Showing papers in "Chemistry of Materials in 2002"
TL;DR: In this article, a novel and simple method for preparing highly photoactive nanocrystalline F-doped TiO2 photocatalyst with anatase and brookite phase was developed by hydrolysis of titanium tetraisopropoxide in a mixed NH4F−H2O solution.
Abstract: A novel and simple method for preparing highly photoactive nanocrystalline F--doped TiO2 photocatalyst with anatase and brookite phase was developed by hydrolysis of titanium tetraisopropoxide in a mixed NH4F−H2O solution. The prepared F--doped TiO2 powders were characterized by differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV−vis absorption spectroscopy, photoluminescence spectra (PL), transmission electron microscopy (TEM), and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results showed that the crystallinity of anatase was improved upon F- doping. Moreover, fluoride ions not only suppressed the formation of brookite phase but also prevented phase transition of anatase to rutile. The F--doped TiO2 samples exhibited stronger absorption in the UV−visible range with a red shift in the band gap transition. The photocatalytic activity of F--doped TiO2 powders prep...
2,074 citations
TL;DR: A solution-phase approach has been demonstrated for the large-scale synthesis of silver nanowires with diameters in the range of 30−40 nm, and lengths up to ∼50 μm as discussed by the authors.
Abstract: A solution-phase approach has been demonstrated for the large-scale synthesis of silver nanowires with diameters in the range of 30−40 nm, and lengths up to ∼50 μm. The first step of this process involved the formation of Pt (or Ag) nanoparticles by reducing PtCl2 (or AgNO3) with ethylene glycol (EG) heated to ∼160 °C. These Pt (or Ag) nanoparticles could serve as seeds for the heterogeneous nucleation and growth of silver (formed by reducing AgNO3 with EG) because of their close match in crystal structure and lattice constants. In the presence of poly(vinyl pyrrolidone) (PVP), the growth of silver could be directed into a highly anisotropic mode to form uniform nanowires with aspect ratios as high as ∼1000. UV−visible spectroscopy, SEM, TEM, XRD, and electron diffraction were used to characterize these silver nanowires, indicating the formation of a highly pure phase, as well as a uniform diameter and bicrystalline structure. Both morphology and aspect ratios of these silver nanostructures could be varie...
1,471 citations
TL;DR: In this paper, the α-MnO2 powder was synthesized by a simple coprecipitation technique and tested as active electrode material for an electrochemical supercapacitor, showing that an average capacitance of 166 F/g can be reproducibly obtained within a voltage range −0.4/+0.5 V vs Hg/Hg2SO4 using a sweep rate of 2 mV/s.
Abstract: α-MnO2 was synthesized by a very simple coprecipitation technique and tested as active electrode material for an electrochemical supercapacitor. The powder presents a poorly crystallized cryptomelane phase with a chemical composition of K0.05MnO2H0.10·0.15H2O. Different aqueous electrolytes were tested including 0.1 M Na2SO4, 0.5 M K2HPO4/KH2PO4 buffer solution, 0.3 M H2SO4, and 1 M NaOH, but interesting pseudocapacitance behavior was only observed in the case of 0.1 M Na2SO4. Further testing using this electrolyte showed that an average capacitance of 166 F/g can be reproducibly obtained within a voltage range −0.4/+0.5 V vs Hg/Hg2SO4 using a sweep rate of 2 mV/s. This interesting value is mainly due to the chimisorption of Na+ ions and/or protons at the surface of the α-MnO2 electrode. Nearly all the Mn surface atoms are involved in the pseudocapacitive process. Therefore, the high specific capacitance seems to be related to the high surface area of the MnO2 powder rather than intercalation of Na+ ions ...
912 citations
TL;DR: By decomposing Zn(OH)42- or Zn[NH3]42+ precursor in various solvents at suitable reaction conditions, zinc oxide with a diversity of well-defined morphologies was synthesized.
Abstract: By decomposing Zn(OH)42- or Zn(NH3)42+ precursor in various solvents at suitable reaction conditions, zinc oxide with a diversity of well-defined morphologies was synthesized. Flowerlike ZnO built ...
840 citations
TL;DR: In this paper, different methods for coating SnO2 nanocrystals with a thin layer of an insulating oxide were compared, and the best results were obtained by adding a soluble metal salt.
