Structural Engineering of Hierarchical Aerogels Hybrid Networks for Efficient Thermal Comfort Management and Versatile Protection

In recent years, growing concerns regarding energy efficiency and heat mitigation, along with the critical goal of carbon neutrality, have drawn human attention to the zero-energy-consumption cooling technique. Passive daytime radiative cooling (PDRC) can be an invaluable tool for combating climate change by dispersing ambient heat directly into outer space instead of just transferring it across the surface. Although significant progress has been made in cooling mechanisms, materials design, and application exploration, PDRC faces challenges regarding functionality, durability, and commercialization. Herein, a silica nanofiber aerogels (SNAs) functionalized poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) membrane (SFP membrane), inspired by constructional engineering is constructed. As-prepared membranes with flexible network structure combined hierarchical structure design and practicability principal. As the host material for thermal comfort management (TCM) and versatile protection, the SFP membrane features a large surface area, porous structure, and a robust skeleton that can render excellent mechanical properties. Importantly, the SFP membrane can keep exceptional solar reflectivity (0.95) and strong mid-infrared emittance (0.98) drop the temperature to 12.5 °C below ambient and 96 W m⁻² cooling power under typical solar intensities over 910 W m⁻². This work provides a promising avenue for high performance aerogel membranes that can be created for use in a wide variety of applications.     

Synthesis of Hierarchical 4H/fcc Ru Nanotubes for Highly Efficient Hydrogen Evolution in Alkaline Media

Hierarchical metal nanostructures containing 1D nanobuilding blocks have stimulated great interest due to their abundant active sites for catalysis. Herein, hierarchical 4H/face‐centered cubic (fcc) Ru nanotubes (NTs) are synthesized by a hard template‐mediated method, in which 4H/fcc Au nanowires (NWs) serve as sacrificial templates which are then etched by copper ions (Cu²⁺) in dimethylformamide. The obtained hierarchical 4H/fcc Ru NTs contain ultrathin Ru shells (5–9 atomic layers) and tiny Ru nanorods with length of 4.2 ± 1.1 nm and diameter of 2.2 ± 0.5 nm vertically decorated on the surface of Ru shells. As an electrocatalyst for the hydrogen evolution reaction in alkaline media, the hierarchical 4H/fcc Ru NTs exhibit excellent electrocatalytic performance, which is better than 4H/fcc Au‐Ru NWs, commercial Pt/C, Ru/C, and most of the reported electrocatalysts.     

Hierarchical Metal/Semiconductor Nanostructure for Efficient Water Splitting

A hierarchically patterned metal/semiconductor (gold nanoparticles/ZnO nanowires) nanostructure with maximized photon trapping effects is fabricated via interference lithography (IL) for plasmon enhanced photo‐electrochemical water splitting in the visible region of light. Compared with unpatterned (plain) gold nanoparticles‐coated ZnO NWs (Au NPs/ZnO NWs), the hierarchically patterned Au NPs/ZnO NWs hybrid structures demonstrate higher and wider absorption bands of light leading to increased surface enhanced Raman scattering due to the light trapping effects achieved by the combination of two different nanostructure dimensions; furthermore, pronounced plasmonic enhancement of water splitting is verified in the hierarchically patterned Au NPs/ZnO NWs structures in the visible region. The excellent performance of the hierarchically patterned Au NPs/ZnO NWs indicates that the combination of pre‐determined two different dimensions has great potential for application in solar energy conversion, light emitting diodes, as well as SERS substrates and photoelectrodes for water splitting.     

Self‐Expansion Construction of Ultralight Carbon Nanotube Aerogels with a 3D and Hierarchical Cellular Structure

A novel and simple strategy is developed to construct ultralight and 3D pure carbon nanotube (CNT) aerogels by the spontaneous expansion of superaligned CNT films soaked in a piranha (mixed H₂SO₄ and H₂O₂) solution, followed by cryodesiccation. The macroscopic CNT aerogels have an extremely low apparent density (0.12 mg cm^?3), ultrahigh porosity (99.95%), high specific surface area (298 m² g^?1), and a hierarchical cellular structure with giant and ultrathin CNT sheets as cell walls. The pure CNT aerogels show high adsorption abilities for various kinds of solvents, and have great potential in widespread applications such as energy storage, catalysis, and bioengineering.     

Emerging Hierarchical Aerogels: Self‐Assembly of Metal and Semiconductor Nanocrystals

Aerogels assembled from colloidal metal or semiconductor nanocrystals (NCs) feature large surface area, ultralow density, and high porosity, thus rendering them attractive in various applications, such as catalysis, sensors, energy storage, and electronic devices. Morphological and structural modification of the aerogel backbones while maintaining the aerogel properties enables a second stage of the aerogel research, which is defined as hierarchical aerogels. Different from the conventional aerogels with nanowire‐like backbones, those hierarchical aerogels are generally comprised of at least two levels of architectures, i.e., an interconnected porous structure on the macroscale and a specially designed configuration at local backbones at the nanoscale. This combination “locks in” the inherent properties of the NCs, so that the beneficial genes obtained by nanoengineering are retained in the resulting monolithic hierarchical aerogels. Herein, groundbreaking advances in the design, synthesis, and physicochemical properties of the hierarchical aerogels are reviewed and organized in three sections: i) pure metallic hierarchical aerogels, ii) semiconductor hierarchical aerogels, and iii) metal/semiconductor hybrid hierarchical aerogels. This report aims to define and demonstrate the concept, potential, and challenges of the hierarchical aerogels, thereby providing a perspective on the further development of these materials.     

