Size-Controlled Silver Nanoparticles Supported by Pyrolytic Carbon from Microcrystalline Cellulose.

A facile method was developed for preparing size-controlled silver nanoparticles supported by pyrolytic carbon from microcrystalline cellulose (MCC). The pyrolysis of cellulose-AgNO3 mixture caused the oxidation of cellulose, resulting in carboxyl groups to which silver ions can bind firmly and act as nuclei for the deposition of silver nanoparticles. The structure and properties of the obtained nanocomposite were characterized by using a scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD). The results suggest that silver nanoparticles were integrated successfully and dispersed uniformly in the pyrolytic carbon matrix. The average particle size varied between 20 nm and 100 nm in correlation to the dose of silver nitrate and temperature of pyrolysis. The products showed high electric conductivity and strong antimicrobial activity against Escherichia coli (E. coli).

One-Pot Green Synthesis of Nitrogen-Doped Carbon Quantum Dots for Cell Nucleus Labeling and Copper(II) Detection.

The doping of nitrogen into carbon quantum dots is vitally important for improved fluorescence performance. However, the synthesis of nitrogen-doped carbon quantum dots (N-CQDs) is usually conducted under strong acid and high temperature, which results in environmental pollution and energy consumption. Herein, the N-CQDs were prepared by a mild one-pot hydrothermal process. The hydrothermal reaction temperature was adjusted to control the particle size, nitrogen/carbon atomic ratio, and quantum yield. The products were water soluble with a narrow particle size distribution and good dispersion stability over a wide pH range. The N-CQDs could penetrate into the HeLa cell nucleus without any further functionalization. Moreover, the fluorescence of N-CQDs could be selectively quenched by Cu2+ , which suggested applications for the detection of Cu2+ in human plasma.

Face-to-Face Interfacial Assembly of Ultrathin g-C3N4 and Anatase TiO2 Nanosheets for Enhanced Solar Photocatalytic Activity.

Face-to-face interfacial assembly of TiO2-g-C3N4 hybrid (2D TCN-A) is developed by surfactant-assisted hydrothermal treatment forming a sandwich structure of anatase TiO2 nanosheets (TiO2-A, 5-6 monolayers) and g-C3N4 nanosheets (∼3 monolayers). Post air-annealing is found effective for insertion of oxygen to the hybrid, which remedies the oxygen vacancies of TiO2 (B) nanosheets and converts it to anatase nanosheets. The enhanced light adsorption, increased donor density, and prolonged life of charge carries are achieved by variation of bandgap and the formation of heterojuction between the two kinds of nanosheets, facilitating separation and transfer of charge carriers. The 2D TCN-A-70 nanosheets show a high photodegradation rate of methyl orange (kapp ≈ 0.189 min-1) and photocatalytic evolution rate of hydrogen (18200 µmol g-1 h-1). This 2D nanosheets hybrid is potentially useful in alleviating environmental and energy issues.

A versatile method for producing functionalized cellulose nanofibers and their application.

A facile method was developed to produce functionalized cellulose nanofibers in one step by ball milling. Through the synergy of mechanical and chemical actions, the produced cellulose nanofibers are ca. 20 nm wide and several micrometers long, with surface properties tailored by choice of modifying reagent. Modified by succinic anhydride, a cellulose nanofiber shows enhanced hydrophilicity, can be readily dispersed in water or DMSO, and gives a zeta potential of -38.7 mV due to carboxyl groups on the surface. Modified by dodecyl succinic anhydride, a cellulose nanofiber has excellent dispersibility in o-xylene and good compatibility with polyethylene. The polyethylene-cellulose nanofiber composite presents overall enhancement of mechanical properties. This method opens a new way to the production of functionalized cellulose nanofibers.

Three-Dimensional Nanoporous Cellulose Gels as a Flexible Reinforcement Matrix for Polymer Nanocomposites.

