Studies on the Radical Cyclization of 3‐Oxopropanenitriles and Alkenes with Cerium(IV) Ammonium Nitrate in Ether Solvents

The radical cyclization of 3‐oxopropanenitriles 1a – 1e and alkenes 2a – 2g with cerium(IV) ammonium nitrate (CAN) in ether solvents was investigated (Tables 1 and 2). In the optimization study, 1,3‐dioxolane, 1,4‐dioxane, 1,2‐dimethoxyethane, Et₂O, and THF were used as ether‐based solvents, and the latter was found to be the most effective solvent in radical cyclizations mediated by cerium(IV). This system (cerium(IV)/THF) was applied to cyclizations of various 3‐oxopropanenitriles and 1,3‐dicarbonyl compounds with alkenes resulting in the formation of 4,5‐dihydrofurans in high yields (Table 2 and Scheme 2). The results of the cerium(IV)/THF radical cyclization were compared with those obtained with manganese(III) acetate/AcOH; the cerium(IV)/THF system turned out to be much more efficient.     

Effects of PEG4000 template on sol-gel synthesis of porous cerium titanate photocatalyst

Porous cerium titanate was synthesized by sol-gel method, using polyethylene glycol (PEG4000) as template agent. Brannerite structured CeTi₂O₆ in monoclinic system is the major substance formed in the materials. Formation of CeO₂ and rutile TiO₂ depends on the amount of PEG4000. The addition of PEG4000 leads to production of fine particles in the samples, but it does not apparently affect the band gap energy. Pore volume of the cerium titanate sample continuously increases with rising PEG4000 amount. The sample obtained using 3.5 g PEG4000 has BET surface area of 16.2 m²/g and pore volume of 0.0232 cm³/g. The addition of PEG4000 can obviously promote photocatalytic activity of cerium titanate, which can be proven by both enhanced production of hydroxyl radical and ofloxacin degradation efficiency. As much as 95.2% of the initial ofloxacin molecules are removed from the solution after 50 min of photocatalytic degradation on the cerium titanate obtained using 3.5 g PEG4000, while only 48.4% ofloxacin is removed on cerium titanate obtained without PEG4000.     

Low-temperature oxidation of carbon monoxide on Pd(Pt)/CeO2 catalysts prepared from complex salts

Catalysts containing cerium oxide as a support and platinum and palladium as active components for the low-temperature oxidation of carbon monoxide were studied. The catalysts were synthesized in accordance with original procedures with the use of palladium and platinum complex salts. Regardless of preparation procedure, the samples prepared with the use of only platinum precursors did not exhibit activity at a low temperature because only metal and oxide (PtO, PtO₂) nanoparticles were formed on the surface of CeO₂. Unlike platinum, palladium can be dispersed on the surface of CeO₂ to a maximum extent up to an almost an ionic (atomic) state, and it forms mixed surface phases with cerium oxide. In a mixed palladium-platinum catalyst, the ability of platinum to undergo dispersion under the action of palladium also increased; as a result, a combined surface phase with the formula Pd _x Pt _y CeO_{2 ? δ}, which exhibits catalytic activity at low temperatures, was formed.     

Das Verhalten der Ceriterdnitrate in 4M HNO3 als Unterphase

The effective distribution coefficients of the cerium earth nitrates were determined with input of 100 g oxide, while those of the yttrium earths were estimated from former work. The values rise to a maximum at Dy, then decrease from Ho to Yb. The separation of cerium earths from each other was distinctly better with 11M HNO₃ than with 4M HNO₃.     

