Conformational analysis of ethylene oxide and ethylene imine oligomers by quantum chemical calculations: solvent effects

Summary  Conformational analyses using quantum chemical calculations were carried out for 1- to 4-mers of ethylene oxide (EO) and ethylene imine (EI) oligomer models (EO-x and EI-x, x = 1 - 4) in the liquid phase using four solvents (permittivity: ε = 2.0 ~80.1). The results were compared against those obtained in the gaseous phase. The calculations involved either RHF/6-31+G(d,p) or B3LYP/6-31G(d) // SCRF/IPCM, based on the observed and calculated results for the energy difference between trans- and cis-dichloroethane. The conformations repeated for a unit of X-C, C-C and C-X bonds (X: O or N) were examined. For both oligomers, the energies of every conformer decreased with increasing ε values, and were linear against the Kirkwood function (K_f = (ε-1)/(2ε+1)). For the EO oligomers, the (ttt)_x conformer was most stable in the gaseous phase. In liquid phases, however, the preference for the gauche-conformation (gauche preference) of the C-C bonds increased with higher values of ε. In the case of EO-3, the (tg⁺t)_x conformer was most stable above an ε value of 8.9, which were in good agreement with those observed for triglyme solutions using NMR analysis. For the EI oligomers, the (tg⁺t)_x conformer was most stable in either gaseous or liquid phase, and the gauche preference of the C-C bonds in both phases were comparable. These results were in good agreement with those observed for di-MEDA solutions using NMR analysis. It was estimated that such small solvent effects on gauche preferences of the EI oligomers result in weakening for hydrogen bonds (NH-N) of neighboring imino groups by solvents.     

Adsorptive stripping voltammetric determination of podophyllotoxin,an antitumour herbal drug,at multi-walled carbon nanotube paste electrode

Adsorption stripping voltammetry, a very sensitive electroanalytical method, was employed to determine podophyllotoxin, a kind of antitumour herbal drug at a multi-wall carbon nanotube (MWCNT)-modified carbon paste electrode (CPE) surface. In the following anodic sweep from 0.5 to 1.5 V, podophyllotoxin, adsorbed at the MWCNT-modified CPE surface, was oxidized and yielded a sensitive oxidation peak with E _1/2/E _p approximately 1.16 V/1.18 V over the scan rates of 10–120 mV s⁻¹. From CV and SWV studies of podophyllotoxin in the acetate buffers of various pH values, it was found that protons were involved in the oxidation of the drug at the H⁺/e⁻ ratio of one (∆E _p/pH = 56 mV at 25 °C). Its electrochemical behaviour was irreversible. The experimental conditions, such as supporting electrolyte, pH value, accumulation time, ionic strength and scan rate, were optimized for the measurement of podophyllotoxin. The best results were obtained in 0.02 M acetate/acetic acid buffer (pH 4.6) containing 0.04 M KCl (1:49, v/v) for 60 s accumulation. The oxidation peak current varies linearly with the concentration of podophyllotoxin over the range of 199–1796 pg mL⁻¹. The limits of detection and quantification of the pure drug are 4.5 and 14.96 pg mL⁻¹, with the correlation coefficient, r = 0.998 and the relative standard deviation, RSD = 1.3% (n = 5). This new method was successfully applied to the determination of podophyllotoxin in a plant sample of the rhizome of Podophyllum hexandrum. Recoveries were 99.173–101.231%. The relative standard deviations of intraday and interday analyses for podophyllotoxin were 0.55 and 0.61%, respectively (n = 3).     

Synthesis and characterization of 5?V LiCoxNiyMn2?x?yO4 (x?=?y?=?0.25) cathode materials for use in rechargeable lithium batteries

Double doped spinel LiCo _x Ni _y Mn_2−x−y O₄ (x = y = 0.25) have been synthesised via sol–gel method using different chelating agents viz., acetic acid, maleic acid and oxalic acid to obtain 5 V positive electrode material for use in lithium rechargeable batteries. The sol–gel route endows lower processing temperature, lesser synthesis time, high purity, better homogeneity, good control of particle size and surface morphology. Physical characterizations of the synthesized powder were carried out using thermo-gravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical behaviour of the calcined samples has been carried out by galvanostatic charge/discharge cycling studies in the voltage range 3–5 V. The XRD patterns reveal crystalline single-phase spinel product. SEM photographs indicate micron sized particles with good agglomeration. The charge–discharge studies show LiCo_0.25Ni_0.25Mn_1.5O₄ synthesized using oxalic acid to be as a promising cathode material as compared to other two chelating agents and delivers average discharge capacity of 110 mA h g⁻¹ with low capacity fade of 0.2 mA h g⁻¹ per cycle over the investigated 15 cycles.     

