Decahedral Particles Research Articles

An oxidoreductase enzyme, fungal laccase immobilized on zeolitic imidazolate frameworks for the biocatalytic degradation of an endocrine-disrupting chemical, dimethyl phthalate

This study investigated a facile one-pot synthesis procedure of zeolitic imidazolate frameworks (ZIF) and laccase immobilization for use in the biodegradation of an endocrine-disrupting chemical (EDC), dimethyl phthalate (DMP). The as-synthesized Lac-ZIF’s characterization results revealed preserved crystallinity of the ZIF particles and lightly enzyme-coated decahedral particles. The immobilized laccase demonstrated enhanced temperature and storage stabilities for up to 65 ℃ and 20 d, respectively, for the DMP removal. While a reduced maximum velocity (Vmax) after the laccase immobilization (0.651–0.238 mg L−1 h−1) was observed, the Lac-ZIF presented a higher DMP removal efficiency (90.1%) compared to the free laccase (53.2%) within 4 h of contact time. Additionally, after 5 cycles of reuse, the Lac-ZIF retained a remarkable 95.2% efficiency and improved effectiveness in DMP decontamination from river water samples than the free laccase. Furthermore, the resulting DMP degradation metabolites were studied and revealed the production of relatively less toxic compounds after probable complete microbial mineralization. The study, therefore, demonstrates that Lac-ZIF has an admirable performance in the effective removal of phthalates from wastewater, making it a promising candidate for environmental remediation.

Investigating negative thermal expansion property of decahedral Sc2Mo3O12 prepared via hydrothermal method

Orthorhombic Sc2Mo3O12 with decahedral structure have been prepared via hydrothermal method. The phase evolution, morphology and negative thermal expansion (NTE) behavior of the decahedral Sc2Mo3O12 were investigated using XRD, SEM, TMA and high-temperature XRD. XRD and SEM analyses indicate that orthorhombic Sc2Mo3O12 particles with decahedral structure were obtained after annealing at 800 °C. The decahedral Sc2Mo3O12 particles are uniform and regular with a size of about 20 μm × 20 μm × 5 μm. Decahedral Sc2Mo3O12 shows stable NTE. TMA analysis shows the coefficient of thermal expansion (CTE) of decahedral Sc2Mo3O12 is −4.12 × 10−6 K−1 in 25–700 °C. High-temperature XRD analysis reveals that it displays anisotropic NTE at the same temperature range. The axial CTEs of decahedral Sc2Mo3O12 are αa = −4.37 × 10−6 K−1, αb = 3.61 × 10−6 K−1 and αc = −2.96 × 10−6 K−1, respectively. The linear CTE is −1.22 × 10−6 K−1.

Formation of a pore as stress relaxation mechanism in decahedral small particles

A theoretical model of mechanical stress relaxation in decahedral particles by the formation of a central spherical pore is suggested and analyzed within an energy approach. The strain energy of a hollow decahedral particle is found in a closed analytical form. It is shown that there is a critical radius of a decahedral particle below which the formation of a central pore is not energetically favorable, while above which it is. The optimal radius of the pore increases with growth of the particle. Theoretical results are verified with available experimental data on observation of hollow decahedral particles.

Does Symmetry Control Photocatalytic Activity of Titania-Based Photocatalysts?

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance.

Enhanced photocatalytic activity of accordion-like layered Ti3C2 (MXene) coupled with Fe-modified decahedral anatase particles exposing {1 0 1} and {0 0 1} facets

New composites consisting of decahedral anatase particles exposing {001} and {101} facets coupled with accordion-like layered Ti3C2 with boosted photocatalytic activity towards phenol and carbamazepine degradation were investigated. The photocatalysts were characterized with X-ray diffraction (XRD), diffuse reflectance spectroscopy (DR/UV–Vis), Brunauer-Emmett-Teller (BET) specific surface area, Raman spectroscopy, scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) spectroscopy, emission spectroscopy, luminescence decay analysis, electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and electrophoretic mobility measurements. The effect of hydrothermal reaction parameters on physicochemical, structural, and photocatalytic properties was studied. In all photodegradation processes, ortho-hydroxyphenol and para-hydroxyphenol were detected as the first intermediates of phenol decomposition. For the TiO2/Ti3C2(140,12) sample containing VTi, a higher concentration of para-hydroxyphenol than ortho-hydroxyphenol was observed, whereas for sample TiO2/Ti3C2(220,24) higher concentration of ortho-hydroxyphenol was noticed. The formation of surface heterojunction between {101} and {001} facets of decahedral anatase particles grown on Ti3C2 surface led to improved photoelectron transfer and enhanced photocatalytic activity towards degradation of carbamazepine - non-biodegradable and susceptible to bioaccumulation in living organisms commonly used pharmaceutical agent. Moreover, modification of TiO2/Ti3C2 surface with iron by magnetron sputtering deposition markedly improved photocatalytic activity in carbamazepine decomposition, with nearly 100% degradation in 60 min of irradiation under simulated solar light.

