Bilayer Hollow Research Articles

Thickness-controlled HsGDY/N-doped double-shell hollow carbon tubes for broadband high-performance microwave absorption

With the increasing deterioration of the electromagnetic environment, it is important to develop new and efficient electromagnetic wave-absorbing materials. In this work, bilayer hollow HsGDY/NC nanotubes with controllable thickness are constructed by introducing high conductivity polydopamine (PDA) and hydrogen-substituted graphdiyne (HsGDY) followed by the etching and carbonization. Subsequently, the effects of the composition, coating order, and structural characteristics of nanotubes on the electromagnetic parameters are thoroughly investigated, thereby analyzing the microwave absorption mechanism. The impedance matching of HsGDY/NC is optimized by changing the thickness of NC layer, while utilizing unique multi-heterogeneous interfaces and hierarchical conductive structures that enhance the interface polarization and conductive loss. As a result, HsGDY@NC-3 displays the optimal absorbing performance with an effective absorption bandwidth (EAB) of 7.8 GHz (10.1–17.9 GHz) and a minimum reflection loss (RLmin) of −47.18 dB at the filler content of only 11 %. This work broadens the application scopes of HsGDY and provides a novel insight into the design of lightweight, high-efficiency, and wide-frequency microwave absorbers, which is expected to be a potentially effective microwave-absorbing material.

MoS2/polyaniline (PANI)/polyacrylonitrile (PAN)@BiFeO3 bilayer hollow nanofiber membrane: Photocatalytic filtration and piezoelectric effect enhancing degradation and disinfection

A novel MoS2/polyaniline (PANI)/polyacrylonitrile (PAN)@BiFeO3 bilayer hollow nanofiber membrane (PPBM-H) was successfully synthesized by coaxial electrospinning technique. In the nanofiber, BiFeO3 nanoparticles (NPs) and MoS2 nanosheets (NSs) were loaded in the middle and outer layers of the PANI/PAN composites, respectively, which constructs a type II heterojunction with spatially separated microtopography, thus significantly improving the charge separation in photocatalysis. Moreover, the hollow structure and the vast number of exposed groups on the surface of PPBM-H help to improve the mass transfer efficiency and pollutant adsorption performance in wastewater treatment. In addition, PPBM-H can generate H2O2 by in-situ activation of BiFeO3/MoS2 for photo-Fenton catalysis, enabling Fe3+ and Fe2+ recycling. Also, PPBM-H can produce piezoelectric polarisation under ultrasonic excitation, which can further enhance the efficiency of electron/hole separation and transfer, and induce the generation of active free radicals. Owing to its wonderful self-cleaning effect, the PPBM-H has good mechanical strength (2.95 Mpa), hydrophilicity (11.6°), water flux (1248 L·m−2·h−1), BSA rejection (98.8 %), and exhibits distinguished photocatalytic filtration efficiencies (99.5 % tetracycline hydrochloride (TCH) and 99.9 % methyl orange (MO) within 60 min), piezo-photocatalysis (99.2 % TCH within 2 h), disinfection performance for Escherichia coli (E. coli) (100 %, within 60 min).

Hollow core-shell nanocoatings with gradient refractive index structure for enhanced photovoltaic performance

Hollow structure-based multifunctional coatings with broadband antireflectivity, self-cleaning performance, stability, and durability can be applied to photovoltaic (PV) modules to maintain high transmittance and increase solar cell power generation. This research prepared bilayer hollow composite nanoparticles by improving and optimizing the nanoparticle synthesis and volume ratios. The optimal volume ratio of hollow SiO2 to TiO2 was determined using refractive index, transmittance, surface area, photocatalysis, and thermogravimetry. With the modification effect of methyltriethoxysilane, the refractive index interval of the composite coating was obtained, while giving the coating better hydrophobicity. A three-layer broadband antireflective coating (HT-TGBA) with a gradient refractive index structure was prepared using pre-designed simulation software. Various morphological and structural characterizations of HT-TGBA nanoparticles were performed. The transmittance of HT-TGBA-coated glass was significantly improved compared with that of uncoated glass. Its self-cleaning properties were confirmed by photocatalysis and surface hydrophobicity. Damp heat, abrasion tests, and pencil hardness tests proved the excellent durability of HT-TGBA, and measurements of sustained water contact angles demonstrated its stability. The short-circuit current density and photoelectric conversion efficiency were significantly improved by dip-coating HT-TGBA onto mini-modules. These results demonstrate that HT-TGBA has broad application prospects, supporting future large-scale applications of composite coatings in PV modules.