Fetal Bovine Serum Concentration Affects Δ<Superscript>9</Superscript> Desaturase Activity of <Emphasis Type="Italic">Trypanosoma cruzi</Emphasis>

Fetal bovine serum (FBS) is an important factor in the culture of Trypanosoma cruzi, since this parasite obtains and metabolizes fatty acids (FAs) from the culture medium, and changes in FBS concentration reduce the degree of unsaturation of FAs in phosphoinositides. When T. cruzi epimastigotes were cultured with 5% instead of 10% FBS, and stearic acid was used as the substrate, ∆⁹ desaturase activity decreased by 50%. Apparent K _m and V _m values for stearic acid, determined from Lineaweaver–Burk plots, were 2 μM and 219 pmol/min/mg of protein, respectively. In studies of the requirement for reduced pyridine nucleotide, ∆⁹ desaturase activity reached a maximum with 8 μM NADH and then remained constant; the apparent K _m and V _m were 4.3 μM and 46.8 pmol/min/mg of protein, respectively. The effect of FBS was observed only for ∆⁹ desaturase activity; ∆¹² desaturase activity was not affected. The results suggest that decreased FBS in culture medium is a signal that modulates ∆⁹ desaturase activity in T. cruzi epimastigotes.     

Influence of voltammetric parameters on Zn–Ni alloy deposition under potentiodynamic conditions

The phase composition of Zn–Ni alloys electrodeposited from acetate-chloride plating solutions containing Zn⁺² and Ni⁺² ions at ratio of 1–12.8 at 50 °C was investigated by the potentiodynamic stripping method. Two anodic current density (i _a) peaks emerged in potentiodynamic stripping curves (PDC) at E < 0.0 V and E > 0.0 V (vs. Ag/AgCl/KCl_sat), that were attributed to oxidation of certain phases of the Zn–Ni alloy. The ratio of these phases in deposited Zn–Ni alloys under potentiodynamic conditions was affected by the potential sweep rate (ν) and maximum cathodic current density (i _c) The ratio of Zn and Ni in certain phases of Zn–Ni alloy was determined by the partial potentiodynamic stripping technique. Experimental data show that Zn–Ni alloy, containing 6.5 at.% Zn and 93.5 at.% Ni and dissolved in i _a peak H (E > 0.0 V), provides the black coloration of the Zn–Ni alloy.     

Synthesis and gas permeability of poly(<Emphasis Type="Italic">p</Emphasis>-phenyleneethynylene)s having bulky alkoxy or alkyl groups

Dipropynylbenzene with branched alkoxy and alkyl groups [CH₃C≡CRC₆H₂RC≡CCH₃, R = 2-methylpropoxy (1a), 3-methylbutoxy (1b), 4-methylpentoxy (1c), cyclohexylmethoxy (1d), 2-ethylhexoxy (1e), 2-octoxy (1f), 2-ethylhexyl (1g), and 2-octyl (1h)] were polymerized with Mo(CO)₆ in the presence of 4-(trifluoromethyl)phenyl to afford poly(2,5-di(alkoxy or alkyl)-p-phenyleneethynylene)s (2a–h). Polymer 2a was insoluble in any solvents, but the other polymers (2b–h) were soluble in common organic solvents. The polymers with relatively long side chains (2e–h) had high molecular weight over 1.6 × 10⁴ and gave free-standing membranes by solution-casting method. The densities of membranes of 2e–h were 0.914–0.998, and their fractional-free volume values were relatively large (0.094–0.158). The oxygen permeability coefficients of membranes of 2e–h were 18.4, 12.7, 4.85, and 19.3 barrers, respectively. It was found that poly(p-phenyleneethynylene) with 2-octyl side groups, which have the branch at the nearest position from main chain, exhibited the highest gas permeability.     

