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The rational design of material structures can be an effective approach to enhance the performance of solar-driven clean water production. In this study, a hollow structural nanofibrous membrane was developed by mimicking the hollow structure of polar bear hair using coaxial electrospinning. The shell layer consisted of carbon nanoparticles (C NPs) decorated CuO nanosheets (C@CuO), that exhibited photothermal conversion capacity. Meanwhile, the core layer containing hydrophilic polyvinylpyrrolidone (PVP) was eliminated to generate the hollow structure. The C NPs enhanced the membrane's light absorption to increase thermal energy harvesting, while the CuO nanosheets improved the membrane's wettability enhancing the water supply. Furthermore, the hollow structure limited air convection, prevented heat conduction, and minimized heat radiation, enabling heat localization to be achieved inside the membrane to suppress heat loss during evaporation. For 3.5 wt% saline water and actual dye wastewater, the C@CuO nanofibrous membrane achieved high evaporation rates of 1.36 kg·m-2·h-1 and 1.31 kg·m-2·h-1, respectively, under 1 sun illumination. Moreover, even after continuous 6-h evaporation tests, the evaporation rate of the C@CuO membrane remained virtually unchanged, highlighting its long-term stability with regard to salt resistance in real-world applications. Additionally, the remarkable flexibility of the C@CuO membrane offers convenience during operation and guarantees dimensional stability when it is subjected to external stresses. These discoveries should inspire subsequent research on developing delicate architectural materials and exploring their potential applications in various fields, including energy generation, clean water production, and thermal insulation.

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Transition metal sulfides (TMSs) show the potential to be competitive candidates as next-generation anode materials for Li-ion batteries (LIBs) due to their high theoretical specific capacity. However, sluggish ionic/electronic transportation and huge volume change upon lithiation/delithiation remain major challenges in developing practical TMS anodes. We rationally combine structural design and interface engineering to fabricate a tubular-like nanocomposite with embedded crystalline Cu9S5 nanoparticles and amorphous MoSx in a carbon matrix (C/Cu9S5-MoSx NTs). On the one hand, the hybrid integrated the advantages of 1D hollow nanostructures and carbonaceous materials, whose high surface-to-volume ratios, inner void, flexibility, and high electronic conductivity not only enhance ion/electron transfer kinetics but also effectively buffer the volume changes of metal sulfides during charge/discharge. On the other hand, the formation of crystalline-amorphous heterostructures between Cu9S5 and MoSx could further boost charge transfer due to an induced built-in electric field at the interface and the presence of a long-range disorder phase. In addition, amorphous MoSx offers an extra elastic buffer layer to release the fracture risk of Cu9S5 crystalline nanoparticles during repetitive electrochemical reactions. Benefiting from the above synergistic effect, the C/Cu9S5-MoSx electrode as an LIB anode in an ether-based electrolyte achieves a high-rate capability (445 mAh g-1 at 6 A g-1) and superior ultralong-term cycling stability, which delivers an initial discharge capacity of 561 mAh g-1 at 2 A g-1 and its retention capacity after 3600 cycles (376 mAh g-1) remains higher than that of commercial graphite (372 mAh g-1).

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Germanium based nanomaterials are very promising as the anodes for the lithium ion batteries since their large specific capacity, excellent lithium diffusivity and high conductivity. However, their controllable preparation is still very difficult to achieve. Herein, we facilely prepare a unique carbon coating Ge nanospheres with a cubic hollow structure (Ge@C) via a hydrothermal synthesis and subsequent pyrolysis using low-cost GeO2 as precursors. The hollow Ge@C nanostructure not only provides abundant interior space to alleviate the huge volumetric expansion of Ge upon lithiation, but also facilitates the transmission of lithium ions and electrons. Moreover, experiment analyses and density functional theory (DFT) calculations unveil the excellent lithium adsorption ability, high exchange current density, low activation energy for lithium diffusion of the hollow Ge@C electrode, thus exhibiting significant lithium storage advantages with a large charge capacity (1483 mAh/g under 200 mA g-1), distinguished rate ability (710 mAh/g under 8000 mA g-1) as well as long-term cycling stability (1130 mAh/g after 900 cycles under 1000 mA g-1). Therefore, this work offers new paths for controllable synthesis and fabrication of high-performance Ge based lithium storage nanomaterials.

