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Serious freshwater shortage and environmental pollution boost the rapid development of solar-driven water production. Although improved evaporation rate has achieved in recent years, undesirable impurity (e.g., pollutant components) can also be inevitably evaporated and collected as impurity in produced freshwater. This work reports new ultra-light three-dimensional (3D) aerogels assembled by hierarchical Al2O3/TiO2nanofibers and reduced graphene oxide (RGO) for exciting synchronized solar-driven evaporation and water purification. Hydrophilic Al2O3/TiO2fibrous channels linked up the graphene hot-spots and water body for sufficient water supply and bulk water insulation. Meanwhile, featured with thermal insulation effect, the Al2O3/TiO2nanofibers effectively locked the converted heat with less energy loss from sunlight. The introducing of Al2O3/TiO2nanofibers into RGO aerogel led to the effective interfacial evaporation for a more rapid water evaporation rate (2.19 kg · m−2· h−1, normalized to evaporation area including both top and side surface), which was 36% higher than that of pristine RGO aerogel. Moreover, simultaneous with the strong steam generation, Al2O3/TiO2nanofibers in situ removed the pollutants within steam by photodegradation, achieving polluted wastewater purification with high contaminant removal ratio of 91.3%. Our work on coupling Al2O3/TiO2nanofibers into photothermal aerogel provides attractive solutions for the challenges of clean water scarcity and serious environmental pollution.

TiO2nanomaterials, especially one-dimensional TiO2nanofibers fabricated by electrospinning, have received considerable attention in the past two decades, for a variety of basic applications. However, their safe use and easy recycling are still hampered by the inherently subpar mechanical performance. Here, we toughened polycrystalline TiO2nanofibers by introducing Al3+-species at the very beginning of electrospinning. The resultant long-and-continuous TiO2nanofibers achieved a Young's modulus of 653.8 MPa, which is ca.25-fold higher than that of conventional TiO2nanofibers. Within each nanofiber, amorphous Al2O3-based oxide effectively hindered the coalescence of TiO2nanocrystals and potentially repaired the surface groves. The solid-state 17O-NMR spectra further revealed the toughening strategy on a molecular scale, where relatively flexible Ti–O–Al bonds replaced rigid O–Ti–O bonds at the interfaces of TiO2and Al2O3. Moreover, the modified TiO2nanofibers exhibited superb sinter-resistance, without cracking over 900 °C, which was dynamically monitored by TEM. Therefore, flexible-in-rigid TiO2fibrous mats can be facilely folded into 3D sponges through origami art. As a potential showcase, the TiO2sponges were demonstrated as a duarable and renewable filtrator with a high filtration efficiency of 99.97% toward PM2.5and 99.99% toward PM10after working for 300 min. This work provides a rational strategy to produce flexible oxide nanofibers and gives an in-depth understanding of the toughening mechanism from the macro-scale to the molecular-scale.

Graphical abstract: Ultrathin core–sheath CeO2/SiO2nanofibers were fabricated by a facile single-spinneret electrospinning method and were subsequently integrated as 2D nanofibrous mats and 3D sponges, exhibiting desirable efficiency in heterogeneous catalysis and water remediation.

Nanocatalysts play a significant role in various valuable reactions, but their scalable production is constrained by the cumbersome and laborious washing in refining after loading active metals species. This work firstly presented a universal continuous-flow washing for simplifying the washing protocol based on the size-matching principle. With pore-size-selected filter membranes, excessive or weakly anchored metal species can be moved away during liquid flow, while the solid nanofibers were efficiently collected. Secondly, to break through the volume limitations of the mixing kettle and realize scalable production, a home-made integrated loading-washing device was well-designed and combined the loading and washing procedures at one time. This device allowed liquid to flow through the supports, where metal species were loaded on while the excessive metal species were carried away. The optimized protocol increased the catalyst output per unit time from 10 mg/h to 500 mg/h, without losing catalytic activity and stability. This work provides a fresh idea for achieving the scalable production of nanocatalysts from the perspective of simplifying the loading and refining.

