Wanguo Hou

A cyclic voltammetric technique for the detection of micro-regions of bmimPF6/Tween 20/H2O microemulsions and their performance characterization by UV-Vis spectroscopy

As green solvents, ionic liquids (ILs) can be substitutes for traditional organic solvents, and form useful microemulsions with water. Microemulsions consisting of the IL, 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), the non-ionic surfactant Tween 20 and water were formed at 30.0 °C, and the phase behavior of the ternary system was investigated. Three regions of the microemulsions: water-in-bmimPF6 (W/IL), bicontinuous, and bmimPF6-in-water (IL/W) were identified by cyclic voltammetry using potassium ferrocyanide K4Fe(CN)6 as an electroactive probe. The polarity of the microemulsion environment was investigated by UV-Visible spectroscopy using methyl orange as a probe. Use of the ionic compound K3Fe(CN)6 in UV-Visible measurements revealed that the bmimPF6/Tween 20/H2O microemulsions could solubilize salt species into the microemulsion droplets. Moreover, the solubilization of riboflavin in the microemulsions was also shown by UV-Visible spectra. These results show that these IL-based microemulsions have potential in the production of metal nanomaterials, in biological extractions or as solvents for enzymatic reactions.

Synthesis of Magnetite–Graphene Oxide-Layered Double Hydroxide Composites and Applications for the Removal of Pb(II) and 2,4-Dichlorophenoxyacetic Acid from Aqueous Solutions

Magnetic composites consisting of magnetite (Fe3O4), graphene oxide (GO), and Mg3Al-OH layered double hydroxide (LDH), denoted as MGL composites, with varying GO contents (RGO) were synthesized by a mechano-hydrothermal (MHT) route using Fe3O4, Mg(OH)2, and Al(OH)3 as the inorganic starting materials. The application of the synthesized MGLs for removing the heavy-metal Pb(II) and the hydrophobic organic pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions was investigated. Chemical bonding among the GO, Fe3O4, and LDH components was observed in the MGLs. The MGL composites showed good water-dispersity, strong magnetic response, and high sorption capacities and removal efficiencies for both Pb(II) and 2,4-D pollutants. The sorption capacities of the MGL for the pollutants significantly increased with an increase in RGO. Increasing pH could increase the removal efficiency for Pb(II) but decrease that for 2,4-D. The MGLs showed more affinity for Pb(II) than for 2,4-D in the competitive sorption. In addition, the MGLs could remain almost constant removal efficiency for the pollutants after reuse over six cycles, indicating their potential use as sorbents in wastewater treatment. Furthermore, a Cs effect was observed in the sorption equilibriums, which could be described using the Langmuir-SCA and Freundlich-SCA isotherms. The removal mechanisms of the MGL for Pb(II) and 2,4-D were discussed. The MHT method provided a simple and environmentally friendly route for synthesizing GO-LDH composite materials.

Synthesis, characterization and enhanced visible light photocatalytic activity of Bi2MoO6/Zn–Al layered double hydroxide hierarchical heterostructures

Bi2MoO6/Zn–Al layered double hydroxide (LDH) hierarchical heterostructures assembled from Bi2MoO6 hierarchical hollow spheres and Zn–Al LDH nanosheets were synthesized by a low-temperature hydrothermal method. X-ray diffraction, Fourier transform-infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS) confirmed the formation of the Bi2MoO6/Zn–Al LDH composites. Morphologies were characterized by scanning electron microscopy and transmission electron microscopy (TEM). XPS and high resolution TEM indicated the formation of a Bi2MoO6/Zn–Al LDH heterojunction. Increasing the LDH content from 0 to 27.0 wt.% caused the Brunauer–Emmett–Teller (BET) specific surface area of the composites to gradually increase. The photocatalytic degradation activity for Rhodamine B (RhB) under visible light irradiation exhibited a large enhancement, followed by a decrease, with increasing LDH content. The Bi2MoO6/Zn–Al LDH heterostructure composite with LDH content of 5.5 wt.% showed the highest photocatalytic activity and degraded 99% of RhB in 80 min, while Bi2MoO6 degraded less than 50%. The average photocatalytic efficiency is enhanced by more than 100%. The enhanced photocatalytic activity of the Bi2MoO6/Zn–Al LDH heterostructure photocatalyst was mainly attributed to the efficient separation of photoinduced electrons and holes. Superoxide radicals and holes were the major active species. The Bi2MoO6/Zn–Al LDH heterostructure photocatalyst exhibited excellent stability and reusability. A detailed mechanism for its enhanced photocatalytic activity was discussed in this study. This work provides an effective way to fabricate a series of Bi-based and LDH-containing heterostructure photocatalysts.