Degradation of toluene gas at the surface of ZnO/SnO2 photocatalysts in a baffled bed reactor

To eliminate volatile organic compounds (VOCs) from contaminated air, a novel medium-scale baffled photocatalytic reactor was designed and fabricated, using immobilized ZnO/SnO₂ coupled oxide photocatalysts. Toluene was chosen as a representative pollutant of VOCs to investigate the degradation mechanism and the parameters affecting photocatalytic degradation efficiency. The preliminary experimental results indicate that the degradation efficiency of toluene increased with the increase of the light irradiation dosage, while it decreased with the increase of concentrations of toluene. The degradation efficiency increased rapidly with the increase of the relative humidity in a low humidity range from 0 to 35%, but decreased gradually in a high relative humidity (i.e., >35%). The optimum experimental conditions for toluene degradation is a toluene concentration of 106 mg m^?3, a relative humidity of 35%, and an illumination intensity of ca. 6 mW cm^?2 at the surface of ZnO/SnO₂ photocatalysts. The intermediates produced during the gaseous photocatalytic degradation process were identified using the GC–MS technique. Based on these identified intermediates, the photocatalytic mechanism of toluene into ZnO/SnO₂ coupled oxide catalyst was also deduced.     

The Influence of Aluminum-Containing Lewis Acids on Polyisobutylene,Isobutylene-lsoprene Copolymers (Butyl Rubber), and Chlorinated Isobutylene-lsoprene Copolymer (Chlorobutyl)

The influence of aluminum-containing Lewis acids, e.g., AlCl₃, AlEtCl₂, AlEt₂Cl, AlEt₃, and AliBu₃, on polyisobutylene, isobutylene-isoprene copolymer (butyl rubber), and chlorinated butyl rubber has been investigated in nonpolar and polar solvents at various Lewis acid concentrations in the temperature range -10 to -78°C. Polyisobutylene does not degrade even under the most aggressive conditions employed (AlEtCl₂, -10°C). Butyl rubber degrades rapidly in the presence of AlEtCl₂ in the range -10 to -50°C. In contrast, no degradation occurs with the milder Lewis acid AlEt₂Cl; however, in conjunction with small amounts of a suitable Bronsted acid (i.e., HCl) immediate and extensive degradation takes place with AlEt₂Cl as well. Chlorobutyl rubber severely and very rapidly degrades in the presence of AlCl₃ and AlEtCl₂. With the less acidic AlEt₂Cl and AlEt₃, molecular weight breakdown can be prevented only when employing milder conditions, i.e., at low Lewis acid concentrations in nonpolar solvents at lowest temperatures. A comprehensive mechanism involving carbonium ions of these degradation processes is proposed.     

Effects of ultraviolet irradiation on substituted polyacetylenes

Effects of UV irradiation on various substituted polyacetylenes were examined. Upon irradiation in air, main-chain scission and crosslinking occurred with a wide range of probabilities dependent on the nature of substituents. For example, poly(2-alkyne)s rapidly degraded to low molecular weights, whereas polymers from aromatic monosubstituted acetylenes [e.g., poly(o-CF₃-phenylacetylene)] were quite stable. Several other polyacetylenes [e.g., poly(1-Me₃Si-1-propyne)] showed intermediate degradability. Polymer degradation was minimal in vaccum. The polymers irradiated in air contained C?O and O? H groups, and dissolved in polar solvents which are nonsolvents for the initial polymers. These results indicate that oxidation causes degradation. Only poly(1-chloro-1-alkyne)s of the polyacetylenes studied, formed gels upon UV irradiation. The amount of the gel was larger, when the polymer was irradiated in vacuum than in air. Further, the longer the alkyl pendant in the polymer, the higher the gel fraction. Differences between photo-and thermal degradations are discussed.     

Separation of <Superscript>139</Superscript>Ce using solvent extraction technique from La<Subscript>2</Subscript>O<Subscript>3</Subscript> target irradiated by 14.7 MeV protons

The radiochemical separation of no-carrier-added cerium from proton irradiated lanthanum was studied by solvent extraction using DEE, TBP and TPPO, the latter reagent being employed for the first time for separation of radiocerium from bulk of lanthanum. Distribution coefficients of cerium and lanthanum were investigated as a function of equilibrium time and concentration of HNO₃. A mixture of 0.05M K₂Cr₂O₇ and 0.1M H₂SO₄ was used as an oxidizing agent to improve the separation efficiency of cerium. A comparative study of the three extractants released that DEE is the best for separation of cerium from bulk of lanthanum oxide. The target was prepared by pressing. The production of ¹³⁹Ce of high radionuclidic purity and chemical purity via irradiation of lanthanum oxide target at MGC-20 cyclotron with protons of energy 14.5 MeV is described. The experimental yield was found to be 153 kBq/μA·h.     