Overdischarge is a severe safety issue that can induce severe mechanical failure of electrode materials in lithium-ion batteries. A considerable volume change of silicon-based composite anodes undoubtedly further aggravates the mechanical failure. However, the mechanical failure mechanism of silicon-based composite anodes under overdischarging conditions still lacks in-depth understanding despite many efforts paid under normal charging conditions. Herein, we have modeled and tracked the mechanical failure evolution of silicon/carbon nanofibers, a typical silicon-based anode, under overdischarging conditions based on the finite element simulation, with derived optimization strategies of optimal Young’s modulus and stable microstructure. The severe contact damage between silicon nanoparticles and carbon nanofibers, which causes larger shedding and breakage risks, has been found to contribute to mechanical failure. To improve the electrode stability, an optimal Young’s modulus interval ranging from ∼75 to ∼150 GPa is found. Furthermore, increasing the embedding depth of silicon nanoparticles in carbon nanofibers has proven to be an effective strategy for improving electrochemical stability due to the faster lithium salt diffusion and more uniform current density distribution, which was further verified by the experimental capacity retention ratio of carbon-coated silicon and silicon/carbon nanofibers (84 vs 75% after 100 cycles). Our results provide meaningful insights into the mechanical failure of silicon-based composite anodes during overdischarging, giving reasonable guidance for electrode safety designs and performance optimization.

This work demonstrates a facile fabrication of stimulus-responsive, periodically wrinkled graphene sheets on grooved microfiber arrays with fast and reversible shape change, multiresponsiveness, and programmable deformation, with the aid of finite element analysis (FEA). The cellulose acetate (CA) microfibers, endowing responsiveness to humidity and solvents, are designed to grooved shape and assembled into a well-aligned fibrous mat by electrospinning. Under the guidance of FEA simulation, the stiff reduced graphene oxide (RGO) sheets, serving as a photoresponsive component, could ably bind on grooved CA microfibers with favorable interlocked interfacial-structure. Through simple direct-writing and hot-pressing, the grooved CA arrays interlocked the conformal RGO sheets by water-induced self-clamping, and enabled the generation of periodic wrinkles within RGO sheets to maximize interfacial areas. By simply adjusting the orientation of written RGO patterns relative to uniaxial CA microfibers, programmed and omnidirectional shape-shifting were obtained to minimize strain energy, consisting with the dynamic deformation process simulated by FEA. Upon remote light or contactless humidity stimuli, the RGO/CA mat shows a rapid response (≤1 s), large amplitude (angle change ≥150°, 1.62 cm–1), sophisticated 3D motions, and lifts objects that weigh 12.7-times its own weight up to over 1/3 of own height within 1 s. After loading catalytical nanoparticles, the RGO/CA mat could rapidly move to the targeted position by continuous crawling even on a slippery surface, and served as a microchannel reactor to trigger a reaction in built-in microchannels with suppressing catalyst leaching while accelerating reaction kinetics by both nanoconfinement and photothermal effect.

Ultrathin oxide nanofibers are widely used in an array of catalytic applications toward energy conversion and environmental protection. Remarkable progress has been made with regard to the development of engineering oxide nanofibers into unique structures to suit or enable various functions. We aim to provide a comprehensive overview of oxide nanofibers, including the structure engineering, derivates, assemblies and their applications. We begin with a brief introduction to the production of nanofibers with diversified compositions, structures and properties, followed by discussions of the wet-chemistry derivates. Afterward, we discuss the applications of catalytic oxide nanofibers, including electrocatalysis, photocatalysis and thermal-catalysis. Then we highlight the most significant role of oxide nanofibers as catalyst support for the immobilization of metal nanoparticles. Moreover, we showcase the advanced assemblies based on oxide nanofibers, including their use as multi-functional membranes and foams. In the end, we offer perspectives on the challenges, opportunities and new directions for future development.

