Rhombic Structure Research Articles

Evaluation of phosphate removal from aqueous solution using metal organic framework; isotherm, kinetic and thermodynamic study.

Phosphate (PO4 3-) is the main etiological factor of eutrophication in surface waters. Metal organic frameworks (MOFs) are novel hybrid materials with amazing structural properties that make them a prominent material for adsorption. Zeolitic imidazolate framework 67 (ZIF-67), a water stable member of MOFs, with a truncated rhombic dodecahedron crystalline structure was synthesized in aqueous environment at room temperature and then characterized using XRD and SEM. PO4 3- adsorption from synthetic solutions using ZIF-67 in batch mode were evaluated and a polynomial model (R2: 0.99, R2 adj: 0.98, LOF: 0.1433) developed using response surface methodology (RSM). The highest PO4 3- removal (99.2%) after model optimization obtained when ZIF-67 dose, pH and mixing time adjusted to 6.82, 832.4mg/L and 39.95min, respectively. The optimum PO4 3- concentration in which highest PO4 3- removal and lowest adsorbent utilization occurs, observed at 30mg/L. PO4 3- removal eclipsed significantly in the presence of carbonate. The equilibrium and kinetic models showed that PO4 3- adsorbed in monolayer (qmax: 92.43mg/g) and the sorption process controlled in the sorption stage. Adsorption was also more favorable at higher PO4 3- concentration, according to the separation factor (KR) graph. Thermodynamic parameters (minus signs of ∆G°, ∆H° of 0.179 KJ/mol and ∆S° of 44.91 KJ/mol.K) demonstrate the spontaneous, endothermic and physisorption nature of the process. High adsorption capacity and adsorption rates, make ZIF-67 a promising adsorbent for PO4 3- removal from aqueous environment.

Experimental investigation of rhombic dodecahedron micro-lattice structures manufactured by Electron Beam Melting

The aim of this scientific work is the analysis of rhombic dodecahedron micro-lattice structures under quasi-static and dynamic loading. The effect of unit cell size and strut diameter on mechanical properties was also considered. The specimens were designed by means of Materialise Magics® software and produced using Ti6Al4V ELI metal powder by Arcam Q10 electron beam melting (EBM) 3D printer, with the scientific collaboration of Mt Ortho Srl. The microstructure effect on the mechanical properties was analysed by optical and electron microscopy and Computed Tomography was used to analyse the morphology of unit cells. The experimental results show that these porous structures are very suitable for building custom-made implants in the field of orthopaedics and reconstructive neurosurgery. Moreover, by means of EBM additive manufacturing complex geometries, which are difficult to produce by conventional technologies, can be designed and produced.

Preparation of Ag@zeolitic imidazolate framework-67 at room temperature for electrochemical sensing of hydrogen peroxide.

In this work, a novel non-enzymatic hydrogen peroxide sensor, Ag@zeolitic imidazolate framework-67 (Ag@ZIF-67)/glassy carbon electrode (GCE), was fabricated by a simple method at room temperature. The morphology and structure of Ag@ZIF-67 were investigated by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, atomic absorption spectrophotometry, and N2 absorption isotherms, which indicated that core-shell Ag@ZIF-67 was successfully synthesized with a porous rhombic dodecahedron structure. Electrochemical investigations demonstrated that the Ag@ZIF-67/GCE had strong electrocatalytic activity towards hydrogen peroxide reduction with a low detection limit of 1.5 μM (S/N = 3), a fast response time of 3 s, and three different linear relationships in the ranges of 5.0 μM-275 μM, 775 μM-2775 μM, and 4775 μM-16 775 μM with sensitivities of 27 μA mM-1 cm-2, 13 μA mM-1 cm-2, and 5.3 μA mM-1 cm-2, respectively. Moreover, the fabricated sensor exhibited an excellent recovery rate in real sample analysis of medical hydrogen peroxide disinfectant. These results proved that Ag@ZIF-67/GCE is an effective electrochemical sensor for detecting hydrogen peroxide.