Chemical recycling of poly(lactic acid)-based polymer blends using environmentally benign catalysts

Typical poly(l-lactic acid) (PLLA)-based polymer blends, PLLA/polyethylene (PE) and PLLA/poly(butylene succinate) (PBS), were degraded into each repolymerizable oligomer using environmentally benign catalysts, clay catalysts and enzymes, with the objective of developing a selective chemical recycling process. Two routes to selective chemical recycling of PLLA/PE blend were tested. One is the direct separation of PLLA and PE first by their different solubilities in toluene, followed by the chemical recycling of PLLA using montmorillonite K5 (MK5). The other is the selective degradation of PLLA in the PLLA/PE blend by MK5 in a toluene solution at 100 °C for 1 h forming the LA oligomer with a molecular weight of M_n = 200-300 g/mol, which is the best M_n for repolymerization. Thus regenerated PLLA had a M_w of greater than 100,000 g/mol. The PE remained unchanged and was quantitatively recovered by the reprecipitation method for material recycling. In a similar procedure, chemical recycling of PLLA/PBS blend was also carried out and compared by two routes. One is the direct separation of PLLA and PBS by solubility in toluene. The other route is the sequential degradation of PLLA/PBS blend using a lipase first to degrade PBS into cyclic oligomer, which was then repolymerized to produce a PBS. Next, PLLA was degraded into repolymerizable LA oligomer by MK5. The former procedure was carried out using a single solvent; however, the latter required mixed solvents, which decreased the efficient recycling use of solvents.     

Simultaneous determination of the cerium content and the thickness of cerium-activated alkaline earth metal sulfide films by x-ray fluorescence spectrometry

The cerium content and the film thickness of cerium-activated alkaline earth metal sulfide films were determined simultaneously. The cerium determination was calibrated by using standard solutions on filter paper. Film thickness was determined by comparing the S K_α intensities with those in zinc sulfide standards. The detection limit for cerium was estimated to be 0.1 μg cm^?2.     

Nanocomposite of CeVO4/BiVO4 Loaded on Reduced Graphene Oxide for the Photocatalytic Degradation of Methyl Orange

A facile procedure, involving one-pot synthesis of CeVO₄/BiVO₄ and in-situ reduction of graphene oxide (GO), has been used to prepare CeVO₄/BiVO₄/rGO nanocomposites. Different ratios of the CeVO₄–BiVO₄ were prepared to afford composites represented as CBVG3, CBVG5, and CBVG7. The ternary nanocomposite materials were characterized by using powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), photoluminescence and UV–vis spectroscopic techniques. Photocatalytic efficiency of the as-prepared ternary nanocomposites was investigated through the photo degradation of methyl orange under a visible light irradiation at 470 nm. The photocatalytic performance was enhanced by loading the CeVO₄/BiVO₄ nanoparticles on reduced graphene oxide (rGO), given MO degradation rate of 57, 65, 80, and 90% for BVG, CBVG3, CBVG5, and CBVG7, respectively after exposure to visible light for 120 min. Effects of experimental process parameters including initial dye concentration, catalysts loading and effect of different modification regimes were studied using CBVG7, which exhibited the highest efficiency. The improvement in the photocatalytic efficiency may be attributed to increased surface area of the nanocomposites, enhanced light absorption capacity and improved charge separation. The study showed a one-pot synthesis route to prepare promising CeVO₄/BiVO₄/GO nanocomposites for the photo-enhanced degradation of dye contaminants.

