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The densification of mono-sized regular octahedral particles under vibration is simulated by a DEM model. The model is validated by physical experiments. The effects of operating parameters including vibration amplitude and frequency are investigated. The obtained packing structures are characterized, and corresponding densification mechanisms are identified. The results indicate that vibration amplitude is more critical for densification compared to frequency, where a wide range of suitable amplitudes exists to realize the dense packing structures. Ordered packing structure exists in boundary region. The central region possesses good particle position randomness and orientation randomness, and the packing density for poured packing (initial loose packing) and vibrated packing (dense packing) in the central region are 0.670 and 0.684, respectively. During densification, contacts and constraints between particles decrease, and the stress within the structure becomes larger. The typical arrangement of neighboring particles is close to but not perfect face to face (F–F) contact. Particles in the boundary region experience more rotations and can form local ordered structures. These structures prevent the relative movement of individual particles but favor their movement as a whole. Particles in the central region have relatively little movement and rotation. The ordered structures formed at boundary is difficult to extend to the central region due to the restricted change of particle contact conditions.

The packing of cohesive particles is of paramount importance in many industries because the packing structure is closely related to process performance. A general relation between packing density and interparticle force was previously proposed based on packing structures formed without dynamic fluid flows. Its universality is examined here in two different packings, formed in settling and defluidization of static and dynamic fluids, respectively. First, it is shown that the packings of the same particles formed by two different methods have different structures because of different impact-induced pressures. Nevertheless, a one-to-one relationship between packing density and structural properties still holds regardless of the different packing methods, and the force distribution in those packings obeys similar rules. Finally, the packing densities obtained by the different methods are demonstrated to be universally correlated with the ratio of the interparticle force to the effective gravity. These findings indicate that different phenomena of particulate systems at a macro- or meso-scale may share similar microscopic origins, with the interparticle force playing a crucial role.

In this paper, the transition from random to ordered packings of mono-sized cylindrical particles under 3D mechanical vibration was simulated by discrete element method (DEM). The effects of particle aspect ratio, size of the particulate system and container wall on the granular crystallization were investigated. And the mechanisms were analyzed through the characterization of the order transition process in terms of packing density, coordination number (CN), orientational ordering parameter (O), nucleation and growth of cluster and granular temperature (θ). The results show that nearly perfect crystallization of mono-sized cylindrical particles can be achieved with specific aspect ratio and proper vibration conditions in a cylindrical container. The orientational ordering parameter demonstrates that the crystallization firstly starts from the container wall and then propagates inward gradually. The lower granular temperature in a cuboid container indicates less vibration energy transferred to the granular assembly compared with that in a cylindrical container, illustrating the critical role of container shape in crystallization. The vibrated crystallization of mono-sized cylindrical particles is analogous to entropy-driven process, which can be gradually achieved by the self-assembly of particles with parallel alignments along the already formed ordered clusters (nuclei) or the container wall. These results can help design complex and ordered granular structures.

Understanding the relationship between a fluid flow and the structural properties of a bed is important for various industrial applications and a proper description of particle–fluid flow. This wor...

Waste water treatment with adsorbents has become one of the most effective methods. In this work, we have reported the preparation of the flower-like Cu2MoS4/g-C3N4 composites. The Cu2MoS4 nanosheets were arranged in a flower-like structure by a simple one-step hydrothermal synthesis method and attached to g-C3N4 nanosheets. The as-prepared flower-like Cu2MoS4/g-C3N4 composites was found to have potential for the adsorption of RhB in aqueous solution. The microstructure of the product was analyzed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscope (XPS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET). The effects of the ratio of the composite material, the initial concentration of the dye and the contact time were explored. The Langmuir maximum adsorption capacity of the flower-like Cu2MoS4/g-C3N4 composites for RhB was reached 420.2 mg/g. Moreover, the adsorption process is consistent with the pseudo second-order kinetic model, the Langmuir isotherms model and the Freundlich isotherms model.

Electroreduction of CO2 to formate (ERCF) over a gas diffusion electrode with a Nafion-bonded carbon-supported Sn-based catalyst layer provides a promising approach for formate production. The ERCF performance is largely dependent on the carbon supports. However, the key influencing factors of the carbon supports for the ERCF performance have not yet been elucidated. We employed a variety of carbon supports with different pore structure features (activated carbon, acetylene black, and ordered mesoporous carbon) to explore the main factors influencing ERCF performance. The results showed that the pore size distribution was crucial for the ERCF performance. The ideal pore size was 5–20 nm. As it had the highest specific surface area within this pore size range among all the carbon supports examined, the ordered mesoporous carbon support obtained the highest ERCF performance (Faraday efficiency and current density for formate were 97.45 ± 2.97% and 80.12 ± 5.91 mA cm−2, respectively). Further analyses revealed that the increased ERCF performance was likely due to the large electroactive surface area, enhanced surface adsorption and activation capability of CO2, mesopore-induced proton transfer limitations for the hydrogen evolution reaction, and excellent charge transfer. This work is of significance for the further design of high-performance gas diffusion electrodes for the ERCF process.

