A modified procedure for bentonite purification and a new method for the quantitative characterization of bentonite using smectite content are reported. Bentonite found in a drill core of Tsunagi Mine, Niigata, Japan was evaluated by the new method to demonstrate the substantial increase in smectite content from 40% in the original bentonite to 75% after purification using a new procedure. Powder samples were prepared by putting blocks of bentonite into acetone to remove water without mechanical crushing. The powdered, acetone-dried bentonite was purified by a dispersion-sedimentation method in water after cation exchange of the interlayer Ca2+ ion with Na+ ion by the reaction of raw bentonite with aqueous NaCl. The purification was evaluated using X-ray diffraction and thermogravimetric analyses (TG). The raw bentonite contained feldspar, quartz, and cristobalite, and feldspar and quartz were removed by the new purification procedure. The purification was evaluated quantitatively by comparing the TG data before and after the purification. The purified bentonite swelled in water to give a stable aqueous suspension and 3 g of purified bentonite dispersed in 60 mL of water was stable for several days. The replacement of interlayer sodium with dibehenyldimethylammonium gave an organophilic clay, which swelled in toluene. The bentonite has potential practical uses as a purified bentonite and an organophilic bentonite.
An organophilic bentonite was prepared by means of a reaction of natural Na-montmorillonite with trimethyldococylammonium which has an especially long n-alkyl chain. The addition of trimethyldococylammonium to montmorillonite was in the range 0.25–3.0 times the cation exchange capacity (CEC) of the clay (i.e. 0.23–2.82 mmol/g clay). The particle morphology in organic liquid suspensions of organoclay complexes was studied by measuring the viscosity based on Eyring’s rate process and Robinson’s relative sediment volume. In toluene, montmorillonite with 1.17 mmol/g clay trimethyldococylammonium (1.25 times the CEC) had the largest specific gel volume, relative sediment volume, and K-factor. The results of the stoichiometry for trimethyldococylammonium-montmorillonite show that practically all of the quaternary ammonium was adsorbed to montmorillonite. Maximum half widths of 001 reflections from X-ray diffraction patterns were obtained in the range 0.74–1.17 mmol/g clay, indicating a disordered arrangement of the organic cation molecules intercalated between the layers. Appreciable shifts to lower-frequency regions in the Fourier transform infrared absorption spectra as a result of CH2-stretching vibrations were observed with increasing amounts of the organic cation. When increasing the amount of organic cation added to the clay from 0.94 to 1.41 mmol/g clay, a large shift occurred to the lower-frequency side, approaching the frequency of the organic cation alone. This indicates that the interaction between adjacent hydrocarbon chains becomes progressively stronger, due to van der Waals attraction, with increases in the amount of organic cation. Interactions of the alkyl chains in trimethyldococylammonium-montmorillonite complexes with irregularly distributed and randomly arranged alkyl chains between the silicate layers were weak, and, as a result, solvation with external organic liquids occurred and gel formation developed through macroscopic swelling of the organoclay.
Solid−solid reactions of an acidic clay and organoamines were investigated to obtain organophilic clays. The reaction is based on the acid−base reaction between the acidic cite in the interlayer space of the clay and the organoamines (n-octadecylamine and oleylamine). The reactions gave organophilic clays identical to the organoammonium clays prepared by a conventional ion exchange reaction with organoammonium chloride in aqueous media. Due to the simple and environmentally benign nature of the solid−solid reactions, the present reactions and the products are applicable to industrial uses. In addition, oleylamine gave better results in terms of viscosity of the suspension if compared with that of the n-octadecylamine system, showing the important roles of surfactant molecular nature on the properties of organophilic clays.
An organophilic clay was obtained by the intercalation of dioctadecyldimethylammonium ions into the interlayer space of a purified bentonite. The organophilic clay was characterized by its excellent whiteness, which originated from the used purified bentonite with a low content of colored impurities, suitable for its practical application in paints, cosmetics, polymer additives, etc. The dioctadecyldimethylammonium− bentonite clay was applied as a support to accommodate polyaromatic molecules to afford luminescent hybrids with high luminescence efficiency, showing its usefulness as a component of photofunctional hybrid materials.
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