Surface Amorphous Structure Research Articles

Improved Cycling Stability of Ni-Rich Cathode Material by In Situ Introduced TM-B-O Amorphous Surface Structure.

Current research has found the amorphous/crystal interface has some unexpected electrochemical behaviors. This work designed a surface modification strategy using NaBH4 to induce in situ conversion of the surface structure of Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) into TM-B-O amorphous interface layer. Oxidizing the surface from transition metals (TM) with high valence and reductive BH4- in a weak polar medium of ethanol results in an easy redox reacton. A TM-B-O amorphous structure is formed on NCM811 surface. The action of reactive wetting ensures a complete and uniform structure evolution of the surface crystals. The complete coverage protects the outer crystal and the heterogeneous interface impedance between the modified layer and bulk is reduced. More importantly, this amorphous interface layer through in situ conversion enhances the heterogeneous link at interface and its own structural stability. The modified NCM811 (TB2@NCM) treated with 1 wt % NaBH4 shows excellent electrochemical performance, especially cyclic stability. At a high cutoff voltage of 4.5 V, the capacity retention was 72.5% at 1 C after 500 cycles. The electrode achieves 173.7 mAh·g-1 at 10 C. This work creates a modifying strategy with potential application prospect due to simple technology with low-cost raw material under mild operating conditions.

Predicting Electronic Structure of Realistic Amorphous Surfaces

AbstractAmorphous materials underlie the functionality of many devices in photocatalysis, electronics, and other technological applications. The performance of such devices is largely altered by the interfacial characteristics of the material motivating better understanding of their structure function relationships. However, open questions remain about how to generate atomistic representations of amorphous surfaces that are realistic while being amenable to computational study using electronic structure methods. Here, model parameters are explored to generate accurate amorphous surface models using prototypical amorphous titanium dioxide and a melt‐quench approach. In particular, non‐standard model considerations such as minimum sample size, unit cell size, and quench conditions are varied to efficiently explore amorphous structural space. The results indicate different modeling parameters have a substantial effect on surface morphology and electronic structure that significantly alters the interpretations gained by computational study of amorphous interfaces. Critically, it is shown that the structural motifs that contribute to such differences are not detectable by short range structural analysis that has traditionally been used to assess the quality of melt‐quench derived amorphous structures.

(Invited, Digital Presentation) Design, Preparation and Characterization of Photofunctional Materials Based on Energy-Resolved Distribution of Electron Traps

How can we design functional solid materials, such as catalysts and photocatalysts? What is the decisive structural parameters controlling their activities, performance or properties? What is obtained as structural properties by popular conventional analytical methods, such as X-ray diffraction (XRD) or nitrogen-adsorption measurement, is limited to bulk crystalline structure and specific surface area, i.e., no structural characterization on amorphous phases, if present, and surface structure has been made so far. This is because there have been no macroscopic analytical methods to give surface structural information including possibly-present amorphous phases. Recently, we have developed reversed double-beam photoacoustic spectroscopy (RDB-PAS) which enables measure energy-resolved distribution of electron traps (ERDT) for semiconducting materials such as metal oxides [1,2]. Those detected electron traps (ETs) seem to be predominantly located on the surface for almost all the metal oxide particles, and therefore they reflect macroscopic surface structure, including amorphous phases, in ERDT patterns. Using an ERDT pattern with the data of CB bottom position (CBB), i.e., an ERDT/CBB pattern, it has been shown that metal oxide powders, and the other semiconducting materials such as carbon nitride, can be identified without using the other analytical data such as XRD patterns or specific surface area, and similarity/differentness of a pair of metal-oxide samples can be quantitatively evaluated as degree of coincidence of ERDT/CBB patterns. In this talk, an approach of material design based on the ERDT/CBB-pattern analyses is introduced [3].[1] Nitta, A.; Takase, M.; Takashima, M.; Murakami, N.; Ohtani, B. A Fingerprint of Metal-oxide Powders: Energy-resolved Distribution of Electron Traps. Chem. Commun. 2016, 52, 12096-12099. [2] Nitta, A.; Takashima, M.; Murakami, N.; Takase, M.; Ohtani, B. Reversed double-beam photoacoustic spectroscopy of metal-oxide powders for estimation of their energy-resolved distribution of electron traps and electronic-band structure. Electrochim. Acta 2018, 264, 83-90. [3] Nitta, A.; Takashima, M.; Takase, M.; Ohtani, B. Identification and characterization of titania photocatalyst powders using their energy-resolved distribution of electron traps as a fingerprint. Catal. Today 2019, 321-322, 2-8.

