Novel aspects of nanocellulose

Novel nanoscaled cellulose particles were prepared using high-pressure homogenization of aqueous media contenting treated cellulose samples in a Microfluidizer^® processor (MF). Here, we present the generation of spherical cellulose nanoparticles as an extension of previously published reports of nano fibrillated cellulose. Although MF treatment of unmodified cellulose yields nanofibrils which are reported in several publications, in the current work different kinds of pretreatments were proven to be necessary to obtain spherical structured cellulose nanoparticles. One such treatment may be the decrystallization of cellulose regenerating it from N-methylmorpholine-N-oxid-monohydrate (NMMNO*H₂O). Nanocellulose was then obtained by a subsequent high-pressure mechanical treatment of the precipitate in aqueous dispersion. Decrystallization was also realized by grinding cellulose in a planetary ball mill. The resulting amorphous intermediates were characterized by Raman spectroscopy. Another approach tested was hydrolysis and subsequent mechanical treatment using an Ultra-Turrax^® and MF. Another alternative was given by the mechanical treatment of aqueous dispersions of low substituted cellulose derivatives such as carboxymethyl cellulose and oxidized cellulose without any further hydrolysis.     

Facile in situ synthesis of nickel/cellulose nanocomposites: mechanisms,properties and perspectives

Nickel/cellulose nanocomposites with tunable magnetic behavior and electrical conductivity were fabricated by a facile in situ synthesis route with aqueous NaOH/urea solution as the solvent to dissolve and regenerate cellulose. It was found that Ni particles are uniformly dispersed in and immobilized by cellulose matrix, which indicates that regenerated cellulose fibers with coarse surface might act as templates to modulate the growth of Ni nanoparticles. Moreover, the size and morphology of Ni nanoparticles as well as the magnetic and conductive properties of Ni/cellulose nanocomposites is dependent on the concentration of Ni²⁺ in NaOH/urea aqueous solution. With an increase in the concentration of Ni²⁺ from 0.2 to 1.0 mol/L, the values of saturation magnetization increased from 16.6 to 38.5 emu/g, while the resistance decreased from 10⁶ to 10^?2 Ω cm. Particularly, multi-layer sample exhibits good absorption capacity and an additional effective bandwidth in the low-frequency region, showing promising potential as candidate electromagnetic functional fabric and cloth.     

Cellulose scaffolds modulated synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals: preparation,characterization and properties

Magnetic Co₃O₄ nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)₂ nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co₃O₄ nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co₃O₄ without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O²⁻ → Co³⁺ and O²⁻ → Co²⁺ charge-transfer processes, respectively. Furthermore, the resulted Co₃O₄ nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery.     

Novel Approaches to Metallization of Cellulose by Reduction of Cellulose-Incorporated Copper and Nickel Ions

Summary: Copper and nickel nanoparticles were synthesized in the insoluble microcrystalline cellulose support by reduction of metal ions with several reducers in various media resulting in cellulose-metal nanocomposites. Wide-angle X-ray scattering results showed that supramolecular structure of cellulose did not change. Crystalline Cu₂O and Cu⁰ nanoparticles were prepared with reducers NaBH₄ and N₂H₄ · H₂SO₄, CuO nanoparticles – with cellulose itself as a reducer. Crystalline Ni⁰ nanoparticles were synthesized with N₂H₄ · 2HCl and NaBH₄; Ni⁰ nanoparticles in amorphous form were prepared with KH₂PO₂ · H₂O. SEM revealed large agglomerates of metal particles on the fibre surface. ASAXS and TEM have shown the nanoparticles to be in the range 5–55 nm.     

