Anodic oxidation of pentachlorophenol at Ti/SnO<Subscript>2</Subscript> electrodes

The electrochemical oxidation of dilute aqueous solutions of pentachlorophenol (PCP) using Ti/SnO₂ as an electrocatalytic material has been investigated. The studies were carried out in a two-compartment electrochemical cell at three different current density values (10, 30 and 50 mA cm^–2) at 25 °C and using 20 mg L^–1 of PCP in 0.1 M NaOH (pH 10) as supporting electrolyte. The PCP concentration and the by-products of the oxidized solution were monitored during the oxidation process using UV and HPLC techniques. For the three current densities investigated it was found that the rate of PCP elimination depends only on the specific electrical charge. Likewise, the oxidation mechanism was proved to occur through the participation of adsorbed hydroxyl radicals (·OH) formed on the SnO₂ surface, whatever the current density used. However, as the applied current density was increased, a current efficiency lower than 2% was obtained, which is due to mass transfer limitations. In addition, it was observed that the PCP was mineralized to CO₂ with conversion percentages as high as 92% and at current density values as low as 10 mA cm^–2. The PCP degradation produces two other by-products of oxidation (<10%), namely carboxylic acids, which are non-toxic compounds. Electronic Publication     

Preparation and characterization of the Ti/IrO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> as supercapacitor electrode materials

WO₃ films have been prepared onto IrO₂-coated Ti substrate by electro-deposition, and as-deposited and annealed films have been characterized by using Raman spectroscopy. It was found that the asdeposited film consists of orthorhombic WO₃ · H₂O phase, which transforms to amorphous WO₃ by annealing at 250°C and to monoclinic phase by annealing at and above 350°C. All electrochemical experiments were carried on Ti/IrO₂/WO₃ annealed at 450°C. The open-circuit potential could change significantly due to the hydration of the coating film. However this process is fairly slow. Reproducible voltammograms could be obtained quickly, further revealing high electrochemical stability of the Ti/IrO₂/WO₃ electrode. And the shapes of CV show the approximate rectangular mirror image, showing the typical characteristic of capacitive behavior. The specific capacitance obtained at a scan rate of 50 mV s⁻¹ is 46 F g⁻¹.     

Oxygen evolution on Ti/Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-coated electrodes in alkaline solution

The electrochemical performances of Co₃O₄ nanopowders, obtained by the sol-gel method, were investigated and compared with those of commercial Co₃O₄ powders, for oxygen evolution reaction in alkaline solution. The active oxide powder was mixed with teflon and assembled on Ti substrate to form thin catalyst film. Cyclic voltammetry, polarization curves, and electrochemical impedance spectroscopy were used to assess the mechanism of oxygen evolution reaction, chemical structure, and morphology of the catalyst. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript>/rGO hybrid nanostructures for efficient electrocatalytic oxygen evolution

We report the synthesis of NiCo₂O₄/reduced graphene oxide (NiCo₂O₄/rGO) hybrid hierarchical structures with unique nanonet and microsphere morphologies by organic polar solvent-assisted solvothermal method. The electrocatalytic oxygen evolution reaction (OER) activity of these materials is studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods in O₂-saturated 0.1 M KOH solution. The NiCo₂O₄/rGO hybrid nanocomposite materials are found to be highly active electrocatalysts for OER at lower overpotentials. The nanonet and microsphere-like NiCo₂O₄/rGO catalysts require overpotentials of 0.450 and 0.530 V at a current density of 10 mA cm^?2, and their corresponding Tafel slopes are 53 and 62 mV dec^?1, which are much lower than values reported for non-precious electrocatalysts. Further, both NiCo₂O₄/rGO catalysts show good catalytic stability with current retention more than 92 % over long period of 15,000 s determined by chronoampirometry and at the end of 1000th cycle determined by linear sweep voltammetry. The enhanced OER activity of nanostructured NiCo₂O₄/rGO hybrid catalysts is attributed to synergistic interaction between rGO and NiCo₂O₄, which seems to be essential for maintaining the large contact area at the electrode-electrolyte interface, better mass, and charge transport and to minimize the aggregation of NiCo₂O₄ nanoparticles.     

