Nitrogen-doped optimizing the pore structure and functional groups of the hierarchical porous materials and its toluene adsorption

Hierarchical porous carbon materials were regarded as highly effective adsorbents for volatile organic compounds (VOCs) due to their large surface area, pore volume, and suitable pore structure. In this paper, the carbon microspheres (about 100 nm diameter) derived from glucose were inserted into the mesopores of hollow carbon spheres (about 450 nm diameter) by the ultrasound-hydrothermal method. Thus, the hierarchical porous carbon spheres (C@HCS) with abundant pores were synthesized. Meanwhile, the influence of nitrogen doping on the pore structure and the nitrogen-containing functional groups of C@HCS were also discussed. The characterization discovered that the moderate nitrogen doping could be beneficial to toluene adsorption capacity due to more pyridinic-N and pyrrolic-N, and more pores with 1.6-3.6 nm diameter. Theoretical analyses also proved that pyridinic-N and pyrrolic-N functional groups had the strongest adsorption energy for toluene. When the mass ratio of glucose to urea was 1:1, the prepared C@HCS-11N had the maximum specific surface area, and pore volume of 1.6-3.6 nm pores, their values were 2056 m2/g and 0.2081 cm3 /g. At the same time, the content of pyridinic-N and pyrrolic-N were also the highest except for C@HCS-21N, about 0.464 % and 0.899 %. Therefore, 898 mg/g toluene adsorption capacity could be achieved by C@HCS-11N (25 degrees C and 1 atm), which was still kept at 826 mg/g after five adsorption-desorption cycles.