Preparation And Photocatalytic Properties Of MXene Based Oxide Composites

Environmental pollution and energy crisis are listed as the top two of the ten most urgent problems to be solved in the next 50 years.The semiconductor photocatalysis technology,which is driven by the inexhaustible solar energy and has no secondary pollution,has become an ideal method favored by researchers.In this thesis,semiconductor nanomaterials and non-noble metal cocatalyst MXene are combined by self-assembly strategy to prepare composites,and the photocatalytic performance and enhancement mechanism were explored.In this research,0D/2D mesoporous Ti O₂nanoparticles/Ti₃C₂nanosheet composites and 2D/0D Bi₂WO₆nanosheet/Ti₃C₂quantum dots（QDs）composites were prepared respectively.And then their physicochemical properties and application in photocatalysis were also investigated.The main research contents are as follows:（1）Mesoporous Ti O₂/Ti₃C₂composites were constructed by immobilization of mesoporous Ti O₂nanoparticles on Ti₃C₂MXene cocatalyst using electrostatic self-assembly strategy,and its photocatalytic degradation of methyl orange（MO）and hydrogen production properties were studied.Zeta potential test results shows that mesoporous Ti O₂and Ti₃C₂with opposite surface charges can construct stable composites through electrostatic interaction.X-ray diffraction（XRD）,Raman spectra,X-ray photoelectron spectroscopy（XPS）,transmission electron microscope（TEM）and high resolution transmission electron microscopy（HRTEM）further confirm the successful preparation of mesoporous Ti O₂/Ti₃C₂composites.In addition,XPS also demonstrate the transfer of photogenerated electrons from Ti O₂to Ti₃C₂cocatalyst in the composites,indicating a strong interaction between the two materials.BET test shows that compared with mesoporous Ti O₂,the composites have larger specific surface area and pore volume,and can provide more active sites,which is beneficial to improve the photocatalytic activity.UV-vis diffuse reflectance spectras shows that the introduction of Ti₃C₂cocatalyst improves the light absorption of the materials.The results of photoluminescence spectrum,time-resolved photoluminescence,photocurrent density and electrochemical impedance show that the composites have excellent ability of photogenerating carrier separation and transfer.In the test of photocatalytic performance,the photocatalytic degradation efficiency of MO by mesoporous Ti O₂/Ti₃C₂composite with the optimized Ti₃C₂content（3 wt%）can reach 99.6%within40 min,and the active species·O₂^–and·OH are confirmed to play the major role in the photocatalytic degradation process by free radical trapping experiment and electron spin resonance（ESR）characterization.In addition,the composite also shows excellent hydrogen production performance(218.85μmol g^–1h^–1),about 5.6 times higher than that of mesoporous Ti O₂,and still maintained stable hydrogen production efficiency after three cycles.In conclusion,MXene family materials can be applied as an efficient nonable-metal-free co-catalyst in the field of photocatalysis.（2）Firstly,ultrathin 2D Bi₂WO₆nanosheets with sizes ranging from tens of nanometers to several microns were prepared by hydrothermal method.Then,Ti₃Al C₂MAX phase was used as precursor to prepare few-layer Ti₃C₂MXene by HF etching and DMSO intercalation assisted ultrasonic stripping.0D Ti₃C₂QDs with uniformly dispersed size within 10 nm were prepared by hydrothermal method.Finally,Bi₂WO₆/Ti₃C₂QDs composite with 2D/0D structure was prepared by self-assembly method.By controlling the loading amount of Ti₃C₂QDs（1 wt%,3 wt%,5 wt%and 7 wt%）,the samples were named BTQDs-1%,BTQDs-3%,BTQDs-5%and BTQDs-7%,respectively.XRD,Raman and XPS were used to characterize the phase,molecular structure,elemental chemical and electronic states of the samples,and TEM and SEM were used to observe the apparent and microscopic morphology of the samples,which fully proved the successful preparation of Bi₂WO₆/Ti₃C₂QDs composites.And it is proved that there exists strong interaction and electrons movement between them.At the same time,the light absorption of the prepared material was measured by UV-vis spectroscopy and its band gap was calculated.The photocatalytic performance was evaluated by photocatalytic degradation of amoxicillin by the prepared materials.The results showed that when Ti₃C₂QDs loading was 3%,the BTQDS-3%had the best photocatalytic performance,and the degradation rate of amoxicillin could reach 69.8%within 2 h,which was about 2.1 times that of pure Bi₂WO₆nanosheets.These results indicate that Ti₃C₂QDs can be used as an efficient nonable-metal-free co-catalyst in the field of photocatalysis while retaining the inherent advantages of MXene family materials.