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Developing a reliable method for constructing mesoporous metal-organic frameworks (MOFs) with single-crystalline forms remains a challenging task despite numerous efforts. This study presents a solvent-mediated assembly method for fabricating zeolitic imidazolate framework (ZIF) single-crystal nanoparticles with a well-defined micro-mesoporous structure using polystyrene-block-poly(ethylene oxide) diblock copolymer micelles as a soft-template. The precise control of particle sizes, ranging from 85 to 1200 nm, is achieved by regulating nucleation and crystal growth rates while maintaining consistent pore diameters in mesoporous nanoparticles and a rhombohedral dodecahedron morphology. Furthermore, this study presents a robust platform for nanoarchitecturing to prepare hierarchically porous materials (e.g., core-shell and hollow structures), including microporous ZIF@mesoporous ZIF, hollow mesoporous ZIF, and mesoporous ZIF@mesoporous ZIF. Such a multimodal pore design, ranging from microporous to microporous/mesoporous and further micro-/meso-/macroporous, provides significant evidence for the future possibility of the structural design of MOFs.

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Photocatalytic splitting of the Cß-O bond is regarded as a prospective strategy for transforming lignin, and it is imperative to develop novel photocatalysts with effective photogenerated charges separation and solar absorption capacity. Herein, a novel hollow ZIF-8/CdS heterostructure photocatalyst was synthesized for the catalytic splitting of lignin Cß-O bonds. The photocatalytic cleavage rate of Cß-O bond of ligin ß-O-4 reached 30.3∙mmol∙h-1∙g-1 within 20 min under visible light exposure. It is noteworthy that the utilization of intricate natural lignin molecules in this photocatalytic system has yielded successful depolymerization. The DFT and XPS results indicate a potential unidirectional electron migration from ZIF-8 to CdS in ZIF-8/CdS composites transfer. This electron transport path follows the direct Z-scheme heterostructure mechanism, resulting in the generation of an internal electric field between ZIF-8 and CdS. Impressively, the synergistic combination of the hollow structure and Z-scheme heterostructure effectively enhances the efficiency of charge carrier separation and maintains a robust redox potential, thereby facilitating Cα-radical generation. This study proposes a novel photocatalyst design strategy that integrates hollow structures and Z-scheme heterojunctions, with the aim of targeting the depolymerization of the Cß-O bond in lignin.

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Exploring high-performance photocatalysts still remains a big challenge due to poor charge separation efficiency. Herein, we prepare a novel anatase/rutile TiO2-Ag3PO4 hollow photocatalyst (A/R-TiO2-Ag3PO4) for addressing this challenge. Microstructural characterization and photoelectric measurements confirm that the synergy of hollow structure and dual-heterojunction can provide abundant active sites and boost efficient charge separation through dual-pathway charge transfer mechanism. The A/R-TiO2-Ag3PO4 photocatalyst exhibits the highest photocurrent density (15.25 µA cm-2), which is 8.4 and 5.2 times than that of A-TiO2-Ag3PO4 (1.82 µA cm-2) and P25-Ag3PO4 (2.93 µA cm-2), respectively. Photo-degradation experiment shows that A/R-TiO2-Ag3PO4 presents a high degradation percentage (98.7 %) of thiamethoxam (THX) within 30 min, which is 1.45 and 1.23 times than that of A-TiO2-Ag3PO4 (68.1 %) and P25-Ag3PO4 (80.7 %), respectively. Furthermore, the degradation percentage of THX by A/R-TiO2-Ag3PO4 is as high as 96.4 % after seven successive cycles, indicating excellent cycling stability. Therefore, this work provides a new insight into exploring other high-performance photocatalysts by combining hollow structure and dual-heterojunction.

