Caichao Wan

Flexible, highly conductive, and free-standing reduced graphene oxide/polypyrrole/cellulose hybrid papers for supercapacitor electrodes

We report a facile scale-up process to fabricate a novel type of hybrid paper electrode composed of reduced graphene oxide (RGO), polypyrrole (PPy) and cellulose. Through the optimization of preparation parameters (including the processes of in situ polymerization of pyrrole and chemical reduction of graphene oxide by using NaBH4), the fabricated hybrid paper had an extremely low sheet resistance of 1.7 Ω sq−1. Also, the hybrid paper possessed favorable mechanical flexibility and outstanding conductance stability. When the paper was evaluated as a free-standing and binder-free supercapacitor electrode, the unique construction (i.e., the cellulose fiber frame supporting interpenetrated RGO–PPy nanoacrhitectures) endowed it with high electrochemical activity, such as high areal capacitance of 1.20 F cm−2 at 2 mA cm−2 and good cycling stability with a capacitance retention of 89.5% after cycling 5000 times, which was tested in a three-electrode configuration. In addition, an all-solid-state laminated symmetric supercapacitor was prepared by assembling two pieces of hybrid paper electrodes and using a H3PO4/PVA gel as the electrolyte. The solid-state supercapacitor had a high areal capacitance of 0.51 F cm−2 at 0.1 mA cm−2 and a high energy density of 1.18 mW h cm−3. These results suggest that the hybrid paper is a promising electrode material and may be useful for the development of flexible high-performance and hand-held energy storage devices. More importantly, this work provides a good reference for the fabrication of other types of hybrid paper electrodes.

Synthesis of well-dispersed magnetic CoFe2O4 nanoparticles in cellulose aerogels via a facile oxidative co-precipitation method.

With the increasing emphasis on green chemistry, it is becoming more important to develop environmentally friendly matrix materials for the synthesis of nanocomposites. Cellulose aerogels with hierarchical micro/nano-scale three-dimensional network beneficial to control and guide the growth of nanoparticles, are suitable as a class of ideal green nanoparticles hosts to fabricate multifunctional nanocomposites. Herein, a facile oxidative co-precipitation method was carried out to disperse CoFe2O4 nanoparticles in the cellulose aerogels matrixes, and the cellulose aerogels were prepared from the native wheat straw based on a green NaOH/polyethylene glycol solution. The mean diameter of the well-dispersed CoFe2O4 nanoparticles in the hybrid aerogels is 98.5 nm. Besides, the hybrid aerogels exhibit strong magnetic responsiveness, which could be flexibly actuated by a small magnet. And this feature also makes this class of magnetic aerogels possibly useful as recyclable adsorbents and some magnetic devices. Meanwhile, the mild green preparation method could also be extended to fabricate other miscellaneous cellulose-based nanocomposites.

Graphene oxide/cellulose aerogels nanocomposite: Preparation, pyrolysis, and application for electromagnetic interference shielding.

Hybrid aerogels consisting of graphene oxide (GO) and cellulose were prepared via a solution mixing-regeneration-freeze drying process. The presence of GO affected the micromorphology of the hybrid aerogels, and a self-assembly behavior of cellulose was observed after the incorporation of GO. Moreover, there is no remarkable modification in the crystallinity index and thermal stability after the insertion of GO. After the reduction of GO in the hybrid aerogels by l-ascorbic acid and the subsequent pyrolysis of the aerogels, the resultant displays some interesting characteristics, including good electromagnetic interference (EMI) shielding capacity (SEtotal=58.4dB), high electrical conductivity (19.1Sm(-1)), hydrophobicity, and fire resistance, which provide an opportunity for some advanced applications such as EMI protection, electrochemical devices, water-proofing agents, and fire retardants. Moreover, this work possibly helps to facilitate the development of both cellulose and GO-based materials and expand their application scope.

Fabrication of hydrophobic, electrically conductive and flame-resistant carbon aerogels by pyrolysis of regenerated cellulose aerogels.

In this paper, we reported miscellaneous carbon aerogels prepared by pyrolysis of regenerated cellulose aerogels that were fabricated by dissolution in a mild NaOH/PEG solution, freeze-thaw treatment, regeneration, and freeze drying. The as-prepared carbon aerogels were subsequently characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), nitrogen adsorption measurements, X-ray diffraction (XRD), Raman spectroscopy, and water contact angle (WCA) tests. The results showed that the carbon aerogels with pore diameters of 1-60 nm maintained interconnected three-dimensional (3D) network after the pyrolysis, and showed type-IV adsorption isotherm. The pyrolysis process leaded to the decomposition of oxygen-containing functional groups, the destruction of cellulose crystalline structure, and the formation of highly disordered amorphous graphite. Moreover, the carbon aerogels also had strong hydrophobicity, electrical conductivity and flame retardance, which held great potential in the fields of waterproof, electronic devices and fireproofing.

