Study On The Photocatalytic Reaction Via The Modulation Of Surface And Interface

With the highlight of growing energy crisis and environmental pollution, theapplication of solar energy has been attracting more attention. Wherein the surfaceand interface properties of the photocatalysts are crucial to photocatalytic research,which will provide the important theoretical basis for design and preparation of novelphotocatalysts. This paper focuses on the modification of metal-oxide photocatalyst ofTiO2and Cu2O, and intensively studies their surface and interface properties.Modifications include doping, crystal-facet tuning, surface-electronic-structuremodulation and quantum dot. Then this work systematically studied the modulation ofmorphology and properties and their effects on the photocatalytic reaction.The doping of metal ions are applied to modify the band structure and chemicalenvironment of lattice of TiO2to increase the charge-separation efficiency. Directlyhydrolysis method was used to prepare the metal doped TiO2. V4+and Fe3+are dopedinto the lattice of TiO2in the structure of Ti-O-M, and the doping type of Ce ions isinterstitial, while Cr and Cu ions cannot enter the skeleton but highly disperse on thesurface. Therefore, V-and Fe-doped catalysts show the highest reactivity in thephotocatalytic isomerization of norbornadiene (NBD). Then, V-and Fe-TiO2withdifferent doping concentration are prepared. With the higher doping concentration,Fe3+can uniformly disperse into the lattice, and when the doping concentration ishigher, the smaller particle can be achieved. Importantly, the sample with Ti/Fe of10shows highest activity. For V doping, higher concentration causes the surfaceenrichment of V2O5, and the best photoactivity is achieved when Ti/V=15.Furthermore, the photocatalytic reactivity is closely related to the lattice oxygen:firstly, the photoinduced hole of TiO2can be trapped by the lattice oxygen andsubsequently transferred to the adsorbed NBD and form the intermediate, finallyresulted into the quadricyclane. Then, a simple strategy was developed to fabricateTi3+-defected V-TiO2quantum dots (QDs) on MCM-41by combining trace V-dopingand MCM-41loading strategies. QDs are highly dispersed on MCM-41without anyaggregations, and exhibit quantum size effect. Ti3+defects and V4+dopants lead tonew band levels near the conduction band of QDs and show more effective chargeseparation. As a result, the materials show higher activity in photodegradation ofRhodamine (RhB) and photoisomerization of NBD than undoped or non-defectedcounterparts.Modulation of anatase towards high-active facets has been attracting many attentions. The facets of {001},{101},{010} and {110} are fabricated in the presenceof F. The result demonstrates the inherent mechanisms for facets nucleation andmorphology evolution, and clarify some vital influences of facets and surface natureon the photoactivity. The photodegradation of positively and negatively charged, andzwitterionic dyes indicates that the type of reactant, adsorption mode and surface areaplay significant roles in photocatalysis. Then, a strategy is developed to in-situfabricate defect-free anatase nanosheets self-decorated with quantum dots. These dotsprovide new and more effective charge separation and transfer pathway over thenanosheets surface, and promote the photoactivity significantly, due to the wellmatched band structures.The dye sensitization is an effective method to utilize the solar light via theenhancement of charge transfer between dye and TiO2. Simple water treatment cansignificantly modulate the surface electron structure of TiO2, switch the adsorptionmode of cationic dyes, and promote the dye (RhB) sensitization of TiO2under visiblelight irradiation. It provides a cheap and green way to improve the efficiency ofdye-sensitized solar cell and environmental photocatalysis. Then the hierarchicalmacro-/mesoporous TiO2were prepared. Solely hydrothermal treatment cannotimplant nonmetals into the lattice, with most of the dopants existing as surfaceimpurities. After calcination, N species get into the lattice whereas S and F are still onthe surface. The samples stored for ca. half a year shows significantly higher activitythan the fresh counterpart, attributed to the water-mediated adsorption switch causedby the pre-bonding of water on surface hydroxyl groups. Specially, the combination ofnon-metal doping and water-mediated adsorption switch produces a very highphotoactivity.Cu2O is the typical p-type semiconductor. Cu2O films were fabricated in thiswork via the in-situ redox reaction between Cu2+and Cu plate. Simply tuning theanionic groups of Cu2+can generate different morphologies including rod-like arrays,cross-linked and truncated octahedrals. Mott-Schottky plots and PL spectra indicatethat the rod-like arrays possess more copper vacancies than the other twomorphologies. In photodegradation, the rod arrays exhibit much better performance,following by truncated and then cross-linked octahedrals. Although different surfacereconstructions occur for the films owing to different charge transfer and consumptionpathway, their photoactivities are all enhanced after the first run. Then rod arrays andcross-linked octahedrals show very stable activity, but truncated octahedrals show agradually decreased activity.This work systematically studied the band structure, facet, morphology and surface properties of TiO2and Cu2O, demonstrated the relationship between chargetransfer and photocatalytic reactivity, developed the approaches to prepare the relatedmaterials and conduct the surface modifications, modulated the surface and interfacestructure to promote the photocatalytic activity. This work may provide the theoreticalsupport for the breakthrough of photocatalysis and preparation of the highly activephotocatalysts.