The packing densification of mono-sized equilateral cylindrical particles under mechanical vibration is numerically reproduced using discrete element method (DEM). The influences of vibration frequency, amplitude and container size on the macro property (e.g. packing density) of each packing are studied. Meanwhile, various micro-properties including coordination number (CN), radial distribution function (RDF), local structures, contact types, particle position/orientation distributions, forces/stresses of the vibrated dense packing are characterized and compared with those of the loose initial poured packing. The results show that properly controlling vibration conditions can realize the transition of equilateral cylindrical particles from random loose packing (RLP) to random close packing (RCP). The maximum packing density without wall effects can reach about 0.7166, which agrees with experimental and numerical results in literature. Micro property analyses demonstrate that the average CN increases slightly after vibration. The RDF curves indicate three obvious peaks for both poured and vibrated packings. The distributions of intersection angles imply that the perpendicular arrangements of the cylindrical particles are common in both packing structures. From RLP to RCP, the probability of side-edge, bottom-edge and edge-edge contacts between two particles decreases, while that of side-side, side-bottom and bottom-bottom contacts increases. Both particle position and orientation distributions illustrate that the structure in the center of the vibrated packing is disordered. The distribution of strong forces follows the exponential law, while that of weak forces follows the power law. The static vertical stresses in both packings can be predicted by Janssen model. After vibration, a much denser and more stable structure with a larger saturation stress is obtained due to the reducing inter-particle friction effects.

To identify the dense packing of cylinder–sphere binary mixtures (spheres as filling objects), the densification process of such binary mixtures subjected to three-dimensional (3D) mechanical vibra...

This paper presents a systematic numerical investigation of static stress profile within a confined granular packing using discrete element method. The vertical and horizontal stress profiles are carefully identified within the packing structure, and the effects of container diameter and friction coefficient on the stress distributions are systematically investigated and analyzed. The results show a quantitative agreement between the vertical stress profile gauged at the bottom and the stress profile calculated within the packing structure. I.e. beyond a hydrostatic region, the static vertical stresses saturate exponentially with the packing depth. A positive correlation between the saturation stress and the container size and a negative correlation with the friction coefficient can be observed. Besides, it is also found that the well-known Janssen coefficient (or Janssen constant) is not a constant value; it decreases asymptotically to a constant with the packing depth, which implies a non-constant friction effects existed between the granular assemblies and the boundaries. And the analysis of contact forces within the packing structure also indicates a stabilized condition beyond the hydrostatic region. It is believed that these findings could develop a comprehensive insight on the stress distribution of granular matter.

A photocatalyst consisting of a cellulose hydrogel loaded with Cd x Zn1−x S (Cd x Zn1−x S-Gel) was prepared, and its photocatalytic water splitting activity was studied. At room temperature, the Cd x Zn1−x S particles with an average size of about 3 nm were loaded in carboxymethyl cellulose hydrogel by an in situ chemical reaction. This synthesis method was simple and repeatable. Diffuse reflectance UV–vis results showed that it is possible to adjust the optical properties of the synthesized photocatalysts by adjusting their composition. Under visible light irradiation, the hydrogen production rate of the photocatalysts was greatly improved. In the absence of a co-catalyst, Cd0.2Zn0.8S-Gel obtained the highest hydrogen production rate of 1762.5 μmol g−1 h−1, which is almost 104 times of that of the pure CdS. Moreover, after four hydrogen production cycles, the hydrogen production rate did not decrease significantly, showing excellent stability. It is noteworthy that the Cd x Zn1−x S-Gel can easily be removed from the aqueous solution after hydrogen production. This is a new approach for manufacturing easy recoverable visible-light-driven photocatalysts, which is vital for hydrogen production through a “green” process.

