Phyllosilicate Clay Research Articles

Preconcentration and voltammetric analysis of mercury(II) at a carbon paste electrode modified with natural smectite-type clays grafted with organic chelating groups

This study is devoted to the evaluation of a carbon paste electrode modified by a natural 2:1 phyllosilicate clay functionalized with either amine or thiol groups as a sensor for mercury(II). Functionalization was achieved by grafting the pristine clay via its reaction with 3-aminopropyltriethoxysilane (APTES) or 3-mercaptopropyltrimethoxysilane (MPTMS), respectively. The electroanalytical procedure comprises two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using differential pulse anodic stripping voltammetry. The different parameters that govern the two steps (accumulation time, concentration of the analyte, composition of the detection medium, potential and duration of electrolysis) were studied in detail. After optimization, a linear response was obtained in the concentration range from 0.1 to 0.7 μM Hg(II). In these conditions, the detection limits of the method were found to be 8.7 × 10 −8 and 6.8 × 10 −8 M, respectively, for the amine- and thiol-functionalized clays, on the basis of a signal-to-noise ratio of 3. The effect of potential interference on the determination of Hg(II) by the carbon paste electrode modified with the thiol-functionalized clay was also studied and the applicability of the method to real sample analysis was evaluated.

Fabrication of functional protein–organoclay lamellar nanocomposites by biomolecule-induced assembly of exfoliated aminopropyl-functionalized magnesium phyllosilicates

An aminopropyl-functionalized magnesium phyllosilicate clay was synthesized and used as an exfoliated precursor for the intercalation of myoglobin (Mb), haemoglobin (Hb) or glucose oxidase (GOx). Intercalation was achieved by exfoliation of the as-synthesized organoclay in water followed by room temperature re-assembly of the lamellar phase in the presence of negatively charged protein molecules. X-Ray diffraction data of the resulting nanocomposites showed an expansion of the interlayer d001 spacing from 1.6 nm in the parent organoclay to 4.3 and 6.4 nm for samples prepared with Mb and GOx, respectively, indicating that these biomolecules were successfully incorporated into the gallery regions. In both cases, FTIR and circular dichroism spectroscopies showed that secondary structures of the intercalated biomolecules were preserved. In addition, UV-vis spectroscopy revealed that the redox and CO/O2 binding properties of the intercalated Mb, as well as the enzymatic activity of GOx, were retained in the protein–organoclay nanocomposites. Significantly, the relative catalytic activities of GOx between pH values of 3 to 10, and up to temperatures of 65 °C, were higher in the hybrid nanocomposites compared with the native enzyme in solution. Similar experiments with Hb produced composites consisting of structurally and functionally intact protein molecules immobilized within a disordered matrix of organoclay lamellae.

Topochemical Transformation of Phyllosilicate Clay into Chlorite and Brucite.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Identification and reduction of urinary aflatoxin metabolites in dogs

Hydrated sodium calcium aluminosilicate (HSCAS) is a phyllosilicate clay commonly used as an anticaking agent in animal feeds. HSCAS tightly and selectively adsorbs aflatoxin. In 1998, 55 dogs died in Texas after eating dog food containing aflatoxin (150–300 ppb). The corn in the diets was contaminated with aflatoxin. Six dogs were given a low-level, sub-clinical dose of aflatoxin B 1. On average, 71.5% of aflatoxin M 1 cleared within 6 h after dosing, increasing to 90.4% after 12 h. Aflatoxin M 1 was no longer detectable in urine after 48 h. Aflatoxin P 1 was not found in urine compared to large amounts of M 1 and trace amounts of Q 1. In a crossover study, six dogs randomly fed a commercial dog food (no-clay control) or coated with HSCAS (0.5% by weight) were subsequently administered a sub-clinical dose of aflatoxin B 1. Diets were switched and the process repeated. The HSCAS-coated diet significantly reduced urinary aflatoxin M 1 by 48.4% ± 16.6 SD versus the control diet. In conclusion, HSCAS protects dogs fed diets with even minimal aflatoxin contamination. Despite regular and careful ingredient screening for aflatoxin, low concentrations may reach the final product undetected. Therefore, HSCAS may provide the pet food industry further assurance of canine diet safety.

