Differentiation of Lard From Other Edible Fats and Oils by Means of Fourier Transform Infrared Spectroscopy and Chemometrics

Fourier transform infrared (FTIR) spectra at mid infrared regions (4,000–650 cm⁻¹) of lard and 16 edible fats and oils were compared and differentiated. The chemometrics of principal component analysis and cluster analysis (CA) was used for such differentiation using FTIR spectra intensities of evaluated fats and oils. With PCA, an “eigenvalue” of about 90% was achieved using four principal components (PCs) of variables (FTIR spectra absorbances at the selected frequency regions). PC1 accounted for 44.1% of the variation, while PC2 described 30.2% of the variation. The main frequency regions that influence the separation of lard from other evaluated fats and oils based on PC1 are 2,852.8 followed by 2,922 and 1,464.7 cm⁻¹. Furthermore, CA can classify lard into its group based on Euclidean distance.     

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.     

Milled rice surface lipid measurement by diffuse reflectance fourier transform infrared spectroscopy (DRIFTS)

Diffuse reflectance Fourier transform infrared spectroscopy was investigated as a method for rice surface lipid determination. Long- and medium-grain rice was milled at four degrees of milling to obtain samples with various levels of residual bran, and total lipids were determined by solvent extraction. Fourier transform infrared spectra were collected between 4000 and 400 cm⁻¹. Weighted regression analysis identified changes in surface chemical functional groups with bran removal. Groups typical of lipids increased with bran content whereas those typical of carbohydrates and protein decreased. Partial least squares (PLS) regression analysis showed a high degree of correlation between the spectra in the 4000–400 cm⁻¹ range and extracted lipids of long-grain rice (R ²=0.96) and medium-grain rice (R ²=0.96); a high degree of correlation was also observed when long- and medium-grain rice data were combined (R ²=0.96). There was a high positive correlation between the spectra and extracted lipids in the 1300–1000 cm⁻¹ range for the long-grain rice (R ²=0.98), medium-grain rice (R ²=0.98), and combined long-/medium-grain rice data (R ²=0.94). PLS selected spectral regions that correlated positively with functional groups of lipid/lipid oxidation products and negatively with functional groups of protein and carbohydrates.     

Rice bran FFA determination by diffuse reflectance IR spectroscopy

Rice bran with FFA levels above 0.1% cannot be used as a food ingredient due to oxidative off-flavor formation. However, extracting high FFA oil from bran by in situ methanolic esterification of rice bran oil to produce methyl ester biodiesel produces greater yields relative to low-FFA rice bran oil. Therefore, high-FFA bran could be exploited for biodiesel production. This study describes an FTIR spectroscopic method to measure rice bran FFA rapidly. Commercial rice bran was incubated at 37°C and 70% humidity for a 13-d incubation period. Diffuse reflectance IR Fourier transform spectra of the bran were obtained and the percentage of FFA was determined by extraction and acid/base titration throughout this period. Partial least squares (PLS) regression and a calibration/validation analysis were done using the IR spectral regions 4000-400 cm⁻¹ and 1731-1631 cm⁻¹. The diffuse reflectance IR Fourier transform spectra indicated an increasing FFA carbonyl response at the expense of the ester peak during incubation, and the regression coefficients obtained by PLS analysis also demonstrated that these functional groups and the carboxyl ion were important in predicting FFA levels. FFA rice bran changes also could be observed qualitatively by visual examination of the spectra. Calibration models obtained using the spectral regions 4000-400 cm⁻¹ and 1731-1631 cm⁻¹ produced correlation coefficients R and root mean square error (RMSE) of cross-validation of R=0.99, RMSE=1.78, and R=0.92, RMSE=4.67, respectively. Validation model statistics using the 4000-400 cm⁻¹ and 1731-1631 cm⁻¹ ranges were R=0.96, RMSE=3.64, and R=0.88, RMSE=5.80, respectively.     

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.     

