The point of zero charge (PZC) of the zeolite beta pellets with
the SiO2/Al2O3 molar ratio of 22, 32 or 78 was measured, which
was similar to the method described by the literatures [14]. 0.04-g
zeolite was added into a 40-mL NaCl solution (0.01 or 0.1 M).
The initial pH (pHi) ranging from 2 to 9 was adjusted by adding
HCl or NaOH solution. The mixtures with varied pHi values were
shaken for 48 h to allow them to reach the equilibrium. The final
pH (pHf) versus pHi was plotted, by which the PZC was determined.