Imogolite Surface Research Articles

Structure and Properties of Hybrid Film Fabricated by Spin-Assisted Layer-by-Layer Assembly of Sacran and Imogolite Nanotubes.

A free-standing (biomacomolecule/synthetic inorganic nanotubes) hybrid film was fabricated through an alternative layer-by-layer (LBL) assembly of sacran and imogolite nanotubes. Sacran is a natural polysaccharide extracted from the cyanobacterium Aphanothece sacrum, while imogolite is a natural tubular aluminosilicate clay found in volcano ash. The hybrid film thickness increased linearly with the number of the bilayers, because of the interaction between the negatively charged surface of sacran and the positively charged surface of imogolite. UV-vis spectroscopy indicated that the LBL film exhibited good transparency. The surface morphology of the LBL film was smooth in the micrometer scale; many imogolite nanotubes were adsorbed onto the sacran layer, while no imogolite clusters were observed. Furthermore, the structure, stability, gas permeability, and mechanical properties of the LBL films were investigated.

Dispersing surface-modified imogolite nanotubes in polar and non-polar solvents

Furthering the development of nanocomposite structures, namely membranes for water treatment applications, requires that methods be developed to ensure nanoparticle dispersion in polar and non-polar solvents, as both are widely used in associated synthesis techniques. Here, we report on a two-step method to graft polyvinylpyrrolidone (PVP), and a one-step method for octadecylphosphonic acid (OPA), onto the outer surfaces of imogolite nanotubes. The goal of these approaches was to improve and maintain nanotube dispersion in polymer compatible polar and non-polar solvents. The PVP coating modified the imogolite surface charge from positive to weakly negative at pH ≤ 9; the OPA made it weakly positive at acidic pH values to negative at pH ≥ 7. The PVP surface coating stabilized the nanotubes through steric hindrance in polar protic, dipolar aprotic, and chloroform. In difference to the PVP, the OPA surface coating allowed the nanotubes to be dispersed in n-hexane and chloroform, but not in the polar solvents. The lack of miscibility in the polar solvents, as well as the better dispersion in n-hexane, was attributed to the stronger hydrophobicity of the OPA polymer relative to the PVP.

Adsorption of Amino Acids and Glutamic Acid-Based Surfactants on Imogolite Clays

Aluminum oxide surfaces are of utmost interest in different biotech applications, in particular for their use as adjuvants (i.e., booster of the immune response against infectious agents in vaccines production). In this framework, imogolite clays combine the chemical flexibility of an exposed alumina surface with 1D nanostructure. This work reports on the interaction between amino acids and imogolite, using turbidimetry, ζ-potential measurements, and Fourier transform infrared spectroscopy as main characterization tools. Amino acids with different side chain functional groups were investigated, showing that glutamic acid (Glu) has the strongest affinity for the imogolite surface. This was exploited to prepare a composite material made of a synthetic surfactant bearing a Glu polar head and a hydrophobic C12 alkyl tail, adsorbed onto the surface of imogolite. The adsorption of a model drug (rhodamine B isothiocyanate) by the hybrid was evaluated both in water and in physiological saline conditions. The findings of this paper suggest that the combination between the glutamate headgroup and imogolite represents a promising platform for the fabrication of hybrid nanostructures with tailored functionalities.

Nanocomposites composed of poly(ɛ-caprolactone) and oligocaprolactone-modified imogolite utilizing biomimetic chelating method

The imogolite modified with a catechol-terminated e-caprolactone oligomer (CLO-imogolite) was synthesized by a biomimetic treatment of imogolite with 4-(hydroxyethylthioacetyl)catechol (HETAC) and subsequent ring-opening polymerization of e-caprolactone (CL). The FT-IR analysis revealed that the catechol moieties certainly chelated to aluminum atoms on the surface of imogolite. The 1H-NMR spectral analysis of the CLO-imogolite revealed that the oligomerization of CL certainly occurred. The organo-fraction of CLO-imogolite was evaluated to be 35.6 wt% from the thermogravimetric analysis. Poly(e-caprolactone) (PCL)/CLO-imogolite nanocomposites prepared by a solution casting method were comprised of homogeneously dispersed nanotubes and some aggregated nanotubes. Crystallization temperature of PCL/CLO-imogolite slightly rose with increasing CLO-imogolite and the formed crystalline particles were slightly finer than those of pure PCL. Tensile strengths and moduli of PCL/CLO-imogolite nanocomposites increased with increasing CLO-imogolite contents. The PCL/CLO-imogolite 3 wt% exhibited the highest elongation at break and tensile toughness, which were much higher than those of pure PCL and PCL/imogolite 3 wt%.

