Direct multipulse laser processing of titanium oxide–graphene oxide nanocomposite thin films

Nanocomposite thin films consisting of titanium oxide (TiO₂) nanoparticles (NPs) and graphene oxide (GO) platelets were deposited by a spin-coating technique. The obtained films were submitted to direct laser irradiation using a frequency quadrupled Nd:YAG (λ=266 nm, τ_FWHM≅3 ns, ν=10 Hz) laser source. The effect of the laser processing conditions, as laser fluence value and number of subsequent laser pulses incident onto the same target location, on the surface morphology, crystalline structure, and chemical composition of the TiO₂/GO nanocomposite thin films was systematically investigated. The laser fluence values were maintained below the vaporization threshold of the irradiated composite material. With the increase of the laser fluence and number of incident laser pulses melting and coalescence of the TiO₂ NPs into inter-connected aggregates as well as rippling of the GO platelets take place. The gradual reduction of GO platelets and the onset of anatase to rutile phase transition were observed at high laser fluence values.     

Thermodynamic and kinetic studies of crystal violet dye adsorption with poly(methyl methacrylate)–graphene oxide and poly(methyl methacrylate)–graphene oxide–zinc oxide nanocomposites

We successfully prepared poly(methyl methacrylate) (PMMA)–graphene oxide (GO) and PMMA–GO–zinc oxide (ZnO) nanocomposites and characterized them using different techniques. The adsorption performances of the as-prepared composites were investigated for crystal violet (CV) dye removal. The contact time as a main factor affecting the adsorption process by adsorbents was studied. Because the adsorption capacity value for CV was found to show no extensive changes after 35 min, 35 min was selected as the best contact time for our system. The adsorption results revealed that the best capacity of CV adsorption onto the PMMA–GO and PMMA–GO–ZnO nanocomposites occurred at pH 12 and 298 K. The respective entropies (−0.208 and −0.168 kJ mol⁻¹ K⁻¹) and enthalpies (−72.86 kJ/mol, and −55.54 kJ/mol) for PMMA–GO and PMMA–GO–ZnO and Gibbs energy revealed that the process of adsorption was exothermic. In addition, the Elovich, pseudo-first-order, intraparticle diffusion, and pseudo-second-order (four types) models were applied to our kinetic study. Our results indicate that CV adsorption onto PMMA–GO and PMMA–GO–ZnO was good with the pseudo-second-order (type 1) and pseudo-first-order models because of the low χ² value and the high correlation coefficient value. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47495.     

Oxidation of isobutane over Mo–V–Sb mixed oxide catalyst

The catalytic performances of Mo–V–Sb mixed oxide catalysts have been studied in the selective oxidation of isobutane into methacrolein. V–Sb mixed oxide showed the activity for oxidative dehydrogenation of isobutane to isobutene. The selectivity to methacrolein increased by the addition of molybdenum species to the V–Sb mixed oxide catalyst. In a series of Mo–V–Sb oxide catalysts, Mo₁V₁Sb₁₀O_x exhibited the highest selectivity to methacrolein at 440°C. The structure analyses by XRD, laser Raman spectroscopy and XPS showed the coexistence of highly dispersed molybdenum suboxide, VSbO₄ and -Sb₂O₄ phases in the Mo₁V₁Sb₁₀O_x. The high catalytic activity of Mo₁V₁Sb₁₀O_x can be explained by the bifunctional mechanism of highly dispersed molybdenum suboxide and VSbO₄ phases. It is likely that the oxidative dehydrogenation of isobutane proceeds on the VSbO₄ phase followed by the oxidation of isobutene into methacrolein on the molybdenum suboxide phase.     

Selective oxidation of ethane over hydrothermally synthesized Mo–V–Al–Ti oxide catalyst

Mo–V-based oxide catalysts are known highly active for various hydrocarbon selective oxidations. Particularly those which are monophasic giving XRD diffraction at d=4 Å are extremely active for alkane oxidations. We succeeded to synthesize this unique monophasic material by hydrothermal method and obtained Mo₆V₂Al₁O_x mixed oxide catalysts which showed activities for gas-phase ethane oxidation to ethene and acetic acid. The addition of titanium to the Mo₆V₂Al₁O_x oxide catalyst was found to result in a marked increase of the activity for the ethane selective oxidation, which was due to the morphological change of the catalyst particles and the increase of surface area by the addition of titanium. During the heat-treatment above 550°C under a nitrogen stream, the structural phase of the Mo₆V₂Al₁Ti_0.5O_x catalyst giving the XRD diffraction at d=4 Å transferred to (Mo_0.93V_0.07)₅O₁₄-like phase with drastic decreases of the oxidation activity and the surface area. On the basis of kinetic data and the fact that the lower reaction temperature and the existence of water vapor in the feed facilitated the formation of acetic acid, it is concluded that the breaking of C–H bond of ethane is the rate determining of the oxidation and acetic acid do not form through ethene.     

