| Since the discovery of carbon nanotubes in 1991,much interest has been focused on the one-dimensional nanostructures due to their exceptional electric, mechanical,and chemical properties.Among such materials,titania nanotubes, nanowires and nanoribbons(or nanobelts) have received a great deal of attention, because TiO2 can exhibit a wealth of important photovoltaic(solar energy conversion),photocatalytic,catalytic support and gas-sensing properties, especially when prepared as nanomaterial.TiO2 is a multifunctional material with remarkable chemical,electronic and optical properties.TiO2 membranes and nanoparticles have been extensively studied.However the applications of TiO2 nanobelts have been rarely studied.Furthermore,the properties of photoelectric, gas-sensitive and photocatalysis of TiO2 nanobelts are still too low to fit for the requirement of application.Herein,the synthesis of titanate nanobelts from commercial TiO2 via the alkali-hydrothermal process was reported.The synthesis route achieves high yield production of TiO2-based nanobelts.In order to improve the properties,TiO2 nanobelts are modified and "surface heterostructured nanobelts" concept is proposed in this paper.Recently,with the development of the techiques for preparation of nanodevices,many ultra-sensitive devices such as field effect transistors, optoelectric devices,gas sensors,biosensors,etc.,have been fabricated using single nanobelt or nanobelt an'ay.Some of them have to be fabricated using complex and high-cost techniques such as focused-ion-beam microscopy of electrical connections and precise photolithography.Although electrical responses of single-nanobelt devices are very sensitive to their environment,the size variation of nanobelts may lead to significant difference in their intrinsic electrical properties.As a result,it is difficult to be well calibrated for practical applications. Based on the as-made nanobelts,a novel preparation route was used to fabricate paper-like nanostructured membrane,which was also called as nanostructured sheet or nanostructrued paper.The nanobelts are packed together forming a porous network structure by a conventional paper making process.Nanodevices,such as photo-electric devices,gas sensor,biosensor,can be made by tailoring,connecting and sealing the nanostructrued paper.This research will be open a new door for the application of nanobelts.The main conclusions arc as followings:1.Titania-based nanobelts from commercial TiO2(annatase phase) were successfully synthesized via an alkali-hydrothermal process.The as-synthesized nanobelts are sodium titanate(Na2Ti3O7),hydrogen titanate(H2Ti3O7) and anatase (TiO2).The nanobelts are characterized by Thermogravimetric/Differential Thermal Analysis(TG/DTA),X-ray Diffraction(XRD),Infrared Spectra(IR), transmission electron microscopy(TEM) and Scanning Electron Microscope (SEM).The characterization indicates that the nanobelts with typical widths of 50 to 200 nm,thicknesses of 20 to 50 nm,were up to one hundred micrometer in length.H2Ti3O7 nanobelts can be obtained from Na2Ti3O7 by exchanging alkali ions with protons using dilute acid solution.The anatase nanobelts can be obtained from H2Ti3O7 by a topochemical reaction and dehydrating process.2.Based on the as-made nanobelts,the conventional paper making process was used to fabricate flexible nanostructured paper.The nanobelts are connected with hydrogen bonds or bridge-oxygen-atoms and packed together forming a porous network structure and the average size of the pores of the nanostructured paper is about 500nm.The electric transport properties of the as-made nanostructured paper were measured and the detectable conductive behavior of the nanostructured paper promises the potential application in sensors by designing a corresponding electronic device.Moreover,it is very convenient for preparing various types of nanobelts-based devices by tailoring the nanostructured paper to the designed sizes and shapes.Gas sensitivity to O2 of TiO2 nanopaper was investigated which revealed ultrasensitive detection for O2.This suggests that TiO2 nanobelt-based paper can be applied in gas sensing with performances suitable for the environment at room temperature.Ag-H2Ti3O7 nanostructured paper with antibacterial effect was obtained by decorating the nanobelts with silver nanoparticles.The zone of inhibition test results showed that an obvious zone inhibition appearing around the Ag-H2Ti3O7 nanostructured paper.3.Noble metals(Ag,Au)/TiO2 heterostructured nanobelts were prepared by the photocatalytic reduction method at room temperature without template and surfactant as additions.The silver particles,with the grain size of about 10nm, deposited on the surface of nanobelts are uniform.And the grain size of Au on the surface of nanobelts is about 30nm.The noble metal nanoparticles attached on the TiO2 nanobelts will not only retain catalytic activity of the noble metals,but also possess the intrinsic photocatalysis of TiO2.Therefore,The promising applications in both heterogeneous and homogeneous catalysis of the as-made samples may exist.4.TiO2 nanobelts and Ag/TiO2 heterostructured nanobelts was used to modify glassy carbon electrode(GCE),respectively.The electrochemical voltammetric properties and the detection of low concentration Logystein in 0.25 M pH 7.0 PBS solutions of the Ag/TiO2 heterostructured nanobelts modified GCE were studied. The results shows that the modified electrode was stable and can be used to detect the very low concentration of L-gystein(1×10-7M).The Ag-TiO2 heterostructured nanobelts offer great advantages to fabricate biosensors.5.ZnO/TiO2 heterostructured nanobelts were successfully synthesized through the liquid phase method.The samples obtained were characterized by different techniques,such as XRD,SEM,and TEM.The products are ZnO nanoflowers self-assembled on the surface of TiO2 nanobelts.The nanobelts are 50-200nm in width and several tens micrometers in length,while the ZnO heterostructure is a bud with 500nm in length and with the petals of about 200nm. The formation mechanisms of the titanium dioxide nanobelts and the composites mentioned above were also discussed briefly.6.The Rutile TiO2 nanoparticles/Anatase TiO2 nanobelts(ANP/ANB TiO2) heterostructrue was prepared by eroding H2Ti3O7 nanobelts in 100℃certain concectration acid solution and then heat-treated the eroded H2Ti3O7 nanobelts at 600℃for 1h.To make the Ag/ANP/ANB TiO2 bi-heterostructrue,Ag nanoparticles were deposited on the ANP/ANB TiO2 heterostructrue by the photocatalytic reduction method at room temperature.The heterostructrued nanobelts were characterized by XRD,TEM,HRTEM and UV-Vis spectra.The photocatalytic properties of the heterostructrued nanobelts were studied by degrading methyl orange solution.The results indicate that the heterostructrued nanobelts possessed higher photoeatalytic properties than that of TiO2 nanobelts.Ag/ANP/ANB TiO2 heterostructrue possessed higher photocatalytic properties than that of ANP/ANB heterostructrue.In conclusion,the concept of TiO2 nanobelt surface hetero-structure is proposed in this paper.The metal/TiO2 nanobelt heterostructure can be synthesized through photo-catalysis reduction technique,and.The adjustment regularity of surface energy level,electric transport properties,photo-electric coupling effect,and gas sensitive effect on the surface heterostructure of the nanobelts will be investigated through optical spectra measurement and electric measurement on individual nanoblets.A novel nanostructured paper based on TiO2 nanobelts and heterostructured nanobelts can be prepared through our patented nanopaper making technique.Some nanodevices,such as photo-electric devices,gas sensor,and biosensor will be prepared by using the nanopaper as building bricks.This research will be open a new door for the application of nanobelts.
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