Direct-hydrothermal synthesis of LiFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> cathode materials

Carbon free LiFe_1−x Mn _x PO₄ (x = 0, 0.05, 0.1, 0.2, 0.4) cathode materials were prepared by a direct-hydrothermal process at 170 °C for 10 h. The structural and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge experiments, cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The electrochemical performance of LiFePO₄ prepared in this manner showed to be positively affected by Mn²⁺-substitution. Among the Mn²⁺-substitution samples, the LiFe_0.9Mn_0.1PO₄ exhibited an initial discharge capacity of 141.4 mA h g⁻¹ at 0.1 C, and the capacity fading is only 2.7% after 50 cycles.     

Direct evidence of oxygen evolution from Li1+ x (Ni1/3Mn1/3Co1/3)1? x O2 at high potentials

Li_1+x (Ni_1/3Mn_1/3Co_1/3)_1−x O₂ (NMC) oxides are among the most promising positive electrode materials for future lithium–ion batteries. A voltage “plateau” was observed on the first galvanostatic charging curve of NMC in the extended voltage region positive to 4.5 V vs. Li/Li⁺ for compounds with x > 0 (overlithiated compounds). Differences were observed in the cycling stability of the overlithiated and stoichiometric (x = 0) NMC oxides in this potential region. A differential plot of the charge vs. potential profile in the first cycle revealed that, for the overlithiated compounds, a large irreversible oxidative peak arises positive to 4.5 V vs. Li/Li⁺, while in the same potential region only a small peak due to the electrolyte oxidation is detected for the stoichiometric material. Differential Electrochemical Mass Spectrometry (DEMS) was used to investigate the high voltage region for both compounds and experimental evidence for oxygen evolution was provided for the overlithiated compounds at potentials positive to 4.5 V vs. Li/Li⁺. No oxygen evolution was detected for the stoichiometric compound.     

Thermal decomposition of 3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane in solution and its use in methyl methacrylate polymerization

The kinetics of the thermal decomposition reaction of diethylketone triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane, DEKTP) in ethylbenzene solution were studied in the temperature range of 120.0–150.0 °C and at an initial concentration range of 0.01–0.10 M. This peroxide was used as a new initiator in methyl methacrylate (MMA) polymerization process at high temperatures (110.0–140.0 °C) in ethylbenzene solution. The effects of initiator concentration and reaction temperature on the polymerization rate were investigated in detail. Thus, activation parameters of the solution polymerization process (ΔE _d* = 83.3 kJ mol⁻¹ and ΔE _p* − ΔE _t*/2 = 54.0 kJ mol⁻¹) will be obtained. DEKTP can effectively act as initiator in MMA polymerization and its performance is similar to that presented by a multifunctional initiator resulting in high-molecular weight polymethylmethacrylate with a high reaction rate.     

Potential of denitrification and nitrous oxide production from agricultural soil profiles (Seine Basin,France)

The denitrification process and the associated nitrous oxide (N₂O) production in soils have been poorly documented, especially in terms of soil profiles; most work on denitrification has concentrated on the upper layer (first 20 cm). The objectives of this study were to examine the origin of N₂O emission and the effects of in situ controlling factors on soil denitrification and N₂O production, also allowing the (N₂O production)/(NO₃ ⁻–N reduction) ratio to be determined through (1) the position on a slope reaching a river and (2) the depth (soil horizons: 10–30 and 90–110 cm). In 2009 and 2010, slurry batch experiments combined with molecular investigations of bacterial communities were conducted in a corn field and an adjacent riparian buffer strip. Denitrification rates, ranging from 0.30 μg NO₃ ⁻–N g⁻¹ dry soil h⁻¹ to 1.44 μg NO₃ ⁻–N g⁻¹ dry soil h⁻¹, showed no significant variation along the slope and depth. N₂O production assessed simultaneously differed considerably over the depth and ranged from 0.4 ng N₂O–N g⁻¹ dry soil h⁻¹ in subsoils (the 90–110-cm layer) to 155.1 ng N₂O–N g⁻¹ dry soil h⁻¹ in the topsoils (the 10–30-cm layer). In the topsoils, N₂O–N production accounted for 8.5–48.0% of the total denitrified NO₃ ⁻–N, but for less than 1% in the subsoils. Similarly, N₂O-consuming bacterial communities from the subsoils greatly differed from those of the topsoils, as revealed by their nosZ DGGE fingerprints. High N₂O-SPPR (nitrous oxide semi potential production rates) in comparison to NO₃-SPDR (nitrate semi potential reduction rates) for the topsoils indicated significant potential greenhouse N₂O gas production, whereas lower horizons could play a role in fully removing nitrate into inert atmospheric N₂. In terms of landscape management, these results call for caution in rehabilitating or constructing buffer zones for agricultural nitrate removal.     