Polyaniline–antimony oxide composites for effective broadband EMI shielding

Conducting polyaniline (PAni)–antimony trioxide (Sb₂O₃) composites with different weight percentages (wt%) of Sb₂O₃ in PAni have been synthesized by in situ chemical oxidative polymerization. The composites were structurally and morphologically characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Measurements of electromagnetic interference (EMI) shielding, complex permittivity and microwave absorbing as well as reflecting properties of the composites were carried out in the frequency range of 8–18 GHz, encompassing the microwave X and Ku bands of practical relevance. All the computations are based on microwave scattering parameters measured by transmission line waveguide technique. It is observed that the presence of Sb₂O₃ in the PAni matrix affects the electromagnetic shielding and dielectric properties of the composites at microwave frequencies. The composites have shown better shielding effectiveness (SE) in both the X (SE in the range ?18 to ?21 dB) and Ku (?17.5 to ?20.5 dB) bands. ε′ and ε′′ values of the PAni–Sb₂O₃ composites are in the range of 64–37 and 63–30, respectively, in the frequency range of 8–18 GHz. Dielectric measurements indicated the decrease in dielectric constant with the increase in wt% of Sb₂O₃. The results obtained for the reflection and absorption coefficients indicated that PAni–Sb₂O₃ composites exhibit better electromagnetic energy absorption throughout the X and Ku bands. The results indicated that PAni–Sb₂O₃ composites can be used as potential microwave absorption and shielding materials.     

Preparation and characterisation of titania-supported vanadium–phosphorus oxide catalysts

A series of vanadium–phosphorus oxides (mainly with V P ) supported on pigmentary anatase (10 m² g^-1) has been prepared using aqueous NH₄VO₃ and (NH₄)H₂PO₄ solutions, with loadings up to 11.3 wt%, equivalent to about 12.7 monolayers. Characterisation by X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction suggests that the main phase present at loadings below about 10 wt% is an amorphous V–P oxide which exists chiefly as blocks of disordered material. The presence of small amounts of crystalline -VOPO₄ and of V₂O₅ is indicated at the highest loadings, especially when and V P ratios are used. The two materials having the lowest loadings are active for methanol oxidation at 473–533 K, and show high selectivity to formaldehyde. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structural development and magnetic phenomenon in Zn–Cr–Fe multi oxide nano-crystals

The Cr³⁺ ions doped multi-oxide ZnFe_2−xCr_xO₄ ferrite nanoparticles have been synthesized by chemical co-precipitation method. Site occupancies of Zn²⁺, Cr³⁺ and Fe³⁺ ions were analyzed using X-ray diffraction data and Buerger's method. The effect of the constituent phase variation on the magnetic hysteresis behavior was examined by saturation magnetization which decreases with the increase in Cr³⁺ content in place of Fe³⁺ ions at octahedral B-site. Typical blocking temperature (T_B) around 90 K was observed by zero field cooling and field cooling magnetization study. Room temperature Mössbauer spectra show two paramagnetic doublets (tetrahedral and octahedral sites). The isomer shifts of both doublets decrease whereas quadrupole splitting and relative area of tetrahedral A-site increases with increasing Cr³⁺ substitution. The dielectric constant (measured on compositions x=0, 0.4, 0.8 and 1.0) increases when the temperature increases as in the semiconductor. This behavior is attributed to the hopping of electrons between Fe²⁺ and Fe³⁺ ions with a thermal activation.     

Tin–Zinc oxide composite ceramics for selective CO sensing

Composite metal oxide gas sensors were intensely studied over the past years having superior performance over their individual oxide components in detecting hazardous gases. A series of pellets with variable amounts of SnO₂ (0–50 mol%) was prepared using wet homogenization of the component oxides leading to the composite tin-zinc ceramic system formation. The annealing temperature was set to 1100 °C. The samples containing 2.5 mol% SnO₂ and 50 mol% SnO₂ were annealed also at 1300 °C, in order to observe/to investigate the influence of the sintering behaviour on CO detection. The sensor materials were morphologically characterized by scanning electron microscopy (SEM). The increase in the SnO₂ amount in the composite ceramic system leads to higher sample porosity and an improved sensitivity to CO. It was found that SnO₂ (50 mol%) - ZnO (50 mol%) sample exhibits excellent sensing response, at a working temperature of 500 °C, for 5 ppm of CO, with a fast response time of approximately 60 s and an average recovery time of 15 min. Sensor selectivity was tested using cross-response to CO, methane and propane. The results indicated that the SnO₂ (50 mol%)-ZnO (50 mol%) ceramic compound may be used for selective CO sensing applications.     