Structure transition from aragonite to vaterite and calcite by the assistance of SDBS.

Structure transition from aragonite to vaterite and calcite with the help of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) was investigated, respectively, by a hydrothermal method. When the experimental temperature was controlled at 90 degrees C, aragonite of crystal calcium carbonate was transformed into vaterite with the assistance of SDBS. Pure vaterite was obtained as the concentration of SDBS reaches to 2.5 mM. When the experimental temperature was controlled at 120 and 150 degrees C, respectively, aragonite was transformed into calcite, and pure calcite was obtained as the concentrations of SDBS were equal to 1.0 and 2.5 mM, respectively. Possible formation mechanism of different CaCO(3) polymorphs was proposed based on the obtained experimental results.

Enhanced visible light photocatalytic activity of bismuth oxybromide lamellas with decreasing lamella thicknesses

BiOBr lamellas were synthesized at different reaction pH values via a hydrothermal process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy and N2 sorption measurements were used to characterize the BiOBr samples. BiOBr samples have the same lamella structures and band gaps but different lamella sizes and thicknesses. Adjusting the pH of the reaction system tunes the BiOBr lamella thickness from 42 to 21 nm. The photodegradation efficiencies of the BiOBr lamellas for rhodamine B (RhB) and methylene blue (MB) in aqueous solution were examined. The degradation efficiency for RhB is much higher than that for MB. The decrease in BiOBr lamella thickness significantly enhances the photocatalytic activity for dye degradation, despite the decrease in exposed photoactive (001) facet percentage. Decreasing the lamella thickness from 42 to 21 nm yields a more than fourfold enhancement in photodegradation efficiency of BiOBr samples for RhB. The most important factor influencing the photocatalytic activity of the BiOBr samples is their lamella thickness, rather than the exposed (001) facet percentage. Thus, even for flaky semiconductors with high exposed photoactive facet contents, the influence of lamella thickness on photocatalytic activity should be preferentially considered.

Surfactant-free microemulsion composed of oleic acid, n-propanol, and H2O.

Generally, a microemulsion consists of oil, water, surfactant, and sometimes cosurfactant. Herein, we report a surfactant-free microemulsion (denoted as SFME), consisting of oleic acid (oil phase), water, and n-propanol without the amphiphilic molecular structure of a traditional surfactant. The phase behavior of the ternary system was investigated, showing that there were a single-phase microemulsion region and a multiphase region in the ternary phase diagram. The electrical conductivity measurement was employed to investigate the microregions of the single-phase microemulsion region, and three different microregions, that is, water-in-oleic acid (W/O), a bicontinuous (B.C.) region, and oleic acid-in-water (O/W), were identified, which were further confirmed by freeze-fracture and cryogenic transmission electron microscopy (FF-TEM and Cryo-TEM) observations. The polarity and the salt solubility of water domains in the W/O SFME were investigated by UV-visible spectroscopy using methyl orange and potassium ferricyanide as probes, respectively. Experimental results showed that the water domains in the W/O microemulsion had a lower polarity than bulk water and a normal solubility for salt species, indicating that the SFMEs have much significance in the preparation of various nanomaterials.

Synthesis of rod-like mesoporous silica using mixed surfactants of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride as templates

Abstract Using sodium silicate as precursors and mixed surfactants of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) as templates, rod-like mesoporous silica with hexagonal appearance were synthesized by controlling the pH value of solution during hydrolysis of ethylacetate. Results showed that at a molar ratio of 9:1 (CTAB to CTAC), regular rod-like shapes were obtained, and that with the decrease of the molar ratio of CTAB to CTAC (from 9:1 to 5.5:4.5), the amount and length of rod-like mesoporous silica decreased, but the amount of irregular particles increased. The diffraction peaks obtained with XRD were assigned to hexagonal symmetry. Type IV adsorption isotherm and an H1 hysteresis loop were observed in N 2 adsorption–desorption curves.

