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- 2019
- Dye-sensitized solar cell
- Hierarchical structure
- Light scattering
- TiO2 photoanode
- Nanomaterials and Technology
- National Sun Yat-sen University
- Wenzao Ursuline University of Languages
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Oxygen-Defected Molybdenum Oxides Hierarchical Nanostructure Constructed by Atomic-Level Thickness Nanosheets as an Efficient Absorber for Solar Steam Generation
摘要： Solar steam generation is a potential approach for fresh water recycling, thus attracting increasing attention recently. To further promote water evaporation rate, some new materials need to be developed, such as plasmonic transition metal oxides. In this work, we report an oxygen-defected molybdenum oxides hierarchical nanostructure (MoOx HNS) composed of ultrathin nanosheets with atomic-level thickness, which is demonstrated as an efficient absorber for solar steam generation. Benefiting from broadband light absorption and special assembled architecture, the resulting MoOx HNS loaded on a PTFE membrane (MoOx HNS Membrane) exhibits excellent performance for boosting steam generation rate. Under 1 sun (1 kW m?2) illumination, the evaporation rate can reach at 1.255 kg m?2 h?1, with the energy conversion efficiency of 85.6%, which is one of the best performance compared with other desalination materials. Meanwhile, the MoOx HNS Membrane can achieve high-performance seawater desalination in both laboratorial and outdoor conditions. The enhanced water evaporation performance can be attributed to the synergistic effects of the efficient solar-to-thermal conversion and the unique channel structure. This work expands the scope of investigated materials which can be applied in seawater desalination system.
关键词： MoOx hierarchical nanostructure,seawater desalination,photothermal conversion,oxygen vacancies,solar steam generation
更新于2025-09-23 15:21:21
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Fabrication of hierarchical sheet-on-sheet WO3/g-C3N4 composites with enhanced photocatalytic activity
摘要： Novel hierarchical sheet-on-sheet WO3/g-C3N4 (WOCN) composites were successfully fabricated by simple calcination method using acid-treated SrWO4/g-C3N4 as precursors. The morphological observation showed that WO3 nanosheets were closely anchored on the surface of g-C3N4 nanosheets to construct a hierarchical nanostructure. The as-synthesized WOCN composites exhibited a significantly higher photocatalytic activity towards the photocatalytic degradation of rhodamine B (RhB) compared to pristine g-C3N4 and WO3 under simulated sunlight irradiation. The optimum photocatalytic activity of the WOCN at a WO3 mass content of 34.6% was 6.5 and 3.0 times higher than that of pristine WO3 and g-C3N4, respectively. The enhanced photocatalytic activities of WOCN composites were attributed to the formation of hierarchical heterostructure, which provided larger specific surface area, better visible-light absorption capability, reduced the recombination of photogenerated electron-hole pairs and enhanced separation efficiency of charge carriers. A Z-scheme photocatalytic mechanism was proposed according to active species trapping experiments.
关键词： Graphitic carbon nitride,Photocatalytic degradation,Tungsten oxide,Hierarchical heterostructure,Strontium tungstate
更新于2025-09-23 15:21:21
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Hierarchically structured metamaterials with simultaneously negative mass density and Young’s modulus by using dynamic homogenization
摘要： We propose one-dimensional hierarchical metamaterials (HMMs) that have simultaneously negative mass density and Young’s modulus in the sense of effective properties. Frequency-dependent effective properties of the HMMs are evaluated by using a dynamic homogenization theory. By considering three necessary conditions for dynamic homogenizability, we verify that our proposed HMMs can have physically meaningful double negativity, whereas the conventional periodic structures cannot. In addition, HMMs yield the broader ranges of the frequency and the effective properties for double negativity due to the large number of geometrical parameters. By exploring all the possible effective properties of HMMs, we discuss whether we can design metamaterials with the opposite sign of material properties in nature, ultimately aiming at perfect impedance matching.
关键词： dynamic homogenization,double negativity,impedance matching,hierarchical metamaterials
更新于2025-09-23 15:21:21
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Efficient Analysis of Inhomogeneous Dielectric Waveguides With Dielectric Strips and Microstrips Using Discrete Mode Matching Method
摘要： In this paper a smooth starter, based on a dc/dc Buck power converter, for the angular velocity trajectory tracking task of a dc permanent magnet motor is presented. To this end, a hierarchical controller is designed, which is integrated by a control associated with the dc motor based on differential flatness at the high level, and a control related with the dc/dc Buck converter based on a cascade control scheme at the low level. The control at the high level allows the dc motor angular velocity to track a desired trajectory and also provides the desired voltage profile that must be tracked by the output voltage of the dc/dc Buck power converter. In order to assure the latter, a cascade control at the low level is designed, considering a sliding mode control for the inner current loop and a proportional-integral control for the outer voltage loop. The hierarchical controller is tested through experiments using MATLAB-Simulink and the DS1104 board from dSPACE. The obtained results show that the desired angular velocity trajectory is well tracked under abrupt variations in the system parameters and that the controller is robust in such operation conditions, confirming the validity of the proposed controller.
