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In this manuscript, N-doped porous carbonaceous CO2 sorbents were synthesized using biomass waste hazelnut shell as the raw materials, melamine as the nitridation agent, and KOH as the porogen. The resultant materials were carefully characterized by different techniques, and the results show that these samples possess a high amount of N content and highly developed porous structure. As a result, high CO2 adsorption capacities were found for this series of sorbents, up to 4.23 and 6.34 mmol/g at 1 bar and 25 and 0 °C, respectively. Comprehensive investigation indicates that, in addition to the well-known narrow microporosity and N content, the pore size distribution of the adsorbent also plays an important role in dictating the CO2 uptake under ambient conditions. Thus, it is proposed that the joint effect of the above three factors dictates the CO2 adsorption capacity of these sorbents. Moreover, these sorbents exhibit many other exceptional CO2 adsorption properties, such as stable recyclability, fast adsorption kinetics, suitable heat of adsorption, high CO2/N2 selectivity, and good dynamic CO2 capture capacity. The wide availability and low cost of raw materials together with a straightforward synthesis procedure and excellent performance disclose the high potential of hazelnut-shell-derived carbons in CO2 capture.

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Porous carbon is considered an effective adsorbent for CO2 uptake thanks to its high textural feature, tunable surface decoration, and stable chemical/physical characteristics. Herein, a one-pot self-activating synthesis approach has been introduced to fabricate disodium 2,6-naphthalene disulfonate (NDS)-derived self-S-doped porous carbon. With this method, there is no external chemical activating agents for the activation process, and the self-activating process occurs by releasing CO, H2O, and CO2 gases during pyrolysis treatment. It was found that activating temperatures can carefully control the porous textural and elemental compositions of the as-prepared carbons. Upon the activating process, the optimal S-doped porous carbon was prepared at 700 °C, providing CO2 uptake capacities of 2.36 and 3.56 mmol/g at 25 and 0 °C and 1 bar, respectively. An in-depth investigation indicates that the joint effect of narrow microporosity and S content determines the CO2 uptake for this series of carbons. In addition, these NDS-derived self-S-doped porous carbons exhibit moderate CO2 heats of adsorption, fast adsorption kinetics, reasonable CO2/N2 selectivities, good dynamic CO2 capture capacities, and stable recyclabilities. The presented synthesis method is promising for fabricating facile carbon-based adsorbents from various organic precursors.

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