Tetra (4-carboxyphenyl) porphyrin (TCPP) was loaded on the surface of Pt/g-C3N4 via a simple adsorption process, and the microstructure and chemical structure of the composites were characterized by high resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV–visible diffused reflectance spectroscopy and photoluminescence spectroscopy. Loading TCPP onto Pt/g-C3N4 enhanced the visible-light-driven photocatalytic evolution of H2 from water. The TCPP/Pt/g-C3N4 composite with a TCPP loading of 1 wt% had the highest photoactivity, which was 2.1 times higher than that of Pt/g-C3N4. This improvement is attributed to enhanced visible light utilization by the TCPP/Pt/g-C3N4 resulting from the strong visible light response of TCPP. In addition, the formed organic heterostructure between TCPP and g-C3N4 with overlapping bad gaps accelerates the electron transfer and inhibits the recombination of the photogenerated electrons and holes on g-C3N4.

A coupled approach of discrete element method and pore network model (DEM-PNM) is developed for simulating particle–fluid flow. By this approach, the particle/solid flow is described at a particle scale by DEM and the fluid flow is described at a pore scale by PNM. The coupling scheme between DEM and PNM and the boundary conditions for realizing particle–fluid flows under different conditions are explicitly introduced. The capability is examined in three systems: a dynamic cell, a gas-fluidized bed, and a packed bed with lateral gas injection. The simulated results by the DEM-PNM approach agree with those results by either DEM-LBM (lattice Boltzmann method) approach or experiments. In particular, the simulated reasonable flow patterns in gas fluidization and lateral gas injection demonstrate the applicability of the proposed approach to complex particle–fluid flow. However, the current model presents less accuracy in dilute flow region and does not consider some important factors, which should be further improved in the future.

Densification of cubic particles under three-dimensional (3D) mechanical vibration was studied experimentally. Effects of vibration time (t), frequency (f), vibration amplitude (A), vibration acceleration (Г), container size (D) and particle sphericity (φ) on packing density (ρ) were comprehensively analyzed. To identify the effects of particle shape, the packing densification of cuboid 1 (12 mm × 12 mm × 28 mm) and cuboid 2 (4 mm × 8 mm × 16 mm) were systematically studied under the same conditions. The results show that the structure of cubic particles can be first densified from random loose packing (RLP) to random close packing (RCP) and then to ordered packing (OP) gradually. In comparison, cuboid 1 and cuboid 2 particles can only form RCP structure, but cannot achieve OP even under further vibration. Vibration parameters (t, f, A and Г) are shown to be important to the packing densification. Based on the results of varying f and A, A - f phase diagrams are established for choosing the optimal vibration parameters to achieve the desired dense packing structures. Besides, it is shown the size of container (wall effect) has monotonic influence on packing density, i.e., the larger container size corresponds to the less wall effect and higher packing density. Cubic particles can form ordered packing because of the geometrical symmetry with aspect ratio of 1. After eliminating the wall effect by extrapolating the packing densities in different sized containers, typical packing densities of the three types of particles are obtained with ρRLP = 0.658, ρRCP = 0.830 and ρOP = 0.965 for cubic particles; ρRLP = 0.625 and ρRCP = 0.740 for cuboid 1 particles; ρRLP = 0.591 and ρRCP = 0.731 for cuboid 2 particles. These findings indicate cubic particles are efficient in densification which can be readily realized through proper 3D mechanical vibration.

Packing densification of cubical particles under mechanical vibrations was dynamically simulated by using discrete element method (DEM). Effects of operating parameters such as vibration amplitude, frequency, vibration intensity, and container size (container wall) on packing densification were comprehensively investigated. The macro property such as packing density and micro properties such as coordination number (CN), radial distribution function (RDF), and particle orientation of the packings were analyzed and compared. It is found that mechanical vibration with proper vibration amplitude and frequency is effective for the densification of cubical particle packing. Packing structures of different packing densities display different properties, based on which random loose packing (RLP) and random close packing (RCP) of cubical particles are identified with the packing density of 0.591 and 0.683, respectively. Two densification mechanisms are discussed as the particle rearrangement is dominant for the transition from RLP to RCP and the crystallization along the container wall is dominant for the transition beyond RCP to ordering. The obtained results are useful for optimizing vibration conditions to generate dense packings and understanding the structural information of some fixed beds with cubical particles.

Bed structure is important to heat and mass transfer in fluidization. This study investigates solid structural transition for cohesive particles by the combined approach of computational fluid dynamics and discrete element method, supported by Voronoi tessellation. Macroscopic behaviors of fluidized beds are first discussed in connection with microscopic structural transitions. Then, the properties of Voronoi polyhedra are analyzed at both bed and particle scales. In addition, the correlation of coordination number and porosity is examined at a particle scale, and their combined probability distribution is analyzed to identify dominant structure of particles in different flow regimes. Finally, an index is proposed as the ratio of coordination number and porosity to differentiate microscopic states of a particle. These findings should be useful for the study of flow, heat, and mass transfer in fluidized beds and for the understanding of solid-like to fluid-like transition of granular materials.