With the world's focus on utilization of sustainable natural resources, the conversion of wood and plant fibers into cellulose nanowhiskers/nanofibers is essential for application of cellulose in polymer nanocomposites. Here, we present a novel fabrication method of polymer nanocomposites by in-situ polymerization of monomers in three-dimensionally nanoporous cellulose gels (NCG) prepared from aqueous alkali hydroxide/urea solution. The NCG have interconnected nanofibrillar cellulose network structure, resulting in high mechanical strength and size stability. Polymerization of the monomer gave P(MMA/BMA)/NCG, P(MMA/BA)/NCG nanocomposites with a volume fraction of NCG ranging from 15% to 78%. SEM, TEM, and XRD analyses show that the NCG are finely distributed and preserved well in the nanocomposites after polymerization. DMA analysis demonstrates a significant improvement in tensile storage modulus E' above the glass transition temperature; for instance, at 95 °C, E' is increased by over 4 orders of magnitude from 0.03 MPa of the P(MMA/BMA) up to 350 MPa of nanocomposites containing 15% v/v NCG. This reinforcement effect can be explained by the percolation model. The nanocomposites also show remarkable improvement in solvent resistance (swelling ratio of 1.3-2.2 in chloroform, acetone, and toluene), thermal stability (do not melt or decompose up to 300 °C), and low coefficients of thermal expansion (in-plane CTE of 15 ppm·K(-1)). These nanocomposites will have great promising applications in flexible display, packing, biomedical implants, and many others.

Dissolution of Wood Pulp in Aqueous NaOH/Urea Solution via Dilute Acid Pretreatment.

Wood pulps with certain amounts of lignin were successfully dissolved in aqueous NaOH/urea solution by subjecting them to the dilute acid pretreatment. After the acid hydrolysis, viscosity-average degree of polymerization (DPv) of the pulps decreased. The results revealed that both the DPv and lignin contents influenced the dissolved proportions of wood pulps. When they were not so high, the wood pulps could almost completely dissolve with dissolved proportions >90%. In particular, the acid-pretreated unbleached kraft pulp with DPv of about 500 and lignin content of 6.9% could dissolve in NaOH/urea solvent and achieve a maximum pulp concentration of 4 wt % in the obtained lignocellulose solution. Moreover, the acid-pretreated bleached thermomechanical pulp with a high lignin content of 14.2% also almost completely dissolved. The lignocellulose films prepared from these wood pulp/NaOH/urea solutions exhibited good transparency and bendability, thus maybe promising as new biobased materials.

Extraordinary reinforcement effect of three-dimensionally nanoporous cellulose gels in poly(ε-caprolactone) bionanocomposites.

Three-dimensionally nanoporous cellulose gels (NCG) were prepared by dissolution and coagulation of cellulose from aqueous alkali hydroxide-urea solution, and used to fabricate NCG/poly(ε-caprolactone) (PCL) nanocomposites by in situ ring-opening polymerization of ε-CL monomer in the NCG. The NCG content of the NCG/PCL nanocomposite could be controlled between 7 and 38% v/v by changing water content of starting hydrogel by compression dewatering. FT-IR and solid-state (13)C NMR showed that the grafting of PCL onto cellulose are most likely occurred at the C6-OH groups and the grafting percentage of PCL is 25 wt % for the nanocomposite with 7% v/v NCG. (1)H NMR, XRD, and DSC results indicate that the number-average molecular weight and crystal formation of PCL in the nanocomposites are remarkably restricted by the presence of NCG. AFM images confirm that the interconnected nanofibrillar cellulose network structure of NCG are finely distributed and preserved well in the PCL matrix after polymerization. DMA results show remarkable increase in tensile storage modulus of the nanocomposites above glass transition and melting temperatures of the PCL matrix. The percolation model was used to evaluate the mechanical properties of the nanocomposites, in which stress transfer among the interconnected nanofibrillar network is facilitated through strong intermolecular hydrogen bonding and entanglement of cellulose nanofibers.

In situ synthesis of robust conductive cellulose/polypyrrole composite aerogels and their potential application in nerve regeneration.

Nanostructured conductive polymers can offer analogous environments for extracellular matrix and induce cellular responses by electric stimulation, however, such materials often lack mechanical strength and tend to collapse under small stresses. We prepared electrically conductive nanoporous materials by coating nanoporous cellulose gels (NCG) with polypyrrole (PPy) nanoparticles, which were synthesized in situ from pyrrole monomers supplied as vapor. The resulting NCG/PPy composite hydrogels were converted to aerogels by drying with supercritical CO2, giving a density of 0.41-0.53 g cm(-3), nitrogen adsorption surface areas of 264-303 m(2) g(-1), and high mechanical strength. The NCG/PPy composite hydrogels exhibited an electrical conductivity of up to 0.08 S cm(-1). In vitro studies showed that the incorporation of PPy into an NCG enhances the adhesion and proliferation of PC12 cells. Electrical stimulation demonstrated that PC12 cells attached and extended longer neurites when cultured on NCG/PPy composite gels with DBSA dopant. These materials are promising candidates for applications in nerve regeneration, carbon capture, catalyst supports, and many others.

X-ray texture analysis indicates downward spinning of chitin microfibrils in tubeworm tube.

