Use of bulk liquid membrane for the removal of chromium (VI) from aqueous acidic solution with tri-n-butyl phosphate as a carrier

Tri-n-butyl phosphate (TBP) was used as carrier for the transport of chromium (VI) through a hexane bulk liquid membrane. The transport efficiency of chromium (VI) by TBP was investigated under various experimental conditions such as pH of the feed phase (Cr (VI) solution), concentration of the receiving phase (NaOH solution), concentration of TBP in membrane, rate of stirring, effect of transport time, type of solvent, Cr (VI) concentration in feed phase, and effect of temperature. The transport efficiency increased with increasing carrier concentration from 7.5 × 10^− 2 to 2.25 × 10^− 1 mol/L. At high pH (donor phase) the transport rate of chromate ions decreased. At high stirring speed (300 rpm) the Cr (VI) transport from the feed phase to the strip phase was completed within 5 h at 27 °C. Under optimum conditions: donor phase 4.8 × 10^− 4 mol/L K₂Cr₂O₇ solution at pH 1.0 ± 0.1, acceptor phase 1.0 mol/L NaOH solution, membrane phase 2.25 × 10^− 1 mol/L, stirring speed 300 rpm, and temperature 27 °C, the flux rate was found to be 2.90 × 10^− 7 mol/m² s.     

Direct synthesis of poly(l-lactic acid) in supercritical carbon dioxide with dicyclohexyldimethylcarbodiimide and 4-dimethylaminopyridine

The direct synthesis of poly(l-lactic acid) (PLLA) from an l-lactic acid oligomer has been performed in supercritical carbon dioxide (scCO₂) using an esterification promoting agent, dicyclohexyldimethylcarbodiimide (DCC), and 4-dimethylaminopyridine (DMAP) as a catalyst. PLLA within M_n of 13,500 g/mol was synthesised in 90% yield at 3500 psi and 80 °C after 24 h. The molecular weight distribution of the products was narrower than PLLA prepared with melt-solid phase polymerisation under conventional conditions. Both DCC and DMAP showed high solubility in scCO₂ (DCC: 7.6 wt% (1.63×10⁻² mol/mol CO₂) at 80 °C, 3385 psi, DMAP: 4.5 wt% (1.62×10⁻²mol/mol CO₂) at 80 °C, 3386 psi) and supercritical fluid extraction was found to be effective at removing excess DMAP and DCC after the polymerisation was complete. We show that DCC and DMAP are effective esterification promoting reagents with further applications for condensation polymerisations in scCO₂.     

Electrooxidation of formic acid on carbon supported PtxPd1−x (x = 0-1) nanocatalysts

In this work, carbon supported Pt_xPd_1−x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt_xPd_1−x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt_xPd_1−x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell.     

Preparation and electrochemical characterization of palladium single crystal electrodes in 0.1 M H2SO4 and HClO4: Part I. Low-index phases

The electrochemical properties of Pd(1 1 1), Pd(1 0 0) and Pd(1 1 0) single crystal bead electrodes, prepared by a novel electron beam heating and inductive annealing technique, have been characterized in 0.1 M sulfuric acid and 0.1 M perchloric acid by cyclic voltammetry and chronoamperometry. Hydrogen and (hydrogen) sulfate adsorption as well as surface oxidation were found to depend strongly on the crystallographic orientation and the nature of the electrolyte. The combination of charge displacement and voltammetric experiments allowed the determination of the potentials of zero total charge (E_pztc) of Pd(1 1 1) and Pd(1 0 0). The values of E_pztc in sulfuric acid were found to be more negative than in perchloric acid. The estimation of E_pztc for Pd(1 1 0) was hampered by the superposition with hydrogen absorption. The electro-oxidation of irreversible adsorbed carbon monoxide monolayers was studied on the three low-index Pd electrodes. The onset potential of the CO oxidation reaction follows the sequence Pd(1 0 0) < Pd(1 1 0) < Pd(1 1 1). Chronoamperometric experiments revealed a pronounced structure sensitivity of the reaction kinetics. The processes involved are determined by nucleation of oxygen-containing species on defect (step) sites and by slow diffusion of CO_ads on (1 1 1) terrace sites.     

