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.     

Sono-assisted preparation of magnetic ferroferric oxide/graphene oxide nanoparticles and application on dye removal☆

A simple ultrasound-assisted co-precipitation method was developed to prepare ferroferric oxide/graphene oxide magnetic nanoparticles (Fe3O4/GO MNPs). The hysteresis loop of Fe3O4/GO MNPs demonstrated ...     

Green electrospun nanocuprous oxide–poly(ethylene oxide)–silk fibroin composite nanofibrous scaffolds for antibacterial dressings

Cuprous oxide (Cu₂O) nanoparticles have attracted extensive attention because of their excellent optical, catalytic, antibacterial, and antifungal properties and low cost. Nano-Cu₂O–poly(ethylene oxide) (PEO)–silk fibroin (SF) composite nanofibrous scaffolds (CNSs) were fabricated through green electrospinning to impart excellent antibacterial properties onto nanofibrous scaffolds. Scanning electron microscopy revealed that the nanofibers became more nonuniform and appeared more and more as beads in the nanofibers with increasing nano-Cu₂O concentration, and no obvious morphological changes were observed after 75% EtOH vapor treatment. Transmission electron microscopy and X-ray photoelectron spectroscopy demonstrated that nano-cuprous oxide (nano-Cu₂O) was successfully loaded into the PEO–SF nanofibers. Fourier transform infrared–attenuated total reflectance spectroscopy results indicate that nano-Cu₂O did not induce SF conformation from random coils to β sheets. The SF conformation converted from random coils to β sheets after 75% EtOH vapor treatment. The results of water contact angle testing and swelling property measurement clarified that nano-Cu₂O–PEO–SF CNSs possessed outstanding hydrophilicity. Nano-Cu₂O–PEO–SF CNSs exhibited better antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria than PEO–SF nanofibrous scaffolds, and the antibacterial activity increased with increasing nano-Cu₂O concentration. Cell viability studies with pig iliac endothelial cells demonstrated that nano-Cu₂O–PEO–SF CNSs had no cytotoxicity. Nano-Cu₂O–PEO–SF CNSs are expected to be ideal biomimetic antibacterial dressings for wound healing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47730.     

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.     

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.     

Rates and controls of nitrous oxide and nitric oxide emissions following conversion of forest to pasture in Rondônia

Tropical soils are important sources of nitrous oxide (N₂O) and nitric oxide (NO) emissions from the Earths terrestrial ecosystems. Clearing of tropical rainforest for pasture has the potential to alter N₂O and NO emissions from soils by altering moisture, nitrogen supply or other factors that control N oxide production. In this review we report annual rates of N₂O and NO emissions from forest and pastures of different ages in the western Brazilian Amazon state of Rondônia and examine how forest clearing alters the major controls of N oxide production. Forests had annual N₂O emissions of 1.7 to 4.3 kg N ha^-1 y^-1 and annual NO emissions of 1.4 kg N ha^-1 y^-1. Young pastures of 1–3 years old had higher N₂O emissions than the original forest (3.1–5.1 kg N ha^-1 y^-1) but older pastures of 6 years or more had lower emissions (0.1 to 0.4 kg N ha^-1 y^-1). Both soil moisture and indices of soil N cycling were relatively poor predictors of N₂O, NO and combined N₂O + NO emissions. In forest, high N₂O emissions occurred at soil moistures above 30 water-filled pore space, while NO emissions occurred at all measured soil moistures (18–43). In pastures, low N availability led to low N₂O and NO emissions across the entire range of soil moistures. Based on these patterns and results of field fertilization experiments, we concluded that: (1) nitrification was the source of NO from forest soils, (2) denitrification was not a major source of N₂O production from forest soils or was not limited by NO- supply, (3) denitrification was a major source of N₂O production from pasture soils but only when NO₃^- was available, and (4) nitrification was not a major source of 3 NO production in pasture soils. Pulse wettings after prolonged dry periods increased N₂O and NO₃^- emissions for only short periods and not enough to appreciably affect annual emission rates. We project that Basin-wide, the effect of clearing for pasture in the future will be a small reduction in total N₂O emissions if the extensive pastures of the Amazon continue to be managed in a way similar to current practices. In the future, both N₂Oand NO fluxes could increase if uses of pastures change to include greater use of N fertilizers or N-fixing crops. Predicting the consequences of these changes for N oxide production will require an understanding of how the processes of nitrification and denitrification interact with soil type and regional moisture regimes to control N₂O and NO production from these new anthropogenic N sources.     

