Acid-base properties of organosmectite in aqueous suspension

•The acid-base properties of HDTMA organocly depends of the interlayer spacing.•Comparing to the smectite, the PZC of HDTMA ogranoclays move to the basic pH.•The modelling of surface charge by ProtoFit gives an idea on the pkas of the organoclays.•The calculated pKas show an increase with the addition of the HDTMA surfactant.

Surfactant modified smectite was prepared using hexadecyltrimethylammonium bromide (HDTMAB) at three CEC levels (0.5, 1 and 2 CEC). Potentiometric titration behavior of Na-smectite and organosmectites was investigated and interpreted according to surface complexation theory. The point of zero charge (PZC) was determined by both the methods potentiometric and mass titrations. The PZC of Na-smectite is about 6.2 and that of the organosmectites (H0.5, H1 and H2) is 6.8, 7.7 and 8, respectively. The titration data was modulated using the ProtoFit program in order to determine the PZC and the equilibrium constants (pKas). The results give a good agreement between the experimental and modeling study.