Formation Of Hollow Structures Research Articles

Experimental and numerical investigations on formation mechanisms of hollow structures in overflow water‐assisted injection‐molded parts of short‐glass‐fiber‐reinforced polypropylene

AbstractIn water‐assisted injection molding processes, it is crucial to understand the mechanisms governing the formation of hollow structures and identify the key factors influencing their morphology and dimensional accuracy. This work combined experimental analysis and numerical simulation to investigate the influence of different mold cavities and main processing parameters on hollow structures in overflow water‐assisted injection molded parts of short‐glass‐fiber‐reinforced polypropylene, that is, hollow shape and hollow ratio. The results show that the hollow shape and hollow ratio depended not only on the cross‐sectional location but also on the cross‐sectional shape of the mold cavity. For the circular parts, the hollow shape resembled the cross‐sectional shape of the mold cavity, with a relatively small and uniform hollow ratio across cross‐sectional locations. For the noncircular parts, the hollow shape varied considerably with increasing distance from the water inlet. Moreover, the results also show that except for the influence of water‐injection delay time on the uniformity of the hollow ratio, higher melt temperature (250°C), shorter water‐injection delay time (0 s), and higher water pressure (10 MPa) contributed to the hollow shape being closer to the cross‐sectional shape of mold cavities and made hollow ratios relatively larger and more uniform.

Formation of hollow spheres structures Co/CoO/ZnO@NC from metal-organic frameworks as a anode for lithium-ion batteries

Transition metal oxides have become a potential anode material for LIBs due to their large theoretical capacity, low cost, abundant resources. However, significant volume changes and severe particle aggregation occur during charge/discharge process. In this work, it is found that the composite of dual component active TMO and single metal, and coating by doped carbon are the effective methods to improve the electrochemical performance and adapt to volume changes in storing lithium. The specific process is based on the co-precipitation of Zn and Co ions in the presence of 2-methylimidazolium salts to produce imidazolium salt frameworks (ZIFs) of bimetallic zeolites, which are then thermally decomposed to form hollow spheres structures Co/CoO/ZnO@NC. The hollow sphere uses Co as the core and CoO/ZnO@NC particles coated with nitrogen doped carbon layer as the shell. These spherical structures exhibit excellent electrochemical performance, high reversible capacity, excellent cycling stability (702 mAh/g at 100 mAg−1 after 100 cycles), and good rate capability (735 mAh/g and 515 mAh/g at 100 mA g−1 and 2000 mA g−1 respectively).

Effects of Mo doping on the structure, adsorption performance, and photocatalytic activity of LaFeO3 nanoparticles: Experimental and DFT studies

In this study, a series of Mo-doped LaFeO3 composite photocatalyst nanoparticles (x-LFMO, x = 0.33, 0.5, 0.67) were synthesized by ultrasonic-assisted sol–gel method under controlled Mo doping. X-ray diffraction (XRD) analyses indicate that Mo substitutes one-third of the Fe atoms in the B site of the LaFeO3 to form orthogonal perovskite structures LaFe0.67Mo0.33O3, which is the only pure phase crystal formed at stoichiometric Fe to Mo ratios of 2:1, 1:1, and 1:2, respectively. SEM and N2 adsorption/desorption revealed significantly smaller particle sizes (30–50 nm) and the formation of rich channels after Mo doping, thus enriching the specific surface area and pore size dispersion. DRS confirmed that the Mo-doped LFO composites exhibit significantly enhanced absorption in the visible region. This can be further explained by DFT theoretical calculations of energy band structures and density of states, which demonstrate that the effective mass of the electrons in LaFe0.67Mo0.33O3 is reduced and the off-domain properties of the electrons are enhanced, facilitating the excitation and transport of the photogenerated electrons. Kinetic studies showed that Mo-doped composite nanoparticles exhibit excellent adsorption capacity for quinoline, indole, and pyridine, and the pure phase LaFe0.67Mo0.33O3 and 0.5-LFMO performed well for them with removal efficiencies (>98 %) under visible light irradiation. Based on experimental observations and theoretical insights, it is suggested that the higher quantum yield and photocatalytic reactivity of x-LFMO composites are attributed to the bulk oxygen mobility and surface oxygen reactivity promoted by the octahedral distortion of BO6 in LaFe0.67Mo0.33O3 and the heterogeneous structure formed at the interface of the two phases.