Abstract: Coating nanocrystalline SnO2 electrodes for dye-sensitized solar cell applications with a thin layer of ZnO, TiO2, ZrO2, MgO, Al2O3, Y2O3, or other insulating oxides was found to improve dye adsorption and increase the sensitized photocurrent. The surface of the oxide coating is more basic than SnO2, which renders dye attachment by its carboxyl groups more favorable. At the same time, the photovoltage and fill factor are strongly enhanced, resulting in much better energy conversion efficiencies. This change is ascribed to inhibition of electron back transfer from SnO2 to the redox electrolyte (I3-) by the insulating oxide. The optimum coating thickness is only a few angstroms, suggesting that electron transfer from the excited dye attached to the oxide surface to the underlying SnO2 occurs by tunneling through the insulator layer. Different methods for coating SnO2 nanocrystals with a thin layer of an insulating oxide were compared. The best results were obtained by adding a soluble metal salt to the SnO2...
761 citations
TL;DR: In this paper, a cubic mesostructure with crystalline TiO2 (anatase) in the walls, stable to 400 °C, was synthesized by varying the volume ratio between the copolymer and inorganic components of the precursor solution.
Abstract: Well-ordered mesostructured silica and titania films were prepared using poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) triblock copolymer species (Pluronic P123) as the structure-directing agents. By varying the volume ratio between the copolymer and inorganic components of the precursor solution, silica and titania thin films with cubic, 2D hexagonal, and lamellar mesostructures were prepared. The regions over which the three phases were obtained correspond well with those of the water−block copolymer binary phase diagram when considered in terms of the volume fraction of copolymer incorporated. In particular, a cubic mesostructure with crystalline TiO2 (anatase) in the walls, stable to 400 °C, was synthesized.
658 citations
TL;DR: In this article, a Pechini sol−gel process combined with soft lithography was used to fabricate nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a pechini sol-gel process.
Abstract: Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol−gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM) and optical microscopy, UV/vis transmission and absorption spectra, photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 400 °C and the crystallinity increased with the increase of annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of grains with an average size of 90 nm. Patterned gel and crystalline phosphor film bands with different widths (5−60 μm) were obtained. Significant shrinkage and a few defects were observed in the patterned films during the heat treatment process. The doped rare earth ions (A) show...
638 citations
TL;DR: In this article, thin films of various metal oxides were prepared on glass substrates by a wet process to determine their photocatalytic ability to decompose adsorbed dye and to evaluate their photoinduced hydrophilicity under UV illumination.
Abstract: Thin films of various metal oxides were prepared on glass substrates by a wet process to determine their photocatalytic ability to decompose adsorbed dye and to evaluate their photoinduced hydrophilicity under UV illumination. The metal oxides used in this study are classified into four categories based on their behavior over the two photochemical reaction: (1) active in both photocatalytic oxidation and photoinduced hydrophilicity (TiO2, SnO2, ZnO); (2) only active in photocatalytic oxidation (SrTiO3); (3) only active in photoinduced hydrophilicity (WO3, V2O5); (4) and inactive over both processes (CeO2, CuO, MoO3, Fe2O3, Cr2O3, In2O3). X-ray photoelectron spectroscopy revealed that oxygen defect sites were produced by Ar+ bombardment on the surface of metal oxides, showing photoinduced hydrophilicity. These results indicate that photoinduced hydrophilicity is not induced by the photocatalytic oxidation of organic compounds adsorbed on the surface, but is based on structural changes of the metal oxide s...
602 citations
TL;DR: In this paper, a new method of synthesizing hydrotalcite-like layered double hydroxides (LDHs) of the type [Mg1-xAlx(OH)2]x+(CO32-)x/2·yH2O (x = 1.7−3.3) is reported.
Abstract: In particle formation, the method can be just as important as the chemical reaction involved. A new method of synthesizing hydrotalcite-like layered double hydroxides (LDHs) of the type [Mg1-xAlx(OH)2]x+(CO32-)x/2·yH2O (x = 1.7−3.3) is reported. The key features of this method are a very rapid mixing and nucleation process in a colloid mill followed by a separate aging process. The properties of the resulting LDHs are compared with those of materials produced using the conventional coprecipitation process at constant pH. The compositions and structural parameters of the materials synthesized using the two routes are very similar, although the crystallinity is slightly higher for the LDHs produced using the new method. The thermal behavior of the materials synthesized using the two routes is also similar. The major advantage of the new method is that it affords smaller crystallites with a higher aspect ratio, having a very narrow distribution of crystallite size. In the conventional coprecipitation process...