Free fatty acid formation and lipid oxidation on milled rice

Milled rice was stored at 37°C and 70% humidity and sampled regularly for 50 d. Rice surface lipid was extracted with isopropanol and analyzed for free fatty acids (FFA) and conjugated diene (CD) contents. Diffuse reflectance Fourier transform infrared (DRIFTS) spectra of the rice samples were also obtained. FFA and CD levels increased together during rice storage and exhibited three distinct phases. DRIFTS identified a decrease in intensity at 1746 cm⁻¹ (ester, −C=O) and increases in intensity at 1731 cm⁻¹ (aldehyde, −CO) and 1714 cm⁻¹ (fatty acid, −C=O) during storage, which correlated well with the chemical analysis data. DRIFTS spectral data were analyzed by a partial least squares regression method to identify spectral regions that correlate strongly with measured FFA and construct prediction models. Overall, the mid-infrared region (4000–400 cm¹) gave the best model (R=0.98, root mean square error of cross-validation=0.05) and also predcted the FFA content of milled rice well. The DRIFTS technique has potential for use in studying qualitative chemical changes on the milled rice surface lipids and for predicting FFA on milled rice.     

Analysis of Cod-Liver Oil Adulteration Using Fourier Transform Infrared (FTIR) Spectroscopy

Analysis of the adulteration of cod-liver oil with much cheaper oil-like animal fats has become attractive in recent years. This study highlights an application of Fourier transform infrared (FTIR) spectroscopy as a nondestructive and fast technique for the determination of adulterants in cod-liver oil. Attenuated total reflectance measurements were made on pure cod-liver oil and cod-liver oil adulterated with different concentrations of lard (0.5–50% v/v in cod-liver oil). A chemometrics partial least squares (PLS) calibration model was developed for quantitative measurement of the adulterant. Discriminant analysis method was used to classify cod-liver oil samples from common animal fats (beef, chicken, mutton, and lard) based on their infrared spectra. Discriminant analysis carried out using seven principal components was able to classify the samples as pure or adulterated cod-liver oil based on their FTIR spectra at the selected fingerprint regions (1,500–1,030 cm⁻¹).     

Conformational analysis for hydrated ethylene oxide oligomer models by quantum chemical calculations

Hydrate effects on the conformations of ethylene oxide oligomers (EO-x, x = 1–8 mers) were examined using quantum chemical calculations (QCC). Conformational analyses were carried out by RHF/6-31G. The models were constructed by locating a water molecule to each ether–oxygen in the structures optimized for non-hydrate oligomers. Hydrate ratio, h (h = H₂O_mol/O_{mol in oligomer}), was set from 0 to 1.0. The six type conformations with repeated units of O–C, C–C and C–O bonds were examined. Conformational energy, E _c (HF), was calculated as difference between the energy of oligomer with water molecules and that of non-hydrogen and/or hydrogen bonding water molecules. Hydrate energies for each conformer, ∆μ _h (kcal/m.u., based on E _c in non-hydrate state), were negative and linearly decreased with the increase of h values, and such effects with the increase of h values were weaken with increasing x values. These results were consistent with our previous results calculated using the permittivity, ε (ε = 0–80.1), by QCC. In non-hydrate (h = 0), the (ttt) _x conformers were the most stable independent of x. However, in hydrate states (h = 0.44–0.67), the (tg⁺t) _x conformers were the most stable independent of x values, and in h = 1, the (tg⁺t)₈ conformer (8-mer) was most stable [∆E _c(g) = −1.3 kcal/m.u., ∆E _c(g): energy difference between a given oligomer and the (ttt) _x oligomer]. These results supported the experimental those based on NMR analyses using dimethoxyethane and triglyme solutions. Molecular lengths (l) of (tg⁺t) _x , (tg⁺g⁻) _x and (g⁺g⁺g⁺) _x conformers having higher x values significantly decreased with increasing h values. Such contraction with hydration, however, was independent of ΔE _c(g) values of each conformer.     

Synthesis of borosilicalite-1 with more than four boron per unit cell from fluoride containing media

More than four boron per unit cell has been introduced into the framework of silicalite-1, using fluorine containing media. The initial gels were of composition 9MF–xH₃BO₃–10SiO₂–1.25TPABr–330 H₂O with M = NH₄, Na, K and Cs and x = 0.1–10. The syntheses were carried out in hydrothermal conditions at 170°C. The amount of incorporated TPA⁺ ions remains quasi constant (3.5–3.8/u.c.) up to 4 B/u.c., while it decreases with increasing boron content. The amount of tetrahedral B/u.c. can be as high as 8 in presence of K⁺ or Cs⁺ ions in the as-synthesized samples. It is observed that the preferential countercations to framework negative charges related to the presence of tetrahedral boron, [SiOB]⁻, are TPA⁺, K⁺ and Cs⁺ ions. It is interpreted, that the −4.0 ppm versus BF₃.OEt₂ NMR line stems from tetrahedral framework boron, while the −2.9 ppm NMR line represents both extraframework and/or tetracoordinated deformed framework boron in the structure.     

