Amorphous Surface Research Articles

Supercapacitance Performance of Mesoporous Mono- and Bi-Metallic Cobalt and Nickel Hydroxides Nanoflakes Chemically Deposited from Foam-Surfactant Liquid Crystal Dual Templates

Mesoporous 2D nanoflakes architectures of mono- and bi-metallic cobalt and nickel hydroxide (meso-Co-Ni(OH)2) hybrids were synthesized using novel chemical precipitation of foam-surfactant liquid crystal dual template (FSDT). The dissolved cobalt and nickel ions within the aqueous region of the Brij®78 surfactant template was reduced by the excess of sodium borohydride reducing agent that simultaneously generates excessive hydrogen foam as a double template. The physicochemical characterizations of the mono- and bi-metallic nanostructured Co-Ni(OH)2 hybrids performed using X-ray diffraction, surface area analyzer, scanning and transmission electrons microscopic techniques showed the formation of highly mesoporous hydroxides 2D nanoflakes architectures having an amorphous structure and surface area up to 253.50 m2/g. The electrochemical and supercapacitance evaluation of the mono-, and bi-metallic mesoporous hydroxides showed excellent Faradaic supercapacitance performance within a wider potential window and a higher charge and discharge rate. In particular the mesoporous monometallic of Co(OH)2, Ni(OH)2, bimetallic Co-Ni(OH)2 with Co/Ni ratios of (1:1), and (1:3), hydroxides showed total capacitances of 204, 869, 943, and 1384, F/g at charging current density of 5.0 A g−1 respectively and capacity retention rate of approximately 99.4% after 300 cycles. This suggests that these materials hold promise as electrode materials for energy storage applications.

Characterisation of the morphology of surface-assembled Au nanoclusters on amorphous carbon.

In this study, aberration-corrected scanning transmission electron microscopy is employed to investigate the morphology of Au clusters formed from the aggregation of single atoms sputtered onto an amorphous carbon surface. The morphologies of surface-assembled clusters of N > 100 atoms are referenced against the morphologies of size-selected clusters determined from previously published results. We observe that surface-assembled clusters (at the conditions employed here) are approximately spherical in shape. The structural isomers of the imaged clusters have also been identified, and the distribution of structural types is broadly in agreement with those from size-selected cluster deposition sources. For clusters of approximately 147 atoms, we find a preference for icosahedra over decahedra and truncated octahedra, but at this size there is a high proportion of unidentified/amorphous structures. At around 309 atoms, we find a preference for decahedra over icosahedra and truncated octahedra, but over half the structures remain unidentifiable/amorphous. For sizes above approximately 561 atoms we are able to identify most of the structures, and find decahedra are still the most favoured, although in competition with single-crystal fcc morphologies. The similarity in structure between surface-assembled and size-selected clusters from a cluster source provides evidence of the relevance of size-selected cluster studies to clusters synthesised by other, industrially relevant, methodologies.

Experimental and theoretical evidence for unprecedented strong interactions of gold atoms with boron on boron/sulfur-doped carbon surfaces.

The 16e square-planar bis-thiolato-Au(iii) complexes [AuIII(1,2-dicarba-closo-dodecarborane-1,2-dithiolato)2][NBu4] (Au-1) and [AuIII(4-methyl-1,2-benzenedithiolato)2][NBu4] (Au-2) have been synthesized and fully characterized. Au-1 and Au-2 were encapsulated in the symmetrical triblock copolymer poloxamer (Pluronic®) P123 containing blocks of poly(ethylene oxide) and poly(propylene oxide), giving micelles AuMs-1 and AuMs-2. High electron flux in scanning transmission electron microscopy (STEM) was used to generate single gold atoms and gold nanocrystals on B/S-doped graphitic surfaces, or S-doped amorphous carbon surfaces from AuMs-1 and AuMs-2, respectively. Electron energy loss spectroscopy (EELS) data suggested strong interactions of gold atoms/nanocrystals with boron in the B/S-doped graphitic matrix. Density-functional theory (DFT) calculations, also supported the experimental findings, pointing towards strong Au-B bonds, depending on the charge on the Au-(B-graphene) fragment and the presence of further defects in the graphene lattice.