596 citations
TL;DR: In this paper, a set of soft-chemical reactions of layered perovskites have been reported, and they can be classified into sets of similar reactions, such as ion exchange and intercalation reactions, and more complex metathesis reactions replace interlayer cations with cationic structural units.
Abstract: In recent years, many soft-chemical reactions of layered perovskites have been reported, and they can be classified into sets of similar reactions. Simple ion-exchange and intercalation reactions replace or modify the interlayer cations of layered perovskites, and more complex metathesis reactions replace interlayer cations with cationic structural units. Topochemical condensation reactions that involve dehydration and reduction provide access to a variety of metastable structural features in three-dimensional perovskites, and similar reactions can be used to convert among higher order layered perovskite homologues. Other techniques, such as high pressure and anion intercalation/deintercalation, also yield interesting metastable phases. When combined, the individual reactions complement each other, and a powerful toolbox of solid-state reactions emerges. By using layered perovskites as templates, it is possible to retrosynthetically design new product perovskites that retain the structural features of the...
595 citations
TL;DR: In this paper, structural and magnetic properties, methods of synthesis, and applications of seven iron(III) oxide polymorphs, including rare beta, epsilon, amorphous, and high pressure forms, are reviewed.
Abstract: Structural and magnetic properties, methods of synthesis, and applications of seven iron(III) oxide polymorphs, including rare beta, epsilon, amorphous, and high-pressure forms, are reviewed. Thermal transformations resulting in the formation of iron oxides are classified according to different parameters, and their mechanisms are discussed. 57Fe Mossbauer spectroscopy is presented as a powerful tool for the identification, distinction, and characterization of individual polymorphs. The advantages of Mossbauer spectroscopy are demonstrated with two examples related to the study of the thermally induced solid-state reactions of Fe2(SO4)3.
TL;DR: In this paper, the supercapacitive properties of electrochemically grown composite films of multiwalled carbon nanotubes (MWNT) and polypyrrole (PPy), a conducting polymer, were reported.
Abstract: This work reports the supercapacitive properties of electrochemically grown composite films of multiwalled carbon nanotubes (MWNT) and polypyrrole (PPy), a conducting polymer. Scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy revealed that the nanoporous three-dimensional arrangement of PPy-coated MWNTs in these films facilitated improved electron and ion transfer relative to pure PPy films. The low-frequency capacitance was measured for films of varying thickness, revealing specific capacitances per mass (Cmass) and geometric area (Carea) as high as 192 F g-1 and 1.0 F cm-2, respectively. Rates of charge and discharge about an order of magnitude faster than similarly prepared pure PPy films were also observed.
TL;DR: In this paper, high surface area nickel−iron nanoparticles (1:3 Ni:Fe) have been studied as a reagent for the dehalogenation of trichloroethylene (TCE).
Abstract: High surface-area nickel−iron nanoparticles (1:3 Ni:Fe) have been studied as a reagent for the dehalogenation of trichloroethylene (TCE). Ni−Fe (0.1 g) nanoparticles reduced TCE from a 40-mL saturated aqueous solution (24 ppm) to <6 ppb in 120 min. The dehalogenation reaction, based on the surface area normalized rate constant, was 50−80 times slower using nanoiron or iron filings, respectively. On the bimetallic particles, the reaction occurs by nickel-catalyzed hydrodechlorination. As the iron actively corrodes, the cathodically protected nickel surface chemisorbs hydrogen ions. TCE adsorbed to the Ni surface is thus hydrogenated. This reaction competes kinetically with the evolution of molecular hydrogen. Hydrogenation of the C−Cl bond results in the formation of linear as well as branched saturated and unsaturated hydrocarbons. The final TCE degradation products are predominantly even-numbered saturated hydrocarbons, such as butane, hexane, and octane. The toxic dehalogenation products vinyl chloride ...
TL;DR: In this article, the atomic layer deposition of smooth and highly conformal films of hafnium and zirconium oxides was studied using six metal alkylamide precursors.
