External Surface Of Clay Research Articles

Probing the Fate of Different Structures of Beta-Lactam Antibiotics: Hydrolysis, Mineral Capture, and Influence of Organic Matter

Beta-lactam antibiotics, which are used extensively in human and veterinary applications, are commonly detected in surface waters. To examine how the distinct structures of different generations of beta-lactam antibiotics can influence their persistence or degradation in environmental aqueous media, we examined the fate of two penams (amoxicillin and cloxacillin) and two cephems (cephalexin and ceftriaxone) at pH 5.0 and pH 7.0. By contrast to the lack of hydrolysis of the penam antibiotics at both pHs, we observed hydrolysis of cephalexin at pH 7.0 (t1/2 = 12 d) and ceftriaxone at pH 5.0 (t1/2 = 2.8 d). Using high-performance liquid chromatography coupled with a diode array detector or a high-resolution mass spectrometer, we were able to confirm thiotriazinone and 3-desacetyl cefotaxime as major hydrolysis products of ceftriaxone, and propose the hydrolytic cleavage of the benzene and cephem moieties from cephalexin. In addition, we studied the effects of smectite clay particles suspended in solutions without or with dissolved organic matter. The adsorption capacity of the clay was 4- to 9-fold higher at pH 7.0 than at pH 5.0. Subsequent X-ray diffraction analysis revealed that the antibiotic adsorption was not within the clay interlayer nanopores but occurred primarily on the external clay surfaces. The addition of dissolved organic matter interfered with the adsorption of a cephem antibiotic (ceftriaxone) on the clay, but the adsorption of a penam antibiotic (amoxicillin) remained unaffected. We employed molecular modeling simulations to probe the mechanisms of adsorption on the mineral surface. Our findings offer new insights on how the compound structures can dictate different fates of the beta-lactam class of antibiotics in environmental media.

Síntesis y caracterización de materiales nanoestructurados de Ni y Mo depositados sobre bentonita

Recently, clay has been accepted as excellent adsorbents, catalyst, fillers in industry. The wide usefulness of bentonite is essentially as a result of its high specific surface area, high chemical and mechanical stabilities, and a variety of surface and structural properties. Nickel and molybdenum nanoparticles with particle size distribution ranging between 30-50 nm were synthesized by chemical reduction of ions using nickel nitrate hexahydrate (Ni(NO3)6.6H2O) and ammonium molybdate tetrahydrate (NH4)6Mo7O24.4H2O) in methanol solution, respectively. The process for reducing Pt nanoparticles was carried out in presence of NaBH4, Poly(N-vinylpyrrolidone) was used as protecting agent of the obtained particles. The synthesis process was performed at room temperature. The colloidal dispersions of Ni and M were supported on bentonite by impregnation method, and then were dried at around l00ºC until the solution was completely evaporated. The anchoring of Ni and Mo nanoparticles on the bentonite surface was carried out by a thermal process in a tubular furnace adapted with a quartz tube, where samples were annealed at 400ºC under nitrogen atmosphere for 30 min with a flow rate of 50 ml min-1. The obtained samples were chacterized using X-ray diffractometer (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectrormeter (EDS). In X-rays analysis for Ni sample was possible to observe peaks of metallic Ni and formation of NiO2, where as for molybdenum appeared diffraction peaks corresponding to the phases of Mo and MoO3. Through SEM waS possible to observe the morphology of the sample and Incorporation of the metal nanoparticles of Ni and Mo, Impregnated on the support. The characterization also reveals the well disperse of these obtained Ni and Mo nanoparticles supported on the external surface of clay with roughly spherical morphology and mean diameter of 30 nm. Finally, using the EDS technique was possible to estimate the actual load on bentonite catalysts.

Spatial Location of Zerovalent Iron Nanoparticles in Montmorillonite

The spatial location of zerovalent iron nanoparticles hybridized with montmorillonite was identified with easily accessible X-ray diffraction, transmission electron microscopy, and element analyses. These hybridized nanoparticles are not intercalated into the interlayer space of clay whereas mainly located on the external surface of clay. This result would be of great importance for the sorption-based applications of these heterostructures.

Core–shell structured iron nanoparticles well dispersed on montmorillonite

Iron nanoparticles have been successfully synthesized using sodium borohydride solution reduction of ferric trichloride hexahydrate in the presence of montmorillonite as an effective protective reagent and support as well. A combination of characterizations reveals the well disperse of these obtained iron nanoparticles supported on the external surface of clay with roughly spherical morphology and mean diameter of 55 nm. The particles are oxidation resistant well with iron core–iron oxide shell structure. The shell thickness of 3 nm remains almost invariable under ambient conditions. Discernable hysteresis loop reveals ferromagnetic behavior of the iron nanoparticles, which make them easy for magnetic separation and potential in some practical applications.

