Pablo C. Schulz

Remotion of the antibiotic tetracycline by titania and titania–silica composed materials

Removal of the antibiotic tetracycline (TC) by TiO(2) and the mesoporous binary system TiO(2)-SiO(2) have been studied in batch experiments by performing adsorption isotherms/kinetics and photodegradation kinetics under different conditions of pH, supporting electrolyte concentration, temperature, adsorbent amount, and TiO(2)-loading. On the one hand, the adsorption of TC on the studied materials is strongly dependent on pH, increasing as pH decreases. The adsorption mechanism, controlled by diffusion processes, is strongly related to electrostatic attractions and H-bond formations mainly between amide, carbonylic and phenolic groups of the antibiotic and the functional groups of TiO(2). The adsorption capacity at constant pH increases in the order TiO(2)<TiO(2)-SiO(2) mainly due to the highly surface area that the silica offers and to the homogenously dispersion of the TiO(2) nanocrystallites. On the other hand, the photodegradation rate is affected by the presence of the studied materials at several pH, although its photocatalytic activities are more important at pH 7 or lower. The photodegradation mechanisms seem to be related to the formation of OH radicals which are responsible for the decomposition of TC. The composed titania-silica materials might act not only as an excellent adsorbent but also act as an alternative photocatalyst for pollution control.

Microemulsion copolymerization of styrene and acrylic acid

Abstract The copolymerization of acrylic acid and styrene in a cationic microemulsion made with dodecyltrimethylammonium bromide is reported. Conversion of 60% and fast reaction rates are achieved. The resulting latex is a monodisperse dispersion of spherical particles of 21 nm in radius. The copolymer backbone consists of isolated acrylic acid units randomly distributed among polystyrene blocks.

Hydrophile–lipophile balance and solubility parameter of cationic surfactants

By using hydrophile/lipophile balance (HLB) values of cationic surfactants obtained from literature, two methods to determine this property were tested to verify if they are applicable to such amphiphiles: Little’s method with the surfactant solubility parameter (d ) and the water number of Greenwald et al., related to their ability to promote inversion of emulsions. Cationic surfactants did not follow the behaviour of anionic and non-ionic surfactants. Little’s method gave non-realistic values of HLB for cationic surfactants, whereas the Greenwald et al. treatment gave a nonlinear relationship. However, both d and water numbers are related with the HLB values, but these relations are different from those for anionic and non-ionic surfactants. This is not surprising on dealing with water number (anionic and non-ionic surfactants follow different equations in the paper of Greenwald et al.), but in the case of d , Little has shown that both, anionic and non-ionic surfactants, follow the same equation. The solubility parameters of dodecyltrimethylammonium and dioctadecyldimethymammonium bromides, and the HLB value of dodecylpyridinium chloride are reported. # 2002 Elsevier Science B.V. All rights reserved.

Photocatalytic degradation of acridine dyes using anatase and rutile TiO2.

The adsorption and photodegradation of acridine orange (AO) and acriflavine (AF) dyes on two mesoporous titania crystalline phases, anatase and rutile, were experimentally studied. Anatase and rutile were characterized by nitrogen adsorption, electron scanning and transmission microscopy, and X-ray diffraction. The adsorption capacity of rutile was higher than that of anatase, while the reverse is observed for photodegradation of both dyes. The adsorption of AF on both adsorbents was higher than that of AO, which was related with the smaller size of AF molecules compared with those of AO, therefore the access of AF to the adsorption sites is favored.

DSC analysis of the state of water in surfactant-based microstructures

A review is made about the different kinds of water in surfactant-based microstructures (liquid crystals, microemulsions and micelles) and their study by DSC.

Thermal transitions in surfactant-based lyotropic liquid crystals

Abstract The state of water and several thermal transitions were examined in several surfactant/water lyotropic liquid crystalline systems. The surfactants studied were Aerosol OT (AOT), didodecyldimethylammonium bromide (DDAB), dioctadecyldimethylammonium bromide (DODAB) and M-decylphosphonic acid (DPA). In the AOT/water system, three types of water were detected: “bulk-like” water, interfacial water and hydration water (about six molecules of water per molecule of AOT). This system does not exhibit the gel-liquid-crystal transition, probably because the branched, short tails of AOT do not allow for crystallization upon cooling because of steric hindrance. In the DDAB/water and DODAB/water systems, only bulk-like water and two molecules of hydration water per molecule of surfactant were observed. The gel-liquid-crystal transition was detected at 15°C for DDAB and at 50°C for DODAB. In the DPA/water system, only bulk-like water was seen. The gel-liquid-crystal transition for this surfactant was detected at about 12°C.

Steric fitting of the rodlike micelle size

Abstract The model developed in a previous paper (P. C. Schulz, Colloid Polym. Sci. 269, 612 (1991)) was applied to rodlike micelles. The dependence of the aggregation number of rodlike micells on ionic strength, polar head size, temperature, and alkyl chain length predicted by the present model agrees well with the experimental data in the literature.

Steric fitting of the spherical micelle size

A model was developed to explain the size of spherical micelles on the basis of steric effects. Here the electrostatic repulsion within polar heads is considered as a steric effect. The predictions of this model concerning micelle size; water penetration into the hydrocarbon micelle core; and the dependence of the aggregation number on temperature, electrolyte addition, hydrocarbon chain length, head group size, and counterion size agreed quite well with literature data.

Adsorption of paraquat on mesoporous silica modified with titania: Effects of pH, ionic strength and temperature

The adsorption of the herbicide paraquat (PQ(2+)) on the binary system titania-silica has been studied in batch experiments by performing adsorption isotherms under different conditions of pH, supporting electrolyte concentration, and temperature. Adsorption kinetic on the studied material has also been carried out and discussed. PQ(2+) adsorption is very low on the bare silica surface but important on the composed TiO(2)-SiO(2) adsorbent. In this last case, the adsorption increases by increasing pH and decreasing electrolyte concentration. There are no significant effects of temperature on the adsorption. The increase of the adsorption in TiO(2)-SiO(2) seems to be related to an increase in acid sites of the supported titania and to the homogenously dispersion of the TiO(2) nanoparticles over the silica support. The adsorption takes place by direct binding of PQ(2+) to TiO(2) leading to the formation of surface species of the type SiO(2)-TiO(2)-PQ(2+). Electrostatic interactions and charge-transfer and outer-sphere complexes formations seem to play a key role in the adsorption mechanism. The analysis of thermodynamic parameters suggests that the adsorption on TiO(2)-SiO(2) is endothermic and spontaneous in nature.

Effect of alkyl chain asymmetry on catanionic mixtures of hydrogenated and fluorinated surfactants

In this work we studied and compared the physicochemical properties of the catanionic mixtures cetyltrimethyl-ammonium bromide-sodium dodecanoate, cetyltrimethyl-ammonium bromide-sodium perfluorodacanoate, octyltrimethylammonium bromide-sodium perfluorodacanoate and cetyltrimethyl-ammonium bromide-sodium octanoate by a combination of rheological, transmission electron microscopy (TEM) and polarized optical microscopy measurements. The binary mixtures of the surfactants have been analyzed at different mixed ratios and total concentration of the mixture. Mixtures containing a perfluorinated surfactant are able to form lamellar liquid crystals and stable spontaneous vesicles. Meanwhile, system containing just hydrogenated surfactants form hexagonal phases or they are arranged in elongated aggregates.