Preparation and Characterization of Imogolite/DNA Hybrid Hydrogels

Imogolite is one of the clay minerals contained in volcanic ash soils. The novel hybrid hydrogels were prepared from imogolite nanofibers and DNA by utilizing strong interaction between the aluminol groups on imogolite surface and phosphate groups of DNA. The hybrid hydrogels of imogolite and DNA were prepared in various feed ratios, and their physicochemical properties and molecular aggregation states were investigated in both dispersion and gel states. The maximum DNA content in the hybrid gels was shown in equivalent molar ratio of imogolite and DNA. The physical properties of the hybrid gels were changed by varying DNA blend ratios. In the dispersion state, the hybrid gels showed a fibrous structure of imogolite, whereas a continuous network structure was observed in pure imogolite, indicating that the hybrid with DNA enhanced the dispersion of imogolite. In the gel state, DNA and imogolite nanofibers formed a 3D network structure.

Molecular Aggregation State and Electrical Properties of Terthiophenes/Imogolite Nanohybrids

Abstract Organic/inorganic nanohybrid materials composed of terthiophenes and imogolite were prepared by means of specific surface interaction between a phosphonic acid group in terthiophene derivatives and aluminol groups on the surface of imogolite. The new materials were investigated by FTIR, UV–vis absorption, fluorescence spectroscopy, TEM observation, nitrogen adsorption–desorption, and I–V measurement. Addition of terthiophene of phosphonic acid derivatives into imogolite brought some changes in absorption and photoluminescence spectra, suggesting the formation of H-type aggregate on imogolite surface. The analysis of UV–vis spectra and nitrogen adsorption–desorption data provided insight into the effect of molecular structure of terthiophenes on the adsorption and aggregation behaviors on the imogolite surface. In addition, a significant enhanced current flow was observed through imogolite film when imogolite was chemisorbed by electron-withdrawing terthiophenes. In contrast, current flow decreased as the electron-donating terthiophene was chemisorbed on imogolite. A possible mechanism for such phenomena is discussed.

Surface Modification of Individual Imogolite Nanotubes with Alkyl Phosphate from an Aqueous Solution

Abstract Synthetic imogolite surface was modified with alkyl phosphate by covalent bonding from an aqueous solution, and the individual imogolite tubes with a hydrophobic external surface were directly observed with transmission electron microscopy.

Synthesis and characterization of hybrid organic/inorganic nanotubes of the imogolite type and their behaviour towards methane adsorption

Imogolite-like nanotubes have been synthesised in which SiCH(3) groups have been introduced in place of the SiOH groups that naturally occur at the inner surface of imogolite, an alumino-silicate with formula (OH)(3)Al(2)O(3)SiOH, forming nanotubes with inner and outer diameter of 1.0 and 2.0 nm, respectively. The new nanotubular material, composition (OH)(3)Al(2)O(3)SiCH(3), has both larger pores and higher specific surface area than unmodified imogolite: it forms as hollow cylinders 3.0 nm wide and several microns long, with a specific surface area of ca. 800 m(2) g(-1) and intriguing surface properties, due to hydrophobic groups inside the nanotubes and hydrophilic Al(OH)Al groups at their outer surface. Adsorption of methane at 30 °C has been studied in the pressure range between 5 and 35 bar on both the new material and unmodified imogolite: it resulted that the new material adsorption capacity is about 2.5 times larger than that of imogolite, in agreement with both its larger pore volume and the presence of a methylated surface. On account of these properties and of its novelty, the studied material has several potential technical applications, e.g. in the fields of gas chromatography and gas separation.

Molecular Aggregation States of Imogolite/P3HT Nanofiber Hybrid

Preparation of novel organic/inorganic nanofiber hybrid composed of one-dimensional P3HT nanofiber and aluminosilicate imogolite was demonstrated. To achieve better compatibility with hydrophobic P3HT, Al-OH group on imogolite surface was modified with terthiophene derivative, 2-[5"-hexyl-2,2':5',2"-terthiophene]-5-ethyl)-phosphonic acid (H3TP). Dissolving the mixture of P3HT and surface modified imogolite in poor solvent of anisole at elevated temperature (> 70°C) followed by subsequent slow cooling (25°C/h) to room temperature induced the formation of P3HT crystallite that winds around the surface modified imogolite core. The thickness of the nanofiber hybrid estimated from DFM is larger than the parent P3HT nanofiber and imogolite. UV-vis spectroscopy spectra indicate that addition of surface modified imogolite can influence the molecular aggregation state of P3HT via van der Waals interaction. Through GIWAXD experiments, it was found that P3HT molecular chains are strongly oriented and lying on surface modified imogolite core.