Synthesis,characterization of nanosized CoAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and its electrocatalytic activity for enhanced sensing application

Nanosized cobalt aluminate (CoAl₂O₄) was prepared by thermolysis of heteronuclear coordination compound, namely [Al₂Co(C₂O₄)₄(OH₂)₆]. The synthesized precursor was characterized by chemical analysis, vibrational spectra and thermal analysis. The cobalt aluminate obtained after a heating treatment of the precursor at 700 °C was characterized by IR, XRD, TEM coupled with SAED measurements. Two types of carbon-based electrodes, glassy carbon and boron-doped diamond electrodes were decorated with the obtained cobalt aluminate in order to enhance the electroanalytical performance for the tetracycline (TC) detection in the aqueous solutions. Cyclic voltammetry technique was used to determine the effect of the nanosized CoAl₂O₄ on the electrochemical oxidation of TC and as consequence, for TC detection at both carbon-based electrodes. The obtained cobalt aluminate exhibited the electrocatalytic activity toward TC detection in direct relation with the type of the carbon substrate, which allowed enhancing the electroanalytical parameters of TC detection in the aqueous solution.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Synthesis and characterization of ZrO<Subscript>2</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanofilms

Processes involved in the preparation of zirconia and yttria thin films by sol-gel technology from film-forming solutions (FFSs) were studied over the entire range of concentrations. The physicochemical properties, composition, and structure of the films were studied.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

Nitrite oxidation on RuO<Subscript>2</Subscript> electrodes

An electrochemical kinetic investigation of nitrite oxidation to nitrate on RuO₂ is discussed. The process is studied by cyclic voltammetry, steady-state measurements and potential step measurements. The overall oxidation reaction is a two-electron process where the first step involves a reversible charge transfer: NO₂⁻ ⇔ NO₂ + e⁻ The one-electron oxidation of nitrite yields adsorbed NO₂ which is further oxidized to adsorbed (NO₂)⁺ and subsequently desorbed via a chemical reaction. In the general case, fit of experimental data is obtained with adsorption described by a Temkin isotherm unless the electrode is pre-treated at a cathodic potential where the (NO₂)_ads is removed. This treatment lowers the degree of coverage by intermediates but not the nature of the slow step. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 1, pp. 142–149. The text was submitted by the authors in English.     

Ethanol electrocatalytic oxidation on highly dispersed Pt-TiO<Subscript>2</Subscript>/C catalysts

Carbon supported Pt-TiO₂(Pt-TiO₂/C) catalysts were prepared with colloidal and chemical reduction method on different conditions and used for ethanol electrooxidation in acidic solution. The size of TiO₂ and Pt crystal varied on the catalysts prepared by different methods and the Electrochemical specific surface area (ESA) also showed different on these catalysts. The catalytic activity on these carbon supported Pt-TiO₂ catalysts showed some different behaviors. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 785–790. The article is published in the original.     

High effective electrocatalytic oxidation of cyclohexanol on stable Fe-Mn/Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> membrane electrode

A new composite electrode material with iron-manganic oxide coating (Fe-Mn/Mn₂O₃) was prepared, and its catalytic performance for oxidizing cyclohexanol was investigated in this work. The new electrode material, based on iron substrate covered with electrolytic manganese, was obtained by further coating the manganese surface with 50 % manganese nitrate solution and then conducting program thermal decomposition treatment. X-ray diffraction (XRD) was used to determine the surface crystal phase compositions, which were Mn and Mn₂O₃. The catalytic results showed an excellent electrocatalytic performance on the oxidation of cyclohexanol, and the main products were cyclohexanone and hexanedioic acid. According to our experiment results and the literature reports, the existence of mixed valent Mn^III and Mn^IV played a key role in the electrocatalytic oxidation process. A probable process was proposed: the Mn^IV seized the hydrogen from cyclohexanol, the resulting cyclohexaneoxy radical was oxidized into cyclohexanone, and then the absorbed cyclohexanone was further oxidized into hexanedioic acid.     

TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> binary xerogels: Synthesis and characterization

Silica/titania binary xerogels were prepared by joint hydrolysis of the ingredients. Gels of various compositions were characterized by ¹H NMR spectroscopy, IR spectroscopy, and thermogravimetry. The spectral characteristics of binary systems differ considerably from mere superposition of the spectra of the two constituent compounds and the spectrum of a mechanical mixture. A feasibility was demonstrated for controlling the acid properties of binary oxide gels via varying the component mole ratio.     

