Facile synthesis of reduced graphene oxide/CeO2 nanocomposites and their application in supercapacitors

The combination of the attractive properties of graphene with excellent characteristics of other functional nanomaterials has become a popular pathway for achieving applications in multiple fields. Herein, reduced graphene oxide (RGO)/CeO₂ nanocomposites with enhanced capacitive performance were designed and synthesized by a facile two-step approach with a self-assembly method followed by thermal treatment. The structure, morphology and composition of the resulting RGO/CeO₂ nanocomposites were systematically investigated. The presence of RGO can prevent the aggregation and control the structures of the CeO₂ nanocrystals in the annealing process. The nanocomposites as electrode materials for supercapacitor exhibited an enhanced capacitive performance due to the synergic effect between RGO nanosheets and CeO₂ nanocrystals. The excellent capacitive performance of the RGO/CeO₂ nanocomposites offer great promise for supercapacitor applications.     

The effect of Nb or Ta substitution into the M1 phase of the MoV(Nb,Ta)TeO selective oxidation catalyst

We use aberration corrected high-angle annular dark field (HAADF) imaging to systematically study, atomic column by atomic column, the effects of substituting Nb or Ta into the M1 phase of the MoV(Nb,Ta)TeO propane (amm)oxidation catalyst. The HAADF results indicate that the x,y coordinates of the metal sites within the M1 framework are unaffected by the substitution of either Nb or Ta for Mo. The HAADF analysis of the Ta-substituted catalyst demonstrated that the Ta preferentially substitutes into the pentagonal bipyramidal site, and by analogy, we anticipate that Nb substitutes similarly. Compositional analysis of the entire framework suggests that Ta/Nb behaves as a director of V among the octahedra that link the pentagonal rings, and the variable V occupancy may be correlated with variations in catalytic activities and selectivities. Finally, HAADF imaging provided evidence of coexistence of Ta-rich and Ta-poor domains. Similar phase segregation behavior may be present in Nb-substituted specimens, but would be very difficult to detect.     

Morphology-controlled therapeutic activity of cerium oxide nanoparticles for mild traumatic brain injury

The design and optimization of nanostructures with unique morphologies and properties are at the forefront of biomedical nanotechnology. Cerium oxides are widely used to investigate the effect of morphology on performance. However, elucidating the morphology–activity relationship of cerium oxide nanocrystals in biomedical applications remains challenging. Herein, the therapeutic effects of cerium oxide nanoparticles with different morphologies: cerium oxide nanorods with two different aspect ratios (CeO_x NRs_A and CeO_x NRs_B), cerium oxide nanopolyhedra (CeO_x NPs), and cerium oxide nanocubes (CeO_x NCs) are investigated in in vivo and in vitro mild traumatic brain injury (TBI) models. Cerium oxide nanoparticles inhibit oxidative stress and inflammation after mild TBI, alleviating cognitive impairment; furthermore, the therapeutic effect is significantly affected by their morphology. Owing to the higher Ce³⁺/Ce⁴⁺ ratio, exposure of more active crystal surfaces, and greater number of exposed oxygen vacancies, CeO_x NRs show better activity than CeO_x NPs and CeO_x NCs for mild TBI. Among the two investigated types of cerium oxide nanorods, CeO_x NRs_A, with a higher Ce³⁺/Ce⁴⁺ ratio on the surface, appear to spread better than CeO_x NRs_B in the injured lesions. The factors causing morphology-controlled biomedical performance, such as Ce³⁺/Ce⁴⁺ molar ratio, surface area, and aspect ratio, are discussed.     

Formation of ordered nanocrystalline CeO2 structures during thermal decomposition of cerium formate Ce(HCOO)3

In this article, we report the formation of ordered porous nanocrystalline ceria CeO₂ during oxidative thermolysis of cerium formate Ce(HCOO)₃. Ordering of the reaction product occurs due to the presence of similar structural elements in the CeO₂ and Ce(HCOO)₃ crystalline lattices. It was shown that the morphology and the structure of the products of thermal decomposition of Ce(HCOO)₃ are greatly influenced by the composition of the gaseous atmosphere, in which the decomposition takes place. During thermal decomposition of Ce(HCOO)₃ in an atmosphere of argon, no ordering of the synthesized CeO₂ nanocrystals is observed. It was concluded that the presence of oxygen in the gaseous atmosphere is crucial for obtaining ordered nanocrystalline CeO₂ from the Ce(HCOO)₃ precursor.     

