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This work focused on the preparation and characterization of a promising biochar as a novel solid adsorbent towards CO2. The biochar was prepared by catalytic pyrolysis of waste roasted peanut shell in molten salt; it was characterized by means of SEM‐EDS, BET, FTIR, and TGA, followed by determining the adsorption characteristics, such as adsorption capacity, isosteric heat of adsorption, uptake rate, and selectivity via adsorption temperature and gas pressure. The results indicated that the as‐prepared biochar had a rich microporous structure with a peak pore size in the range of 0.69–1.3 nm, and exhibited a good performance of CO2 adsorption with a capacity of 3.8 mmol/g at 273 K and 100 kPa. Moreover, the adsorption selectivity of CO2 over N2, O2, CO, and CH4 was found to be above 12, 11, 8, and 7, respectively. In addition, an interesting phenomenon of an initial increase and then a decrease in the selectivity of CO2/N2 adsorption with increasing gas pressure was experimentally revealed.

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A promising biochar as solid adsorbent for CO 2 uptake was prepared by the catalytic pyrolysis of coconut shell in moderate-temperature ionic liquid (IL). Then, it was characterized by means of SEM, EDS, BPEA, BET, NLDFT, FTIR, and TG-DSC, and a mechanism interpretation of the porous biochar formation was conducted. In addition, the adsorption characteristics of CO 2 on the asprepared biochar, such as adsorption capacity, adsorption potential, isosteric heat, and static selectivity at different adsorption temperatures and pressures, were systematically evaluated. The results indicated that the as-prepared biochar exhibited an adequate CO 2 adsorption with a capacity of 4.5 mmol/g at 273 K and 100 kPa. Then, a significant number of slit-like pores were revealed to exist on the as-prepared biochar with a peak pore size between a range of 0.6 nm-2 nm. The porous structure formation was ascribed to the release of carbon-, hydrogen-, oxygen-, sulphur-, and nitrogen-containing compounds during biochar preparation. Meanwhile, both the adsorption potential and isosteric heat of the CO 2 uptake under the tested conditions decreased with an increase in the adsorption capacity, which ranged from 33 kJ/mol-21 kJ/mol and 23 kJ/mol-7 kJ/mol, respectively. Therefore, the isosteric heat could be considered as a piecewise function of adsorption capacity. In addition, the molar ratios of CO 2 over N 2 adsorbed under the tested conditions were above 11 and were accompanied by molar ratio peaks of 26 at 273 K and 19 at 298 K, respectively. Moreover, an interesting phenomenon occurred: the static adsorptive selectivity of CO 2 over N 2 first increased and then decreased and there was an increase in the adsorption pressure at the tested adsorption temperatures. K E Y W O R D Sadsorption potential, biochar, CO 2 adsorption, isosteric heat, selectivity

This work focused on thermodynamic analysis of carbon dioxide (CO2) adsorption on a promising biochar as a CO2 adsorbent. The biochar was prepared by catalytic pyrolysis of cellulose material in ionic liquid at moderate temperature. The adsorption characteristics, such as adsorption capacity, interfacial potential, Gibbs free energy change, enthalpy change, entropy change, and internal energy change, influenced by adsorption temperature and gas pressure, were systematically investigated. The results indicated that CO2 adsorption on cellulose‐derived biochar was a spontaneous, physical, exothermic, and entropic decrement process, accompanied by adsorption capacity of 5.2 mmol/g and interfacial potential of −18.2 J/g at 273 K and 100 kPa. The process could be well described by adsorption potential theory. Then a quasi‐Gaussian distribution of site energy was verified for CO2 adsorption. The interfacial potential was found to be a monotropic function of the amount of CO2 adsorbed, and the latter was actually a differential of the former via adsorption potential. The positive temperature effect and negative pressure effect on negative Gibbs free energy change indicated that reducing adsorption temperature and increasing gas pressure were beneficial to CO2 uptake, accompanied by the increase of adsorption capacity and the reduction of interfacial energy, entropy, enthalpy, and internal energy. The strongest temperature effects on entropy change, enthalpy change, and internal energy change existed at given pressure or temperature. The pressure effect was stronger and more sensitive to pressure at lower adsorption pressure. More interestingly, the peak pressure or peak temperature with the strongest pressure effect possibly existed during CO2 adsorption.