Truncated Octahedron Structure Research Articles

Electrochemical denitrification by a recyclable cobalt oxide cathode: Rapid recovery and selective catalysis

Cathodic aging and fouling have presented significant challenges in the realm of electrochemical denitrification for engineering applications. This study focused on the development of an economical and recyclable nanoporous Co3O4/Co cathode through anodization for nitrate reduction. What distinguished our cathode was its exceptional sustainability. Cobalt from the inactive catalyst could be reclaimed onto the substrate, enabling the regeneration of a new Co3O4 layer. This innovative approach resulted in an exceptionally low Co catalyst consumption, a mere 1.936 g/1 kg N, making it the most cost-effective choice among all Co-based cathodes. The Co3O4 catalyst exhibited a truncated octahedron structure, primarily composed of surface Co2+ ions. Density functional theory calculations confirmed that the bonding between the O atom in NO3- ions and the Co atom in Co3O4 was thermodynamically favorable, with a free energy of − 0.89 eV. Co2+ ions acted as "electron porters" facilitating electron transfer through a redox circle Co2+–Co3+–Co2+. However, the presence of two energy barriers (*NH2NO to *N2 and *N2 to N2) with respective heights of 0.83 eV and 1.17 eV resulted in a N2 selectivity of 9.84% and an NH3 selectivity of 90.02%. In actual wastewater treatment, approximately 78% of TN and 93% of NO3- were successfully removed after 3 h, consistent with the prediction kinetic model. This anodization-based strategy offers a significant advantage in terms of long-term cost and presents a new paradigm for electrode sustainability.

Lattice origin of few-layer edge-on MoS2@TiO2 octahedral clusters for piezoelectric enhancement

Imaging the lattice origin of few-layer edge-on MoS2/TiO2 heterostructure at different growth stages could provide direct information for understanding the mechanism of its enhanced piezoelectric property. Via modifying the substrate surface to grow anatase TiO2 nanoparticles with truncated octahedron structure, few-layer MoS2 was exquisitely grown along the {101} basal planes of TiO2 by Van der Waals contact, and finally form an edge-on structure at the top edge of TiO2 nanoparticles due to steric hindrance. The vertical growth of few-layer MoS2 on the TiO2 surface endows not only better electronic contact between MoS2 and TiO2 substrate for fast electrons transfer but also high structure stability of piezoelectric properties. The piezocatalytic degradation ability is enhanced with the increase of hydrothermal reaction time, and the MoS2/TiO2-24 h sample exhibits the highest piezocatalytic activity under dark condition which demonstrates a high removal efficiency of 96.0% Rhodamine B within 60 min. This study establishes a relationship between the piezoelectric property of few-layer edge-on MoS2/TiO2 heterostructure and its growth mechanisms, and sheds light on the rational design of electric contact between transition metal dichalcogenide and semiconductor with specific crystal plane which is significant to the improvement of carrier separation and transport.

Synthesis of Cu2O Nanostructures with Tunable Crystal Facets for Electrochemical CO2 Reduction to Alcohols.

Electrochemical CO2 reduction enables the conversion of intermittent renewable energy to value-added chemicals and fuel, presenting a promising strategy to relieve CO2 emission and achieve clean energy storage. In this work, we developed nanosized Cu2O catalysts using the hydrothermal method for electrochemical CO2 reduction to alcohols. Cu2O nanoparticles (NPs) of various morphologies that were enclosed with different crystal facets, named as Cu2O-c (cubic structure with (100) facets), Cu2O-o (octahedron structure with (111) facets), Cu2O-t (truncated octahedron structure with both (100) and (111) facets), and Cu2O-u (urchin-like structure with (100), (220), and (222) facets), were prepared by regulating the content of a polyvinyl pyrrolidone (PVP) template. The electrochemical CO2 reduction performance of the different Cu2O NPs was evaluated in the CO2-saturated 0.5 M KHCO3 electrolyte. The as-synthesized Cu2O nanostructures were capable of reducing CO2 to produce alcohols including methanol, ethanol, and isopropanol. The alcohol selectivity of the different Cu2O NPs followed the order of Cu2O-t < Cu2O-u < Cu2O-c < Cu2O-o (with the total Faradaic efficiencies of alcohol products of 10.7, 25.0, 26.2, and 35.4%). The facet-dependent effects were associated with the varied concentrations of oxygen-vacancy defects, different energy barriers of CO2 reduction, and distinct Cu-O bond lengths over the different crystal facets. The desired Cu2O-o catalyst exhibited good reduction activity with the highest partial current density of 0.51 mA/cm2 for alcohols. The Faradaic efficiencies of alcohol products were 4.9% for methanol, 17.9% for ethanol, and 12.6% for isopropanol. The good electrochemical CO2 reduction performance was also associated with the surface reconstruction of Cu2O, which endowed the catalyst with abundant Cu0 and Cu+ sites for promoted CO2 activation and stabilized CO* adsorption for enhanced C-C coupling. This work will provide a new route for enhancing the alcohol selectivity of nanostructured Cu2O catalysts by crystal facet engineering.