РЕЛАКСАЦИЯ ОСТАТОЧНЫХ НАПРЯЖЕНИЙ В ДЕКАЭДРИЧЕСКИХ ЧАСТИЦАХ ПУТЕМ ОБРАЗОВАНИЯ ЦЕНТРАЛЬНОЙ СФЕРИЧЕСКОЙ ПОРЫ

Small metal particles with a body-centered crystal lattice (BCC) often take the form of polyhedrons with fifth-order symmetry axes such as the icosahedron, decahedron, and pentagonal prism. The quintic symmetry axes, forbidden by the traditional crystallography laws, cause inhomogeneous elastic stress and strain in these particles. Under certain conditions, these stress and strain could relax through the change in the particle structure: the formation of partial and perfect dislocations, misfit layers, and the nucleation of cracks and voids. Within the quasi-equilibrium energy approach, the authors proposed a theoretical model of residual stress relaxation in decahedral particles due to the formation of a central spherical void. The explicit analytical expressions for energies of solid and hollow decahedral particles are found. The elastic energy of a hollow decahedral particle is defined as the work spent on the nucleation of a positive wedge disclination with the power ω≈0.0163 rad (≈7°20') in the elastic spherical shell under its own stress field. The authors determined the change in the surface energy due to the formation of a void considering the influence of the relaxation effect of the first coordination sphere surrounding the vacancy on the particle volume change. The energy change of decahedral particles during the formation of a spherical void is calculated and the optimal and critical parameters of this process are determined. The study shows that there some critical radius of a particle, if reached the formation of the central spherical void becomes energetically favorable. Moreover, the study shows that a pore germ will grow until it reaches a certain optimal size corresponding to the greatest change in the system energy. The numerical calculations correspond with experimental observations of unstable voids in the rather small silver and gold decahedral particles with the diameter of 30–40 nm and stable voids in relatively large copper decahedral particles with the diameter of ~1 μm.

Computational assessment of the efficacy of halides as shape-directing agents in nanoparticle growth

We report a comprehensive study of aqueous halide adsorption on nanoparticles of gold and palladium that addresses several limitations hampering the use of atomistic modeling as a tool for understanding and improving wet-chemical synthesis and related applications. A combination of thermodynamic modeling with density functional theory (DFT) calculations and experimental data is used to predict equilibrium shapes of halide-covered nanoparticles as a function of the chemical environment. To ensure realistic and experimentally relevant results, we account for solvent effects and include a large set of vicinal surfaces, several adsorbate coverages as well as decahedral particles. While the observed stabilization is not significant enough to result in thermodynamic stability of anisotropic shapes such as nanocubes, non-uniformity in the halide coverage indicates the possibility of obtaining such shapes as kinetic products. With regard to technical challenges, we show that inclusion of surface-solvent interactions lead to qualitative changes in the predicted shape. Furthermore, accounting for non-local interactions on the functional level yields a more accurate description of surface systems.

In Situ Seed-Mediated High-Yield Synthesis of Copper Nanowires on Large Scale.

Copper nanowires (Cu NWs) are among ideal candidates for fabricating various advanced nanodevices, especially flexible electronics and transparent conductive electrodes. However, although many efforts have been made, the commercialization of Cu NWs is still difficult. Herein, we report an in situ seed-mediated two-step strategy to synthesize well-defined Cu NWs in high yield. In the first step, that is, seed formation process, most Cu ions (85%) in situ transform to nondecahedral Cu nanodots (NDs). These Cu NDs can promote the formation of decahedral multiply twinned particles (DMTPs) and the subsequent growth of Cu NWs by selectively inhibiting the spontaneous ripening of nanoparticle (NP) byproducts in the second step. The amount and quality of Cu NDs play an important role in high-yield production of Cu NWs, and the yield was successfully increased to 2.4 times higher than that of the conventional methods. Furthermore, an effective shaking-rotating purification technique was developed to fully separate Cu NWs from the final product solution. After scaling up the reaction, 50 g of high-quality Cu NWs can be produced with a uniform size and high aspect ratio at a very low material cost of $ 0.99/g. These promising results not only provide a high-yield and low-cost synthetic route but also can promote the widespread commercialization of Cu NWs in advanced nanodevices.

