The suspensions were then agitated in a water-bath shaker for 12 h at 120 rpm after which the final pH of the liquid-phase were measured.The final pH of the liquid-phase were measured.
The final pH was plotted against the initial pH and the pHPZC
was taken as the final pH value in the range where a plateau occurs
in the curve. This procedure was repeated using 0.01 and 0.1 M
KNO3 solutions and the pHPZC used was the average of the three
values.