One-pot electrochemical synthesis of graphene by the exfoliation of graphite powder in sodium dodecyl sulfate and its decoration with platinum nanoparticles for methanol oxidation

We demonstrate a method which directly grows large areas of graphene on carbon paper and glassy carbon (GC) substrates from graphite powder and anionic surfactant, sodium dodecyl sulfate, assisted electrochemical exfoliation. The electrochemically reduced graphene has been carefully characterized by scanning electron microscopy (SEM) and electrochemical techniques. Particularly, SEM images show enhanced growth of graphene structures formed of ‘urchin’ objects. The CV spectra illustrate that a variety of the oxygen-containing functional groups has been thoroughly removed from the graphite plane via electrochemical reduction. Potential peak (Ep) of graphene electrode in [Fe(CN)₆]^3−/4− solution is as small as 212 mV which is 168 mV smaller than that of graphite electrode. This could be attributed to the high quality graphene accelerating the electron transfer rate in [Fe(CN)₆]^3−/4− electrochemistry. Finally, platinum was electro reduced onto the GC and graphene modified GC based electrodes for use in methanol oxidation. The catalytic activities of graphene-supported Pt nanoparticles and Pt-GC electrocatalysts for methanol oxidation were 1900 and 915.5 A g⁻¹ Pt, which can reveal the particular properties of the exfoliated graphene supports.     

Influences of pH on the structure,morphology and dielectric properties of bismuth titanate ceramics produced by a low-temperature self-combustion synthesis without an additional fuel agent

Bismuth titanate (BIT) ceramics were prepared by incorporating low-temperature self-combustion synthesis and pH modification. The pH value of the initial precursor was adjusted to 3, 5 and 7 by the addition of ammonium hydroxide (NH₄OH) with different amount. The reaction between ammonium ions (NH₄⁺) and nitrate ions (NO₃^?) induced the formation of ammonium nitrate (NH₄NO₃), in turn to favor the combustion by enhancing the decomposition rate. Excessive hydroxyl ions (OH^?) at higher pH value dominated the chelating of the metal carboxylate and the metal ions, resulting in a strong hybridization between bismuth (Bi) and oxygen (O), and also the suppression of the independent volatility of Bi and bismuth oxide (Bi₂O₃). Such conditions contributed to the formation of pure BIT via the low-temperature self-combustion synthesis without the use of an additional fuel agent. A BIT ceramic with high relative density (91.35%) that exhibited a high dielectric constant of ～340 and a low dissipation factor ～0.028 was obtained by the synthesis method at the neutral condition. Furthermore, it offers ability for the use in high temperature applications up to 675 °C.     

Cationic polyelectrolytes,XI. Polymers with quaternary N-atoms in the main chain obtained by condensation polymerization of epichlorohydrin with amines

Water soluble cationic polyelectrolytes containing quaternary nitrogen atoms within the main chain were prepared via condensation polymerization of epichlorohydrin (ECH) with dimethylamine (DMA) and N,N-dialkylaminoalkylamines. The main parameters of the reaction that influence the polymer properties are: DMA/asymmetrical diamine molar ratio, the initial concentration of amine solution, NaOH/amine molar ratio, ECH/amine molar ratio, and asymmetrical diamine structure. The feature of flexible polyelectrolyte own to the investigated polymers was emphasized by the viscosimetric behaviour in dilute aqueous solutions with and without salt presence.     

New method for the study of surface acidity of zeolites by NH3-TPD, using a pH-meter equipped with an ion selective electrode

Desorbed ammonia is captured by an acetic acid solution whose concentration of ammonium ions formed by neutralization, is continuously recorded by a pH-meter equipped with an ion-selective electrode (ISE). This technique allows the study of both the acidity density and the distribution of acid site strengths. Such “strength profile” was obtained by plotting the relative rate of desorbed NH₃ versus the temperature. Results obtained can be fairly well correlated with those already published. It is shown that by investigating several H-ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios, the data of acid density obtained by the ISE method are very close to those calculated from the Al content. The slight shift of the desorption peaks towards higher temperature suggests a slightly higher strength for more isolated acid sites. Zeolite structures, which are richer in Al, contain weaker acid sites, as evidenced by the H-Y when compared to the H-mordenite, while the acid sites density of the former is much higher. The ultra-stabilized Y zeolite (H-USY) shows a lower acidity density than the parent H-Y owing to the removal of some of the tetrahedral Al atoms from the framework during the preparation. The strength profile of the H-USY is also quite different from that of the H-Y. The new technique appears to be much simpler, more rapid, more informative and quite accurate when compared to the technique using a gas chromatograph equipped with a thermal conductivity detector (GC-TCD).     

Determination of the ionization constant of water between 100 to 200°C by emf measurements,with some derived thermodynamic quantities

The first experimentally derived values of the ionization constant of water and associated thermodynamic quantities, by emf measurements, are reported, within the range 100–200°C. The derived values of the ionization constant of pure water from these measurements support the findings obtained by purely thermochemical observations. The effects of a recalculation of the observed discrepancies, both in the heats of ionization and molal heat capacity, between emf measurements and thermochemical values at 25°C are also discussed, by an appraisal of the empirical methods that are available and that have been used for the treatment of experimental data. A method, producing a new family of equations based on theoretical-structural considerations, is also suggested for the behaviour of the ionization constant of water as a function of temperature. Values for the heats of ionization of water between 100 and 200°C are also proposed.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. II. Properties of copolymer obtained by beaker-scale copolymerization