Controllable Atomic Migration in Microstructures and Defects for Electromagnetic Wave Absorption Enhancement

AbstractDefects and microstructures have been utilized to effectively modulate electromagnetic (EM) wave absorption for mitigating electromagnetic pollution and stealth issues. However, precisely feasibly tailoring them still remains challenging. Here, by using a multilevel hollow cobalt sulfide embedded in a heteroatomic sulfur (S) ‐doped carbon aerogel, a preferential reaction strategy of modulating point defects and hollow microstructures via controllable S atoms migration is proposed to improve the EM wave absorption. S atoms contribute to the creation of hollow structures via Kirkendall effects, as well as inducing point defects in the carbon lattice through doping. More significantly, the mechanisms prioritizing the formation of hollow structures over defects have been discovered, with low‐velocity atomic migration primarily modulating the microstructure for interfacial polarization and impedance matching, and high‐velocity atom migration focused on introducing defects to achieve polarization and conductive loss. The resulting aerogel exhibits an exceptionally maximum reflection loss of −52.82 dB and an effective absorption bandwidth of 8.82 GHz, which far exceeds most of the currently reported materials. Experimental and theoretical approaches, including microwave heating, Tesla interaction, first principles, and far‐field simulation, are comprehensively employed to verify its absorption effect and mechanism. Furthermore, the combination of excellent infrared stealth and self‐cleaning properties opens up its potential applications in complex environments.

Polymer Binder-Free aqueous spinning of biomimetic CNT based hierarchical hollow fiber for structural and energy storage application

Assembly of functional nanomaterials into structural–functional integrated materials, such as structural-energy storage materials, are highly desirable for lightweight, high-performance wearable electronics, automobiles, and aviation/aerospace vehicles, yet extremely challenging due to the paradox between functional properties and the maintenance of mechanical properties. Herein, inspired by wheat-straw structures, we reported a polymer binder-free aqueous spinning strategy to manufacture biomimetic hollow carbon nanotube-based fibers (H-CNTF), where two-dimensional graphene oxide (GO) nanosheets are employed as an alternative to polymer binder for assisting the formation of hollow structures by rapid interaction with cations in coagulation, forming strong interaction with CNTs and tunning rheological property of spinning dope. The hierarchical hollow structure consisting of micron-scale hollow tubular space and porous walls endows H-CNTF with large surface area and abundant loading sites for guest materials, and the good CNT orientation and the absence of polymer binder enable H-CNTF excellent electrical and mechanical properties. As a proof of concept, the resulting H-CNTF supercapacitor electrodes exhibit high electrochemical energy storage performance with a specific capacity of 163 F/cm3 and high tensile strength of 0.35 N/tex. In addition, the polymer composite based on H-CNTF is about 100 % stronger than that based on solid fiber owing to the more uniform composite structure. The combination of outstanding electrochemical and mechanical properties makes this hollow fiber a promising material for future structural and energy storage applications.

MOF-derived flower-like Fe-doped Co3O4 porous hollow structures with enhanced n-butanol sensing properties at low temperature

Metal oxide-based gas sensors are widely used in the detection of toxic and harmful gases due to their advantages of high precision, convenient use and stable performance, but their application range is limited due to the high working temperature. In this work, MOF-derived flower-like Fe-doped Co3O4 porous hollow structures are obtained using a simple solvothermal method. The obtained samples are characterized in terms of their crystalline structure, morphology, chemical composition, optical properties and specific surface area. This study systematically investigates the sensing performance of pristine and Fe-doped Co3O4 samples. The results show that the 2 at% Fe-Co3O4 sample has the best n-butanol sensing properties. This sample exhibits high response and rapid response/recovery speed at a low working temperature of 110 °C, as well as good repeatability and anti-humidity features. The enhanced sensing properties can be attributed to several factors, including the adjustment of baseline resistance, increase in oxygen vacancies, decrease in bandgap, and the formation of unique hollow and porous structures. Overall, this work provides valuable insights into the potential applications of Fe-doped Co3O4 materials in sensing technologies.

