Rational introduction of nitridizing agent to hydrothermal carbonization for enhancing CO2 capture performance of tobacco stalk-based porous carbons

Abstract

The introduction of nitridizing agents to the hydrothermal carbonization may change the CO2 capture performance of the porous carbons, but this ideal still needs investigation. Herein, N-doped porous carbons were prepared by hydrothermal carbonization of waste tobacco stalk together with melamine, ethanediamine, or urea before activation. It was found that the introduction of nitridizing agents during preparation didn't necessarily increase the CO2 uptake of the yielded porous carbon. Among the three nitridizing agents, only urea increased the 1-bar CO2 uptake of the yielded porous carbon without decreasing its low-pressure adsorption capacity or CO2/N2 selectivity. The porous carbon prepared by using urea exhibited excellent CO2 uptakes of 7.35 mmol/g at 0 °C and 4.83 mmol/g at 25 °C, with good recyclability. Both the uptakes exceeded the most values ever reported for biomass-derived porous carbons. The excellent CO2 adsorption performance was attributable to synthetic effect of the content of pyrrolic N and the volume of narrow micropores (pore size <1 nm). Additional investigation demonstrated that the narrow micropore volume for these porous carbons played key roles in deciding the CO2 uptake at low pressure (0.15 bar). The physicochemical properties of the yielded porous carbon were attributed to the changes of the physicochemical properties of the yielded hydrothermal carbon prepared by the introduction of different nitridizing agents. The research showed the necessity to carefully select nitridizing agents during hydrothermal treatment and offered an effective way to yield biomass-based porous carbons with high CO2 capture performance.