Jia-Fu Chen

Ultralight, Flexible, and Fire-Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose†

Carbon-based aerogels, composed of interconnected threedimensional (3D) networks, have attracted intensive attention because of their unique physical properties, such as low density, high electrical conductivity, porosity, and specific surface area. As a result, carbon-based aerogels are promising materials used as catalyst supports, artificial muscles, electrodes for supercapacitors, absorbents, and gas sensors. Especially, ultralight or flexible carbon-based aerogels have many potential applications. For example, ultralight nitrogen-doped graphene framework, used as an absorbent for organic liquids or the active electrode material, exhibits a high absorption capacity and specific capacitance; stretchable conductors, fabricated by infiltrating flexible graphene foam with elastic polymers, show high stability of electronic conductivity even under high stretching and bending strain. Traditionally, to fabricate carbon aerogels, resorcinol– formaldehyde organic aerogels were pyrolyzed in an inert atmosphere to form a highly cross-linked carbon structure. 12] The carbon aerogels always have a high density (100–800 mgcm ) 13] and tend to break under compression. Carbon nanotube (CNT) sponges, graphene foam, and CNT forests have been prepared through chemical vapor deposition (CVD). Meanwhile, CNTs and graphene can be employed as building blocks and assembled into macroscopic 3D architectures. However, the harmful and expensive precursors or complex equipments involved in these syntheses dramatically hamper the large-scale production of these carbon-based aerogels for industry application. Recently, we have developed a template-directed hydrothermal carbonization process for synthesis of carbonaceous nanofiber hydrogels/aerogels on macroscopic scale by using glucose as precursors. However, the use of expensive nanowire templates in this synthesis pushes us to explore a facile, economic, and environmentally friendly method to produce carbon-based nanostructured aerogels. Nowadays, there is a trend to produce carbon-based materials from biomass materials, as they are very cheap, easy to obtain, and nontoxic to humans, etc. Bacterial cellulose (BC), a typical biomass material, is composed of interconnected networks of cellulose nanofibers, 22] and can be produced in large amounts in a microbial fermentation process. Recently, we reported a highly conductive and stretchable conductor, fabricated from BC, shows great electromechanical stability under stretching and bending strain. Herein, we report a facile route to produce ultralight, flexible, and fire-resistant carbon nanofiber (CNF) aerogels in large scale from BC pellicles. When used as absorbents, the CNF aerogels can absorb a wide range of organic solvents and oils with excellent recyclability and selectivity. The absorption capacity can reach up to 310 times the weight of the pristine CNF aerogels. Besides, the electrical conductivity of the CNF aerogel is highly sensitive to the compressive strain, thereby making it a potential pressure-sensing material. For fabricating the CNF aerogels, a piece of purified BC pellicle with the size of 320 240 12 mm was first cut into rectangular or cubic shape and then freeze-dried to form BC aerogels (see the Supporting Information). The dried BC aerogels were pyrolyzed at 700–1300 8C under argon atmosphere to generate black and ultralight CNF aerogels. After pyrolysis, the volume of obtained CNF aerogel is only 15% of that of the original BC aerogel. Meanwhile, the density decreases from 9–10 mg cm 3 for BC aerogels to 4–6 mgcm 3 for CNF aerogels, owing to evaporation of volatile species. The macroscopic sizes of the as-synthesized CNF aerogels are dependent on the sizes of the BC pellicles cut in the fabrication procedure. It is well-known that temperature has a great influence on pyrolysis products. To create ideal CNF aerogels, BC aerogels were pyrolyzed separately at different temperatures. Scanning electron microscopy (SEM) images show that BC aerogels exhibit a porous, interconnected, well-organized 3D network structure, which was formed through self-assembly in the bacteria culture process (Figure 1a). A high-magnification SEM image indicates that the nanofibers with a diameter of 20–80 nm are highly interconnected with large numbers of junctions (see the Supporting Information, Figure S1). After the pyrolysis treatment, the porous 3D structure of BC aerogels was maintained, and the diameter of the nanofibers decreased to 10–20 nm (Figure 1b, also see the Supporting [*] Z. Y. Wu, C. Li, Dr. H. W. Liang, Prof. Dr. J. F. Chen, Prof. Dr. S. H. Yu Division of Nanomaterials and Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemistry, CAS Key Laboratory of Mechanical Behavior and Design of Materials, the National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei, Anhui 230026 (P.R. China) E-mail: shyu@ustc.edu.cn Homepage: http://staff.ustc.edu.cn/~ yulab/

Coating colloidal carbon spheres with CdS nanoparticles: microwave-assisted synthesis and enhanced photocatalytic activity.

