Preparation Of Titanium-based Network Nanocomposites And Their Applications In Energy Storage And Photocatalysis

One-dimensional titanium-based(Ti-based)nanomaterials have high research value and broad application prospects in energy conversion and storage,and photocatalysis,due to their excellent physical and chemical properties.However,pure Ti-based nanomaterials have many shortcomings in their applications,which seriously hinder their further development.For example,Ti-based nanomaterials have poor electronic conductivity and low Li+/Na+mobility due to their large bandgap and high ion diffusion barrier.Na2Ti3O7 has low coulombic efficiency and continuous decay capacity due to the instability of the solid electrolyte interface layer and structural distortion upon sodiation/desodiation.Nanosized TiO2 with a wide bandgap(3.2 eV)presents low visible light photocatalytic activity and poor recyclability.To develop the potential of Ti-based materials in high-performance energy storage and visible light photocatalysis,we employ one-dimensional titanium-based nanomaterials to construct Ti-based network nanocomposites.Ti-based networks provide a more direct diffusion path for rapid ion deintercalation/intercalation or photocatalytic degradation reactions;on the other hand,it avoids the common agglomeration problems of nanomaterials,achieves long cycle life,and thus obtains better electrochemical and visible light photocatalytic performance.(1)Ultralong mischcrystal TiO2 nanowires and reduced graphene oxide nanocomposites for high performance lithium storage:Ultralong TiO2 nanowire/reduced graphene oxide(RGO)conductive network electrodes were prepared by electrostatic attraction method combined with vacuum heat treatment.The TiO2/RGO electrode exhibits a high reversible capacity of 259.9 mA h g-1 at 0.1 C(1 C=335 mA g-1),and excellent cycling performance with a high reversible capacity of 111.9 mA h g-1 at 25 C after 5000 cycles.The excellent electrochemical performance of TiO2/RGO is due to the robust interpenetrating network composed of ultralong TiO2(B)/anatase heterogeneous nanowires,which avoids the use of electrochemically inert polymer binders and conductive agents,provides direct ion/electron transport paths and additional Li+storage sites,and also effectively prevents agglomeration of TiO2/RGO components during long-term charge/discharge cycles.Furthermore,RGO sheets synergistically enhance the conductivity and specific surface area of the TiO2/RGO electrode.(2)Chemically bonded N-doped TiO2 nanowires/reduced graphene oxide hybrid for high performance lithium storage:The Ti3+-C bonded N-doped TiO2 nanowires/RGO conductive network freestanding electrodes were fabricated by photocatalytic reduction approach combined with vacuum filtration and vacuum heat treatment.This freestanding electrode achieves lightweight properties by avoiding the use of electrochemically inert Cu foil current collectors and exhibits excellent rate and cycling performance,maintaining a high specific capacity of 101.8 mA h g-1 after 10,000 cycles at 50 C(1 C=335 mA g-1).The excellent electrochemical performance of the freestanding electrode is due to the Ti3+-C bond and anti-agglomeration architecture of the N-doped heterogeneous TiO2 network enhancing the electron conductivity,Li+diffusion kinetics,and cycle life of the electrode.(3)Core-double-shell Na2Ti3O7@TiO2@N-doped carbon interpenetrating network for superior sodium storage:Based on Na2Ti3O7 interpenetrating network,core-double-shell Na2Ti3O7@TiO2@N doped carbon sodium-ion battery anode was synthesized by controlled surface H+ion exchange and dopamine/pyrrole modification combined with vacuum heat treatment.This electrode retains a high specific capacity of 67.2 mA h g-1 after 1000 cycles of a high current density 50 C(1 C=177 mA g-1).The excellent electrochemical performance of the core-double-shell network anode is attributed to avoiding the use of electrochemically inert polymer binders,providing direct Na+/electron diffusion paths,as well as the rational structural design that enhances the stability and conductivity of Na2Ti3O7.(4)Ag nanoparticle decorated electrospun TiO2 membrane for high performance visible light photocatalytic degradation:To form a recyclable TiO2-based network,TiO2 shells were grown in situ on electrospun polyacrylonitrile(PAN)fibers driven by electrostatic attraction and modified with polydopamine and Ag to obtain visible-light photocatalytic PAN@TiO2/Ag films.The prepared film has enhanced visible light photocatalytic activity and good recyclability for methylene blue degradation as the PAN@TiO2 network realizes the recyclability of nanosized TiO2,and polydopamine and Ag nanoparticle modifications enhance visible light absorption and reduce electron/hole recombination.