Systematic physical experiments examining the packing densification of mono-sized cylindrical particles subject to 3D mechanical vibration were carried out. The influence of vibration conditions such as vibration time, frequency, amplitude, vibration strength, container size, and the aspect ratio and sphericity of the particle on the packing density were analyzed and discussed. For each initial packing density with a certain aspect ratio, operating parameters were optimized to achieve much denser packing. The results indicate that the packing density initially increases with vibration time and then remains constant. The effects of vibration frequency and amplitude on the packing densification have similar trends, i.e. the packing density first increases with the vibration frequency or amplitude to a high value and then decreases; too large or small frequency or amplitude does not enhance densification. Increasing the container size can reduce container wall effects and help achieve a high packing density. Varying the particle aspect ratio and sphericity can lead to different dense random packing structures. Overall, based on results of the examined systems, the highest random packing density obtained in an infinite sized container can reach 0.73, which agrees well with corresponding numerical and analytical results in the literature.

The dynamic crystallization of cubic granular particles under three-dimensional mechanical vibration is numerically investigated by the discrete element method. The effects of operational conditions (vibration, container shape and system size) and particle properties (gravity and friction) on the formation of crystals and defects are discussed. The results show that the formation and growth of clusters with face-to-face aligned cubic particles can be easily realized under vibrations. Especially, a single crystal with both translational and orientational ordering can be reproduced in a rectangular container under appropriate vibrations. It is also found that the gravitational effect is beneficial for the ordering of a packing; the ordering of frictional particles can be improved significantly with an enlarged gravitational acceleration. The flat walls of a rectangular container facilitate the formation of orderly layered structures. The curved walls of a cylindrical container contribute to the formation of ring-like structures, whereas they also cause distortions and defects in the packing centers. Finally, it is shown that the crystallization of inelastic particles is basically accomplished by the pursuit of a better mechanical stability of the system, with decreasing kinetic and potential energies.

Sn-based gas diffusion electrodes (GDEs) are promising for electroreduction of CO2 to formate (ERCF) as they can alleviate CO2 mass transfer limitations. However, current electrodes suffer from large catalyst size or poor electron and/or ion connections. This limits ERCF performance. Here, we report a Sn-based GDE (IE-Sn) for ERCF fabricated via deposition of Sn nanoparticles onto a gas diffusion layer by using an impregnation-electroreduction method. The characterization results showed that the IE-Sn has small Sn catalyst size (16 nm) and excellent electronic and ionic transfer properties. Moreover, the faradaic efficiency (87.12 ± 4.28%) and partial current density for formate (62.79 ± 5.33 mA cm−2) obtained from the IE-Sn is 2.45-fold and 4.86-fold, respectively, of those of the traditional electrode. This ERCF performance is one of the best among recently reported Sn-based GDEs under similar conditions. Further analyses reveal that the enhanced ERCF performance of the IE-Sn is linked to the large electroactive surface area, enhanced adsorption capacity and chemisorption ability of CO2, better stabilization of CO2.– intermediate, and excellent ion/electron transfer. This study offers design rules to fabricate high-performance electrode materials for ERCF.

Porous polyacrylamide hydrogel (PAM) was prepared by polymerization at room temperature. Cadmium sulfide/polyacrylamide hydrogels (CdS/PAM) was synthesized by in situ loading CdS nanoparticles and used for photocatalytic decomposition of water for the first time. The size distribution of the loaded CdS nanoparticles is 3–12 nm. We studied the enhanced photocatalytic activity and photo-corrosion inhibition of CdS/PAM the compared with pure CdS and probed the mechanism of the improvement. In particular, the CdS/PAM prepared in 0.003 M CdCl2 solution exhibited the highest hydrogen production efficiency of 2.929 mmol g−1 h−1, about 79 times that of pure CdS. The results demonstrate that the formation of new N–Cd bond and high transmittance of CdS/PAM dramatically enhance photocatalytic activity. The electron cloud of nitrogen atom can attract holes and repel photogenerated electrons, which lowers the carrier recombination probability. The results also reveal that the excellent hydrophilicity of hydrogel plays an important role in the inhibition of photocorrosion. In addition, CdS/PAM is easily recycled and processed. The present work will pave a good way for the application of smart hydrogels in the field of photocatalytic hydrogen production.

