Cellulose Template Research Articles

Effect of Steam Activation on Development of Light Weight Biomorphic Porous SiC from Pine Wood Precursor

Biomorphic SiC materials with tailor-made microstructure and properties similar to ceramic materials manufactured by conventional method are a new class of materials derived from natural biopolymeric cellulose templates (wood). Porous silicon carbide (SiC) ceramics with wood-like microstructure have been prepared by carbothermal reduction of charcoal/silica composites at 1300-1600 °C in inert Ar atmosphere. The C/SiO2 composites were fabricated by infiltrating silica sol into porous activated biocarbon template. Silica in the charcoal/silica composite, preferentially in the cellular pores, was found to get transformed in forms of fibers and rods due to shrinkage during drying. The changes in the morphology of resulting porous SiC ceramics after heat treatment to 1600 °C, as well as the conversion mechanism of wood to activated carbon and then to porous SiC ceramic have been investigated using scanning electron microscope, x-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. Activation of carbon prior to silica infiltration has been found to enhance conversion of charcoal to SiC. The pore structure is found to be uniform in these materials than in those made from as-such charcoal/silica composites. This provides a low-cost and eco-friendly route to advanced ceramic materials, with near-net shape potential.

FABRICATION OF HOLLOW SILICA NANORODS USING NANOCRYSTALLINE CELLULOSE AS TEMPLATES

A simple approach to fabricate hollow silica nanorods is reported, using nanocrystalline cellulose (NCC) as templates. Uniform NCC with the length of ca. 100 nm and a diameter of ca. 10 nm were prepared by hydrolysis of microcrystalline cellulose (MCC) in strong sulfuric acid condition. NCC was used as a template to prepare a core-shell composite of silica and NCC. The sol-gel reaction of tetraethyl orthosilicate (TEOS) was employed to coat NCC with a nano thickness of silica in the presence of ammonia. Finally, hollow silica nanorods were obtained by calcination of the composite at 600°C to remove the organic cellulose template completely. The obtained hollow silica nanorods were found to have uniform size and shape: with a length of ca. 100 nm, an inner diameter close to the original diameter of NCC, and a thickness of around 10 to 15 nm. These results suggest that NCC is an excellent template for manufacturing nano hollow materials with uniform shape and size.

Nematic ordered cellulose templates mediating order-patterned deposition accompanied with synthesis of calcium phosphates

In a previous study, the nematic ordered cellulose (NOC) templates successfully induced biodirected epitaxial nanodeposition of cellulose nanofibers secreted by Gluconacetobacter xylinus along the orientation of the molecular tracks (Kondo et al. 2002). As an extended concept for the NOC, this article attempts to propose a sort of biomimic mineralization using the template. It combines morphologically controlling process with synthesis of the calcium phosphate as a major component of bones. This process was initially mediated by the modified NOC template having a pair of roles of the ion supply sources and scaffolds for 3D-ordering architecture of the calcium phosphate as a biomineral in the key functions for biomineralization. The successful establishment of such an ordered deposition of the inorganic on the template was confirmed by several surface characterizations such as atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and so on. Moreover, similarly to human bones, the obtained major assemble states of the calcium phosphates exhibited amorphous. The above process using the bifunctional cellulose template can be considered as a biomimic mineralization, which also opens pathways toward preparation of potentially versatile organic–inorganic order-patterned composites under a less energy consumption.

Effect of the preparation method on high-temperature de-N2O performance of Na–CaO catalysts. A mechanistic study

A simple cellulose-templating (CT) method was used to prepare Na–CaO catalysts for high-temperature N2O decomposition to N2 and O2 in excess of NO, O2, and H2O. According to this method, cellulose materials were soaked in aqueous solution of calcium and/or sodium nitrates followed by burning out the template material. Depending on the nature of cellulose template and calcination procedure, the obtained catalysts consisted of regularly shaped particles of 100–400nm. Conventionally prepared Na–CaO reference materials had randomly shaped particles on a micron scale. Compared to the latter catalysts, the CT ones showed higher de-N2O activity and resistance against inhibition by NO and O2, which make them interesting from industrial point of view. Transient analysis of NO interaction with the studied catalysts in the presence and the absence of O2 enabled us to conclude that the superior de-N2O performance of the CT materials is due to improved desorption of surface NOx species acting as inhibitors for N2O decomposition.