Bio-inspired chemical hydrogen storage and discharge as a source of electrical energy

Reversible bio-inspired chemical hydrogen storage systems accumulate electrical energy in the form of electrons and proton ions located on biomolecules or bio-like storage molecules. Electro-active biomolecules (EAB) in Yeast media show such behavior: 2e⁻ + 2H⁺ + EAB_(aq)⁺ ⇆ EABH/H_(aq)⁺, also electro-active Methylene Blue (MB): 2e⁻ + 2H⁺ + MB_(aq)⁺ ⇆ MBH/H_(aq)⁺. The power characteristics of microbial fuel cell stacks equipped with such bio-inspired hydrogen storage systems were examined. E. coli cultures charged these bio-inspired separate chemical hydrogen storage units up to E = 0.50 ± 0.06 V; cell potentials increased proportionally in serial double, triple, and quadruple hydrogen storage stacks up to E _OCV = 1.98 V; the maximum power densities that were obtained improved proportionally with stack length by an increment of 1.4. The bio-inspired chemical hydrogen storage principle is of great interest for application in low-cost batteries that store renewable energy.     

Intense Red Photoluminescence Emission of Sol–Gel‐Derived Nanocrystalline Mg2TiO4 Thin Films

In this work, undoped Mg₂TiO₄ thin films were fabricated on p‐type Si(111) substrates by the sol–gel method, and the red photoluminescence (PL) of the films is introduced and discussed. According to the experimental results, the red emission appears when the films have been thermally treated at higher temperatures, which have a long range and well‐organized crystalline arrangement. Furthermore, to have better realization of the red emission mechanism of Mg₂TiO₄ films, the optical band gap of Mg₂TiO₄ (E_g^Mg2TiO4) was estimated at ~3.7 eV; furthermore, 325 nm (corresponding energy, hν = 3.82 eV > E_g^Mg2TiO4) and 633 nm (corresponding energy, hν = 1.96 eV < E_g^Mg2TiO4) excited light sources were used to clarify the position of the defect levels. In addition, the influence of annealing atmospheres (O₂, air, and vacuum) on the red emission of our samples is also discussed. A significant variety of red emissions can be found between these annealing conditions: the red emission can be effectively enhanced by O₂ annealing, but weakened by vacuum annealing. Results reveal that the red emission of Mg₂TiO₄ thin films may be highly dependent on the completeness of the O–X–O (X = Mg, Ti) bonds.     

Electrochemical properties of amorphous Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>2</Subscript>O<Subscript>5−<Emphasis Type="Italic">y</Emphasis></Subscript> thin film deposited by r.f.-sputtering

The electrochemical properties of amorphous vanadium pentoxide (V₂O₅) thin films deposited by reactive r.f.-sputtering were investigated using galvanostatic charge/discharge cycling and galvanostatic intermittent titration technique (GITT). As x in Li _x V₂O_5−y increased (x = 0–2.0), the electromotive force of the lithium (Li)∣1 M LiClO₄–propylene carbonate∣Li _x V₂O_5−y cell decreased gradually without a potential plateau or an abrupt potential reduction, demonstrating that an irreversible structural change did not occur in the entire Li content. Chemical diffusivity of the Li ion in the Li _x V₂O_5−y thin film measured using GITT was determined to be 4 × 10⁻¹³–7 × 10⁻¹⁴ cm² s⁻¹ in the Li content range investigated.     

Polymerization of rac-lactide catalyzed by group 4 metal complexes containing chiral N atoms

The hydroxyl- and phenoxy-bridged dinuclear zirconium and hafnium complexes, 1 and 2, containing a chiral N atom in the N₂O₂ ligand (H₂L = 2-(((2-pyridylmethyl)(2-hydroxyphenyl)amino)methyl)-4,6-di(tert-butyl)phenol) were used as catalysts for the ring-opening polymerization of rac-lactide. Experiments prove that 1 and 2 are living and controlled catalytic systems with activity up to 3.25 g_pol mmol_ini ⁻¹ h⁻¹. The isotactic-rich polylactides in a narrow polydispersity (M _w/M _n = 1.01–1.13) were produced with enantiomeric complexes 1 and 2 (P _m = 0.65–0.73). The kinetic studies show a first-order dependency in both monomer and initiator. The initiation mechanism is discussed on the basis of the MALDI-TOF MS and ¹H NMR spectra of the rac-LA oligomer prepared by 1.     

