The procedure for determining the pHPCZ consisted of
performing a mixture of 50 mg of the adsorbent in 50 mL
aqueous KCl at two concentrations (0.05 and 0.5 mol L-1), with
initial pH values ranging from 2.0 to 10.0, which were buffered
with solutions of HCl and NaOH (0.01 mol L-1). After the
contact for 24 h, the final pH values were obtained and plotted
on a graph correlating the variation of initial and final pH, with
pHPZC corresponding to the range in which the final pH is kept
constant (regardless of the initial pH), i.e., the adsorbent surface
behaves as a buffer (Mimura et al., 2010).