X-ray photoelectron spectroscopy (XPS) was used to quantify the carbon changes and nitrogen forms present in hydrothermally-treated low rank coals (HTT temperatures between 200-350℃) and weathered coals. For HTT coals, the content of carboxyl group greatly decreased due to the treatment, and some quaternary nitrogen species changed to pyridinic form. In case of the weathered coals, the content of carboxyl group increased with the increasing of weathering days, and the content of quaternary nitrogen species also increased.
