Phase Of Nanomaterials Research Articles

Unconventional phase engineering of fuel-cell electrocatalysts

• Influences of unconventional phase on catalytic performance are manifested. • Methods for unconventional phase engineering and phase transformation are also summarized. • Representative fuel cell catalysts with unconventional phases are also provided. • Perspective sights and challenges for the unconventional phase engineering are added. The commercialization of fuel cells is greatly hampered by the poor stability, sluggish kinetics, and limited catalytic activity of electrocatalysts of both the cathodic oxygen reduction reaction (ORR) and anodic hydrogen oxidation reaction (HOR) or small molecules oxidation reaction (SMOR). Thus far, the exploration of highly active and durable electrocatalysts has emerged as a promising strategy for improving the performance of fuel cells. Accordingly, increasing attention has been devoted to optimizing the geometric and electronic properties of catalysts and modifying the adsorption/desorption of intermediates via phase engineering, especially for unconventional phase engineering. Herein, in this review, unconventional phase engineering is introduced in terms of the phase definition, classification, characterization, and understanding. Subsequently, we highlight the recent advances in the unconventional phase engineering by focusing on the rational design, preparation and transformation of different phases in nanomaterials. Moreover, the latest progress of electrocatalysts with unconventional phase for driving electrocatalytic ORR, HOR or SMOR are scientifically and systematically summarized, along with a deep understanding on the structure–activity relationship. Furthermore, we also provide personal perspectives on challenges and opportunities in this emerging field, covering the exploitation of phase-dependent properties of electrocatalysts.

Ptychography Reduces Spectral Distortions Intrinsic to Conventional Zone-Plate-Based X-Ray Spectromicroscopy

Abstract Scanning transmission X-ray microscopy is a powerful method for mapping chemical phases in nano-materials. The point spread function (PSF) of a conventional zone-plate-based microscope limits the achievable spatial resolution and also results in spatially resolved spectra that do not accurately reflect the spatial heterogeneity of the samples when the scale of the detail approaches the probe size. X-ray ptychography, a coherent-scattering-based imaging scheme that effectively removes the probe from the image data, returns accurate spectra from regions smaller than the probe size. We show through simulation how the long tails on the PSF of an x-ray optic can cause spectral distortion near a boundary between two spectrally distinct regions. The resulting apparent point spectra can appear mixed, with the species on one side of the boundary seeming to be present on the other even at a distance from the boundary equal to several times the spatial resolution. We further demonstrate the effect experimentally and show that ptychographic microscopy can return the expected spectra from a model system, whereas conventional microscopy does not.

Effect of Dispersion and Improper Bonding of Nanofiller Polymer Composites

Nanofiller is used to enhance the properties in composite materials, with at least one phase of nanomaterials that can be referred as nanocomposites. The nanomaterial due to uniform dispersion recently used in advanced polymer nanocomposites, to mix effectively in the polymer matrix. The production of polymer composites with nanofiller is limited due to the unresolved issues such as agglomeration during processing, high production cost and limited availability of good quality. Graphene filled nanocomposites is a novel material and considered in different applications. The properties of the nanocomposites mainly depend on the arrangement of graphene layers with the polymer matrix and interfacial bonding between them. Here an attempt is made to develop polymer composites using graphene as reinforcements and epoxy as matrix materials. Sonication is a process of applying ultrasound energy to disperse nanoparticles in epoxy. The sound waves that are created in sonication are generally large ultrasound waves and during this process, considerable heat is produced. If the sonication treatment is too long, nanoparticles were seriously damaged, particularly when a probe sonicator is used. The localized damage causes nanoparticles to deteriorate the mechanical properties of the polymer composites. The study from XRD and SEM showed that the use of graphene at higher weight % resulted in a decrease in strength of the composites. Hence, it is not a better choice to produce nanocomposites at increased addition of nanofiller.

Phase engineering of nanomaterials.