Comparative study of the sonication effect on the thermal behaviour of 1:1 and 2:1 aluminium phyllosilicate clays

The aim of this work is to compare the effect of sonication on the thermal behaviour of kaolinite and pyrophyllite. The results show that sonication produces a significant particle size reduction of both clays. Besides, this treatment modifies the thermal behaviour of these samples. Nevertheless, the change in particle size and in the modification of the thermal behaviour is different for both clays. Sonication facilitates the dehydroxylation of both clays, although, the temperature shift of the dehydroxylation is more significant for pyrophyllite than for kaolinite. Additionally, the exothermic effect at 987 °C for kaolinite is not affected by sonication while that at 1210 °C for phyrophyllite is shifted to lower temperatures.

Topochemical Transformation of Phyllosilicate Clay into Chlorite and Brucite

The intralayer structure of phyllosilicate clay could be manipulated into chlorite and brucite depending on the degree of leaching by the NaOH content. Selective leaching of tetrahedral Si sheets would result in the topochemical transformation of the 2:1 type silicate clay into chlorite, whereas complete removal of tetrahedral Si sheets would lead to the formation of brucite.

Sorption and oxic degradation of the explosive CL-20 during transport in subsurface sediments

The abiotic sorption and oxic degradation processes that control the fate of the explosive CL-20, Hexanitrohexaazaisowurtzitane, in the subsurface environment were investigated to determine the potential for vadose and groundwater contamination. Sorption of aqueous CL-20 is relatively small ( K d=0.02–3.83 cm 3 g −1 for 7 sediments and 12 minerals), which results in only slight retardation relative to water movement. Thus, CL-20 could move quickly through unsaturated and saturated sediments of comparable composition to groundwater, similar to the subsurface behavior of RDX. CL-20 sorption was mainly to mineral surfaces of the sediments, and the resulting isotherm was nonlinear. CL-20 abiotically degrades in oxic environments at slow rates (i.e., 10s to 100s of hours) with a wide variety of minerals, but at fast rates (i.e., minutes) in the presence of 2:1 phyllosilicate clays (hectorite, montmorillonite, nontronite), micas (biotite, illite), and specific oxides (MnO 2 and the ferrous-ferric iron oxide magnetite). High concentrations of surface ferrous iron in a dithionite reduced sediment degraded CL-20 the fastest (half-life < 0.05 h), but 2:1 clays containing no structural or adsorbed ferrous iron (hectorite) could also quickly degrade CL-20 (half-life < 0.2 h). CL-20 degradation rates were slower in natural sediments (half-life 3–800 h) compared to minerals. Sediments with slow degradation rates and small sorption would exhibit the highest potential for deep subsurface migration. Products of CL-20 oxic degradation included three high molecular weight compounds and anions (nitrite and formate). The 2–3.5 moles of nitrite produced suggest CL-20 nitro-groups are degraded, and the amount of formate produced (0.2–1.2 moles) suggests the CL-20 cage structure is broken in some sediments. Identification of further degradation products and CL-20 mineralization rates is needed to fully assess the impact of these CL-20 transformation rates on the risk of CL-20 (and degradation product) subsurface movement.

Retention of dissolved organic matter by phyllosilicate and soil clay fractions in relation to mineral properties

