Anomalous IR optical properties of aggregates of Pd nanoparticles induced through electrochemical cyclic voltammetry

IR optical properties of Pd nanoparticles with different size and aggregation state were studied in the current paper. The dispersed Pd nanoparticles () stabilized with poly(N-vinylpyrrolidone) (PVP) were synthesized by the seeding growth method, in which the seeds were formed step by step through reducing H₂PdCl₄ with ethanol. The dispersed Pd nanoparticles of much large size () were grown from the by keeping the colloid of undisturbed for 150 days at room temperature around 20 °C. The aggregates of () were prepared through an agglomeration process induced during a potential cyclic scanning between −0.25 V and 1.25 V for 20 min at a scan rate of 50 mV s⁻¹. Scanning electron microscope (SEM) patterns confirmed such aggregation of . Fourier transform infrared (FTIR) spectroscopy together with CO adsorption as probe reaction was employed in studies of IR optical properties of the prepared Pd nanoparticles. The results demonstrated that CO adsorbed on films substrated on CaF₂ IR window or glassy carbon (GC) electrode yielded two strong IR absorption bands around 1970 cm⁻¹ and 1910 cm⁻¹, which were assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. Similar IR bands were observed in spectra of CO adsorbed on films, except the IR bands were much weak, whereas CO adsorbed on film produced an IR absorption band near 1906 cm⁻¹, and an anomalous IR absorption band whose direction has been completely inverted around 1956 cm⁻¹. The direction inversion of the IR band of CO bonded to asymmetric bridge sites on was ascribed to the interaction between Pd nanoparticles inside the aggregates. Based on FTIR spectroscopic and cyclic voltammetric results, the aggregation mechanism of Pd nanoparticles from to has been suggested that the agglomeration of Pd nanoparticles was driven by the alteration of electric field across electrode-electrolyte interface, when the PVP stabilizer was stripped via oxidation during cyclic voltammetry.     

Li-ion diffusion kinetics in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn₂O₄ thin films were deposited on Au substrates by pulsed laser deposition (PLD). The Li-ion chemical diffusion coefficients of the films, , were measured by cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). It was found that the values by CV and PITT were in the order of 10⁻¹³ cm² s⁻¹, and those by EIS and GITT were in the range of 10⁻¹³ to 10⁻¹¹ and 10⁻¹⁴ to 10⁻¹¹ cm² s⁻¹, respectively. These data were compared with the previously reported values.     

Relative stabilities of Ce(IV) and Ce(III) limiting carbonate complexes at 5-50 °C in Na aqueous solutions, an electrochemical study

The normal potential of the Ce(IV)/Ce(III) redox couple was determined by square wave voltammetry (SWV) at different temperatures in solutions with a constant ratio [CO₃²⁻]/[HCO₃⁻] ≈10 for high ionic strengths (3.29 mol dm⁻³ at 4.39 mol dm⁻³): varies from 259.5 to 198.0 mV/S.H.E. in the 15-50 °C range. Linear variations were found for versus (RT/F)ln(mCO₃²⁻), leading to the stoichiometry, Ce(CO₃)₆⁸⁻ for the Ce(IV) limiting complex. But the slopes of these linear variations were actually found in the range 1.8-1.9, not exactly 2. This was interpreted as dissociation of the Ce(IV) limiting complex following the reaction: Ce(CO₃)₅⁶⁻ + CO₃²⁻ → Ce(CO₃)₆⁸⁻ and as dissociation of the Ce(III) limiting complex following the reaction: Ce(CO₃)₃³⁻ + CO₃²⁻ → Ce(CO₃)₄⁵⁻; for which maximum possible values of log₁₀ K_IV,6 and log₁₀ K_III,4 were estimated via fitting in the 15-50 °C temperature range (log₁₀ K_IV,6 = 0.42 (0.97) and log₁₀ K_III,4 = 0.88 (7.00) at 15 °C (50 °C). The normal potential was found to decrease linearly with T, these variations correspond to , with T⁰ = 298.15 K and . The apparent diffusion coefficient of Ce(IV) was determined by direct current polarography (DCP), cyclic voltammetry (CV) and square wave voltammetry. It was found to depend on the ionic strength and to be proportional to T.     