The packing densification of mono-sized spheres under compression is numerically modelled and studied by using the discrete element method (DEM). The obtained macro packing property such as packing density and micro properties such as coordination number (CN), radial distribution function (RDF), angular distribution function (ADF), and pore structure (Voronoi/Delaunay tessellation) are characterised and compared with those properties of random loose packing (RLP) obtained under natural packing and random close packing (RCP) obtained under one-dimensional (1D) vibration. The results indicate that by properly controlling the pressure, the maximum random packing density of about 0·64 can be realised, implying that external compression is an effective way to realise the transition from RLP to RCP. Besides, the properties of RCP obtained under compression in this study are much comparable with that obtained under 1D vibration. The pushing filling mechanism of macro pores under compression was also identified b...

Bottom pressure of confined granular assemblies saturates at a certain value even this packing bed is being continuously charged. Corresponding formulation has been established to describe this interesting phenomenon. In this work, the influences of particle size and friction on the bottom stresses of granular matter were numerically investigated by discrete element method (DEM). It is found that the Janssen model can well predict the stress profile only when the size ratio of the container versus the particle is larger than 16. Moreover, a hydrostatic linear relation between apparent mass and filling mass can be obtained when the friction coefficient becomes insignificant (μ ≤ 0.01). To further interpret the Janssen effects, the granular assemblies are characterized and evaluated from the overall interactions with sidewalls, angular distribution function, void size distribution, coordination number, contact networks, contact orientation and distributions of contact forces within the packing structure. It is believed that these results will be helpful to comprehend the granular behaviors and may offer instructive reference to industrial processes in related fields.

A simple and convenient method was used to synthesize a graphitic carbon nitride (g-C3N4) nanoporous-tube by using SiO2 nanoparticles as pore formers. The structure of the g-C3N4 nanoporous-tube was characterized by the SEM and TEM images. Taking photodegradation of RhB as an example, the photocatalytic activity of the as-prepared g-C3N4 nanoporous-tube was investigated. It can photodegrade 90% RhB in 40 min under visible-light irradiation and obtain a k value of 0.04491 min-1, which is 8.16 times that of bulk g-C3N4, 3.09 times that of tubular g-C3N4 and 1.48 times that of tubular g-C3N4-SiO2. The significant enhancement in photocatalytic efficiency is due to the edge effect of the pores and the special structure of the tubes. In addition, the possible mechanism of photocatalytic degradation of RhB was also proposed based on the trapping experiment of active species, which indicated that the superoxide radicals ([Formula: see text]) and the holes (h +) were the main reactive species in this photocatalyst. This work may open up a new idea of innovation in g-C3N4 structure and inspire its follow-up study.

The magnetic properties and magnetocaloric effect in Fe 4 MnSi 3 B x compounds with x =0, 0.05, 0.10, 0.15, 0.20, 0.25 have been investigated. X-ray diffraction study shows that all these compounds investigated crystallize in the Mn 5 Si 3 -type structure with space group P6 3 /mcm. Boron insertion in the host ternary silicide Fe 4 MnSi 3 does not change the crystal symmetry, only leads to an increase of the lattice parameters, indicating the B atoms entered the interstitial sites. With increasing B content, the Curie temperature shifts to higher temperatures. The maximal magnetic-entropy changes of the Fe 4 MnSi 3 B x compounds with x =0, 0.10 and 0.20 are about 1.8 J/(kg·K), 1.8 J/(kg·K) and 1.6 J/(kg·K), respectively, for a field change from 0 to 1.5 T.

Based on the ‘average stress in the matrix’ concept of Mori and Tanaka (Mori, T., Tanaka, K., 1973. Average stress in matrix and average elastic energy of materials with misfitting inclusion. Acta Metall. 21, 571–580) a micromechanical model is presented for the prediction of the elastic fields in coated inclusion composites with imperfect interfaces. The solutions of the effective elastic moduli for this kind of composite are also obtained. In two kinds of composites with coated particulates and fibers, respectively, the interface imperfections are taken to the assumption that the interface displacement discontinues are linearly related to interface tractions like a spring layer of vanishing thickness. The resulting effective shear modulus for each material and the stress fields in the composite are presented under a transverse shear loading situation.

Stress fields and failure mechanisms have been investigated in composites with particles either surface treated or untreated under uniaxial tension. Previous experimental observation of failure mechanisms in a composite with untreated particles showed that tensile cracks occurred mostly at the polar region of the particle and grew into interfacial debonding. In a composite with surface-treated particles, however, shear yielding and shear cracking proceeded along the interphase-matrix interface at the polar area of the matrix and thus may improve the mechanical behaviour of the material. The finite element calculations showed that octahedral shear stress at the polar and longitudinal areas of the particle treated by coupling agents is much larger than that of materials with untreated particles, and the shear stress distribution around the interface is sensitive to the interphase property. The results suggest that a th ree-phase model can describe the composites with surface-treated fillers.