     

The physicochemical and catalytic properties of the Pt-CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> system

The properties of the Pt-CeO _x system prepared by the oxidation of the Pt₂Ce intermetallic compound were studied. The sample was characterized by X-ray diffraction in situ, thermogravimetry, scanning electron microscopy (with an accessory for energy dispersion analysis), transmission electron microscopy, and temperature-programmed reduction with hydrogen. The catalytic properties of the sample were studied in the model reaction of toluene hydrogenation. The oxidation of the intermetallic compound caused the appearance of metallic platinum and cerium oxide phases and high-dispersity platinum particles encapsulated in cerium oxide. Metallic platinum on the surface of the catalyst experienced rapid deactivation in the presence of hydrogen sulfide; high-dispersity platinum particles encapsulated in cerium oxide exhibited enhanced stability toward sulfur compounds.     

Conditional solubility versus pO2− of cerium(III) oxide in molten equimolar NaCl+KCl at 727°C

Reactions between cerium trichloride and oxide ions were studied in NaCl+KCl (1/1) at 1000°K, by potentiometry with a calcia-stabilized zirconia membrane electrode. Titration curves clearly demonstrated the existence of soluble cerium oxychloride (CeO⁺) and precipitated cerium oxide (Ce₂O₃), with respective dissociation constants 10^?11 and 10^?30 (molality scale). The corresponding conditional solubility diagram {log S (Ce^III)=f(pO^2?)} is presented and discussed.     

Effect of Dielectric Constant of Solvents on the Particle Size and Bandgap of La/SnO2‐TiO2 Nanoparticles and Their Catalytic Properties

Lanthanum (La) supported on tin oxide‐titanium oxide (SnO₂‐TiO₂ ) nanoparticles were prepared by a sol–gel method followed by a hydrothermal method. Effect of different solvents (ethyl acetate, benzyl alcohol, ethylene glycol) on the particle size and catalytic activity was investigated. The nanomaterial was characterized by transmission electron microscopy, powder X‐ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, and energy dispersive X‐ray. The catalytic and optical properties were studied using solid‐phase spectrophotometry and ultraviolet–visible spectroscopy, respectively. Gas chromatography‐mass spectrometry (GC‐MS) was used to detect the intermediates during the catalytic degradation of methylene blue. It was observed that with decrease in the dielectric constant (ε) of the solvent, the bandgap and particle size decrease and catalytic efficiency increases. Hence, the highest catalytic activity was observed with the solvent having the least dielectric constant.     

Films of certain oxides of rare-earth elements as the activators of platinum electrode on ZrO<Subscript>2</Subscript> + 10 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> electrolyte

The characteristics of porous Pt/YSZ (ZrO₂ + 10 mol % Y₂O₃) electrodes activated with small amounts of either oxides of rare-earth elements (REE) of the cerium subgroup (CeO₂, PrO _x , TbO _x ) or a mixed oxide with the Сe₂Tb₄O₁₁ composition by the procedure of impregnating the electrodes with ethanol solutions of REE nitrates and subsequent heating at 850°С are studied by the impedance method. The studies are carried out for those cases where the REE oxides after thermal treatment form a film on the electrolyte and also where no activator film is formed. The characteristics of films and activated electrodes are compared. Film-activated Pt/YSZ electrodes are discussed within the framework of the model of compact oxide electrodes.     

Green Synthesis of CeO2 Nanoparticles from the Abelmoschus esculentus Extract: Evaluation of Antioxidant,Anticancer, Antibacterial,and Wound-Healing Activities

Metal oxide nanoparticles synthesized by the biological method represent the most recent research in nanotechnology. This study reports the rapid and ecofriendly approach for the synthesis of CeO₂ nanoparticles mediated using the Abelmoschus esculentus extract. The medicinal plant extract acts as both a reducing and stabilizing agent. The characterization of CeO₂ NPs was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), and Fourier transform infrared spectroscopy (FTIR). The in vitro cytotoxicity of green synthesized CeO₂ was assessed against cervical cancerous cells (HeLa). The exposure of CeO₂ to HeLa cells at 10–125 µg/mL caused a loss in cellular viability against cervical cancerous cells in a dose-dependent manner. The antibacterial activity of the CeO₂ was assessed against S. aureus and K. pneumonia. A significant improvement in wound-healing progression was observed when cerium oxide nanoparticles were incorporated into the chitosan hydrogel membrane as a wound dressing.     