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Avoiding the stacking of active sites in catalyst structural design is a promising route for realizing active oxygen evolution reaction (OER). Herein, using a CoFe Prussian blue analoge cube with hollow structure (C-CoFe PBA) as a derived support, a highly effective Ni2P-FeP4-Co2P catalyst with a larger specific surface area is reported. Benefiting from the abundant active sites and fast charge transfer capability of the phosphide nanosheets, the Ni2P-FeP4-Co2P catalyst in 1 m KOH requires only overpotentials of 248 and 277 mV to reach current density of 10 and 50 mA cm-2 and outperforms the commercial catalyst RuO2 and most reported non-noble metal OER catalysts. In addition, the two-electrode system consisting of Ni2P-FeP4-Co2P and Pt/C is able to achieve a current density of 10 and 50 mA cm-2 at 1.529 and 1.65 V. This work provides more ideas and directions for synthesizing transition metal catalysts for efficient OER performance.

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The efficiency of photocatalytic hydrogen evolution can be significantly enhanced while maintaining cost-effectiveness through the synergistic effect of defect surface engineering and multi-component heterojunctions. The structure and properties of NiCo2O4 nanorods were modified by inducing oxygen vacancies at different temperatures in this study, resulting in improved optical properties and electron adsorption capacity. The presence of oxygen vacancies leads to a reduction in the band gap of NiCo2O4, thereby enhancing electron transport efficiency through band gap engineering. Simultaneously, surface properties undergo changes, and vacancy defects serve as electron trapping centers, facilitating an increased participation of electrons in the hydrogen evolution reaction process. The dodecahedron KMP with a cavity structure is additionally introduced to form an S-scheme heterojunction with NiCo2O4. This establishes a novel mechanism for electron transport, which effectively enhances the separation of electron-hole pairs and improves the redox capacity of the photocatalytic system. The adsorption of intermediates in the hydrogen production process is enhanced through synergistic regulation of d-band centers via surface defect engineering and S-scheme heterojunction. Additionally, this approach improves the separation efficiency of electron-hole pairs and accelerates electron transfer dynamics, significantly enhancing hydrogen production efficiency.

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The construction of heterostructure photoelectrodes can enhance the performance of photoelectrochemical (PEC) sensors. However, it is still a critical challenge to achieve efficient transfer of interface carriers. In this paper, we propose a strategy of "photo-modulated interface charge" to design a PEC sensor based on a hollow hexagonal tubular In2S3/AgInS2 in situ Z-type heterojunction for the susceptible detection of Programmed Death-ligand 1 (PD-L1). The hollow structured In2S3/AgInS2 is ingeniously synthesized employing indium-sourced MIL-68 as a sacrificial template and in situ cation exchange technique. This composite material has close contact interfaces due to in situ growth, which facilitates the spontaneous establishment of a robust and stable built-in electric field between the interfaces. Moreover, the inner cavity structure promotes multiple light refractions and scatterings, significantly enhancing light trapping capability. Under the influence of both light irradiation and electric field force, the migration direction of the interfacial charge is reversed, forming a Z-transfer path, which effectively delays the compounding of the electron-hole pairs (e-/h+) and further improves the sensitivity of the sensor. The minimum detection threshold of the PEC sensor is 26.58 fg/mL, and the feasibility of real samples is investigated, providing new insights for early diagnosis and prognostic treatment of diseases.

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Doping heteroatoms into metal phosphides to modify their electronic structure is an effective method, but the incomplete exposure of active sites is its inherent drawback. In this experiment, both Se doping and P vacancies are simultaneously introduced into CoP-Fe2P (named CoFe-P-Se) to enhance the internal reactivity. Benefiting from the unique hollow porous structure derived from the MOF-on-MOF template, as well as the enhanced intrinsic activity achieved by P defects and Se doping, CoFe-P-Se exhibits a high specific capacitance of 8.41 F cm-2 at a current density of 2 mA cm-2 when used as a supercapacitor electrode. When assembled into a hybrid supercapacitor with activated carbon, the energy density reaches 0.488 mWh cm-2 at a power density of 1.534 mW cm-2, and the capacity retention after 5000 charge-discharge cycles is as high as 90.65%. As an oxygen evolution reaction (OER) electrode, the CoFe-P-Se electrode shows a low overpotential of only 230 mV at a current density of 10 mA cm-2 and 278 mV at 100 mA cm-2. Additionally, it exhibits excellent stability for over 50 h at a current density of 100 mA cm-2. The designed element doping and vacancy engineering in this work will provide an insight for constructing high-performance electrodes.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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