Plasma-Wind-Assisted In2S3 Preparation with an Amorphous Surface Structure for Enhanced Photocatalytic Hydrogen Production.

Photocatalytic production from water is considered an effective solution to fossil fuel-related environmental concerns, and photocatalyst surface science holds a significant interest in balancing photocatalysts’ stability and activity. We propose a plasma-wind method to tune the surface properties of a photocatalyst with an amorphous structure. Theoretical calculation shows that the amorphous surface structure can cause an unsaturated coordination environment to adjust the electron distribution, forming more adsorption sites. Thus, the photocatalyst with a crystal–amorphous (C–A) interface can strengthen light absorption, harvest photo-induced electrons, and enrich the active sites, which help improve hydrogen yield. As a proof of concept, with indium sulfide (In2S3) nanosheets used as the catalyst, an impressive hydrogen production rate up to 457.35 μmol cm−2 h−1 has been achieved. Moreover, after plasma-assisted treatment, In2S3 with a C–A interface can produce hydrogen from water under natural outdoor conditions. Following a six-hour test, the rate of photocatalytic hydrogen evolution is found to be 400.50 μmol cm−2 g−1, which demonstrates that a catalyst prepared through plasma treatment is both effective and highly practical.

Straightforward synthesis of magnetized activated carbon particles

To develop new sustainable processes, the production of materials with specific physico-chemical properties is highly desirable. Creating hybrid multi-functional materials by combining​ complementary components represents a suitable approach to meet the requirements of various industrial processes. In this work, a straightforward production route to synthesize magnetic (electrode) particles from low cost starting materials is presented. The particles were produced from iron(II) hydroxide and activated carbon (AC) via a microwave-assisted synthesis, creating a magnetite and AC hybrid material (PMAG/AC). SEM imaging shows that the particles are characterized by an amorphous surface structure, typical for AC. Visible cavities are covered by magnetite nanoparticles, confirming the specific surface area measurements, which show a reduction of the surface area when magnetite is added. Cyclic voltammetry shows increasing current densities, ranging from ＋0.49 to ＋1.31 mA cm−2 and from −0.58 to −1.47 mA cm−2 at ＋/−1000 mV vs. Ag/AgCl with increasing immobilized particle mass (25 to 124 mg cm−2). Finally, adsorption experiments were conducted by adding the particles to a culture of electroactive Shewanella oneidensis showing a time-dependent adsorption behavior. These findings represent a promising perspective for future applications of magnetic, conductive and biocompatible particles across a broad range of biotechnological and (bio-)electrochemical processes.

Dissipation and adhesion in collisions between amorphous FeO nanoparticles

How dust grains aggregate into planetesimals is still an open question. It is experimentally observed that binary collisions between micron-sized dust grains result in adhesion for collisions up to ∼1 ms−1. However, aggregates at scales ∼1 mm and above have been shown to exhibit fragmentation or bouncing at relevant collision velocities, resulting in a barrier preventing the formation of larger aggregates. One key factor is the weak adhesion observed between dust particles in aggregates leading to ruptures even in low-velocity collisions. To better understand the structure and strength of the adhered interface resulting from collisions, we performed molecular-dynamics simulations of head-on collisions between amorphous FeO nanoparticles. The results demonstrate several important phenomena which indicate how bonding between aggregates might become stronger than is often observed in experiments. For nanograins, it is shown that strong attractive interactions result in a minimum relative collision speed vc determined just before impact. The values of vc for particle radii 7 nm and below are computed to be in the range 40–100 ms−1. This high collision speed is shown to result in strong bond reordering at the interface. Moreover, increasing the incident collision speed vrel is shown to increase the work of adhesion Wadh, which is correlated to substantial bond rearrangement. Specifically, for values of vrel in the range between 10–90 ms−1, the interface between adhered grains is structured very closely to perfectly coordinated FeO amorphous solid. The reported results suggest stronger bonding results from collisions between particles with unpassivated surfaces, especially when particles are small, have amorphous surface structures, or when collisions occur at higher relative speeds. These factors should generate aggregates with stronger bonds that are less easily broken in subsequent collisions, and hence might be responsible for aggregates less likely to fragment at larger length scales.