Bactericidal Properties of Plasmonic Photocatalysts Composed of Noble Metal Nanoparticles on Faceted Anatase Titania.

Octahedral anatase particles (OAP) with eight equivalent {101} facets and decahedral anatase particles (DAP) with two additional {001} facets were modified with nanoparticles of noble metals (silver, copper, gold and platinum) by photodeposition, and applied for inactivation of Escherichia coli K12. XRD, DRS, XPS and STEM analyses confirmed the presence of noble metals nanoparticles (NPs) on the surface of faceted titania samples. Both OAP and DAP samples modified with silver and copper exhibited high bactericidal activities under visible light irradiation. It was also found that DAP under UV irradiation showed surprisingly high bactericidal activity, which could be attributed to efficient generation of reactive oxygen species, due to intrinsic properties of DAP, i.e., charge carriers' separation (migration of electrons and holes to {101} and {001} facets, respectively). However, an unexpected decrease in activity after DAP modification with gold and platinum NPs (mainly deposited on {101} facets) suggested that bacteria cells were directly decomposed on DAP surface. SEM images revealed that silver-modified samples caused severe damages of cell walls and membranes, due to antibacterial properties of silver (in the dark) and photocatalytic effect under visible and UV irradiation.

From titania nanoparticles to decahedral anatase particles: Photocatalytic activity of TiO2/zeolite hybrids for VOCs oxidation

In this work, zeolite/TiO2 hybrid photocatalysts based on TiO2 particles of different nature for photooxidation of VOCs in air have been developed. TiO2 with different morphologies, namely, TiO2 nanoparticles (Ti-NP) and decahedral anatase particles (DAPs), have been synthetized and characterized. A commercial TiO2 (Ti-C) catalyst has been used as a reference. Titania has been incorporated on ZSM-5 by different techniques: incipient wetness impregnation, freeze-drying, or mechanical mixing from a TiO2 sol, DAPs, or commercial TiO2. The TiO2 and hybridized photocatalysts were characterized by SEM, TEM, XRD, UV–vis spectroscopy, N2 adsorption-desorption and electrophoretic migration. Moreover, the formaldehyde or trichloroethylene adsorption ability of the composites has been analysed. The photocatalytic performance for the HCHO or C2HCl3 photooxidation under UV-A irradiation and continuous air flow has been evaluated. TiO2 nanoparticles of 5 nm, DAPs of ca. 100 nm, and 1.0 μm clusters of TiO2 made of 15 nm mean particle size characterized the three types of TiO2. These characteristics are maintained in the zeolite/TiO2 composites. In spite of the lower BET area, DAPs presented the highest VOCs reaction rate comparing to the other TiO2. The incorporation of titanium oxide to the microporous material results in the improvement of the photocatalytic performance, regardless of the actual nature of the TiO2 particles. Nevertheless, a relationship between the particle size and the improvement of the photocatalytic performance can be established. Thus, the incorporation of TiO2-NP into the zeolitic material, lead to composites with around ten times more photoactivity that the single titania particles. This effect is less pronounced for larger TiO2 particles such as DAPs and less evident for TiO2 aggregates present in commercial material. TiO2 nanoparticles homogeneous distributed on the hierarchical material shows the highest VOCs photooxidation and CO2 formation rates of the series.

Noble metal-modified faceted anatase titania photocatalysts: Octahedron versus decahedron

Octahedral anatase particles (OAP, with eight equivalent {101} facets) and decahedral anatase particles (DAP, with two additional {001} facets) were modified with nanoparticles of noble metals (Au, Ag, Cu). The titania morphology, expressed by the presence of different arrangements of exposed crystal facets, played a key role in the photocatalytic properties of metal-modified faceted titania. In the UV/vis systems, two-faceted configuration of DAP was more favorable for the reaction efficiency than single-faceted OAP because of an efficient charge separation described by the transfer of electrons to {101} facets and holes to {001} facets. Time-resolved microwave conductivity (TRMC) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) confirmed that distribution of electron traps (ET) and mobility of electrons were key-factors of photocatalytic activity. In contrast, metal-modified OAP samples had higher photocatalytic activity than metal-modified DAP and metal-modified commercial titania samples under visible light irradiation. This indicates that the presence of single type of facets ({101}) is favorable for efficient electron transfer via shallow ET, whereas intrinsic properties of DAP result in fast charge carriers’ recombination when gold is deposited on {101} facets (migration of “hot” electrons: Au→{101}→Au).

