Synthesis of N-doped hierarchical porous carbon with excellent toluene adsorption properties and its activation mechanism

Typical organic pollutants from coal-combustion flue gas such as volatile organic compounds (VOCs) need to be effectively controlled. This work synthesized a series of nitrogen-doped hierarchical porous carbons (NHPCs) by one-step activation with various proportions of cellulose, (NH4)(2)C2O4 and KHCO3/NaHCO3. The NHPCs have a high specific surface area and pore volume up to 2816 m(2)/g and 1.413 cm(3)/g as well as a hierarchical porous structure with micro-meso-macropores distribution. The dynamic adsorption tests of toluene at 600 ppm showed that NHPCs have a high adsorption capacity up to 585 mg/g (NHPC(K)131), this was about 3 times more than that of AC (208 mg/g), and is a better absorbent compared to many other carbon adsorbents. The porous characteristics and toluene adsorption properties of NHPCs improved along with the fluctuation of the proportions of raw materials and active agents. The micropore size of the material is the main factor that affecting the toluene adsorption capacity. The analysis of toluene dynamic adsorption breakthrough curves revealed that NHPCs had great toluene adsorption kinetics with high adsorption rate constants and short mass transfer zone. The excellent toluene adsorption kinetics of NHPCs can be attributed to the hierarchical porous structure. The abundant 2-10 nm mesopores and macropores of NHPCs act as mass transfer channels for toluene molecules. The XPS analysis showed that the NHPCs have nitrogen doping up to 6.71% (NHPC(Na)161) and they effectively promote toluene adsorption. The nitrogen doping mechanism can be attributed to the reactions between cellulose pyrolysis substances and NH3 which decomposed from (NH4)(2)C2O4. Moreover, the pore forming reactivity of KHCO3 is better than that of NaHCO3 in the NHPCs activation process. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study synthesized a series of nitrogen-doped hierarchical porous carbons (NHPCs) with high specific surface area and pore volume. NHPCs showed high adsorption capacity for toluene and the characteristics improved with fluctuations in raw materials and active agents proportions. The micropore size of the material is the main factor affecting the toluene adsorption capacity.