Comprehensive Survey of the Structures of C4, C4−, and C4+ Clusters

AbstractHistoric debates on the true structure of C4 cluster based on the experimental results of EPR, infrared spectroscopy and Coulomb explosion, as well as theoretical calculations have prompted us to comprehensively survey the geometries of C4 clusters. A total of 37 possible geometries for neutral C4, 24 C4 anions (C4−) and 27 C4 cations (C4+) have been optimized with both MP2 and density functional theory (B3LYP) calculations and verified with subsequent frequency calculations. The results align very well with all experimental observations, including the detection of rhombic C4 structure in Coulomb explosion experiment and the cis‐bent structure, in addition to the most stable linear geometries for C4 and C4−, and the electron affinity and ionization potential of C4.

Additively Manufactured CP-Ti (Grade 2) Single Strut SizeEffect of Mechanical Response Under Building Direction

The open cell structure is commonly used in the medical device industry and consists of small struts connected to each other. Relatively new additive manufacturing technique “SLS” has been used in this study. This approach allows to create a sufficiently small specimens to represent each strut in a commercially available orthopaedic porous structure. Pure titanium Grade 2 (CP-Ti grade 2) powder has been used during the experiments because of higher resistance to corrosion and it is one of the most biocompatible metal. The mechanical response of each strut affects the general behaviour of the porous system which influences stress shielding and bone attachment. In this study, small strut size effect and building direction of mechanical response have been investigated in order to provide vital data for upcoming rhombic dodecahedron structure FEM research

Predicting grain boundary structure and energy in BCC metals by integrated atomistic and phase-field modeling

We predict structure and energy of low-angle (11¯0) pure twist grain boundaries (GBs) in five BCC transition metals (β-titanium, molybdenum, niobium, tungsten, and tantalum) using a combination of atomistic and microscopic phase-field (MPF) modeling. The MPF model takes as inputs solely the generalized stacking fault energy surfaces (i.e., the γ-surface) and elastic constants obtained from the atomistic simulations. Being an energy-based method, the MPF model lifts the degeneracy of the geometric models in predicting GB structures. For example, the multiple indefinite solutions offered by the Frank-Bilby equation are shown to converge to exactly the same equilibrium structure. It predicts a transition of the equilibrium GB structure from a pure screw hexagonal network (Mo and W) to mixed hexagonal networks (Nb and Ta) to a rhombus network (β-Ti) of dislocations. Parametric simulation studies and detailed analyses of the underlying dislocation reactions that are responsible for the formation of the rhombus and hexagonal structures reveal a close correlation between material properties (including the elastic anisotropic ratio and the local curvature on the γ-surface) and the GB structure and energy in BCC metals. This integrated approach allows one to explore, through high throughput calculations, the potential to tailor the structure and energy of special GBs in BCC metals by alloying.

Fabrication of ZIF-8 based on lignin with high yield for dye removal from water

The hybrid nanocomposites ZIF@L composed of Zn-based MOFs (ZIF-8) and lignin were successfully synthesized via a simple one-step method at room temperature. The yield of the hybrid nanocomposites ZIF@L were up to 52% and the synthesis time was greatly shortened. Characterization using FT-IR, XRD, SEM and N2-sorption analysis indicated that ZIF@L composites exhibited rhombic dodecahedral structure such as the parent ZIF-8 synthesized in the absence of lignin and the incorporation of lignin did not destroy the framework integrity of ZIF-8. The ZIF@L composites were used to remove methyl violet (MV). The ZIF@L nanocomposites had a remarkable improvement in adsorption capacity of MV compared with the parent ZIF-8. The modified Langmuir model fitted better the equilibrium data of MV adsorption on the ZIF@L-4 composite and the maximum adsorption capacity of MV is 1001.2 mg g−1. The pseudo-second-order model could describe well the kinetics process of MV dye onto the prepared adsorbents.

Why different water models predict different structures under 2D confinement.