Probing anodic reaction kinetics and interfacial mass transport of a direct formic acid fuel cell using a nanostructured palladium-gold alloy microelectrode

The anodic reaction kinetics and interfacial mass transport of a direct polymer electrolyte membrane formic acid fuel cell have been investigated in an all solid-state electrochemical cell using a highly active nanostructured palladium-gold alloy microelectrode as an in situ probe. Well-defined “S-shaped” steady-state cyclic voltammograms exhibiting current-rising region at lower overpotentials and limiting current region at higher overpotentials have been first obtained for the electrochemical oxidation of formic acid at varying temperature. The “S-shaped” steady state polarization curves and chronoamperometric curves enable convenient measurements of the anodic reaction kinetics and interfacial mass transport of formic acid under real polymer electrolyte membrane conditions. It is encouragingly found that formic acid can be directly oxidized to CO₂ with the first electron transfer being the likely rate-determining step and the formation of surface poison can be neglected. The exchange current density for the electrooxidation of formic acid is on the order of magnitude of 10⁻⁷ A cm⁻² in the temperature range of 20-60 °C. The permeability and diffusion coefficient of formic acid through a Nafion^® 117 membrane are of the order of magnitude of 10⁻⁹ mol cm⁻¹ s⁻¹ and 10⁻⁶ cm² s⁻¹, respectively. The combination of a nanostructured microelectrode and an all solid-state electrochemical cell offers a versatile approach to evaluate potential electrocatalysts for fuel cells and electrochemical sensors employing polymer electrolyte membranes.     

Investigations of electrochemical oxygen transfer reaction on boron-doped diamond electrodes

In this paper, the electrochemical oxygen transfer reaction (EOTR) is studied on boron-doped diamond electrodes using simple C₁ organic compounds (methanol and formic acid). The kinetics of both oxygen evolution (side reaction) and organics oxidation (main reaction) has been investigated using boron-doped diamond microelectrodes-array (BDD MEA). Oxygen evolution, in the high-potential region, takes place with a Tafel slope of 120 mV dec⁻¹ and zero reaction order with respect to H⁺. In the presence of organics, a shift of the polarization curves to lower potentials is observed while the Tafel slopes remain close to 120 mV dec⁻¹. A simplified model of C₁ organics oxidation is proposed. Both water discharge and organics oxidation are assumed to be fast reactions. The slowest step of the studied EOTR is the anodic discharge of hydroxyl radicals to oxygen. Further in this work, electrolysis of formic acid on boron-doped diamond macroelectrode is presented. In order to achieve 100% current efficiency, electrolysis was carried out under programmed current, in which the current density was adjusted to the limiting value.     

The effect of nano-Cr2O3 on solid-solution assisted sintering of MgO refractories

The effect of Cr₂O₃ particle size on the densification of magnesia refractories was investigated. Magnesia grains (<45 μm) were mixed with 2 wt% of micro-Cr₂O₃ (2 μm) and nano-Cr₂O₃ particles (10–20 nm) and sintered at 850–1450 °C, for 5 h in air. The progress of the densification and phase evolution of samples was studied with the support of X-ray diffraction phase analysis (XRD), Fourier transformer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was shown that the densification of magnesia was enhanced by reducing the particle size of the added chromia to the range of 20 nm. According to the phase analysis results, the higher dissolution rate of Cr₂O₃ in MgO in the MgO–Cr₂O₃ system was responsible for the faster densification of nano-Cr₂O₃ containing mixes.     

Influence of Au contents of AuPt anode catalyst on the performance of direct formic acid fuel cell

We reported that various compositions of AuPt nanoparticles synthesized as an anode material for formic acid fuel cell were investigated. Its surface characteristics were systematically analyzed using XRD and TEM and anodic electrocatalytic activity was studied using a linear sweep voltammetry technique in 0.5 M H₂SO₄ + 1 M HCOOH. In addition, the voltage-current curve and power density of home-made AuPt-based membrane-electrode-assembly (MEA) and commercial Pt_0.5Ru_0.5-based MEA was measured at 60 °C in 9 M formic acid. The maximum power density of Au_0.6Pt_0.4-based MEA was 30% higher than that of PtRu-based MEA which were 200 mW cm⁻² and 155 mW cm⁻², respectively.     