This manuscript describes the accurate coating of CdS nanoparticles on the surface of colloidal carbon spheres by a facile two-step, microwave-assisted method and the studies on the photocatalytic activity of the C@CdS core-shell spheres. For the coating of CdS nanoparticles, cadmium ions were incorporated into the hydrophilic shell of colloidal carbon spheres and reacted with an introduced sulfur source under a microwave field to obtain the C@CdS hybrid spheres. Using this process, the as-prepared hybrid structures preserved the good dispersity and uniformity of initial carbon spheres, and the thickness of the CdS nanoparticles shell could be varied or controlled by the irradiation time. A photoluminescence spectrum showed that the C@CdS hybrid spheres feature a broad green emission at around 494 nm (λ(ex) = 337 nm). Additionally, CdS nanospheres were successfully prepared in aqueous solution via a microwave-assisted route, and the effect of irradiation time on the products was also investigated. The studies of the photocatalytic property demonstrate that these fabricated functional hybrid structures evinced a higher photocatalytic degradation activity when exposed to visible light irradiation than that of CdS nanospheres under the same conditions.

Carbon nanofiber aerogels for emergent cleanup of oil spillage and chemical leakage under harsh conditions

To address oil spillage and chemical leakage accidents, the development of efficient sorbent materials is of global importance for environment and water source protection. Here we report on a new type of carbon nanofiber (CNF) aerogels as efficient sorbents for oil uptake with high sorption capacity and excellent recyclability. Importantly, the oil uptake ability of the CNF aerogels can be maintained over a wide temperature range, from liquid nitrogen temperature up to ca. 400°C, making them suitable for oil cleanup under harsh conditions. The outstanding sorption performance of CNF aerogels is associated with their unique physical properties, such as low density, high porosity, excellent mechanical stability, high hydrophobicity and superoleophilicity.

Dyeing bacterial cellulose pellicles for energetic heteroatom doped carbon nanofiber aerogels

The energy crisis and environmental pollution are serious challenges that humanity will face for the long-term. Despite tremendous efforts, the development of environmentally friendly methods to fabricate new energy materials is still challenging. Here we report, for the first time, a new strategy to fabricate various doped carbon nanofiber (CNF) aerogels by pyrolysis of bacterial cellulose (BC) pellicles which had adsorbed or were dyed with different toxic organic dyes. The proposed strategy makes it possible to remove the toxic dyes from waste-water and then synthesize doped CNF aerogels using the dyed BC pellicles as precursors. Compared with other reported processes for preparing heteroatom doped carbon (HDC) nanomaterials, the present synthetic method has some significant advantages, such as being green, general, low-cost and easily scalable. Moreover, the as-prepared doped CNF aerogels exhibit great potential as electrocatalysts for the oxygen reduction reaction (ORR) and as electrode materials for supercapacitors.

Photothermal Poly(N‐isopropylacrylamide)/Fe3O4 Nanocomposite Hydrogel as a Movable Position Heating Source under Remote Control

Multifunctional nanocomposite hydrogel: swelling-shrink transition of the magnetic sensitive poly(N-isopropylacrylamide)/Fe3O4 (PNIPAM/Fe3O4) nanocomposite hydrogel can be controlled via near-infrared (NIR) laser exposure or non-exposure, which shows potential as a movable position heating source manipulated by combination of an external magnet and near-infrared laser irradiation.

Ultralight Multifunctional Carbon‐Based Aerogels by Combining Graphene Oxide and Bacterial Cellulose

Nanostructured carbon aerogels with outstanding physicochemical properties have exhibited great application potentials in widespread fields and therefore attracted extensive attentions recently. It is still a challenge so far to develop flexible and economical routes to fabricate high-performance nanocarbon aerogels, preferably based on renewable resources. Here, ultralight and multifunctional reduced graphene oxide/carbon nanofiber (RGO/CNF) aerogels are fabricated from graphene oxide and low-cost, industrially produced bacterial cellulose by a three-step process of freeze-casting, freeze-drying, and pyrolysis. The prepared RGO/CNF aerogel possesses a very low apparent density in the range of 0.7-10.2 mg cm-3 and a high porosity up to 99%, as well as a mechanically robust and electrically conductive 3D network structure, which makes it to be an excellent candidate as absorber for oil clean-up and an ideal platform for constructing flexible and stretchable conductors.