Experiments of nanoconfined water between graphene sheets at high pressure suggest that it forms a square ice structure (Algara-Siller et al., Nature, 2015, 519, 443). Molecular dynamics (MD) simulations have been used to attempt to recreate this structure, but there have been discrepancies in the structure formed by the confined water depending on the simulation set-up that was employed and particularly on the choice of water model. Here, using classical molecular dynamics simulations, we have systematically investigated the effect that three different water models (SPC/E, TIP4P/2005 and TIP5P) have on the structure of water confined between two rigid graphene sheets with a 0.9 nm separation. We show that the TIP4P/2005 and the TIP5P water models form a hexagonal AA-stacked structure, whereas the SPC/E model forms a rhombic AB-stacked structure. Our work demonstrates that the formation of these structures is driven by differences in the strength of hydrogen bonds predicted by the three water models, and that the nature of the graphene/water interaction only mildly affects the phase diagram. Considering the available experimental data and first-principle simulations we conclude that, among the models tested, the TIP4P/2005 and TIP5P force fields are for now the most reliable when simulating water under confinement. © 2018 Wiley Periodicals, Inc.

A Plesiohedral Cellular Network of Graphene Bubbles for Ultralight, Strong, and Superelastic Materials.

Advanced materials with low density and high strength impose transformative impacts in the construction, aerospace, and automobile industries. These materials can be realized by assembling well-designed modular building units (BUs) into interconnected structures. This study uses a hierarchical design strategy to demonstrate a new class of carbon-based, ultralight, strong, and even superelastic closed-cellular network structures. Here, the BUs are prepared by a multiscale design approach starting from the controlled synthesis of functionalized graphene oxide nanosheets at the molecular- and nanoscale, leading to the microfluidic fabrication of spherical solid-shelled bubbles at the microscale. Then, bubbles are strategically assembled into centimeter-scale 3D structures. Subsequently, these structures are transformed into self-interconnected and structurally reinforced closed-cellular network structures with plesiohedral cellular units through post-treatment, resulting in the generation of 3D graphene lattices with rhombic dodecahedral honeycomb structure at the centimeter-scale. The 3D graphene suprastructure concurrently exhibits the Young's modulus above 300 kPa while retaining a light density of 7.7 mg cm-3 and sustaining the elasticity against up to 87% of the compressive strain benefiting from efficient stress dissipation through the complete space-filling closed-cellular network. The method of fabricating the 3D graphene closed-cellular structure opens a new pathway for designing lightweight, strong, and superelastic materials.

Tri- and Tetranuclear Copper Hydride Complexes Supported by Tetradentate Phosphine Ligands.

Three types of tetradentate phosphine ligands with different central methylene chains and configurations, meso- and rac-Ph2PCH2P(Ph)(CH2) nP(Ph)CH2PPh2 ( n = 2, meso- and rac-dpmppe; n = 3, meso-dpmppp) were utilized to synthesize a new series of tri- and tetranuclear copper hydride complexes. Reactions of meso-dpmppe or meso-dpmppp with CuCl/NH4PF6 or [Cu(CH3CN)4]PF6 in the presence of NaBH4 afforded trinuclear copper hydride complexes, [Cu3(μ3-H)( meso-dpmppe)2](PF6)2 (1) and [Cu3(μ3-H)( meso-dpmppp)2](PF6)2 (2), while a similar reaction with rac-dpmppe resulted in the formation of a tetranuclear copper dihydride complex, [Cu4(μ3-H)2( rac-dpmppe)2](PF6)2 (5). Complexes 1 and 5 further reacted with RNC (R = tBu, Cy, Xyl) to give [Cu3(μ3-H)( meso-dpmppe)2(XylNC)](PF6)2 (3), [Cu4(μ3-H)2( meso-dpmppe)2(RNC)2](PF6)2 (R = tBu (4a), Cy (4b)) and [Cu4(μ3-H)2( rac-dpmppe)2(RNC)2](PF6)2 (R = tBu (6a), Cy (6b), Xyl (6c)), respectively. Complexes 1-6 were characterized by ESI-MS and 1H and 31P NMR spectroscopy and X-ray diffraction analyses, demonstrating that a hydride ligand is located at the center of triangular Cu3 plane of 1-3, while two μ3-hydride-capped Cu3 planes are fused to result in rhombic Cu4H2 structures in 4a,b, 5, and 6a-c. Complexes 1-6 in CD3CN solutions notably showed high thermal stability and no reactivity toward H2O and CO2. DFT calculations indicated an interesting correlation between the Wiberg bond indices (WBI) of Cu-H bonds and their natural atomic charge (NAC), where the isocyanide ligands had an appreciable influence on the Cu-H interactions.