Enhanced catalytic activity and stability of SOFC electrodes through plasma-driven surface modification

Plasma-induced surface amorphization prevents Sr phase separation, boosting the catalytic activity and stability of SOFC cathode. This finding expands the application of amorphous features to practical electrodes, previously limited to model studies.

Hydrogen irradiation-driven computational surface chemistry of lithium oxide and hydroxide.

We have investigated, using molecular dynamics, the surface chemistry of hydrogen incident on the amorphous and crystalline lithium oxide and lithium hydroxide surfaces upon being slowed down by a collision cascade and retained in the amorphous surface of either Li2O or LiOH. We looked for the bonding of H to the resident structures in the surface to understand a possible chain of chemical reactions that can lead to surface transformation upon H atom impact. Our findings, using Density-Functional Theory (DFT) trained ReaxFF force field/electronegativity equalization method potentials, stress the importance of inclusion of polarization in the dynamics of a Li-O-H system, which is also illustrated by DFT energy minimization and quantum-classical molecular dynamics using tight binding DFT. The resulting polar-covalent chemistry of the studied systems is complex and very sensitive to the instantaneous positions of all atoms as well as the ratio of concentrations of various resident atoms in the surface.

Characteristics of virgin coconut oil (VCO) microencapsulation using O/W emulsification and complex coacervation methods

Virgin coconut oil (VCO) is produced by processing the flesh of coconut (Cocos nucifera L.). It has beneficial health effects due to the medium-chain fatty acids (MCFA), vitamins, and antioxidant contents. Since liquid VCO is not widely accepted by consumers for direct consumption, further processing into powder VCO can be achieved using microencapsulation methods, such as single-layer emulsification (SL), layer-by-layer emulsification (LBL), and complex coacervation (CC). Therefore, the present work aimed to determine the characteristics of microencapsulation of VCO powder by emulsification and coacervation complex methods over 30 days of storage period. Results showed that SL VCO emulsion remained stable for three days of storage, while LBL VCO emulsion experienced syneresis. The particle size of the reconstituted VCO powder was also larger than the fresh emulsion. LBL microcapsule had the highest yield at 74.17%, and there was an increase in moisture content (MC) during 30 days of storage in CC microcapsule. Meanwhile, MC of SL microcapsule was constant, and the equilibrium MC of LBL was retained during 15 days of storage. A microencapsulation efficiency of up to 78.65% was obtained for CC, and the value decreased for all microcapsules during the 30 days of storage. Different oxidative characteristics were also reported, resulting in increased peroxide value of VCO powder. Furthermore, all microcapsules had amorphous and glassy surface morphology, as well as different characteristics and stability during storage.

Co-pyrolysis of orange peel and eggshell for oxygenated rich composite: Process optimization with response surface methodology

Co-pyrolysis of orange peel and chicken eggshell was performed for the synthesis of the composite, a co-pyrolysis technique used to promote natural fabrication and to allow the raw material elemental combination effect and the preparatory conditions such as pyrolysis temperature, residence time, and eggshell/orange peel mixing ratio, to be optimized with the response surface methodology through Box-Behnken Design(BBD). BBD involved a randomized series of 17 experimental runs, and the best optimal conditions were found with a pyrolysis temperature of 300 °C, a residence time of 1 h, and 0.5 as the mixing ratio. These conditions gave a maximum adsorption capacity of 167 mg/g for removal of the modal pollutant methylene blue. FTIR spectra of the composite showed new functional peaks of oxygenated groups, at two different bands. XRD confirmed an amorphous surface with inorganic component peaks, while SEM-EDS revealed rich defects sites along with an enhanced percentage of oxygen elements on the surface; the surface area was enhanced from 1 m2 with unmodified peel to 64 m2 with composite. The adsorption behavior of the composite was studied for dye removal and the adsorption behavior was well explained by the Langmuir isotherm model.