Bimetallic Pt-Hg Aerogels for Electrocatalytic Upgrading of Ethanol to Acetate

Electrochemical upgrading of ethanol to acetic acid provides a promising strategy to couple with the current hydrogen production from water electrolysis. This work reports the design of a series of bimetallic Pt Hg aerogels, where the PtHg aerogel exhibits a 10.5-times higher mass activity than that of commercial Pt/C toward ethanol oxidation. More impressively, the PtHg aerogel demonstrates nearly 100% selectivity toward the production of acetic acid. The operando infrared spectroscopic studies and nuclear magnetic resonance analysis verify the preferable C2 pathway mechanism during the reaction. This work opens an avenue for the electrochemical synthesis of acetic acid via ethanol electrolysis.     

Hierarchical Graphene Foam for Efficient Omnidirectional Solar–Thermal Energy Conversion

Efficient solar–thermal energy conversion is essential for the harvesting and transformation of abundant solar energy, leading to the exploration and design of efficient solar–thermal materials. Carbon‐based materials, especially graphene, have the advantages of broadband absorption and excellent photothermal properties, and hold promise for solar–thermal energy conversion. However, to date, graphene‐based solar–thermal materials with superior omnidirectional light harvesting performances remain elusive. Herein, hierarchical graphene foam (h‐G foam) with continuous porosity grown via plasma‐enhanced chemical vapor deposition is reported, showing dramatic enhancement of broadband and omnidirectional absorption of sunlight, which thereby can enable a considerable elevation of temperature. Used as a heating material, the external solar–thermal energy conversion efficiency of the h‐G foam impressively reaches up to ≈93.4%, and the solar–vapor conversion efficiency exceeds 90% for seawater desalination with high endurance.     

Microfluidics: Nanostructuring of Titania Thin Films by a Combination of Microfluidics and Block‐Copolymer‐Based Sol–Gel Templating (Small 7/2011)

Sol–gel templating of titania thin films with the amphiphilic diblock copolymer poly(dimethyl siloxane)‐block‐methyl methacrylate poly(ethylene oxide) is combined with microfluidic technology to control the structure formation. Due to the laminar flow conditions in the microfluidic cell, a better control of the local composition of the reactive fluid is achieved. The resulting titania films exhibit mesopores and macropores, as determined with scanning electron microscopy, X‐ray reflectivity, and grazing incidence small angle X‐ray scattering. The titania morphology has three features that are beneficial for application in photovoltaics: 1) a large surface‐to‐volume ratio important for charge generation with disordered hexagonally arranged mesopores of 25 nm size and a film porosity of up to 0.79, 2) enhanced light scattering that enables the absorption of more light, and 3) a dense titania layer with a thickness of about 6 nm at the substrate (bottom electrode) to prevent short circuits. An optical characterization complements the structural investigation.     

Energy‐Efficient Oil–Water Separation of Biomimetic Copper Membrane with Multiscale Hierarchical Dendritic Structures

Membrane‐based materials with special surface wettability have been applied widely for the treatment of increasing industrial oily waste water, as well as frequent oil spill accidents. However, traditional technologies are energy‐intensive and limited, either by fouling or by the inability of a single membrane to separate all types of oil–water mixtures. Herein, a biomimetic monolayer copper membrane (BMCM), composed of multiscale hierarchical dendritic structures, is cleverly designed and successfully fabricated on steel mesh substrate. It not only possesses the ability of energy‐efficient oil–water separation but also excellent self‐recovery anti‐oil‐fouling properties (<150 s). The BMCM even keeps high separation efficiency (>93%) after ten‐time cycling tests. More importantly, it retains efficient oil–water separation capacity for five different oils. In fact, these advanced features are benefited by the synergistic effect of chemical compositions and physical structures, which is inspired by the typical nonwetting strategy of butterfly wing scales. The findings in this work may inspire a facile but effective strategy for repeatable and antipollution oil–water separation, which is more suitable for various applications under practical conditions, such as wastewater treatment, fuel purification, separation of commercially relevant oily water, and so forth.     

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition

Semiconductors with native ferromagnetism barely exist and defined nanostructures are almost unknown. This lack impedes the exploration of a new class of materials characterized by a direct combination of effects on the electronic system caused by quantum confinement effects with magnetism. A good example is EuO for which currently no reliable routes for nanoparticle synthesis can be established. Bottom‐up approaches applicable to other oxides fail because of the labile oxidation state +II. Instead of targeting a direct synthesis, the two steps—“structure control” and “chemical transformation”—are separated. The generation of a transitional, hybrid nanophase is followed by its conversion into EuO under full conservation of all morphological features. Hierarchical EuO materials are now accessible in the shape of oriented nanodisks stacked to tubular particles. Magnetically, the coupling of either vortex or onion states has been found. An unexpected temperature dependence is governed by thermally activated transitions between these states.