Ultrafine noble metals have emerged as advanced nanocatalysts in modern society but still suffer from unavoidable sintering at temperatures above 250 °C (e.g., Pt). In this work, closely packed CeO2grains were confined elegantly in fibrous nanostructures and served as a porous support for stabilizing sub-3 nm Pt clusters. Through precisely manipulating the asymmetry of obtained nanofibers, uneven strain was induced within C-shaped CeO2nanofibers with tensile strain at the outer side and compressive strain at the inner side. As a result, the enriched oxygen vacancies significantly improved adhesion of Pt to CeO2, thereby boosting the sinter-resistance of ultraclose sub-3 nm Pt clusters. Notably, no aggregation was observed even after exposure to humid air at 750 °C for 12 h, which is far beyond their Tammann temperature (sintering onset temperature, below 250 °C). In situHAADF-STEM observation revealed a unique sintering mechanism, wherein Pt clusters initially migrate toward the grain boundaries with concentrated stain and undergo slight coalescence, followed by subsequent Ostwald ripening at higher temperatures. Moreover, the sinter-resistant Pt/C-shaped CeO2effectively catalyzed soot combustion (over 700 °C) in a durable manner. This work provides a new insight for developing sinter-resistant catalysts from the perspective of strain engineering within nano-oxides.

The advent of porous ceramic nanofibers offers tremendous opportunities for new applications in heterogeneous catalysis, due to their intrinsic features such as high surface area, tunable compositions and extraordinary stability. This paper provides a brief review of current research activities that focus on the fabrication of porous ceramic nanofibers by electrospinning, as well as their applications in heterogeneous catalytic reactions. We begin with a brief introduction of electrospinning in the context of ceramic nanofibers, and then discuss the approaches of the functionalization of nanofibers with a porous structure. Afterward, we continue with a highlight of some recent applications of porous ceramic nanofibers, with a focus on the physiochemical properties of porous ceramic nanofibers as well as their applications in heterogeneous catalysis towards energy and environmental aspects. At the end, we conclude this review with some perspectives on the challenges, opportunities, and new directions for their future development.

Chemisorption–titration, as a surface sensitive analysis method, is widely applied for direct measurement of the specific surface area of metallic clusters on heterogeneous catalysts. However, on active oxide supports, the product yield of this method is strongly affected by the exchange of oxygen between the support and the titration gases. In this study, Pt- and Cu-based catalysts are used as the source for metallic site characterization through isothermal titration experiments within a wide temperature range. Pt/Fe2O3catalysts were characterized using CO oxidation, and Cu/CeO2catalysts were characterized using N2O decomposition. The titration products are CO2and N2, respectively. Detailed measurements require instant online mass spectroscopy characterization and temperature control from subzero to room temperatures; for this purpose an online micro reactor is developed and applied for quantitative product calibration. For both series of catalysts, MS signals are also measured on pure metallic powder and calibrated using a commercial chemisorption measurement system. The temperature dependence of both total titration products from the supported samples reveals that for each catalyst, there are narrow subzero temperature windows in which the titration products are only related with metallic sites. The results provide an approach towards a one-step chemisorption–titration procedure for measurement of dispersion on active oxide supported catalysts, which is a possible benchmark that bridges fundamental model catalysts and industrial applied catalysts in performance evaluation.

Recently, hollow nanofibers could be fabricated by coaxis electrospinning method or template method. However, they are limited to applications because of the hardship in actual preparation. In this work, hollow γ-Al2O3nanofibers with loofah-like skins were first fabricated by using a single spinneret during electrospinning. These intriguing nanofibers were explored as new Pt supports with excellently sinter-resistant performance up to 500 °C, attributed to the unique loofah-like surface of γ-Al2O3nanofibers and the strong metal–support interactions between Pt and γ-Al2O3. When applied in the catalytic reduction of p-nitrophenol, the Pt/γ-Al2O3calcined at 500 °C exhibited 4-times higher reaction rate constant (6.8 s–1·mg–1) over free Pt nanocrystals.

Abstract

Holey support: The generation of a porous coating of SiO2on Pt‐decorated TiO2nanofibers enables the preparation of a sinter‐resistant catalytic system (see picture). The Pt nanoparticles could resist sintering at temperatures up to 750 °C in air, as the SiO2coating acts as a physical barrier that slows down surface migration, but the system remained catalytically active because of the porous nature of the coating.

