorption are found to be 2.22 and 2.45 mmol/g for the synthesized zeolite RA and RX respectively. The obtained isotherms are fitted using Langmuir, Freundlich and Toth non-linear adsorption isotherms. From the fitted isotherm models, the correlation coefficient is found to be nearly 1, which indicates the heterogeneous nature of the materials. 

Keywords: Rice husk ash, zeolite A and X, CO₂ adsorption