Dual function of carboxymethyl cellulose scaffold: A one-stone-two-birds strategy to prepare double-layer hollow ZIF-67 derivates for flame retardant epoxy composites.

Aluminum hypophosphite (AHP) has been used as a flame retardant for a long time. Previous studies about AHP employed in flame retardant materials mostly focus on coating, modification, and complex system. It is valuable to explore simple experimental steps to prepare nano hybrids with AHP and metal-organic frameworks (MOFs). We found acidic substances could etch zeolitic imidazolate framework-67 (ZIF-67) to obtain MOF derivatives. Unfortunately, AHP and ZIF-67 could not directly form a hybrid. Therefore, carboxymethylcellulose (CMC) is introduced as a dual function layer (buffer and support). The CMC resists the complete conversion of ZIF-67 etched by phosphoric acid to amorphous cobalt phosphate hydrate (ACP). Meanwhile, CMC containing hydroxyl groups combines with AHP through electrostatic interaction and coordination bonds. A double-layer hollow MOF derivative is synthesized through this one-stone-two-birds strategy. Due to multiple flame retardant elements and unique nanostructure, this MOF derivative endows epoxy (EP) resin with excellent flame retardancy. With 2.0 wt% addition, the peak heat release rate (pHRR) and total heat release (THR) of EP/AHP/ACP@CMC are decreased by 47.8 and 21.0 %, respectively. This study proposes a novel scheme that converts AHP into MOF derivatives as high-performance FRs.

Role of midsole hollow structure in energy storage and return in running shoes.

Understanding the relationship between footwear features and their potential influence on running performance can inform the ongoing innovation of running footwear, aimed at pushing the limits of humans. A notable shoe feature is hollow structures, where an empty space is created in the midsole. Presently, the potential biomechanical effect of the hollow structures on running performance remains unknown. We investigated the role of hollow structures through quantifying the magnitude and timing of foot and footwear work. Sixteen male rearfoot runners participated in an overground running study in three shoe conditions: (a) a shoe with a hollow structure in the forefoot midsole (FFHS), (b) the same shoe without any hollow structure (Filled-FFHS) and (c) a shoe with a hollow structure in the midfoot midsole (MFHS). Distal rearfoot power was used to quantify the net power generated by foot and footwear together. The magnitude and timing of distal rearfoot work and ankle joint work were compared across shoe conditions. The results indicated that MFHS can significantly (p = 0.024) delay distal rearfoot energy return (3.4 % of stance) when compared to Filled-FFHS. Additionally, FFHS had the greatest positive (0.425 J/kg) and negative (-0.383 J/kg) distal rearfoot work, and the smallest positive (0.503 J/kg) and negative (-0.477 J/kg) ankle joint work among the three conditions. This showed that the size and location of the midsole hollow structure can affect timing and magnitude of energy storage and return. The forefoot hollow shoe feature can effectively increase distal rearfoot work and reduce ankle joint work during running.

Stable Structure and Fast Ion Diffusion: A Flexible MoO2@Carbon Hollow Nanofiber Film as a Binder-Free Anode for Sodium-Ion Batteries with Superior Kinetics and Excellent Rate Capability.

Designing innovative anode materials that exhibit excellent ion diffusion kinetics, enhanced structural stability, and superior electrical conductivity is imperative for advancing the rapid charge-discharge performance and widespread application of sodium-ion batteries. Hollow-structured materials have received significant attention in electrode design due to their rapid ion diffusion kinetics. Building upon this, we present a high-performance, free-standing MoO2@hollow carbon nanofiber (MoO2@HCNF) electrode, fabricated through facile coaxial electrospinning and subsequent heat treatment. In comparison to MoO2@carbon nanofibers (MoO2@CNFs), the MoO2@HCNF electrode demonstrates superior rate capability, attributed to its larger specific surface area, its higher pseudocapacitance contribution, and the enhanced diffusion kinetics of sodium ions. The discharge capacities of the MoO2@HCNF (MoO2@CNF) electrode at current densities of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 A g-1 are 195.55 (155.49), 180.98 (135.20), 163.81 (109.71), 144.05 (90.46), 121.16 (71.21) and 88.90 (44.68) mAh g-1, respectively. Additionally, the diffusion coefficients of sodium ions in the MoO2@HCNFs are 8.74 × 10-12 to 1.37 × 10-12 cm2 s-1, which surpass those of the MoO2@CNFs (6.49 × 10-12 to 9.30 × 10-13 cm2 s-1) during the discharging process. In addition, these prepared electrode materials exhibit outstanding flexibility, which is crucial to the power storage industry and smart wearable devices.