关键词： sliding mode control (SMC),Cascade control,differential flatness,dc/dc Buck power converter,trajectory tracking,hierarchical controller,dc motor,proportional-integral (PI) control,smooth starter
更新于2025-09-23 15:21:01
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Hierarchical Microswarms with Leader-Follower-Like Structures: Electrohydrodynamic Self-Organization and Multimode Collective Photoresponses
摘要： Swarming micro/nanomotors can self-organize into cohesive groups to execute cooperative tasks. To date, research work has focused on the construction of egalitarian microswarms composed of similar individuals. The construction and collective behaviors of hierarchical leader–follower-like microswarms are demonstrated. By inducing converging electrohydrodynamic flows under an AC electric field, dielectric microparticles with different sizes and dielectric properties can hierarchically self-organize into leader–follower-like microswarms under attractive electrohydrodynamic interactions, and show novel emergent collective behaviors. First, different from immobile single constituents or egalitarian clusters, the hierarchical microswarms autonomously move with tunable speed. Second, they exhibit multimode collective photoresponses emerging from different behaviors of the constituents in response to light signals. With a vertical UV signal, the photoresponsive followers tend to surround the leader and stop the microswarm. In response to sidewise UV signals, the constituents with stronger phototaxis would migrate to the position away from light stimuli, and thus the microswarms reorient parallel/antiparallel to the light direction and perform collective positive/negative phototaxis. Due to differential roles and huge design spaces of constituents, the hierarchical microswarms are envisioned to possess merits of high-efficiency, multiresponsiveness, and multifunctions, and may serve as intelligent micro/nanorobot systems for biomedicine and microengineering.
关键词： micromotors,nanomotors,hierarchical swarms,electrohydrodynamic flow
更新于2025-09-23 15:21:01
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Rapid Generation of Hierarchically Porous Metal-Organic Frameworks through Laser Photolysis
摘要： Hierarchically porous metal–organic frameworks (HP-MOFs) facilitate mass transfer due to mesoporosity while preserving the advantage of microporosity. This unique feature endows HP-MOFs with remarkable application potential in multiple fields. Recently, new methods such as the construction of HP-MOFs have emerged. To further enrich the synthetic toolkit of MOFs, we report a controlled photolytic removal of linkers to create mesopores within microporous MOFs at tens of milliseconds. Ultraviolet (UV) laser has been applied to eliminate “photolabile” linkers without affecting the overall crystallinity and integrity of the original framework. Presumably, the creation of mesopores can be attributed to the missing-cluster defects, which can be tuned through varying the time of laser exposure and ratio of photolabile/robust linkers. Upon laser exposure, MOF crystals shrank while metal oxide nanoparticles formed giving rise to the HP-MOFs. In addition, photolysis can also be utilized for the fabrication of complicated patterns with high precision, paving the way towards MOF lithography, which has enormous potential in sensing and catalysis.
关键词： linker photolysis,metal-organic frameworks,hierarchical pores
更新于2025-09-23 15:21:01
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Rapid Generation of Hierarchically Porous Metal-Organic Frameworks through Laser Photolysis
摘要： Hierarchically porous metal–organic frameworks (HP-MOFs) facilitate mass transfer due to mesoporosity while preserving the advantage of microporosity. This unique feature endows HP-MOFs with remarkable application potential in multiple fields. Recently, new methods such as the construction of HP-MOFs have emerged. To further enrich the synthetic toolkit of MOFs, we report a controlled photolytic removal of linkers to create mesopores within microporous MOFs at tens of milliseconds. Ultraviolet (UV) laser has been applied to eliminate “photolabile” linkers without affecting the overall crystallinity and integrity of the original framework. Presumably, the creation of mesopores can be attributed to the missing-cluster defects, which can be tuned through varying the time of laser exposure and ratio of photolabile/robust linkers. Upon laser exposure, MOF crystals shrank while metal oxide nanoparticles formed giving rise to the HP-MOFs. In addition, photolysis can also be utilized for the fabrication of complicated patterns with high precision, paving the way towards MOF lithography, which has enormous potential in sensing and catalysis.