Codeposition of copper and tin from acid sulphate solutions containing polyether sintanol DS-10 and micromolar amounts of halides

Cu(II) and Sn(II) reduction in acid sulphate solutions containing polyether laprol DS-10 was investigated using voltammetric XPS and XRD techniques. Bright yellow bronze coatings can be deposited at potentials (E) that are positive than equilibrium potential () of Sn|Sn²⁺ electrode. Here, Sn(II) reduction might be treated as underpotential deposition (UPD) of tin on foreign (copper) substrate. Further incorporation of tin into integral Cu-Sn crystallic lattice yields the mixture of pure copper, α-CuSn phase and intermediate hexagonal hcp phase. The formation of free tin phase occurs at . This gives rise for strong inhibitive adsorption of sintanol that manifests itself in the development of deep voltammetric minimum.Addition of halides results in the shift of codeposition potential to more negative values and in the increase of copper content in the coatings deposited in the UPD region. The action of halides intensifies in the sequence Cl⁻ < Br⁻ < I⁻. If iodide concentration exceeds 2-3 μM, deposition of yellow bronze becomes impossible.     

Electroreduction of peroxycitric acid coexisting with hydrogen peroxide in aqueous solution

The electrochemical reduction of peroxycitric acid (PCA) coexisting with citric acid and hydrogen peroxide (H₂O₂) in the equilibrium mixture was extensively studied at a gold electrode in acetate buffer solutions containing 0.1 M Na₂SO₄ (pH 2.0-6.0) using cyclic and hydrodynamic voltammetric, and hydrodynamic chronocoulometric measurements. The reduction of PCA was characterized to be an irreversible, diffusion-controlled process, and the cyclic voltammetric reduction peak potential () was found to be more positive by ca. 1.0 V than that of the coexisting H₂O₂, e.g., the values obtained at 0.1 V s⁻¹ for PCA and H₂O₂ were 0.35 and −0.35 V, respectively, vs. Ag|AgCl|KCl (sat.) at pH 3.3. The of PCA was found to depend on pH, i.e., at pH > 4.5, the plot of vs. pH gave the slope (−64 mV decade⁻¹) which is close to the theoretical value (−59 mV decade⁻¹) for an electrode process involving the equal number of electron and proton in the rate-determining step, while at pH < 4.5, the was almost independent of pH. The relevant electrochemical parameters, Tafel slope, number of electrons, formal potential (E⁰′), cathodic transfer coefficient and standard heterogeneous rate constant (k⁰′) for the reduction of PCA and the diffusion coefficient of PCA were determined to be ca. 100 mV decade⁻¹, 2, 1.53 V (at pH 2.6), 0.29, 1.2 × 10⁻¹² cm s⁻¹ and 0.29 × 10⁻⁵ cm² s⁻¹, respectively, and except for E⁰′, the obtained values were almost independent of the solution pH. The overall mechanism of the reduction of PCA was discussed.     

Kinetic modelling of VOC catalytic steam pyrolysis for tar abatement phenomena in gasification/pyrolysis technologies

