Fabrication And Photocatalytic Performance Of TiO₂with Porous Structure And Surface Plasmon Resonance

As an efficient pollution control technology, photocatalysis has attracted widespread attention because of its environmental friendly property, excellent photocatalytic activity. The catalyst serves as the core of photocatalytic reaction. However, the common photocatalyst TiO2is troubled by the shortcomings of narrow optical response and low quantum efficiency, limiting the further development of photocatalytic technology. The macro/mesoporous structure and photonic crystal (PC) could enhance the mass transfer and light absorption due to their excellent physicochemical properties, such as large surface area, high pore volume, band gap scattering effect and slow photon effect. Noble-metal nanoparticles like Au, Ag show efficient visible light absorption because of the Localized Surface Plasmon Resonance (LSPR). The incorporation of noble-metal nanoparticles with wide band gap semiconductor can efficiently enlarge the visible light response range, meanwhile, the heterojunction between this two could enhance the separation of photogenerated charge carriers. In this dissertation, several works have been done as follows:(1) Hierarchically lung-like macro/mesoporous TiO2with high thermal stability and specific surface area was successfully fabricated through a facile combination of hydrothermal treatment and calcination process. The catalyst exhibited relatively homogeneous and long-range periodical channels, which were arranged parallel to each other and orthogonal to one side of the monolithic particles, with pore diameter of2-3μm and pore wall thickness of2-3μm. Further observation revealed that the wall of the macroporous structure was composed of many small interconnected TiO2spheres with size of100-300nm. The introduction of hydrothermal treatment enhanced the stability of the macro/mesoporous structure, at the same time, the crystallinity and surface area was also improved. During the photocatalytic degradation of RhB under UV light irradiation, the kinetic constant of porous TiO2experienced the combined thermal treatment was1.9fold higher than that of the one calcined only.(2) The visible-light-responded photocatalyst HT-400/Au was fabricated by depositing Au nanoparticles on macro/mesoporous TiO2prepared from the above combined thermal treatment. The porous structure of TiO2has been fully utilized, both inside and outside of the macropores, even the microspheres were decorated by the Au nanoparticles with the diameter around30-40nm. Additionally, the loading amount of Au nanoparticles could be controlled by changing the charged state of gold precursor. The HT-400/Au exhibited visible light absorption due to the LSPR of Au nanoparticles. During the2,4-DCP degradation under visible light (λ>420nm) irradiation, the HT-400presented high photocatalytic activity, whose kinetic constant was2.2fold larger than that of the sample HT-400without the decoration of Au nanoparticles;1.5fold greater than that of the sample Crushed HT-400without this macro/mesoporous structure.(3) The3D plasmonic photocatalyst TiO2PC/Au NPs was prepared via the liquid-phase deposition and in situ hydrothermal reduction method. The thickness of the TiO2PC structure was about2.5-3μm, and the average diameter of the hollow spheres was around223nm. The Au NPs with the size around15-20nm were uniformly distributed and anchored along the heterogeneous macroporous surface of the3D PC structure. The band gap scattering effect and slow photon effect efficiently intensified the plasmonic absorption of Au nanoparticles. Compared with TiO2NC/Au NPs, the TIO2PC/Au NPs exhibited stronger optical absorption. During the photocatalytic degradation of RhB and2,4-DCP under visible light (λ>420nm) irradiation, the kinetic constant of TiO2PC/Au NPs was3.5and2.3fold higher than that of TiO2NC/Au NPs, respectively. The hydroxyl radicals derived from the electroreduction of dissolved oxygen with electrons via chain reactions was the main reactive oxygen species and finally resulted in the efficient pollutant degradation.The above results illuminated that the well-designed nanostructure like macro/mesoporous, photonic crystal could enhance the mass transfer and light utilization. The proper decoration of wide band gap semiconductor such as the plasmonic Au nanoparticles could expand the light response range, and the separation of photoinduced charge carriers could also be intensified by forming the heterojunction. These studies provide a feasible approach to design photocatalyst with high activity, which would promote the application of photocatalytic technology in the environmental pollution control.