Fabrication And Properties Research Of Natural Cellulose Substances Derived Functional Materials

The global human society keeps developing at an astonishing pace even at the current moment, which accompanies with increasing demand for functional materials as well as growing consumptions of non-renewable resources such as coal,petroleum and natural gas and causes serious environmental pollusions. This severe problem drives people to explore environmental friendly approaches to design and develop advanced functional materials. One effective strategy is to take advantage of the natural species. Cellulose is one of the most widely available natural substances in the world, which possesses a series of advantages such as non-toxity, bio-degradability, bio-compatibility, and natural structure derived high porosity, flexibility, and strong mechanical property. By transcribing the unique natural cellulose structures into man-made materials, the structure-related functions of cellulose are readily introduced to the guest species, realizing environmentally benign advanced functional materials.Herein, the unique surface properties of natural cellulose substrances are applied to direct the self-assembly of guest substrates such as inorganic oxides, organic molecules, polymer chains, and protein molecules. Thus, the macro-scale, micro-level, and nanoscopic unique functional morphology and structure of natural cellulose substances are combined with the designed functions of the guest species, resulting in a great variety of advanced functional nanostructured materials. The details are described as following:(1) Size tunable ultrafine rutile titania/silica hybrids:Based on the covalent bonding between the surface hydroxyl groups of cellulose nanofibers and alkoxide, titania gel layer sandwiched thin silica gel film was deposited coating each cellulose nanofiber surface and then flame burned in air, resulting in crystallite size controllable ultrafine rutile titania/silica hybrid. The cellulose network, rapid flame burning, and tight silica film enwrapping on titania inhibited the crystallite growth of titania upon phase transition at high temperature,and the average diameter of the rutile titania nanocrystallites formed is adjusted in from3.3nm to16.0nm at a crystallite growth rate of-2.4nm per titania gel layer deposition step. Through the crystallite size regulation, the nanotubular ultrafine rutile titania/silica hybrids with rutile titania nanocrystallite size of16.0nm is found to show the highest photocatalytic activity, which is superior to the cellulose derived anatase titania material. Moreover, this approach is also suitable for the crystallite control of anatase titania to enhance the photocatalytic behavior.(2) Cellulose derived natural hierarchical nanotubular polymeric sheet:Based on the covalent bonding between the surface hydroxyl groups of cellulose nanofibers and poly(vinyl alcohol) with alkoxide, thin titania/polyvinyl alcohol composite layers were layer-by-layer assembled on each cellulose nanofiber surface of filter paper. Then, the cellulose component was selectively dissolved away from the as-prepared composite sheet by applying sodium hydroxide/urea aqueous solution,forming bulk structured nanotubular titania/poly(vinyl alcohol)hybrid sheet with cellulose templated natural morphological hierarchy. The resulting polymeric hybrid sheet not only attained the randomly cross-linked network of filter paper, but also inherited the unique swelling property of cellulose. This polymeric hybrid sheet was further treated with acidic solution to remove titania component, leading to the natural porous structurd pure poly(vinyl alcohol) material.(3) Cellulose derived functional nanotubular polymeric hybrid materials:Based on the chemically active surface of titania pre-coated cellulose nanofiber, the self-assembly of various guest polymeric species was induced, giving versatile nanotubular structured polymeric hybrid material. Cationic polyelectrolyte (e.g., poly(diallyldimethylammonium chloride), polyethylenimine, and Poly(allylamine hydrochloride)) and anionic polyelectrolyte poly(styrene sulfonate) were alternatively layer-by-layer assembled on the nanofiber surface through electrostatic force by using the surface electronegativity of titania, while heparin or heparin/poly(vinyl alcohol) composite layers were formed on the nanofiber surface via covalent bonds.Finally, the cellulose component was dissolved away through sodium hydroxide/urea aqueous solution treatment, leaving nanotubular polymeric hybrid materials with faithfully copied natural cellulose structures. Meanwhile, the resultant materials retained the properties of the original guest species such as the anticoagulative activity of heparin.(4) Cellulose based colorimetrie detector towards gaseous ammonia:On the basis of the hydrongen bondings between the surface hydroxyl groups of cellulose and aniline monomers, the aniline molecules adsorbed onto the cellulose nanofiber surface and formed thin polyaniline film covering the cellulose nanofibers through further in-situ oxidative polymerization process. The ultrathin nature of the as-deposited polyaniline film (-10nm) perfectly reserved the high porosity as well as flexibility of cellulose and the obvious color change of polyaniline from green to blue in the presence of ammonia, realizing sensitive, reusable ammonia colorimetric detector. The respective detection limit of the as-prepared detector by the naked eye observation achieved100ppm for ammonia gas and10ppm for ammonia vapor at room temperature, and the detector endured repeated ammonia sensing for at least50times.(5) Cellulose induced mild chemical synthesis of graphene:On the basis of the hydrogen bondings between surface hydroxyl groups of crystalline cellulose region and aniline monomer, the aniline molecules were guided to align and polymerized into ordered polyaniline chains along with the crystalline region of cellulose through the in-situ oxidative polymerization process. The unique supermolecular structure facilitated the denitrogenation of polyaniline chains during sodium hydroxide/urea aqueous solution treatment, and the benzene units remained linked with each other, realizing synthesis of high quality graphene nanosheets at low temperature. This mild chemical approach avoided high temperature which would damage the graphene, and achieved electrical conductivity of3.47S m-1even at the porous state.(6) Bio-inspired superparamagnetic bulk sheet:On the basis of high biological affinity and covalent links between silica pre-coated cellulose and protein molecules, ferritin was immobilized on to the ultrathin silica film pre-coated cellulose nanofiber. The initial Fe(Ⅲ) cores of ferritin was substituted with Fe(Ⅱ) ones, and then silica film was further coated on the surface of each ferritin molecule and nanofiber surface. The as-prepared composite sheet was finally calcined in air at500℃, yielding natural hierarchical structured bulk material with superparamagnetism. The large surface area of natural cellulose network guaranteed high amount of protein immobilized, and the silica film stabilized the y state iron oxide even at500℃. Furthermore, due to the protection by the protein shell and the ultrathin silica film, the formed magnetic nanoparticles were well-isolated and the size was controlled to be～7nm, achieving stong superparamagnetism.With this method, bulk structured sheets are endowed with the unique specific nano-functions.