Hierarchical,Titania‐Coated,Carbon Nanofibrous Material Derived from a Natural Cellulosic Substance

Hierarchical, titania‐coated, nanofibrous, carbon hybrid materials were fabricated by employing natural cellulosic substances (commercial filter paper) as a scaffold and carbon precursor. Ultrathin titania films were firstly deposited by means of a surface sol–gel process to coat each nanofiber in the filter paper, and successive calcination treatment under nitrogen atmosphere yielded the titania–carbon composite possessing the hierarchical morphologies and structures of the initial paper. The ultrathin titania coating hindered the coalescence effect of the carbon species that formed during the carbonization process of cellulose, and the original cellulose nanofibers were converted into porous carbon nanofibers (diameters from tens to hundreds of nanometers, with 3–6 nm pores) that were coated with uniform anatase titania thin films (thickness ≈12 nm, composed of anatase nanocrystals with sizes of ≈4.5 nm). This titania‐coated, nanofibrous, carbon material possesses a specific surface area of 404 m² g^?1, which is two orders of magnitude higher than the titania–cellulose hybrid prepared by atomic layer deposition of titania on the cellulose fibers of filter paper. The photocatalytic activity of the titania–carbon composite was evaluated by the improved photodegradation efficiency of different dyes in aqueous solutions under high‐pressure, fluorescent mercury‐lamp irradiation, as well as the effective photoreduction performance of silver cations to silver nanoparticles with ultraviolet irradiation.     

Tensile,thermal, and antibacterial characterization of composites of cellulose/modified Pennisetum purpureum natural fibers with in situ generated copper nanoparticles

Eco-friendly all cellulose composites were developed using cellulose as matrix and nanocomposite (in situ generated copper nanoparticles modified Napier Grass Fibers (NGFs)) as fillers for the antibacterial applications. The content of the nanocomposite filler was increased from 1?wt.% to 5?wt.% in the cellulose matrix. All these composites were characterized by Scanning Electron Microscopy (SEM), Tensile, Thermo Gravimetric Analysis (TGA), and antibacterial tests. SEM-EDX analysis revealed the in situ generation of copper nanoparticles on the surface of the films. Further, all cellulose composites showed good thermal stability. A minimum of 30% increase in char residue was observed in all cellulose nanocomposites compared to matrix. Antibacterial analysis indicated an excellent clear zone formation against both Gram Negative (Escherichia coli) and Gram Positive (Staphylococcus) bacteria. Hence, all these cellulose nanocomposite films can be considered as antibacterial packaging and dressing materials in medical field.     

Luminescent cellulose fibers activated by Eu3+-doped nanoparticles

UV- active cellulose fibers were obtained by dry-wet method spinning an 8?% by weight α-cellulose solution in N-methylomorpholine-N-oxide (NMMO) modified by europium-doped gadolinium oxyfluoride Gd₄O₃F₆:Eu³⁺ containing 5?mol (%) of the dopant. Photoluminescent nanoparticles were introduced in the in powder form into a polymer matrix during the process of cellulose dissolution in NMMO. The dependencies of emission intensity on excitation energy and the concentration of Gd₄O₃F₆:Eu³⁺ nanoparticles in the final cellulosic products were examined by photoluminescence spectroscopy (excitation and emission). The fiber structure was studied by X-ray powder diffraction analysis. The size and dispersity of the nanoparticles in the polymer matrix were evaluated using scanning electron microscopy and X-ray microanalysis. The influence of different concentration particles (in the range from 0.5 to 5?% by weight) on the mechanical properties of the fibers, such as tenacity and elongation at break, were determined.     

Chiral Separation of Organic Phosphonate Compounds on Polysaccharide-Based Chiral Stationary Phases

Four polysaccharide-based chiral stationary phases have been used to separate the enantiomers of fourteen O,O-dialkyl-1-benzyloxycarbonyl-aminoarylmethyl phosphonates. These polysaccharide-based chiral stationary phases are Chiralpak AD, Chiralpak AS, Chiralcel OG and Chiralcel OJ. The data obtained indicate that the chiral separation ability for these organophosphonate compounds are in the order Chiralpak AD > Chiralcel OG > Chiralcel OJ > Chiralpak AS. With Chiralpak AD, all of the studied compounds could be easily baseline separated. Those two polysaccharides possess different chiral discrimination mechanism due to of the difference of the conformational structures of amylose and cellulose. The chiral discrimination of derivatized amylose chiral stationary phases were based on the stereogenic fit of the analytes in the helical structures of amylose and the transient diastereomeric complex formation between the analyte and the amylose CSP through π–π interaction H-bond interactions and induced dipole interactions exerted by the substituents on the analyte molecules. The chiral discrimination, in case of derivatized cellulose chiral stationary phase is based on the stereogenic fit of the analytes in the grooves of cellulose followed by interactions mentioned above between the analytes and the cellulose CSP.     