Abstract: Atomic layer deposition (ALD) of smooth and highly conformal films of hafnium and zirconium oxides was studied using six metal alkylamide precursors for hafnium and zirconium. Water was used as an oxygen source during these experiments. As deposited, these films exhibited a smooth surface with a measured roughness equivalent to that of the substrate on which they were deposited. These films also exhibited a very high degree of conformality: 100% step coverage on holes with aspect ratios greater than 35. The films were completely uniform in thickness and composition over the length of the deposition reactor. The films were free of detectable impurities and had the expected (2:1) oxygen-to-metal ratio. Films were deposited at substrate temperatures from 50 to 500 °C from precursors that were vaporized at temperatures from 40 to 140 °C. The precursors were found to be highly reactive with hydroxylated surfaces. Their vapor pressures were measured over a wide temperature range. Deposition reactor design and ...
TL;DR: In this article, the optical properties of polycrystalline inverse opals were modified in predictable manners by numerous methods, including tailoring the pore size, filling the pores with fluids of various refractive indices, and changing the compositions of the solid material.
Abstract: Colloidal crystal-templating methods have been used to prepare inverse opal photonic crystals of silica, mercaptopropyl-functionalized silica, titania, and zirconia. Ordered arrays of uniformly sized polymer spheres were infiltrated with fluid precursors capable of condensation or crystallization. After solidification of the material in the void spaces between the spheres, the polymer templates were removed by calcination or solvent extraction, leaving inverse replicas of the template arrays. By carefully controlling the synthetic procedures, gram-scale quantities of powdered macroporous materials exhibiting photonic crystal properties were obtained. For materials with crystalline walls (titania and zirconia), this required minimization of the size of the nanocrystalline grains. Because the periodicity introduced into the wall structure by the colloidal crystal templates was on the order of optical wavelengths, Bragg diffractions from the planes produced photonic stop bands in the visible spectra of these materials. The stop bands were manifested as brightly colored reflections and an optical filtering behavior of the materials. A crystallographic indexing of the optical spectrum of a polycrystalline inverse opal confirmed the fcc ordering of the pores. The optical properties of these materials were modified in predictable manners by numerous methods, including tailoring the pore size, filling the pores with fluids of various refractive indices, and changing the compositions of the solid material. The wavelengths of the colorful reflections (stop bands) were found to be proportional to the pore size and to vary linearly with the refractive index of the fluid filling the pores. The physical and synthetic modifications reported here allowed for the preparation of powders with optical reflections and bright colors spanning the entire visible spectrum.
TL;DR: In this article, a mixed transition metal oxide was used for the negative electrode of a sodium-ion battery, which showed reversible capacities of ca. 300 mA h g-1 in sodium ion cells versus NaxCoO2.
Abstract: This is the first time that a mixed transition metal oxide is used for the negative electrode of a sodium-ion battery. The NiCo2O4 spinel was prepared by thermal decomposition of oxalate precursors at 320 °C. The electrochemical reactions of this material with sodium lead to the complete reduction of the transition metals and the formation of Na2O. The new electrode material shows reversible capacities of ca. 300 mA h g-1 in sodium-ion cells versus NaxCoO2.
TL;DR: In this paper, a novel approach, i.e., ultrasonic irradiation, was used to prepare polyaniline/nanocrystalline TiO2 composite particles.
Abstract: A novel approach, i.e., ultrasonic irradiation, was used to prepare polyaniline/nanocrystalline TiO2 composite particles. Polymerization of aniline proceeded under ultrasonic irradiation in the presence of nanocrystalline TiO2. The aggregation of nano TiO2 can be reduced under ultrasonic irradiation, and the nanoparticles can be redispersed in the aqueous solution. The polyaniline deposits on the surface of the nanoparticle, which leads to a core−shell structure. The resulting polyaniline/nano TiO2 composite particles are spherical, and the sizes vary with the content of TiO2. The polyaniline/nano TiO2 composite particles prepared by the conventional stirring method have a “raspberry” aggregate structure, which is different from that obtained through ultrasonic irradiation. The presence of nanocrystalline TiO2 strengthens the UV absorption of polyaniline and leads to a blue shift of the π-polaron absorption of polyaniline. Ultrasound can enhance the doping level. When polyaniline deposits on the surface o...
TL;DR: In this article, the role of the synthesis parameters (surfactant and acid concentrations and temperature) is thoroughly discussed to understand their influence on the hybrid mesostructures and it is suggested that hydrophilic Ti-oxo nanometric building blocks formed in the acidic synthesis conditions self-assemble upon solvent evaporation to produce organized structures.