Determination of the length of polymethylene chains in salts of saturated and unsaturated fatty acids by infrared spectroscopy

The length of polymethylene chains is determined by counting the number of, or measuring the position of, methylene vibration peaks in the 1070–710 cm⁻¹ and/or the 1380–1170cm⁻¹ regions of the IR spectrum of salts of fatty acids. Plotting this peak position against the phase relationship of the vibration in adjacent methylenes gives a curve which is independent of the chain length. (Thephase relationship, Φ/π=k/(m+1); where φ is the phase difference in radians between adjacent methylenes in a chain;m is the number of methylenes in the chain;k=1,2,3,…m, withk=1 generally assigned to the in-phase vibration.) Separate curves are obtained for methylene wagging and for two arrays of coupled twisting-rocking vibrations. Coupled twisting-rocking vibrations give as many as one peak per methylene group in the 1070–710 cm⁻¹ region with silver, sodium, potassium and barium salts of saturated acids. Lead salt peaks split. These peaks show the total length of salts of both saturated andtrans-unsaturated acids, but only the length of the carboxylate segment in salts ofcis-unsaturated acids. (The carboxylate segment comprises the carbons from the carboxylate carbon to the first unsaturated carbon, inclusive.) Wagging vibrations in the 1380–1170 cm⁻¹ region show the total chain length of saturated salts and the length of the carboxylate segment in unsaturated salts, bothcis andtrans. This region also has peaks for twisting-rocking vibrations, and they are most conspicuous in the spectra of silver and barium salts. Presented in part at the AOCS meeting in Toronto, Canada, 1962.     

Synthesis and Properties of Novel Double-Tail Trisiloxane Surfactants

To improve the hydrolysis resistant ability of trisiloxane surfactants, ethoxylated single-tail and double-tail trisiloxane surfactants of the general formulas Me₃SiOSiMeR¹OSiMe₃ (R ¹ = (CH₂)₃NHCH₂CH(OH)CH₂(OCH₂CH₂) _x OCH₃; x = 8.4, 12.9, 17.5, 22) and Me₃SiOSiMeR²OSiMe₃ (R ² = (CH₂)₃NR³CH₂CH(OH)CH₂(OCH₂CH₂) _x OCH₃; R ³ = CH₂(CH₂) _y CH₃; x = 8.4, 12.9, 17.5, 22; y = 2, 6) were synthesized. Their structures were characterized by ¹H NMR and ¹³C NMR. The surface activity and hydrolysis resistant properties of the trisiloxane surfactants prepared were also studied. The values of the critical micelle concentration of all trisiloxane surfactants prepared were at levels of 10⁻⁵ and 10⁻⁴ mol/L. They can reduce the surface tension of water to less than 24 mN/m. The hydrolysis resistant properties of double-tail trisiloxane surfactants are superior to those of single-tail trisiloxane surfactants. The double-tail trisiloxane surfactants 1B (x = 8.4; y = 2) and 2C (x = 12.9; y = 6) can be stable for 8 days in an acidic solution (pH 4.0) and 11 days in an alkaline environment (pH 10.0).     

Application of FTIR Spectroscopy for the Determination of Virgin Coconut Oil in Binary Mixtures with Olive Oil and Palm Oil

Rapid Fourier transform infrared (FTIR) spectroscopy combined with attenuated total reflectance (ATR) was applied for quantitative analysis of virgin coconut oil (VCO) in binary mixtures with olive oil (OO) and palm oil (PO). The spectral bands correlated with VCO, OO, PO; blends of VCO and OO; VCO and PO were scanned, interpreted, and identified. Two multivariate calibration methods, partial least square (PLS) and principal component regression (PCR), were used to construct the calibration models that correlate between actual and FTIR-predicted values of VCO contents in the mixtures at the FTIR spectral frequencies of 1,120–1,105 and 965–960 cm⁻¹. The calibration models obtained were cross validated using the “leave one out” method. PLS at these frequencies showed the best calibration model, in terms of the highest coefficient of determination (R ²) and the lowest of root mean standard error of calibration (RMSEC) with R ² = 0.9992 and RMSEC = 0.756, respectively, for VCO in mixture with OO. Meanwhile, the R ² and RMSEC values obtained for VCO in mixture with PO were 0.9996 and 0.494, respectively. In general, FTIR spectroscopy serves as a suitable technique for determination of VCO in mixture with the other oils.     