Morphological evolution of spinel disordered LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries by modified solid-state method

The LiNi0.5Mn1.5O4 cathode material with high working voltage is a promising cathode material for next-generation lithium-ion batteries. In this investigation, LiNi0.5Mn1.5O4 materials with different particle sizes and crystal morphologies were synthesized by a modified solid-state method at different temperatures (750, 800, 850, and 900 °C). The evolution panorama of morphology and surface orientation with the temperature change of LiNi0.5Mn1.5O4 cathode materials were studied. The X-ray diffraction and scanning electron microscopy results showed that with the increase of temperature, the particle sizes increased and the crystal growth became more and more complete. Electrochemical tests showed that the material calcined under 850 °C exhibits a truncated octahedral structure and the best electrochemical performance. It delivers a discharge capacity of 124 mA h g−1 at 1 C; even at a high rate of 10 C, a capacity of 90 mA h g−1 can be obtained. The discharge capacity retention of the material is 91.2% after 150 cycles. In addition, the sample prepared by acetate reactant shows excellent electrochemical performance due to the truncated octahedron structure consisted of {111} and {100} surface as well as the appropriate particle size of ~ 1 μm. The {111} surface is conducive to stabilize the material structure, and {100} surface is conducive to the transfer of Li+ ion and electrons. At the same time, it also founded that the appropriate particle size could reduce the electrolyte corrosion of the material and easy for Li+ ion migration. As a result, the material exhibits an improved electrochemical performance.

Effect of gold nanoparticle on stability of the DNA molecule: A study of molecular dynamics simulation

ABSTRACTAn understanding of the mechanism of DNA interactions with gold nanoparticles is useful in today medicine applications. We have performed a molecular dynamics simulation on a B-DNA duplex (CCTCAGGCCTCC) in the vicinity of a gold nanoparticle with a truncated octahedron structure composed of 201 gold atoms (diameter ∼1.8 nm) to investigate gold nanoparticle (GNP) effects on the stability of DNA. During simulation, the nanoparticle is closed to DNA and phosphate groups direct the particles into the major grooves of the DNA molecule. Because of peeling and untwisting states that are occur at end of DNA, the nucleotide base lies flat on the surface of GNP. The configuration entropy is estimated using the covariance matrix of atom-positional fluctuations for different bases. The results show that when a gold nanoparticle has interaction with DNA, entropy increases. The results of conformational energy and the hydrogen bond numbers for DNA indicated that DNA becomes unstable in the vicinity of a gold nanoparticle. The radial distribution function was calculated for water hydrogen–phosphate oxygen pairs. Almost for all nucleotide, the presence of a nanoparticle around DNA caused water molecules to be released from the DNA duplex and cations were close to the DNA.

Preparation and Photochemical Properties of Layered MoS2/Cu2o Heterojunction Nanocomposites