Metal–organic framework derived cobalt phosphosulfide with ultrahigh microwave absorption properties

Nanostructure composites of ferromagnetic materials embedded in nanoporous carbon (NC) derived from metal–organic frameworks (MOFs) have attracted enormous attention due to their potential application in many fields, such as microwave absorption, energy storage, and conversion. The rational design of nanocomposites holds a determinant factor for overcoming the challenges involving the microwave absorption performance. Herein, CoS2/NC, CoP/NC, and CoS2−xPx/NC with a rhombic dodecahedral structure have been successfully fabricated by using the template cobalt-based MOFs (ZIF-67). A morphology analysis indicates that ferromagnetic nanoparticles are embedded in NC matrix. It is obvious that the rhombic dodecahedron can be maintained after the phosphorization and sulfurization of Co/NC derived from the thermal decomposition of ZIF-67. The microwave absorption performance can obviously be improved by the phosphorization and sulfurization of Co/NC. CoS2−xPx/NC exhibits an excellent microwave absorption property and the minimum reflection loss (RL) of CoS2−xPx/NC can reach −68 dB at 14.6 GHz with a thickness of 1.5 mm. An RL value less than −10 dB can be achieved in the microwave frequency range of 12.7–17.3 GHz (4.6 GHz) with a thickness of 1.5 mm for CoS2−xPx/NC. This article offers a novel way to fabricate cobalt-based materials/carbon composites for an excellent microwave absorber.

Super adsorption capability of rhombic dodecahedral Ca-Al layered double oxides for Congo red removal

In this work, a novel rhombic dodecahedral structure of Ca-Al-layered double hydroxides (Ca-Al-LDHs) was synthesized by a two-phase solvothermal method. Subsequently, Ca-Al layered double oxides (Ca-Al-LDOs) were obtained by calcinating Ca-Al-LDHs at 600 °C which maintained the rhombic dodecahedral structures well. The morphologies of as-obtained samples were characterized by both transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The phase structure and elemental composition were analyzed by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), respectively. Fourier transformed infrared (FT-IR) spectra were performed to confirm the existence of LDH structures. The Ca-Al-LDOs exhibited high adsorption rates and superb adsorption capacities for removal of Congo red (CR) from aqueous solution. The maximum adsorption capacities of Ca-Al-LDOs towards CR reached to 1536.1 mg g−1, which is extremely higher than most of hydrotalcite-like materials. The adsorption process of Ca-Al-LDHs and Ca-Al-LDOs were described by the Langmuir isotherm model and pseudo-second-order model well. The adsorption mechanisms mainly dominated by electrostatic adsorption, ion exchange process, hydrogen bonding interactions and surface complexation. This general strategy afforded a wide possibility to prepare a novel and advanced LDOs adsorption material for water treatment.

Self-Assembly of Two Unit Cells into a Nanodomain Structure Containing Five-Fold Symmetry.

Five-fold symmetry was forbidden for the periodic crystals until the discovery of the Al-Mn icosahedral quasicrystal. We report a kind of precipitated rod-shaped nanophase containing five-fold symmetry but not belonging to any crystals or quasicrystals discovered so far. These metastable nanodomain phases, which precipitated in Mg-6Zn alloy during isothermal aging at 200 °C, contain two separate unit cells in the 2D plane perpendicular to the five-fold axis but with periodic atom arrangement along the five-fold axis, that is, 72° rhombus structure and 72° equilateral hexagon structure. The self-assembly of two unit cells under some geometrical constraints into a nanodomain contains the 2D five-fold, C14, and C15 structures. This finding confirms the existence of solid matters in a special structure between the crystals and quasicrystals, and it is expected to provide a way to understand the atomic arrangement and stacking behavior in condensed matters.

