Zehang Zhou

Nanofibrillated cellulose as the support and reductant for the facile synthesis of Fe3O4/Ag nanocomposites with catalytic and antibacterial activity

In this paper, we have demonstrated a facile and environmentally friendly approach to prepare Fe3O4/Ag@nanofibrillated cellulose (NFC) nanocomposites which enables tunability from highly porous, flexible aerogels to solid and stiff films. In the procedure, NFC acts as (i) a biocompatible support for the magnetic silver nanoparticles and (ii) a reducing agent for the silver ions. Neither additional reducing agents nor toxic organic solvents were used during the preparation process. The Fe3O4/Ag@NFC nanocomposite aerogel exhibited excellent catalytic properties (both in efficiency and recyclability) for the reduction of 4-nitrophenol. Moreover, both the Fe3O4/Ag@NFC nanocomposite aerogel and film can be actuated by a small household magnet, and both possess high antibacterial activity against the model microbe S. aureus.

Facile synthesis of tunable silver nanostructures for antibacterial application using cellulose nanocrystals.

In this study, we report a facile and environmentally friendly strategy for synthesis of well dispersed and stable silver nanostructures using cellulose nanocrystals in aqueous solution without employing any other reductants, capping or dispersing agents. Importantly, it is feasible to adjust the morphology of the silver nanostructures by varying the precursor AgNO3 concentration. Silver nanospheres were formed when the AgNO3 concentration was 0.4 mM, while the dendritic nanostructures predominated when the AgNO3 concentration was increased to 250 mM. The antibacterial activity of the two different silver nanostructures against Escherichia coli and Staphylococcus aureus was characterized. Dendritic nanostructure showed a better antibacterial activity than that of silver nanosphere. The approach presented in this paper offers a very promising route to noble metal nanoparticles using renewable reducing agents.

Cellulose nanocrystals as a novel support for CuO nanoparticles catalysts: facile synthesis and their application to 4-nitrophenol reduction

Metal and metal oxide nanoparticles (NPs) have attracted considerable attention due to their excellent catalytic activities in various organic transformation reactions. However, their widespread application is limited because of their self-agglomeration in solution and the resulting reduced catalytic performance. Here we report that cellulose nanocrystals (CNs), which are sustainable and globally available in large quantities from plants, can be used as a novel support for copper oxide (CuO) NPs with enhanced catalytic performance. The high surface area of CNs and the abundant hydroxyl groups-induced immobilization of CuO NPs make the CNs-supported CuO NPs nanohybrids significantly stable, with CuO NPs/CNs suspensions remaining well-distributed even after a month. The obtained nanohybrids exhibited much higher catalytic activities than the unsupported and other materials-supported metal NPs (e.g. graphene oxide-supported CuO) in the catalyzed reduction of 4-nitrophenol. The facile processes used to make the nanohybrids catalysts are readily scalable to industrial levels.

Green synthesis and formation mechanism of cellulose nanocrystal-supported gold nanoparticles with enhanced catalytic performance

Deposition of precious metal catalysts onto the surface of various supporting materials to enhance the stability and catalytic activity is highly desired. Although extensive studies have been focused on the supported metal catalysts, their preparations are mainly based on the use of reducing agents which are not environmentally benign. Herein, we report a one-pot and green synthesis of gold nanoparticles (Au NPs) deposited on cellulose nanocrystals (CNs) under hydrothermal conditions using CNs as a reducing agent and stabilizing template. Our experimental results showed that the abundant electron-rich hydroxyl groups on the surface of CNs played a key role in the reduction and immobilization of Au NPs. The obtained nanohybrid catalyst exhibited much better catalytic activity and stability than the unsupported Au NPs and other Au-containing catalysts for the reduction of 4-nitrophenol. These findings pave the way for the green synthesis of bio-supported nanohybrid catalysts and can spur advancements in nanocellulose-based nanohybrids for their application in sensors, antibacterial materials and electronic devices.

Biotemplate synthesis of polyaniline@cellulose nanowhiskers/natural rubber nanocomposites with 3D hierarchical multiscale structure and improved electrical conductivity.

Development of novel and versatile strategies to construct conductive polymer composites with low percolation thresholds and high mechanical properties is of great importance. In this work, we report a facile and effective strategy to prepare polyaniline@cellulose nanowhiskers (PANI@CNs)/natural rubber (NR) nanocomposites with 3D hierarchical multiscale structure. Specifically, PANI was synthesized in situ on the surface of CNs biotemplate to form PANI@CNs nanohybrids with high aspect ratio and good dispersity. Then NR latex was introduced into PANI@CNs nanohybrids suspension to enable the self-assembly of PANI@CNs nanohybrids onto NR latex microspheres. During cocoagulation process, PANI@CNs nanohybrids selectively located in the interstitial space between NR microspheres and organized into a 3D hierarchical multiscale conductive network structure in NR matrix. The combination of the biotemplate synthesis of PANI and latex cocoagulation method significantly enhanced the electrical conductivity and mechanical properties of the NR-based nanocomposites simultaneously. The electrical conductivity of PANI@CNs/NR nanocomposites containing 5 phr PANI showed 11 orders of magnitude higher than that of the PANI/NR composites at the same loading fraction,; meanwhile, the percolation threshold was drastically decreased from 8.0 to 3.6 vol %.