Assessment of magnetic effects on soot characteristics in inverse diffusion ethylene flames

The magnetic effect on soot properties in ethylene inverse diffusion flames (IDF) was investigated in this study. The investigation involved the use of high-resolution transmission electron microscopy analysis (HRTEM), Raman spectroscopy analysis, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction spectroscopy (XRD) to examine the nanostructure and graphitization degree of soot collected from flame exhaust gas at various height above burner surface (HAB) under both magnetic and non-magnetic conditions. Increasing the magnetic flux density resulted in modifications to soot properties. When the sampling height was HAB = 4 cm, increasing magnetic flux density resulted in longer fringe lengths, lower fringe tortuosity, less amorphous carbon content and surface oxygen content for the collected soot from flame exhaust gas. These results indicated higher graphitization degrees, which may be attributed to longer residence time and oxidation of soot particle in flames. Moreover, when the sampling height increased from HAB = 4 cm to 6 cm under non-magnetic condition, the nanostructure of soot in the flame exhaust gas was more organized, possible due to the oxidation of soot at the region between HAB = 4 and 6 cm region. However, with the magnetic field on, the crystalline structure of soot in the flame exhaust gas became increasingly disordered as the sampling height increased. This suggested that the soot may also be affected by the magnetic effects in addition to oxidation at the region between HAB = 4 and 6 cm region. The magnetic effect could trigger the transformation of graphitic carbon to amorphous carbon in soot particles as they passed through the magnetic field. With more elaborated magnetic fields, the magnetic effect on soot could contribute to strategies controlling soot emissions and removal.

The hydrogen activation, migration, and hydrogenation on metal-free TiH2(O)

Hydrogen activation and migration of active hydrogen species are of great significance for the hydrogen-involving reaction and have attracted much attention. Herein, we reported an unexpected result that H2 activation occurred on a TiH2(O) material, which possesses a unique structure with TiH2 in the core and an amorphous TiOxHy surface layer. The TiOxHy surface layer enriched with defects and “TiOO” species account for the intrinsic activity of TiH2(O) for H2 heterolytic cleavage. As a hydrogen-rich material, TiH2(O) acts as a hydrogen reservoir, favoring not only the spillover of active hydrogen species on the surface layer but also their migration into the bulk phase of TiH2. Without the addition of extra active metals, TiH2(O) exhibited excellent catalytic performance in the hydrogenation of biomass-derived vanillin.

Enhancing tribological performance of NiAl–Bi2O3–Cr2O3 composite coating via in-situ grown NiBi compound

To provide a feasible solution for realizing low friction and wear on the surface of moving parts in a wide temperature range, we report a facile strategy to achieve the improved tribological capability of a NiAl–Bi2O3–Cr2O3 composite coating by applying heat treatment. The heat treatment delivers structural densification and compositional homogeneity of the coating while promoting the in-situ generation of a diffusely distributed intermetallic compound of nickel bismuth (NiBi). When performing rotational dry sliding tests against Al2O3 counterpart ball in air, the tribo-induced decomposition of the NiBi compound and the spontaneous interaction between NiBi and its oxidative environment lead to the formation of an amorphous yet deformable oxide surface, which is responsible for exceptional tribological properties in a wide temperature range. Particularly, the tribological performance is improved significantly from room temperature (RT) to 400 °C for the annealed samples compared to the non-annealed ones: The friction coefficient decreases by 23.6 % at RT and 27.9 % at 400 °C, and the wear rate decreases by 51.4 % at RT and 81.2 % at 400 °C. With these findings, we establish a general approach to the improvement of friction-reduction and anti-wear properties in cermet coatings.

Oxide dependent textured crystallization on amorphous alloy surface

Amorphous alloys produced through rapid solidification offer a host of exceptional properties, with the caveat that achieving a fully amorphous structure. In our laboratory, the FeSiBPC alloy has demonstrated substantial industrial potential, but it contends with a persistent challenge in the form of surface crystallization during large-scale manufacturing. This study delves into the phenomenon of surface crystallization, variables influencing surface crystallization and elucidate its distinctive characteristics were studied. A noteworthy breakthrough emerges with the inaugural characterization of a high-quality fiber texture within an Fe-based amorphous alloy, achieved through Electron Backscattered Diffraction. Our findings underscore the remarkable sensitivity of air pressure within the chamber, revealing its significant impact on the intensity of Bragg peaks related to surface crystals. Moreover, the crucial role of an oxide atmosphere in effectively mitigating surface crystallization and offer insights into the mechanisms governing this preventive action. This study provides valuable insights into the intricate interplay of factors governing surface crystallization in amorphous alloys, offering promising avenues for enhanced industrial applications.

