Hydrochar-derived activated carbons from cow manure for enhanced co₂ adsorption: role of microporosity and surface heterogeneity

This study presents the development of low-cost adsorbent from the renewable biomass, specifically cow manure. Hydrochar was produced from the cow manure using hydrothermal carbonization method under controlled conditions such as temperature, pressure, time and solid to liquid ratio. Activated carbons derived from hydrochars and dry cow manure were successfully prepared via chemical activation and systematically characterized to evaluate their structural, thermal, morphological and textural features followed by investigation of CO2 adsorption performance at different temperatures. Nitrogen physisorption results revealed a substantial increment in the textural properties of activated carbons compared to dry cow raw manure, hydrochars, as the surface area increases up to 1200 m2/g in the activated carbons. Total pore volumes also significantly increase which indicated the formation of porous structures. Pore size distribution of the activated carbons demonstrates that activated carbons are microporous with the pore size centered in the range of 1.1-1.9 nm. Functional groups analysis showed a progressive transformation in the functional groups from oxygen-rich structures in dry cow manure to carbonized aromatic framework in hydrochars and activated carbons. CO2 adsorption studies revealed the typical Type-I isotherm which indicate that adsorption is primarily govern by the micropore filling. The CO2 adsorption was observed as highest (>5.5 mmol/g) at low temperature compared to high temperatures indicating the exothermic physisorption process. All the results derived from characterizations and the CO2 adsorption performance demonstrates a strong correlation between the textural features and CO2 adsorption indicating microporosity play a dominant role compared to surface heterogeneity. This study established a reliable experimental approach for preparing and evaluating the hydrochar-derived activated carbons providing a robust platform for future material developments and applications in adsorption studies.