Interface and electronic structure dual-engineering on MoSe2 with multi-ion/electron transportation channels for boosted sodium-ion half/full batteries

It is of great significance to design and prepare high performance anode materials for the development of sodium ion batteries (SIBs). In this work, the innovative approach of interface and electronic structure dual-engineering is applied on MoSe2 to fabricate novel C/N co-doped bilayer hollow structured MoSe2 nanosheets (BH-MoSe2@CNBs). With the comparison of traditional MoSe2/C composite, the sandwich structured MoSe2 with double carbon coating can bring multi-ion/electron transportation channels, favoring the Na+ storage and charge transfer kinetics. Specifically, the inner carbon shell as a supporting skeleton not only restrains the agglomeration of lamellar MoSe2, but also buffers the stress of sodium ions (de)insertion. The outer carbon layer plays a crucial role in adsorbing the polyselenide intermediates, maintaining the stability and reversible capacity of the middle MoSe2 electrode. As anode for SIBs, BH-MoSe2@CNBs exhibit 347 mAh g−1 at 10 A g−1 after 1300 cycles, which is comparable with the previously reported MoSe2-based electrode in SIBs. Additionally, the BH-MoSe2@CNBs//Na3V2(PO4)2O2F full cell can reach an energy density of 107.4 Wh kg−1 at a power density of 3832 W kg−1, indicating the potential practical application. The theoretical calculation is also conducted to confirm the superior Na+ adsorption of BH-MoSe2@CNBs. The interface and electronic structure dual-engineering on MoSe2 can provide innovative points for the exploitation of efficient anode materials for SIBs.

Electrochemical template synthesis of Ni–Cu bilayer hollow microtubes for green hydrogen production through electrocatalytic reforming of ethanol

This article is devoted to the investigation of the processes occurring at the synthesis of Ni–Cu hollow tubes (NC-HT) and their application as an electrocatalyst in the hydrogen evolution reaction from water-ethanol solution. The reactions at the electrochemical reduction of CuO to Cu and during the electrodeposition of nickel were investigated by chronopotentiometry. Depending on the thickness of the nickel layer, morphology (SEM) and chemical composition (EDX-mapping, XRD) of tubes, as well as electrocatalytic activity (CVA, ECSA, TOF, and stability tests) were studied. The synthesized materials have a structure with a high electrochemically active surface area (ECSA) from 1.38 to 3.50 m2g-1, which makes it possible to fulfill low activation overpotential values equal to −86 and −250 mV at 10 and 50 mAcm−2 after 100 cycles. The stability test results demonstrate the overpotential values −160, −183, −265 mV for NC-HT15, NC-HT30, and NC-HT60, respectively, after 24 h examinations.

Bi-layered hollow amphoteric composites: Rational construction and ultra-efficient sorption performance for anionic Cr(VI) and cationic Cu(II) ions

Here, we have developed a novel bilayer hollow amphiphilic biosorbent (BHAB-3) with large adsorption capacity, rapid adsorption kinetics, and cost-effective for the removal of Cr(VI) and Cu(II) from aqueous solutions. The synthesis was based on the clever use of freeze-drying to fix the structure, secondary modification of the carboxymethyl cellulose microspheres with polyethyleneimine and cross-linking by glutaraldehyde. The consequences of pH, initial concentration, contact time and temperature on adsorption were investigated. The Langmuir model fits showed that the maximum adsorption capacities of the two target heavy metal ions reached 835.91 and 294.79 mg/g, respectively. Moreover, BHAB-3 was characterized by SEM, FT-IR, TGA, and XPS synergistically, showing that it exhibits a strong complexation ability for Cu(II) and a strong electrostatic effect for Cr(VI). Adsorption and desorption experiments showed only a slight decrease in the adsorption capacity of the BHAB-3 for Cr(VI) and Cu(II) ions after 5 and 26 cycles, respectively. Given the excellent properties of this adsorbent, it is a promising candidate for heavy metal ion removal.

Carbon Nanotubes/Regenerated Silk Composite as a Three-Dimensional Printable Bio-Adhesive Ink with Self-Powering Properties.