Modification of poly(vinylidene fluoride) membranes with aluminum oxide nanowires and graphene oxide nanosheets for oil–water separation

To improve the hydrophilic and oleophobic properties of membrane, we adopted aluminum oxide (Al₂O₃) nanowires and graphene oxide (GO) nanosheets to modify poly(vinylidene fluoride) (PVDF) membranes. The experimental results show that the intercalation of Al₂O₃ nanowires between GO nanosheets effectively improved the roughness of the GO–Al₂O₃–PVDF membrane, and the permeability of the membrane with an optimal mass ratio of Al₂O₃ to GO of 7.5 was 31 times that of the GO–PVDF membrane. Furthermore, the addition of Al₂O₃ nanowires significantly enhanced both the hydrophilic and oleophobic properties of the GO–Al₂O₃–PVDF membrane. On the basis of the extended Derjaguin–Landau–Verwey–Overbeek theory, the energy barriers between the oil droplets and GO–PVDF and GO–Al₂O₃–PVDF membranes were 0.63 and 0.9 KT, respectively; this indicated improvements in the anti-oil-fouling ability of the GO–Al₂O₃–PVDF membranes. We also found that both the GO–PVDF and GO–Al₂O₃–PVDF membranes had great oil–water separation rates (97.9 and 99.4%, respectively) with an initial oil concentration of 200 mg/L. The findings of this study show that the GO–Al₂O₃–PVDF membrane is a promising oil–water separation membrane, and further investigation of the cleaning procedure is needed to promote its practical application in oil–water separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47493.     

Lead-free bimetallic oxide loaded on reduced graphene oxide‒poly(dopamine) hybrid nanocomposite with enhanced crystallinity and piezoelectric performance

The increased demand for electricity with low environmental impact has prompted researchers to find solutions to obtain the maximum output. This effort has imparted a significant focus on piezoelectric materials owing to their high piezoelectric coefficient and electromechanical coupling factor. In this study, reduced graphene oxide encapsulated with polydopamine and incorporated with zinc manganate hybrid nanocomposite (rGO?pDA?ZnMnO₃ HNC) was prepared. The as-prepared HNC, of different weight percentages, was blended with 15 wt% poly(vinylidene fluoride) (PVDF) to form different PVDF@rGO?pDA?ZnMnO_3(R) thin films. Subsequently, the flexible piezoelectric sensors (FPSs) were fabricated by a solution-casting method. The as-prepared HNC and thin films were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The PXRD data revealed the increased degree of crystallinity of the thin films from 54% to 68% with the increase in filler loading. The β-phase of PVDF also increased, as obtained from the FT-IR analysis. Electrical characterization of the prepared FPSs was carried out by estimating the sensitivity of the devices on different loads. The acquired response at a force of 1 N for PVDF@rGO?pDA?ZnMnO_3(0.2 wt%) improved by 44% than that of PVDF@rGO?pDA?ZnMnO_3(0 wt%). The force applied by the finger on the device also generated voltages, which were used to charge the capacitor, thereby used to glow the light-emitting diodes with amplifications. These promising results demonstrate the potential for developing lead-free efficient piezoelectric nanogenerators for energy-harvesting applications and self-powered devices.     