Synthesis, characterization, and visible-light photocatalytic activity of BiOI hierarchical flower-like microspheres

BiOI hierarchical flower-like microspheres were hydrothermally prepared, using tetrabutylammonium iodide as an iodine source and template. Many BiOI hierarchical structures have been synthesized using KI, NaI, HI or ionic liquids as the iodine source, but the use of alkyl ammonium iodide as the iodine source was not reported in the literature. The so-obtained BiOI samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen sorption measurements, and ultraviolet-visible diffuse reflectance spectroscopy. The effects of hydrothermal temperature and time on the BiOI crystal structure and morphology were investigated. The BiOI microspheres were composed of BiOI nanosheets. The photocatalytic performance of the BiOI samples was determined from the degradation of Rhodamine B, under visible light irradiation. BiOI microspheres prepared at 160 °C over 30 h exhibited excellent photodegradation efficiency, which was more than five and seven times higher than those of BiOI nanoplates and N-doped TiO2, respectively. The high photocatalytic performance was attributed to the high specific surface area and low nanosheet thickness. A morphologic factor was proposed to represent the ratio of specific surface area to nanosheet thickness, and correlated to the photodegradation efficiency of the BiOI samples. The photocatalytic efficiency increased with increasing morphologic factor. The BiOI photocatalyst exhibited excellent stability and reusability, and has potential in environment remediation.

Studies on intrinsic ionization constants of Fe-Al-Mg hydrotalcite-like compounds.

The theoretical analysis of the intrinsic ionization constant (K(a2)(int)) of Fe-Al-Mg hydrotalcite-like compounds (HTlc) possessing permanent charges was first performed using the double extrapolation method proposed by James et al. The theoretical permanent charge density (sigma(p,T)) of the HTlc sample was calculated from the crystal structure of HTlc, and the influence of sigma(p,T) on the K(a2)(int) was also examined. From the experimental results, these conclusions can be obtained: the zero point of the charge (pH(ZPC)) of Fe-Al-Mg HTlc increases with decreased Fe3+ content and increases with increased Mg2+ in the HTlc. The pK(a2)(int) of Fe-Al-Mg HTlc also increases with decreased Fe3+ and increased Mg2+ content in the sample; furthermore, the pK(a2)(int) of Fe-Al-Mg HTlc increases with decreased sigma(p,T).

Influence of measuring conditions on the thixotropy of hydrotalcite-like/montmorillonite suspension

Abstract The influence of the measuring conditions on the thixotropy of suspensions, which were made up of hydrotalcite-like compounds (HTlc) and Na-montmorillonite (MT), was studied. Usually, the structure recovery at rest after preshear is considered the fundamental thixotropic process. And the recovery process was performed under the steady shear experiments, then the thixotropic type can be judged according to the recovery process. In this paper, the influence of rest time (ts) and the shear rate ( γ ) on the recovery process was studied. Three kinds of HTlc/MT suspension were studied, their mass ratios of HTlc to MT, which were signed as R (e.g. R=WHTlc/WMT), were 0.013, 0.051, 0.091, respectively. It is found the HTlc/MT suspension with R=0.013 showed positive thixotropy at ts=0, but it changed to negative one with the increase of ts. The suspension with R=0.051 transformed from complex thixotropy at low γ or positive thixotropy at high γ into negative one with the increase of ts. The suspension with R=0.091 behaved as complex thixotropy when γ is 1022 s−1, and it behaved as negative thixotropy when γ is 10 s−1. Whereas, the suspension transformed from negative thixotropy to the weak complex one as the increase of ts when γ is 170 or 341 s−1. For all the systems, the equilibrium viscosity decreased gradually with ts at the low γ , but the equilibrium viscosity increased with ts at high γ because of the memory effect. The mechanism has been discussed.