The pHpzc values were determined by a mass titration method
proposed by Noh and Schwarz (1989). Various amounts of the activated
carbons were put in 10mL0.1 mol/L NaCl solutions (prepared
in boiled water to eliminate CO2), and the bottles were shaken in
a thermostat shaker overnight. The equilibrium pH values of the
mixtures were measured and the limiting pH value was taken as
the pHpzc.