The mineralogy and structure of use-wear polish on chert

Polished edges of archaeological stone tools are commonly investigated to obtain information on the tools’ uses in prehistory. Yet to this day, it remains unclear what exactly such polishes are and how they form. Answering these questions should allow the elaboration of new interpretative methods based on objective measurements. Two major competing hypotheses of polish formation have been proposed: abrasion and the formation of a thin amorphous film on the chert or flint surface. We employ reflectance infrared spectroscopy, a technique particularly sensitive to thin amorphous films, to investigate these two hypotheses. We found no added amorphous layer that would have formed upon friction against bone, antler, ivory or wood. Our observations suggest polish formation by abrasion, notwithstanding previous claims of added amorphous surface structures. This has implications for our understanding of the physical processes taking place during friction of chert and flint against different materials. Our results also open the possibility to propose new pathways for identifying different use-wear processes, based on the degree of abrasion.

Landfill leachate wastewater treatment to facilitate resource recovery by a coagulation-flocculation process via hydrogen bond

Recent trend to recover value-added products from wastewater calls for more effective pre-treatment technology. Conventional landfill leachate treatment is often complex and thus causes negative environmental impacts and financial burden. In order to facilitate downstream processing of leachate wastewater for production of energy or value-added products, it is pertinent to maximize leachate treatment performance by using simple yet effective technology that removes pollutants with minimum chemical added into the wastewater that could potentially affect downstream processing. Hence, the optimization of coagulation-flocculation leachate treatment using multivariate approach is crucial. Central composite design was applied to optimize operating parameters viz. Alum dosage, pH and mixing speed. Quadratic model indicated that the optimum COD removal of 54% is achieved with low alum dosage, pH and mixing speed of 750 mgL−1, 8.5 and 100 rpm, respectively. Optimization result showed that natural pH of the mature landfill leachate sample is optimum for alum coagulation process. Hence, the cost of pH adjustment could be reduced for industrial application by adopting optimized parameters. The inherent mechanism of pollutant removal was elucidated by FTIR peaks at 3853 cm−1 which indicated that hydrogen bonds play a major role in leachate removal by forming well aggregated flocs. This is concordance with SEM image that the floc was well aggregated with the porous linkages and amorphous surface structure. The optimization of leachate treatment has been achieved by minimizing the usage of alum under optimized condition.

Surface plasmon resonance and defects on tungsten oxides synergistically boost high-selective CO2 reduction for ethylene

Photocatalytic CO2 reduction reaction (CO2-RR) driven by solar energy is one expected “green technology” to produce hydrocarbon, however, the high-valuble C2/Cx-compounds converted from CO2 face great challenges. Herein, high-selective ethylene production is achieved via photocatalytic CO2-RR by using plasmonic tungsten oxides as catalyst under solar light irradiation. Tungsten oxides (WO3-x-2) synthesized by using acid-assisted solvothermal method exhibits thin amorphous surface structure with abundant oxygen vacancies and low-valence tungsten ions (26.1 mol% W5+ and 7.1 mol% W4+). Under full-spectrum light irradiation, ethylene generation rate of WO3-x-2 is 61.6 μmol g − 1h − 1 (selectivity of 89.3%) and is 20-fold higher than that of WO3-x-0 with thick amorphous surface. The amorphous surface of tungsten oxides with abundant defects is clearly observed by atomic-resolution high-angle annular dark field scanning transmission electronic microscopy (HAADF-STEM). Light-dependent photocatalytic results demonstrate the synergetic effect of oxygen vacancies, plasmonic hot electrons and photothermal heating boosting CO2-RR on tungsten oxide catalysts for ethylene generation. One possible ethylene generation pathway is proposed based on the detected intermediates during CO2-RR. As far as we known, our work is the first report on plasmonic photocatalytic CO2-RR for high-selective ethylene generation.

Molecular dynamics exploration of the amorphous surface structures and properties of the biomimetic β-tricalcium phosphate

β-Tricalcium phosphate (β-TCP) is one of the main components in bone matrix. Its synthetic analogue has been widely applied as bioceramics or catalysts. Experimental evidences have shown that the surface area of the bioactive calcium phosphate materials is in amorphous state rather than perfect crystal phase. In this work, based on molecular dynamics annealing simulation, we have constructed the amorphous surface structures for β-TCP (100) plane. INTERFACE force field (IFF) shows very good performance for simulating the properties of r β-TCP such as lattice parameters, infrared spectroscopy, and melting points. Our calculations show that the amorphous surface structures of β-TCP have obvious nano-grooves, which might be beneficial to the adsorption of biomolecules and the enhancement of biological activity. The mechanical properties of annealed structure of β-TCP were also calculated and discussed. Our results show that the annealing temperatures have obvious effects on the surface energy but not mechanical properties. As a results, in designing or optimizing the biomaterials, the sintering should not be the only way to improve the mechanical properties of β-TCP. The present amorphous surface models for the β-TCP show interesting properties and are useful in further investigations on the interactions between biomaterial surface and proteins.

