Self-modified TiO₂ Nanomaterials Promote Their Photocatalytic Performance

Titanium dioxide（TiO₂）as an efficient,stable,environmentally friendly photocatalyst,has many applications in energy and the environment.How to design and synthesize TiO₂ catalyst,optimize its performance,and explore the mechanism is an important research issue.In this thesis,from the four aspects of phase,doping,crystal face,and photocatalytic mechanism of TiO₂,the new high-performence TiO₂-based materials were prepared by using simple synthesis methods and studied with single-molecule and single-particle approaches to improve their energy conversion and pollutant degradation.The main research contents and achievements are summarized as follows:1.Phase-junction TiO₂ was directly synthesized from Ti foil by using a simple calcination method with hydrothermal solution as the precursor below the phase transition temperature.Moreover,the ratio of rutile to anatase in the TiO₂ samples could be readily tuned by changing the ratio of weight of Ti foil to HCl.In the photocatalytic reaction by the TiO₂ nanocomposite,a synergistic effect between the two phases within a certain range of the ratio was clearly observed.The results suggest that an appropriate ratio of anatase to rutile in the TiO₂ nanocomposite could create more efficient solid-solid interfaces upon calcination,thereby facilitating interparticle charge transfer in the photocatalysis.2.Boron-doped（B-doped）TiO₂ with a tunable anatase/rutile ratio was successfully synthesized for efficient atrazine degradation by using a simple one-step calcination method.The formation of the surface-phase junctions between anatase and rutile nanoparticles enabled effective interparticle electron transfer and resulted in more efficient charge separation.Also,the B-doping served as charge traps,which were able to mediate oxidative electron transfer.The prepared B-doped TiO₂ exhibited a higher photocatalytic activity for the degradation of atrazine,with a reaction rate of 4 times faster than that of the non-doped counterpart.The photogenerated reactive species and degradation intermediates of atrazine were identified,and the photocatalytic atrazine degradation mechanism was elucidated.These findings provide a new approach to prepare phase-junction photocatalysts and demonstrate that the anatase/rutile ratio can be tuned by doping element.3.Inspired by our previous theoretical calculations about the roles of crystal surface in Pt-loaded TiO₂ in its enhanced photocatalytic capacity,TiO₂ nanocrystals with interspersed polyhedron nanostructures and co-exposed（001）and（101）surfaces as a support of Pt nanoparticles were prepared in a simple and relatively green route.Also,their performance for photocatalytic degradation of nitrobenzene（NB）,a model organic pollutant,was evaluated.The experimental results demonstrate that the NB photodegradation and photoconversion efficiencies were significantly enhanced by uniformly loading Pt nanoparticles on the crystal surfaces,but the Pt nanoparticles deposited on only the（101）surface had no contribution to the improved NB photodegradation.This work provides a new route to design and construct advanced photocatalysts toward pollutant photoredox conversions and deepens our fundamental understanding about crystal surface engineering.4.Non-stoichiometric anatase TiO₂ microspheres with designed（101）facets were successfully synthesized by using one-step solvothermal reaction method.The prepared non-stoichiometric anatase TiO₂ microspheres with designed（101）facets exhibited a great photocatalytic activity for H₂ evolution with a reaction rate of 3.4 times faster than that of anatase TiO₂ that was neither etched nor doped.The（101）facets of anatase TiO₂ were found to be able to generate and transmit more reductive electrons to promote the H₂ evolution.With the femtosecond time-resolved diffused reflectance measurement,the roles of self-doping Ti³⁺ as the photogenerated electrons trapping and（101）facets were further elucidated.Our findings might provide a new opportunity to develop an efficient,cost-effective and promising TiO₂-based catalyst for enhanced photocatalytic H₂ production.5.The photocatalytic activity sites on the single TiO₂ particles with high exposure（001）facet were examined.Time-resolved confocal fluorescence microscope combined with femtosecond laser and high-speed camera could provide simultaneous photoluminescence spectrum and lifetime of photogenerated hole-electron pair at the single-particle and-molecule level.It was found that holes and electrons tended to reach and react at the same surface sites within anatase TiO₂ particle.The results show that the redox activity sites of TiO₂ were located near the similar edges.This work provides experimental basis for the design and synthesis of efficient TiO₂ photocatalyts.