Fabrication And Applications Of Hierarchical Titanium-containing Inorganic Nanomaterials Derived From Natural Cellulose Substance

The rapid progress in global economy has not only brought us fabulous wealth but also environmental problems.Energy exhaustion and environment pollution has become global problems faced today.Thus,providing abundant, clean, and secure renewable energy sources is one of the key technological challenges facing mankind. Nanomaterial possesses unique physical and chemical properties and an exponential growth of research activities has been seen in nanoscience and nanotechnology in the past decades. As one of the most promising photocatalysts, titania has attracted much attention due to its chemical stability, high phocatalytic activity, nontoxicity and low cost. Amongst various preparation methods, biotemplate synthesis is one of the most attractive production methods for its effectiveness and easy control of nanostructure and morphology. Particularly, natural cellulose substance is an ideal biotemplate due to its unique structures and properties.Herein, titania thin film was first deposited on natural cellulose substance (filter paper) by the surface sol-gel method using titanium(Ⅳ)n-butoxide as precursor. Subsequently, the titania/filter paper nanocomposite was carbonized in nitrogen or calcined in air to obtain titania coated carbon nanofibrous material or titania nanotubular material.Metal nanoparticles such as Ag or Pt nanoparticles can be deposited on the titania coated carbon nanofibrous material or titania nanotubular material to obtain composite material with tailored properties.(1)Titania coated carbon nanofibrous material. Ultrathin titania films were firstly deposited by the 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, with3-6nm pores) that coated with uniform anatase titania thin films (thickness-12nm, composed of anatase nanocrystals with sizes of～4.5 nm). This titania-coated nanofibrous carbon material possesses specific surface area of404m2/g, 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. Experimental results showed that·OH radicals were detected under UV irradiation.(2) Titania-carbon composite material deposited with silver nanoparticles.Titania ultrathin film was first deposited on natural cellulose substance by means of a surface sol-gel method using titanium (Ⅳ) n-butoxide as precursor. Subsequently, the titania/filter paper composite material was carbonized in nitrogen atmosphere to obtanin titania coated carbon nanofibrous material. Sliver nanoparticles were then deposited on the titania-carbon composite to achieve titania-carbon nanofibrous material by photoreduction method. ICP-MS analysis showed that the content of deposited silver nanoparticles is as high as (9.5±0.1) wt.%, and TEM observation revealed that the deposited silver nanoparticles are uniform with small sizes (-5nm). The antibacterial activity of the hierarchical nanofibrous titania-carbon composite material deposited with silver nanoparticles was tested against both Gram-positive and Gram-negative bacteria and the material exhibited high inactivation of bacteria due to the synergistic effect of porous carbon nanofibres, anatase titania ultrathin film coating and high loading content of silver nanoparticles with small sizes.(3) Hierarchical nanotubular titanium nitride material. Titania film was first deposited on natural cellulose substance by sol-gel method and titania replicas of filter paper was obtained after removal of filter paper by calcination in air at600℃for5h.Subsequently, magnesiothermic reduction of the prepared titania replicas of filter paper mentioned above was carried out in a homemade stainless steel autoclave. The titania replicas of filter paper and magnesium granules were separately spread evenly within two different steel boats and placed in the autoclave.The molar ratio of magnesium granules and titania replicas of filter paper was2.5:1. After filled with nitrogen gas, the autoclave was sealed into a vertical tube furnace and heated to1200℃for3h and allowed to cool to room temperature in the flowing N2atmosphere to avoid oxidation. The raw product was then collected and treated with2.0M HC1aqueous solution for6h to selectively dissolve the by-product magnesia. Electron micrographs of the material showed that the hierarchical nanotubular material replicated the hierarchical structure of the original filter paper and the wall of the nanotube was uniform with thickness of ca.46nm. The hierarchical titanium nitride material possessed high specific surface of31.4m2/g. Electrochemical measurements of the hierarchical nanotubular titanium nitride shows that the specific capacitance of the material was74.2F/g at current density of0.16A/g, which can be a used as potential electrode material.(4) Hierarchical nanotubular titania material deposited with platinum nanoparticles. Titania ultrathin film was first deposited on natural cellulose substance by means of a surface sol-gel method using titanium (Ⅳ) n-butoxide as precursor and titania nanotubular material was obtained after removal of filter paper. Different mass ratio of platinum nanoparticles were subsequently deposited on the nanotubular titania material by photoreduction method. Electron micrograph of the material showed that platinum nanoparticles distributed on the nanotubular titania material uniformly with particle size of2-4nm. Photocatalytic hydrogen production catalyzed by the titania nanotubular material was conducted and results revealed that the highest photocatalytic activity was obtained when the mass ratio of the deposited platinum nanoparticles was1wt.%. Study on the mechanism of the photocatalytic hydrogen production showed that more·OH radicals were produced by deposition of platinum nanoparticles compared with bulk titania.