Morphological Features and Sorption Performance of Materials Based on Birnessite Exposed to Various Reductive Conditions

The article is devoted to the evolution of structural, morphological, and sorption characteristics of layered manganese oxide (birnessite) under various conditions close to the real operating regime of the sorbents for radioactive waste processing. To identify the phase composition in the birnessites, we implemented XRD analysis, while SEM and temperature-programmed reduction (TPR) were used to study morphological and redox features of the materials, respectively. Structural changes after various kinds of treatment of birnessites were tracked using low temperature nitrogen sorption. Sorption characteristics were assessed under static and in dynamic conditions on the efficiency of Sr2+ removal from simulated seawater. TPR combined with kinetic analysis revealed the decrease of particle sizes in the birnessites after repeated use in sorption-regeneration cycle and reduction with hydrazine. Despite the fact that the porous structure of the materials remains preserved, the surface morphology of birnessite changes drastically depending on the reducing agent. Hydrazine treatment increases the sorption performance of the birnessite followed by degradation of mechanical properties, thus, preventing such sorbent from repeated use. Kinetic analysis of TPR allows quantifying differences in morphology and porous structure of manganese oxide materials. The specific surface area, amorphous surface structure, and accessibility of Mn+3 sites are the most important factors for birnessite sorption performance.

Atomic and electronic structure of tetrahedral amorphous carbon surfaces from density functional theory: Properties and simulation strategies

We present a computational study of tetrahedral amorphous carbon surfaces within density functional theory. The samples studied contain of the order of 250–300 atoms with densities in the range 2.78–3.12g/cm3. Bulk samples within and below that range are also studied as reference. The morphological features are characterized by calculating local density and sp2/sp3 fraction, and with a new tool based on the analysis of the topology of the 4-atom sp2 chains found in the structures. This allows to establish that sp2 clustering occurs predominantly with the formation of olefinic chains, with a smaller amount of aromatic-ring structures formed. This preference for olefinic chains is present both in bulk and reconstructed surfaces. The degree of localization of the electronic states is obtained with a participation ratio analysis, showing a direct relation with density and sp2 fraction. The position of the surfaces Fermi level is calculated about 4eV below the vacuum level, a result that appears to be almost independent of sample density. Finally, a passivation scheme is presented that allows to reduce the overall number of atoms in the surfaces without compromising the level of description of their properties, optimizing them in terms of the associated computational cost.

Porous structure SnSb/amorphous carbon core-shell composite as high capacity anode materials for lithium ion batteries

SnSb/C core-shell powder has been successfully prepared by modified carbothermal reduction method. The shape, size, morphology, and electrochemical properties of the SnSb/C core-shell powder have been investigated. SnSb particles are completely encapsulated by amorphous carbon shell, and the surface of SnSb/C composite has been characterized with porous structure. The composite has a relatively high BET surface area of 253 m2g−1. The composite exhibits relatively good capacity retention for 50 cycles at a constant current density of 100 mA g−1 and show excellent rate performance when the current ranges from 50 to 200 mA g−1. The improvement of reversible capacity and cyclic performance is attributed to loose and amorphous surface structure which could buffer volume variations through cycle process.

The Structure of Silica Surfaces Exposed to Atomic Oxygen

In this work we use molecular dynamics (MD) simulations with the ReaxFFSiOGSI potential to model the structure of quartz and amorphous silica surfaces exposed to atomic oxygen. The ReaxFFSiOGSI pot...

The Nature of Lithium Battery Materials under Oxygen Evolution Reaction Conditions

Transition-metal oxide and phosphate materials, commonly used for lithium battery devices, are active as oxygen evolution reaction (OER) catalysts under alkaline and neutral solution conditions. Electrodes composed of LiCoO(2) and LiCoPO(4) exhibit progressive deactivation and activation for OER catalysis, respectively, upon potential cycling at neutral pH. The deactivation of LiCoO(2) and activation of LiCoPO(4) are coincident with changes in surface morphology and composition giving rise to spinel-like and amorphous surface structures, respectively. The amorphous surface structure of the activated LiCoPO(4) is compositionally similar to that obtained from the electrodeposition of cobalt oxide materials from phosphate-buffered electrolyte solutions. These results highlight the importance of a combined structural and electrochemical analysis of the materials surface when assessing the true nature of the OER catalyst.