Photocatalytic studies of CdS nanoparticles assembled on carbon microsphere surfaces with different interface structures: from amorphous to graphite-like carbon

A rapid microwave-assisted method was used for the accurate coating of CdS nanoparticles on the surface of colloidal carbon microspheres to form C/CdS hybrid microspheres, which demonstrated enhanced visible-light-photocatalytic activity for the degradation of rhodamine B (RhB). To investigate the optimal photocatalytic synergistic effect, the above as-prepared of C/CdS hybrid microspheres were treated in a tube furnace by annealing at different temperatures (from 300 to 800 °C) in a N2 flow, which resulted in CdS nanoparticles assembled on different carbon layers (from amorphous to graphite-like carbon). The changes in FT-IR and Raman spectra that were caused by different interfaces were studied. Further, the synergic effect between CdS nanoparticles and different carbon layers, which influence the photocatalytic activity, was then investigated systematically. The results show that the photocatalytic activity of these samples was gradually enhanced as the calcination temperature increased. But compared to the sample without calcination, the photocatalytic activity decreases first and then increases. The combination of CdS and graphite-like carbon may be an ideal system to cause a rapid photoinduced charge separation and decreased possibility of recombination of electron–hole pairs by taking advantage of graphite-like carbons unique electron transport properties, which increase the number of holes participating in the photooxidation process and enhance the photocatalytic activity.

Selective Synthesis of Zn1 − xMnxSe Nanobelts and Nanotubes from [Zn1 − xMnxSe](DETA)0.5 Nanbelts in Solution (x = 0−0.15) and Their EPR and Optical Properties

Zn(1 - x)Mn(x)Se (x = 0-0.15) nanobelts and nanotubes can be synthesized via the removal of diethylenetriamine (DETA) in 1-octadecene (ODE) and ethylene glycol (EG), respectively, using [Zn(1 - x)Mn(x)Se](DETA)(0.5) nanobelts as a template. The as-prepared ZnSe nanobelts are single-crystalline and grown along the [001] direction, and the ZnSe nanotubes consist of nanoparticles assembled along the [001] direction. In addition, Mn(2+)-doped Zn(1 - x)Mn(x)Se (x = 0.05, 0.10, 0.15) nanotubes are prepared for the first time if doped [Zn(1 - x)Mn(x)Se](DETA)(0.5) nanobelts are used as the template. The formation process of Zn(1 - x)Mn(x)Se nanobelts and nanotubes has been studied, and a plausible mechanism is proposed. Photoluminescence (PL) and electron paramagnetic resonance (EPR) spectra of Zn(1 - x)Mn(x)Se nanobelts and Zn(1 - x)Mn(x)Se nanotubes have been investigated.

Stability and protection of nanowire devices in air

Nanowire devices have attracted considerable attention because of their unique structure and novel properties, and have opened up significant development opportunities. However, not many studies have focused on their stability and durability under practical conditions, which limits the rapid development of real applications. Herein, we systematically investigate three different treatments,polymer coating, inert atmosphere protection, and thickness-induced self-protection, to protect the tellurium nanowire devices from oxidation when exposed to open air. The degree of oxidation was monitored by examining changes in the valence states of tellurium element and in the morphology of the nanowires. After the protective treatments, the tellurium nanowire devices showed improved stability and remained stable even after 800 days of storage. This work highlights the importance of investigating the stability of nanowire devices, especially for their practical applications.

Ultrathin Tungsten Oxide Nanowires/Reduced Graphene Oxide Composites for Toluene Sensing

Graphene-based composites have gained great attention in the field of gas sensor fabrication due to their higher surface area with additional functional groups. Decorating one-dimensional (1D) semiconductor nanomaterials on graphene also show potential benefits in gas sensing applications. Here we demonstrate the one-pot and low cost synthesis of W18O49 NWs/rGO composites with different amount of reduced graphene oxide (rGO) which show excellent gas-sensing properties towards toluene and strong dependence on their chemical composition. As compared to pure W18O49 NWs, an improved gas sensing response (2.8 times higher) was achieved in case of W18O49 NWs composite with 0.5 wt. % rGO. Promisingly, this strategy can be extended to prepare other nanowire based composites with excellent gas-sensing performance.