Controllable hydrothermal synthesis of hollow ZnS nanospheres: Morphological evolution mechanism and photocatalytic performance

ZnS hollow nanostructures have attracted much attention due to their special structural advantages and wide range of application. Exploring a convenient method for controllable synthesis of ZnS hollow nanostructures and clarifying the formation mechanisms are important prerequisites for subsequent performance regulation. In this article, we propose a facile method for controllable preparation of homogeneous ZnS hollow nanospheres and clarified the morphological evolution mechanism. ZnS hollow nanospheres with uniform size and good dispersibility were synthesized by adding PVP and excessive thiourea during the hydrothermal process. By systematically studying the influence of experimental parameters on the morphology, the influence diagram of thiourea and PVP on the product morphology was drawn. It is found that excess thiourea is the determining factor for the formation of hollow structures, and PVP plays a key role in the size uniformity and dispersion of the product. The formation mechanism is proposed in which thiourea serves as the reaction source and adsorbed molecule, while PVP serves as a dispersant, both of which worked together to the product morphology and size. The photocatalytic experiments indicate that hollow nanospheres with small size and good dispersibility exhibit a better photocatalytic degradation effect. This work elaborates on how the adsorption of thiourea molecules and the steric hindrance of PVP affect the grain aggregation and growth, which inspirational for the controllable synthesis of the required ZnS nanostructures and further research on their properties.

Ultrathin TiO2(B) nanosheets-decorated hollow CoFeP cube as PMS activator for enhanced photocatalytic activity

A novel TiO2(B)/phosphidated CoFe Prussian blue analogs (CoFeP) photocatalyst with core–shell structure was synthesized by hydrothermal method for the activation of peroxymonosulfate (PMS) to degrade TC under solar light. TiO2(B), an ultrathin two-dimensional (2D) layered material, is widely used in photocatalysis. However, the low light absorption efficiency and slow electron mobility limit the application of TiO2(B) in photocatalysis. Here, TiO2(B) was in-situ grown on the surface of phosphidated CoFe Prussian blue analogs (CoFeP). The composites with a core–shell structure can activate peroxymonosulfate (PMS) to degrade tetracycline (TC) under solar light. The optimized TiO2(B)/CoFeP heterojunction achieves a TC degradation rate of 94 % within 5 min, due to that it effectively suppresses the recombination of photogenerated charges and improves light absorption ability. The phosphorization of CoFePBA (CoFe Prussian blue analogs) not only promoted the formation of hollow structures but improved the carrier mobility between TiO2(B) and CoFeP. At the same time, the rapid redox cycle of Fe and Co metal ions promoted the activation of PMS and the rapid degradation of TC. This work provides a new core–shell TiO2(B)/CoFeP heterojunction for sustainable water purification via PMS activation.

The Effect of the Pd Precursors on the Shape of Hollow Ag-Pd Alloy Nanoparticles Using Ag Nanocubes as Seeds.

Hollow Ag-Pd nanoparticles have potentially high catalytic performance owing to their larger surface area compared to their corresponding solid nanoparticles. We successfully fabricated hollow Ag-Pd alloy nanodendrites and nanoboxes by using different Pd precursors (H2PdCl4 and Pd(acac)2) to achieve large surface area nanoboxes. Interestingly, the use of a H2PdCl4 precursor led to the formation of hollow nanodendrite structures, whereas the slower reduction of Pd(acac)2 led to the formation of hollow nanoboxes. The microstructure and chemical composition of Ag-Pd nanoparticles and properties of their growth solutions were investigated by transmission electron microscopy, energy-dispersive X-ray spectroscopy, and ultraviolet-visible spectroscopy.

