Bottom-up synthesis of carbon materials with high pyridinic-nitrogen content from dibenzacridine isomers with zigzag and armchair edges

Nitrogen-doped carbon materials, especially pyridinic nitrogen, have attracted attention because of the high performance for various applications such as electrodes for fuel cells and other catalytic reactions. However, the selective introduction of pyridinic nitrogen without using catalysts and the mass production of such carbon materials are challenging. In this work, carbon materials with selectively introduced pyridinic nitrogen were synthesized by just simple heat treatment of aromatic compounds containing pyridinic nitrogen in the absence of catalysts. Dibenzacridine isomers, C21H13N, with different molecular frameworks such as either zigzag or armchair edges were selected as precursors to investigate the influence of edges on the percentage of pyridinic nitrogen. The percentage of pyridinic nitrogen of precursors heated at 973 K was in the order of dibenz[c,h]acridine (DCHA) (80%) > dibenz[a,h]acridine (60%) > dibenz[a,j]acridine (39%) > dibenz[a,i]acridine (33%). The percentage of pyridinic nitrogen of DCHA was further enhanced to 94% at 923 K. Experimental X-ray photoelectron, infrared, and Raman spectra combined with calculation of spectra and formation energy and calculation of carbonization reaction pathways by molecular dynamics simulation with reactive force field (ReaxFF) precisely revealed the reasons why the high percentage of pyridinic nitrogen was attained. The steric hindrance generated by the bay structure of DCHA provided the high formation energy of C–N bond (tertiary nitrogen) and N–H bonds (secondary nitrogen), avoiding the side reactions such as the formation of tertiary nitrogen and secondary nitrogen.