In this study, the effect of nanoclay on the gas storage in the hydrate phase was investigated. Nanoparticles were modified with polyethyleneimine (PEI) to improve their surface properties, and these modified nanoparticles were subsequently characterized. Subsequently, gas hydrate formation experiments were conducted for CO2 storage in the hydrate phase. A rocking reactor was employed to form the gas hydrate. In addition, the effect of different nanoparticle concentrations (200, 400, and 500 ppm), the PEI concentration loaded on nanoparticles (30% and 50%), the initial volume of suspension, and initial pressure were investigated. Data on CO2 consumption, water-to-hydrate conversion, and storage capacity were collected throughout the experiments. This study is a continuation of the research by Jafari Khamirani et al. (2024). The results indicated that nanoparticles increased gas consumption and storage capacity compared to water in the rocking vessel. Additionally, compared to the study by Jafari Khamirani et al. (2024), the nanoparticles demonstrated better effectiveness, in the rocking vessel compared to the stirrer-type vessel. Among the experiments, nanoparticles modified with 50% PEI outperformed compared to those with 30% PEI and unmodified nanoparticles, which indicates the positive impact of amino groups on hydrate formation. The surface-grafted nanoclay with a mass fraction of 500 ppm with 50% PEI had the highest CO2 gas consumption, with an improvement of approximately 33.26% compared to pure water; this concentration also has a maximum amount of storage capacity of 70.78 V/V. (c) 2025 Society of Chemical Industry and John Wiley & Sons, Ltd.