The dependence of dissolved organic carbon (DOC) retention on mineral phase properties is uncertain where soil solution pH is neutral. Therefore, ten soil and phyllosilicate clay fractions were used (after carbon oxidation) to investigate relationships between DOC retention at pH 7 and content of dithionite-extractable iron (Fe d), specific surface area (SSA) and cation exchange capacity (CEC). DOC sorption sites were identified by blocking reactive hydroxyl groups with phosphate on subsamples. Reversibility of DOC sorption was determined by desorption experiments. Soil clay fractions sorbed about twice as much DOC as phyllosilicates. A positive relationship between DOC sorption and Fe d content suggests that this is due to pedogenic oxides in soil clays. Positive trends were also observed with SSA or CEC. Sorption of 9–44 μg DOC m −2 indicates that DOC interacts only with fractions of the mineral surfaces. Phosphate treatment of subsamples reduced DOC sorption by 39–64% indicating a contribution of reactive hydroxyl groups as well as of siloxane surfaces of phyllosilicate clay minerals to DOC sorption. Desorption experiment removed 13–50% of sorbed DOC. Samples with and without phosphate treatment desorbed similar absolute amounts of DOC indicating that DOC associations with siloxane surfaces may be weaker than interactions with hydroxyl groups.

Higher‐Order Synthesis of Organoclay Pipes Using Self‐Assembled Lipid Templates

The template‐directed synthesis of helical ribbons and cylindrical micropipes (see Figure) of organically functionalized magnesium phyllosilicate clay is achieved by high fidelity decoration of self‐assembled phospholipid tubules. The replicas are produced by electrostatic interactions between the positively charged organoclay precursors and charged lipid headgroups exposed on the surfaces of the organic template.

Proton binding at clay surfaces in water

This article discusses the points that have more impact in the protonation–deprotonation behavior of a phyllosilicate clay surface in aqueous media. Some concepts that are currently used to explain the behavior of the oxide–water interface are now applied to the clay–water interface, and a rather new interpretation of the role of structural charges on the affinity of edge groups for protons is also given. Proton binding at a phyllosilicate clay surface takes place at oxygen-containing groups. As in the case of oxygen-containing molecules, the groups behave as monoprotic entities and undergo only one protonation–deprotonation step in a normal pH range. The protonation behavior depends on the intrinsic affinity of surface groups and long-range electrostatics. The MUSIC model confirms that the proton affinity of siloxane and gibbsite-like groups located at the basal surfaces (001 planes) of 2:1 or 1:1 clays is very low. On the contrary, the proton affinity of surface groups at the broken edges is adequate to undergo protonation–deprotonation reactions in a normal pH range. The reactivity of edge groups is also affected by the presence of structural charges within the clay layer. These charges produce an electric field that modifies not only the reactivity of the basal surfaces but also that of the edge surfaces. When the edge surface has a zero net charge, the electrical potential is negative due to the presence of the mentioned negative charges. Evidences for this are obtained from proton adsorption curves performed at different supporting electrolyte concentration.

Mineral neoformation in pore spaces during alteration and weathering of andesitic rocks in humid tropical Indonesia

The morphology, chemistry, and mineralogy of minerals newly formed in voids—products of weathering of andesitic rocks—were studied using optical and submicroscopic techniques on thin sections, combined with scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDXRA), and X-ray diffraction analysis on subsamples. Samples were taken from the core, the outer core, and the soft outer layers of weathered andesitic boulders in the Cigudeg area, West Java, about 75 km south of Jakarta, Indonesia, with udic moisture and isohyperthermic temperature regime. The neoformed minerals observed in planar voids and cavities comprise 1:1 phyllosilicates, goethite, and gibbsite, and juxtaposed coatings of halloysite, mixed layer phyllosilicates, goethite, and gibbsite. The mineral sequences observed confirm former studies on the groundmass of the boulder: in the first weathering layer, an absolute accumulation of gibbsite takes place; further away from the core, the gibbsite is redissolved, and replaced by illuvial phyllosilicate clay. The possibility of inheritance of the 2:1 layer silicates from a hydrothermal alteration is discussed. The sharp boundaries in the juxtaposed coatings point to a stepwise, sequential—rather than a gradual—evolution of the microenvironment.

Halloysite: A Low-Cost Alternative

Filling ('loading') of nanotubes has been of interest for over a decade. [ 1 ] Past investigations have focussed on carbon nanotubes (CNTs) or boron nitride nanotubes (BNNTs), both of which are expensive and technologically demanding to produce in bulk. A cheap, low-tech alternative, morphologically similar to multiwalled CNTs, is halloysite, a hydrated polymorph of the 1:1 phyllosilicate clay kaolinite. Halloysite nanotubes (HNTs) form in natural deposits. Preparation involves simply digging them from the ground and drying. HNTs are ideal for applications involving loading because the external (tetrahedral sheet) and internal (octahedral sheet) HNT surfaces differ, offering scope for chemical control of preferential internal, rather than external, loading of desired components.