Stützt ohne zu stören: Das Aufbringen einer porösen SiO2‐Schicht auf Pt‐modifizierte TiO2‐Nanofasern ergibt einen sinterbeständigen Katalysator (siehe Bild). Die Pt‐Nanopartikel sinterten bei Temperaturen bis 750 °C an Luft nicht, weil die SiO2‐Schicht die Oberflächenwanderung physikalisch behindert; wegen der Porosität der Beschichtung behielt das System seine katalytische Aktivität aber bei.

No Abstract

Fünffach verzwillingte, Seestern‐förmige Rh‐Nanokristalle mit fünf Armen (siehe TEM‐Bild) wurden in hohen Ausbeuten ausgehend von [{Rh(CF3COO)2}2] synthetisiert. Die Synthese vermeidet oxidative Ätzvorgänge, und die frisch hergestellten Rh‐Nanokristalle eignen sich sehr gut als SERS‐Substrate.

Fabricating flexible and large-scale graphene-based films through a simple process to achieve excellent electromagnetic interference (EMI) shielding performance is still a daunting challenge. Herein, the flexible and large-area EMI shielding films with ultrathin coating thickness (i.e., 10 μm) and low coating density (i.e., 2.4 mg/cm2) were fabricated through a simple drop-casting approach by using graphene-based conductive ink at room temperature. With the aid of electromagnetic simulation, the optimal square resistance of conductive film for desirable EMI shielding effectiveness is predicted, avoiding the unnecessary costs of error and trial. To solve the vital issue of poor conductivity of reduced graphene oxide (RGO) arising from defects and the serious agglomeration of each filler in ink, a three-dimensional network was constructed by connecting RGO with flexible one-dimensional (1D) conductive fibers (i.e., carbon nanotubes (CNT) and Ag nanowire (AgNW)). The square resistance of the RGO/CNT@Epoxy/AgNW composite film could reach as low as 1.94 ± 0.63 Ω/sq, which exhibited the shielding effectiveness value of 40 dB at a minimum in 8.2–12.5 GHz. These attributes could satisfy the EMI shielding and flexibly conformal demands of most communication equipment.

Surface engineering of one-dimensional (1D) TiO2-based heterostructures is extremely vital to the development of new photocatalysts with superior performances. Herein, the Al2O3heterojunctions onto TiO2nanofibers were facilely fabricated by a surfactant-free approach, viaemploying graphene oxide (GO) sheets as a reliable catalyst of regulating the growth kinetics of heterojunctions. Through adjusting the GO content, the oxygen-containing functional groups of GO provided nucleation sites of Al2O3species while restricting their growth in the limited space. As a result, the morphology of Al2O3heterojunctions evolved from nanoflakes to nanospikes outside the TiO2nanofibers that served as robust skeletons. Owing to the distinctive morphology and the effective electron transfer pathway, the photocurrent density of the spiny RGO/Al2O3/TiO2nanofibers was 3.5-times higher than that of pure Al2O3/TiO2nanofibers counterparts toward photoelectrochemical reaction under visible-light irradiation. The present work highlights the pivotal role of graphene sheets in controlling the hierarchical growth of TiO2-based heterostructures with tunable morphology and compositions.

The development of non-contact flexible electronic-sensor with high sensitivity and stable connection is urgently needed for the advanced human-machine interactions. Here, with the aid of theoretical simulation, a novel cellulose acetate/aluminum (CA/Al) flexible humidity sensor was designed. Aligned CA fibrous mat with groove structures exhibited high sensitivity and programmable deformation ability to humidity. The conductive Al layer possessed ordered wrinkle geometry and perfectly balanced the high deformability and stable electronic connectivity. Based on these features, the non-contact CA/Al sensor could sensitively capture the sweat changing of a human finger, and exhibit stable on-off signals under continuous deformations, which is highly promising in wearable human-machine interaction devices. This work paves the way for designing high-performance non-contact flexible electronic sensors under the direction of artificial intelligence in the future.