Titania nanotube/hollow sphere hybrid material: Dual-template synthesis and photocatalytic property

Inspired by the complicated structure of natural substances, we designed and fabricated nanotube/hollow sphere hybrid structured functional anatase titania material. Cellulosic substance (commercial filter paper) was chosen as nanotube template while silica and polystyrene colloidal microspheres with different diameters were employed as hollow sphere templates. The ultrathin nature of titania layer enabled faithful replication of the nanoscopic structural details of both the template substances. The microsphere and cellulose templates were removed by calcination for polystyrene microsphere template case, and further alkali treatment was carried out to dissolve away the silica component for silica microsphere template case. The obtained anatase titania nanotubes were decorated with nanoscale titania hollow spheres with wall thickness of about 7.5 nm. The resulted hybrid materials exhibited similar but superior photocatalytic efficiency compared with simple titania nanotube structured materials due to the higher surface area endowed by the complex highly porous structure.

Functional polymeric hybrid nanotubular materials derived from natural cellulose substances

Template synthesis is regarded as an effective pathway to replicate the unique structures and morphologies of natural substances with guest substrates to introduce designed functions into artificial materials, but it is generally limited to inorganic materials syntheses due to the severe calcination treatment to remove the template during the fabrication process. Here, a series of polymeric hybrid nanotubular materials were fabricated employing natural cellulosic substances as templates via versatile alternative layer-by-layer deposition strategies and successive removal of cellulose component by a solution dissolving process under mild conditions. Thin layers of various polyelectrolytes and polysaccharide such as heparin were deposited onto titania thin film pre-coated cellulose nanofibers of natural cellulose substance (e.g. commercial filter paper) through electrostatic interaction and covalent links, respectively. The cellulose substance template was dissolved away by low-temperature sodium hydroxide/urea solution treatment, resulting in corresponding polymeric hybrid nanotubular materials. In spite of the employed raw polymers and deposition strategies, all the obtained nanotubular products successfully memorized the original structures and morphologies of the natural cellulose template. Importantly, since a mild chemical dissolution process was employed instead of calcination to selectively remove the template cellulose substrate, the final polymeric hybrid products were left undamaged, and furthermore, brought their unique instinct properties such as significant anticoagulative properties originated from heparin. Our present research broadens the availability of raw materials for synthesizing bio-inspired products, and provides such products with advanced bio-organic functions.

Luminescent silica nanotubes and nanowires: Preparation from cellulose whisker templates and investigation of irradiation-induced luminescence

Luminescent silica nanotubes and nanowires were fabricated from cellulose whisker templates by sol-gel processing. The cellulose templates were removed by calcination at 650 °C to generate silica nanotubes with diameters of 15 nm and lengths up to 500 nm. At temperatures of 900 °C the core region previously occupied by the cellulose template was closed yielding silica nanowires. Cathodoluminescence spectra of the silica nanotubes and nanowires were measured in the transmission electron microscope during irradiation with 150 keV electrons. A blue emission at 450 nm was observed for the silica nanowires calcined at 900 °C. This luminescence was found to be related to defects induced by electron irradiation and was investigated in situ as a function of irradiation dose. The as-synthesized and 650 °C calcined nanowires and nanotubes showed a fast decay of the signal. The observed irradiation dose dependent changes in the luminescence spectra will be discussed in terms of defect formation and transformation mechanisms.

Hierarchically mesoporous–macroporous bioactive glasses scaffolds for bone tissue regeneration

Hierarchically 2D/3D mesoporous-macroporous bioactive glasses (MMBG) with good molding capabilities and compressive modulus were synthesized by sol-gel method and evaporation-induced self-assembly process in the presence of both nonionic triblock copolymers, EO(70)PO(20)EO(70) (P123) or EO(100)PO(65)EO(100) (F127), templates and methyl cellulose template. P123 or F127 acts as both a template, inducing the formation of mesopore, and an effective dispersant of MC, which produces macropores. In vitro bioactivity studies were carried out in simulated body fluid and showed superior bone-forming bioactivities of hierarchical MMBG. Human osteoblastlike cells, MG63, were seeded on MMBG and were determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5,-diphenyl-tetrazolium bromide] assay to confirm biocompatibilities of MMBG.