Interference of Saturated Fats in the Determination of Low Levels of <Emphasis Type="Italic">trans</Emphasis> Fats (below 0.5%) by Infrared Spectroscopy

The mandate to label food products with the content of total trans fatty acids has led to an increase in demand for sensitive and accurate methodologies for the rapid quantitation of trans fats. Unfortunately, the latest official infrared (IR) spectroscopic method lacks the required sensitivity. A more sensitive IR procedure that requires the measurement of the height of the second derivative (2D) of the trans absorption band at 966 cm⁻¹ was recently proposed; however, a reported inconsistency at low trans levels between GC (0% of total fat) and IR (1.2% of total fat) results for a fully hydrogenated vegetable oil could not be reconciled, and triggered further investigations. For the first time, we recognize and report the presence of weak interference bands (962–956 cm⁻¹) attributed to saturated fats in the IR spectra of trans fats; these interference bands have an adverse impact on the sensitivity and accuracy of the IR determination at low trans levels (≤0.5% of total fat). Therefore, weak spectral features observed at energies below the one expected for trans bands (966 cm⁻¹) in test samples high in saturated fat (coconut oil and cocoa butter) must not be mistaken for trans bands.     

Influence of Substructures on the Spreading Ability and Hydrolysis Resistance of Double-Tail Trisiloxane Surfactants

Four types of novel double-tail trisiloxane surfactants of the general formula Me₃SiOSiMeR¹OSiMe₃ (R ¹ = –(CH₂)₃NR²CH₂CH(OH)CH₂(OCH₂CH₂)_xOCH₃; R ² = –CH₂CH(OH)CH₂OCH₂(CH₂)_yCH₃, –CH₂(CH₂)₃CH₃, –CH₂CH₂CH(CH₃)₂; x = 8.4, 12.9, 17.5, 22; y = 2, 6), have been synthesized. Their structures were characterized by proton and carbon nuclear magnetic resonance. Most of them are able to reduce the surface tension of water to less than 24 mN/m at concentration levels of 10⁻⁵ mol/L and 10⁻⁴ mol/L. The emphasis was on the influence of substructures on their spreading ability and hydrolysis resistance. The results showed that a weaker hydrophilicity of a surfactant molecule, a larger molar ratio of methyl to methylene in the whole hydrophobic groups, more flexible hydrophobic groups and introduction of a methyl group in the spacer can all improve the spreading ability of the double-tail trisiloxane surfactant solutions on low-energy solid surfaces. The double-tail trisiloxane surfactants 1F and 2F are stable for more than 270 days in a neutral environment (pH 7.0). The hydrolysis resistance of the double-tail trisiloxane surfactants can be improved by a weaker hydrophilicity of the surfactant molecule, and a larger volume of the hydrophobic groups.     

Co-decorated carbon nanotube-supported Co–Mo–K sulfide catalyst for higher alcohol synthesis

