Synthesis of TiO2-based Nanocomposites and Its Applications in Photocatalysis and Energy Storage
Author:Ge Ming Zheng
Supervisor:zhang ke qin lai yue kun
The rapid development of global economy and industrializationin the past century has brought serious environmental pollution and energy crisis problems to the world’s population,which is urgent to be addressed.Titanium dioxide(TiO2),has been paid much attention and widely used in photocatalysis,water splitting,and lithium-ion batteries due to large surface area,low toxicity and good stability,which is promising to solve these issues.However,the wide application of 1D TiO2 nanostructured materials in some fields was limited due to several critical issues.Associated with the wide band gap(anatase: 3.2 e V,rutile: 3.0 e V),TiO2 occupies only 3-5% of the total solar spectrum.Besides,fast recombination of photogenerated electron/hole pairs also leads to decreased efficiency in the photo-electric conversion efficiency and photocatalytic activity.Therefore,in my thesis,carbon materials,global nanoparticles and other semiconductors are adopted to modify TiO2 nanotubes,which makes them more widely used.Firstly,a combination of electrodeposition and carbonization technique was adopted to deposit reduced grapheneoxide films on TiO2 nanotube arrays(RGO/TiO2 NTAs),where graphene oxide turned into RGO and TiO2 nanotube changed into crystal structure at the same time.The RGO/TiO2 NTAs exhibit a significantly enhanced photocatalyticdegradation ability(2.9 times)for methyl orange(MO)than annealed TiO2 NTAs under the sameconditions due to the enhanced light absorption and suppressed combination of electron/hole pairs.Secondly,an ultrasonication-assisted successive ionic layer adsorption and reaction strategy was developedfor uniform deposition of high density p-type Bi2O3 quantum dots on n-type TiO2 nanotube arrays.After modification,the photocatalytic activity of Bi2O3/TiO2 NTAs was nearly 1 times than that of the pristine TiO2 NTA counterpart under the synergistic effect between the formation of a uniform p-n heterojunction with high-density forenhancing light absorption and facilitating photogenerated electron-hole separation/transfer.Lastly,an ultrasonication-assisted in situ deposition strategy was utilized to uniformly decorate plasmonic Agnanoparticles on vertically aligned TiO2 nanotube arrays to construct Ag/TiO2 NTAs composites.Under ultrasonication,it can avoid Ag nanoparticles aggregation.And by adjusting the deposition time and concentration of Ag NO3,the size of Ag nanoparticles can be controlled precisely.It wasfound that the hydrogen production rate of the Ag@TiO2 NTAs was approximately 15 times higher than that of its pristine TiO2 NTAs counterpart,which is attributed to the surface plasmon resonance effect of Ag for enhancedvisible light absorption and boosted the photogenerated electron-hole separation/transfer.Except for photolysis,TiO2 also plays an important role in energy storage.C@Si/TiO2 heterostructured electrode with high energy density and long lifetime is constructed to confine the electrode swelling and stabilize SEI layer.In this design,the conductive rigid TiO2 framework can provide large free space for volume changes of Si.Besides,it can also provide fast ionic/electronic transport pathway and facilitate formation of a stable SEI layer.And when compared to bare Si and C@Si electrode,the capacity of the electrode exceeds 1000 m Ah g-1,and it exhibits excellent rate capabilities and cycling performance.Furthermore,the full cell demonstrates a high energy density(368 Wh kg-1)and stable cycling performance without a significant capacity decay.In this paper,different modification techniques are adopted to improve the performance of TiO2-based nanocomposites,especially photocatalytic activity and photo-electric conversion efficiency.Besides,we construct the C@Si/TiO2 electrode by confining the Si nanoparticles in the porous TiO2 framework,which can be applied in other potential anode materials(Ge,Sn,P etc.)that experience large volume changes,low conductivity and unstable SEI formation,exhibiting great potential in the practical applications.In this thesis,it is innovative for the design and preparation of new TiO2-based nanocomposites and,the obtained results have important practical and guiding significance for solving the problem of dye contamination in the textile prospect and constructing wearable energy devices.