The direction of ß-chitin deposition in the tube of tubeworm Lamellibrachia satsuma was investigated by texture analysis using X-ray diffraction. The ß-chitin crystallite in the tube has planar orientation with the (110) plane perpendicular to the surface, and the c-axis is aligned parallel to the tube. The monoclinic unit cell of ß-chitin allowed determination of the sense of c-axis from the orientation of (010) and (100) planes. This means that the reducing end of ß-chitin is pointing up in the tube. This orientation can be ascribed to possible secretion mechanisms of the ß-chitin microfibrils, i.e. the chitin-synthesizing enzyme complex travels unidirectionally from top to bottom when the worm body contracts in the tube.

Drug release from nanoparticles embedded in four different nanofibrillar cellulose aerogels.

Highly porous nanocellulose aerogels prepared by freeze-drying from various nanofibrillar cellulose (NFC) hydrogels are introduced as nanoparticle reservoirs for oral drug delivery systems. Here we show that beclomethasone dipropionate (BDP) nanoparticles coated with amphiphilic hydrophobin proteins can be well integrated into the NFC aerogels. NFCs from four different origins are introduced and compared to microcrystalline cellulose (MCC). The nanocellulose aerogel scaffolds made from red pepper (RC) and MCC release the drug immediately, while bacterial cellulose (BC), quince seed (QC) and TEMPO-oxidized birch cellulose-based (TC) aerogels show sustained drug release. Since the release of the drug is controlled by the structure and interactions between the nanoparticles and the cellulose matrix, modulation of the matrix formers enable a control of the drug release rate. These nanocomposite structures can be very useful in many pharmaceutical nanoparticle applications and open up new possibilities as carriers for controlled drug delivery.

One-step dispersion of cellulose nanofibers by mechanochemical esterification in an organic solvent.

Got a crush: Native cellulose can be dispersed as nanofibers in organic solvents by ball milling with esterification agents. Milling with hexanoyl chloride/DMF gives hexanoyl-coated nanofibers dispersible in several organic solvents. Milling with succinic anhydride/DMSO results water-dispersible nanofibers. The results open the way to new cellulose mechanochemistries.

Mechanism of cellulose gelation from aqueous alkali-urea solution.

Molecular process of regeneration-gelation of cellulose from aqueous alkali-urea solvent was monitored by synchrotron-radiation X-ray. The wide-angle diffraction from cellulose during regeneration, both by coagulant and heating, gave information on behavior of cellulose molecules, i.e. the glucopyranoside rings first stack by hydrophobic interaction to form monomolecular sheets, which then line up by hydrogen bonding to form Na-cellulose IV type crystallites (hydrate form of cellulose II). While such a process in regeneration of cellulose has been hypothesized and supported by molecular dynamics or monitoring of mercerization process, our observation finally confirmed it experimentally. This knowledge will be useful in understanding behavior of cellulose molecules during regeneration, leading to better controls of resulting structure and properties.

Internal surface polarity of regenerated cellulose gel depends on the species used as coagulant.

Cellulose gels regenerated from aqueous alkali-urea solvent were found to have different surface polarity depending on coagulant species. Gels coagulated by alcohols adsorbed Congo red about twice as much as those coagulated by aqueous coagulants. The difference was also noted in the iodine reaction; the alcohol-coagulated gels showed blue coloration similar to that of iodine-starch reaction in contrast to those from aqueous coagulants, which gave light yellow colors similar to that of the original iodine solution. These phenomena can be ascribed to the influence of coagulant species on the surface nature of cellulose fibrils internal to the gels. X-ray diffractometry indicated that the hydrophobicity was likely to result from exposure of glucopyranoside ring planes on the surface of cellulose fibrils. Scanning electron microscopy showed characteristic differences in nanometer-scale morphologies between the two types of cellulose gel.

Crystal analysis and high-resolution imaging of microfibrillar α-chitin from Phaeocystis.

The ultrastructure of α-chitin microfibril produced by marine alga Phaeocystis was investigated by FT-IR spectroscopy, X-ray diffraction and electron microscopy. The average size of the microfibril was 17.1±1.8 µm in length and 39.8±8.8 nm in width. The FT-IR spectrum shows typical α-chitin pattern, and each band was sharper than crustacean chitin's, indicating higher crystallinity of the Phaeocystis chitin. The X-ray diffraction gave crystallite size more than twice of crustacean tendon's. The fiber diffraction pattern is consistent with previous studies with two-chains orthorhombic unit cell (Minke and Blackwell, 1978; Sikorski et al., 2009), and refined unit cell dimensions are a=4.742 Å, b=18.871 Å, c=10.338Å. High-resolution electron microscopy of ultrathin sections gave the cross-sectional shape of microfibril as hexagon. The lattice images of (020) plane (d=0.94 nm) were frequently observed extending the entire cross-section of microfibril, indicating its single crystalline nature. These results allowed construction of a molecular packing model for α-chitin crystal.

