Adsorption kinetic, isotherm and thermodynamic studies of Sr2+ onto hexagonal tungsten oxide

Hexagonal tungsten oxide (hex-WO₃) with exchangeable sodium and ammonium cations located in hexagonal channel was synthesized by a facile hydrothermal treatment of sodium tungstate dihydrate in concentrated HCl solution in the presence of ammonium sulfate. An attempt was made to assess the potential of hex-WO₃ for the adsorption of Sr²⁺ ions from acidic radioactive waste solutions. Adsorption of Sr²⁺ reached equilibrium very quickly in 2 h in acidic aqueous solution. Maximum removal of Sr²⁺ ions occurred at pH 4. Equilibrium studies showed that the extent of Sr²⁺ ions uptake by hex-WO₃ was better described by the Freundlich isotherm in comparison with the Langmuir model. The thermodynamic parameters showed that the adsorption of Sr²⁺ ions onto hex-WO₃ was spontaneous and exothermic under the studied conditions.     

Semi-micro-monolithic columns using macroporous silica rods with improved performance

Monolithic silica columns in semi-micro-format have been synthesized using poly(acrylic acid) as a phase-separation inducer via a sol–gel route. The absence of a thick skin layer accompanied by deformation of the micrometer-sized gelling skeletons on the outermost part of the macroporous silica rod contributed to improve the efficiency of monolithic silica columns as thick as 2.4 mm in diameter. The kinetic plot analysis revealed that monolithic silica columns with macropore diameter of 1 μm and skeleton thickness of 1 μm with decreased macroporosity behave similarly to columns packed with 3 μm particles with slightly lower back pressure.     

Photo-induced carbon dioxide reduction on hexagonal tungsten oxide via an oxygen vacancies-involved process

Although converting the greenhouse gasses carbon dioxide (CO₂) into solar fuels is regarded as a convenient means of solar energy storage, the intrinsic mechanism on how the high chemical inertness linear CO₂ molecules is activated and converted on a semiconductor oxide is still elusive. Herein, by creating the oxygen vacancies on the typical hexagonal tungsten oxide (WO₃), we realize the continuous photo-induced CO₂ reduction to selectively produce CO under light irradiation, which was verified by isotope labeling experiment. Detailed oxygen vacancies evolution investigation indicates that light irradiation can simultaneously induce the in-situ formation of oxygen vacancies on hexagonal WO₃, and the oxygen vacancies promote the adsorption and activation of CO₂ molecules, leading to the CO₂ reduction to CO on the hexagonal WO₃ via an oxygen vacancies-involved process. Besides, the existence of water further promotes the formation of CO₂ reduction intermediate, further promote the CO₂ photoreduction. Our work provides insight on the mechanism for converting CO₂ into CO under light irradiation.     

Preparation and electronic properties of monolayer tungsten oxide on silica particles

Monolayer tungsten oxide on silica particles was prepared by a controlled hydrolysis technique. The material displays a bandgap which is 0.3 eV higher in energy than that for bulk WO₃. The quasi-Fermi level for electrons, in this material, as determined by electrochemical measurements, is 170 mV more negative for SiO₂/WO₃ than that for particulate WO₃.     

Adsorption and desorption behaviors of DNA with magnetic mesoporous silica nanoparticles

The interaction between DNA and mesopores is one of the basic concerns when mesoporous silica nanoparticle (MSN) is used as a DNA carrier. In this work, we have synthesized a type of mesoporous silica nanoparticle that has a Fe(3)O(4) inner core and mesoporous silica shell. This magnetic mesoporous silica nanoparticle (denoted as M-MSN) offers us a convenient platform to manipulate the DNA adsorption and desorption processes as it can be easily separated from solution by applying a magnetic field. The DNA adsorption behavior is studied as a function of time in chaotropic salt solution. The maximum amount of adsorbed DNA is determined as high as 121.6 mg/g. We have also developed a method to separate the DNA adsorbed onto the external surface and into the mesopores by simply changing temperature windows. The desorption results suggest that, within the whole adsorbed DNA molecules, about 89.5% has been taken up by M-MSN mesopores. Through the dynamic light scattering experiment, we have found that the hydrodynamic size for M-MSN with DNA in its mesopores is higher than the naked M-MSN. Finally, the preliminary result of the adsorption mechanism study suggests that the DNA adsorption into mesopores may generate more intermolecular hydrogen bonds than those formed on the external surface.     