Nickel-Cobalt Bimetal Hierarchical Hollow Nanosheets for Efficient Oxygen Evolution in Seawater.

The electrochemical splitting of seawater is promising but also challenging for sustainable hydrogen gas production. Herein, ZIF-67 nanosheets are grown on nickel foam and then etched by Ni2+ in situ to obtain a hierarchical hollow nanosheets structure, which demonstrates outstanding OER performance in alkaline seawater (355 mV at 100 mA cm-2). Diven by a silicon solar panel, an overall electrolysis energy efficiency of 62% is achieved at a high current of 100 mA cm-2 in seawater electrolytes. This work provides a new design route for improving the catalytic activity of metal organic framework materials.

Synergy of Oxygen Vacancy and Surface Modulation Endows Hollow Hydrangea-like MnCo2O4.5 with Enhanced Capacitive Performance.

Surface chemistry and bulk structure jointly play crucial roles in achieving high-performance supercapacitors. Here, the synergistic effect of surface chemistry properties (vacancy and phosphorization) and structure-derived properties (hollow hydrangea-like structure) on energy storage is explored by the surface treatment and architecture design of the nanostructures. The theoretical calculations and experiments prove that surface chemistry modulation is capable of improving electronic conductivity and electrolyte wettability. The structural engineering of both hollow and nanosheets produces a high specific surface area and an abundant pore structure, which is favorable in exposing more active sites and shortens the ion diffusion distance. Benefiting from its admirable physicochemical properties, the surface phosphorylated MnCo2O4.5 hollow hydrangea-like structure (P-MnCoO) delivers a high capacitance of 425 F g-1 at 1 A g-1, a superior capability rate of 63.9%, capacitance retention at 10 A g-1, and extremely long cyclic stability (91.1% after 10,000 cycles). The fabricated P-MnCoO/AC asymmetric supercapacitor achieved superior energy and power density. This work opens a new avenue to further improve the electrochemical performance of metal oxides for supercapacitors.

Molecular Engineering and Morphology Control of Covalent Organic Frameworks for Enhancing Activity of Metal-Enzyme Cascade Catalysis.

Metal-enzyme integrated catalysts (MEICs) that combine metal and enzyme offer great potential for sustainable chemoenzymatic cascade catalysis. However, rational design and construction of optimal microenvironments and accessible active sites for metal and enzyme in individual nanostructures are necessary but still challenging. Herein, Pd nanoparticles (NPs) and Candida antarctica lipase B (CALB) are co-immobilized into the pores and surfaces of covalent organic frameworks (COFs) with tunable functional groups, affording Pd/COF-X/CALB (X = ONa, OH, OMe) MEICs. This strategy can regulate the microenvironment around Pd NPs and CALB, and their interactions with substrates. As a result, the activity of the COF-based MEICs in catalyzing dynamic kinetic resolution of primary amines is enhanced and followed COF-OMe > COF-OH > COF-ONa. The experimental and simulation results demonstrated that functional groups of COFs modulated the conformation of CALB, the electronic states of Pd NPs, and the affinity of the integrated catalysts to the substrate, which contributed to the improvement of the catalytic activity of MEICs. Further, the MEICs are prepared using COF with hollow structure as support material, which increased accessible active sites and mass transfer efficiency, thus improving catalytic performance. This work provides a blueprint for rational design and preparation of highly active MEICs.

Inhibiting the "isolated island" effect in simulated bone defect repair using a hollow structural scaffold design.