Tar elimination and hot-gas conditioning in thermochemical conversion processes, i.e. thermal gasification, pyrolysis of heterogeneous materials involved two main classes of catalysts and/or additives: metallic and mineral oxides. This communication focused on the experimental kinetic data on catalytic steam cracking of vaporized toluene ( space-time ) as a tar-derived species and/or Volatile Organic Compound (VOC). Toluene (C₇H₈) has been chosen as a model formula for reactive tar-derived one-ring species determined from tar constituents. Gaseous product distribution data were obtained at atmospheric pressure steam pyrolysis temperature range of 923-1223 K and GHSV 1200-2300 Nm³ (m³ h)⁻¹. The overall catalytic pyrolysis of toluene over a commercial available metal based catalyst NiMo/γ-Al₂O₃ was compared to the pyrolysis in presence of basic non-metallic mineral additives, i.e. Norwegian (Norsk Hydro) dolomitic magnesium oxide [MgO], Swedish low surface quicklime [CaO], and calcined dolomite [CaMg(O)₂]. The operational conditions were applied without internal or external mass-transfer limitations. Kinetics for the pyrolysis could be described by first-order reactions for all the studied additives. The influence of hydrogen gas (30 vol%, ) and water vapor () in vaporized toluene cracking runs over low surface quicklime [CaO] was determined. A mechanistic model of the Langmuir-Hinshelwood type describing toluene decomposition was also developed.     

Study on physical and electrostatic interactions of counterions in poly(perfluorosulfonic) acid matrix: Characterization of diffusion properties of membrane using radiotracers

The self-diffusion coefficients of water and ions were used to study the physical (tortuosity) and electrostatic interactions of counterions in poly(perfluorosulfonic) acid membrane (Nafion-117) matrix. The self-diffusion coefficients of water were measured in the water swollen Nafion-117 membrane with Zn²⁺, Ca²⁺, Sr²⁺, and Fe²⁺ counterions by analyzing the experimental exchange rates between tritium tagged water (HTO) in membrane and equilibrating water. In order to study the effects of equilibrating solution, the HTO-desorption rate profiles between the membrane samples in H⁺ or Cs⁺ forms and equilibrating solution containing CsCl or HCl (0.25 mol/L) were measured. It was observed that the HTO-exchange rate profile was slower in case of membrane sample in Cs⁺-from equilibrated with salt/acid solution than that equilibrated with deionized water in same ionic form. However, HTO-exchange rate profile did not alter in case of H⁺-form of membrane on equilibration with salt or acid solution. The variation of ln  with polymer volume function V_p/(1 − V_p), where V_p is polymer volume fraction, indicated that: (i) in the membrane with multivalent counterions was lower than that reported for membrane with monovalent counterions at same V_p, and (ii) the linear trends observed in variation of ln  with V_p/(1 − V_p) for multivalent and monovalent counterions were significantly different. The values of in membrane normalized with at V_p = 0 were taken as an estimate of the tortuosity factor for self-diffusion of ions in the membrane matrix. The self-diffusion coefficients of ions reported in the literature along with tortuosity factor obtained from in the corresponding ionic forms of the membrane were analyzed to obtain the charge (Z_i) independent electrostatic interaction parameter g(φ) of monovalent and divalent ions in the membrane. This analysis indicated that g(φ) also vary exponentially as a function of V_p/(1 − V_p) irrespective of charge on counterions. In order to study the influence of V_p on diffusional transport rates of Na⁺ and Cs⁺ ions in membrane, a permeation experiment was carried out using H⁺-form of membrane having high water volume fraction. The diffusional transport rates of Cs⁺ and Na⁺ in H⁺-form of membrane were found to be similar indicating that the water volume fraction in membrane has strong influence on the parameters that govern the diffusion across the Nafion-117 membrane.     

Oxidation kinetics of Iron(II) complexes of trans-1,2-diaminocyclohexanetetraacetate (cdta) with dissolved oxygen: Reaction mechanism, parameters of activation and kinetic salt effects

