Low-pressure selective adsorption of CO2 and CH4 on carbon-based materials

The increasing demand for sustainable technologies to mitigate greenhouse gas emissions has intensified research on efficient adsorbent materials for carbon dioxide and methane capture. In this work, three carbon-based materials, phenol formaldehyde xerogels, nickel-modified xerogels, and activated carbons derived from olive stones, were synthesized and systematically compared in terms of textural, structural, and adsorption properties. Comprehensive characterization revealed that both the pyrolysis temperature and nickel incorporation strongly influence porosity and surface functionality. Adsorption experiments demonstrated that activated carbon based on olive stones exhibits the highest total uptake for both gases, reaching 6.41 mmol/g for carbon dioxide and 2.75 mmol/g for methane compared to 4.41 and 2.79 mmol/g for phenol formaldehyde xerogels. In comparison, nickel-modified xerogels present an adsorption capacity of around 1.34 and 0.65 mmol/g, respectively, for carbon dioxide and methane under the same conditions. These results due to the large surface area and dominant microporosity of biomass-based samples. In contrast, the nickel-decorated sample shows superior surface-normalized adsorption efficiency, particularly at low pressures where surface interactions prevail. The presence of nickel introduced electroactive sites that enhanced carbon dioxide affinity by way of quadrupolar interactions and improved methane adsorption through localized polarization effects. These findings highlight that surface chemistry plays a more decisive role than textural parameters in determining selectivity and adsorption performance under realistic conditions. Overall, this study establishes a rational design strategy for next-generation carbon adsorbents combining engineered porosity and functionalized surfaces, paving the way for energy-efficient carbon dioxide and methane separation processes.