Influence of Zr dopant on polarization in rutile (In0.5Nb0.5)0.005(Ti1-xZrx)0.995O2 ceramics

(In_0.5Nb_0.5)_0.005(Ti_1-xZr_x)_0.995O₂ (INZT, x = 0-0.10) ceramics were synthesized using a conventional sintering method, and the effects of Zr content on the microstructures, dielectric properties and electron-pinned defect-dipoles (EPDD) polarization of the resultant products were investigated. The solubility limit of INZT was x = 0.075, and a secondary ZrTiO₄ phase appeared at x = 0.10. Ceramics with x = 0-0.10 exhibited excellent dielectric properties, ie, colossal permittivity (CP, εʹ > 10³) and low dielectric loss (tanδ < 0.1), over a wide range of frequencies (10⁰-10⁶ Hz at 300 K) and temperatures (50-350 K at 1 kHz). The dielectric spectra and XPS results confirmed that the CP property of the ceramics could be ascribed to their EPDD polarization. The activation energy (E_a) for EPDD polarization was continuously enhanced by increasing x values. EPDD relaxation parameters at different x values were revealed using Cole-Cole equation fitting. Moreover, α, which characterize the relaxation time τ distribution, increased with x values, thus indicating that Zr was involved in and affected electron localized states. The high E_a, temperature T_p of the peak εʹʹ at 1 kHz, and dielectric relaxation time τ_p at 30 K were related to increases in hopping distance of electrons among defect clusters with Zr addition.     

Detection of lard mixed with body fats of chicken, lamb, and cow by fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) spectroscopy provides a simple and rapid means of detecting lard blended with chicken, lamb, and cow body fats. The spectral bands associated with chicken, lamb, and cow body fats and their lard blends were recorded, interpreted, and identified. Qualitative differences between the spectra are proposed as a basis for differentiating between the pure animal fats and their blends. A semiquantitative approach is proposed to measure the percent of lard in blends with lamb body fat (LBF) on the basis of the frequency shift of the band in the region 3009–3000 cm⁻¹, using the equation y=0.1616x+3002.10. The coefficient of determination (R ²) was 0.9457 with a standard error (SE) of 1.23. The percentage of lard in lard/LBF blends was also correlated to the absorbance at 1417.89 and 966.39 cm⁻¹ by the equations y=0.0061x+0.1404 (R ²=0.9388, SE=0.018) and y=0.004x+0.1117 (R ²=0.9715, SE=0.009), respectively. For the qualitative determination of lard blended with chicken body fat (CF), the FTIR spectral bands in the frequency ranges of 3008–3000, 1418–1417, 1385–1370, and 1126–1085 cm⁻¹ were employed. Semiquantitative determination by measurement of the absorbance at 3005.6 cm⁻¹ is proposed, using the equation y=0.0071x+0.1301 (R ²=0.983, SE=0.012). The percentage of lard in lard/GF blends was also correlated to the absorbance at 1417.85 cm⁻¹ (y=0.0053x+0.0821, with R ²=0.9233, SE=0.019) and at 1377.58 cm⁻¹ (y=0.0069x+0.1327, with R ²=0.9426, SE=0.022). For blends of lard with cow body fat (CBF) bands in the range 3008–3006 cm⁻¹ and at 1417.8 and 966 cm⁻¹ were used for qualitative detection. The equation y=−0.005x+0.3188 with R ²=0.9831 and SE=0.0086 was obtained for semiquantitative determination at 966.22 cm⁻¹.     