Possible role of aluminum in stabilizing organic matter in particle size fractions of Chernozemic and solonetizic soils

Although phyllosilicate clays, with their large surface areas, are often considered to play the leading role in stabilizing soil organic matter against microbial attack, several studies have suggested recently that oxides of Al and Fe may stabilize organic matter in some soils. The distribution of organic C and oxides in clay (&lt; 0.2 and 0.2–2 mm) and silt fractions (2–5, 5–20, and 20–50 mm) of four Saskatchewan soils (organic C ranged from 21 to 46 g kg-1) was examined to differentiate the contributions of oxides and specific surface to organic matter retention. Carbon concentrations in the particle size fractions (separated following ultrasonic dispersion of the soils) tended to be highest in the fine silt and coarse clay fractions, not in the fine clay as would be expected if specific surface was the sole factor governing organic matter content. When data for the four soils were pooled there was a strong relationship between organic C (y) in the size fractions and Al (x) extracted by dithionite-citrate-bicarbonate [y = 33.9 x0,5 - 7.3; R2 = 0.90***], suggesting a role for A1 in determining the C storage capacity of the size fractions. The C: A1 ratio increased from an average of 12:1 in clay-sized material to 28:1 in coarse silt. Because it had less A1 per unit mass of C, organic matter in the silt separates may be more weakly bonded to mineral material than is clay-associated organic matter. This may imply that organic matter bound to silt is less stable, and thus susceptible to mineralization, than is organic matter residing in the clay fraction. Key words: Organic matter stabilization, particle size separates, extractable A1 and Fe

Highly effective adsorption of heavy metal ions by a thiol-functionalized magnesium phyllosilicate clay.

A thiol-functionalized layered magnesium phyllosilicate material (called Mg-MTMS), prepared by a direct and cost-effective co-condensation synthesis, has been investigated as a high-capacity adsorbent for heavy metal ions. Structural characterization by powder X-ray diffraction, infrared spectroscopy, solid-state 13C and 29Si NMR spectroscopies, and elemental analyses confirms the smectite-type structure and the high organic moiety content of this material. Mg-MTMS was found to be highly effective for the adsorption of Hg(II), Pb(II), and Cd(II) ions, exhibiting unprecedented metal ion uptake capacities of 603, 365, and 210 mg of metal/g of adsorbent, respectively. Mg-MTMS shows an equivalent affinity for the three metal ions, removing them from mixed metal solutions with an equal ion uptake capacity (approximately 400 mg of metal/g of adsorbent). Metal-loaded Mg-MTMS can be regenerated by acid treatment without altering the adsorbent properties. The high effectiveness of Mg-MTMS for the capture of metal ions is attributed to both the high concentration of complexing thiol groups (6.4 mmol of SH/g of Mg-MTMS) and the expansion capability of the framework, which facilitates the accessibility of the binding sites.

Immobilization of Pseudomonas cepacia lipase in a phyllosilicate sol-gel matrix: effectiveness as a biocatalyst.

A novel procedure is described for immobilizing a lipase from Pseudomonas cepacia (PS-30) within a phyllosilicate sol-gel matrix. The method is based on cross-linking a phyllosilicate clay with silicate polymers produced by the controlled hydrolysis of tetramethyl orthosilicate (TMOS). The activity of the phyllosilicate sol-gel-immobilized lipase was dependent upon the type of alkylammonium salt, inorganic catalyst and volume ratio of phyllosilicate clay to TMOS used. Lipase PS-30 immobilized in this way was more stable and had higher activity compared with the free lipase. Studies on the lipase-catalysed esterification of lauric acid with octan-1-ol in iso-octane showed that under controlled water activity conditions the phyllosilicate sol-gel-immobilized lipase had better activity compared with other supported lipase preparations. In addition, the phyllosilicate sol-gel-immobilized lipase was reusable for at least five esterification cycles without significant loss of activity.