Using chemical reduction-deposition method, a type of metallic cobalt-decorated multi-walled carbon nanotubes, noted as y%(mass percentage)Co/MWCNTs, was prepared. TEM, SEM and XRD measurements demonstrated that the metallic cobalt was evenly coated on the MWCNT substrate, with granule-diameter of the Co _x ⁰ -crystallites of 5–8 nm. Using the y%Co/MWCNTs as support, a type of supported Co–Mo–K sulfide catalysts, noted as x%(Co _i Mo _j K _k )/(y%Co/MWCNTs), for higher alcohol synthesis (HAS) was developed. It was experimentally shown that using the Co-modified MWCNTs in place of simple MWCNTs or activated carbon (AC) as the catalyst support led to a significant increase in activity of CO hydrogenation conversion and improvement in the selective formation of C₂₊-alcohols. Under the reaction condition of 5.0 MPa, 613 K, CO/H₂/N₂ = 45/45/10 (v/v) and GHSV = 3600 ml_STPh⁻¹ g _−cat. ⁻¹ , the observed STY of C_1–4-alcohols reached 154.1 mgh⁻¹g _−cat. ⁻¹ at 12.6% conversion of CO over the 11.6%(Co₁Mo₁K_0.6)/(6.4%Co/MWCNTs) catalyst, which was 1.76 and 2.33 times as high as that (87.7 and 66.1 mgh⁻¹g _−cat. ⁻¹ ) of the reference systems supported by simple MWCNTs and AC respectively. Ethanol became the predominant product of the CO hydrogenation, with carbon-based selectivity ratio of C_2–4-alcohols to CH₃OH reaching 3.6 in the products. It was experimentally found that using the Co-modified MWCNTs in place of simple MWCNTs or AC as the catalyst support caused little change in the apparent activation energy for the conversion of CO, but led to a slight increase in the molar percentage of catalytically active Mo-species (Mo⁴⁺) in the total Mo-amount at the surface of the functioning catalyst. Based upon the results of TPD investigation, it could be inferred that, under the reaction condition of HAS, there existed a considerably larger amount of adsorbed H-species and CO-species on the functioning catalyst, thus in favour of increasing the rate of a series of surface hydrogenation reactions in HAS.     

Reaction between Hydrosulfide and Iron/cerium (hydr)oxide: Hydrosulfide Oxidation and Iron Dissolution Kinetics

Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N₂) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide initial concentration (0.90–3.30 mmol/L), oxide initial surface area (16–143 m²/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by means of capillary electrophoresis, while iron dissolution was monitored through atomic absorption spectroscopy. Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments. The hydrosulfide oxidation by the iron/cerium (hydr)oxide was found to be surface-controlled, with rates (R_i) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: R_i = k_i[HS⁻]_t=0^−0.5[A]_t=0[H⁺]_t=0^−0.5 , where k_i represents the apparent rate constants for the oxidation of HS⁻ (k_HS) or the dissolution of Fe(II) (k_Fe), [HS⁻]_{t = 0} is the initial hydrosulfide concentration, [A]_{t = 0} is the initial Fe/Ce (hydr)oxide surface area and [H⁺]_{t = 0} is the initial proton concentration. The rate constant, k_HS, for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 ± 0.65) × 10⁻⁴ mol² L⁻¹ m⁻² min⁻¹, with the rate of hydrosulfide oxidation being ca. 10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric ratio between HS⁻ oxidized and Fe(II) produced; k_Fe = (3.9116 ± 0.41) × 10⁻⁵ mol² L⁻¹ m⁻² min⁻¹).     

Influence of alloying and microstructure on the electrochemical hydriding of TiNi-based ternary alloys

Nanostructured ternary TiNi-type alloys, namely Ti_0.8M_0.2Ni (M = Zr, V), TiNi_0.8N_0.2 (N = Cu, Mn) and TiNi_1−x Mn _x (x = 0.2, 0.4, 0.6, 1.0), were synthesized by mechanical alloying. Depending on the intensity and time of milling alloys with different microstructure were obtained. The as-milled TiNi_1−x Mn _x alloys contain substantial amount of amorphous phase, which crystallizes during annealing. Annealing of the as-milled fine nanocrystalline materials at 500 °C results only in slight coarsening of the microstructure, which remains still nanocrystalline. Fully crystalline material (with crystal size larger than 50 nm), consisting of mainly cubic TiNi was obtained by annealing the ball-milled alloys at T ≥ 700 °C. Electrochemical hydrogen charge/discharge cycling of the as-milled as well as of annealed alloys were carried out at galvanostatic conditions. It was found that among the nanocrystalline Ti_0.8M_0.2Ni_0.8N_0.2 (M = Zr, V; N = Cu, Mn) alloys TiNi_0.8Mn_0.2 revealed the highest discharge capacity of 56 mAh g⁻¹ in the as-milled state and 75 mAh g⁻¹ after short-time annealing at 500 °C. Annealing at higher temperature does not increase the capacity further. The as-milled TiNi_1−x Mn _x alloys with x ≤ 0.4 reveal noticeably higher discharge capacity and better cycle life than the Mn-richer alloys. Based on potentiostatic experiments the diffusion coefficients of hydrogen into TiNi alloys in two different microstructural states (fine and coarser nanocrystalline) as well as in as-milled amorphous/nanocrystalline and nanocrystalline TiNi_0.8Mn_0.2 were determined. The hydrogen diffusion coefficients of the TiNi alloys are comparable (1.9–2.7 × 10⁻¹² cm² s⁻¹). The diffusion coefficient in the as-milled amorphous/nanocrystalline TiNi_0.8Mn_0.2 was found to be 3–4 times higher than that of the as-milled nanocrystalline alloy.     