In order to elucidate the copolymerization mechanism, the properties of the copolymer obtained by the iodine-initiated copolymerization of the tetraoxane–1,3-dioxolane–methylal system have been studied using gas chromatography, microscopy, scanning electron microscopy, differential scanning calorimetry, and gel permeation chromatography. From the behavior of the thermal stability and gas chromatography of the reaction mixture, it was found that reactivity of 1,3-dioxolane with active center is larger than that of tetraoxane, i.e., more than 90% 1,3-dioxolane is consumed at an early stage of the polymerization. The results obtained by microscopy, DSC, and GPC of the copolymer suggested that the copolymerization proceeds from the surface to the center of the tetraoxane crystal as if it were a core model. It was also suggested that the heterogeniety in copolymer properties can be explained not only by heterogeneous dispersion of 1,3-dioxolane in tetraoxane crystal, but also by the difference of reactivity of 1,3-dioxolane with the active center.     

Atrazine removal by catalytic oxidation processes with or without UV irradiation: Part II: an analysis of the reaction mechanisms using LC/ESI–tandem mass spectrometry

The transformation mechanisms of atrazine (ATZ) degradation by sole-UV, dark-catalytic oxidation process (dark-COP), and UV-assisted catalytic oxidation process (UVCOP) were examined and compared. Depending on the selection of the processes, one to fourteen ATZ derivatives were detected by liquid chromatography electrospray tandem mass spectrometry (LC/ESI–MS/MS). For sole-UV, a single dechlorinated product (OIET) was identified due to the homolytic or heterolytic cleavage of ATZ. On the other hand, in dark-COP, seven chlorinated (CDET, CMIT, CDIT, CEAT, CIAT, CDAT, and CAAT) and three dechlorinated (OIET, ODIT, and OAAT) intermediates were identified. However, the dechlorinated derivatives, in dark-COP, appeared in low concentrations. In UVCOP, four more dechlorinated derivatives (ODET, OEAT, OIAT, and ODAT) were found. It was suggested that alkylic-oxidation, dealkylation, and dechlorination–hydroxylation (minor in dark-COP) are the leading pathways in dark-COP and UVCOP. The final products of sole-UV, dark-COP, and UVCOP were found to be OIET, CAAT, and OAAT, respectively. In addition, the ratio of dechlorinated versus chlorinated derivatives as well as OAAT to CAAT were used to quantify the detoxification effect of dark-COP and UVCOP, where the UVCOP was suggested as a more environmentally friendly process.     

Investigation on the anti-reduction mechanism of Ti4+ in high dielectric constant system Ca0.9La0.067TiO3 by doping with Al2O3

Ca_0.9La_0.067TiO₃ (abbreviated as CLT) ceramics doped with different amount of Al₂O₃ were prepared via the solid state reaction method. The anti-reduction mechanism of Ti⁴⁺ in CLT ceramics was carefully investigated. X-ray diffraction (XRD) was used to analyze the phase composition and lattice structure. Meanwhile, the Rietveld method was taken to calculate the lattice parameters. X-ray photoelectron spectroscopy (XPS) was employed to study the valence variation of Ti ions in CLT ceramics without and with Al₂O₃. The results showed that Al³⁺ substituted for Ti⁴⁺ to form solid solution and the solid solubility limit of Al³⁺ is near 1.11 mol%. Furthermore, the reduction of Ti⁴⁺ in CLT ceramics was restrained by acceptor doping process and the Q × f values of CLT ceramics were improved significantly. The CLT ceramic doped with 1.11 mol% Al₂O₃ exhibited good microwave dielectric properties: ε_r = 141, Q × f = 6848 GHz, τ_f = 576 ppm/°C.     

Calculation of the efficiency of counter-current stage-wise mass transfer processes with constant distribution factor,when in the stationary state: II. Stage requirements for the separation of two components by two solvent extraction

The equations governing counter-current extraction as derived in Part I, “Distribution of one component only,” are applied to the two component of a binary mixture.Methods are described to derive the minimum number of stages required for the separation of a given feed into products of a given composition.The results were applied to experiments reported by Scheibel.     

Interpretation of the chain structures of PMMAs, PANs and PAAms obtained by using Ce(IV) and KMnO4 in combination with NTA and DTPA as initiator systems by FTIR spectroscopic analysis

Polyacrylamides (PAAms), polyacrylonitriles (PANs) and poly(methyl methacrylate)s (PMMAs) were synthesized by using Ce(NH₄)₂(NO₃)₆, Ce(SO₄)₂·4H₂O and KMnO₄ in combination with nitrilotriacetic acid (NTA) and diethylenetriamine pentaacetic acid (DTPA), which have strong chelating properties, as redox initiators. Polymerizations were carried out in the aqueous acidic solutions at 25°C and 55°C in the presence of air. The chain structures of the resulting products were studied by Fourier-transform infrared (FTIR) spectroscopic measurements. From the comparison of the spectroscopic results with gravimetric and viscometric data it was concluded that both the differences between the solubility behaviour in aqueous solutions of MMA, AN, AAm and their polymers, and catalyst–activator–monomer combinations were important parameters effecting the polymerization mechanisms, conversions and the structures of the polymers. The FTIR and viscosity results indicated that PAAms obtained in our experimental conditions formed crosslinked structures with sulphated complexes of Ce(III) and MnSO₄ produced by the redox reactions between catalysts (MnO₄⁻ and Ce(IV)), NTA and AAm. Further, it was observed that PAN chains were terminated by hydrated and sulphated complexes of Ce(III) while the termination of PMMA radicals took place by primary radicals because PMMAs were formed by emulsion polymerization kinetics.