Abstract: Mesostructured TiO2−hexadecyltrimethylammonium bromide hybrid powders, displaying a bidimensional hexagonal pattern (p6m), have been synthesized by an evaporation-induced self-assembly (EISA) method, in ethanol/HCl/H2O media. Thermal treatment of these “titaniatropic” hybrid phases leads to phosphorus-free, high surface area (280−370 m2 g-1) mesoporous titania, with 20−25 A pores. The role of the synthesis parameters (surfactant and acid concentrations and temperature) is thoroughly discussed to understand their influence on the hybrid mesostructures. It is suggested that hydrophilic Ti-oxo nanometric building blocks formed in the acidic synthesis conditions self-assembly upon solvent evaporation to produce organized structures.
TL;DR: The reaction between TiCl4 and benzyl alcohol is a simple and nonaqueous procedure for the synthesis of highly crystalline titania nanoparticles at temperatures as low as 40 °C as mentioned in this paper.
Abstract: The reaction between TiCl4 and benzyl alcohol is a simple and nonaqueous procedure for the synthesis of highly crystalline titania nanoparticles at temperatures as low as 40 °C. XRD measurements prove the exclusive presence of the anatase phase. The particle growth depends strongly on temperature so that with the appropriate thermal conditions the particle size can be selectively adjusted in the range of 4−8 nm. Fine-tuning of the particle size is possible by a proper choice of the relative amounts of benzyl alcohol and titanium tetrachloride. Lowering the titanium tetrachloride concentration leads to a considerable decrease of particle size. BET measurements show particularly high surface areas, up to 345 m2/g for the smallest particles and 115 m2/g for the calcined material. TEM investigations reveal that the nanoparticles are nearly uniform in size and shape. The as-synthesized particles display only minor agglomeration, whereas the calcined material consists of completely nonagglomerated particles, wi...
TL;DR: A series of long-chain 1-alkyl-3-methylimidazolium (LSM) and tetrafluoroborate (TFL) anions, including trifluoromethanesulfonate (OTf) and bis(trifluorsulfonyl)imide (TFI), have been synthesized and characterized as mentioned in this paper.
Abstract: A series of long-chain 1-alkyl-3-methylimidazolium salts ([Cn−mim]X, n = 12−18) containing the anions, chloride, bromide, trifluoromethanesulfonate (OTf), and bis(trifluoromethanesulfonyl)imide (TFI), have been synthesized and characterized. The salts have amphiphilic characteristics, and the thermotropic phase behavior of these salts and the analogous tetrafluoroborate salt has been investigated by variable temperature small-angle X-ray scattering, polarizing optical microscopy, and differential scanning calorimetry. The salts form lamellar, sheetlike arrays in the crystalline phase and an enantiomeric smectic liquid crystalline phase at higher temperatures, except for the salts containing the bis(trifluoromethanesulfonyl)imide anion which melt directly to form isotropic liquids. The nature of the anion influences the size of the interlayer spacing in both the crystal and in the mesophase. The interlayer spacing in the mesophase is largest for the anions with the greatest ability to form a three-dimensio...
TL;DR: The double-layered nanotubular structures of the titanium dioxide were created by sol−gel polymerization of Ti(OiPr)4] using 1 as a template in 1-butanol.
Abstract: The helical ribbon and double-layered nanotubular structures of the titanium dioxide were created by sol−gel polymerization of Ti(OiPr)4] using 1 as a template in 1-butanol. All TiO2 nanotubes consist of two layers, 8−9 nm of nanospace between layers. In addition, the helicity of the helical ribbon titanium dioxide showed a right-handed motif.
TL;DR: In this article, the combustion behavior of organically modified phyllosilicates (organoclay) and poly(ethylene-co-vinyl acetate) (EVA) was studied by melt processing to study their combustion behavior.
Abstract: Polymer composites based on organically modified phyllosilicates (organoclay) and poly(ethylene-co-vinyl acetate) (EVA) were prepared by melt processing to study their combustion behavior. Their degrees of dispersion and intercalation spacings as determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD) were typical of either a microcomposite or an exfoliated nanocomposite, depending on the type of organoclay. Combustion experiments showed that the microcomposite burns in the same way as pure EVA, whereas the heat release is reduced by 70−80% when nanocomposites with low silicate loadings (2−5%) are burned, because a protective charred ceramic surface layer is formed as a result of reassembly of the clay layers and catalyzed charring of the polymer. A chemical mechanism for this charring is proposed.
