Study On Structural Modification And Photocatalytic Performance Of Titanium Dioxide Nanosheets

With the development of industrial civilization,environmental pollution and energy deficiency are becoming increasingly serious problems.The semiconductor photocatalytic technology with solar energy as the driving force provides a new way to solve these problems.As a typical semiconductor catalyst,titanium dioxide（TiO₂）has been extensively applied in photocatalytic field owing to its high stability,low cost,nontoxicity and environmental friendliness.Among the various structural morphologies of TiO₂,two-dimensional TiO₂nanosheets exhibit higher phtocatalytic activity due to its high specific surface area,sufficient attachment sites and highly exposed active crystal surfaces.However,TiO₂can only absorb ultraviolet light due to its wide band gap,besides that,rapid recombination of electron-holes also greatly inhibits the photocatalytic performance of TiO₂.To overcome these defects,this paper devotes to modify TiO₂nanosheets from two aspects of improving optical absorption and carrier separation efficiency.The photocatalytic performances of as-prepared catalysts were evaluated by degrading organic pollutants molecules,and corresponding characterization and analysis were carried out.The specific research contents are as follows:1.Preparation of 2D-2D N-TiO₂/Ti₃C₂photocatalyst and study on photocatalytic performance.N-TiO₂/Ti₃C₂photocatalyst was prepared by HF etching and hydrothermal oxidation.As controls,TiO₂nanosheets,Ti₃C₂MXenes and TiO₂/Ti₃C₂composites were prepared via solvothermal method or HF etching.The prepared samples were investigated by various characterization methods and tests.The UV-visible diffuse reflection spectra（UV-Vis DRS）shows that the light adsorption range of N-TiO₂/Ti₃C₂composite was extended to visible light region.The degradation experiments shows that N-TiO₂/Ti₃C₂composite exhibited excellent photocatalytic degradation performance toward Rh B under visible light,which was much higher than TiO₂/Ti₃C₂,Ti₃C₂MXenes and TiO₂.According to the results of fluorescence（PL）and electrochemical impedance（EIS）,the efficient separation and transport of photogenerated carriers were achieved in N-TiO₂/Ti₃C₂composite,which may be because that excellent conductivity of Ti₃C₂MXenes deduces the efficient migration of electrons form N-TiO₂to Ti₃C₂MXenes.Finally,we proposed a possible photocatalytic reaction mechanism based on the radical capture experiments and electron spin resonance（ESR）tests.2.Ternary MQDs/NCDs/TiO₂composite cooperated with persulfate for photocatalytic degradation toward organic pollutants.Mo S₂quantum dots（MQDs）and N-doped carbon dots（NCDs）were loaded on TiO₂nanosheets through a simple and gentle process.Compared with pure TiO₂,the MQDs/NCDs/TiO₂composite showed distinctly enhanced photocatalytic degradation efficiency.The results of PL illustrated that NCDs had excellent photoconversion function and can transfer long-wavelengths of visible light to shorter-wavelengths of ultraviolet light that can be adsorbed by TiO₂,thus improving the visible light absorption performance of TiO₂.Moreover,the results of energy band structure analysis showed that two heterojunctions would form in MQDs/NCDs/TiO₂composite,which effectively facilitates the separation and transfer of photogenerated carriers.In addition,we also explored the influence of persulfate on the photocatalytic degradation efficiency of MQDs/NCDs/TiO₂composite.As a result,the degradation efficiency was further increased by 2.14 times after adding a certain amount of persulfate.In the end,combined with free radical trapping experiments and ESR tests,we can conclude that the persulfate was effectively activated by photogenerated electrons to generate abundant sulfate radicals(SO₄^·-)and hydroxyl radicals（·OH）,and meanwhile the electrons consumption caused by the persulfate effectually restrained surface electron-holes recombination,inducing more holes（h⁺）to participate in pollutant degradation.3.Synthesis of 2D-2D 1T-2H Mo S₂/TiO_2-xphotocatalyst and study on photocatalytic performance.The 1T-2H mixed phase Mo S₂nanobelts were deposited on Ti³⁺self-doped TiO₂nanosheets via a facile hydrothermal and in-situ chemical reduction process.The prepared 1T-2H Mo S₂/TiO_2-xcomposite exhibits excellent photocatalytic degradation performance toward Rh B under visible light,which is much higher than that of pristine TiO₂.The defect of Ti³⁺and oxygen vacancies can form a new electron energy level under the conduction band of TiO₂,which narrows the band-gap of TiO₂and improves its visible light response ability.Furthermore,as demonstrated by PL and EIS analyses,the metallic 1T phase Mo S₂can effectively accelerate charge transfer between 2H phase Mo S₂and TiO_2-x.To the end,a feasible photocatalytic reaction mechanism of 1T-2H Mo S₂/TiO_2-xphotocatalytic system was proposed in view of the active species trapping experiments,ESR tests and energy band analysis.