Fabrication and characterization of CMC‐based magnetic superabsorbent hydrogel nanocomposites for crystal violet removal

In this research work, novel magnetic superabsorbent hydrogel nanocomposites (MSHNs) based on carboxymethyl cellulose were prepared via a facile “one‐pot” two step approach. Magnetic iron oxide nanoparticles were in situ synthesized and incorporated into carboxymethyl cellulose/poly(acrylic acid) polymer hydrogel. The morphology and chemical composition of MSHNs as well as the presence of magnetic iron oxide nanoparticles were evaluated by using Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, X‐Ray diffraction, ultraviolet–visible spectroscopy, thermogravimetric analysis, and vibrating sample magnetometer. The effect of different reaction parameters on the swelling capacity of MSHNs was investigated. Furthermore, batch adsorption experiments of crystal violet dye onto MSHNs were studied by varying solution pH, initial dye concentration, and temperature. Evaluation of thermodynamic parameters of crystal violet adsorption confirmed that the adsorption was spontaneous and endothermic process in nature. The equilibrium study revealed that the dye adsorption behavior of MHSNs followed the Redlich‐Peterson isotherm model. Finally, the dye adsorption experiment data was well fitted by the pseudo‐second‐order kinetic model with the regression coefficient (R²) of 0.9979. Our results suggest that the MHSNs with facile preparation method, high swelling capacity, and high dye adsorption capacity may be used as promising adsorbents for fast removal of various dyes from aqueous solutions. Copyright © 2016 John Wiley & Sons, Ltd.     

Moisture and solvent responsive cellulose/SiO<Subscript>2</Subscript> nanocomposite materials

Water responsive SiO₂/cellulose nanocomposite hydrogels and films were constructed, for the first time, by dispersing SiO₂ nanoparticles into cellulose solution in LiOH/urea solvent, and then by crosslinking with epichlorohydrin or regeneration in coagulation bath, respectively. The cellulose nanocomposite materials were characterized by Field emission scanning electron microscopy, FTIR, dynamic rheology, wide angle X-ray diffraction and mechanical test. The SiO₂/cellulose nanocomposites at wet state or in water displayed unique behaviors, showing higher light transmittance than those before contacting with water. The results revealed that strong hydrogen-bonding interaction among water, cellulose and SiO₂ led the good dispersion of SiO₂ nanoparticles in the cellulose matrix. The incorporation of SiO₂ nanoparticles improved the transmittance and mechanical strength of the cellulose hydrogels, and also enhanced the mechanical strength of the films. Especially, the cellulose/SiO₂ nanocomposite films were milky at dry state, and changed to transparent after being soaked in water, different from the cellulose film without the SiO₂ nanoparticles. In our findings, SiO₂ and cellulose with water could form strong hydrogen bonding to create a homogenous network structure. The cellulose/SiO₂ composite as a smart material exhibited moisture and solvent responsiveness, showing potential applications in moisture detection.     

Sustainable and Robust Graphene Cellulose Paper Decorated with Lithiophilic Au Nanoparticles to Enable Dendrite-free and High-Power Lithium Metal Anode