The role of concentration waves in synthesizing hollow multi-shelled structures

Recently in Angewandte Chemie International Edition, Wang and co-workers presented a comprehensive study that combines a mathematical model with experiments to reveal the key role of concentration waves in the formation of hollow multi-shelled structures (HoMSs) and provides a theoretical guideline for the precise engineering of HoMSs for targeted applications. Recently in Angewandte Chemie International Edition, Wang and co-workers presented a comprehensive study that combines a mathematical model with experiments to reveal the key role of concentration waves in the formation of hollow multi-shelled structures (HoMSs) and provides a theoretical guideline for the precise engineering of HoMSs for targeted applications.

Flexible Thermal Protection Polymeric Materials with Self-Sensing and Self-Adaptation Deformation Abilities

Based on the strategy of killing two birds with one stone, we introduce thermally expandable microspheres into a silicone rubber matrix to fabricate temperature-responsive controllable deformation materials, which exhibit intelligent deformation properties as well as enhanced thermal protection performance, for dynamic thermal protection in the next-generation morphing aircrafts. The formation of hollow structures endows the material with intelligent thermal management ability and makes the thermal conductivity controllable, meeting the requirements of rapid deformation and excellent thermal insulation. The dimensions of the material adaptively expand with increasing temperature, and a constant 50N force can be provided to ensure reliable sealing. Moreover, benefiting from the synergistic effect of the hollow structure and zinc borate in the ceramization process of the silicone rubber, the 10 mm thick material can reduce the temperature from 2000 to 63 °C, and the mass ablation rate is only 4.8 mg/s. To broaden the application of our material, a sensor with a sandwich structure composed of different functional layers is designed. It is pleasantly surprising to observe that the sensor can provide real-time remote warning of fire and overheating sites with a response time as short as 1 s. This synergistic strategy opens a new possibility to fabricate intelligent thermal protection materials.

Organic Hollow Microstructures with Room Temperature Phosphorescence

AbstractMolecular self‐assembly into hollow microstructures has great potential in catalysis, drug delivery, sensors, and nanoreactors. In contrast to well‐studied fluorescent hollow microstructures, the assembly of phosphorescent hollow microstructures has not yet been fully demonstrated. Here, two types of hollow microstructures based on organic room temperature phosphorescence (RTP) materials are prepared through a convenient vapor‐phase growth method. The observation of the assembly process and the calculations of surface energy reveal that thermodynamically driven Ostwald ripening process plays an essential role in the formation of tunable hollow structures. The universality of this growth technique for hollow microstructures is further demonstrated in various materials and even composites. Compared with non‐hollow structures, the phosphorescent hollow microstructures exhibit high sensitivity to oxygen, indicating the potential of organic hollow microstructure with RTP.

One-step synthesis of anatase-free hollow titanium silicalite-1 by the solid-phase conversion method

Development of economic routes for synthesis of hollow titanium silicalite-1 (TS-1) zeolite is of great importance in industry. However, there are still challenges to synthesize hollow TS-1 zeolite without anatase TiO 2 . In this work, a one-step strategy without mesoporogen by the solid-phase conversion method was successfully developed to synthesize anatase-free hollow TS-1. The appropriate low amount of TPAOH (TPA/SiO 2 = 0.13) and the suitable crystallization temperature (170 °C) can not merely induce the formation of hollow structures, but also enable more titanium to enter the framework. Moreover, the transformation mechanism based on crystallization rate and dissolution rate was proposed according to the investigation of the transformation process. The hollow TS-1 with large cavities exhibits high catalytic activity and recycle stability in 1-hexene epoxidation. The efficient strategy reported in this paper will provide new opportunities for further promoting the industrial application of hollow TS-1. • Hollow TS-1 has been synthesized by the solid-phase conversion method. • No extra anatase TiO 2 exists in Hollow TS-1. • The TPAOH content and temperature are essential for the synthesis of Hollow TS-1. • The transformation mechanism based on crystallization rate and dissolution rate was proposed.