Montmorillonite incorporated with magnesium oxide

MgO was incorporated into montmorillonite (MMT) though the controlled formation of Mg(OH)2 followed by calcination. The evidence for Mg2+ in MMT before calcination was concluded from TG curves where two different temperature ranges for Mg(OH)2 dehydroxylation suggested that the location of Mg2+ at its internal and external surfaces. FTIR by diffuse reflectance technique of calcined sample showed a typical MgO band. XRD indicated a decrease in structural order and no collapse of clay structure. The organic compounds adsorption to MMT modified with MgO as suggested by increased degradation temperatures occurred at internal and external clay surfaces besides in an area formed probably by MgO and MMT layers.

Investigation of rheological and collodial properties of bentonitic clay dispersion in the presence of a cationic surfactant

The effect of cationic surfactant dodecyltrimethylammonium bromide (DTABr) on the flow behavior of Na activated bentonite dispersions was characterized by plastic viscosity, relative viscosity and yield values. In order to make definite the type of flow behavior, three common empirical equations were tested: Bingham, Power law and Casson equations. The constants for the three models were determined by using least square approximation and in each case the coefficient of determination ( r 2) was calculated. The interaction of the surfactant with external surfaces of clay was investigated by electrokinetic measurements. Whether DTABr molecules penetrate into interlayers of clay structures or not can be determined on basis of d (0 0 1) -spacing measurements using XRD after addition of each additives. All experimental results were evaluated by considering the interaction modes between the particles and surfactant molecules.

A novel system for reducing leaching from formulations of anionic herbicides: clay-liposomes.

A new approach was developed for reducing leaching of herbicides and contamination of groundwater. Liposome-clay formulations of the anionic herbicides sulfometuron and sulfosulfuron were designed for slow release by incorporating the herbicide in positively charged vesicles of didodecyldimethylammonium (DDAB), which were adsorbed on the negatively charged clay, montmorillonite. Freeze fracture electron microscopy demonstrated the existence of DDAB vesicles and aggregated structures on external clay surfaces. X-ray diffraction results for DDAB with montmorillonite imply the existence of DDAB bilayers with an oblique orientation to the basal plane within the clay interlayer space at adsorbed amounts beyond the cation exchange capacity of the clay. Adding DDAB with sulfometuron or sulfosulfuron to montmorillonite yielded 95% or 83% adsorption of the herbicide at optimal ratios. Liposome-clay formulations exhibited slow release of the herbicides in water. Analytical measurements in soil columns demonstrated 2-10-fold reduction in leaching of the herbicides from liposome-clay formulations in comparison with commercial formulations. Percents of root growth inhibition of a test plant in the upper soil depths were severalfold higher for the liposome-clay formulations than for the commercial ones. Consequently, liposome-clay formulations of anionic herbicides can solve environmental and economical problems by reducing their leaching.

Towards Establishing the Age, Location, and Identity of the Inert Soil Organic Matter of a Spodosol

AbstractAn interlayer clay‐organic complex has been isolated from a near‐surface horizon of a recent Spodosol from New Zealand. Treatment with hydrogen peroxide selectively removed the organic material attached to external clay surfaces. The radiocarbon age of the treated complex, determined by accelerator mass spectrometry, was 6716 ± 524 years B.P. Since this value refers to the interlayer organic species which has been completely protected against microbial attack, and contamination by “young” carbon, it may be regarded as the “true” age of the soil, that is, the starting point of humus formation and pedogenesis. The interlayer organic carbon comprised approximately 13 percent of the total carbon in the soil horizon.We propose that a biologically inert organic matter (IOM) fraction may be isolated from most soils as this fraction is commonly associated with clay‐size particles. Evidence is also accumulating to indicate that IOM is dominantly composed of polymethylenic structures, probably derived from natural waxes, and aliphatic biopolymers present in protective layers of vascular plants.

Methane Solubilities in Clay Slurries

AbstractMethane solubilities at 25°C were measured at 350, 550, and 750 psia in dilute (< 11 wt. %) clay slurries of Na-montmorillonites and argillaceous sediment. Methane solubilities were not significantly affected by the presence of clay. Water hydrated onto the external clay surfaces did not appear to exclude methane. In addition there was no detectable sorption of methane onto the clays. The measured solubilities are consistent with an open structure of the water hydrated onto the clay surface for which the partial molal volume is larger than that of normal water. The results imply that aqueous methane solubilities measured in the laboratory can be used to determine degrees of methane saturation in interstitial solutions in unconsolidated sediments.