Amorphous solid foam structures on germanium by heavy ion irradiation

Ge (100) surfaces were irradiated by heavy Bi+ and Bi++ ions extracted from a Bi-liquid metal ion source in a mass separated focused ion beam system with energies of 30 and 60 keV, respectively. Networks of different nanoporous (or sponge like) structures were found depending on ion energy, fluence, angle of incidence, and irradiation temperature. The porous and amorphous surface structures are explained in terms of high concentration vacancies close to the surface. The surface modification was investigated using SEM and AFM imaging and FIB for cross section preparation.

Vibrational dynamics and surface structure of amorphous selenium

In contrast to crystalline solids in which structural order governs dynamics and thermodynamics, the lack of long-range periodicity in amorphous materials is responsible for several anomalies. Although the relation between these anomalies and the 'bulk structure' is generally understood, the surface structure and the corresponding vibrational spectrum of amorphous solids is practically an unexplored theme. In this study, we resolve the differences in vibrational dynamics and atomic structure between bulk and surface (top 5 nm) atoms of amorphous selenium. We combine experimental (grazing incidence inelastic X-ray scattering) and computational (ab initio and semiempirical molecular orbital theoretical calculations) methods to scrutinize a variety of possible structural models. We find that a high concentration of particular types of 'coordination defects' in the surface layer is responsible for the observed differences. Resolving the structure of amorphous surfaces is, for example, important for understanding nanoparticles' properties where the surface-to-bulk ratio has a crucial role.

Separation of water‐soluble polymers using capillary‐channeled polymer fiber stationary phases

Chromatographic separations of synthetic and natural polymers are usually affected by a size exclusion chromatography (SEC) mechanism. Although SEC is a proven method of separation based on hydrodynamic size, a chromatographic method based solely on chemical interactions would present certain advantages. This laboratory has been investigating the use of capillary-channeled polymer (C-CP) fibers as stationary phases in HPLC for the separation of biomacromolecules. C-CP fibers allow highly efficient fluid transport and an amorphous surface structure, minimizing mass transfer effects commonly associated with porous, packed-bed technologies. Choice of the base fiber identity allows flexibility in the potential types of solute-surface interactions. Two water-soluble polymers, glycolic acid ethoxylate 4-nonylphenyl ether, and poly(4-vinylpyridine hydrochloride), were used as test solutes because of their similarities to polymers of interest in the consumer products industry. SEC separation of this pair was not possible due to the similarities in hydrodynamic size. Poly(ethylene terephthalate), polyester and nylon-6 C-CP fibers were evaluated as stationary phase materials. The former was found to offer superior chromatographic separations and recoveries when operating under what would be considered to be typical RP separation conditions: a flow rate of 1 mL/min and gradient of 0-100% H(2)O/ACN with 0.06% TFA over 5 min.

The special features of equilibrium adsorption of argon on homogeneous and inhomogeneous surfaces

Comparative patterns of equilibrium adsorption of argon on the surface of graphitized thermal carbon black (GCB) and the inhomogeneous surfaces of nongraphitized carbon black and silica at 77 and 87.3 K were considered. It was shown that argon acquires the properties of a special phase with a layered structure and exhibits two-dimensional phase transitions with the formation of crystal-like layers near the homogeneous surface of GCB even at a temperature exceeding the triple point. However, already at a distance of three-four molecular diameters from the surface, adsorbed argon behaves as a bulk phase in a weak external field. The defect surface of nongraphitized carbon black and the amorphous surface structure of silica destroy the longrange order of adsorbed argon and lower its solidification temperature. Therefore, argon adsorbed at a temperature of 77 K, i.e., below the triple point, exhibits the properties of a supercooled liquid. The applicability of density functional theory to describe argon isotherms and heat of adsorption on inhomogeneous surfaces was demonstrated.

Theoretical study of an amorphous chalcogenide surface

The structure of amorphous surfaces is a challenging frontier yet to be thoroughly explored. Standard surface characterization techniques like STM are difficult to apply to these surfaces. We have studied GeSe2 glass surfaces using first principle methods in a slab geometry. The glass surfaces are obtained by quenching a slab of an equilibrated liquid. We have found that these surfaces are well characterized by the distribution of rings. A detailed study of ring formation and associated properties is presented. We also briefly describe the electronic/optical and vibrational structure of these surfaces.