Sorption and immersional wetting on clay minerals having modified surface. I. Surface properties of nonswelling clay mineral organocomplexes

Facile Synthesis of Visible Light-Induced g-C₃N₄/Rectorite Composite for Efficient Photodegradation of Ciprofloxacin

A novel kind of g-C₃N₄/rectorite composite with high visible-light photoactivity was developed via a mild and cost effective two-step process. Ciprofloxacin (CIP), a typical antibiotic, was applied to evaluate the photoactivity of the received catalysts. Furthermore, the by-products of CIP photodegradation were analyzed and the possible degradation pathways were also discussed. Compared with bare photocatalysts, the received composite possessed well reusability and higher photoactivity towards CIP. According to the characterization analysis results, layered g-C₃N₄ was successfully immobilized on layered rectorite, which could not only promote its adsorption capacity but also provide more reactive sites for CIP adsorption and photodegradation. Compared with bare g-C₃N₄, the photoactivity of the prepared composite was significantly enhanced. The enhancement should be mainly due to the lower recombination rate of photogenerated carriers and the improved adsorption capacity toward CIP. This study demonstrated that the obtained g-C₃N₄/rectorite composite should be a promising alternative material in wastewater treatment.

Swelling behavior of organoclays in styrene and exfoliation in nanocomposites

Organoclays were prepared by cationic exchange of montmorillonite (MMT) with three commercial surfactants: octadecylamine (ODA), hexadecyltrimethylammonium bromide (HTAB), benzalkonium chloride (BAC), and an in-house synthesized surfactant, vinylbenzylalkyldimethylammonium chloride (VDAC). The swelling behaviors of organoclays in styrene were compared by wettability and rheology measurements. VDAC-MMT had the slowest capillary rise rate in styrene. The Washburn equation was found not suitable for the swellable organoclay powders. All organoclay-styrene and organoclay-toluene mixtures demonstrated yield stress. However, VDAC-MMT-styrene and VDAC-MMT-toluene mixtures showed significant higher yield stresses than the other organoclay mixtures. The wettability and rheology measurements indicate that VDAC-MMT bearing a styryl functional group has the strongest interaction with styrene monomer and toluene. In order to further evaluate the extent of swelling and the microstructure, polystyrene (PS)-clay nanocomposites were prepared by in situ polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that ODA and HTAB-MMT led to intercalated PS-clay nanocomposites, while VDAC-MMT formed exfoliated PS-clay nanocomposites.

Chemical instability of octadecylammonium monolayers

Octadecylammonium in monolayers transforms into a carbamate derivative, as observed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and 13C nuclear magnetic resonance (NMR) spectroscopy.

Aggregation and Decomposition of a Pseudoisocyanine Dye in Dispersions of Layered Silicates

The optical properties of reaction systems composed from a pseudoisocyanine (PIC) solution and dispersed layered silicates were studied using visible spectroscopy. Two series of reduced-charge montmorillonites were used as the silicate materials. Each series consisted of eight samples with different layer charges, which were prepared from one parent material. Observed trends were verified with another series of dioctahedral and trioctahedral smectites of different layer charges, structure, and origin. The layer charge density of the silicates significantly affected the aggregation of PIC cations. In addition to the formation of J-aggregates, dye spectral bleaching was also observed. Silicates with very low charge densities induced neither significant aggregation nor spectral bleaching of the dye. The highest levels of PIC J-aggregate formation were found in dispersions of the layered silicates with a medium surface charge. However, reversible spectral bleaching was also observed in some cases. PIC dye cations probably change their conformations during the adsorption process, due to the tension resulting from the large size of the cations and the relatively high charge density at the silicate surface. The bleached dye recovers, at least partially, with the rearrangement and redistribution of the dye cations over the time. In contrast, the presence of silicates with very high charge densities (synthetic taeniolite and fluorohectorite) led to the very fast and irreversible decomposition of the PIC. Perhaps, the tension in adsorbed dye cations, induced by the high charge density at the silicate surface, resulted in significant destabilization and a decomposition reaction of the chromophore.

The Effect of Cadmium Ion Adsorption on the Growth of CdS Nanoparticles at Colloidal Silica Particle Interfaces in Binary Liquids

Adsorption isotherms have been determined for the binding of Cd2+ onto the surfaces of hydrophilic A200 SiO2 and hydrophobic R972 SiO2 particles dispersed in ethanol (1>)-cyclohexane (2) mixtures at ethanol mole fractions of x1 = 0.05, 0.10, 0.20, and 0.40. CdS nanoparticles have been generated in situ within the ethanolic nanoreactors at surfaces of SiO2 particles in the different ethanol-cyclohexane binary liquids by the addition of hydrogen sulfide. Absorption spectra of the CdS particles provided information on their quantity, absorption edges, optical band gaps, and mean diameters. Good correlations have been obtained between the adsorption isotherms and size of the CdS particles as well as between the adsorption isotherms and the amount of CdS formed. The smallest CdS particles (ca. 6 nm diameter) have been obtained on the surfaces of SiO2 particles dispersed in ethanol (1>)-cyclohexane (2) mixtures at ethanol mole fractions of x1 = 0.05. More CdS particles have been observed to coat the hydrophilic A200 SiO2 than the hydrophobic R972 particles. In the x1 = 0.10 ethanol (1)-cyclohexane (2) liquid mixtures up to 10% of the SiO2 surface can be covered by CdS nanoparticles. Immersion wetting enthalpy measurements in methanol established the surface of the SiO2 particles to be hydrophilic, which became partially hydrophobic upon and the binding of cadmium ions and hence upon the subsequent formation of CdS. Copyright 1997 Academic Press. Copyright 1997Academic Press