Yanzi Gou

Hierarchically porous SiC ultrathin fibers mat with enhanced mass transport, amphipathic property and high-temperature erosion resistance

Porous silicon carbide (SiC) has attracted considerable attention as an alternative catalyst support, particularly in corrosive and high-temperature environment. Herein, we report a facile strategy to controllably fabricate macroporous, meso-microporous and macro-meso-microporous SiC ultrathin fibers (M-SFs, MM-SFs and MMM-SFs, respectively) mats with good flexibility via electrospinning combined with polymer-derived ceramics route. The formation mechanism of different porous structures has been discussed. The MMM-SFs mat is found to exhibit simultaneously hydrophilic and lipophilic behaviors. Compared with M-SFs and MM-SFs, the MMM-SFs showed higher adsorption capacity, excellent adsorption durability and particularly faster adsorption rate (mass transport) in the adsorption experiments using methylene blue dye as a model. After being treated in dilute sulphuric acid for 5 h and subsequently heated at 800 °C for 1 h, the MMM-SFs retained their long-fiber shape and intact porous structure. Such a MMM-SFs mat may be of interest in high-temperature catalyst support, biosensor and biomedicine, energy storage, gas separation, particularly in harsh environment.

Three-dimensional (3D) interconnected networks fabricated via in-situ growth of N-doped graphene/carbon nanotubes on Co-containing carbon nanofibers for enhanced oxygen reduction

The strategy of combining highly conductive frameworks with abundant active sites is desirable in the preparation of alternative catalysts to commercial Pt/C for the oxygen reduction reaction (ORR). In this study, N-doped graphene (NG) and carbon nanotubes (CNT) were grown in-situ on Co-containing carbon nanofibers (CNF) to form three-dimensional (3D) interconnected networks. The NG and CNT bound the interlaced CNF together, facilitating electron transfer and providing additional active sites. The 3D interconnected fiber networks exhibited excellent ORR catalytic behavior with an onset potential of 0.924 V (vs. reversible hydrogen electrode) and a higher current density than Pt/C beyond 0.720 V. In addition, the hybrid system exhibited superior stability and methanol tolerance to Pt/C in alkaline media. This method can be extended to the design of other 3D interconnected network architectures for energy storage and conversion applications.

Mesoporous silicon carbide nanofibers with in situ embedded carbon for co-catalyst free photocatalytic hydrogen production

Silicon carbide (SiC) has been considered a promising metal-free photocatalyst due to its unique photoelectrical properties and thermal/chemical stability. However, its performance suffers from the fast recombination of charge carriers. Herein, we report mesoporous SiC nanofibers with in situ embedded graphitic carbon (SiC NFs-Cx) synthesized via a one-step carbothermal reduction between electrospun carbon nanofibers and Si powders. In the absence of a noble metal co-catalyst, the hydrogen evolution efficiency of SiC NFs-Cx is significantly improved under both simulated solar light (180.2 μmol·g–1·h–1) and visible light irradiation (31.0 μmol·g–1·h–1) in high-pH solution. The efficient simultaneous separation of charge carriers plays a critical role in the high photocatalytic activity. The embedded carbon can swiftly transfer the photogenerated electrons and improve light absorption, whereas the additional hydroxyl anions (OH–) in highpH solution can accelerate the trapping of holes. Our results demonstrate that the production of SiC NFs-Cx, which contains exclusively earth-abundant elements, scaled up, and is environmentally friendly, has great potential for practical applications. This work may provide a new pathway for designing stable, lowcost, high efficiency, and co-catalyst-free photocatalysts.

Vertical SnO2 nanosheet@SiC nanofibers with hierarchical architecture for high-performance gas sensors

Increasing demands for detection of harmful gases in harsh environments have stimulated considerable efforts to develop a novel gas sensor with high sensitivity, superior thermal/chemical stability and fast response/recovery rate. In this paper, we report the vertical growth of ultrathin SnO2 nanosheets (SnO2 NSs) on quasi-one-dimensional SiC nanofibers (SiC NFs) forming a hierarchical architecture via a simple hydrothermal method. In comparison to pure SnO2 NSs, the SnO2 NS@SiC NF hierarchical composite shows an ultrafast response/recovery rate, high sensitivity, and simultaneously excellent reproducibility to various target gases including ethanol, methanol, hydrogen, isopropanol, acetone and xylene, even at high temperature. The response times are less than 5 s with corresponding recovery times <15 s. Furthermore, the SnO2 NS@SiC NF gas sensor shows a superior sensing selectivity and long-term stability to ethanol. The hierarchical architecture and synergetic effect of the SnO2–SiC heterojunction as well as plenty of active sites from the vertically ultrathin SnO2 NSs have critical effect on the superior sensing performance of SnO2 NS@SiC NFs. This work highlights the possibility to develop a novel high-performance gas sensor for application in harsh environments.

Electrospun interconnected Fe-N/C nanofiber networks as efficient electrocatalysts for oxygen reduction reaction in acidic media

One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts. However, contact resistance among the neighbouring nanofibers hinders the electron transport. Here, we report the preparation of interconnected Fe-N/C nanofiber networks (Fe-N/C NNs) with low electrical resistance via electrospinning followed by maturing and pyrolysis. The Fe-N/C NNs show excellent ORR activity with onset and half-wave potential of 55 and 108 mV less than those of Pt/C catalyst in 0.5 M H2SO4. Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions. Additionally, it also displays much better durability and methanol tolerance than Pt/C catalyst. The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers. Thus, our findings provide a novel insight into the design of functional electrospun nanofibers for the application in energy storage and conversion fields.