Behavioral and Modal Analysis of Graphene-Based Polygonal Optical Antenna for Enhanced Bio-molecular Detection

Graphene-based polygonal optical antenna is designed and analyzed for enhanced bio-molecular detection. Absorption cross section and electric field enhancement factors of three polygonal structures are compared. The hexagonal structure has exhibited 50% better absorption cross section as compared to that of other structures. Variation of electric field enhancement with frequency is studied and observed on the basis of mode theory. The hexagonal structure has shown an increment in electric field enhancement by 16.60 and 24.11% in contrast to the circular and rhombic structures respectively. Approximation of the hexagonal antenna structure using lumped equivalent circuit is done for better intuition. The vitality of the hexagonal optical antenna for bio-molecular detection is discussed with the aid of chemical potential tuning.

Mechanical properties of an improved 3D-printed rhombic dodecahedron stainless steel lattice structure of variable cross section

A new modified rhombic dodecahedron lattice structure is proposed by redefining the cross section of the struts of the original one with a shape parameter, and the detailed design method of the proposed lattice structure is also provided. For verification, some representative configurations of the proposed lattice structure were 3D-printed via Selective Laser Melting (SLM) with the material 316 L stainless steel. Quasi-static compression test of the fabricated samples was conducted. Finite element model was also established to investigate the mechanical properties of all the as-designed configurations. Finite element results are in good agreement with the experiment results. Compared with the original lattice structure, the proposed one exhibited better mechanical properties and energy absorption. In addition, the effects of the shape parameter on the deformation mode and the mechanical properties of the rhombic dodecahedron (RD) lattice structures were also discussed, while an optimal shape parameter of the proposed RD lattice structure is obtained.

Templating Colloidal Crystal Growth Using Chirped Surface Relief Gratings.

We report a method for controlling the lattice geometry of monodisperse colloidal crystals formed by confined convective self-assembly on a substrate patterned with a chirped surface relief grating. Chirped gratings were fabricated using laser interference lithography and a curved mirror reflector to create photoresist patterns with pitch values ranging from ∼500 to >10 000 nm spread over a planar surface. These surface nanostructures are shown to guide the formation of various lattice geometries not normally found via colloidal assembly on planar surfaces. It is shown that when the pitch of the grating is much larger than the diameter of the colloidal particles, the grating trenches serve as compartments for deposition and the particles form close-packed, linear chains. Various ordered structures are observed as the dimensions of the grating pitch decrease and approach the diameter of the particles. The grating nanostructures guide the formation of various lattice geometries due to specific particle-surface and particle-particle interactions. Observed crystal lattices include square, hexagonal, and rhombic structures. The formation of these structures is explained in terms of the geometrical constraints imposed by the surface pattern and the particle diameter. These crystal lattices can be translated into large area samples when using corresponding single-pitch grating substrates. The initial monolayer lattice can also serve as a template for the growth of unique, bilayer structures that include rectangular lattices, chains of particle pairs or triplets, and graphitelike structured lattices. In addition, when coated with a thin silver layer, these various lattice configurations are shown to produce optical reflection features that are precisely controlled by the underlying structure as it varies from widely spaced particle chains to close-packed lattice geometries.

Structural evolution and bonding properties of Au2Sin-/0 (n = 1-7) clusters: Anion photoelectron spectroscopy and theoretical calculations.

