Nitrogen-doped carbon materials produced from hydrothermally treated tannin Original Research Article

This manuscript presents a simple one-pot synthesis for producing nitrogen-doped carbon materials (NCMs) with nitrogen content up to 6.3 wt.%. Carbon gels were produced by direct pyrolysis without the expensive step of supercritical drying in CO2. NCMs were synthesized by hydrothermal carbonization (HTC) of aminated tannin. Amination of tannin was carried out in aqueous ammonia solution according to two different methods: (1) amination at room temperature followed by evaporation and HTC of the resultant powder in pure water at 180 °C for 24 h, or (2) direct HTC in the same conditions of the tannin–ammonia solution. In both cases, further pyrolysis was carried out at 900 °C under nitrogen flow. We obtained very different NCMs depending on the method. Method (1) led to microporous carbon gels having a surface area of 500 m2 g−1 without need of supercritical drying, and a nitrogen content of 2.9 wt.%, whereas method (2) led to carbons microspheres arranged in pearl-necklace structure, having a surface area around 60 m2 g−1 and a higher nitrogen content of 6.3 wt.%. In both cases, X-ray photoelectron spectroscopy showed mainly pyrrolic and pyridinic nitrogen functionalities.