In recent years, environmental problems induced by organic pollutants have become an important problem for our society. Semiconductor photochemical treatment is a potential technology for solving the environmental issues. Therefore, lots of efforts have been devoted to develop high-efficiency visible light assisted semiconductor photocatalysts. Cu2O nanoparticle is a well-known p-type semiconductor with a direct band gap of 2.17eV, which endows it a reasonable alternative for photocatalytic applications [1-3]. However, high recombination rate of the electron-hole pairs excited from Cu2O nanoparticles seriously hinders its practical application. Coupling p-type Cu2O nanoparticles with n-type semiconductor to form a P-N heterojunction for carrier separation and produce appropriate energy level difference for charge transfer from one semiconductor to another is a potential approach to decrease recombination rate for high-efficiency degradation. Graphene-like n-type semiconductor MoS2 multilayered nanoplates are the reasonable alternative due to its tunable bandgap with different layers and large amounts of unsaturated active sites [4-5]. In this work, two-dimensional (2D) MoS2 nanoplates with different multilayer thickness were prepared by liquid exfoliation and gradient centrifugation. Then, the MoS2 nanoplates were utilized to match the energy level of Cu2O nanoparticles to form MoS2/Cu2O nanocomposites, which have been achieved by the method of hydrothermal synthesis. Scanning Electrom Microscope images and X-ray diffraction (XRD) pattern of nanoparticles Cu2O and MoS2/Cu2O nanocomposites are shown in Fig.1. It can be seen that the morphology of Cu2O nanoparticles are truncated octahedron structure and closely attached on MoS2 nanosheets with different thickness, which was obtained at the centrifugation speed of 2000 rpm, 4000 rpm, 6000 rpm and 8000 rpm. The photochemical behaviors of Cu2O nanoparticles and different MoS2/Cu2O nanocomposites are characterized through the degradation behaviors of methyl orange (MO) under visible light irradiation (Fig.2). The experimental results show that the degradation efficiency of MoS2/Cu2O nanocomposites can be improved by optimizing the thickness of MoS2 nanoplates from few layers to bulk. The degradation ratios of MO after 3 h are 57.9%, 61.1%, 92.2%, 95.3%, 93.1%, and correspond respectively to the MoS2/Cu2O nanocomposites in which the MoS2 nanosheets were obtained at the centrifugation speed of 0 rpm, 2000 rpm, 4000 rpm, 6000 rpm and 8000 rpm. The possible reason is that the increasing surface area and bandgap of MoS2 may provide large reaction area and produce appropriate energy level difference, which is beneficial for accelerating the degradation process of methyl orange. In summary, the different MoS2/Cu2O heterojunction nanocomposites were prepared through adjusting the thickness of multilayered MoS2 nanoplates. The results show that the optimized degradation ratio of MO can be greatly improved from 57.9% up to 95.3% after 3h using MoS2/Cu2O nanocomposites in comparison with Cu2O nanoparticles.

Temperature Dependence of the Surface Energy of the Low-index Planes of CaF2, BaF2 and SrF2

The temperature dependence of the surface energy γ of the low-index (111), (110) and (100) planes of CaF2, BaF2 and SrF2 was evaluated for the first time, using a simple method which is based on physical and thermodynamic quantities and considerations. The extrapolated to 0 K surface energy values agree well with the available theoretical data reported in the literature for the (111) plane and are close to those for the (110) plane, whereas they are significantly lower than those for the (100) plane. The calculated γ111 values for 298 K agree well with the corresponding experimentally determined literature values. The calculated γ100/γ111 ratio revealed formation of crystals with truncated octahedron structure in thermodynamic equilibrium. This structure remains practically constant with temperature. The surface energy values of fluoride melts formed by melting of octahedron structures, calculated via extrapolation of the surface energy of the solids to the melting points, were compared with experimentally determined literature values for melts resulting from single or polycrystalline materials.

Temperature Dependence of the Surface Energy of the Low Index Planes of UO2 and ThO2

The temperature dependence of the surface energy γ of the low index (111), (110), and (100) planes of UO2 and ThO2 was calculated for the first time, using a simple method based on physical and thermodynamic quantities and considerations. The extrapolated to 0 K surface energy values agreed well with the available theoretical data reported in literature for the (111) and (110) surfaces, whereas they were significantly lower for the (100) surface. The γ 100/γ 111 ratio for UO2 and ThO2 revealed the formation of crystals with truncated octahedron structure in thermodynamic equilibrium. This structure shifts to octahedral with increasing temperature. Comparison with experimentally determined surface energies of the polycrystalline oxides showed that their values are in the range between γ 111 and γ 100.