Effect of aluminosilicates and bentonite on aflatoxin‐induced developmental toxicity in rat

Numerous studies have established that aflatoxin is a potent developmental toxin in animals. Previous research has demonstrated that a phyllosilicate clay, hydrated sodium calcium aluminosilicate (HSCAS or Novasil PIE TM), tightly binds and immobilizes aflatoxins in the gastrointestinal tract of animals and markedly reduces the bioavailability and toxicity of aflatoxin. Our objective in this study was to utilize the pregnant rat as an in vivo model to compare the potential of HSCAS and bentonite to prevent the developmental toxicity of aflatoxin. Aluminosilicates (HSCAS) and bentonite were added to the diet at a level of 0.5% (w/w) and fed to the pregnant rat throughout pregnancy (i.e. days 0–20). Test animals were fed an aflatoxin-contaminated diet (2.5 mg kg−1 diet) with or without sorbents during gestation days 6–15. Evaluations of toxicity were performed on day 20. These included maternal (mortality, body weights, feed intake and litter weights), developmental (embryonic resorptions and fetal body weights) and biochemical (ALT, AST and AP) evaluations. Sorbents alone were not toxic and aflatoxin alone resulted in significant maternal and developmental toxicity. Animals treated with phyllosilicate (plus aflatoxin) were comparable to controls following evaluations for resorptions, live fetuses and fetal body weights, as well as biochemical parameters. While bentonite plus aflatoxin resulted in significant reduction in fetal body weight, none of the fetuses from HSCAS or bentonite plus aflatoxin-treated groups had any gross, internal soft tissue or major skeletal malformations. Copyright © 1999 John Wiley & Sons, Ltd.

Effect of aluminosilicates and bentonite on aflatoxin-induced developmental toxicity in rat.

Numerous studies have established that aflatoxin is a potent developmental toxin in animals. Previous research has demonstrated that a phyllosilicate clay, hydrated sodium calcium aluminosilicate (HSCAS or Novasil), tightly binds and immobilizes aflatoxins in the gastrointestinal tract of animals and markedly reduces the bioavailability and toxicity of aflatoxin. Our objective in this study was to utilize the pregnant rat as an in vivo model to compare the potential of HSCAS and bentonite to prevent the developmental toxicity of aflatoxin. Aluminosilicates (HSCAS) and bentonite were added to the diet at a level of 0.5% (w/w) and fed to the pregnant rat throughout pregnancy (i.e. days 0-20). Test animals were fed an aflatoxin-contaminated diet (2.5 mg kg(-1) diet) with or without sorbents during gestation days 6-15. Evaluations of toxicity were performed on day 20. These included maternal (mortality, body weights, feed intake and litter weights), developmental (embryonic resorptions and fetal body weights) and biochemical (ALT, AST and AP) evaluations. Sorbents alone were not toxic and aflatoxin alone resulted in significant maternal and developmental toxicity. Animals treated with phyllosilicate (plus aflatoxin) were comparable to controls following evaluations for resorptions, live fetuses and fetal body weights, as well as biochemical parameters. While bentonite plus aflatoxin resulted in significant reduction in fetal body weight, none of the fetuses from HSCAS or bentonite plus aflatoxin-treated groups had any gross, internal soft tissue or major skeletal malformations.