Fabricating polypyrrole/tungsten oxide hybrid based electrochromic devices using different ionic liquids

A facile approach of polypyrrole (PPy)/tungsten oxide (WO₃) composites electrosynthesized in ionic liquids for fabrication of electrochromic devices is discussed. The electrochromic properties of PPy/tungsten oxide nanocomposite films (PPy/WO₃) prepared in the presence of four different ionic liquids, 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF₄), 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIMTFSI), and 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMPTFSI) were investigated in detail. Cyclic voltammetry results revealed that PPy/WO₃ nanocomposite films have much more electrochemical activity than those of WO₃ and PPy film. The electrochromic contrast, coloration efficiency, and switching speed of the composite films were determined for electrochromic characteristics. The maximum contrast and the maximum coloration efficiency values were measured as 33.25% and 227.89 cm²/C for the PPy/WO₃/BMIMTFSI composite film. Copyright © 2015 John Wiley & Sons, Ltd.     

Inorganic electrochromic materials based on tungsten oxide and nickel oxide nanostructures

Electrochromic devices, which dynamically change color under applied potentials, are widely studied for use in energy-efficient smart windows. The operation of electrochromic materials and devices involves the gain or loss of electrons and simultaneous insertion/extraction of ions with opposite charges to balance the internal electric fields. The performance is therefore limited by kinetics of charge transport in the electrochromic materials as well as ion migration in the electrolyte, materials and at their interfaces. Nanostructured electrochromic materials have an extremely short charge transport distance facilitating charge transport in electrochromic devices and large specific surface area for interaction with electrolytes, and thus may provide fast charge and ions transport, high electrochemical activities and remarkable enhancement of electrochromic properties. The recent progress in application of nanostructures, including nanoparticles, 1D and 2D nanostructures, in metal oxide electrochromic materials and devices is reviewed. A perspective on the development trends in electrochromic materials and devices is also proposed.     

Polypeptide-templated synthesis of hexagonal silica platelets

Several studies have demonstrated the use of biomimetic approaches in the synthesis of a variety of inorganic materials. Poly-L-lysine (PLL) promotes the precipitation of silica from a silicic acid solution within minutes. The molecular weight of PLL was found to affect the morphology of the resulting silica precipitate. Larger-molecular weight PLL produced hexagonal silica platelets, whereas spherical silica particles were obtained using low-molecular weight PLL. Here we report on the polypeptide secondary-structure transition that occurs during the silicification reaction. The formation of the hexagonal silica platelets is attributed to the PLL helical chains that are formed in the presence of monosilicic acid and phosphate ions. Hexagonal PLL crystals can also serve as templates in directing the growth of the silica in a manner that generates a largely mesoporous silica phase that is oriented with respect to the protein crystal template.     

Adsorption from ternary liquid mixtures on silica gel and aluminium oxide

Formation of mixed adsorbed layers was tested for ternary liquid mixtures containing methanol or acetone and the binary solvent benzene+n — heptane. The specific excess adsorption isotherms from the liquid phase were measured on silica gel, silanized silica gel and aluminium oxide. The experimental adsorption data are discussed on the basis of the changes in the mixed solvent composition.     

Thermal stability of hexagonal tungsten trioxide in air

We studied the thermal stability of different hexagonal tungsten trioxide, h-WO₃ samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.33−xWO_3−y, or by soft chemical synthesis from Na₂WO₄. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and ¹H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO₃ samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations were all affected.     

Unit-cell intergrowth of pyrochlore and hexagonal tungsten bronze structures in secondary tungsten minerals

Structural relations between secondary tungsten minerals with general composition A_x[(W,Fe)(O,OH)₃]_·yH₂O are described. Phyllotungstite (A=predominantly Ca) is hexagonal, , , space group P6₃/mmc. Pittongite, a new secondary tungsten mineral from a wolframite deposit near Pittong in Victoria, southeastern Australia (A=predominantly Na) is hexagonal, , , space group P-6m2. The structures of both minerals can be described as unit-cell scale intergrowths of (111)_py pyrochlore slabs with pairs of hexagonal tungsten bronze (HTB) layers. In phyllotungstite, the (111)_py blocks have the same thickness, 6 Å, whereas pittongite contains pyrochlore blocks of two different thicknesses, 6 and 12 Å. The structures can alternatively be described in terms of chemical twinning of the pyrochlore structure on (111)_py oxygen planes. At the chemical twin planes, pairs of HTB layers are corner connected as in hexagonal WO₃.     