关键词： linker photolysis,metal-organic frameworks,hierarchical pores
更新于2025-09-23 15:21:01
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Hierarchical Sub-Pixel Anomaly Detection Framework for Hyperspectral Imagery
摘要： Anomaly detection is an important task in hyperspectral processing. Some previous works, based on statistical information, focus on Reed-Xiaoli (RX), as it is one of the most classical and commonly used methods. However, its performance tends to be affected when anomaly target size is smaller than spatial resolution. Those sub-pixel anomaly target spectra are usually much similar with background spectra, and may results in false alarm for traditional RX method. To address this issue, this paper proposes a hierarchical RX (H-RX) anomaly detection framework to enhance the performance. The proposed H-RX method consists of several different layers of original RX anomaly detector. In each layer, the RX’s output of each pixel is restrained by a nonlinear function and then imposed as a coef?cient on its spectrum for the next iteration. Furthermore, we design a spatial regularization layer to enhance the sub-pixel anomaly detection performance. To better illustrate the hierarchical framework, we provide a theoretical explanation of the hierarchical background spectra restraint and regularization process. Extensive experiments on three hyperspectral images illustrate that the proposed anomaly detection algorithm outperforms the original RX algorithm and some other classical methods.
关键词： hyperspectral image (HSI) analysis,RX,hierarchical structure,anomaly detection
更新于2025-09-23 15:21:01
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In situ decoration of g-C3N4 quantum dots on 1D branched TiO2 loaded with plasmonic Au nanoparticles and improved the photocatalytic hydrogen evolution activity
摘要： The hybrid 1D branched TiO2 loaded with surface plasmonic Au and decorated with g-C3N4 QDs were successfully fabricated which played a significant role in photocatalysis. The 1D branched TiO2 prepared by electrospinning followed by an alkali-hydrothermal process. The Au particles decorated by photo deposition and after that g-C3N4 QDs were grafted over it by a chemical vapor deposition method. The composite shows great improvement in photocatalytic hydrogen evolution and evolved about 2.22 mmol g?1 h?1 hydrogen. The composite sample has a quantum efficiency of 19.5% for hydrogen production at 420 nm light that depicts the performance behavior of the composite. The 1D branched TiO2 fiber facilitates the fast transfer of electrons and Au reduces the charge recombination due to its surface plasmonic effect while g-C3N4 QDs facilitate the visible light absorption by improving the optical properties and reduces the bandgap. The formation of the type II heterostructure system remarkably promotes the separation and transfer of electron holes and facilitates the photo-reduction reaction.
关键词： Quantum dots,Photocatalyst,Plasmonic,Hydrogen,Hierarchical
更新于2025-09-23 15:21:01
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Hierarchical 3D VO2/ZnV2O4 microspheres as an excellent visible light photocatalyst for CO2 reduction to solar fuels
摘要： The photocatalytic reduction of CO2 has a great potential to produce fuels and chemicals, as well as, it reduces CO2 emission and addresses the environmental issues. To date single metal based catalysts still su?er from lower e?ciency, uncontrollable selectivity and instability. In this study, hierarchical microspheres (HMs) of ZnV2O4 with VO2 impurity were synthesized through the single step reduction process, to explore highly e?cient photocatalyst towards visible light responsive photocatalytic CO2 reduction. HMs of ZnV2O4 were successfully synthesized with mesoporous structure, higher surface area and functional under visible light irradiations. The ?1 were obtained over ZnV2O4 synthesized after highest yield of CO and CH3OH of 378 and 202 μmole g-cat 24 h of reaction time, respectively. The performance of optimized 3D HMs of ZnV2O4 for CO and CH3OH pro-duction was 2.30 folds and 10.7 folds higher than using ZnO/V2O5 composite sample, respectively. Other products detected with appreciable amounts were CH4 and C2H6. This reveals, HMs structure of ZnV2O4 not only allows the transfer of electrons towards CO2, but also provides short pathways for electron transfer and empty space in the microspheres will serve as the reservoirs to store the electrons, hence leading to enhanced photo-activity. In addition, VO2 presents in the sample further contribute to enhance performance of ZnV2O4 HMs due to enabling e?cient charge carrier separation. The prolong stability of ZnV2O4 in the CO2 reduction system con?rmed that 3D HMs structure provides controllable selectivity and stability. This brings to conclusions that fabrication of hierarchical structures will stimulate further development towards high performance photo-cat-alysts for the photocatalytic CO2 reduction to solar hydrocarbon fuels.
关键词： Hierarchical structure,CO2 reduction,Ternary metal oxide,Zinc vanadium oxide,3D microspheres of ZnV2O4,Hydrocarbon fuels
更新于2025-09-23 15:21:01