Poly(methyl methacrylate) grafted imogolite nanotubes prepared through surface-initiated ARGET ATRP

Poly(methyl methacrylate) grafted imogolite clay nanotubes were fabricated via activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) by designing a water-soluble amphiphilic ATRP initiator that can adsorb onto imogolite surface in an aqueous solution.

Adsorption of methylene blue on raw and MTZ/imogolite hybrid surfaces: Effect of concentration and calorimetric investigation

The synthetic imogolite sample was used for organofunctionalization process with 2-mercaptothiazoline (MTZ). The compound 2-mercaptothiazoline was anchored onto imogolite surface by heterogeneous route. Due to the increment of basic centers attached to the pendant chains the dye adsorption capability of the final chelating material, was found to be higher than is precursor. The ability of these materials to remove methylene blue from aqueous solution was followed by a series of adsorption isotherms at room temperature and pH 4.0. The maximum number of moles adsorbed was determined to be 40.32 × 10 −2 and 65.13 × 10 −2 mmol g −1 for IMO and IMO MTZ, respectively. The energetic effects caused by dye cations adsorption were determined through calorimetric titrations. Thermodynamics indicated the existence of favorable conditions for such methylene blue-nitrogen and sulfur interactions.

Preparation of hybrid films of aluminosilicate nanofiber and conjugated polymer

We have demonstrated the preparation of hybrid films of aluminosilicate nanofiber (imogolite) and water-soluble poly( p-phenylene) (WS-PPP), which has sulfonate groups. The imogolite/WS-PPP hybrid gel could be prepared by mixing a solution of these two materials and subsequent centrifugation. The aluminol (Al OH) groups on the surface of imogolite would be protonated under acidic conditions to afford Al OH 2 + groups that can interact with sulfonate groups (SO 3 −) of WS-PPP. Based on this ionic interaction, a layer-by-layer (LBL) assembly was applied to fabricate the hybrid films of imogolite nanofibers and WS-PPP. The deposited amounts of WS-PPP and imogolite were measured by quartz crystal microbalance (QCM) measurements and scanning electron microscopy (SEM) observation. Atomic force microscopy (AFM) observation revealed that imogolite nanofibers were well networked in the LBL hybrid film.

Current-voltage Characteristics of Water-adsorbed Imogolite Film

Electric current flow was observed through imogolite film when imogolite () was exposed to water molecules and connected to external electrodes. Current flow was due to the bound water on the surface of imogolite. Current flow increased as the pH of the water decreased. The current-voltage (I-V) measurements from a field effective transistor (FET) using /imogolite film revealed that the current carrier in / imogolite had p-type characteristics, i.e. the carrier was probably . The possible mechanism for current transportation in imogolite/water was also suggested in this paper.

Molecular dynamics study of hydrated imogolite : 2. Structure and dynamics of confined water

The behaviour of water confined in an imogolite nanotube was studied by means of molecular dynamics simulations. The results of the study show an important difference between the interaction of water molecules with the internal and external surfaces of the nanotube. The analysis of the density profiles of confined molecules, of their spatial organisation, of the size of molecular clusters, of the lifetime of H-bonds in the system and of dynamical characteristics of molecules permits us to qualify the external imogolite surface as hydrophobic, whereas the internal surface reveals a hydrophilic character.

Surface-modified imogolite by 3-APS–OsO 4 complex: Synthesis, characterization and its application in the dihydroxylation of olefins

We modified the surface of imogolite nanorods by silylation using 3-aminopropyltriethoxysilane (3-APS) and subsequent attachment of osmium tetroxide (OsO 4) onto the amine groups of the silylated imogolite surface. In order to characterize surface-modified imogolite by 3-APS–OsO 4 complex, powder X-ray diffraction (powder XRD), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet/visible (UV–vis) spectroscopy and X-ray photoelectron spectroscopy (XPS) experiments were carried out, and we verified the formation of the osmium tetroxide complex on the surface-modified imogolite by 3-APS. As a heterogeneous catalyst, this osmium-bound imogolite (I-APS–OsO 4) was applied in the achiral dihydroxylation of olefins, and revealed excellent catalytic activity while leaching of osmium was observed. Introduction of chelating ligands instead of the primary amine group to improve the reusability of the catalyst is currently in progress.