Effects of Clay Surfaces on the Adsorption and Biological Decomposition of Proteinaceous Components of Fulvic Acid

AbstractShaking of an aqueous fulvic acid (FA) solution with montmorillonite at pH 2.5 at room temperature, removed about 43 % of the FA fraction containing proteinaceous components. About 65 % of this fraction was adsorbed reversibly in interlayers, 20 % on external surfaces and 15 % was adsorbed irreversibly. The relative molar distribution of the amino acids (after hot acid hydrolysis) in the original FA, the FA fraction adsorbed in clay interlayers and in the FA fraction not adsorbed by montmorillonite was relatively uniform, indicating that clay interlayers were relatively inefficient for separating proteinaceous constituents from main structural FA components. External clay surfaces, however, appeared to adsorb peptides and/or proteins that differed qualitatively from those adsorbed on internal clay surfaces.Five successive treatments with fresh clay showed that only 61 % of the FA fraction containing proteinaceous components could be adsorbed.The original FA and all fractions separated from it by montmorillonite were able to support microbial growth without the addition of an external N source. The rate of biodegradation decreased when the FA was complexed with montmorillonite.

Surface and intercalate chemistry of layered silicates. Part V. Infrared, ultraviolet, and visible spectroscopic studies of benzidine–mont-morillonite and related systems

Clay minerals of the montmorillonite family provide a matrix on which radical cations of a variety of amines may be formed. The origin of the different colours associated with the benzidine (bzn)–. NNN′N′-tetramethylbenzidine (tbzn)–, and trans-4.4′-diaminostilbene (dsn)-montmorillonite complexes has been further elucidated by u.v. and visible reflectance and i.r. spectroscopy. It is established that both uni- and di-positive bzn radical cations and protonated bzn moieties can exist at the internal and external clay surfaces. This is in contrast to the situation which prevails for tbzn where only the unipositive radical cation and protonated moieties appear to be formed. The interaction of montmorillonite with dsn dihydrochloride is similar to that of bzn but the nature of the product is modified by the precence of protons in cation-exchange sites.

Reactions between Fulvic Acid and Cu2+-Montmorillonite

AbstractShaking of water-soluble fulvic acid with Cu2+-montmorillonite at pH 2·5 increased the interlamellar spacing from 10·0 to 15·1 A. The spacings were measured at ≈ 0% relative humidity. The extent of interlayer adsorption decreased with increase in pH. Differential thermal analysis and thermogravimetric examinations showed that in addition to interlayer adsorption, fulvic acid was also retained on external clay surfaces. The FA was held so tightly by the Cu2+-clay that > 3/4 of the total amount adsorbed, including degradation products formed from it, resisted decomposition even when heated to 1000°C. I.R. spectra showed that β-diketone groups in fulvic acid reacted with Cu2+ in or on the clay to form acetylacetonate-type chelates. Indications were obtained that the mechanism postulated for the FA-Cu2+-clay interaction may also apply to reactions between FA and montmorillonite saturated with other di- and trivalent metal ions. Reactions of FA in aqueous solutions with metal ions in the presence of clays differ from those in the absence of clay. Montmorillonite appears to affect the conformation of the fulvic acid polymer in a way that favours reactions between C=O groups and metal ions, a type of reaction that has so far not been observed in aqueous solutions in the absence of clay.

Ion Mobilities and Electric Charge of External Clay Surfaces Inferred from Potential Differences and Osmotic Flow

AbstractBentonite, illite, and kaolinite clays were compacted, made homoionic with various cations, and placed between chloride solutions of the respective cations of different concentrations. Rates of osmotic flow, electric potentials in the solutions and streaming potentials were measured across these compacted clay membranes. The osmotic flow was often from the high salt to low salt concentration side and was generally in the direction of more negative potential, indicating electroosmosis as the mechanism involved in osmotic flow. Diffuse layer theory was used to estimate the concentration ranges in which the measured external potential differences were not appreciably different from the respective potentials in solution inside the clay. Assuming the osmotic movement to be electroosmosis, the ζ potentials were calculated from the observed potential gradients and the osmotic flux. The portion of adsorbed cations participating in the diffuse portion of the double layer was then calculated from ζ. This “mobile” fraction of the adsorbed cations appears to decrease for multivalent cations as the equilibrium solution concentration decreased. La3+ kaolinite and Willalooka illites were positively charged and adsorbed Cl‐ as diffuse layers. The mobile fractions estimated by this method for bentonite are in reasonably good agreement with mobile fractions estimated from diffusion and conductance measurements.