Photoluminescence properties of praseodymium doped cerium oxide nanocrystals

The structure and photoluminescence (PL) properties of CeO₂ nanocrystals synthesized by the microwave-assisted hydrothermal (MAH) method with different praseodymium (Pr³⁺) ions contents were performed. X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance ultraviolet-visible (UV-vis), Fourier transform Raman (FT-Raman) spectroscopies and PL measurements at room temperature were employed. XRD patterns indicated that the nanocrystals are free of secondary phases and crystallize in the cubic structure while FT-Raman revealed a typical scattering mode of fluorite type. The UV-vis spectra suggested the presence of intermediate energy levels in the band gap of these nanocrystals. The most intense PL emission was obtained for CeO₂ nanocrystals doped with 1.6% of Pr³⁺ ions and smaller particle size.     

Ternary CdxZn1−xSe deposited on Ag (1 1 1) by ECALE: Electrochemical and EXAFS characterization

This paper reports the characterization of ternary II-VI semiconductor nanocrystals, deposited by the electrochemical atomic layer epitaxy (ECALE) technique.In particular, morphological and structural properties of the ternary compounds of formula Cd_xZn_1−xSe deposited on Ag (1 1 1) have been characterized as a function of composition. The number of the attainable x values is limited by the necessity of using well-defined ZnSe/CdSe deposition sequences. However, the quantitative analysis carried out on the basis of both electrochemical and extended X-ray absorption fine structure (EXAFS) experiments indicates that the ECALE method is a successful way of controlling the composition of Cd_xZn_1−xSe. In addition, the electrochemical measurements show that the amount of deposition is minimum in correspondence to the compound with x = 0.5, thus corroborating the hypothesis of a higher degree of disorder suggested both by morphological and structural investigation. The morphology was studied by atomic force microscopy (AFM). The structure of the films is estimated by EXAFS which is a powerful technique for the analysis of the local structure around chosen atoms.     

Rippled and Helical MoS<Subscript>2</Subscript> Nanowire Catalysts: An Aberration Corrected STEM Study

Abstract  

Aberration corrected (C_s) scanning transmission electron microscopy (STEM) has been used for the first time to characterize MoS₂ catalysts (supported on Al₂O₃ substrates) to provide detailed information of its shape and structure. The high-resolution imaging reveals unprecedented morphologies present in the MoS₂ catalyst that have never been observed before with other experimental techniques because of the insufficient image contrast and/or resolution. High angle annular dark field (HAADF)-STEM images shows very clearly that the catalyst is formed by elongated chains with a twisted and helical structure. Based on the HAADF-STEM images, we built three atomic models to illustrate the different morphologies found in the MoS₂ catalyst. The existence of these nanostructures opens the posibility for novel catalyticaly active edge morphologies in MoS₂-based nanocatalysts.     

Defect induced magnetic transition in Co doped CeO2 sputtered thin films

Cobalt-doped cerium dioxide thin films exhibit room temperature ferromagnetism due to high oxygen mobility in doped CeO₂ lattice. CeO₂ is an excellent doping matrix as there is a possibility of it losing oxygen while retaining its structure. This leads to increased oxygen mobility within the fluorite CeO₂ lattice, leading to formation of Ce³⁺ and Ce⁴⁺ species. Magnetic ceria materials are important in several applications from magnetic data storage devices to magnetically recoverable catalysts. In this paper, the room temperature ferromagnetism of rf sputtered Co doped CeO₂ thin films is reported whereas undoped CeO₂ thin films exhibit paramagnetic behavior. The ferromagnetic properties of the Co doped films were explained based on oxygen vacancies created by Co ions in Ce sites. This is further supported by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman. Change in surface morphology due to Co doping of the samples were analyzed using atomic force microscopy (AFM).     

Morphological and Rheological Characteristics of PVP–CeO2 Blends

This work focuses on the flow behavior of the blend comprising polyvinyl pyrrolidone and cerium (IV) oxide (CeO₂) particles in submicron size, under low shear rates. The polyvinyl pyrrolidone–CeO₂ blends have been prepared and characterized by scanning electron microscopy, X-ray diffraction, and viscometry. The generation of core–shell morphology was verified from the scanning electron micrographs. Scanning electron microscopy shows that the blend formed is of porous nature. The particle size of CeO₂ increases with the concentration of both CeO₂ and polymer due to aggregation. The blend containing as high as 35?wt% of CeO₂ was found to exhibit pseudo-plastic response under low shear rate. The reasons for the observed morphology and other properties along with mechanism were explained. The main factor, which governs the properties of the end product, was van der Waals attractive forces that exist among the constituents of the system prepared.     

Copper oxide catalysts supported on ceria for low-temperature CO oxidation

Copper oxide catalysts supported on ceria were prepared by wet impregnation method using finely CeO₂ nanocrystals, which was derived from alcohothermal synthesis, and copper nitrate dissolved in the distilled water. The catalytic activity of the prepared CeO₂ and CuO/CeO₂ catalysts for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The samples were characterized using BET, XRD, SEM, HRTEM and TPR.     