Bismuth based oxide electrolytes— structure and ionic conductivity

Bismuth oxide systems exhibit high oxide ion conductivity and have been proposed as good electrolyte materials for applications such as solid oxide fuel cells and oxygen sensors. However, due to their instability under conditions of low oxygen partial pressures there has been difficulty in developing these materials as alternative electrolyte materials compared to the state-of-the-art cubic stabilised zirconia electrolyte. Bismuth oxide and doped bismuth oxide systems exhibit a complex array of structures and properties depending upon the dopant concentration, temperature and atmosphere. In this paper we comprehensively review the structures, thermal expansion, phase transitions, electrical conductivity and stability of bismuth oxide and doped bismuth oxide systems. ©     

Polybutylene Succinate (PBS) – Polycaprolactone (PCL) Blends Compatibilized with Poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) Copolymer for Biomaterial Applications

This study reports the preparation and characterization of Polybutylene Succinate (PBS)-Polycaprolactone (PCL) melt blends (10–40 wt.% PCL) in the presence of a compatibilizer, in order to explore their potential use as a biomaterial. The thermal transitions, as well as the crystallinity of the polymer blends were analyzed by Differential Scanning Calorimetry, the thermomechanical properties were analyzed via Dynamic Mechanical Analysis and phase morphologies were characterized by Scanning Electron Microscopy. Degradation profiles of the blends were analyzed in PBS buffer solution at pH 7.4 at 37°C via pH measurements. Cytotoxicity of the PBS/PCL films were tested by MTS assay.     

Synthesis,mechanical property,and thermal stability of reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin composites

Reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin (RGO–ZnO/CE/BMI) composites were synthesized via a blending method. The RGO–ZnO composite was incorporated into the CE/BMI copolymer to improve the properties of RGO–ZnO/CE/BMI composites. The structure, elements, and morphology of the RGO–ZnO composite were studied with XPS, FTIR, XRD, and SEM analyses. It indicated that the ZnO micro-sphere was attached to RGO by electrostatic attraction and the RGO–ZnO composite was prepared successfully. The mechanical properties and thermal stability of RGO–ZnO/CE/BMI composites were investigated. When RGO–ZnO composite was 1 wt.%, the flexural and impact strengths of RGO–ZnO/CE/BMI composites were 1.07 and 1.35 times of the CE/BMI copolymer, respectively. However, the RGO–ZnO composite tended to aggregate in the CE/BMI matrix with high loading. According to the SEM analysis, appropriate RGO–ZnO composite was evenly dispersed in the CE/BMI copolymer. Compared to the CE/BMI copolymer, the thermal stability of the RGO–ZnO/CE/BMI composites was good. Thus, the RGO–ZnO composite was successfully filled in the CE/BMI matrix; the mechanical properties and thermal stability of the RGO–ZnO/CE/BMI composites were enhanced.     

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.     

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.     

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.     

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.     

Double stimuli responsive mixed aggregates from poly(acrylic acid)-block-poly(ε-caprolactone)-block-poly(acrylic acid) and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymers

Well defined ABA triblock copolymer comprising a biodegradable poly(ε-caprolactone) (PCL) middle block and two pH responsive poly(acrylic acid) (PAA) outer blocks was synthesized by atom transfer radical polymerization of tert-butyl acrylate, initiated by PCL-based macroinitiator, followed by selective hydrolysis of the poly(tert-butyl acrylate) blocks. The cooperative self-assembly of the synthesized poly(acrylic acid)-block-poly(ε-caprolactone)-block-poly(acrylic acid) (PAA₂₂PCL₂₆PAA₂₂) copolymer with a temperature-responsive poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO₂₆PPO₄₀PEO₂₆, Pluronic P85) triblock copolymer at different compositions in aqueous media was investigated. Based on experimental data, copolymer properties and composition, formation of nano-sized aggregates comprising a mixed PCL/PPO core and a mixed PEO/PAA corona is suggested. The binary mixture of PAA₂₂PCL₂₆PAA₂₂:PEO₂₆PPO₄₀PEO₂₆ copolymers at molar ratio 3:1 favors the formation of mixed aggregates only, while at higher PEO₂₆PPO₄₀PEO₂₆ content the aggregates coexist with pure PEO₂₆PPO₄₀PEO₂₆ micelles.