In this study, regenerated silk (RS) obtained from Bombyx Mori cocoons is compounded with carboxyl-functionalized carbon nanotubes (f-CNTs) in an aqueous environment for the fabrication of functional bio-adhesives. Molecular interactions between RS and carboxyl groups of CNTs result in structural increase of the β-sheet formation, obtaining a resistant adhesive suitable for a wet biological substrate. Moreover, the functionalization of CNTs promotes their dispersion in RS, thus enabling the production of films with controlled electrical conductivity. The practical utility of such a property is demonstrated through the fabrication of a piezoelectric device implanted in a rat to monitor the breathing in vivo and to be used as a self-powered system. Finally, RS/f-CNTs were used as a printable biomaterial ink to three dimensionally print bilayer hollow tubular structures composed of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and RS. Initial tests carried out by seeding and growing human skin fibroblasts demonstrated that the 3D printed bilayer hollow cylindrical structures offer a suitable surface for the seeded cells to attach and proliferate. In general, the herein proposed RS/f-CNT composite serves as a versatile material for solvent-free dispersion processing and 3D printing, thus paving a new approach to prepare multifunctional materials with potential applications of great interest in sealing biological substrates and implantable devices for regenerative medicine.

The dispersion of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder with the initial inhomogeneous thermal stresses

The paper studies the influence of the initial inhomogeneous thermal stresses on the dispersion of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder within the scope of the 3D linearized theory of elastic waves in initially stressed bodies. The initial static thermal stresses are determined within the scope of the uncoupled classical linear theory of thermo-elasticity and it is assumed that the temperature change in the cylinder is caused by the heating or cooling of the inner and outer surfaces of the cylinder. The discrete analytical solution method is employed for the solution to the corresponding equations of the wave propagation. Concrete numerical results are obtained for the cylinder, the materials of the layers of which are steel and aluminum, as well for the cylinder made of steel only. Numerical results on the influence of the initial inhomogeneous thermal stresses on the dispersion curves related to the first, second and third modes are presented and discussed. In particular, it is established that the cooling or the heating of the outer and inner surfaces of the bi-layered hollow cylinder influences the dispersion curves not only in the quantitative sense, but also in the qualitative sense.

Torsional wave dispersion in a bi-layered hollow cylinder with inhomogeneous initial stresses caused by internal and external radial pressures

The present paper studies the influence of the inhomogeneous initial stresses in the bi-layered hollow cylinder and it is assumed that these stresses are caused by the hydrostatic pressures acting on the interior and outer free surfaces of the cylinder. The study is made by utilizing the version of the three-dimensional linearized theory of elastic waves in bodies with initial stresses for which the initial stress-strain state in bodies is determined within the scope of the classical linear theory of elasticity. For the solution to the corresponding eigenvalue problem, the discrete-analytical method is employed. Numerical results are presented and analyzed for concrete selected pairs of materials. According to these results and their analyses, it is established that, unlike homogeneous initial stresses, the influence of the inhomogeneous initial stresses on the torsional wave dispersion has not only quantitative but also qualitative character. For instance, in particular, it is established that as a result of the initial stresses caused by the hydrostatic pressure acting in the interior free surface of the cylinder, the cut-off frequency appears for the fundamental dispersive mode and the values of this frequency increase with the intensity of this pressure.

Ionic Strength and Thermal Dual-Responsive Bilayer Hollow Spherical Hydrogel Actuator.

As one of the most promising intelligent materials, polymeric hydrogel actuators could produce reversible shape change upon external stimuli. Although complex shape deformation from 2D to 3D have been achieved, the realization of actuating behavior from 3D to 3D is still a significant challenge. Herein, an effective strategy to develop a novel bilayer hollow spherical hydrogel actuator is proposed. Through immersing a Ca2+ incorporated gelatin core into alginate solution, an ionic-strength-responsive alginate layer will be formed along the gelatin core via alginate-Ca2+ crosslinks, and then another thermo-responsive alginate-poly(2-(dimethylamino)ethyl methacrylate)(Alg-PDMAEMA) layer is introduced to achieve a bilayer hydrogel with ionic strength and temperature dual responsiveness. A hollow hydrogel capsule could be obtained if a spherical gelatin core is applied, and it could produce complex shape deformations from 3D to 3D upon the trigger of ionic strength and temperatures changes. The present work may offer new inspirations for the development of novel intelligent polymeric hydrogel actuators.