Photocatalytic degradation of formic acid with simultaneous production of hydrogen over Pt and Ru-loaded CdS/Al-HMS photocatalysts

The CdS/Al-HMS, Pt- and Ru-loaded CdS/Al-HMS photocatalysts were prepared by template, ion exchange and precipitation reaction, and were characterized by N₂ adsorption/desorption measurements, X-ray diffraction (XRD), UV-Visible diffuse reflectance spectra (UVDRS), X-ray fluorescence (XRF), transmission electron microscopy (TEM) and fluorescence emission spectra (FES). The result showed that CdS in the form of clusters was highly dispersed inside the channels of Al-HMS. The reaction activities of photocatalysts were examined by photocatalytic degradation of formic acid under visible light irradiation (λ ≥ 420 nm). The photocatalyst, CdS/Al-HMS loaded 0.34 wt.% Pt, showed the highest H₂ evolution at a rate of 7.63 mL h^− 1 with an apparent quantum yield of 2%.     

Influence of underpotentially deposited Sb onto Pt anode surface on the performance of direct formic acid fuel cells

We first reported on electrocatalytic activity and stability of antimony modified platinum (PtSb_upd) as anode catalyst in direct formic acid fuel cells. Sb modified Pt (PtSb_upd) was prepared by underpotential deposition technique applying constant potential of 0.2 V (vs. Ag/AgCl, 3M KCl) and its modified surface was characterized by XRD and XPS. The electrocatalytic oxidation activity by cyclic voltammograms and the single cell power performance of Sb modified Pt were measured and their results were compared with the data of unmodified Pt electrode. PtSb_upd induced lower onset potential of formic acid oxidation and twice higher power density of 250 mW cm⁻² was observed.     

Oxidative desulfurization of tire pyrolysis naphtha in formic acid/H2O2/pyrolysis char system

Waste tires are one potential source of alternative energy because of their long chain hydrocarbon with a high calorific heating value. However, the pyrolysis oil that is derived from waste tires is not appropriate for direct use in a combustion process due to its high sulfur content. Therefore, the oxidative desulfurization (ODS) process was evaluated for its ability to reduce the sulfur content of the naphtha fraction distillated from light oil derived from waste tire pyrolysis. The addition of formic acid to pH of 4.0 in the presence of 25 vol.% hydrogen peroxide (H₂O₂) and tire pyrolysis char enhanced the level of sulfur removal to ca. 70% due to the simultaneous adsorption and oxidation of sulfurous compounds on the surface of the pyrolysis char. The chemical treatment to form surface-modified char promoted the benefit for ODS process in the presence of formic acid (pH 4) and H₂O₂ (25 vol.%) by increasing the sulfur reduction in the pyrolysis naphtha up to 75%.     

Pyrolysis of poly-l-leucine under combustion-like conditions

The protein poly-l-leucine has been used as a model compound for the nitrogen in biomass fuels. It was pyrolysed in a fluidised bed at 700 and 800 °C and the pyrolysis gases were analysed with a FT-IR spectrometer. HCN, NH₃ and HNCO were identified as the main nitrogen-containing species, while neither NO nor N₂O were found among the pyrolysis gases. At 700 °C, as much as 58% of the nitrogen content was converted into HCN and 31% into NH₃. The HCN/NH₃ ratio increased from about 1.9 at 700 °C to above 2.2 at 800 °C. Pyrolysis of another protein, poly-l-proline, at 800 °C gave a HCN/NH₃ ratio close to 10. This revealed that the protein's amino acid composition has a marked impact on the composition of the pyrolysate.     