The treatment of bone tissue defects remains a complicated clinical challenge. Recently, the bone tissue engineering (BTE) technology has become an important therapeutic approach for bone defect repair. Researchers have improved the scaffolds, cells, and bioactive factors used in BTE through various existing bone repair material preparation strategies. However, due to insufficient vascularization, inadequate degradation, and fibrous wrapping, most BTE scaffolds impede new bone ingrowth and the reconstruction of grid-like connections in the middle and late stages of bone repair. These non-degradable scaffolds become isolated and disordered like independent "isolated islands", which leads to the failure of osteogenesis. Consequently, we hypothesized that the "island effect" prevents successful bone repair. Accordingly, we proposed a new concept of scaffold modification-osteogenesis requires a bone temporary shelter (also referred to as the empty shell osteogenesis concept). Based on this concept, we consider that designing hollow structural scaffolds is the key to mitigating the "isolated island" effect and enabling optimal bone regeneration and reconstruction.

"Cave Effect" Induces Self-Assembled Bimetallic Hollow Structure for Three-in-One Lateral Flow Immunoassay.

Bimetallic hollow structures have attracted much attention due to their unique properties, but they still face the problems of nonuniform alloys and excessive etching leading to structural collapse. Here, uniform bimetallic hollow nanospheres are constructed by pore engineering and then highly loaded with hemin (Hemin@MOF). Interestingly, in the presence of polydopamine (PDA), the competitive coordination between anionic polymer (γ-PGA) and dimethylimidazole does not lead to the collapse of the external framework but self-assembly into a hollow structure. By constructing the Hemin@MOF immune platform and using E. coli O157:H7 as the detection object, we find that the visual detection limits can reach 10, 3, and 3 CFU/mL in colorimetric, photothermal, and catalytic modes, which is 4 orders of magnitude lower than the traditional gold standard. This study provides a new idea for the morphological modification of the metal-organic skeleton and multifunctional immunochromatography detection.

Three-Dimensional-Printed Spherical Hollow Structural Scaffolds for Guiding Critical-Sized Bone Regeneration.

The treatment of bone tissue defects continues to be a complex medical issue. Recently, three-dimensional (3D)-printed scaffold technology for bone tissue engineering (BTE) has emerged as an important therapeutic approach for bone defect repair. Despite the potential of BTE scaffolds to contribute to long-term bone reconstruction, there are certain challenges associated with it including the impediment of bone growth within the scaffolds and vascular infiltration. These difficulties can be resolved by using scaffold structural modification strategies that can effectively guide bone regeneration. This study involved the preparation of biphasic calcium phosphate spherical hollow structural scaffolds (SHSS) with varying pore sizes using 3D printing (photopolymerized via digital light processing). The chemical compositions, microscopic morphologies, mechanical properties, biocompatibilities, osteogenic properties, and impact on repairing critical-sized bone defects of SHSS were assessed through characterization analyses, in vitro cytological assays, and in vivo biological experiments. The results revealed the biomimetic properties of SHSS and their favorable biocompatibility. The scaffolds stimulated cell adhesion, proliferation, differentiation, and migration and facilitated the expression of osteogenic genes and proteins, including Col-1, OCN, and OPN. Furthermore, they could effectively repair a critical-sized bone defect in a rabbit femoral condyle by establishing an osteogenic platform and guiding bone regeneration in the defect region. This innovative strategy presents a novel therapeutic approach for assessing critical-sized bone defects.

Hollow Microcavity Electrode for Enhancing Light Extraction.

Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction enhancement. A corrugated semi-transparent electrode incorporating a periodic hollow-structure array was designed through a simulation that utilizes finite-difference time-domain computational analysis. The corrugated profile, stemming from the periodic hollow structure, was fabricated using laser interference lithography, which allows the precise engineering of various geometrical parameters by controlling the process conditions. The semi-transparent electrode consisted of a 15 nm thick Ag film, which acted as the exit mirror and induced microcavity resonance. When applied to a conventional green organic light-emitting diode (OLED) structure, the optimized nVPCL-integrated device demonstrated a 21.5% enhancement in external quantum efficiency compared to the reference device. Further, the full width at half maximum exhibited a 27.5% reduction compared to that of the reference device, demonstrating improved color purity. This study presents a novel approach by applying a hybrid thin film electrode design to optoelectronic devices to enhance optical efficiency and color purity.

Development of lightweight and high-strength hollow titanium-plated denture material using three-dimensional printing.

