Natural Cellulose Derived Nanocomposites as Anodic Materials for Lithium‐Ion Batteries

Bio‐inspired synthetic method provides an effective shortcut to fabricate functional nanostructured materials with specific morphologies and designed functionalities. Natural cellulose substances (e. g., commercial laboratory cellulose filter paper) possesses unique three‐dimensionally cross‐linked porous structures and abundant functional groups for the functional modification on the surfaces. The deposition of metal oxide gel film on the surfaces of the cellulose nanofibers is facilely to be achieved through the surface sol‐gel process, resulting in metal oxide replicas of the initial cellulose substance or metal‐oxide/carbon nanocomposites. Moreover, the as‐deposited metal oxide gel films coated on the cellulose fiber surfaces provide ideal platforms for the further formation of specific functional assemblies, and eventually to the corresponding nanocomposite materials. Based on this methodology, various nanostructured composites were prepared and employed as anodic materials for lithium‐ion batteries, including metal‐oxides‐based (such as SnO₂, TiO₂, MoO₃, Fe_xO_y, and SiO₂) and Si‐based composites, as summarized in this personal account. Benefiting from the unique hierarchically porous network structures and the synergistic effects among the composite components of the anodic materials, the transfer of electrons/ions is accelerated and the structural stability of the electrode is enhanced, leading to the improved lithium storage performances and promoted cycling stability.     

Self-assembly of various guest substrates in natural cellulose substances to functional nanostructured materials

Biological organisms are produced from self-assembly of highly ordered functional units and are inherently complex and hierarchical, possessing macro-to-nanoscale features. It is a facile, low-cost and environmentally benign short-cut to artificial functional materials with unique multilevel structures and morphologies employing biological substances as platform for the self-assembly of various guest substrates. This review summarizes the recent advances in the fabrication of nanostructured materials with designed properties and functionalities by means of self-assembly of different guest substrates (such as metal oxide thin films, small molecules, polymers, biomacromolecules, nanoparticles, carbon nanotubes and colloidal spheres) on the surfaces of cellulose nanofibers of bulk natural cellulose substances. The combination of the specific chemical properties of the guest substrates and the unique physical features of the natural cellulose substances sheds new light on the design and syntheses of new functional nanomaterials.     

Comparison of nano- and microfibrillated cellulose films

Nanocellulose is an interesting building block for functional materials and has gained considerable interest due to its mechanical robustness, large surface area and biodegradability. It can be formed into various structures such as solids, films and gels such as hydrogels and aerogels and combined with polymers or other materials to form composites. Mechanical, optical and barrier properties of nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) films were studied in order to understand their potential for packaging and functional printing applications. Impact of raw material choice and nanocellulose production process on these properties was evaluated. MFC and NFC were produced following two different routes. NFC was produced using a chemical pretreatment followed by a high pressure homogenization, whereas MFC was produced using a mechanical treatment only. TEMPO-mediated oxidation followed by one step of high pressure (2,000 bar) homogenization seems to produce a similar type of NFC from both hardwood and softwood. NFC films showed superior mechanical and optical properties compared with MFC films; however, MFC films demonstrated better barrier properties against oxygen and water vapor. Both the MFC and NFC films were excellent barriers against mineral oil used in ordinary printing inks and dichlorobenzene, a common solvent used in functional printing inks. Barrier properties against vegetable oil were also found to be exceptionally good for both the NFC and MFC films.     

Adsorption of carboxymethyl cellulose on polymer surfaces: evidence of a specific interaction with cellulose