Environmentally Benign Formation of Nickel Hexacyanoferrate-Derived Mesoframes for Heterogeneous Catalysis.

The tetramethylammonium hydroxide (TMAH)-controlled alkaline etching of nickel hexacyanoferrate (NiHCF) mesocrystals is explored. The alkaline etching enables the formation of hollow framework structures with an increased surface area, the exposure of active Ni and Fe sites and the retention of morphology. The ambient reaction conditions enable the establishment of a sustainable production. Our work reveals novel perspectives on the eco-friendly synthesis of hollow and colloidal superstructures for the efficient degradation of the organic contaminants rhodamine-B and bisphenol-A. In the case of peroxomonosulfate (PMS)-mediated bisphenol-A degradation, the rate constant of the etched mesoframes was 10,000 times higher indicating their significant catalytic activity.

Facile transformation of carboxymethyl cellulose beads into hollow composites for dye adsorption

Novel millimeter hollow microspheres were fabricated from carboxymethyl cellulose microspheres and polyethyleneimine using glutaraldehyde as a crosslinking agent. The hollow microspheres prepared with different polyethyleneimine usages and different polyethyleneimine treatment time were investigated deeply and characterized via SEM-EDX, FT-IR, and BET surface area analysis. It was shown that polyethyleneimine could break the coordination bonds between the carboxyl and Al (III) in carboxymethyl cellulose microspheres, leading to the formation of hollow structures. Most importantly, the usage and treatment time of polyethyleneimine can distinctly tailor the structure of the carboxymethyl cellulose microspheres, resulting in the formation of different hollow microspheres with varied shell thickness and size. Most importantly, we found that the prepared hollow microspheres have excellent adsorption performance toward targeted methyl blue under testing conditions. By virtue of the large accessible amount of -NH2 groups and its unique hollow structure, this type of millimeter hollow microspheres have broad application prospects in the treatment of emerging contaminants in wastewater.

Photoregulated Morphological Transformation of Spiropyran Derivatives Achieving the Tunability of Interfacial Hydrophilicity.

Regulation of self-assembly morphology is an effective strategy to obtain advanced functional materials with expected properties. However, achieving remarkable morphological transformation by light irradiation is still a challenge. Herein, three simple spiropyran derivatives (SP1, SP2, and SP3) are constructed, achieving different degrees of morphological transformation from nanospheres to hollow tadpole-like structures (SP3), tubular structures (SP2), and microsheets (SP1) after ultraviolet light irradiation. Interestingly, the hollow tadpole-like structures (SP3) can further extend to Y-shaped or T-shaped tubular morphology. In the process, SP1, SP2, and SP3 can be isomerized from a closed-ring form (hydrophobicity) to an open-ring form (hydrophilicity) in different degrees, interacting differently with methanol solvent molecules. The formation of hollow structures or microsheets along with the isomerization of spiropyran derivatives contributes to the adjustment of the hydrophilicity of the interface. Therefore, SP1, SP2, and SP3 with photoregulated morphological transformation show promising applications in tunable interface materials.

Green BTX production from methyl oleate over hierarchical HZSM-5 zeolites prepared by NaOH treatment

BTX production from methyl oleate over four HZSM-5 zeolites with various pore structure was evaluated in a fixed-bed microreactor. HZSM-5 zeolite (SiO2/Al2O3 = 38) was synthesized by the hydrothermal method, and treated using NaOH solutions with different concentrations (0.1 M, 0.3 M, and 0.5 M) to prepare hierarchical HZSM-5 zeolites with different cavity volumes and mesopores in shells. Multi-characterizations (including XRD, NH3-TPD, SEM, TEM, Py-IR, XPS and N2 adsorption–desorption isotherms) revealed that the NaOH treatment induced the formation of hollow structures and mesopores in the HZSM-5 crystals without destroying the topological structure, increased the acid amount and pore volume and decreased the molar SiO2/Al2O3 ratio and BET surface, resulting in high aromatic yields in the catalytic aromatization of methyl oleate. The BTX yields and aromatic content in liquid over hierarchical HZSM-5 zeolites increased with increasing NaOH concentration. The HZSM-5 zeolite treated with a 0.5 M NaOH solution with a high amount of acid and large cavity volume led to a high aromatic yield of 51.28 wt%.