Deformation modeling of polyvinylidenedifluoride (PVDF) symmetrical microfiltration hollow-fiber (HF) membrane

The tensile deformation behavior of polyvinylidenedifluoride (PVDF) symmetrical microfiltration hollow-fiber (HF) membranes was studied. The membranes had submicron pores with a three-dimensional open-cell structure. The surface and cross section of the porous membranes were observed by FESEM (field emission scanning electron microscope) to investigate the microstructure of the cell, namely, its size and ligament geometry. During uniaxial tensile tests, the membranes underwent elastic deformation and plastic deformation. Large deformation induced pore growth along the tensile direction, resulting in an increase in water permeability. In order to establish a mechanical model for tensile deformation, the finite element method (FEM) was employed. In this model, the Kelvin polyhedron (truncated octahedron structure) was used to mimic a three-dimensional open-cell structure. A one-unit cell based on this structure was created, and a periodical boundary condition was employed for the FEM computation. The FEM model could reproduce the overall elastoplastic deformation behavior of the porous membrane and provide useful insight into the fabrication of porous membranes and reliable operation of water purification.

Three-dimensional flowerlike iron oxide nanostructures: Morphology, composition and metal ion removal capability

The flower-like precursors of Fe alkoxide constructed by the self-assembly of nanoflakes were prepared. Time-dependent experiments confirmed the formation mechanism of flower-like precursors. After calcination, α-Fe2O3 and Fe3O4 nanostructures with different morphologies were created. Fe3O4 nanostructures containing blocks with a truncated octahedron structure were obtained under N2 protection. α-Fe2O3 nanostructures were prepared in an air atmosphere. The values of maximum adsorption capacity of α-Fe2O3 nanostructures for Cr6+ ions were much higher than that of commercial bulk α-Fe2O3. Ag NPs were deposited on α-Fe2O3 nanostructures through an aqueous synthesis and light irradiation using l-cysteine as a linker. Such procedure is utilizable for the preparation of the composites of noble metals and magnetic materials.

Magnetic field controlled particle-mediated growth inducing icker-like silver architectures

An unusually anisotropic growth or quasi-one-dimension growth of silver architectures can be achieved when an external magnetic field is applied to a simple replacement reaction. The external magnetic field greatly promotes the growth of trunks along 〈111〉 directions but weakens the growth of branches along 〈311〉 directions, resulting in a silver icker-like architectures. The influences of the external magnetic field, solution concentration and reaction time have been investigated in detail. The formation of silver icker-like architectures could be attributed to shape magnetic anisotropy and fast complex micro-magnetohydrodynamic (MHD) convection effects induced by the external magnetic field of the nanoparticles possessing a truncated octahedron structure. Moreover, the magnetic field effect on the crystal growth of nanostructures generally involves the ion-mediated growth process or the aggregations of numerous nanoparticles along the magnetic field directions because of dipolar interactions. Our experiments and discussions, however, indicate that metal crystals are grown through a multistep particle-mediated growth process with the nanoparticles as basic building blocks.

Surface self-diffusion of adatom on Pt cluster with truncated octahedron structure

Surface diffusion of single Pt adatom on Pt cluster with truncated octahedron structure is investigated through a combination of molecular dynamics and nudged elastic band method. Using an embedded atom method to describe the atomic interactions, the minimum energy paths are determined and the energy barriers for adatom diffusion across and along step are evaluated. The diffusion of adatom crossing step edge between {111} and {100} facets has a surprisingly low barrier of 0.03 eV, which is 0.12 eV lower than the barrier for adatom diffusion from {111} to neighboring {111} facet. Owing to the small barrier of adatom diffusion across the step edge between {111} and {100} facets, the diffusion of adatom along the step edge cannot occur. The molecular dynamics simulations at low temperatures also support these results. Our results show that mass transport will prefer step with {100} microfacet and the Pt clusters can have only {111} facets in epitaxial growth.

Atomistic study of metal clusters supported on oxide surface

Metal clusters on oxide surface are a widely studied topic in surface science and technology. In this work, we use the ab initio based pair potentials to study the shape evolution of these clusters with their width from 3 Å to 90 Å. The clusters have a basic polyhedron shape covered by (0 0 1) and (1 1 1) faces, with four undetermined parameters. The main purpose of this work is to determine the structure parameters numerically. Here, we use a combination of energy minimization calculation, least square method and Lagrange multiplier method, and go through a series of metals including Ag, Al, Au, Pd and Rh. As a result, we find that these clusters have a truncated octahedron structure on MgO(0 0 1) surface, with a square contact face for Ag, Al and Au, and an octagon one for Pd and Rh. Also, we see that misfit dislocation appears when the cluster becomes large, first at the edge, then inside the contact area.