Lithium metal anodes (LMAs) with high energy density have recently captured increasing attention for development of next-generation batteries. However, practical viability of LMAs is hindered by the uncontrolled Li dendrite growth and infinite dimension change. Even though constructing 3D conductive skeleton has been regarded as a reliable strategy to prepare stable and low volume stress LMAs, engineering the renewable and lithiophilic conductive scaffold is still a challenge. Herein, a robust conductive scaffold derived from renewable cellulose paper, which is coated with reduced graphene oxide and decorated with lithiophilic Au nanoparticles, is engineered for LMAs. The graphene cellulose fibres with high surface area can reduce the local current density, while the well-dispersed Au nanoparticles can serve as lithiophilic nanoseeds to lower the nucleation overpotential of Li plating. The coupled relationship can guarantee uniform Li nucleation and unique spherical Li growth into 3D carbon matrix. Moreover, the natural cellulose paper possesses outstanding mechanical strength to tolerate the volume stress. In virtue of the modulated deposition behaviour and near-zero volume change, the hybrid LMAs can achieve reversible Li plating/stripping even at an ultrahigh current density of 10 mA cm⁻² as evidenced by high Coulombic efficiency (97.2 % after 60 cycles) and ultralong lifespan (1000 cycles) together with ultralow overpotential (25 mV). Therefore, this strategy sheds light on a scalable approach to multiscale design versatile Li host, promising highly stable Li metal batteries to be feasible and practical.     

Polysaccharides for Medical Technology: Properties and Applications

Over the past decade, the use of polysaccharides has gained tremendous attention in the field of medical technology. They have been applied in various sectors such as tissue engineering, drug delivery system, face mask, and bio-sensing. This review article provides an overview and background of polysaccharides for biomedical uses. Different types of polysaccharides, for example, cellulose and its derivatives, chitin and chitosan, hyaluronic acid, alginate, and pectin are presented. They are fabricated in various forms such as hydrogels, nanoparticles, membranes, and as porous mediums. Successful development and improvement of polysaccharide-based materials will effectively help users to enhance their quality of personal health, decrease cost, and eventually increase the quality of life with respect to sustainability.     

Efficient and Bio‐inspired Conversion of Cellulose to Formic Acid Catalyzed by Metalloporphyrins in Alkaline Solution

A bio‐inspired approach for efficient conversion of cellulose to formic acid (FA ) was developed in an aqueous alkaline medium. Metalloporphyrins mimicking cytochrome P450 exhibit efficiently and selectively catalytic performance in catalytic conversion of cellulose. High yield of FA about 63.7% was obtained by using sulfonated iron(III ) porphyrin as the catalyst and O₂ as the oxidant. Iron(III )‐peroxo species, TSPPFe^IIIOO ⁻, was involved to cleave the C‐C bonds of gluconic acid to FA in this catalytic system. This approach used relatively high concentration of cellulose and ppm concentration of catalyst. This work may provide a bio‐inspired route to efficient conversion of cellulose to FA .     

Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films

Formation of a composite from Se⁰ nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films was studied. The optimal sorption parameters at which the amorphous form of the selenium complex is preserved in the composite were suggested.     

Nano cellulose particles covered with block copolymer of cellulose and methyl methacrylate produced by solid mechano chemical polymerization

Nano cellulose particles covered with a block copolymer of microcrystalline cellulose and poly(methyl methacrylate) (MCC-block-PMMA) were produced by a solid mechano-chemical polymerization. The polymerization of methyl methacrylate was initiated by chain-end-type microcrystalline cellulose (MCC) radicals (i.e., MCC mechano radicals) on the surface of MCC that were induced by mechanical fracture of β-1,4 glycosidic linkages. The chemically modified cellulose particles with MCC-block-PMMA were fractionated by Soxhlet extraction with chloroform, and resulted in MCC-block-PMMA residue from residue on the filter and MCC-block-PMMA filtrate from filtrate solution. The surface of the MCC particles chemically modified with MCC-block-PMMA in MCC-block-PMMA residue was partially covered with PMMA chains of the MCC-block-PMMA. In contrast, the surfaces of the MCC nanoparticles chemically modified with MCC-block-PMMA in MCC-block-PMMA filtrate were fully covered with PMMA chains of the MCC-block-PMMA. A dispersion of the chemically fully modified MCC nanoparticles in chloroform was optically transparent. The average diameter of the chemically fully modified MCC nanoparticles in chloroform was estimated to be 52 nm. These were confirmed by electron spin resonance, Fourier transform infrared, and ¹H nuclear magnetic resonance spectroscopy, by gel permeation chromatography and dynamic light scattering.     

