| One of the most important problems for prohibiting industrial applications of photocatalysis is low photocatalytic activity caused by photo-induced carrier recombination in semiconductor photocatalyst, which causes neutralization of the photo-induced electrons and holes before they can initiate the photocatalytic processes. Although some measures based on heterostructures have been proposed and put into practice to solve this problem, the efficiency is still too low to separate electron-hole pairs completely during photocatalysis. Although the P-N junction can separate photo-induced carriers, but the enhancement of the photocatalysis is limited so as to hinder its practical application. In order to further improve the photocatalytic efficiency and exptend the light response from UV to visible light and to NIR light. Ultrafine TiO2 nanobelts, BaTiO3nanocubes and Ag2O are selected for semiconductor photocatalysts in view of the narrow spectral absorption of photocatalyst, low carrier separation efficiency and easy recombination. The basic properties and the enhancement mechanism of photocatalysis were studied,The main conclusions are as followings:1. We propose sono-photocatalysis based on a new hybrid photocatalyst, which combines ferroelectric nanocrystals (BaTiO3) and semiconductor nanoparticles (Ag2O) to form an Ag2O-BaTiO3 hybrid photocatalyst. The built-in electric field originated from the spontaneous polarization potential of ferroelectric nanocrystal can be used to enhance the photocatalytic activity of semiconductor photocatalysts through the enhancement of photo-induced charge carrier separation based on the built-in filed-induced periodical absorption and release process of the carriers. Based on stress-induced spontaneous polarization potential alternately variation of ferroelectrics and photocatalytic activity of semiconductor photocatalyst, sono-photocatalysis was suggested as a way of introducing a noncontact energy-supplying source to obtain continuous enhancement of the photocatalytic activity of semiconductor photocatalyst attached on the surface of ferroelectric nanocrystal. Under periodic ultrasonic pressure driving, the built-in field of a ferroelectric nanocrystal can be alternately altered by piezoelectric effect of ferroelectrics, which can induce momentarily absorb and suddenly release some photo-induced carriers and avoid saturating the built-in field. During sono-photocatalysis, piezo-phototronic effect is the key for obtaining high photocatalytic performance of semiconductor/ferroelectrics hybrid sono-photocatalyst. In this paper, Ag2O/BaTiO3 hybrid nanocubes synthesized by assembling Ag2O nanoparticles on BaTiO3 nanocubes were used as a model sono-photocatalyst, and responded favorably to ultrasonic irradiation as an effective sono-photocatalyst. Ferroelectric based hybrid photocatalyst and sono-photocatalysis will provide a new strategy for high performance photocatalysis applications.2. We also report a development of ferroelectric-enhanced photocatalysis on the basis of 3D dendritic TiO2/BaTiO3 hybrid microspheres under periodic ultrasonic excitation. Through a simple hydrothermal method, nanosized TiO2 nanowires with a length of 200-300 nm was uniformly and epitaxially assemble to the surface of tetragonal BaTiO3 nanocubes forming 3D dendritic TiO2/BaTiO3 hybrid microspheres. The spontaneous electrical polarization on the BaTiO3 nanocube increased the band bending of TiO2 nanowires and enhanced the charge generation and separation efficiency, in the meantime, piezoelectric effect combined with spontaneous electrical polarization and photo-electric conversion realizes an ultrasonic wave driven piezo-phototronic process in the 3D dendritic TiO2/BaTiO3 hybrid photocatalyst, which is the fundamental of sono-photocatalysis resulting in improved redox reactions. This research provided a successful demonstration of the ferroelectric effect in nanostructured heterojunctions as an effective strategy for improving the photocatalysis in H2 generation.3. Ultrafine TiO2 nanobelts with high specific surface area (72.2 m2·g-1) were synthesized through a one-step hydrothermal method. Heterostructured MoS2/TiO2 hybrid nanobelts were prepared by wrapping few-layered MoS2 nanosheets on TiO2 nanobelts via a simple hydrothermal method, which enhances UV-visible light-driven photocatalytic activity. In addition, the coating of only few layers of MoS2 nanosheets on TiO2 nanobelts not only broadens the photocatalytic light region from UV to visible, but also enhances the photocatalytic activity of the hybrid nanobelts both in UV and in visible light bands due to the band matching between MoS2 and TiO2. Due to the favorable electrical conductivity, MoS2 nanosheets here work as an electron mediator and transporter for improving the charge separation efficiency, while the heterojunctions in the MoS2/TiO2 hybrid nanobelts can effectively improve charge separation of the few-layered MoS2/TiO2 nanobelts, leading to much enhanced photocatalytic activity. This ultrafine TiO2 nanobelt based MoS2/TiO2 heterostrctures not only possesses very high photocatalytic activity in UV-Visible region, but also have good recyclability compared with P25 or other granular nano-photocatalysts, which will have great applications in water splitting for H2 generation, and water treatment for cleaning wastewater.4. We demonstrate that Ag2O nanoparticles possesses a very high NIR-light photocatalytic activity with good UV and Vis photocatalytic property. However, under UV and Vis irradiation, Ag2O nanoparticles could lose its photocatalytic activity due to the photo-reduction of Ag2O. By surface sulfurization process, a layer of Ag2S2O7 grown on the surface of Ag2O to form heterostructured nanoparticles. The resulting Ag2O/Ag2S2O7 heterostructures can not only keep NIR photocatalytic activity, but also enhance UV and Vis photocatalytic activity of Ag2O. Most importantly, the stability of Ag2O/Ag2S2O7 heterostructures is dramatically improved. The improved stability and enhanced photocatalytic activity of Ag2O/Ag2S2O7 heterostructures is derived from the band matching between Ag2O and Ag2S2O7 as well as excellent chemical stability of Ag2S2O7 under UV and Vis irradiation. The stable and full-solar-spectrum photocatalytic activity of Ag2O/Ag2S2O7 heterostructures have great potential for the applications in photodegradation and fabrication of efficient solar-cells for full utilization of the solar spectrum. This stable full-solar-spectrum photocatalysts will have great potential for the application in photodegradation of organic pollutants in water treatment industry... |
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