Adsorption of Sodium Dodecyl Sulfate and 2-Naphthol Adsolubilization on Titanium Dioxide with Quaternary Ammonium Groups

Abstract

The adsorption behavior of sodium dodecyl sulfate (SDS) was investigated on titanium dioxide with quaternary ammonium groups (XN m, m is the carbon number of the alkyl chain, 4−16) by measuring amount adsorbed, ζ potential, and dispersion stability. The amount of SDS adsorbed increased sharply at low SDS concentration, reached a constant level on XN4, XN8, and XN12, and gradually increased on XN16. However, the amount of SDS adsorbed on untreated titanium dioxide was significantly low compared with that on XN m . The suspensions of XN m created by adsorption of SDS showed a dispersion−flocculation−redispersion sequence, accompanying a change in the ζ potential from positive to negative for all XN m . The flocs formed could be transferred to a toluene phase by adding toluene to the XN m suspensions, indicating that the flocs of all XN m are hydrophobic regardless of different alkyl chain lengths. The order parameter of methyl 12-doxylstearate located in the SDS adsorbed layer estimated by electron spin resonance shows that the mobilities of the probe are not restricted in the SDS adsorbed layer for all XN m . Adsolubilization behavior of 2-naphthol in the SDS adsorbed layer on XN m was peculiar; the amount of 2-naphthol adsolubilized was insensitive to the SDS concentration and was almost the same as the amount of 2-naphthol adsorbed on XN m in the absence of SDS, where the amount of 2-naphthol adsorbed increased with increasing alkyl chain length of XN m . In the case of untreated titanium dioxide, the amount of 2-naphthol adsolubilized increased with the SDS concentration, reached a maximum, and then decreased. Thus, the adsolubilization behavior of 2-naphthol for XN m was significantly different from that for untreated titanium dioxide.