Fabrication of flexible graphene oxide paper-like adsorbent doped with magnetite nanoparticles for removal of dyes

Organic dyes are used in many industries, e.g., textile, cosmetics and food. Hence, contamination of organic dyes to water sources is a critical issue. To reduce water pollution by organic dyes, we propose a paper-like adsorbent with a practical and economical production procedure. Subsequently, a flexible adsorbent was produced using a one-step approach by vacuum filtration of graphene oxide (GO) and iron oxide nanoparticles (Fe₃O₄-NPs) containing dispersion through a membrane and quoted as GO/Fe₃O₄ paper. For comparison, GO paper was also prepared using the same procedure. Both papers were characterized using UV–VIS absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, electron diffraction X-ray analysis, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. At the steady-state conditions, GO/Fe₃O₄ and GO papers were performed as adsorbent for cationic dyes of methylene blue, neutral red, and anionic dyes of methyl orange and fluorescein. In general, the removal efficiency of GO/Fe₃O₄ paper was higher than that of GO paper for adsorption of all dyes and this adsorbent revealed satisfactory adsorption properties for cationic dyes when compared to anionic dyes.

     

Effect of the cerium content on the activity of Cu-Ce-Al-O catalysts in the methanol steam reforming reaction in a flow reactor

The Cu_18.5Ce _x Al_{81.5 ? x} (where x = 2, 7.4, and 14) oxide catalysts were synthesized by coprecipitation and tested in the methanol steam reforming reaction in an integral flow reactor at 270°C. It was found that the activity of the catalysts increased with the calcination temperature and catalysts with intermediate cerium contents exhibited the highest activity; these catalysts exhibited the greatest values of S _BET and S _Cu. The phase analysis demonstrated that copper in these samples occurred almost entirely as a CuO-CeO₂ solid solution. The concentration of carbon monoxide at the reactor outlet decreased with the calcination temperature. For the most active sample with a cerium content of 7.4% calcinated at 700°C, the concentration of CO reached a minimum of no higher than 0.3%.     

Influence of X-ray tube spectral distribution on uncertainty of calculated fluorescent radiation intensity

The relative radiation intensity (R_i) defined as fluorescent radiation intensity of analyte in specimen to fluorescent radiation intensity of pure element or compound, e.g., oxide is used in calculation in both fundamental parameter methods and in theoretical influence coefficient algorithms. Accuracy of calculated R_i is determined by uncertainties of atomic parameters, spectrometer geometry and also by X-ray tube spectral distribution. This paper presents the differences between R_i calculated using experimental and theoretical X-ray tube spectra evaluated by three different algorithms proposed by Pella et al., Ebel, and Finkelshtein–Pavlova. The calculations are performed for the most common targets, i.e., Cr, Mo, Rh and W. In this study, R_i is calculated for V, Cr, Mn, Fe, Co, Ni, Cu and Mo in steels as an example. The differences between R_i calculated using different X-ray tube spectrum algorithms are presented when pure element standard, multielement standard similar to the analyzed material and one pure element standard for all analytes is used in X-ray fluorescence analysis. The differences between R_i for intermediate-thickness samples (and also for thin films) and for X-ray tube, which ran for many hours, are also evaluated.     

New hydrazinium lanthanide sulphite hydrates

Some new hydrazinium lanthanide sulphite hydrates of the formula N₂H₅Ln(SO₃)₂(H₂O)₂ where Ln=La, Pr, Nd and Sm and N₂H₅Ce(SO₃)₂ have been prepared and characterized by chemical analyses, magnetic studies and electronic and infrared spectroscopy. Thermal degradation of these complexes has been investigated by simultaneous TG-DTA techniques. These complexes decompose in air after dehydration to give the respective lanthanide sulphate as the final residue. However, cerium complex gives a mixture of cerium sulphate and ceric oxide as the end products. Cerium and neodymium complexes have also been subjected to thermal degradation in nitrogen atmosphere and the dehydration of neodymium complex was observed at a higher temperature than in air. The anhydrous neodymium and cerium complexes decompose in one step to give the respective sulphate in nitrogen atmosphere.