壳聚糖基载药纳米微粒制备研究进展

有关可生物降解多糖类纳米微粒用作给药载体的研究，近年颇受重视。简要评述了壳聚糖基载药纳米微粒的制备方法，包括共价交联、离子诱导、沉淀析出、大分子复合和自组装方法及其研究进展。     

Polymeric membranes based on cellulose acetate loaded with candle soot nanoparticles for water desalination

This study is concerned with modifying cellulose acetate (CA)/polyethylene glycol (PEG) membranes prepared via phase inversion technique in the presence of carbon nanoparticles; candle soot (CS) resulting from combusted candle. CS nanoparticles were analyzed via Fourier transform infrared spectroscopy and transmission electron microscopy. The developed membranes were characterized for their surface morphology, mechanical properties as well as thermal stability. CS nanoparticles contributed in improving the salt rejection % with a slight reduction in the water flux behavior. Employing the annealed cellulose acetate/polyethylene glycol membranes loaded with candle soot nanoparticles provides an adequate approach towards water desalination implementations.     

In situ synthesis of plate-like Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in porous cellulose films with obvious magnetic anisotropy

Nanocomposite cellulose films with obvious magnetic anisotropy have been prepared by in situ synthesis of plate-like Fe₂O₃ nanoparticles in the cellulose matrix. The influence of the concentrations of FeCl₂ and FeCl₃ solutions on the morphology and particle size of the synthesized Fe₂O₃ nanoparticles as well as on the properties of the composite films has been investigated. The Fe₂O₃ nanoparticles synthesized in the cellulose matrix was γ-Fe₂O₃, and its morphology was plate-like with size about 48 nm and thickness about 9 nm, which was totally different from those reported works. The concentration of FeCl₂ and FeCl₃ solution has little influence on the particle size and morphology of the Fe₂O₃ nanoparticles, while the content of Fe₂O₃ nanoparticles increased with the increase of the concentration of the precursor solution, indicating that porous structured cellulose matrix could modulate the growth of inorganic nanoparticles. The unique morphology of the Fe₂O₃ nanoparticles endowed the composite films with obvious magnetic anisotropy, which would expand the applications of the cellulose based nanomaterials.     

Cellulose Filter Paper with Antibacterial Activity from Surface-Initiated ATRP

Poly(tert-butyl acrylate) (PtBA) bruhes were successfully grafted on the cellulose filter papers via surface-initiated atom transfer radical polymerization (ATRP). Then the grafting PtBA brushes were transferred into poly(acrylic acid) (PAA) in the presence of trifluoroactic acid (TFA), which can form chelate complexes with Ag⁺. The Ag⁺ was reduced in situ to obtain the silver nanoparticles decorated cellulose filter papers. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to characterize the chemical structure of the resulting product. The morphologies of the filter paper at different stages of surface modification were investigated by field emission scanning electron microscopy (FESEM). The silver nanoparticles decorated filter paper performed good antibacterial ability against E. coli as compared with the original filter paper and PAA modified filter paper.     

Bacterial cellulose based flexible multifunctional nanocomposite sheets

Bacterial cellulose is an ideal material that is sustainable, biodegradable and inherently capable of functionalization. Hence this has been functionalized with a single component, Ni to exhibit multiple functionalities such as electrical conductivity, magnetic sensitivity as well as catalytic activity in both dried and hydrogel forms. A novel, simple ‘inverse chemical reduction’ technique has been developed to incorporate this component and make bacterial cellulose multifunctional. This technique mercerizes and opens the interfibrillar spaces which results in the formation of nanoparticles that lead to percolating paths for conduction. The flexible sheet becomes electrically conducting with just 20 vol% of nanoparticles in the composite as determined by thermogravimetry. The room temperature electrical conductance increases by about 7 orders of magnitude, 10^?6–10 S on changing the Ni-precursor solution concentration from 0.015 to 0.02 M, indicating this to be the critical concentration for conduction percolation. The composites are highly magnetic at room temperature with a maximum energy product of 140 J m^?3, comparable to some of the commercially available bonded oxide magnets. The hydrogel form of the nanocomposite is found to be catalytically active. The catalytic activity is retained even after leaving the nanocomposite hydrogel in water for 12 h in water.