Patent Abstracts on Cellular Plastics

(US5019292): Granular detergent composition comprises: at least 1% detersive surfactant (I): 5–35% detergency builders (II); 1–25% naturally occurring hectorite clay ((Mg_3x Li _x )Si_4-y MeIII _y O₁₀(OH_2-z F _z )) - [(x+y) (x+y) Mn⁺]/n (III); and 1–10% additional fabric softener (IV) of formula (a) R₁R₂R₃N, (b) R₁OR₁NCOR₁₂: where MeIII is Al, Fe, or B, or y = 0; Mn⁺ is mono- or divalent metal; the clay (III) has a layer charge distribution (x+y) such that at least 50% of the layer charge is 0.23–0.31; R₁, = 6–20 C hydrocarbyl; R₂ = 1–20 C hydrocarbyl; R₃ = H or 1–20 C hydrocarbyl; R₁₀, R₁₁ = 1–22 C alk(en)yl, hydroxy alkyl, aryl, alkaryl; R₁₂ = H, 1–22 C alk(en)yl, aryl, alkaryl or OR₁₃; R₁₃ = 1–22 C alk(en)yl, aryl, alkaryl, or (c) a 1-(12–22 C alkyl) amide (1–4 C alkyl)-2-(12–22 C alkyl) imidazoline.     

Photoelectrochemical characterization of the synthetic crednerite CuMnO<Subscript>2</Subscript>

High quality crednerite CuMnO₂ was prepared by solid state reaction at 950 °C under argon flow. The oxide crystallizes in a monoclinically distorted delafossite structure associated to the static Jahn–Teller (J–T) effect of Mn³⁺ ion. Thermal analysis showed that it converts reversibly to spinel Cu _x Mn_3−x O₄ at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO₂ is p-type, narrow semiconductor band gap with a direct optical gap of 1.31 eV. It exhibits a long-term chemical stability in basic medium (KOH 0.5 M), the semi logarithmic plot gave an exchange current density of 0.2 μA cm⁻² and a corrosion potential of ~−0.1 V_SCE. The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential (V _fb = −0.26 V_SCE) and the holes density (N _A  = 5.12 × 10¹⁸ cm⁻³) were determined, respectively, by extrapolating the curve C ⁻² versus the potential to the intersection with C ⁻²  = 0 and from the slope of the Mott–Schottky plot. From photoelectrochemical measurements, the valence band formed from Cu-3d wave function is positioned at 5.24 ± 0.02 eV below vacuum. The Nyquist representation shows straight line in the high frequency range with an angle of 65° ascribed to Warburg impedance originating from oxygen intercalation and compatible with a system under mass transfer control. The electrochemical junction is modeled by an equivalent electrical circuit thanks to the Randles model.     

Study of Oxygen Reactivity in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoO<Subscript>3−δ</Subscript> Perovskites for Total Oxidation of Toluene

Abstract  

The total oxidation of toluene is studied over catalytic systems based on perovskite with general formula AA′CoO_3-δ (A = La, A′ = Sr). The systematic and progressive substitution of La³⁺ by Sr²⁺ cations in the series (La_1−x Sr _x CoO_3−δ system) of the perovskites have been studied to determine their influence in the final properties of these mixed oxides and their corresponding reactivity performance for the total oxidation of toluene as a model volatile organic compound with detrimental effects for health and environment. The structure and morphology of the samples before and after reaction have been characterized by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O₂ in vacuum and reduction in H₂ were also performed to identify the main surface oxygen species and the reducibility of the different perovskites. It is remarkable that the La_1−x Sr _x CoO_3−δ series presents better catalytic performance for the oxidation of toluene, with lower values for the T₅₀ (temperature of 50 % toluene conversion) than the previously studied LaNi_1−y Co _y O₃ series.