Owing to its desirable ability to fabricate complex shapes, three-dimensional printing is preferred over casting for manufacturing dentures. Furthermore, titanium is widely used in dental implants and dentures because of its high corrosion resistance, biocompatibility, strength, and low density. In this study, we aimed to develop a new metal denture material from three-dimensional-printed (3DP) to achieve lighter weight and greater strength than those of PMMA dentures. Hollow (3DP-H) structure and solid (3DP-S) structure titanium plate specimens of 0.5, 1.0, and 3.0 mm in thickness were used. Casted Ti, casted Co-Cr, and PMMA plates were fabricated for comparison. Elastic modulus, density, thermal conductivity, hardness, and proof stress of the specimens were measured and plotted on a radar chart to enable multifaceted evaluation. The results indicated that the density of the 3DP-H plates reduced by 28-36% compared with those of 3DP-S and cast Ti plates. The weight of the metal-denture-equivalent section of the 0.5-mm-thick 3DP-H titanium-plated denture reduced to two-thirds that of the 2.0-mm-thick PMMA denture. The proof stress of the 0.5-mm-thick 3DP-H plate increased to about 3 times that of the 2.0-mm-thick PMMA plate. The total value of the 0.5-mm-thick 3DP-H titanium plates was higher than it of the 1.0-mm-thick PMMA plates. This study suggests that it is possible to produce 3DP-H titanium plate dentures exhibiting not only extremely lightweight compared to conventional PMMA dentures but also sufficient strength.

Hollow CoP/carbon as an efficient catalyst for the peroxymonosulfate activation derived from phytic acid assisted metal-organic framework.

The catalyst's composition and rationally designed structure is significantly interlinked with its performance for wastewater remediation. Here, a novel hollow cobalt phosphides/carbon (HCoP/C) as an efficient catalyst for activating peroxymonosulfate (PMS) was prepared. The ZIF-67 was synthesized first, followed by phytic acid (PA) etching and then heat treatment was used to get HCoP/C. The PA was used as an etching agent and a source of phosphorus to prepare HCoP/C. To analyze catalytic performance, another solid cobalt phosphides/carbon (SCoP/C) catalyst was prepared for comparison. In contrast to SCoP/C, the HCoP/C exhibited higher catalytic efficiency when used to activate PMS to degrade Bisphenol A (BPA). The results showed that about 98 % of targeted pollutant BPA was removed from the system in 6 min with a rate constant of 0.78 min-1, which was 4 times higher than the solid structure catalyst. The higher catalytic performance of HCoP/C is attributed to its hollow structure. In the study, other parameters such as BPA concentration, temperature, pH, and different catalyst amount were also tested. Moreover, the electron paramagnetic resonance (EPR) and radical quenching analysis confirmed that sulfate radicals were dominant in the HCoP/C/PMS system.

Morphological and structural characteristics of the elytra reduce impact damage to ladybird beetles.

Beetle elytra act as natural protective covers and effectively shield their flexible abdomens and fragile hindwings from damage. The existing studies have attributed this contribution of the elytra to its honeycomb structures. In this combined experimental and theoretical study, we used the seven-spotted ladybird beetle to demonstrate that both biological morphology and the hollow structure of the dome-like elytra combined to reduce damage during falling. The falling ladybird beetles had a high probability (59.52%) of hitting the ground with the costal edge of the elytra. This strategy could assist with converting the translational energy into rotational kinetic energy, resulting in the reduction of the impulse during falling. In addition, the hollow structures on the elytra could further absorb the residual impact energy. In the future, this biological paradigm could be used as a basis for the development of falling/landing techniques for advanced robots.

Photoelectron Migration Boosted by Hollow Double-Shell Dyads Based on Covalent Organic Frameworks for Highly Efficient Photocatalytic Hydrogen Generation.

Photocatalytic hydrogen production based on noble metal-free systems is a promising technology for the conversion of solar energy into green hydrogen, it is pivotal and challenging to tailor-make photocatalysts for achieving high photocatalytic efficiency. Herein, we reported a hollow double-shell dyad through uniformly coating covalent organic frameworks (COFs) on the surface of hollow Co9S8. The double shell architecture enhances the scattering and refraction efficiency of incident light, shortens the transmission distance of the photogenerated charge carriers, and exposes more active sites for photocatalytic conversion. The hydrogen evolution rate is as high as 23.15 mmol g-1 h-1, which is significantly enhanced when compared with that of their physical mixture (0.30 mmol g-1 h-1) and Pt-based counterpart (11.84 mmol g-1 h-1). This work provides a rational approach to the construction of noble-metal-free photocatalytic systems based on COFs to enhance hydrogen evolution performance.