Properties of films composed of cellulose nanowhiskers and a cellulose matrix regenerated from alkali/urea solution.

All-cellulose composite films were prepared, for the first time, from native cellulose nanowhiskers and cellulose matrix regenerated from aqueous NaOH-urea solvent system on the basis of their temperature-dependent solubility. The cellulose whiskers retained their needlelike morphology with mean length and diameter of 300 and 21 nm as well as native crystallinity when added to the latter solution at ambient temperature. The structure and physical properties of the nanocomposite films were characterized by scanning electron microscope, X-ray diffraction, and tensile tests. The composite films were isotropic and transparent to visible light and showed good mechanical properties as a result of the reinforcement by the whiskers. By varying the ratio of the cellulose whiskers to regenerated cellulose matrix (cellulose II), the tensile strength and elastic modulus of the nanocomposite films could be tuned to reach 124 MPa and 5 GPa, respectively. The tensile strength of the nanocomposite films could reach 157 MPa through a simple drawing process, with the calculated Hermans' orientation parameter of 0.30. This work provided a novel pathway for the preparation of biodegradable all-cellulose nanocomposites, which are expected to be useful as biomaterials and food ingredients.

Nanoporous cellulose as metal nanoparticles support.

Despite considerable progress in the field of metal nanoparticles synthesis, major challenges remain in many practical applications of nanoparticles which require their immobilization on solid substrates, presenting additional difficulty in separation and processing. Here, transparent nanoporous cellulose gel obtained from aqueous alkali hydroxide-urea solution was examined as supporting medium for noble metal nanoparticles. Silver, gold, and platinum nanoparticles were synthesized in the gel by hydrothermal reduction by cellulose or by added reductant. Both methods gave nanoparticles embedded with high dispersion in cellulose gels. Supercritical CO2 drying of the metal-carrying gel gave corresponding aerogels with high transmittance, porosity, surface area, moderate thermal stability, and good mechanical strength. The cellulose and metal-cellulose gels were characterized by UV/vis spectroscopy, optical microscopy, SEM, TEM, XRD, nitrogen physisorption, TGA, and tensile testing, systematically.

Quasi-one-dimensional arrangement of silver nanoparticles templated by cellulose microfibrils.

We demonstrate a simple, facile approach to the deposition of silver nanoparticles on the surface of cellulose microfibrils with a quasi-one-dimensional arrangement. The process involves the generation of aldehyde groups by oxidizing the surface of cellulose microfibrils and then the assembly of silver nanoparticles on the surface by means of the silver mirror reaction. The linear nature of the microfibrils and the relatively uniform surface chemical modification result in a uniform linear distribution of silver particles along the microfibrils. The effects of various reaction parameters, such as the reaction time for the reduction process and employed starting materials, have been investigated by transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy. Additionally, the products were examined for their electric current-voltage characteristics, the results showing that these materials had an electric conductivity of approximately 5 S/cm, being different from either the oxidated cellulose or bulk silver materials by many orders of magnitude.

Cellulose aerogels from aqueous alkali hydroxide-urea solution.

Highly porous and strong cellulose aerogels were prepared by gelation of cellulose from aqueous alkali hydroxide/urea solution, followed by drying with supercritical CO2. Their morphology, pore structure, and physical properties were characterized by scanning and transmission electron microscopy, X-ray diffraction, nitrogen adsorption measurements, UV/Vis spectrometry, and tensile tests. The cellulose hydrogel was composed of interconnected about 20 nm wide. By using supercritical CO2 drying, the network structure in the hydrogel was well preserved in the aerogel. The results are preliminary but demonstrate the ability of this method to give cellulose aerogels of large surface areas (400-500 m2 g(-1)) which may be useful as adsorbents, heat/sound insulators, filters, catalyst supports, or carbon aerogel precursors.

A sesquiterpene hydrocarbon from the bogwoods of Cryptomeria japonica D. Don, presumably formed by diagenetic hydrogenation.

Structure of an hitherto unknown component of the essential oils from two bogwoods of Cryptomeria japonica D. Don was determined by mass spectrometry and NMR analyses. It was identified as cadina-1(10)-ene, a new cadinane-type sesquiterpene hydrocarbon with a single double bond.