Catalytic activity, stability and structure of multi-walled carbon nanotubes in the wet air oxidation of phenol

Multi-walled carbon nanotubes (MWCNTs), with no supported metal, were used as catalysts in the wet air oxidation of phenol. The MWCNTs were chemically modified using HCl or HNO₃-H₂SO₄. They were characterized by BET, SEM, TEM, FT-IR and Raman spectroscopy. The functionalized MWCNTs exhibited both high activity and good stability in the wet air oxidation of phenol. At 160 °C and 2.0 MPa with an initial phenol concentration of 1000 mg/L, 100% phenol conversion and 76% total organic carbon abatement could be achieved after 120 min reaction. Upon reaction, the short chain carboxylic acids mainly maleic/fumaric, malonic, oxalic, formic and acetic acid were produced. Surface functional groups (-COOH) were shown to play a key role in the high activity of the functionalized MWCNTs. A mechanism for the CWAO of phenol was proposed.     

Kinetics and mechanism of ?-caprolactone and l,l-lactide polymerization coinitiated with zinc octoate or aluminum acetylacetonate: The next proofs for the general alkoxide mechanism and synthetic applications

Following our previous papers on mechanism of cyclic esters' polymerization coinitiated by tin(II) octoate [tin(II) bis-(2-ethylhexanoate), (Sn(Oct)₂)] in the presence of either the low molar mass coinitiator (an alcohol, hydroxy acid, or H₂O) or a macromolecule fitted with a hydroxy end group (ROH), the present work deals with ?-caprolactone (CL) and l,l-lactide (LA) polymerizations coinitiated with zinc octoate (Zn(Oct)₂) or aluminum acetylacetonate (Al(Acac)₃). A series of kinetic measurements revealed that similarly as in the Sn(Oct)₂ coinitiated process, these polymerizations proceed by simple monomer insertion into the …Mt-OR bond, reversibly formed in the reaction -Mt-L + ROH ? …-Mt-OR + LH (where Mt = Sn, Zn or Al; L = Oct or Acac), taking place throughout the whole polymerization process. MtL_n itself does not play an active role in the polymerization. Applicability of the commercially available Zn(Oct)₂ or Al(Acac)₃ for the aliphatic polyester (10³ ≤ M_n ≤ 4 × 10⁵) synthesis is also discussed.     

Electrochemically oxidized carbon anode in direct l-ascorbic acid fuel cells

The activity of electrochemically oxidized carbon electrode was investigated in the operation of a direct l-ascorbic acid fuel cell anode. The surface oxygen species placed on electrochemically oxidized carbon electrode were analyzed by X-ray photoelectron spectroscopy and cyclic voltammetry. The electrochemical oxidation process of carbon electrode can facilitate the pore-filling process (i.e., wetting) of the electrolyte into the microstructure of the carbon electrode by increasing the number of more polar functional groups on the electrode surface. The electrochemically oxidized carbon electrode exhibited significantly enhanced electro-catalytic oxidation activity of l-ascorbic acid compared to an unmodified carbon electrode. Moreover, the simplified electrode structure using carbon paper without an additional powder-based precious catalyst layer is very favorable in creating percolation network and generates power density of 18 mW/cm² at 60 °C.     

Kinetic study of formic acid oxidation on Ti/IrO2 electrodes prepared using the spin coating deposition technique

In the first part of this paper, IrO₂ electrodes produced by thermal decomposition of H₂IrCl₆ precursor were manufactured using the spin coating deposition technique, where centrifugal forces spread the precursor solution with simultaneous evaporation of the solvent on the rotating Ti substrate. It was found using this technique, that it is possible to obtain thin and uniform IrO₂ coatings with controlled loadings. The influence of the concentration of iridium salt in the precursor solution (c₀) as well as the influence of the rotation speed at which the substrate spins (ω) on the IrO₂ loading have been studied using voltammetric charge measurements. From these results, a simple relation has been proposed for the estimation of the IrO₂ loading for a given c₀ and ω.In the second part of this paper and from measurements performed using different IrO₂ loadings and formic acid concentrations, the kinetic parameters of the oxidation of formic acid have been quantitatively determined using a model that involves the redox couple IrO₃/IrO₂ as mediator of this reaction. Furthermore, using the kinetic parameters obtained together with the Nernst equation and the I-V curves of the supporting electrolyte (1 M HClO₄), theoretical I-V curves could be constructed for different concentrations of formic acid and different IrO₂ loadings.     

