Physical and chemical properties of carbons synthesized from xylan, cellulose, and Kraft lignin by H3PO4 activation

Physical and chemical properties of activated carbons produced from commercial xylan, cellulose, and Kraft lignin by H3PO4 activation at various process conditions were studied. The results show that the more reactive the precursor under acidic conditions, the easier the porosity development, particularly mesoporosity. In addition, Boehm titration and Fourier Transform Infrared Spectroscopy (FTIR) characterization results demonstrated that the functional groups on the surfaces of these carbons consist of both temperature-sensitive and temperature-insensitive components. The temperature-sensitive component is primarily caused by the hydrolysis of raw materials under acidic conditions at low temperature, and the reaction between activation mixture and oxygen in the process of activation, particularly at low impregnation ratio. These surface groups decompose at high temperature. The temperature-insensitive contribution is mainly composed of phosphorus-containing groups arising from the reaction of H3PO4 (or pyro- and polyphosphoric acids) with precursor, and carbonyl-containing groups. This part of surface functional group is stable, even at high activation temperatures. This study also confirmed that the nature of precursor, impregnation ratio between H3PO4 and precursor, and activation temperature are important factors affecting the properties of final activated carbon products.