Hydrophilic-amorphous versus hydrophobic-crystalline Sb2S3: The battle for higher photocatalytic efficiency

The dependence of crystallinity and hydrophilicity of the material on its photocatalytic activity is rarely explored and understood. In this work, the influence of crystallinity and surface wettability is demonstrated through the photocatalytic activity of Sb2S3 thin films. Amorphous and crystalline thin films of Sb2S3 having bandgaps of 2.36 and 1.89 eV respectively are prepared using thermal evaporation. Photocatalytic activity of both the films are evaluated in the degradation of methylene blue dye under visible light. Amorphous sample degraded 88 % of dye in 180 min of irradiation, with a reaction rate constant of 0.01/min. The crystalline sample removed only 64 % of the dye under the same condition. The analysis of the surface nature of the film using contact angle measurement revealed that, amorphous sample is hydrophilic and crystalline sample hydrophobic with water contact angles of 68° and 92° respectively. The role of surface wettability on photocatalysis is also analysed by modifying the film surface with the help of plasma treatment. The treatment reduced the hydrophilicity of the amorphous surface and at the same time transformed the crystalline surface from hydrophobic to hydrophilic. The change in the surface morphology such as formation of micro/nanostructures and variation in roughness, which contribute to the hydrophobicity is observed through AFM. The surface changes are reflected in the dye degradation efficiencies as well. The dye degradation efficiency reduced to 79 % in the amorphous sample and increased to 72 % in the crystalline sample. The study unveils the exciting efficiency of the hydrophilic, amorphous Sb2S3 films without any thermal or surface treatments as photocatalyst.

Boosting Low Temperature Performance of Lithium Ion Batteries at −40°С Using a Binary Surface Coated Li3V2(PO4)3 Cathode Material

AbstractSevere capacity degradation at low temperatures (<−20°С) hampers wide applications of lithium‐ion batteries (LIBs) in consumer electronics and electric vehicles. Existing works are dedicated to electrolyte modification because that electrolyte controls both Li+ transportation and interfacial reaction. However, the efforts on electrolytes are always hard to balance rate performance and low‐temperature capacity due to their high viscosity. Herein, a binary coating layer for Li3V2(PO4)3 cathode material without changing electrolyte formulation is proposed, which significantly improves the high‐rate capability and low‐temperature performance of batteries. YPO4 nanoparticles are in situ formed in the amorphous surface carbon layer under the reaction between Li3V2(PO4)3 and Y(NO3)3 during post‐thermal treatment. The C+YPO4 binary coating reduces the side reactions of Li3V2(PO4)3 at high voltage. In addition, the binary surface coating also improves the interfacial kinetics of the electrode at low temperatures. Benefiting from these advantages, the Li3V2(PO4)3 cathode material can cycle stably at ultra‐high rates up to 50 C. In addition, the capacity retention at −20 and −40 °С are improved to 89.1% and 75.7%, respectively. This binary surface‐coated Li3V2(PO4)3 cathode material shows promising application potential in low‐temperature LIBs.

Architecting the metal-nonmetal oxide layers for boosting the oxygen-evolving intrinsic activity of amorphous alloy

Designing high-efficiency and freestanding electrocatalysts hold immense importance in addressing the limitations of powdered electrocatalysts and accelerating the sluggish kinetics of the oxygen evolution reaction (OER) in advancing energy technologies. While dealloyed amorphous ribbons have been shown to be active and self-supporting electrocatalysts toward OER, the underlying enhancement mechanism remains unclear. Here, we developed a dealloyed Ni-Fe-B-Si-P amorphous electrocatalysts with a mixed oxide layer (including oxo-anions: phosphate, silicate, and borate). The dealloyed oxide layer optimizes the surface properties and chemical local environment of the amorphous ribbon, then shortens the multistep evolution path (Ni0 → Ni2+ → Ni3+ → Ni4+) toward Ni4+ species during the surface reconstruction process and decreased energy barriers for the dealloyed Ni-Fe-B-Si-P electrocatalyst during OER. Benefiting from the changes, the dealloyed Ni-Fe-B-Si-P enables a 56-fold increase in current density (at overpotential: 320 mV) and an 8-fold increase in turnover frequency values compared to undealloyed Ni-Fe-B-Si-P, demonstrating the major effect of the intrinsic activity on the OER performance of the dealloyed ribbon. This work sheds light on the enhancement mechanism of amorphous bulk electrocatalysts and offers valuable insights into the rational design of amorphous components and surface treatment processes.