SnO<sub>2</sub> Nano/Microfibers for Gas Sensors

SnO2 is an n-type semiconductor with the band gap energy of 3.6 eV. It has been widely studied for gas sensing applications, the sensitivity of which can be easily tuned by the operating temperature. The presented paper is focused on the preparation and detailed characterization of the hollow SnO2 nano/microfibers suitable for gas detection sensors. Ceramic SnO2 fibers were produced by needleless electrospinning and followed by the calcination process. The characterization was performed by SEM, TEM, XRD, and Raman spectroscopy. The precursor PVP/SnO2 fibers had amorphous nature. The calcination of the electro spun precursor resulted in the formation of hollow crystalline fibrous structures. The formation mechanism of hollow fibers has been described. Subsequently, a homogeneous fibrous layer was created by the spin coating method for gas sensing applications.

Ultra-small hollow ternary alloy nanoparticles for efficient hydrogen evolution reaction.

Hollow nanoparticles with large specific surface area and high atom utilization are promising catalysts for the hydrogen evolution reaction (HER). We describe herein the design and synthesis of a series of ultra-small hollow ternary alloy nanostructures using a simple one-pot strategy. The same technique was demonstrated for hollow PtNiCu nanoparticles, hollow PtCoCu nanoparticles and hollow CuNiCo nanoparticles. During synthesis, the displacement reaction and oxidative etching played important roles in the formation of hollow structures. Moreover, our hollow PtNiCu and PtCoCu nanoparticles were single crystalline, with an average diameter of 5 nm. Impressively, ultra-small hollow PtNiCu nanoparticles, containing only 10% Pt, exhibited greater electrocatalytic HER activity and stability than a commercial Pt/C catalyst. The overpotential of hollow PtNiCu nanoparticles at 10 mA cm−2 was 28 mV versus reversible hydrogen electrode (RHE). The mass activity was 4.54 A mgPt−1 at −70 mV versus RHE, which is 5.62-fold greater than that of a commercial Pt/C system (0.81 A mgPt−1). Through analyses of bonding and antibonding orbital filling, density functional theory calculations demonstrated that the bonding strength of different metals to the hydrogen intermediate (H*) was in the order of Pt > Co > Ni > Cu. The excellent HER performance of our hollow PtNiCu nanoparticles derives from moderately synergistic interactions between the three metals and H*. This work demonstrates a new strategy for the design of low-cost and high-activity HER catalysts.

Electrostatic assisted fabrication and dissociation of multi-component proteinosomes

Self-assembly of proteins into well-organized proteinosomes has attracted great interest due to the potential medical and biological applications of the structures. Herein, a new concept of electrostatic assisted fabrication of proteinosomes is proposed. The self-assembly is performed by using multi-step dialysis approach, where negatively charged bovine serum albumin-poly(N-isopropylacrylamide) (BSA-PNIPAM) bioconjugate and positively charged enzyme (lysozyme or trypsin) are initially dissolved in phosphate buffer (PB) solution at a high salt concentration, and subsequently the protein solution is dialyzed against PB solutions at low salt concentrations, resulting in the formation of biofunctional proteinosomes. Transmission electron microscopy (TEM), cryo-TEM and light scattering results all demonstrate the formation of hollow structures. The wall of a proteinosome is composed of BSA and enzyme (lysozyme or trypsin), and PNIPAM chains of the bioconjugate are in the corona stabilizing the structure. In comparison with the native enzymes, the enzyme molecules in the assemblies basically retain their bioactivities. The proteinosomes formed by BSA-PNIPAM and lysozyme can be dissociated in the presence of trypsin, and those self-assembled by BSA-PNIPAM and trypsin are able to be self-hydrolyzed, resulting in the dissociation of the structures in aqueous solution. The size and morphology changes of the proteinosomes in the hydrolysis are studied.