Preparation of hexagonal platy particles of nanoporous silica using hydrotalcite as morphology template

Hexagonal platy composite particles with a hydrotalcite core and a nanoporous silica shell with a thickness of ca. 100 nm were synthesized by the reaction of a Mg-Al hydrotalcite with a homogeneous aqueous solution containing tetraethoxysilane, hexadecyltrimethylammonium chloride, ammonia and methanol at 3 degrees C. The calcination of the products at 500 degrees C in air led to the composite particle with a Mg/Al mixed oxide core and a nanoporous silica shell. Hexagonal platy particles of nanoporous silica with a pore diameter of 2.3 nm and BET surface area of 700 m(2) (g of silica)(-1) were obtained by removing the Mg/Al mixed oxide core.     

Synthesis of rod-like mesoporous silica with hexagonal appearance using sodium silicate as precursor

Using sodium silicate as precursor, rod-like mesoporous silica with hexagonal appearance was synthesized by controlling the pH value of a mixed micelles solution of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) during hydrolysis of ethyl acetate. The resulting mesoporous silica was characterized by small angle X-ray diffraction, nitrogen gas adsorption-desorption measurement and scanning electron microscopy. Results showed that the regular rod-like shapes with hexagonal appearance were obtained at a 9:1 molar ratio of CTAB to CTAC, and that the amounts and lengths of the rod-like mesoporous silica particles decreased with decreasing CTAB to CTAC molar ratio. There existed a type IV adsorption isotherm and an H1 hysteresis loop in N₂ gas adsorption-desorption curves.     

大孔硅胶的制备及其在多糖衍生物手性固定相上的应用

为制备孔径为100 nm的大孔硅胶,考察了热液法和焙烧法对球形硅胶（粒径5 μm,孔径10 nm）的扩孔效果。采用热液法扩孔时,在水溶液中加入22 g/L氟化钠,可以有效增强扩孔效果,在高压釜内160℃加热48 h便可扩孔至100 nm,但孔径不均匀。采用焙烧法扩孔时,通过调节焙烧温度、时间以及复盐LiCl-NaCl的加入量可以方便地控制扩孔速度与效果;在每10 g硅胶中加入1.125 g LiCl·H₂O和0.75 g NaCl,于500℃焙烧3~5 h,可得到100 nm大孔硅胶;该方法简单、高效,扩孔后的硅胶孔径分布均匀,表面形态与商品化的Fuji-1000硅胶相似。将两种扩孔方式得到的硅胶经氨基修饰后,涂覆纤维素-三（3,5-二甲基苯基氨基甲酸酯）制得了相应的手性固定相。结果表明,采用焙烧法扩孔得到的硅胶制备的固定相明显具有较好的分离选择性及分离度。     

Ultralow temperature synthesis of ordered hexagonal smaller supermicroporous silica using semifluorinated surfactants as template

Ordered hexagonal smaller supermicroporous silica (JLU-14L and JLU-11L) has been successfully synthesized at ultralow temperature (0 approximately -20 degrees C) by semifluorinated surfactants, which is extensively investigated by X-ray diffraction, N2 adsorption, and transmission electron microscopy. X-ray diffraction shows that the peak intensity of the samples increases with decreasing synthesis temperatures in the range of 0 approximately -20 degrees C, indicating that the ordering of porous silica improves with decreasing synthesis temperature. N2 adsorption/ desorption isotherms show that JLU-14L has both ordered smaller hexagonal supermicropores (1.27 and 1.28 nm) and disordered micropores (0.67 nm). Such hierarchically porous materials with micro/supermicroporosity should be potentially important for fast diffusion of reactants and products in catalytic reactions. The ultralow temperature synthesis is a crucial factor for the formation of ordered smaller supermicropores and the control of microporosity in JLU-14L.     

Adsorption and separation behavior of strontium and yttrium using a silica-based CMPO adsorbent

Journal of Radioanalytical and Nuclear Chemistry - To separate Y(III) from a Sr(II)–Y(II) mixture, two silica-based adsorbents, CMPO/SiO2-P and (CMPO?+?Dodec)/SiO2-P were prepared...