A new class of Sol–gel derived LiM1xM2yMn2?x?yO3.8F0.2 (M1?=?Cr, M2?=?V; x?=?y?=?0.2) cathodes for lithium batteries

A series of LiM_1xM_2yMn_2−x−yO_3.8F_0.2 (M₁ = Cr, M₂ = V; x = y = 0.2) cathodes, viz., LiMn₂O_3.8F_0.2, LiCr_0.2Mn_1.8O_3.8F_0.2 and LiCr_0.2V_0.2Mn_1.6O_3.8F_0.2 along with native LiMn₂O₄ have been synthesized by Citric Acid assisted Modified (CAM) sol–gel method, with a view to understand the effect of synthesis methodology and the effect of dual category dopants, viz., anion and/or cation upon spinel cathodes individually. An acceptable capacity retention (94%) observed up to 50 cycles for native LiMn₂O₄ cathodes is attributed to the significance of CAM sol–gel method. Similarly, the encouraging charge–discharge results of LiMn₂O_3.8F_0.2 (130 mAh g⁻¹) and LiCr_0.2Mn_1.8O_3.8F_0.2 (142 mAh g⁻¹) cathodes revealed a possible augmentation in the reversible capacity behavior of the spinels upon F⁻ substitution at 32e site and the simultaneous substitution of Cr³⁺ and F⁻ at 16d and 32e sites respectively.     

Synthesis of LiFe0.4Mn0.6?xNixPO4/C by co-precipitation method and its electrochemical performances

LiFe_0.4Mn_0.6−x Ni _x PO₄/C(x = 0, 0.05, 0.1, and 0.2) composite cathode materials for lithium ion batteries have been prepared by the co-precipitation method using oxalic acid as a precipitator. The structure and morphology of precursors and products have been investigated. Electrochemical tests demonstrate that LiFe_0.4Mn_0.55Ni_0.05PO₄ can deliver a specific capacity of 142 mAh g⁻¹ at 0.1 C, and retains 133 mAh g⁻¹ after 60 cycles. The rate performance of LiFe_0.4Mn_0.6PO₄ is obviously improved by doping Ni. The capacity of LiFe_0.4Mn_0.55Ni_0.05PO₄ at 2 C is 110 mAh g⁻¹.     

Investigation of lithium ion kinetics through LiMn2O4 electrode in aqueous Li2SO4 electrolyte

Spinel LiMn₂O₄ was prepared by sol–gel method and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope. Cyclic voltammogram, galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy (EIS) techniques were employed to evaluate the electrochemical behaviors of LiMn₂O₄ in 1 M Li₂SO₄ aqueous solution. Two redox couples at E _SCE = 0.78/0.73 and 0.91/0.85 V were observed, corresponding to those found at E _Li/Li ⁺= 4.05/3.95 and 4.06/4.18 V in organic electrolyte. The discharge capacity of pristine LiMn₂O₄ in aqueous electrolyte was 57.57 mAh g⁻¹, and the capacity retention of the electrode is 53.7 % after 60 cycles. Only one semicircle emerged in EIS at different potentials in aqueous electrolyte, while three semicircles were observed in organic electrolytes. There was no solid electrolyte interface film on the surface of spinel LiMn₂O₄ electrode in aqueous electrolyte. The change of kinetic parameters of lithium ion insertion in spinel LiMn₂O₄ with potential in aqueous electrolyte for initial charge process was discussed in detail, and a suitable model was proposed to explain the impedance response of the insertion materials of lithium ion batteries in different electrolytes.     

Gemini surfactant controlled preparation of well-ordered lamellar mesoporous molybdenum oxide

A series of well-ordered lamellar mesoporous molybdenum oxides were prepared using gemini surfactant [C _n H_2n+1N⁺(CH₃)₂–(CH₂)₂–N⁺(CH₃)₂C _n H_2n+1] · 2Br⁻(denoted as C _n-2-n , n = 12, 14 and 16) as the structure-directing agent and ammonium heptamolybdate tetrahydrate (NH₄)₆Mo₇O₂₄ · 4H₂O as the precursor. The obtained samples were characterized by X-ray powder diffraction, thermal analysis, transmission electron microscopy and nitrogen adsorption–desorption. Results showed that contrary to complete structure collapse after removing tetradecyltrimethylammonium bromide (TTAB) from molybdenum oxide/TTAB composite, the lamellar mesostructure was retained after removal of C _n-2-n from corresponding composite. The effects of alkyl chain length and concentration of gemini surfactants on the structure of the mesoporous molybdenum oxide were also investigated. The specific surface area of extracted sample was as high as 116 m² g⁻¹. The maintenance of the lamellar mesostruture was due to the strong self-assembly ability of gemini surfactants and the strong electrical interaction between gemini surfactants and molybdenum oxide.