Binding of Aromatic Anions to Cetylpyridinium Aggregates Either Adsorbed at Silica/Water, Alumina/Water, Titanium Dioxide/Water Interfaces or in Solution

Abstract

The influence of the counterions on the adsorption properties of cetylpyridinium salicylate, cetylpyridinium 4-aminosalicylate, cetylpyridinium 5-aminosalicylate, and cetylpyridinium chloride has been investigated at silica/water interfaces using adsorption isotherm determinations and electrophoretic and surface tension measurements. Earlier results are confirmed which showed that replacing the chloride ion by the salicylate ion results in a 6-fold increase in the plateau value of the surfactant ion. It is suggested that this is the consequence of a close packing of the cationic surfactants when associated to the salicylate ion at either the solid/water or air/water interface. The results are compatible with the formation of a surfactant monolayer with the headgroups facing the solid surface. The binding constants of the organic anions to the cationic headgroups have been evaluated using a Langmuir type isotherm and were shown to be larger for adsorbed aggregates as compared to free micelles by a factor of about 3. Although the binding constant is larger by a factor of 10 for the salicylate ion as compared to the aminosalicylate derivatives, the surfactant adsorption isotherms and the electrophoretic mobilities are similar for the three cetylpyridinium salts. It is suggested that the unusually large adsorption of these surfactants at the silica/water interface is related to the surface stacking of the aromatic counterions which favors the close packing of the surfactant ions. Results obtained at the titanium dioxide/water and the alumina/water interfaces do not contradict these conclusions. The case of 2,4,6-trichlorophenol either as a neutral molecule or as an ionized counterion species in association with the cetylpyridinium ion was also investigated in solution and at the silica/water interface.

Adsorption of Cetylpyridinium Chloride at Silica Nanoparticle/Water Interfaces (I): Dependence of Adsorption Equilibrium on Particle Size

“…With an increase in r , the Γ m increases, while Γ m g decreases, which is consistent with the prediction of our size-effect model. The Γ m values for the four silica samples at pH 9.00 are in the range of 4.18–6.28 μmol/m 2 , similar to the previous reports. − Furthermore, with an increase in r , the K ad and |Δ G̃ ad 0 | values increase, indicating that the spontaneous tendency of adsorption is enhanced, also similar to the previous reports. − …”

“…Amorphous silica (SiO 2 ) is one of the most widely used adsorbents. ,,,,− Especially, it is suitable for studying the size-dependence of adsorption because it can easily form uniform spherical nanoparticles with adjustable sizes. Cetylpyridinium halide (CPy + X – , commonly X – = Cl – and Br – ) is one kind of quaternary ammoniums surfactant and widely used in various fields ranging from biological to industrial applications. − The aggregation behaviors of CPyX in bulk solutions − and at solid/liquid interfaces − have been widely investigated. However, there have been no reports on the size-dependence of its adsorption at solid/liquid interfaces so far.…”

Adsorption Kinetics and Structural Arrangements of Cetylpyridinium Bromide at the Silica−Aqueous Interface

“…CPBr and its chloride analogue (CPCl) have been the subject of several adsorption studies. − Harrop 18 found that the adsorption of CPBr was highly dependent on pH, with physisorption predominating at low pH values and chemisorption increasing with pH. Gao et al studied the effect of inorganic salts, alcohols, and urea on the adsorption of CPBr to silica and found that all isotherms exhibited two plateau regions with or without various additives .…”

Studies of Cetylpyridinium Chloride and Cetylpyridinium Salicylate in Solution and Adsorbed on Silica Surfaces Using X- and W-Band Electron Paramagnetic Resonance Spectroscopy

“…Only a handful of studies have dealt with this topic, − despite the knowledge that the type of counterion has an important effect on the adsorption of the surfactant . Recently, Favoriti and Treiner ,, have investigated the effect of salicylate counterions on the adsorption of cetylpyridinium onto silica surfaces and on the physical properties of the solloids formed. They observed that salicylate is strongly coadsorbed with cetylpyridinium cations onto silica surfaces and results in a 6-fold increase in the plateau value for adsorption compared to cetylpyridinium chloride.…”

“…From analysis of the line widths of the EPR spectra, it was concluded that CPSa on silica surfaces forms two coexisting aggregate phases, one which excludes HTAB* and one in which HTAB* is concentrated. The HTAB* is believed to be excluded from the former phase because of ordering of the salicylate counterion and pyridinium headgroups as proposed by Favoriti and Treiner …”