Molecular characterization of high affinity, high capacity clays for the equilibrium sorption of ergotamine

Ergot alkaloids (mycotoxins) produced by Claviceps and Neotyphodium species of fungi may contaminate animal feedstuffs and result in disease in livestock. In this study, diverse phyllosilicate clays and other adsorbent materials, differing in chemical and structural characteristics, were tested for their ability to sorb ergotamine, a prevalent ergot mycotoxin, from acidic solution. Results indicated minimal binding to those sorbents possessing low surface area, cation exchange capacity and inaccessible interlayer regions. Cetyl pyridinium-exchanged montmorillonite (organoclay) exhibited decreased propensity for ergotamine in acidic solution as compared with the unexchanged hydrophilic parent clay. The highest ergotamine sorption was observed with cation exchanged montmorillonite clays; whereas, when collapsed, these same clays sorbed very little ligand. Based on initial binding experiments, calcium and sodium montmorillonite clays were prioritized for further characterization, including: capacity, affinity, and heat (enthalpy) of adsorption. Computer models of energy-minimized ergotamine isomers and clay were used to illustrate possible mechanisms of ergot alkaloid sorption at interlayer sites. Additional studies are warranted to assess the stability of ergot alkaloid/clay complexes under alkaline conditions to further understand the mechanism of adsorption.

P3A10 - Effect of phyllosilicate clay and zeolite on the metabolic profile of aflatoxin B 1 in Sprague-Dawley rats

P3A10 - Effect of phyllosilicate clay and zeolite on the metabolic profile of aflatoxin B 1 in Sprague-Dawley rats

Prevention of maternal and developmental toxicity in rats via dietary inclusion of common aflatoxin sorbents: potential for hidden risks.

In earlier work, we have reported that a phyllosilicate clay (HSCAS or NovaSil) can tightly and selectively bind the aflatoxins in vitro and in vivo. Since then, a variety of untested clay and zeolitic minerals have been added to poultry and livestock feeds as potential "aflatoxin binders." However, the efficacy and safety of these products have not been determined. A common zeolite that has been frequently added to animal feed is clinoptilolite. Our objectives in this study were twofold: (1) to utilize the pregnant rat as an in vivo model to compare the potential of HSCAS and clinoptilolite to prevent the developmental toxicity of aflatoxin B1 (AfB1), and (2) to determine the effect of these two sorbents on the metabolism and bioavailability of AfB1. Clay and zeolitic minerals (HSCAS or clinoptilolite) were added to the diet at a level of 0.5% (w/w) and fed to pregnant Sprague-Dawley rats throughout pregnancy (i.e., day 0 to 20). Treatment groups (HSCAS or clinoptilolite) alone and in combination with AfB1 were exposed to sorbents in the feed as well as by gavage. Untreated and AfB1 control animals were fed the basal diet without added sorbent. Between gestation days 6 and 13, animals maintained on diets containing sorbent were gavaged with corn oil in combination with an amount of the respective sorbent equivalent to 0.5% of the estimated maximum daily intake of feed. Animals receiving AfB1 were dosed orally (between days 6 and 13) with AfB1 (2 mg/kg body wt) either alone or concomitantly with a similar quantity of the respective sorbent. Evaluations of toxicity were performed on day 20. These included: maternal (mortality, body weights, feed intake, and litter weights), developmental (embryonic resorptions and fetal body weights), and histological (maternal livers and kidneys). Sorbents alone were not toxic; AfB1 alone and with clinoptilolite resulted in significant maternal and developmental toxicity. Animals treated with HSCAS (plus AfB1) were comparable to controls. Importantly, clinoptilolite (plus AfB1) resulted in severe maternal liver lesions (more severe than AfB1 alone), suggesting that this zeolite may interact with dietary components that modulate aflatoxicosis. In metabolism studies, adult male Sprague-Dawley rats, maintained on diets containing 0.5% (w/w) HSCAS or clinoptilolite, were dosed orally with 2.0 mg AfB1/kg body wt. The concentration of the major urinary metabolite (AfM1) was considerably decreased in the presence of HSCAS. These results suggest that the mechanism of protection of AfB1-induced maternal and developmental toxicities in the rat may involve adsorption and reduction of AfB1 bioavailability in vivo. Importantly, this study demonstrates the potential for significant hidden risks associated with the inclusion of nonselective aflatoxin binders in feeds. Aflatoxin sorbents should be rigorously tested individually and thoroughly characterized in vivo, paying particular attention to their effectiveness and safety in sensitive animal models and their potential for deleterious interactions.