Upgrading of bitumen with formic acid in supercritical water

Upgrading of bitumen was examined with formic acid in supercritical water (SCW) from 673 to 753 K and at a water/oil ratio from 0 to 3. Decomposition of bitumen in SCW + HCOOH gave higher conversions of asphaltene and lower coke yields than those of pyrolysis or with only SCW. Decomposition of bitumen was also conducted in SCW + H₂, SCW + CO, toluene and tetralin, which revealed that decomposition of asphaltene was promoted and coke formation was suppressed when using SCW + HCOOH. In SCW + HCOOH, an increase in the water/oil ratio promoted both decomposition of asphaltene and suppression of coke formation. Formic acid in SCW seemed to enhance the conversion of bitumen to lower molecular weight compounds because formic acid seems to produce active species in SCW. The low temperature region (ca. 723 K) was suitable for upgrading bitumen with formic acid in SCW since coke formation was strongly promoted at high temperature (>753 K). A reaction model was proposed and the model predicted that hydrogenation of the asphaltene core was important for the suppression of coke formation.     

Microwave heated polyol synthesis of Pt3Te/C catalysts

Pt₃Te/C nanoparticles supported on Vulcan XC-72 carbon were prepared within a few minutes under different reaction conditions by using a microwave-polyol method. Their physical and electrochemical characterization were carried out by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectrometer (XPS), selected-area electron diffraction (SAED), H₂ adsorption-desorption, ethanol oxidation and CO stripping. TEM shows that the Pt₃Te/C (pH 3) catalyst has uniform nanoparticles and is well dispersed with average particle size of about 2.8 nm. Electrochemical results show that the electrochemical activity of Pt₃Te/C catalysts synthesized at different pH values are in the order of pH 3 > pH 7 > pH 9 > pH 13. The Pt₃Te/C catalyst (pH 3) is also better than the Pt₃Te/C catalyst synthesized by formic acid as reductant. From a practical point of view, the microwave-polyol method at the pH value of 3 could be an appropriate method for synthesizing nanocatalysts.     

Crystallization behavior of poly(l-lactic acid)

The crystallization behavior of poly(l-lactic acid) was studied in the range of 80-160 °C. The peak crystallization time (τ_p) was defined and obtained from the crystallization isotherm measured with a differential scanning calorimeter (DSC). Isothermal crystallization temperature (T_c) dependence of log(τ_p) discretely changed at 113 °C (= T_b). The linear growth rate of spherulite, G, was measured with a polarizing microscope. The T_c dependence of G and the size of the spherulite also discretely changed at T_b. Crystal structures for samples isothermally crystallized at temperatures which were higher and lower than T_b were orthorhombic (α-form) and trigonal (β-form), respectively. The discrete change of the crystallization behavior was explained by the formation of different crystal.     

Size-controlled high magnetization CoFe2O4 nanospheres and nanocubes using rapid one-pot sonochemical technique

Highly crystalline single phase spherical and monodisperse cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) with uniform shape and size distribution have been synthesized by one pot-rapid sonochemical method. The effect of different solvents, such as aqueous, alcoholic, and a mix of water/ethanol in 1:1 volume ratio on the shape, size, and crystalline structure of CoFe₂O₄ NPs were studied using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The size of CoFe₂O₄ nanoparticle was controlled in the range from 20 to 110 nm based on the solvent medium used in the synthesis process. Furthermore, the evolution from spherical to cubic morphology of cobalt ferrite NPs is achieved by simply changing the solvent medium from aqueous to alcoholic medium. The magnetic properties of all the synthesized CoFe₂O₄ NPs were studied by vibrating sample magnetometer (VSM) at room temperature. The magnetization value was found to be particle size dependent, and high magnetization (Ms) of 92.5 emu/g was obtained for the CoFe₂O₄ NPs sample synthesized in a mixed solution of water and ethanol. A possible reaction mechanism for the formation of cobalt ferrite NPs by the sonochemical technique was discussed. The facile method adopted in our study appears to be a promising route for synthesis of highly crystalline nanoparticles within short times and without the need for using any calcination process.