Hollow Zeolite Nanoreactor with Double Shells for Methanol Aromatization: Explicit Recognition on Catalytic Function of Inverse Elemental Zone and Shell-Cavity.

Core@shell catalyst composited of dual aluminosilicate zeolite can effectively regulate the distribution of acid sites to control hydrocarbon conversion process for the stable formation of target product. However, the diffusion restriction reduces the accessibility of inner active sites and affects synergy between core and shell. Herein, hollow ZSM-5 zeolite nanoreactor with inverse aluminum distribution and double shells are prepared and employed for methanol aromatization. It is demonstrated that the intershell cavity alleviated the steric hindrance from zeolites channel and provided more paths and pore entrance for guest molecule. Correspondingly, olefin intermediates generated from methanol over the external shell are easier to adsorb at internal acid sites for further reactions. Importantly, the diffusion of generated aromatic macromolecules to the external surface is also promoted, which slows down the formation of internal coke, and ensures the use of internal acid sites for aromatization. The aromatics selectivity of the nanoreactor remained at 8% after 154 h, while that of solid core@shell catalyst decreased to 2% after 75 h. This finding promises broader insight to improve internal active site utilization of core@shell catalyst at the diffusion level and can be great aid in the flexible design of multifunctional nanoreactors to enhance the relay efficiency.

Hollow structured CdS@ZnIn2S4 Z-scheme heterojunction for bifunctional photocatalytic hydrogen evolution and selective benzylamine oxidation.

Photocatalytic hydrogen evolution (PHE) is frequently constrained by inadequate light utilization and the rapid combination rate of the photogenerated electron-hole pairs. Additionally, conventional PHE processes are often facilitated by the addition of sacrificial reagents to consume photo-induced holes, which makes this approach economically unfavorable. Herein, we designed a spatially separated bifunctional cocatalyst decorated Z-scheme heterojunction of hollow structured CdS (HCdS) @ZnIn2S4 (ZIS), which was prepared by a sacrificial hard template method followed by photo-deposition. Consequently, PdOx@HCdS@ZIS@Pt exhibited efficient PHE (86.38 mmol·g-1·h-1) and benzylamine (BA) oxidation coupling (164.75 mmol·g-1·h-1) with high selectivity (97.34 %). The unique hollow core-shelled morphology and bifunctional cocatalyst loading in this work hold great potential for the design and synthesis of bifunctional Z-scheme photocatalysts.

Recyclable fabrication of hollow N-doped amorphous carbon nanospindles with abundant short-range curved carbon fragments as bifunctional anode for lithium/sodium ion storage.

A recyclable hard-template method is proposed to exploit spindle-shaped hollow nitrogen-doped amorphous carbon (h-NAC) with a large number of short-range curved carbon fragments as anodes for lithium/sodium ion batteries (LIBs/SIBs). Besides providing adsorption sites due to the high existence of oxygen-containing functional groups (CO and COOH), the heavily exposed edge regions also provide a favorable storage environment with high adsorption energy for Li+/Na+ due to their short-range curved structure. Importantly, the etching solution of hard templates can be recycled to generate the FeOOH nanospindles as a precursor through a simple chemical titration, which supplies a new idea for the green preparation of hollow materials. The h-NAC electrode is proven to be bifunctional for storing lithium and sodium ions, displaying favorable rate capability (255 mAh g-1 and 106 mAh g-1 at 5 A g-1 for LIBs and SIBs, respectively). After 1000 cycles at 1 A g-1, the reproducible capacities of the LIBs and SIBs kept 496 mAh g-1 and 181 mAh g-1, respectively.

Glucose-Regulated Protein 78 Targeting ICG and DOX Loaded Hollow Fe3O4 Nanoparticles for Hepatocellular Carcinoma Diagnosis and Therapy.

