A novel activating strategy to achieve highly porous carbon monoliths for CO2 capture

Highly porous N-doped carbon monoliths have been successfully prepared by using binary H3PO4-HNO3 mixed acid as a co-activating agent for the first time and sodium alginate (SA), a natural biopolymer, as a carbon precursor. The resultant N-doped carbon monoliths have a narrow size distribution and high content of pyrrolic N. Particularly, the sample SA-2N-P with the highest surface area (1740 m(2) g(-1)) exhibits the highest CO2 adsorption capacity of 8.99 mmol g(-1) at 273 K and 4.57 mmol g(-1) at 298 K, along with an initial CO2 adsorption energy of 43 kJ mol(-1) at lower CO2 coverage and 32 kJ mol(-1) at higher CO2 coverage. Remarkably, this sample also shows the highest CO2 capacity [66.44 mg (CO2) g(-1) (adsorbent) at 25 degrees C and 0.15 atm] under low CO2 pressures, which is of more relevance for flue gas applications. Furthermore, the selectivity of CO2 over N-2 is also calculated for the binary gas mixture [V (N-2) : V (CO2) = 85 : 15] according to the ideal adsorbed solution theory (IAST). Combined with its simple preparation, high adsorption capacity, and high selectivity for CO2, the sample SA-2N-P is one of the promising solid-state absorbents reported so far for CO2 capture and storage.