Investigations On Functionalization Of Titanate Nanotube Arrays Prepared By Hydrothermal Synthesis

One-dimensional (1D) nanostructured materials are attracting great attentions inthe fields of electronics, biotechnology, catalysis and sensors due to highsurface-to-volume ratio, efficient electron transport, good chemical and thermalstabilities.1D titanate nanotubes (TNTs) are attracting great research interests,because of the advantages of cost-effectiveness, mild reaction conditions, low energyconsumption and simple equipment involved in the hydrothermal synthetic approach.These TNTs posses intrinsic multi-functionality, rising not only from combination ofthe property and application of TiO2nanomaterials with the ion exchange property oflayered titanates with tubular morphology, but also from the distinct property oftubular regions (like tube opening, inner, outer and the interstitial regions). Besides,TNTs also have great potential in catalysis via loading large amount of metal cations,based on their high cation exchange capacity, and generating hybrid nanostructurewith desirable catalytic activity. Interestingly, the morphology of hydrothermallyproduced TNTs can be modulated by tuning a large number of variable factors, andvertically aligned TNTs (VATNTs) were successfully achieved directly on Ti substrateby a modified hydrothermal process. VATNTs often exhibited an orientedmultilayered structure, consisted of vertically aligned individual nanotube with ananometer-scale inner-core cavity exposed to the outer surface. One interestingfeature of VATNTs includes uniform pore size and high available surface area, whichare ready for hybridization with functional groups or molecules. Another is the facilecharge transfer between the underlying conductive substrate and the hybridizedfunctional groups or molecules, due to the good contact of each vertically oriented TNT with Ti slide. These imply a possibility of designing VATNTs-based hybridelectrode with improved activity and signal sensitivity for catalysis and sensing.In Chapter1, the property, synthesis and application of TNTs nanomaterials werechiefly introduced. The preparation and application of electrochemical sensors werealso briefly introduced. In Chapter2, VATNTs with high available surface area anduniform pore size was directly achieved on titanium substrate by a facile yet efficienthydrothermal route. By tuning hydrothermal conditions (including the concentrationof NaOH solution, reaction temperature and time, as well as the post treatmentprocedures), the morphology and structure of the titanate nanotubes arrays wereobtained. Based on these results, a general formation mechanism of titanate nanotubesarrays via the hydrothermal route was proposed. The optimum hydrothermalconditions of formation of titanate nanotubes arrays were in10mol·L-1NaOHsolution at140°C for6h. In Chapter3, TNTs possesses unique ion-exchange abilityand presents a uniform pore size and better stability as compared to non-alignednanotubes. These features increase the available surface area and allow greaterpenetration for catalyst loading, further simplify the optimization of the hybridizationprocesses. Here, VATNTs were in situ grew hydrothermally on titanium substrate, andthe possibility of electrochemically hybridizing VATNTs with CuxO nanocubes(CONC) to achieve VATNTs/CONC hybrid nanostructure for electrocatalysis andanalytic application was firstly demonstrated. Results revealed the distinctly enhancedsensing properties of VATNTs/CONC towards glucose, showing significantly loweredoverpotential, ultrafast and ultrasensitive current response in a wide linear range. InChapter4, VATNTs were functioned with graphene oxide (GO) sheets via layer bylayer assembly, and then GO was reduced by electrochemical reduction method. TheVATNTs functionalized RGO (RGO/VATNTs) not only exhibits excellent stability,which demonstrated as good electrocatalysts for small molecules. Simultaneousdetection of catechol (CC) and hydroquinone (HQ) was demonstrated in detail,showing promising application in medical and environmental fields. In Chapter5,3DTNT network via the hydrothermal route was proposed, which possess uniqueion-exchange ability and present uniform pore size and high stability.3D TNT network decorated with Au nanoparticles was obtained by assembly process, whichwas utilized as an efficient biomolecule immobilization platform. The heme was thenintroduced into3D TNT network, which used for determination of NO-2in water. Itsporous structures can enable rapid diffusion of analytes across a large surface area andpore, resulting in reduced response time. In addition, electronic transfer center ofheme facile charge transfer, favorable for electrochemical confining AuNPsnanostructure for catalysis and sensing. In Chapter6, VATNTs possessed increasedavailable surface area and uniform pore size, as well as additional features of highion-exchange capacity and facile charge transfer, which anchoring significant Aucations on the basis of electrostatic self-assembled strategy and producing highlydispersed AuNPs catalysts via a simple one-step chemistry reduction of chitosan (CS).They were demonstrated directly as electrode materials for electrocatalytic oxidationof peroxide. The VATNTs@Au exhibited excellent electrochemical performances forperoxide oxidation, presenting a low peak potential, high current, and highcurrent-to-background ratio. This sensor is expected to play an important role in thefield of peroxide monitoring. In Chapter7, TiO2@C nanorod was prepared throughdirect carbonization of polydopamine on VATNTs. The structures and morphologiesof TiO2@C nanorods were characterized and analyzed in detail by XRD, EDX, SEMand TEM. The TiO2@C nanorod was used as a novel immobilization platform forglucose oxidase (GOD). The entrapped enzyme retains good bioactivity and exhibitssatisfied performance due to the biocompatibility and efficient electron transfer ofTiO2@C nanorod. With satisfactory selectivity, reproducibility, and stability, thenanostructure we proposed offered an alternative for electrode fabricating and glucosebiosensing.