Effect of substrate (ZnO) morphology on enzyme immobilization and its catalytic activity

In this study, zinc oxide (ZnO) nanocrystals with different morphologies were synthesized and used as substrates for enzyme immobilization. The effects of morphology of ZnO nanocrystals on enzyme immobilization and their catalytic activities were investigated. The ZnO nanocrystals were prepared through a hydrothermal procedure using tetramethylammonium hydroxide as a mineralizing agent. The control on the morphology of ZnO nanocrystals was achieved by varying the ratio of CH₃OH to H₂O, which were used as solvents in the hydrothermal reaction system. The surface of as-prepared ZnO nanoparticles was functionalized with amino groups using 3-aminopropyltriethoxysilane and tetraethyl orthosilicate, and the amino groups on the surface were identified and calculated by FT-IR and the Kaiser assay. Horseradish peroxidase was immobilized on as-modified ZnO nanostructures with glutaraldehyde as a crosslinker. The results showed that three-dimensional nanomultipod is more appropriate for the immobilization of enzyme used further in catalytic reaction.     

Optical Active Nano-Glass-Ceramics

This paper reviews the synthesis and characterization of several transparent glass-ceramics with optical active nanocrystals. Glass-ceramics containing ferroelectric Sr_xBa_1-xNb₂O₆ nanocrystals with an ellipsoidal shape show optical phase modulations in the presence of alternative electric fields. In the glass-ceramics with Ba₂TiSi₂O₈ (BTS) nanocrystals, BTS crystalline layers with a thickness of approximately 120 nm are formed at the surface and ellipsoidal-shaped crystallites with a diameter of 100–200 nm are dispersed in the glass matrix. Some TeO₂-based and GeO₂-based glasses show a prominent nanocrystallization. RE-doped CaF₂ nanocrystals are patterned in a spatially selected region by laser irradiations. The size, morphology, and dispersion state of nanocrystals should be carefully checked in each glass system and composition. The basic concept for the design of glass system and composition is also discussed. Some data on optical active performances in transparent glass-ceramics with nanocrystals were introduced.     

Deficiency of O2 molecules enhances ionic conductivity in Cr-doped O-Ce-O for solid oxide fuel cell applications

Production of high performance low-energy loss solid oxide fuel cells (SOFCs) is a challenge and is the global demand of the current market. We have focused on to develop SOFCs that can be operated at 600–800 °C with better ionic conductivity when compared to the conventional SOFCs functioning at 1000–800 °C. Bulk cerium oxide (CeO₂)-based solid electrolyte lessens ionic conductivity at room temperature, thus nanocrystalline CeO₂ has been used to improve the conductivity and to control the temperature. The transition metal-doped CeO₂ (Ce_(1−X)Cr_(X)O₂) nanocrystalline is used to increases the deficiency of oxygen molecules which in turn enhances ionic conductivity in electrolyte material for SOFC applications. The structural and morphological characterization have been done using XRD, RAMAN and FESEM, while electrical and magnetic characterization at room temperature was analysed using vibrating sample magnetometer, impedance spectroscopy and cyclic voltammetery shows better ionic conductivity in Cr doped CeO₂ in comparison with pure nanocrystalline CeO_2.     

Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7?δ coated conductors by RF magnetron sputtering

La₂Zr₂O₇ (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa₂Cu₃O_7−x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO₂), yttria-stabilized zirconia (YSZ)/CeO₂, and CeO₂/YSZ/CeO₂. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO₂, YSZ/CeO₂, and CeO₂/YSZ/CeO₂ buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO₂ single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO₂ and CeO₂/YSZ/CeO₂ buffer architectures had cracks. The highly textured LZO film grown on CeO₂-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.     

Synthesis of CeO2 nano-aggregates of complex morphology

Cerium oxide with spheric, flowerlike and needle-like shapes has been synthesized by a simple microwave assisted method using diethylene glycole in mild conditions. The effect of reaction temperature on the crystal structure and morphology were thoroughly discussed. The structural evolutions and morphological characteristics of the nanostructures were investigated using X-ray diffractometery, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, TGA/DSC and BET analysis. By changing experimental conditions pure CeO₂ fluoritic phase or cerium formate with complex morphology were formed. High porosity CeO₂ nanostructures, retaining the end-reaction morphology, were readily obtained by calcination of cerium precursor. This simple and economic soft chemical method leads to nanostructured–micrometric aggregates of cerium oxide with high specific surface area suitable for catalytic applications.     