The photoelectron spectra of Au2Sin- (n = 1-7) clusters were measured, and the structural evolution and bonding properties of Au2Si1-7- anions and their corresponding neutral counterparts were investigated by theoretical calculations. The two Au atoms in Au2Si1-7-/0 prefer to occupy low coordinate sites and form fewer Au-Si bonds. The aurophilic interaction is fairly weak in these clusters. The most stable structures of both Au2Sin- anions and Au2Sin neutrals can be described as the two Au atoms interacting with the Sin frameworks. The most stable isomers of Au2Sin- anions are in spin doublet states, while those of the neutral clusters are in spin singlet states. The lowest-lying isomers of Au2Si1-/0 have C2v symmetric V-shaped structures. The global minimum of the Au2Si2- anion has a D2h symmetric planar rhombus structure, while that of the Au2Si2 neutral adopts a C2v symmetric dibridged structure. In Au2Si3-/0, the two Au atoms independently interact with the different Si-Si bonds of the Si3 triangular structure. The global minima of Au2Si4-7-/0 primarily adopt prismatic based geometries. Interestingly, Au2Si6-/0 have significant 3D aromaticity and possess σ plus π double bonding characters, which play important roles in their structural stability.

Elastic properties of rhombic mesh structures based on computational homogenisation

Flat mesh structures are used in a wide variety of applications. In particular, meshes with a rhombic unit cell are frequently employed due to their simplicity and relative ease of manufacture. This paper studies the in-plane elastic properties of such a structure as a function of the geometrical parameters by means of homogenisation techniques. We compare predicted elastic in-plane properties (i) including only bending mode of the struts, cf. Gibson-Ashby model, (ii) including both bending and stretching modes of the struts, obtained by homogenisation using beam elements and (iii) by homogenisation using beam-spring elements accounting additionally for strut joint deformation, and (iv) numerical results of elastic properties obtained by homogenisation using solid elements. The expressions of the predicted elastic properties are presented in analytical form. The homogenised elastic properties accounting for both bending and stretching matches very well with those from the model including only bending. The axial deformation of struts thus has negligible impact on the overall elastic behaviour. The complex deformation in the strut joint was also captured in the homogenised using beam-spring elements, and the results agree better with the solid element results. It is concluded that a finite-element-based homogenisation approach could serve as a straightforward analytical method to obtain elastic properties of mesh structures. This approach automatically includes all deformation mechanisms as opposed to the classical unit cell analyses of bending beams.

Simultaneous formation of trimetallic Pt-Ni-Cu excavated rhombic dodecahedrons with enhanced catalytic performance for the methanol oxidation reaction

Multimetallic Pt-based alloys with excavated structures have attracted great interest owing to their compositional and morphological tunability, high specific surface areas, and impressive electro-catalytic activities. Herein, we report the first facile one-pot synthesis of trimetallic Pt-Ni-Cu highly excavated rhombic dodecahedrons (ERDs) with a yield approaching 100%. More importantly, these highly uniform nanocrystals have three-dimensionally accessible excavated surfaces, where abundant stepped atoms are observed. Benefiting from the highly excavated rhombic dodecahedral structures, electronic and synergistic effects within the trimetallic alloy, and abundant stepped atoms, the as-prepared trimetallic Pt-Ni-Cu ERDs exhibit an enhanced electro-catalytic performance for the electro-oxidation of methanol compared to commercial Pt/C and bimetallic Pt-Cu ERDs and Pt-Ni-Cu solid rhombic dodecahedrons solid rhombic dodecahedrons (SRDs).

Electrical Properties of GeTe-based Ternary Alloys

Ge50-xSb x Te50 and Ge50-xBi x Te50 ternary alloys were synthesized by vacuum melting at 1273 K with the starting materials of Ge, Bi, Sb, and Te. The lattice structures were analyzed based on X-ray diffraction patterns, which could all be indexed to R3m rhombic structure. Electrical properties measurements revealed that the Ge-Sb-Te ternary alloys were p-type semiconductors with high electrical conductivity of 4.5×105 S∙m-1 near room temperature. And the maximum electrical property was obtained at Ge45Sb5Te50, with the power factor of 2.49×10-3 W∙m-1K-2 at 640 K. Due to the existence of secondary phases, the electrical conductivity of Ge-Bi-Te system was lower and Seebeck coefficient was higher comparing with those of Ge-Sb-Te system.