Fluorine-doped CoP/Ni2P nanowires for enhanced hydrogen evolution activity

Doping hetero-atoms into non-noble metal phosphides is an important strategy for enhancement of hydrogen evolution reaction (HER) performance. Herein, we prepare a self-supported F-doped CoP/Ni2P nanowire arrays grown on Ni foam by using a strategy with three steps including hydrothermal reaction, fluorination, and low-temperature phosphorization. The F-CoP/Ni2P nanowire consists of a well-defined crystalline core and a thin amorphous surface layer. The F-doping and amorphous surface layers effectively expose a large number of active sites, optimize the electronic configuration of Ni, Co and P on the surface, and promote the electron transport performance. As a result, the prepared F-CoP/Ni2P@NF-II exhibits excellent electrocatalytic activity for HER in alkaline electrolyte with a lower overpotential of 75 mV at 10 mA cm−2, a small Tafel slope of 54.8 mV dec−1, and good durability. This work provides a simple method for developing transition metal phosphate-based catalysts towards hydrogen evolution reaction.

Adsorption of 4-(N,N-Dimethylamino)-4'-nitrostilbene on an Amorphous Silica Glass Surface.

Stilbenes are a compelling class of organic photoswitches with a high degree of tunability that sensitively depend on their environment. In this study, we investigate the adsorption properties of 4-(N,N-dimethylamino)-4'-nitrostilbene (DANS), a push-pull stilbene, on amorphous silica glass. Plane-wave density functional theory (DFT) calculations are used to understand how the trans and cis isomers of DANS interact with the amorphous surface and which are the most preferred modes of adsorption. Our calculations revealed that the O-H···O hydrogen bonds between the nitro group and hydroxyl groups of the silica surface dominate the intramolecular interaction. In addition to hydrogen bonding, O-H···π interactions with the aromatic ring and double bond play a critical role in adsorption, whereas C-H···O interactions are present, but contribute little. Therefore, both isomers of DANS favor parallel orientations such that not only the functional groups but also the aromatic parts can strongly interact with the glass surface.

Generation of Amorphous Silica Surfaces with Controlled Roughness.

Amorphous silica (a-SiO2) surfaces, when grafted with select metals on the active sites of the functionalized surfaces, can act as useful heterogeneous catalysts. From a molecular modeling perspective, one challenge has been generating a-SiO2 slab models with controllable surface roughness to facilitate the study of the effect of surface morphology on the material properties. Previous computational methods either generate relatively flat surfaces or periodically corrugated surfaces that do not mimic the full range of potential surface roughness of the amorphous silica material. In this work, we present a new method, inspired by the capillary fluctuation theory of interfaces, in which rough silica slabs are generated by cleaving a bulk amorphous sample using a cleaving plane with Fourier components randomly generated from a Gaussian distribution. The width of this Gaussian distribution (and thus the degree of surface roughness) can be tuned by varying the surface roughness parameter α. Using the van Beest, Kramer, and van Santen (BKS) force field, we create a large number of silica slabs using cleaving surfaces of varying roughness (α) and using two different system sizes. These surfaces are then characterized to determine their roughness (mean-squared displacement), density profile, and ring size distribution. This analysis shows a higher concentration of surface defects (under-/overcoordinated atoms and strained rings) as the surface roughness increases. To examine the effect of the roughness on surface reactivity, we re-equilibriate a subset of these slabs using the reactive force field ReaxFF and then expose the slabs to water and observe the formation of surface silanols. We observe that the rougher surfaces exhibit higher silanol concentrations as well as bimodal acidity.