A simply prepared flexible SiBOC ultrafine fiber mat with enhanced high-temperature stability and chemical resistance

Boron containing silicon-based ceramics with enhanced high-temperature stability have attracted great attention. An ultrafine and flexible silicon boron oxycarbide (SiBOC) fiber mat fabricated by electrospinning with a sol–gel system and subsequent pyrolysis is reported. The formation, composition and structure of the SiBOC fibers were studied by FT-IR, XRD, TG-MS, FE-SEM, HRTEM, XPS and MAS NMR. In comparison with the SiOC fibers, the SiBOC fibers showed better high-temperature stability. After being heated at 800 °C in air for 1 h, or immersed in 2 M NaOH and 1 M H2SO4 solutions for 24 h, the SiBOC fibers remained intact without of any detectable change. The SiBOC fibers illustrated superior amphiphilic affinity to water and xylene. Such a flexible SiBOC fiber mat may be of interest as a high-temperature catalyst support, LIB anode, capacitor, and so on.

Facile synthesis of melt-spinnable polyaluminocarbosilane using low-softening-point polycarbosilane for Si-C-Al-O fibers

Melt-spinnable polyaluminocarbosilane (PACS) is of importance as the precursor to prepare the Si–C–Al–O ceramic fibers, which can be employed for the preparation of SiC fibers with high tensile strength and good thermal stability. In this work, low-softening-point polycarbosilane (LPCS) was synthesized by pyrolysis of polydimethylsilane and applied to prepare PACS precursors with variable aluminum content by the reaction with aluminum(III) acetylacetonate. GPC, 1H NMR, UV–Vis, FT-IR, 29Si NMR, 27Al MAS NMR, TGA, and elemental analysis were used to analyze the composition and structure of the PACS precursors. Finally, Si–C–Al–O fibers were obtained successfully by melt-spinning, curing, and final pyrolysis of the precursors. The method demonstrated in this work can be further extended to synthesize other melt-spinnable metal-containing polycarbosilane (PMCS, M: Zr, Ti, Fe, Co, et.) of high ceramic yield and adjustable M content by reacting LPCS with other corresponding metal-containing compounds.

Synthesis of hyperbranched polyferrocenylsilanes as preceramic polymers for Fe/Si/C ceramic microspheres with porous structures

As organometallic polymers containing Fe and Si in the main chain, hyperbranched polyferrocenylsilanes (PFS) have great potential to be Fe/Si/C ceramic precursors. In this study, three kinds of hyperbranched PFS with different crosslinking structures were synthesized by the reaction between ferrocenyl dilithium and one or two of trichloromethylsilane, dichlorodimethylsilane, and dichloromethylvinylsilane. The compositions and structures of these polymers were characterized by nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared (FT-IR) spectroscopy, and thermal gravimetric analysis. With respect to their ceramic yield and solubility, the potential of the obtained PFS to be used as ceramic precursors was evaluated. Moreover, ceramic microspheres with porous structures were obtained by pyrolysis of the hyperbranched PFS at different temperatures, which were characterized by FT-IR, X-ray diffraction, vibrating sample magnetometer, and element analysis. By introducing Fe to the original precursors, the ceramic microspheres exhibited catalytic properties with the presence of Fe nanoparticles on the surface of the internal pores. The porous Fe/Si/C ceramic microspheres made from the hyperbranched PFS have significant potential applications in the field of catalyst supports, energy storage, and gas separation, especially in harsh environments.Graphical abstract

Tailoring of Porous Structure in Macro-Meso-Microporous SiC Ultrathin Fibers via Electrospinning Combined with Polymer-Derived Ceramics Route

Porous SiC has attracted extensive attention for its wide applications, especially in harsh environment, due to its unique properties. In the present paper, novel macro-meso-microporous SiC ultrathin fibers (MMM-SFs) were synthesized through electrospinning process associated with polymer-derived ceramics route, and the porous structure in the SFs can be conveniently tailored by tuning the composition of the spinning solvents and the concentration of the precursor (polycarbosilane). The surface features and microstructures of the resultant MMM-SFs were characterized in detail. These fibers presented a high specific surface area of 86.1–128.2 m2 g−1. The formation mechanism of hierarchically porous structure was discussed as well. N,N′-dimethylformamide (DMF) played a critical role in forming macropores, while the decomposition of SiOxCy phase was responsible for the meso-/micropores. Our method utilized to synthesize hierarchically porous SFs is easily capable of designing other ceramic fibers.

Synthesis and characterization of well-defined PVBCz-b-PDMAEMA multifunctional block copolymer prepared via ATRP

A functional polymer containing carbazole unit, PVBCz, was successfully prepared via atom transfer radical polymerization (ATRP) of 9-(4-vinylbenzyl)-9H-carbazole (VBCz). The controlled features of ATRP were confirmed by the linear increment of the molecular weight with the monomer conversion, while the molecular weight distribution was relatively narrow (Mw/Mn≤1.33). The block copolymer PVBCz-b-PDMAEMA was synthesized via ATRP, using PVBCz-Br as a macro-initiator and DMAEMA as the second monomer. 1H-NMR, GPC and FT-IR characterization confirmed the successful synthesis of PVBCz-b-PDMAEMA. The resulting copolymer exhibited both fluorescence from PVBCz segments and thermoresponsiveness from PDMAEMA segments. Moreover, the fluorescent intensity of PVBCz-b-PDMAEMA in aqueous solutions increased as the temperature rose, which could be attributed to the coupling of two different functions.