The adsorption of carboxymethyl cellulose (CMC), one of the most important cellulose derivatives, is crucial for many scientific investigations and industrial applications. Especially for surface modifications and functionalization of materials, the polymer is of interest. The adsorption properties of CMC are dependent not only on the solutions state, which can be influenced by the pH, temperature, and electrolyte concentration, but also on the chemical composition of the adsorbents. We therefore performed basic investigation studies on the interaction of CMC with a variety of polymer films. Thin films of cellulose, cellulose acetate, deacetylated cellulose acetate, polyethylene terephthalate, and cyclo olefin polymer were therefore prepared on sensors of a QCM-D (quartz crystal microbalance) and on silicon substrates. The films were characterized with respect to the thickness, wettability, and chemical composition. Subsequently, the interaction and deposition of CMC in a range of pH values without additional electrolyte were measured with the QCM-D method. A comparison of the QCM-D results showed that CMC is favorably deposited on pure cellulose films and deacetylated cellulose acetate at low pH values. Other hydrophilic surfaces such as silicon dioxide or polyvinyl alcohol coated surfaces did not adsorb CMC to a significant extent. Atomic force microcopy confirmed that the morphology of the adsorbed CMC layers differed depending on the substrate. On hydrophobic polymer films, CMC was deposited in the form of larger particles in lower amounts whereas hydrophilic cellulose substrates were to a high extent uniformly covered by adsorbed CMC. The chemical similarity of the CMC backbone seems to favor the irreversible adsorption of CMC when the molecule is almost uncharged at low pH values. A selectivity of the cellulose CMC interaction can therefore be assumed. All CMC treated polymer films exhibited an increased hydrophilicity, which confirmed their modification with the functional molecule.     

Self-assembly on natural cellulose: Towards high-efficient catalysts

Nanoarchitectures based on the layer-by-layer self-assembly technique hold great potential for the availability and applicability of bio-inspired functional materials. The introduction of various specific functional building blocks onto the nanofibers of natural cellulose substances (e.g., commercial filter paper, cotton, etc.) through the self-assembly approach provides a facile strategy for the fabrication of artificial nanomaterials. This review summarizes a series of cellulose-based catalytic materials fabricated by utilizing the natural cellulose substance as the structural scaffolds or templates through the LbL self-assembly process. The unique three-dimensional network porous structures and high surface areas of the cellulose substances were maintained by the resultant cellulose-derived catalysts, while the excellent mechanical strength of the cellulose-based membrane catalysts was inherited from the initial cellulose substrates. When employed for the photodegradation of organic dyes, the photocatalytic hydrogen production from water splitting, and the antibiosis, these cellulose-based catalysts exhibited high activities and excellent cycling stabilities.     

Plasma-enhanced synthesis of bactericidal quaternary ammonium thin layers on stainless steel and cellulose surfaces

We have investigated bottom-up chemical synthesis of quaternary ammonium (QA) groups exhibiting antibacterial properties on stainless steel (SS) and filter paper surfaces via nonequilibrium, low-pressure plasma-enhanced functionalization. Ethylenediamine (ED) plasma under suitable conditions generated films rich in secondary and tertiary amines. These functional structures were covalently attached to the SS surface by treating SS with O 2 and hexamethyldisiloxane plasma prior to ED plasma treatment. QA structures were formed by reaction of the plasma-deposited amines with hexyl bromide and subsequently with methyl iodide. Structural compositions were examined by electron spectroscopy for chemical analysis and Fourier transform infrared spectroscopy, and surface topography was investigated with atomic force microscopy and water contact angle measurements. Modified SS surfaces exhibited greater than a 99.9% decrease in Staphylococcus aureus counts and 98% in the case of Klebsiella pneumoniae. The porous filter paper surfaces with immobilized QA groups inactivated 98.7% and 96.8% of S. aureus and K. pneumoniae, respectively. This technique will open up a novel way for the synthesis of stable and very efficient bactericidal surfaces with potential applications in development of advanced medical devices and implants with antimicrobial surfaces.     

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.     

Precise Size Control over Ultrafine Rutile Titania Nanocrystallites in Hierarchical Nanotubular Silica/Titania Hybrids with Efficient Photocatalytic Activity

Hierarchical‐structured nanotubular silica/titania hybrids incorporated with particle‐size‐controllable ultrafine rutile titania nanocrystallites were realized by deposition of ultrathin titania sandwiched silica gel films onto each nanofiber of natural cellulose substances (e.g., common commercial filter paper) and subsequent flame burning in air. The rapid flame burning transforms the initially amorphous titania into rutile phase titania, and the silica gel films suppress the crystallite growth of rutile titania, thereby achieving nano‐precise size regulation of ultrafine rutile titania nanocrystallites densely embedded in the silica films of the nanotubes. The average diameters of these nanocrystallites are adjustable in a range of approximately 3.3–16.0 nm by a crystallite size increment rate of about 2.4 nm per titania deposition cycle. The silica films transfer the electrons activated by crystalline titania and generate catalytic reactive species at the outer surface. The size‐tuned ultrafine rutile titania nanocrystallites distributed in the unique hierarchical networks significantly improve the photocatalytic performance of the rutile phase titania, thereby enabling a highly efficient photocatalytic degradation of the methylene blue dye under ultraviolet light irradiation, which is even superior to the pure anatase‐titania‐based materials. The facile stepwise size control of the rutile titania crystallites described here opens an effective pathway for the design and preparation of fine‐nanostructured rutile phase titania materials to explore potential applications.     

