In this study, a new nanocomposite composed of zeolite Y incorporated into the UiO-66 framework has been synthesized by solvothermal growth of UiO-66 on the support of zeolite Y, and investigated for CO2 adsorption and separation of CO2/CH4 gas mixtures. The aim of this work was to increase the CO2 uptake and the selectivity of the base framework, as well as to increase its thermal stability. Various weight ratios of UiO-66/zeolite Y were prepared to achieve the optimal composition subject to the highest adsorption capacity. The formation of UiO- 66/zeolite Y nanocomposites was verified with different characterization methods. It was observed that UiO-66/ zeolite Y with a weight ratio of 90:10 has the same morphology as pristine UiO-66 but with superior porosity. Compared to base UiO-66, its surface area and micropore volume increased by about 80 % and 50 %, respec- tively. Moreover, the results indicate a substantial improvement of 50 % in the CO2 adsorption capacity of nanocomposite (14.6 mmol/g, 298 K, 30 bar) compared to pristine UiO-66. To our knowledge, the newly syn- thesized nanocomposites exhibited the record-highest CO2 adsorption capacity among the reported UiO-66 composites. The predicted CO2/CH4 adsorption selectivity of the nanocomposite based on IAST is also higher than that of the pristine MOF. Finally, the cyclic adsorption/desorption test revealed more than 95 % desorption efficiency after ten cycles. Due to the high capacity, selectivity, and reversibility of CO2 adsorption on the UiO- 66/zeolite Y, and also the high thermal stability of the nanocomposite, it is suggested as an excellent potential adsorbent for the practical application of biogas and natural gas purification. Furthermore, this contribution also presents an insight into the role of zeolite Y in the nanocomposite framework which could comprehend pore size distribution control by varying its amount.

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