Phase has emerged as an important structural parameter - in addition to composition, morphology, architecture, facet, size and dimensionality - that determines the properties and functionalities of nanomaterials. In particular, unconventional phases in nanomaterials that are unattainable in the bulk state can potentially endow nanomaterials with intriguing properties and innovative applications. Great progress has been made in the phase engineering of nanomaterials (PEN), including synthesis of nanomaterials with unconventional phases and phase transformation of nanomaterials. This Review provides an overview on the recent progress in PEN. We discuss various strategies used to synthesize nanomaterials with unconventional phases and induce phase transformation of nanomaterials, by taking noble metals and layered transition metal dichalcogenides as typical examples. Moreover, we also highlight recent advances in the preparation of amorphous nanomaterials, amorphous-crystalline and crystal phase-based hetero-nanostructures. We also provide personal perspectives on challenges and opportunities in this emerging field, including exploration of phase-dependent properties and applications, rational design of phase-based heterostructures and extension of the concept of phase engineering to a wider range of materials.

Comparative study on photocatalytic activity of transition metals (Ag and Ni)-doped ZnO nanomaterials synthesized via sol-gel method.

Ag and Ni/ZnO photocatalyst nanostructures were successfully synthesized by a sol–gel method. In this work, the photocatalyst sample was systematically studied based on several factors affecting the performance of photocatalyst, which are size, morphology, band gap, textural properties and the number of active sites presence on the surface of the nanocatalyst. X-ray diffraction revealed that Ag/ZnO nanomaterials experienced multiple phases, meanwhile for Ni/ZnO the phase of nanomaterials were pure and single phase for stoichiometry less than 5%. Field emission scanning electron microscope (FESEM) showed almost all of the synthesized nanomaterials possessed a mixture of nanorods and spherical-like shape morphology. The Ag/ZnO showed high photocatalytic activity, producing at least 14th trials of nanocatalyst reusability on degradation of methyl orange under UV irradiation. Interestingly, this phenomenon was not observed in larger surface area of Ni/ZnO nanomaterials which supposedly favour photocatalytic activity, but instead producing poor photocatalytic performance. The main reasons were studied and exposed by temperature-programmed desorption of carbon dioxide (TPD–CO2) which showed that incorporation of Ag into ZnO lattice has enhanced the number of active sites on the surface of the nanocatalyst. Whereas incorporation of Ni in ZnO has lowered the number of active sites with respect to undoped ZnO. Active sites measurement is effective and significant, providing opportunities in developing an intensive study as an additional factor.

Preparation and Characterization of Zinc and Cerium Co-doped Titania Nano-materials with Antibacterial Activity

Zinc and cerium co-doped titania (Zn/Ce-TiO2) nano-materials were synthesized by a Sol-Gel method at different calcination temperatures. Zn/Ce-TiO2 nano-materials were characterized by X-ray diffraction (XRD), trans- mission electron microscope (TEM), X-ray photoelectron spectroscope (XPS) and UV-Vis diffuse reflectance spectra (DRS). With the test of bacterial inhibition zone, the antibacterial properties of Zn/Ce-TiO2 nano-materials on E. coli. were investigated. The results show that crystallinity and the crystal phase of nano-materials are closely dependent on the calcination temperature. Zinc ions and cerium ions exist in the form of Zn2Ti3O8 and CeO2 phase, respectively. The Zn/Ce-TiO2 nano-materials synthesized exhibit enhanced antibacterial activity under visible light irradiation compared with it in the dark. Ultimately, the action mechanism of Zn/Ce co-doping is discussed.

Probing the structure of heterogeneous diluted materials by diffraction tomography

The advent of nanosciences calls for the development of local structural probes, in particular to characterize ill-ordered or heterogeneous materials. Furthermore, because materials properties are often related to their heterogeneity and the hierarchical arrangement of their structure, different structural probes covering a wide range of scales are required. X-ray diffraction is one of the prime structural methods but suffers from a relatively poor detection limit, whereas transmission electron analysis involves destructive sample preparation. Here we show the potential of coupling pencil-beam tomography with X-ray diffraction to examine unidentified phases in nanomaterials and polycrystalline materials. The demonstration is carried out on a high-pressure pellet containing several carbon phases and on a heterogeneous powder containing chalcedony and iron pigments. The present method enables a non-invasive structural refinement with a weight sensitivity of one part per thousand. It enables the extraction of the scattering patterns of amorphous and crystalline compounds with similar atomic densities and compositions. Furthermore, such a diffraction-tomography experiment can be carried out simultaneously with X-ray fluorescence, Compton and absorption tomographies, enabling a multimodal analysis of prime importance in materials science, chemistry, geology, environmental science, medical science, palaeontology and cultural heritage.