Synthesis of Titania Nanofibers for Photocatalytic Applications

Titania nanofibers were prepared using a colloidal solution of Titania nanoparticles and a templating method. The preparation comprises impregnation of cellulose fibers in the solution containing Titania nanoparticles followed by thermal removal of the cellulose template. It is evidenced by scanning electron microscopy (SEM) that the residue substance consists of micron size fibers with a microstructure of nanofibers. The pore size distribution of the substance is multi‐scale and fractal morphology was demonstrated with two fractal regimes with dimensions of 1.78 and 2.97 for sizes below and above 7.5 nm, respectively. The surface area of the Titania fibers was measured about 250 m2/g. The photocatalytic property of nanofibers was measured using methanol and cigarette smoke.

Biomimetic Growth of Biomorphic CaCO3 with Hierarchically Ordered Cellulosic Structures

Biomorphic CaCO3 with different hierarchically ordered micro- and nanostructures was fabricated with natural cellulose substances as the host templates. The fabrication involves two mild sonication processes in which calcium and carbonate ions are sequentially added to the template, together with subsequent calcination in air. The specific pseudo-1D and pseudo-2D structures of the resultant crystalline calcite can be tailored by mimicking both natural and artificially woven cellulosic substances, with the former following the ribbon/tube form of cellulose fiber and the latter following the netlike architectures of the woven cotton cloth. The building block of these structures is a layer of CaCO3 grains grown on the surfaces of each cellulose fiber. By choosing Ca2+, CO32-, or HCO3- ions as the first adsorption species on the cellulose template, we show that the resultant CaCO3 grain size can be fine-tuned in a nanoscopic scale, most probably due to the differences in the nature of ion adsorption on the cellulose molecules and the resultant CaCO3 nucleation and growth. The impact of this new route is that we can precisely predict the morphologies of the final CaCO3 products that were not realized in other chemical approaches.

Biomimetic mineralisation of apatites on Ca 2+ activated cellulose templates

We investigated the activation of regenerated cellulose 2D model thin films and 3D fabric templates with calcium dihydroxide. The Langmuir–Blodgett (LB) film technique was applied for manufacturing of the model thin films using a trimethylsilyl derivative of cellulose (TMS-cellulose). Regenerated cellulose films were obtained by treating the TMS-cellulose LB-films with hydrochloric acid vapours. For 3D templates, regenerated cellulose fabrics (Lyocell®) were used. The regenerated cellulose templates were activated with a Ca(OH) 2-suspension and subsequently exposed to 1.5 × SBF to induce the in situ formation of biomimetic calcium phosphate phases. FTIR and Raman spectroscopy showed that the Ca(OH) 2 and calcite present from reaction with HCO 3 − on the template surface were dissolved in the initial stage of exposure to the 1.5 × SBF. After 1 day, the formation of apatitic phases in 1.5 × SBF was observed. According to detailed calculations, high supersaturation levels S in close vicinity to the template surface ( S > 16) resulting from the Ca 2+ diffusion induced the formation of biomimetic calcium phosphate. The biomimetic calcium phosphates were identified by FTIR and Raman spectroscopy as highly carbonated apatites (HCA) lacking hydroxyl ions. 3D fabric templates of regenerated cellulose covered with a biomimetic coating of apatite might be of particular interest for novel scaffold architectures in bone repair and tissue engineering.

Electro-conductive nanotubular sheet of indium tin oxide as fabricated from the cellulose template

Free-standing, nanotubular ITO sheet with different In/Sn ratios was fabricated by the surface sol–gel process using cellulose filter paper as template. The resulting materials have a hierarchical structure originating from the morphology of cellulosic paper, and the ITO nanotubes are composed of interconnected layers of ITO nanocrystals of a few nanometres. Semiconducting behavior was observed at temperatures above room temperature, probably because electronic migration is strongly affected by the scattering at the boundary between nanocrystals. The ITO sheet with In/Sn ratio of 93.5/6.5 showed an intrinsic electronic conductivity (0.53 S cm−1) that is higher than those of other nanostructured ITO, and a very low apparent density (3.3% of neat ITO). These features indicate that the nanotubular ITO sheet has a potential use for chemical sensors and other devices.