Incorporation into paper of cellulose triacetate films containing semiconductor nanoparticles

CdSe/ZnS quantum dots (QDs) were embedded in films of cellulose triacetate (CTA) to give clear films with the broad absorbance and well-defined, size-tunable fluorescence characteristic of QDs. The relative quantum yields of the QDs in polymer were compared to that of the initial QDs dispersed in toluene. Alkaline hydrolysis of the film surfaces to regenerated cellulose rendered the previously hydrophobic CTA film surfaces hydrophilic and compatible with aqueous papermaking. Films containing combinations of different sized QDs gave more complex emission patterns. Small pieces of fluorescent films were added to pulp slurries and incorporated into laboratory paper sheets through hydrogen bonding between the regenerated cellulose film surfaces and cellulosic pulp fibers. The film system (cellulose ester bulk/cellulose surface) can be used to incorporate hydrophobic particles or molecules compatible with solutions of cellulosic polymers into paper products at both high and low loadings. QDs in paper may prove useful for security applications, such as sheets with unique optical signatures.     

Formation of nematic ordered cellulose and chitin

We proposed in a previous paper a unique form of β-glucan association, nematic ordered cellulose (NOC) that is molecularly ordered, yet non-crystalline. NOC has unique characteristics; in particular, its surface properties provide with a function of tracks or scaffolds for regulated movements and fiber-production of Acetobacter xylinum [Kondo et al. 2002. Proc. Natl. Acad. Sci. USA 99: 14008–14013]. In order to extend the usage of this NOC film as a functional template, the present article attempts to clarify how β-glucan association is initiated and established by uniaxial stretching of water swollen cellulose gel films. Wide angle X-ray diffraction, high-resolution transmission electron microscopy and atomic force microscopy were employed to exhibit molecular behavior of the ordering at various scales. Then, the preparative method for NOC was applied to the other carbohydrate polymers such as α-chitin and cellulose/α-chitin blends, leading to nematic ordered states as well as cellulose. However, the method did not necessarily provide the typical structure like NOC at the molecular scale. Instead, it yielded a variety of hierarchical nematic ordered states at various scales, which allows development of new artificial ordered sheet structures.     

超疏水性聚二甲基硅氧烷膜的制备及其表面吸附性研究

采用简单的激光刻蚀方法制备了具有类“菜花”状多级结构的粗糙聚二甲基硅氧烷(PDMS)膜, 并用CCD与高敏感性微电力学天平观察和测量PDMS表面对水的吸附情况. 结果表明, 该膜表面具有超疏水性, 同时对水滴具有超低的吸附力. 还对其表面特殊多级结构产生的机理进行了分析, 并探讨了在化学组成和表面结构对超疏水性以及吸附性产生的影响.     

Direct Assembly of Metal-Phenolic Network Nanoparticles for Biomedical Applications

Coordination assembly offers a versatile means to developing advanced materials for various applications. However, current strategies for assembling metal-organic networks into nanoparticles (NPs) often face challenges such as the use of toxic organic solvents, cytotoxicity because of synthetic organic ligands, and complex synthesis procedures. Herein, we directly assemble metal-organic networks into NPs using metal ions and polyphenols (i.e., metal-phenolic networks (MPNs)) in aqueous solutions without templating or seeding agents. We demonstrate the role of buffers (e.g., phosphate buffer) in governing NP formation and the engineering of the NP physicochemical properties (e.g., tunable sizes from 50 to 270 nm) by altering the assembly conditions. A library of MPN NPs is prepared using natural polyphenols and various metal ions. Diverse functional cargos, including anticancer drugs and proteins with different molecular weights and isoelectric points, are readily loaded within the NPs for various applications (e.g., biocatalysis, therapeutic delivery) by direct mixing, without surface modification, owing to the strong affinity of polyphenols to various guest molecules. This study provides insights into the assembly mechanism of metal-organic complexes into NPs and offers a simple strategy to engineer nanosized materials with desired properties for diverse biotechnological applications.     