Ab initiosimulation of the structural and electronic properties of aluminosilicate and aluminogermanate natotubes with imogolite-like structure

A theoretical study of imogolite-like single wall nanotubes as a function of silicon and germanium content and their tubular radius is presented along with mapping of silicon-germanium content properties in models that contain from 9 gibbsite-like units $({N}_{u}=9)$ to 13 gibbsite-like units $({N}_{u}=13)$ with a silicon-germanium content $[X=\mathrm{Si}∕(\mathrm{Si}+\mathrm{Ge})]$ of 0, 0.20, 0.40, 0.60, 0.80, and 1.00. The imogolite nanotubes were built setting periodic boundary conditions to density functional theory (DFT) geometry-optimized models along both radial and axial directions in order to obtain the stable structure. The DFT calculations were carried out on the $\ensuremath{\Gamma}$ point and for various $k$ points, using the GGA-PW91 functional, finding an optimal unit cell length of 8.72 and $8.62\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ using a double numeric (DN) and double numeric with polarization (DNP) basis set, respectively, along the axial direction. The structural properties were analyzed through the evolution of the x-ray diffraction pattern as a function of both ${N}_{u}$ and $X$. A linear correlation between the tube radius and the position of the first two peaks on the x-ray diffraction is found. The imogolite surface charge was mapped with the Hirshfeld charge showing the characteristic acid tendency experimentally reported. The reactivity of imogolite-like structures was studied employing the total density of states and the band gap evolution as a function of ${N}_{u}$ and $X$ showing an increasing behavior with $X$. The local reactivity was analyzed by looking at the local density of states in models with $X=0.0$ and 1.0 with ${N}_{u}=10$. Finally, the frequency analysis was carried out in the optimized structure on the $\ensuremath{\Gamma}$ point finding a good agreement in the $\mathrm{O}\text{\ensuremath{-}}\mathrm{H}$ vibrations with those reported in the literature.

Preparation of Novel Polymer Hybrids from Imogolite Nanofiber

Polymer hybrids designed on a nanometer scale were prepared by several methods with an aluminosilicate nanofiber, “imogolite.” This review paper introduces the preparation of polymer hybrid materials from imogolite nanofiber by two different approaches. In order to realize the fine dispersion of imogolite in polymer matrix, poly(vinyl alcohol)/imogolite hybrids were prepared by in situ synthesis method of imogolite in polymer solution. In addition, through utilizing the strong interaction between phosphoric acid group and Al–OH on the surface of imogolite, poly(methyl methacrylate)/imogolite hybrid, and enzyme/imogolite hybrid gel were prepared and characterized.

FIELD EMISSION AND ELECTRICAL PROPERTIES OF IMOGOLITE

We demonstrate field emission (FE) properties of imogolite including turn-on field and life time stability. Imogolite is found to be a good electron emitter under external electric field. The conductance of bound water molecules adsorbed on imogolite surface is measured and compared with bulk water molecules at various pH values, i.e., at various proton concentrations. At low concentration, most protons pass through bound water on imogolite rather than bulk water. At high concentration, on the other hand, protons move more easily through bulk water than bound water. Explanations are given in this paper.

Uranyl adsorption and surface speciation at the imogolite–water interface: Self-consistent spectroscopic and surface complexation models

Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH ∼7–8 ( I = 0.1 M NaNO 3 solution, suspension density = 0.4 g/L [U(VI)] i = 0.01–30 μM, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1–0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and β charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in controlling U(VI) mobility in low-temperature geochemical environments over a wide pH range (∼5–9), even at the partial pressure of carbon dioxide of ambient air ( p CO2 = 10 −3.45 atm).

Preparation and properties of [poly(methyl methacrylate)/imogolite] hybrid via surface modification using phosphoric acid ester

Novel polymer nanohybrid was prepared by free radical polymerization of methyl methacrylate in the presence of inorganic nanofiber ‘imogolite’ as reinforcing nanofiller. Imogolite is a hydrous aluminosilicate with a unique nanofiber structure. The surface of imogolite was modified with 2-acidphosphoxyethyl methacrylate, which has a polymerizable methacrylate group and a phosphoric acid moiety, before preparation of polymer hybrid. The polymer nanohybrid was prepared by free radical polymerization in the presence of surface modified imogolite. The mechanical properties of (PMMA/modified imogolite) hybrid with the modified imogolite were improved in comparison with those of PMMA and (PMMA/unmodified imogolite) blend. Furthermore, the hybrid film prepared from the surface modified imogolite kept the transparency similar to PMMA film. These results indicate the usefulness of the surface modification method with phosphoric acid groups and imogolite nanofibers as a reinforcing material.