Platinization of sunlight active Ti–W mixed oxide photocatalysts

The photocatalytic effects of the platinization on sunlight-active nanosize Ti–W mixed oxide materials with anatase structure were investigated. Platinization was shown to promote the photocatalytic mineralization of toluene, leading to an enhanced reaction rate of ca. 2.3 with respect to the parent Ti–W mixed oxide. This reaction rate increase is significantly higher than that obtained using ultraviolet excitation for titania-based oxides in the degradation of toluene and seems intimately related to the presence of PtO bonds located at the platinum–anatase interface. The chemical/physical bases of such behavior are discussed on the light of a structural/electronic characterization of the solids with the help of X-ray diffraction and Raman/UV–visible spectroscopy, along with additional in situ experiments run under sunlight excitation using infrared and electron paramagnetic resonance spectroscopy.     

Acetonylacetone conversion on AlPO4–cesium oxide (5–30 wt%) catalysts

The effect of hydrogen spillover over Pd/SiO₂ + USY on pyridine chemisorbed on acid sites of USY zeolite was investigated. According to FTIR measurement, pyridine adsorbed on Lewis acid sites migrated to Brønsted acid sites under hydrogen-flowing atmosphere. The rate of migration was drastically promoted by physically mixed Pd/SiO₂ catalysts. This suggests that spilt-over hydrogen enhance the migration of pyridine adsorbed on Lewis acid sites.     

A study of the NOx storage catalyst of Ba–Fe–O complex oxide

The complex oxide Ba–Fe–O catalysts were prepared by sol–gel method. The XRD, DTA, NO-TPD, XPS and NSC measurements were used to characterize the structures, NO_x storage property and sulfur resistance ability. It is concluded that when coadsorption of NO and O₂ at 400 °C, the sample calcined at 750 °C possesses high NO_x storage capacity and sulfur resistance. The perovskite type BaFeO₃ and BaFeO_3−x phases are the active centers in the catalyst for NO_x storage.     

Controlled partial oxidation of methane to methanol/formaldehyde over Mo–V–Cr–Bi–Si oxide catalysts

The non-catalytic and catalytic oxidations of CH₄ over Mo–V–Cr–Bi–Si oxide catalysts were investigated in a tubular reactor and the catalysts were characterized by XRD, XPS and TPR. Contents of Bi in the catalysts influenced the combination of Mo–V–Bi–O species and, consequently, influenced the TPR reduction temperature of the catalysts. The catalysts exhibited more selective production of methanol when the TPR reduction peaks shifted to lower temperature.     

Steam reforming of methanol over copper–manganese spinel oxide catalysts

The steam reforming of methanol was studied over a series of copper–manganese spinel oxide catalysts prepared with the urea–nitrate combustion method. All catalysts showed high activity towards H₂ production with high selectivity. Synthesis parameters affected catalyst properties and, among the catalysts tested, the one prepared with 75% excess of urea and an atomic ratio Cu/(Cu + Mn) = 0.30 showed the highest activity. The results show that formation of the spinel Cu_xMn_3 − xO₄ phase in the oxidized catalysts is responsible for the high activity. Cu–Mn catalysts were found to be superior to CuO–CeO₂ catalysts prepared with the same technique.     

Alumina-supported manganese- and manganese–palladium oxide catalysts for VOCs combustion

Alumina-supported manganese- and palladium–manganese oxide catalysts were prepared and tested in the combustion of formaldehyde. Total combustion of formaldehyde/methanol was achieved at 220 °C over a 18.2% Mn/Al₂O₃ catalyst. This temperature decreased either to 90 or 80 upon adding 0.1% or 0.4% Pd, respectively, to the base 18.2% Mn/Al₂O₃ catalyst. The combined use of X-ray diffraction, temperature-programmed reduction and photoelectron spectroscopy (XPS) techniques revealed that a Mn⁴⁺/Mn³⁺ oxide(s) and PdO_x species are present on the surface of the fresh catalysts and remain along the catalytic reaction.     