Purpose: Liver cancer is considered as the third leading cause of cancer-related deaths, with hepatocellular carcinoma (HCC) accounting for approximately 90% of liver cancers. Improving the treatment of HCC is a serious challenge today. The primary objective of this study was to construct SP94-Fe3O4@ICG&DOX nanoparticles and investigate their potential diagnosis and treatment effect benefits on HCC. Methods: Firstly, we synthesized and characterized SP94-Fe3O4@ICG&DOX nanoparticles and confirmed their in vitro release behavior, photothermal and photodynamic performance. Moreover, the in vivo imaging capability was also observed. Finally, the inhibitory effects on Hepa1-6 in vitro and in vivo were observed as well as biosafety. Results: SP94-Fe3O4@ICG&DOX nanoparticles have a size of ~22.1 nm, with an encapsulation efficiency of 45.2% for ICG and 42.7% for DOX, showing excellent in vivo MPI and fluorescence imaging capabilities for precise tumor localization, and synergistic photo-chemotherapy (pH- and thermal-sensitive drug release) against tumors under irradiation. With the assistance of a fluorescence molecular imaging system or MPI scanner, the location and contours of the tumor were clearly visible. Under a constant laser irradiation (808 nm, 0.6 W/cm2) and a set concentration (50 µg/mL), the temperature of the solution could rapidly increase to ~45 °C, which could effectively kill the tumor cells. It could be effectively uptaken by HCC cells and significantly inhibit their proliferation under the laser irradiation (100% inhibition rate for HCC tumors). And most importantly, our nanoparticles exhibited favorable biocompatibility with normal tissues and cells. Conclusion: This versatile agent can serve as an intelligent and promising nanoplatform that integrates multiple accurate diagnoses, precise positioning of cancer tissue, and effective coordination with synergistic tumor photodynamic therapy.

Transformation of 2D Flakes to 3D Hollow Bowls: Matthew Effect Enables Defects to Prevail in Electromagnetic Wave Absorption of Hollow rGO Bowls.

High-efficiency electromagnetic (EM) wave (EMW)-absorbing materials have attracted extensive scientific and technical interest. Although identifying the dominant EM loss mechanism in dielectric-loss materials is indispensable, it is challenging due to a complex synergism between dipole/interfacial polarization and conduction loss. Modulation of defects and microstructures can be a possible approach to determine the dominant EM loss mechanism and realize high-efficiency absorption. Herein, 2D reduced graphene oxide (rGO) flakes are integrated into a 3D hollow bowl-like structure, which increases defect sites (i.e., oxygen vacancy and lattice defect) and reduces the stacked thickness of rGO. Despite their lower stacked thicknesses, the hollow rGO bowls with more defects exhibit lower conductivities but higher permittivities. Accompanied by the transformation from 2D flakes to 3D hollow bowls, the dominant EM loss mechanism of rGO transforms from conduction loss to defect-induced polarization. Furthermore, the defect engineering and structural design endow rGO with well-matched impedance and strong EMW-absorbing capacity. A minimum reflection loss of -41.6 dB (1.3 mm) and an effective absorption bandwidth of 4.8 GHz (1.5 mm) is achieved at a filler loading of 5 wt%. This study will provide meaningful insights into the development of materials with superior EMW-absorbing performances via defect engineering and structural design.

AgNWs/Fe3O4@NC Conductive Network Hierarchical Assembly to Prepare Flexible EMI Shielding Textile.

With the rapid development of high-power electronic instruments and communication technology, efficient electromagnetic shielding materials with strong absorption of electromagnetic waves and low reflection characteristics have become the focus of the world's attention. This study designs and synthesizes N-doped carbon-coated hollow Fe3O4 nanospheres (Fe3O4@NC) by spraying Ag nanowires (AgNWs) on textiles as conductive networks. Because of the high permeability and hollow structure Fe3O4@NC, electromagnetic wave goes through a unique process of "absorption, reflection, and reabsorption" when it passes through the surface of the composite textile. In X-band (≈8.2-12.4 GHz), the average electromagnetic interference shielding effectiveness (EMI SE) reaches 50.1 dB, while the reflectance shielding efficiency (SER) is only 2.6 dB, and the average reflectance power coefficient (R) is as low as 0.45. The composite fabric has excellent properties and provides an effective strategy for electromagnetic interference shielding based on absorption.