Fracture of hollow multiply-twinned particles under chemical etching

Abstract The stress-strain state in a hollow decahedral small particle is modeled as that caused by a positive wedge disclination in an elastic hollow sphere. The stress and dilatation distribution in the particle is analyzed in relation to crack nucleation and the particle's catastrophic fracture during chemical etching. A two-stage process of the fracture is suggested, which includes nucleation of initial cracks along twin boundaries around their quintuple junction and subsequent pattern formation in a fivefold star-shaped crack at the junction. The critical sizes of the initial crack and the decahedral small particle at which this two-stage fracture process occurs, are estimated.

Generation of circular prismatic dislocation loops in decahedral small particles

A theoretical model is proposed which describes stress relaxation in decahedral particles by generation of circular prismatic dislocation loops. Providing that the particle size exceeds a certain critical value, the nucleation of circular prismatic dislocation loops becomes an effective channel for residual stress relaxation in the particle. Under these circumstances, the loop expands until it reaches its optimal radius which increases with an increase of the particle radius. It is shown that both the critical particle radius and optimal loop radius strongly depend on the dislocation core energy, as well as on the material properties of the particle.

Evolution of the morphology of small pentagonal particles and microcrystals during the electrodeposition of silver in a potentiostatic regime

A procedure for obtaining icosahedral and decahedral small particles and microcrystals of silver is presented. The evolution of the morphology during growth is studied in detail. Mechanisms of the relaxation of elastic stress fields in small silver particles and microcrystals with pentagonal symmetry are found experimentally.

Growth morphology and special diffraction characteristics of multifaceted gold nanoparticles

This paper deals with morphology of synthesized nano gold particles through seed based growth. Various types of morphologies have been observed. They primarily relate to decahedral and truncated tetrahedral shapes. Their relative abundance is dependent on temporal evolution of nanoparticles. These shapes are understood to have evolved from a seed having symmetry that is a supergroup of the point groups possessed by these nanoparticles. The usual pentagonal twinned morphologies observed under High Resolution Transmission Electron Microscopy have displayed two distinct types of interfaces. They have been attributed to cubic and icosahedral three-fold orientations. Such a discussion is lacking in literature. The five triangular faces of decahedral particles are essentially rotational twins resulting out of a common five-fold axis. Two special diffraction features for truncated tetrahedral particles have been observed. They refer to (i) triangular streaks around Braggs spots conforming to three fold symmetry of these particles and (ii) by observation of forbidden reflections of the type 1/3{422} and 2/3{422} along 〈422〉 directions. Latter has been understood in terms of intrinsic fault whereas former arises owing to shape transform of nanoparticles. The presence of faults has helped rationalize decrease of lattice parameter vis-à-vis that of standard FCC gold. The variation of intensities of these forbidden reflections seems to be arising out of density of such intrinsic faults in nano gold particles in addition to dynamical effects.

Decahedral anatase titania particles immobilized on zeolitic materials for photocatalytic degradation of VOC

Decahedral anatase titania particles (DAPs) immobilized on zeolites (zeolite/DAP hybrids), have been prepared by the first time. DAPs have been synthesized from titanium chloride (TiCl4) through a gas-phase reaction process by rapid heating and quenching. DAPs with well-defined {101} and {001} facets were synthetized and dispersed onto the zeolites. The incorporation of an 8wt% of DAPs into the zeolites has been achieved by means of the freezing-drying technique. Two types of zeolites (ZSM-5 and zeolite Y) with different SiO2/Al2O3 contents have been selected as adsorbents. The photocatalytic properties for the degradation of representative volatile organic compounds (VOC), i.e. acetaldehyde, formaldehyde or trichloroethylene were analyzed under batch and continuous flow reactors. Raw materials and composites were characterized by SEM, N2 adsorption-desorption, UV–vis spectroscopy, XRD, zeta potential and the amount of VOC adsorbed was measured at dynamic conditions. Zeolite/DAP hybrids combine the textural and crystalline properties of zeolite and DAPs phases. The zeolite type (crystal structure, SiO2/Al2O3 ratio and surface net charge) play a relevant role in the dispersion of DAPs. Zeolite/DAP composites show better photocatalytic performance than those prepared with commercial TiO2 due to the presence of {001} facets in the former. The composites prepared with hydrophobic ZSM-5 and DAPs, are the most versatile materials for photooxidation of aldehydes and organochloride compounds, with substantially less formation of non-desirable reaction products respect to those based on benchmark TiO2.