Syntheses, properties and applications of periodic mesoporous organosilicas prepared from bridged organosilane precursors

Periodic mesoporous organosilicas (PMOs) prepared by surfactant-directed polycondensation of bridged organosilane precursors are promising for a variety of next-generation functional materials, because their large surface areas, well-defined nanoporous structures and the structural diversity of organosilica frameworks are advantageous for functionalization. This critical review highlights the unique structural features of PMOs and their expanding potential applications. Since the early reports of PMOs in 1999, various synthetic approaches, including the selection of hydrolytic reaction conditions, development of new precursor compounds, design of templates and the use of co-condensation or grafting techniques, have enabled the hierarchical structural control of PMOs from molecular- and meso-scale structures to macroscopic morphology. The introduction of functional organic units, such as highly fluorescent π-conjugates and electroactive species, into the PMO framework has opened a new path for the development of fluorescent systems, sensors, charge-transporting materials and solid-state catalysts. Moreover, a combinational materials design approach to the organosilica frameworks, pore wall surfaces and internal parts of mesopores has led to novel luminescent and photocatalytic systems. Their advanced functions have been realized by energy and electron transfer from framework organics to guest molecules or catalytic centers. PMOs, in which the precise design of hierarchical structures and construction of multi-component systems are practicable, have a significant future in a new field of functional materials (93 references).     

Improvement of bonding between cellulose and polypropylene by plasma treatment

Plasma treatments can be utilized to upgrade the value of lignocellulosic materials for applications such as biobased composites. Poor adhesion in biobased composites is caused by incompatibility between polar cellulosics and non-polar thermoplastics. Plasma modification of both cellulose and polypropylene was evaluated by a T-peel test for improved compatibility and adhesion between these materials. Oxygen and argon plasmas were used to modify the surface of polypropylene films, while a cyclohexane plasma was used to modify the cellulose surface through deposition of a hydrophobic polymer layer. For plasma treatment of polypropylene, changes in power input had a greater effect on adhesion than changes in pressure. Surface oxidation and increased acid/base characteristics were found on both argon- and oxygen-plasma-treated polypropylene based on ESCA and wetting measurements. With the non-reactive argon plasma the persistence of reactive species, such as free radicals, was very important for enhanced adhesion. The amount of polar carbonyl groups introduced onto the surface was also an important factor for adhesion improvement. Modification of the cellulose (filter paper) surface to a hydrophobic character with a cyclohexane plasma did not improve adhesion to polypropylene.     

Surface forces and friction tuned by thermo-responsive polymer films

Thermo-responsive polymer films have enabled the development of various functional surfaces with switchable interfacial properties. Assessing the surface forces and friction on such films is of paramount importance. On the one hand, it allows us to extract a great deal of information on the interfacial properties of the films, e.g., adhesiveness and lubricity, and how they could be tuned using different stimuli. On the other hand, surface force measurements complement other thin-film analysis methods, e.g., ellipsometry, to better perceive the correlation between the molecular properties of the polymer chains and the interfacial properties of the film. On this basis, we will, herein, provide a concise review of some recent studies on surface forces and friction tuned by thermo-responsive polymer films. This outline comprises a summary of several research works addressing the effects of temperature, solvent composition, and salts on surface forces and friction. In the end, we briefly discuss a few select studies in which the regulation of surface forces by thermo-responsive polymers is examined with an emphasis on the potential applications.     

