Role of oxidant during phosphoric acid activation of lignocellulosic material

Lignin-based and wood-based activated carbons were prepared by phosphoric acid activation conducted using the oxidant ammonium persulfate ((NH4)2S2O8) as the activation additive. Results showed that at a (NH4)2S2O8 dosage of less than 10%, the oxidant increased the activated carbon yield and promoted pore development. However, at a (NH4)2S2O8 dosage of higher than 10%, an over-oxidation condition was created so that the activated carbon yield was reduced and pore development was negatively affected. It is suggested that oxidants play two roles during phosphoric activation, promotion of phosphate ester formation on the matrix and over-oxidation of carbon.