Hydration of ethene over W–P mixed metal oxide catalysts

W–P mixed metal oxide catalysts are active and selective for the gas-phase hydration of ethene to ethanol. The activity and selectivity of this catalytic reaction depend on the W/P atomic ratio. However, ethene conversion slightly decreases at higher W/(W + P) atomic ratio. The selectivity for ethanol increases with the W/P atomic ratio and reaches the highest value (92%) at W_0.81P_0.19O_x. The W_0.81P_0.19O_x catalyst is less active than the conventional H₃PO₄/SiO₂ catalyst, but the activity is maintained for a long time without the supply of any catalyst components. The reaction temperature does not affect substantially the rate of ethene hydration over the W_0.81P_0.19O_x catalyst. The H₂O/ethene molar ratio of 0.4 is the most appropriate for both reaction rate and selectivity. The active species of W–P mixed metal oxide are amorphous. But there is Keggin structure of W–P oxide species (PW₁₂O₄₀ ³⁻) in the presence of steam. And the species are the active sites for the hydration of ethene, confirmed by in situ Raman spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adsorption of Anionic–Cationic Surfactant Mixtures on Metal oxide Surfaces

This research evaluates the adsorption of anionic and cationic surfactant mixtures on charged metal oxide surfaces (i.e., alumina and silica). For an anionic-rich surfactant mixture below the CMC, the adsorption of anionic surfactant was found to substantially increase with the addition of low mole fractions of cationic surfactant. Two anionic surfactants (sodium dodecyl sulfate and sodium dihexyl sulfosuccinate) and two cationic surfactants (dodecyl pyridinium chloride and benzethonium chloride) were studied to evaluate the effect of surfactant tail branching. While cationic surfactants were observed to co-adsorb with anionic surfactants onto positively charged surfaces, the plateau level of anionic surfactant adsorption (i.e., at or above the CMC) did not change significantly for anionic–cationic surfactant mixtures. At the same time, the adsorption of anionic surfactants onto alumina was dramatically reduced when present in cationic-rich micelles and the adsorption of cationic surfactants on silica was substantially reduced in the presence of anionic-rich micelles. This demonstrates that mixed micelle formation can effectively reduce the activity of the highly adsorbing surfactant and thus inhibit the adsorption of the surfactant, especially when the highly adsorbing surfactant is present at a low mole fraction in the mixed surfactant system. Thus surfactant adsorption can be either enhanced or inhibited using mixed anionic–cationic surfactant systems by varying the concentration and composition.

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Catalytic reduction of NO by hydrocarbons over a mechanical mixture of spinel Ni–Ga oxide and manganese oxide

NO reduction with propylene over Mn₂O₃, spinel Ni–Ga oxide and their mechanical mixtures has been investigated. Mn₂O₃ has no activity to NO reduction, but has a high activity for NO oxidation to NO₂. Spinel Ni–Ga oxide showed an apparent activity to NO reduction only at temperatures above 400°C. Mixing of Mn₂O₃ to the Ni–Ga oxide resulted in a significant enhancement of NO reduction in the temperature range of 250–450°C. The optimal Mn₂O₃ content in the mixture catalyst was about 10–20 wt%. It is suggested that the synergetic effect of Mn₂O₃ and Ni–Ga oxide plays an important role in the catalysis of NO reduction. The Ni–Ga oxide and Mn₂O₃ mixture catalyst is superior to Pt/Al₂O₃ and Cu-ZSM-5 by showing a higher NO reduction conversion, resistance to water and negligible harmful by-product formation. Other lower hydrocarbons C₂H₄, C₂H₆ and C₃H₈ also give a maximum NO reduction conversion as high as 50%. The difference from using C₃H₆ is that the temperature at the maximum NO reduction is higher than it is with C₃H₆. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polystyrene–poly(ethylene oxide) diblock copolymers micelles in water

Micellization in water of polystyrene–poly(ethylene oxide) diblock copolymers is achieved by the stepwise dialysis technique in order to prepare micellar solutions for copolymers with a wide range of molecular parameters. Hydrodynamic radii, determined by quasielastic light scattering, are correlated with the molecular parameters, e.g. molecular weight and composition, and compared with the theory. Two couples of phenanthrene and anthracene labelled copolymers are used to prepare micellar solutions by mixing them before and after dialysis. The non radiative energy transfer is determined on these solutions to prove that polystyrene-poly(ethylene oxide) diblock copolymers micelles in water are "frozen" micelles even when heated near the Tg of polystyrene. Received: 3 November 1997/Revised version: 1 December 1997/Accepted: 2 December 1997