The carbon yield decreased from 61.2% at 200W to 45.5% at
400 W, because the fierce reaction at high microwave power level
resulted in a greater weight loss of the carbon precursor. The carbon
yield in this study was close to the results obtained in other
studies dealing with phosphoric acid activation, which was commonly
in the range of 40–50% (Molina-Sabio et al., 1995; Gratuito
et al., 2007; Altenor et al., 2009).