Crystal structures of Ti(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript> and Sn(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>

The characteristics of crystal structures of the titanium(IV) diammonium (Ti(NH₄)₂P₄O₁₃) and tin(IV) diammonium (Sn(NH₄)₂P₄O₁₃) tetraphosphates, which are isostructural with similar silicon(IV) and germanium(IV) salts, have been obtained by the Rietveld method using X-ray powder diffraction data. The compounds crystallize in the triclinic system, space group P \(\overline 1 \), Z = 2, a = 15.0291(7) Å, b = 7.9236(4) Å, c = 5.0754(3) Å, α = 99.168(3)°, β = 97.059(3)°, γ = 83.459(3)° for Ti(NH₄)₂P₄O₁₃ and a = 15.1454(7) Å, b = 8.0103(5) Å, c = 5.1053(3) Å, α = 99.898(6)°, β = 96.806(3)°, γ = 83.881(4)° for Sn(NH₄)₂P₄O₁₃. The structure is refined in the isotropic approximation using the pseudo-Voigt function: R _p = 0.077, R _Bragg = 0.045, R _F = 0.057 for Ti(NH₄)₂P₄O₁₃; R _p = 0.082, R _Bragg = 0.044, R _F = 0.046 for Sn(NH₄)₂P₄O₁₃. The hydrogen atoms of the ammonium cations are placed in the calculated positions. A comparative analysis of the structures of the compounds of the M^IV(NH₄)₂P₄O₁₃ (M^IV = Si, Ge, Ti, Sn) series has been carried out.     

Synthesis and characterization of ferroelectric SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> nanotubes arrays

Ferroelectric SrBi₂Ta₂O₉ nanotubes were fabricated by sol–gel dipping template technique and characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. They had a single orthorhombic perovskite structure, and most of SBT nanotubes showed highly preferential crystal growth along the [115] orientation. FE-SEM and TEM investigations showed that nanotubes have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. From HRTEM results, the clear lattice fringes indicated that the nanotubes are structurally uniform and well crystallized. The growth mechanisms of SBT nanotubes into the AAO templates were explored.     

Hydrogen generation from H<Subscript>2</Subscript>O/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/MnWO<Subscript>4</Subscript> system

Hydrogen gas as a clear energy resource was found to be largely bubbled from a H₂O/H₂O₂/MnWO₄ system. MnWO₄ powder was fabricated by an aqueous reaction method. The powder was characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectrometry (XPS). The efficiency of the hydrogen generation increases with an increase in initial pH in the appropriate range, H₂O₂ proportion, MnWO₄ proportion, and intensity of light resource. Calcining at 400 °C for 1 h can make the MnWO₄ powder synthesized by an aqueous reaction more effective for H₂ generation and more stable in higher initial pH. The MnWO₄ catalyst shows a long-term stability for photocatalytic H₂ generation. A mechanism was suggested for the hydrogen generation from the H₂O/H₂O₂/MnWO₄ system together with XPS analysis.     

Synthesis and characterization of Co<Subscript>0.8</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Cobalt zinc ferrite, Co_0.8Zn_0.2Fe₂O₄, nanoparticles have been synthesized via autocatalytic decomposition of the precursor, cobalt zinc ferrous fumarato hydrazinate. The X-ray powder diffraction of the ‘as prepared’ oxide confirms the formation of single phase nanocrystalline cobalt zinc ferrite nanoparticles. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been determined as Co_0.8Zn_0.2Fe₂(C₄H₂O₄)₃·6N₂H_4. The Curie temperature of the ‘as-prepared oxide’ was determined by AC susceptibility measurements.     

Synthesis and structure of [UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>){CONH<Subscript>2</Subscript>N(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

The single crystals of [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 7.461(2) Å, b = 8.828(2) Å, c = 11.756(2) Å, β = 107.21(3)°, space group Pc, Z = 2, R = 2.94%. The structure comprises infinite chains [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] extended along [001] and corresponding to the AT¹¹M ₂ ¹ crystallochemical group (A = UO ₂ ²⁺ , T¹¹ = C₂O ₄ ^2? , M¹ = N,N-CONH₂N(CH₃)₂) of uranyl complexes. The chains are connected into a three-dimensional framework by hydrogen bonds involving the oxygen atoms of oxalate and uranyl ions and the N,N-dimethylcarbamide methyl groups.     

Carbon ceramic electrodes modified with mixed oxides SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> for determination of levofloxacin

The preparation of a carbon ceramic electrode modified with SnO₂ (CCE/SnO₂) using tin dibutyl diacetate as precursor was optimized by a 2³ factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO₂ provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO₂, indicating that SnO₂ when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10^?5 to 6.97×10^?4 mol L^?1 with quantification and detection limits of 3.80×10^?5 mol L^?1 (14.07 mg L^?1) and 1.13×10^?5 mol L^?1 (4.18 mg L^?1), respectively.