TL;DR: In this article, solid-state dye-sensitized photovoltaic cells have been fabricated with TiO2 as the electron conductor and CuSCN as the hole conductor, and the results are discussed and compared to those for equivalent photoelectrochemical cells, and similar solid cells composed of ZnO/dye/CuSCN.
Abstract: Solid-state dye-sensitized photovoltaic cells have been fabricated with TiO2 as the electron conductor and CuSCN as the hole conductor. The cells show photocurrents of ≈8 mA/cm2, voltages of ∼600 mV, and energy efficiencies of ≈2% at 1 sun. The CuSCN was deposited into the pores of the nanoparticulate TiO2/dye film from dilute solution in propylsulfide. The degree of pore filling achieved is near 100% for TiO2 films <2-μm thick and falls to ≈65% for films near 6 μm. The final drying step after the CuSCN deposition is shown to be critical; drying in vacuum or argon is required for photocurrents above 2 mA/cm2. The photocurrent IVs of these cells are fit to a single diode equation and the results are discussed and compared to those for equivalent photoelectrochemical cells, and similar solid cells composed of ZnO/dye/CuSCN.
TL;DR: The use of a cluster-based single-source precursor allows nanomaterial growth to be initiated at low temperature without the pyrolytic step for nucleus formation traditionally required for lyothermal growth processes as mentioned in this paper.
Abstract: Molecular inorganic clusters, which are stable under ambient conditions, can be used as convenient single-source precursors for controlled preparation of 2−9-nm CdSe and CdSe/ZnS nanocrystals and 2−5-nm nanocrystals of ZnSe. The use of a cluster-based single-source precursor allows nanomaterial growth to be initiated at low temperature without the pyrolytic step for nucleus formation traditionally required for lyothermal growth processes. The elimination of the pyrolytic step allows greater synthetic control, slow thermodynamic growth at lower temperatures, high crystallinity, and reaction scalability (>50 g/L) while maintaining size dispersity at ∼5%.
TL;DR: In this paper, the authors report the characteristics of aminosilane-grafted mesoporous silicas as adsorbents of oxyanions in acidic conditions and examine the influence of amino group density.
Abstract: We report the characteristics of aminosilane-grafted mesoporous silicas as adsorbents of oxyanions in acidic conditions. Mono-, di-, and triamino-functionalized silicas were prepared to examine the influence of amino group density. The triaminosilane-grafted mesoporous silica adsorbed more chromate and arsenate than expected from the increased number of sites, suggesting stable complex formations. Functionalized SBA-1 showed larger adsorption capacities than MCM-41 derivatives. The adsorption capacity was independent of the average surface density of monoamino groups, demonstrating domain formation of fixed silanes. These structural characteristics on molecular and meso scales may offer insights into understanding the mechanism of heterogeneous oxyanion capture by amino-functionalized solids, which are promising inexpensive reagents for reducing toxic anion pollution.
TL;DR: In this article, the gallery spacing of organoclay and polylactide (PLA) nanocomposites was investigated in different types of clays, smectite, montmorillonite (MMT), and mica, to prepare their corresponding organoclays.
Abstract: In the preparation of polymer/clay nanocomposites, organoclay plays an important role in lipophilizing and dispersing the clay into less polar polymer matrixes. Organic modifiers of various chain lengths were examined in different types of clays, smectite, montmorillonite (MMT), and mica, to prepare their corresponding organoclays. The layered structure and gallery spacing of organoclays and polylactide (PLA) nanocomposites shows that, with a modifier of the same chain length, the gallery spacing of the organoclay was largest for mica and smallest for smectite because of the higher ion-exchange capacity of mica and physical jamming of the modifier due to a restricted conformation at the core part of the clay of larger size. The increment of the modulus in a smectite nanocomposite, compared to that of PLA, is higher than MMT or mica nanocomposite due to better dispersion in a smectite system for the same clay loading. Being a well-dispersed system, smectite nanocomposites have better gas barrier properties...
