One-step synthesis of microporous nitrogen-doped biochar for efficient removal of CO2 and H2S

It is still a great challenge to prepare an ideal adsorbent for the removal of CO2 and H2S from biogas efficiently. In this study, urea phosphate (UP) was selected as both activator and nitrogen (N) source to prepare the biochar adsorbent from plant biomass with microporous structure and N-rich functional groups through "one-step" synthesis. The results show that the yield of biochar increased from about 20% to 50%, and the S-BET and V-mic of the obtained biochar were 1189 m(2)/g and 0.433 cm(3)/g, respectively, which was much higher than those without UP addition (524 m(2)/g and 0.17 cm(3)/g). Moreover, N was successfully doped on the surface of biochar, and the N content was up to 4.24 at.% with the majority of basic species such as pyridinic and pyrrolic N. This could be attributed to a large amount of N-containing functional groups and phosphoric acid released gradually at the presence of UP during the heating process. The prepared biochar exhibited good CO2 and H2S adsorption capacities up to 1.34 mmol/g and 54.8 mg/g, respectively, which was much higher than those without UP addition (0.958 mmol/g and 0.24 mg/g). The excellent adsorption properties of CO2 and H2S were tightly related to the improved microporous structure and surface basic N-containing functional groups on the biochar.