Moleular simulation of surface reorganization and wetting in crystalline cellulose I and II

Cellulose is one of the most versatile substances in the world. Its immense variety of applications was in recent years complemented by nanotechnological applications such as cellulose nanoparticle dressed surfaces for filtration purposes or cellulose matrices for microelectronics. The fabrication of such complex materials asks for thorough understanding of the surface structure and its interactions with adsorbates. In this study we investigate several surface model systems of nanotechnological interest, which are obtained by reorganization of the cellulose-vacuum or cellulose-water interfaces of slabs of crystalline cellulose. To do this, we equilibrated first bulk supercells of different cellulose allomorphs, which were constructed from crystallographic data, and then optimized the interface structures. From the bulk and surface systems we calculated structural properties such as unit cell parameters, dihedral conformation distributions, density profiles and hydrogen bonding. The results suggest that no overall geometrical restructuring occurs at the interface. However, the hydrogen bond network is strongly reconstructed, as is inferred from the dihedral conformations and hydrogen bond occurrences, although only within the first few layers. This holds for low index close packed structures as well as for high index loosely packed surfaces. Replacing the vacuum by ambient pressure water molecules we find less rearrangements of the cellulose surface, because the water allows formation of hydrogen bonds similar to those in the bulk phase. The water near the cellulose surface shows, however, strong structural changes. We observe reduced mobility of the water molecules, which corresponds to a cooling of water by about 30°, in a slab that is about 10 Å thick. Although structuring and adsorption is observed on all surfaces, no actual penetration of water into the cellulose structure could be observed. This suggests that pure water is not sufficient to produce cellulose swelling at mesoscopic timescales. This work lays the basis for current quantum chemical investigations on specific interaction terms within cellulose.     

Smooth model cellulose I surfaces from nanocrystal suspensions

Removal of lignin, hemicelluloses and other minor components during pulping results in a porous fibrillar structure. Interactions of cellulose fibre surfaces with wet-end additives and other materials depend both on the interfacial properties of the cellulose and on the morphology of the surface. It would be useful to be able to separate the interactions with the cellulose from those that depend on surface roughness and porosity by preparing flat cellulose surfaces. Current methods give surfaces of amorphous cellulose or of cellulose II, differing in density and crystallinity from the original cellulose I surface. We propose a new route to prepare smooth model surfaces of cellulose I, starting from colloidal dispersions of cellulose I nanocrystals. The nanometer-sized width of these rod-like colloidal particles allows a relatively flat surface to be prepared from the suspension by casting an aqueous suspension on an appropriate surface and allowing the water to evaporate. Oriented films can be prepared by spin-coating or shearing. The surface composition and morphology of the films were examined by X-ray photoelectron spectroscopy and atomic force microscopy.     

Nanocellulose properties and applications in colloids and interfaces

In this review we introduce recent advances in the development of cellulose nanomaterials and the construction of high order structures by applying some principles of colloid and interface science. These efforts take advantage of natural assemblies in the form of fibers that nature constructs by a biogenetic bottom-up process that results in hierarchical systems encompassing a wide range of characteristic sizes. Following the reverse process, a top-down deconstruction, cellulose materials can be cleaved from fiber cell walls. The resulting nanocelluloses, mainly cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC, i.e., defect-free, rod-like crystalline residues after acid hydrolysis of fibers), have been the subject of recent interest. This originates from the appealing intrinsic properties of nanocelluloses: nanoscale dimensions, high surface area, morphology, low density, chirality and thermo-mechanical performance. Directing their assembly into multiphase structures is a quest that can yield useful outcomes in many revolutionary applications. As such, we discuss the use of non-specific forces to create thin films of nanocellulose at the air–solid interface for applications in nano-coatings, sensors, etc. Assemblies at the liquid–liquid and air–liquid interfaces will be highlighted as means to produce Pickering emulsions, foams and aerogels. Finally, the prospects of a wide range of hybrid materials and other systems that can be manufactured via self and directed assembly will be introduced in light of the unique properties of nanocelluloses.     

Superspreading on Immersed Gel Surfaces for the Confined Synthesis of Thin Polymer Films

Liquid spreading is of significant interest in science and technology. Although surface topography engineering and liquid surface‐tension regulating can facilitate spreading, the spreading layers in these strategies are inevitably inhomogeneous or contaminated with surfactants. Herein, we show a general strategy to realize the superspreading of liquids on mutually soluble gel surfaces. The cooperation of the hydraulic pressure under liquid phase and liquid‐like property of gel surfaces can dramatically eliminate the local pinning effect and enhance the advancement of three‐phase contact line, thus forming stable and homogeneous superspreading liquid layers. Such liquid layers can be converted into various functional thin polymer films with controlled thicknesses (nm‐ to µm‐scale) through one‐step polymerization of the reactants. Our strategy offers opportunities for large‐scale synthesis of versatile functional thin films for various applications.