Highly porous TiO2 nanofibres with a fractal structure

TiO2 nanofibres were prepared using a templating method with tetraisopropylorthotitanate(TiPT) as a precursor. The preparation comprises liquid phase deposition oncellulose fibres followed by thermal removal of the cellulose template. The obtainedTiO2 fibrous substance consists of micron-size fibres with a microstructure of nanofibres. It wasdemonstrated that nanofibres are basically formed through the aggregation ofTiO2 nanoparticles and nanorods into chain structures during thethermal treatment process. The measured surface area of theTiO2 fibreswas about 250 m2 g−1. It was shown that the pore size distribution is multi-scale and a fractal morphologywas demonstrated with two fractal regimes with dimensions of 1.78 and 2.97for sizes below and above 7.5 nm, respectively. The crystalline phase of theTiO2 nanofibres, as well as the nanoparticles in the solution, could be controlled by the pH of thesolution. A pH of 1.2 resulted in rutile phase, while a pH of 1.8 resulted in anatase phase.

Behavior of cellulose production of Acetobacter xylinum in 13C-enriched cultivation media including movements on nematic ordered cellulose templates

Acetobacter xylinum NQ-5 (ATCC 53582) and AY-201 (ATCC 23769) cultivated in the Hestrin–Schramm medium containing d-glucose with a natural 13C-abundance of 1.1% were investigated regarding their cell division rates and the bacterial movements. Comparative studies were carried out in the presence of d-glucose-U- 13C 6 with a uniform 13C-labeling of 99% as the sole carbon source. The bacterial growth rates in numbers were found to increase in the 13C-enriched media by about 13% for NQ-5 and 26% for AY-201, respectively. The movements of single cells caused by the inverse force of the secretion and deposition of cellulose nanofibers on nematic ordered cellulose (NOC) templates were investigated by real-time video analyzes using light microscopy. As a result, d-glucose-U- 13C 6 reduced the speed of motion for both strains, which was an opposite trend to the above growth rates in the cell division. The deposited cellulose fibers were proved to be in a cellulose crystalline form by CP/MAS 13C NMR and NIR FT Raman spectroscopic measurements, although the biosynthesized and thereafter-deposited cellulose has a strong interaction with the surface of NOC.

Accelerated Biomimetic Deposition of Bonelike Apatite on Fibrous Cellulose Templates

Fibrous cellulose templates are attractive candidates for the use as tissue engineering scaffolds due to their biocompatibility and the adjustable porosity. Nevertheless, a direct bond between cellulose and bone is not formed under physiological conditions. A simulated body fluid solution with a high degree of supersaturation (5*SBF) was used to accelerate the biomimetic formation of bonelike apatite on cellulose templates. After generating calcium phosphate nuclei on the cellulose fibers in 5*SBF with high Mg2+and HCO3 - concentrations the cellulose templates were immersed in a modified 5*M-SBF which was optimized in respect to crystal growth kinetics by reduced Mg2+and HCO3- concentrations. After 48 hours a hydroxy carbonated apatite (HCA) layer with a thickness of 20 µm was obtained.

Biosynthetic interdependence of lignins and secondary metabolites in angiosperms

The morphology and metabolism of angiosperms are connected to lignin production. Morphology depends on the structure of genetically controlled cellulose templates for lignin deposition; metabolism is the consequence of lignin-requirement directed biosynthesis of secondary metabolites. Hence, it is possible to correlate morphological features (such as evolutionary replacement of woodiness by herbaceousness) with general chemical features (such as evolutionary replacement of aromatics by aliphatics) and with particular chemical features (such as oxidative diversification of biosynthetic categories of metabolites). The first correlation is useful for the systematic classification of plants at higher levels (e.g. orders). The last correlation is useful for the evolutionary assessment of plants at lower levels (e.g. families). These concepts allow the construction of an integrated system of angiosperm classification based on morphology for the circumscription of taxa and on chemistry for the evolutionary assessment of plant groups.