Synthesis and characterization of highly stable optically passive CeO2-ZrO2 counter electrode

Transparent and adherent CeO₂-ZrO₂ thin films having film thicknesses ∼543-598 nm were spray deposited onto the conducting (fluorine doped tin oxide coated glass) substrates from a blend of equimolar concentrations of cerium nitrate hexahydrate and zirconium nitrate having different volumetric proportions (0-6 vol.% of Zr) in methanol. CeO₂-ZrO₂ films were polycrystalline with cubic fluorite crystal structure and the crystallinity was improved with increasing ZrO₂ content. Films were highly transparent (T ∼ 92%), showing decrease in band gap energy from 3.45 eV for pristine CeO₂ to 3.08-3.14 eV for CeO₂-ZrO₂ films. The different morphological features of the film obtained at various CeO₂-ZrO₂ compositions had pronounced effect on the ion storage capacity and electrochemical stability. CeO₂-ZrO₂ film prepared at 5 vol.% Zr concentration exhibited higher ion storage capacity of 24 mC cm⁻² and electrochemical stability of 10,000 cycles in 0.5 M LiClO₄ + PC electrolyte due to its film thickness (584 nm) coupled with relatively larger porosity (8%). The optically passive behavior of such CeO₂-ZrO₂ film (with 5 vol.% Zr) is affirmed by its negligible transmission modulation irrespective of repeated Li⁺ and electron insertion/extraction. The coloration efficiency of spray deposited WO₃ thin film is found to enhance from 47 to 107 cm² C⁻¹ when CeO₂-ZrO₂ is coupled as a counter electrode with WO₃ in an electrochromic device (ECD). These films can be used as stable ‘passive’ counter electrodes in electrochromic smart windows as they retain full transparency in both the oxidized and reduced states and ever-reported longevity.     

Preparation and characterization of silver nanocomposite textile

Nanostructured silver films of different thicknesses were deposited on surfaces of polypropylene nonwovens by magnetron sputter coating to obtain antibacterial and electrical conductive properties. The surface morphology of nanostructured silver films was investigated by atomic force microscopy (AFM). The antibacterial properties of the nonwovens coated with relatively thinner films were evaluated using the shake flask test. The conductivity of the nonwovens coated with relatively thicker films was examined using an ohm-meter. The results of the antibacterial test revealed that the antibacterial performance improved gradually as the film thickness increased from 0.5 to 3 nm. It is believed that the total amount of silver ions released from the coating was increased along with the increase in film thickness. As sputtering time prolonged, the grain sizes of the silver particles were increased and the coating became more compact. The results of the electrical conductivity test showed that the increased film thickness led to the improved electrical conductivity when the film was relatively thicker. The AFM images clearly revealed the change in surface morphology formed by sputter coating. The growth and coverage of the coating layer contributed to the improvement in its antibacterial and conductive properties.     

Analyzing three‐dimensional structure and geometrical shape of individual cellulose nanocrystal from switchgrass

The three‐dimensional morphology, size distribution, and structure of individual cellulose nanocrystals (CNCs) isolated from switchgrass (Panicumvirgatum L), a representative raw biomass material, were investigated in this research. Width and height evolutions along the individual CNC longitudinal direction were statistically and quantitatively characterized using transmission electron microscopy (TEM) and atomic force microscopy (AFM). Lognormal distribution was identified as the most likely for cellulose nanocrystals’ size distribution. Height and width dimensions were shown to decrease toward the ends from the midpoint of individual CNCs, implying a spindle shape. The observed rough surfaces of CNCs were explainable as the results of acid etching of the subcrystalline and disordered region located at the surface. X‐ray diffraction analysis of crystallite size accompanied with TEM and AFM measurements revealed that the cross‐sectional dimensions of individual switchgrass CNC were either rectangularly or elliptically shaped, with an approximately 3–5 nm lateral element length range. POLYM. COMPOS., 38:2368–2377, 2017. © 2015 Society of Plastics Engineers     

Defect generation and morphology transformation mechanism of CeO2 particles prepared by molten salt method

Ceria is widely used in industrial fields due to its unique chemical properties. In this work, a series of CeO₂ particles with controllable morphology, size, and defect concentration were obtained by a simple molten salt method. The adjustment of temperature and molten salt concentration has a considerable effect on the morphology and particle size of the final CeO₂ particles while prolonging the holding time has little effect. Ion doping and reducing atmosphere calcination were used to regulate the defect concentration to improve the chemical activity of CeO₂ particles. SEM results show that the morphology of CeO₂ particles transforms from sphere to octahedron under the two treatments. The Rietveld refinement results and the XPS spectra indicate that increasing calcination temperature, reducing atmosphere calcination and ion doping are beneficial to improving the oxygen vacancies and Ce³⁺ concentration of CeO₂ samples, which are the reason for enhancing the photocatalytic activity of the samples. Moreover, the oriented attachment, agglomeration and merging of crystals formed by the decomposition of cerium precursors are the key to the growth of CeO₂ particles. Aggregates with exposed low-energy planes merge directly to form particles of various morphologies to maintain their own low energy.