Axisymmetric longitudinal wave dispersion in a bi-layered circular cylinder with inhomogeneous initial stresses

The paper studies the axisymmetric longitudinal wave propagation in a bi-layered hollow cylinder with inhomogeneous initial stresses by utilizing the 3D linearized theory of elastic waves in initially stressed bodies. It is assumed that the initial stresses in the cylinder are caused by the internal and external hydrostatic pressures. Assuming that the materials of the layers of the cylinder are sufficiently stiff, these initial stresses are determined within the scope of the classical linear theory of elasticity. The discrete analytical method is employed for the solution to the corresponding 3D linearized equations of motion. The dispersion equation is obtained which is solved numerically for various values of the problem parameters. As a result of this solution, the dispersion curves are constructed and, according to these curves, the character of the influence of the inhomogeneous initial stresses on the dispersion curves obtained for the lowest first and second modes is established. Analysis of the results shows that the inhomogeneous initial stresses not only quantitatively but also qualitatively act on the character of the dispersion curves.

The influence of the rheological parameters on the dispersion of the flexural waves in a viscoelastic bi-layered hollow cylinder

The paper investigates the influence of the rheological parameters which characterize the creep time, the long-term values of the mechanical properties of viscoelastic materials and a form of the creep function around the initial state of a deformation of the materials of the hollow bi-layered cylinder on the dispersion of the flexural waves propagated in this cylinder. Constitutive relations for the cylinder\'s materials are given through the fractional exponential operators by Rabotnov. The dispersive attenuation case is considered and numerical results related to the dispersion curves are presented and discussed for the first and second modes under the first harmonic in the circumferential direction. According to these results, it is established that the viscosity of the materials of the constituents causes a decrease in the flexural wave propagation velocity in the bi-layered cylinder under consideration. At the same time, the character of the influence of the rheological parameters, as well as other problem parameters such as the thickness-radius ratio and the elastic modulus ratio of the layers\' materials on the dispersion curves, are established.

On the attenuation of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder made of viscoelastic materials

The paper studies the attenuation of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder made of linear viscoelastic materials. Investigations are made by utilizing the exact equations of motion of the theory of viscoelasticity. The dispersion equation is obtained for an arbitrary type of hereditary operator of the materials of the constituents and a solution algorithm is developed for obtaining numerical results on the attenuation of the waves under consideration. Specific numerical results are presented and discussed for the case where the viscoelasticity of the materials is described through fractional-exponential operators by Rabotnov. In particular, how the rheological parameters influence the attenuation of the axisymmetric longitudinal waves propagating in the cylinder under consideration, is established.

On the dispersion of the axisymmetric longitudinal wave propagating in a bi-layered hollow cylinder made of viscoelastic materials

The paper deals with the study of axisymmetric longitudinal fundamental wave propagation (dispersion) in the bi-layered hollow circular cylinder made of linear viscoelastic materials. The investigations are made by utilizing the exact equations of linear viscoelasto-dynamics. The corresponding dispersion equation is derived for an arbitrary type of hereditary operator and the algorithm is developed for its numerical solution. Concrete numerical investigations are made for the case where constitutive relations of the layers’ materials of the cylinder are described through fractional exponential operators. The influence of the viscosity of the layers’ materials of the hollow cylinder on the wave dispersion is studied through the rheological parameters which indicate the characteristic creep time and long-term values of the elastic constants of these materials. Dispersion curves are presented for certain selected dispersive and non-dispersive attenuation cases under various values of the problem parameters and the influence of the aforementioned rheological parameters on these curves is discussed. As a result of the numerical investigations, in particular, it is established that in the case where the rheological parameters of the layers are the same, the viscosity of the layers’ materials causes the axisymmetric wave propagation velocity to decrease.

Ultra-fast and highly-sensitive gas sensing arising from thin SnO2 inner wall supported hierarchical bilayer oxide hollow spheres

Hierarchical SnO2/α-Fe2O3 bilayer hollow spheres with thin inner shell were successfully synthesized by using SnO2 contained carbon spheres as sacrificial templates. The heterojunction formed at the interface as well as the hierarchical structures which provide an effective gas diffusion path resulted in significant enhancement in sensing response to ethanol and acetone as compared to pristine urchin-like α-Fe2O3. Response values of the hollow spheres based sensors towards 100ppm acetone and ethanol could reach to 47.1 and 29.5. Moreover, in contrast to many other types of α-Fe2O3/SnO2 composites reported previously, gas sensors based on the bilayer hollow spheres here exhibited ultra-fast response and recovery speed. The dynamic transients of the sensors demonstrated both their fast response (3–4s) and fast recovery (6–9s) towards acetone in the concentration of 10–100ppm. The unique hierarchical hollow structure with thin inner shell might be responsible for the ultra-fast gas sensing properties. This simple template based strategy is expected to be extended for the fabrication of similar hollow structure semiconductor oxide composites, and this work might provide an effective principle for designing high performance hybrid gas sensing materials.