The present investigation takes concern about a spiny environmental problem afflicting the pulp mill industry exploiting the Kraft sulfate-pulp process where dilute total reduced sulfur contaminants are co-mixed with oxygen in large-volume gas effluents. A potential Redox process for removing the total reduced sulfurs consists in oxidizing them by means of iron(III) organometallic complexes while the co-mixed oxygen mediates the oxidative regeneration of iron(II) into iron(III) complexes. In this work, the oxidation kinetics of iron(II) trans-1,2,-diaminocyclohexanetetraacetate (cdta) complexes with molecular oxygen (O₂) as the source oxidant was investigated for a wide pH range (1.75<pH<12) in a 3.2 dm³ single-phase stirred cell reactor within the [281-323 K] temperature range. Simultaneous measurements of iron(II)-cdta (50-) and O₂ (0.5-) were used to clarify the reaction mechanism which has been interpreted differently in previous works. The observed kinetic data in alkaline solutions could be accounted for in terms of three forward [Fe²⁺cdta^4-+O₂ (rate-limiting, k_1,app), , 2Fe²⁺cdta^4-+H₂O₂] and one reverse [ (k_-1,app,n=0 or 1)] elementary steps. Assessment of the rate-limiting apparent rate constant led to the following results ( at and , , ). Fe³⁺OH^-cdta^4-, being the dominating iron(III) product at pH>10, was found to be less reactive than Fe³⁺cdta^4- with the superoxide intermediate , thus reducing the effect of the reverse step at higher pH. A study on the effect of electrolytes on the reaction rate led to the conclusion that salts increase the rate constant k_1,app. Finally, kinetic results in acidic conditions leading to the formation of other iron(II)-cdta complexes (i.e., Fe²⁺cdta^4-H⁺) and another superoxide intermediates are reported and discussed.     

Synthesis, characterization and thermodynamic properties of poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone)

Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by ¹H ¹³C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔH_a, molar evaporation enthalpy, ΔH_v, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, T_g, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.     

Effect of N(4)-substituent groups on transfer of 2-benzoylpyridine thiosemicarbazone derivates at the water/1,2-dichloroethane interface

Dependent on the pH of the aqueous phase, the transfer of protonated forms of 2-benzoylpyridine N(4)-phenyl thiosemicarbazone (BPPT) (which has antimicrobial, antifungal and anticytotoxic activities) and 2-benzoylpyridine N(4)-ethyl thiosemicarbazone (BPET) across water/1,2-dichloroethane (1,2-DCE) interface has been studied by cyclic voltammetry. The protonation constants of the ligands ( and ) were determined by spectrophotometry. The standard partition coefficients () and the standard Gibbs energies of ionic (cationic) species of ligands () were calculated from the standard transfer potentials (). The standard Gibbs energies of their transfer () and partition coefficients of neutral species (log P_N) were determined by shake-flask method. These thermodynamic parameters were evaluated as a quantitative and qualitative measure of the lipophilicities of two compounds. The differences between the partition coefficients of cationic and neutral form of compounds [diff(log PI⁺−N)] were interpreted by results obtained from voltammetric data. Effect of N(4)-phenyl and ethyl groups for transfer of 2-benzoylpyridine thiosemicarbazone derivatives at macro-liquid/liquid interface was investigated. The antimicrobial activity of BPET was tested against four types of bacteria and found to be active against Staphlylococcus aureus.     

Melt complex viscosity and molecular weights for homo-polypropylene modified by grafting bifunctional monomers under electron beam irradiation

High melt viscosity polypropylene was manufactured by grafting bifunctional monomers, HDDA (1,6-hexanediol diacrylate) and TPGDA (tripropyleneglycol diacrylate), onto homo-polypropylene under an electron beam irradiation. Melt complex viscosity (η^∗) of modified polypropylene was sensitive to irradiation dose and monomer content. The melt viscosity of the polypropylene modified with TPGDA increased to 132,290 Pa s (at 190 °C and 0.1 rad/s of frequency) from 5039 Pa s for virgin homo-polypropylene. TPGDA monomer could give higher melt viscosity at low dosages than HDDA monomer, probably due to the structural feature of TPGDA with three numbers of methyl groups.Modified polypropylene with high melt complex viscosity had a broad molecular weight distribution with remarkable shift to higher molecular weight leading to high values of both and . Melt viscosity of modified polypropylene could be properly correlated by the equation , where the term gave a dominant effect for the estimation of η^∗.     