TL;DR: In this paper, a simple one-step procedure is described for the synthesis of spherical mesoporous silica, in which the size of the particles is controlled over a range of diameters from 65 to 740 nm by varying the initial silicate/surfactant concentration under dilute conditions.
Abstract: A simple one-step procedure is described for the synthesis of spherical mesoporous silica, in which the size of the particles is controlled over a range of diameters from 65 to 740 nm by varying the initial silicate/surfactant concentration under dilute conditions. The particles were characterized using X-ray diffraction, transmission electron microscopy, and liquid nitrogen adsorption. Synthesis using a charged template, cetyltrimethylammonium bromide, under aqueous conditions yielded particles of irregular spherical shape with highly ordered mesoporous channels. Synthesis under ethanol/water cosolvent conditions yielded smooth spheres with a starburst mesopore structure extending from the center of the particle to the circumference. All materials were thermally stable and exhibited two steps in their liquid nitrogen isotherms corresponding to reversible channel filling and non-reversible adsorption between particles. Mesopore volumes varied from 0.64 to 0.93 cm3 g-1 and surface areas varied from 917 to ...
TL;DR: In this paper, a dipping method was developed to fabricate three-dimensional colloidal crystal films, which can be precisely controlled from one layer to several tens of layers by controlling the particle concentration and the film formation speed.
Abstract: A dipping method was developed to fabricate three-dimensional colloidal crystal films. The thickness of the films fabricated by this method can be precisely controlled from one layer to several tens of layers by controlling the particle concentration and the film formation speed. Experimental results showed that the spheres form a face-centered cubic structure and that single crystals in the film can extend to centimeter dimensions.
TL;DR: In this article, the non-oxidative thermal degradation chemistry of alkyl and aryl quaternary phosphonium-modified montmorillonites (P-MMT) was examined using TGA combined with pyrolysis/GC-MS.
Abstract: Organically modified layered silicates (OLS) with high thermal stability are critical for synthesis and processing of polymer layered silicate nanocomposites (PLSN). In the current study, the non-oxidative thermal degradation chemistry of alkyl and aryl quaternary phosphonium-modified montmorillonites (P-MMT) was examined using TGA combined with pyrolysis/GC-MS. The morphology evolution at elevated temperature was investigated using in-situ high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The onset decomposition temperature via TGA of these P-MMTs ranged from 190 to 230 °C. The initial degradation of the alkyl P-MMTs follows potentially two reaction pathways - ‚-elimination [E‚] and nucleophilic displacement at phosphorus [SN(P)] reflecting the multiple environments of the surfactant in the silicate. Aryl P-MMT decomposition proceeds via either a reductive elimination through a five-coordinate intermediate or radical generation through homologous cleavage of the P-phenyl bond. Overall, the interlayer environment of the montmorillonite has a more severe effect on stability of the phosphonium surfactant than previously reported for ammonium-modified montmorillonite (N-MMT). Nonetheless, the overall thermal stability of P-MMT is higher than that of N-MMT. These observations indicate that, in addition to their conventional purpose as stabilizers, phosphonium salts offer unique opportunities for melting processing polymer layered silicate nanocomposites.
TL;DR: In this article, a simple and versatile technique for the preparation of novel macroporous three-dimensional gold and platinum films with regular submicron spherical holes arranged in a close-packed structure was reported.
Abstract: Here we report a simple and versatile technique for the preparation of novel macroporous three-dimensional gold and platinum films with regular submicron spherical holes arranged in a close-packed structure. Gold and platinum films were prepared by electrochemical reduction of gold or platinum complex ions dissolved in aqueous solution within the interstitial spaces between polystyrene latex spheres (500 or 750 nm in diameter) assembled on gold surfaces. The latex sphere templates were subsequently removed by dissolving in toluene to leave the structured metal films. Scanning electron microscopy of the gold and platinum films shows a well-formed regular three-dimensional, porous structure consisting of spherical voids arranged in a highly ordered face-centered cubic (fcc) structure. The spherical voids have the same diameter as the latex spheres used to form the template. Within the metal film the spherical voids are interconnected through a series of smaller pores. The metallic framework is dense, self-supporting, and free from defects. X-ray studies show the metal to be polycrystalline with a grain size smaller than 100 nm. The optical reflectivity of the macroporous gold and platinum films shows strong diffractive optical properties, which are potentially useful in many existing and emerging applications.