Cellulose aerogels functionalized with polypyrrole and silver nanoparticles: In-situ synthesis, characterization and antibacterial activity

Green porous and lightweight cellulose aerogels have been considered as promising candidates to substitute some petrochemical host materials to support various nanomaterials. In this work, waste wheat straw was collected as feedstock to fabricate cellulose hydrogels, and a green inexpensive NaOH/polyethylene glycol solution was used as cellulose solvent. Prior to freeze-drying treatment, the cellulose hydrogels were integrated with polypyrrole and silver nanoparticles by easily-operated in-situ oxidative polymerization of pyrrole using silver ions as oxidizing agent. The tri-component hybrid aerogels were characterized by scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectroscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and X-ray diffraction. Moreover, the antibacterial activity of the hybrid aerogels against Escherichia coli (Gram-negative), Staphylococcus aureus (Gram-positive) and Listeria monocytogenes (intracellular bacteria) was qualitatively and quantitatively investigated by parallel streak method and determination of minimal inhibitory concentration, respectively. This work provides an example of combining cellulose aerogels with nanomaterials, and helps to develop novel forms of cellulose-based functional materials.

Preparation, characterization and oil adsorption properties of cellulose aerogels from four kinds of plant materials via a NAOH/PEG aqueous solution

In this paper, cellulose aerogels based on four kinds of plant materials including wheat straw, bamboo fiber, filter paper and cotton were prepared by alternative chemical pretreatment, dissolution in a green NaOH/PEG solution, freeze-thaw treatment, regeneration and freeze drying, respectively, and were subsequently characterized by scanning electron microscopy (SEM), nitrogen adsorption measurements, X-ray diffraction (XRD), thermogravimetric analysis (TGA). The differences in morphology, pore feature, crystalline structure and thermal property for the four kinds of aerogels were investigated. Meanwhile, the oil adsorption capacities differences of the aerogels were also studied after the aerogels were subjected to hydrophobic modifications by methyltrichlorosilane (MTCS); besides, the effect of the hydrophobic modifications was explored by Fourier transform infrared spectroscopy (FTIR).

Cellulose-derived carbon aerogels supported goethite (α-FeOOH) nanoneedles and nanoflowers for electromagnetic interference shielding

We describe a rapid and facile chemical precipitation method to grow goethite (α-FeOOH) nanoneedles and nanoflowers on the carbon aerogels which was obtained from the pyrolysis of cellulose aerogels. When evaluated as electromagnetic interference (EMI) shielding materials, the α-FeOOH/cellulose-derived carbon aerogels composite displays the highest SEtotal value of 34.0dB at the Fe3+/Fe2+ concentration of 0.01M, which is about 4.8 times higher than that of the individual α-FeOOH (5.9dB). When the higher or lower Fe3+/Fe2+ concentrations were used, the EMI shielding performance deterioration occurred. The integration of α-FeOOH with the carbon aerogels transforms the reflection-dominant mechanism for α-FeOOH into the adsorption-dominant mechanism for the composite. The adsorption-dominant mechanism undoubtedly makes contribution to alleviating secondary radiation, which is regarded as more attractive alternative for developing electromagnetic radiation protection products.

Core–shell composite of wood-derived biochar supported MnO2 nanosheets for supercapacitor applications

Eco-friendly wood-derived biochar (WDB) was used as a substrate material to support sheet-like nano-MnO2 via an easily-operated in situ redox reaction between the biochar and KMnO4. WDB was readily obtained by pyrolyzing wood waste of agriculture and industry. The MnO2/WDB composite displays a core–shell structure and can be utilized as a free-standing and binder-free supercapacitor electrode. The MnO2/WDB electrode has a moderate specific capacitance of 101 F g−1, an excellent coulombic efficiency of 98–100%, and a good cyclic stability with a capacitance retention of 85.0% after 10 000 cycles, making it useful for supercapacitor applications. Moreover, it is expected that such porous inexpensive WDB can serve as a novel harmless substrate material to combine with other electrochemical active substances for the development of high-performance energy storage devices.

Cellulose aerogels from cellulose-NaOH/PEG solution and comparison with different cellulose contents

Abstract A green mild NaOH/polyethylene glycol solution was employed to dissolve the cellulose extracted from waste wheat straw. Subsequently combined with the freezing−thawing treatment, regeneration process and freeze drying, the cellulose aerogels with different cellulose contents were fabricated at mass ratios of 1∶100, 3∶100, 5∶100 and 7∶100 cellulose to the solution. Moreover, the influences of cellulose contents on the morphologies, crystal structures, crystallinity indexes, thermal stabilities and pore characteristic parameters of the aerogels were investigated by scanning electron microscope, X-ray diffraction, thermogravimetric analysis and nitrogen adsorption. Meanwhile, the oil adsorption properties of the aerogels with different cellulose contents were also surveyed; besides, for improving lipophilicity, the hydrophobic modifications of trimethylchlorosilane for the aerogels were carried out before the adsorption tests.

A facile low-temperature hydrothermal method to prepare anatase titania/cellulose aerogels with strong photocatalytic activities for rhodamine B and methyl orange degradations

A facile low-temperature hydrothermal method for in situ preparation of anatase titania (TiO2) homogeneously dispersed in cellulose aerogels substrates was described. The formed anatase TiO2 aggregations composed of a mass of evenly dispersed TiO2 nanoparticles with sizes of 2-5 nm were embedded in the interconnected three-dimensional (3D) architecture of the cellulose aerogels matrixes without large-scale reunion phenomenon; meanwhile, the obtained anatase titania/cellulose (ATC) aerogels also had a high loading amount of TiO2 (ca. 35.7%). Furthermore, compared with commercially available Degussa P25, ATC aerogels displayed comparable photocatalytic activities for Rhodamine B and methyl orange degradations under UV radiation, which might be useful in the fields of catalysts, wastewater treatment, and organic pollutant degradation. Meanwhile, the photocatalytic reaction behaviors of ATC aerogels under UV irradiation were also illuminated.