Conductive natural rubber/carbon black nanocomposites via cellulose nanowhisker templated assembly: tailored hierarchical structure leading to synergistic property enhancements

The development of novel and versatile strategies to construct conductive polymer composites with low percolation thresholds and high mechanical properties is of great importance. In this work, a simple, facile and effective strategy was developed to fabricate tailored carbon black (CB) based 3D hierarchical conductive structures in a natural rubber (NR) matrix using renewable and biodegradable cellulose nanowhiskers (CNs) as templates. Specifically, needle-like CNs can direct the arrangement of CB nanoparticles along the CNs, yielding nodular CB@CN nanohybrids with excellent suspension stability and high aspect ratios. As a result, CB@CN nanohybrids could be selectively located in the interstitial space between NR latex microspheres and assembled into a continuous 3D hierarchical network via a latex blending technique. This 3D hierarchical conductive structure dramatically enhanced the electrical and mechanical properties of the NR based composites. With the addition of 5 vol% CB, the electrical conductivity of the composite was significantly enhanced by 12 orders of magnitude and the tensile strength was increased by 760% after the incorporation of the CN templates. Moreover, CB@CNs/NR nanocomposites showed a much lower electrical conductivity percolation threshold (2.9 vol%) than the traditionally prepared CB/NR composites (7.3 vol%). This novel strategy of CN templated fabrication of effective 3D conductive structures in a polymer matrix could significantly promote the functional use of natural cellulose resources and extend the application of CB in the production of conductive composites.

Polyaniline-decorated cellulose aerogel nanocomposite with strong interfacial adhesion and enhanced photocatalytic activity

Cellulose aerogel has attracted considerable attention due to its high surface area and the added advantages of being cost-effective and environmentally benign. It has been applied as supporting material for noble metal nanoparticle catalysts to prevent their agglomeration. In this paper, we have demonstrated a facile method to prepare polyaniline (PANI)-decorated cellulose aerogel via a dissolve/regeneration route using ionic liquid as solvent. Cellulose aerogel acted as a supporting material for PANI nanoparticles to prevent their agglomeration as confirmed by scanning electron microscopy. The strong interfacial interaction between PANI and cellulose aerogel was verified by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and X-ray diffraction. PANI-cellulose aerogel exhibited excellent photocatalytic activity towards the degradation of methylene blue. The degradation efficiency reached 95% after 2 h. The approach promotes the use of renewable natural resources to prepare a variety of nanofibrillated cellulose-supported nanocomposites for catalysis, sensors, and other potential applications.

A new application of ionic liquids for heterogeneously catalyzed acetylation of cellulose under solvent-free conditions

We have developed a simple and effective route for high yield production of cellulose acetate from waste cotton fabric. A small amount of Bronsted acidic ionic liquid (15 mol%) was used as the heterogeneous catalyst in this solvent-free process to synthesize cellulose acetate with a yield of 124.7%.

Reductant- and stabilizer-free synthesis of graphene–polyaniline aqueous colloids for potential waterborne conductive coating application

The chemical reduction of graphene oxide (GO) typically involves highly toxic reducing agents which could contaminate and have a negative effect on the conductivity of the resulting materials. Herein we report a facile approach to prepare stable reduced graphene oxide (rGO) aqueous colloids using reduced polyaniline nanofiber (rPANI-NFs) as both a reducing and a stabilizing agent. The efficient reduction of GO is verified by infrared spectroscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The adsorption of polyaniline nanofibers onto the rGO nanosheets allows a stable rGO aqueous dispersion to be formed through electrostatic stabilization. Since the rPANI-NFs could be easily doped and converted to a highly conductive material after reduction of GO, this approach provided a new method for large-scale production of aqueous rGO dispersions with great potential applications in environmentally friendly waterborne conductive coatings and construction of various graphene-based materials as demonstrated in this study of cellulose nanofiber–graphene composites.

Solvent free synthesis of polyaniline with improved molecular weight through solid state mechanochemical milling at ambient temperature

Abstract Mechanochemical synthesis of polyaniline was conducted by our self-designed pan mill equipment, which has a unique and smart structure and can exert fairly strong squeezing and shearing forces on the milled materials. The obtained product was examined by SEM, Fourier transform infrared (FTIR) and UV–Vis spectroscopy, viscometric average molecular weight measurement, X-ray diffraction (XRD) and thermogravimetric analysis. Comparative analysis of polyaniline prepared by solid state mechanochemical milling and mortar grinding was carried out. The formation of polyaniline was confirmed by FTIR and UV–Vis spectroscopy. Measurement of viscosity molecular weight showed that the molecular weight of pan milling prepared polyaniline was over three times higher than that of the mortar ground ones. The analysis of XRD patterns showed that polyaniline exposed to longer time shearing force tends to have a higher degree of crystallinity, and after milling for a certain time, pan milling prepared polyaniline would be more crystalline than the mortar ground polyaniline. Enhanced thermal stability of the pan milling prepared polyaniline further confirmed the improvement of the molecular weight.