Mechanisms of Zn removal from water by amorphous geopolymer: Molecular-level insights from X-ray absorption spectroscopy, isotope fractionation, and surface complexation modeling

Porous geopolymers have attracted widespread attention as promising heavy metal adsorbents that can be synthesized from aluminosilicate solid wastes. However, the precise microstructural evidence for adsorbed heavy metals on geopolymers remains unclear due to the insensitivity of conventional characterization techniques on minerals with amorphous structure and surface disorder. Batch adsorption and column experiments coupled with X-ray absorption spectroscopy (XAS), Zn stable isotope, and surface complexation model (SCM) were employed to reveal the Zn removal mechanisms with coal fly ash porous geopolymer (CFAPG) at a molecular scale. The macroscopic kinetic and isothermal adsorption of Zn on CFAPG were well described by the pseudo-second-order model and Bi_Langmuir equation, respectively, indicating the presence of abundant heterogeneous active sites on the CFAPG surface. Two types of active sites on the CFAPG surface were identified by XAS coupled with Zn isotopes in batch experiments at pH ≤ 6.0: one is pH-dependent and associated with tetrahedral zinc coordination, and the other is pH-insensitive and associated with octahedral zinc coordination; these sites were confirmed by the bidentate SCM as the variable charge site (surface complexation, >S-OH) and the permanent negative charge site (cation exchange, >X–), respectively. Furthermore, the important contribution of surface co-precipitation besides surface complexation and cation exchange to the Zn adsorption on CFAPG was identified by XAS coupled with SCM in a flow-through column experiment at pH >6.0. These investigations provide a systemic understanding of the Zn adsorption mechanisms on CFAPG and an SCM reference for the application and prediction of geopolymers in heavy metal-contaminated water remediations.

Experimental investigation and molecular simulation on the chemical bonding between laser-treated titanium alloy amorphous surface and epoxy adhesive

ABSTRACT Laser surface modification is employed to enhance the interfacial bonding performance of metal-adhesive structures, and chemical bonding plays a crucial role in achieving strong interfacial adhesion. Understanding the mechanism of interfacial chemical bonding between laser-treated metal surface and adhesive at the molecular/atomic scale is key to further optimizing the interfacial bonding performance. In this study, the morphology and chemical composition of laser-induced amorphous titanium oxide on titanium alloy surfaces, as well as its enhanced effect on interfacial bonding performance, were characterized using scanning electron microscopy, energy dispersive spectroscopy, and single lap-shear testing.Through X – ray photoelectron spectroscopy analysis, experimental evidence is provided for the formation of Ti-O-C chemical bonds between the amorphous titanium oxide and adhesive. Transmission electron microscopy observations and molecular dynamics simulations reveal that the strong non-bonding intereactions between amorphous titanium oxide and adhesive enables the adhesive molecules to fully infiltrate the amorphous titanium oxide, providing more sites for chemical bond formation. Density functional theory calculations demonstrate that Ti-O-C chemical bonds tend to form between the dissociated hydroxyl group of the adhesive and titanium oxide, facilitated by a relatively low reaction barrier. This chemical bonding promote the formation of a strong bonding structure at the adhesive interface.

Effective multi-stage biodegradation of commercial bulk polyurethane by Clonostachys and Purpureocillium spp

Dealing with plastic waste in an environmentally friendly and effective manner has been a conundrum that much research has attempted to address. An attractive approach is biodegradation by microorganisms; however microorganisms that have shown such potential are generally only able to degrade surface layers of polymer materials. Herein we describe the multi-stage degradation of commercial bulk polyurethane by two strains of fungi isolated from a landfill. Moreover, we demonstrate that the mechanisms of degradation are not hydrolysis alone as is usually reported, but decarboxylation as well. The data presented here suggest that chain scission at urethane groups involves hydrolysis and decarboxylation of the terminal functional groups and the release of CO2. Two strains, Clonostachys sp. PB54 and Purpureocillium sp. PB57 were both able to decrease the mass of commercial bulk polyurethane by 40 % after 90 days. Spectroscopic analysis revealed the breakage of urethane and ester linkages but also detected variations in hydrogen bonding over time, indicating initial degradation of amorphous surface regions followed by destabilization of more ordered, crystalline layers. Subsequent Liquid Chromatography Mass Spectrometry (LCMS) analysis demonstrated that the fungi were capable of liberating monomer-equivalent molecules (4,4′-methylenedianiline) from the bulk material. In this work, these fungi are shown to be capable of significantly degrading commercial bulk polyurethane in a short period of time, producing small organic molecules and CO2, and as such, are good prospects for the development of large-scale plastic biodegradation processing.