A mechanism study of chloride and sulfate effects on Hg reduction in sulfite solution

This paper studied the effects of sulfate and chloride ions on bivalent mercury (Hg²⁺) absorption and reduction behaviors in a simulated WFGD system. The aqueous mercuric ion-sulfite system reduction behaviors were monitored and investigated using a UV-visible spectrum. Thereafter, the mechanism of Hg²⁺ reduction in the presence of sulfate and chloride ions was proposed. Experimental results revealed that both sulfate and chloride ions had inhibition effects on aqueous Hg²⁺ reduction to Hg⁰. The inhibition was assumed due to the formation of (in the presence of ) and / (in the presence of Cl⁻). And it was found that complex was more stable than in excess of Cl⁻. The formation of the above-mentioned complexes in the presence of and Cl⁻ would damp the formation of HgSO₃, whose decomposition was assumed to be the key step of Hg²⁺ reduction.     

Electrochemical performances of gel polymer electrolytes using tetra(ethylene glycol) diacrylate

A gel polymer electrolyte (GPE) was prepared using tetra(ethylene glycol) diacrylate monomer, benzoyl peroxide, and (). The LiCoO₂/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures.The viscosity of the precursor containing the tetra(ethylene glycol) diacrylate monomer was around . The ionic conductivity of the gel polymer electrolyte at 20°C was around . The gel polymer electrolyte had good electrochemical stability up to vs. Li/Li⁺. The capacity of the LiCoO₂/GPE/graphite cell at rate was 63% of the discharge capacity at rate. The capacity of the cell at −10°C was 81% of the discharge capacity at 20°C. Discharge capacity of the cell with gel polymer electrolyte was stable with charge-discharge cycling.     

The influence of iron on the precipitation behaviour of nickel powder

The effect of iron on the precipitation behaviour of nickel powder was investigated. Reduction experiments were conducted on a 0.5 L laboratory autoclave fitted with a Teflon reaction beaker and a double impeller configuration consisting of an upper axial impeller and lower Rushton turbine. Reduction was conducted in the presence of a morphology modifier at a temperature between 180 and and 2800 kPa pressure using a synthetic nickel ammine sulphate solution (, free NH₃:Ni²⁺ and (NH₄)₂SO₄:Ni²⁺ molar ratios of 2.0-2.1 and 2.2, respectively). Nickel seed was used to initiate reduction and iron was added to the reduction solution as ferrous sulphate solution (acidified to pH 2.5 to prevent oxidation) to give a reduction solution with Fe²⁺ concentration of 6, 20 and 200 mg/L. The effect of iron was investigated by studying the evolution of the moments, volume or mass moment mean D(4.3), number based mean size , nickel depletion rate and population balance in the absence of sampling between batch reductions. Iron was found to act as a growth promoter and nucleation agent through reversible adsorption and hydrolysis on the surface of the seed particles. Growth was preferentially favoured over nucleation up to a Fe²⁺ concentration of 6 mg/L, thereafter the extent of nucleation increased with increasing Fe²⁺ concentration up to 200 mg/L. Nucleation and growth promotion in the presence of high shear rates gave rise to rapid aggregation, which ceased at a critical size of approximately and in the presence of iron and without. However, the sharp increase in the D(4.3) towards the end of the cycle and the general decrease in surface area shows that aggregation of larger particles plays a major role in size enlargement. Comparison of the scanning electron microscopy (SEM) micrographs of the powder with undesirable morphology produced in industrial practice and that produced in the laboratory in the presence of iron showed that iron was one of the factors responsible for the production of powder with undesirable morphology. Based on these laboratory scale experiments, iron levels in reduction solutions should not exceed 6 mg/L for effective control of particle morphology.