Formation of double layer hollow nanostars of Pd/CuIr by utilizing a Kirkendall effect and a facile Cu atom movement along twinning boundaries and their usage as efficient water splitting catalysts

Hollow nanostructures with an inherent high surface area per mass are attractive candidates as economically viable catalysts. Conceptually, a hollow nanostructure can be obtained by forming a desired material phase on a removable template and then by subsequently removing the template core. We recently reported the synthesis of a core–shell type structure with a Cu-rich core and Ir rich shell. However, the Cu phase could not be removed from the core due to the imperviousness of the single crystalline Ir-rich shell. In order to facilitate the Cu phase removal, we introduced the polycrystalline Pd seed into the growth of the CuIr nanocrystal, which resulted in the formation of Pd@CuIr nanocrystals with multiple radial grain boundaries. By placing the Pd@CuIr nanocrystal under oxidizing conditions, we could initiate the outward movement of the Cu phase along the grain boundaries. Herein we report the synthesis of an unusual bilayer hollow nanostructure with a CuIr surface layer and a Pd inner-coating layer, following a facile CuPd alloy phase formation and an outward movement of the Cu phase under oxidizing conditions. We also report the high catalytic performance of the hollow nanostructure in oxygen evolution reaction (OER).

Bi-layer steady state current cloak

Abstract We report that bi-layer copper and polystyrene cylinders can cloak steady current. We fabricated two hollow cylinders, the one made of copper, and the other made of polystyrene. Two hollow copper and polystyrene cylinders nested concentric bi-layer hollow copper and polystyrene cylinders. The background media are made of aluminum. Theory and experiment demonstrated that the electric potential gradients are parallel and equal outside the outer circle, the iso-potential lines are parallel outside the outer circle, and the electric potential is zero in the inner circle.

Preparation of bilayer hollow billets by horizontal electromagnetic continuous casting

The possibility for producing a bimetallic hollow billet by means of direct connection of liquid phases was investigated. Bilayer hollow billets with diameter of 83 mm and external thickness of 6 mm were fabricated by horizontal electromagnetic continuous casting. Surface features and microstructures of ingots were observed and the effect of rotating magnetic field on grain size was studied. The results show that when the casting speed is 120 mm min−1 and input current intensity is 100 A, bilayer hollow billets with well surface features combine the external and internal alloys by metallurgical bonding, and the defect free bonding interface can be seen clearly.

Formation of porous bilayer hollow fibre membranes

Support membranes in bioartificial organs contact blood or plasma on one-side and adhesion dependent cells on the other side. Since membranes for biomedical applications, such as for haemodialysis, are optimised for blood contact and membranes for biotechnological applications for cell contact, there are no membranes available addressing the requirements of artificial organ technology. One approach is the preparation of porous bilayer membranes with a wall consisting of two chemical different polymer layers. Results of the preparation of such membrane types using triple spinnerets and a wet phase inversion process are shown here. It is demonstrated that one of the most important parameter is the structural integrity of the membrane wall at the interface between both layers. A new spinneret construction is presented where the membrane forming polymer solutions are layered in the spinneret before extrusion. As a result porous bilayer hollow fibre membranes with a high structural integrity could be manufactured using different composed polysulfone (PSu) polymer solutions for model investigation.

Nonsteady-state temperature field and thermoelastic state of a bilayer hollow circular cylinder upon frictional heating

The operation of many machines and mechanisms is based on the relative motion of coupled parts (friction assemblies), which is accompanied by frictional heating. The development of methods for assessing the reliability of friction assemblies is of great importance, since the reliability of operation of the entire machine depends mainly on this. Along the route to solution of this problem, the important problem arises of determining the temperature fields and the contact pressures in the elements of the assembly in contact, taking into account heating from frictional forces. Among the widely used friction assemblies, we look at a coupling which may be modeled by a bilayer hollow circular cylinder.