Silver- and copper-modified decahedral anatase titania particles as visible light-responsive plasmonic photocatalyst

Decahedral anatase particles (DAPs) with eight equivalent (101) facets and two (001) facets were prepared by the gas-phase process. Monometallic and bimetallic photocatalysts were prepared by photodeposition of silver and copper on DAP. It was found that the method of metal deposition (sequential/simultaneous) is crucial for resultant properties and thus for photocatalytic performance. The fastest hydrogen evolution during metal deposition was observed for copper deposited on premodified DAP with silver (DAP/Ag/Cu), probably due to partial coverage of silver with fine clusters of Cu and thus facilitation of proton adsorption and reduction on well-dispersed Cu nanoclusters. Although DAP/Ag/Cu exhibited the fastest rate of hydrogen evolution, single-modified DAP with silver exhibited the best performance for oxidative decomposition of organic compounds under vis irradiation.

Surface-enhanced Raman scattering measurement from a lipid bilayer encapsulating a single decahedral nanoparticle mediated by an optical trap.

We present a new technique for the study of model membranes on the length-scale of a single nano-sized liposome. Silver decahedral nanoparticles have been encapsulated by a model unilamellar lipid bilayer creating nano-sized lipid vesicles. The metal core has two roles (i) increasing the polarizability of vesicles, enabling a single vesicle to be isolated and confined in an optical trap, and (ii) enhancing Raman scattering from the bilayer, via the high surface-plasmon field at the sharp vertices of the decahedral particles. Combined this has allowed us to measure a Raman fingerprint from a single vesicle of 50 nm-diameter, containing just ∼104 lipid molecules in a bilayer membrane over a surface area of <0.01 μm2, equivalent to a volume of approximately 1 zepto-litre. Raman scattering is a weak and inefficient process and previous studies have required either a substantially larger bilayer area in order to obtain a detectable signal, or the tagging of lipid molecules with a chromophore to provide an indirect probe of the bilayer. Our approach is fully label-free and bio-compatible and, in the future, it will enable much more localized studies of the heterogeneous structure of lipid bilayers and of membrane-bound components than is currently possible.

Facile Synthesis of Decahedral Particles of Anatase TiO2 with Exposed {001} Facets.

This paper reports a facile synthesis of decahedral particles of anatase TiO2 dominated by {101} and {001} faces. The decahedral particles has been enhanced by means a microwave-assisted hydrothermal method using TiF4 as a titanium precursor and HF as capping agent to promote oriented growth and formation of {001} faces in only 4 h. The prepared samples were characterized by scanning electron microscopy, high resolution of transmission electron microscopy and X-ray diffraction. The morphology of anatase TiO2 particles is consisted of near-perfect-truncated-bipyramid-shape. Reaction time is a key factor to obtain truncated-bipyramid-shaped particles with sharp and well-defined edges. Reaction times longer than 4 h induce irregular particles. Decahedral anatase TiO2 particles are truncated bypiramid crystals which have eight {101} and two {001} facets at top/bottom surfaces. The average size of decahedral anatase TiO2 particles are -250 nm for the samples obtained without applying the microwave irradiation and -350 nm for reaction 4 h.

STEM characterization of Gold-Copper anisotropic nanocrystals

Alloy nanoparticles are an important group of nanomaterials exhibiting size, shape, structure and composition dependent properties. In bulk, gold-copper alloys exhibits ordered phases Au3Cu (L12), AuCu (L10), AuCu3 (L12) [1]. Theses phases could be modified in temperature and composition at the nanoscale. For instance, ligands play an important role in the synthesis of bi-metallic nanoparticles because they influence the final shape and size of the nanoparticle. The most common method used to synthesize alloyed nanoparticles is wet-chemistry that make use of phosphoric acids, polymeric chains or thiol groups as surfactants in organic solvents such as toluene that control the spatial and shape distribution of the nanoparticles. However, the knowledge of the internal structure of the crystals provides insights to understand the crystal growth of the nanosystem. In recent years it has been reported the relationship between shape and internal features such as stacking faults and twin boundaries on nanowires and decahedral particles [2]. This features (twins, stacking faults and other defects) can modified the final shape of nanoparticles. Some other factors that affect in the same way are the concentration of the reactants and the temperature ranges. Therefore, in this work we present a systematic study on gold-copper bimetallic system to analyze the internal structure of ultrathin nanowires, decahedral nanostars and nanocubes. Modifying few conditions during the synthesis, such as metal concentrations and surfactant used, namely hexadecylamine (HDA), octadecylamine (ODA), oleylamine (OLA) or 1-dodecanethiol (DDT), we obtained Au-Cu nanocrystals with the different morphologies aforementioned. Through high resolution transmission electron microscopy (HRTEM), High Angle Annular Dark Field (HAADF) imaging and Energy Dispersive X-Ray Spectroscopy (EDS) we have obtained atomic resolution that allow us to describe the internal structure of the synthesized particles.