The Application Of Titanium-based Hierarchical Nanostructures In Photocatalysis And Energy Storage

The development and exploration of clean and green energy play the key role in effectively dealing with the current challenges faced in environmental pollutions and energy crisis.The efficient conversion and storage of solar energy,as well as improving the efficiency of photo/electrochemical processes using solar light as the driven force based on proper materials are of great importance in solving the energy crisis and environmental pollutions.In this study,we focused our research on the design and synthesis of various flexible conductive carbon cloth supported hierarchical titanium-based nanostructures,the applications of as-prepared hierarchical nanostructures in high performed visible/solar light photocatalysis,and photoelectrochemcial water splitting and lithium ion batteries were also systematically investigated.The main results including:?1?We designed and synthesized a flexible carbon cloth substrate supported hierarchical TiO₂ nanorod arrays nanostructures decorated with Au nanoparticles?Au-TiO₂ NRAs?by the combination of hydrothermal and chemical vapor deposition processes.The visible light photocatalysis property of as-prepared Au-TiO₂ NRAs has also been systematically investigated.Compared with the bare TiO₂ NRAs,a 13 times improvement in the visible light photocatalytic efficiency was obtained by Au-TiO₂NRAs.In addition,there is no observable decay in the photocatalytic efficiency after the Au-TiO₂ NRAs was continuously stirred at a high speed in aqueous condition for60 days,indicating the high cycling stability and 100%recyclability of Au-TiO₂NRAs.We also carefully explored the mechanism of the improved visible light photocatalytic performance of Au-TiO₂ NRAs by FDTD.Based the results,we ound that the strong LSPR of Au nanoparticles in visible light excited hot electrons at first.After striding over the Schottky barriers formed on the interfaces between Au nanoparticle and neighboring TiO₂,the hot electrons injected to the conduction band of TiO₂,and then transferred to the surface of photocatalysts to react with the absorbed pollutants.Such an efficient excitation and following transitions of hot carriers effectively suppress the recombination of electrons and holes,thus improving the visible light photocatalytic activity of whole system.?2?We designed and engineered a hierarchical high energy{001}facets exposed anatase TiO₂ nanosheet structures?TiO₂ NS?based on facet engineering principle.After decorated with Au nanoparticles,the obtained Au-TiO₂ NS demonstrated high solar light photocatalytic activity.We can controllable change the thickness of nanosheets and the ratio of{001}facet and{101}facet easily by manipulating the composition of precursor.The as-prepared high{001}facets exposed Au-TiO₂ NS demonstrated an 8 times of solar light photocatalytic efficiency improvement under the illumination of AM 1.5G light source,and the system also claimed a high cycling stability.Combining the UV-Vis light adsorption spectrum and the FDTD simulations of the materials,we found that the Au nanoparticles account for a strong LSPR adsorption in visible light,and lot of‘hot spot'with high electromagnetic field localization formed on the interface of Au and TiO₂,which increase the utilization of solar light and the reaction rate photo/electrochemical process of the whole system.Besides,the“tandem type”transition of LSPR induced hot electron from Au to the{001}face of TiO₂ and then to the{101}face of TiO₂ efficiently impeding the recombination of photo-generated electron-hole pairs,enhancing the photocatalytic performance of the system.?3?We developed a new magnesium assisted strategy to synthesize the excellent lithium ion batteries performed porous TiN nanorod arrays?TiN NRs?using TiO₂ NRs as the precursor,the environmental friendly,low cost and safety N₂ as the nitrogen source.Based on the systematic experiment results,we revealed the nitriding mechanism of TiO₂ in N₂ atmosphere,which includes two steps:the metal Mg firstly reacted with N₂ to form reductive Mg₃N₂,and then the Mg₃N₂ reacted with TiO₂ to form final TiN nanostructures.The porous TiN NRs almost cloned the morphology and structure of TiO₂ NRs precursor due to the high conformality of current nitriding process.The as-prepared TiN NRs was directly used as a binder-free anode electrode material for lithium ion batteries,which demonstrated high cycling stability and excellent rate performance.?4?We engineered a nanocrystals constructed porous three dimensional Li₄Ti₅O₁₂ hierarchical nanostructure?LTO NCs?supported by flexible carbon cloth by etching and lithiating anatase TiO₂ NS precursor.The as-prepared LTO NCs was directly assembled in lithium ion batteries as the binder-free anode electrode,which demonstrated excellent long-term charging-discharging stability at a high current density and remarkable rate performance.The interconnected porous structure of LTO NCs formed during the in situ etching and lithiation processes effectively not only improves the diffusion of electrons,ions and electrolyte,but also increase the specific surface areas of the electrode,which benefits to enhance the rate performance and cycling stability of system in high current density.In addition,we obtained a C@LTO NCs system by coating a carbon layer on the surface of LTO NCs.The results revealed that the coated carbon layer not only improved the conductivity of whole system,but also stabilized the interconnected structure of porous nanocrystals.Our study focused on designing and preparing titanium-based hierarchical nanostructure systems supported by flexible carbon cloth,and investigated their applications in solar light conversion,energy storage and solar light driven photoelectrochemical reactions such as visible light photocatalysis and lithium ion batteries.Such flexible hierarchical nanostructures demonstrated high cycling stability and excellent photo/electrochemical performance,which may have bright future in flexible and wearable electronic devices.