| Controllable preparation of single-crystal ferroelectric nanostructures and the physi-chemical properties of their surface and interface have become a hot research topic in the field of functional nanomaterials. Lead titanate is a typical kind of perovskite-type ferroelectric oxides. Investigation into its nanostructures and size effects are significant in better understanding the ferroelectricity of ferroelectric nanomaterials and expanding their applications. In this paper, lead titanate nanomaterials with different morphologies are synthesized by hydrothermal method and characterized to investigate their nucleation-growth mechanisms with the variation of alkali concentration. On the other hand, single-domain lead titanate nanoplates are used as substrates to prepare such composites as Ag2O/PbTiO3. The selective growth behaviors are discussed and their photocatalytic performances are investigated. The innovative research results are shown in the following:(1) Three formation processes of perovskite PbTiO3 nanoparticles with different morphologies are proposed by comparing the microstructures of the intermediate products obtained at different hydrothermal time and in different mineralizer concentrations. When the concentration of NaOH is low (1～2g), PbTiO3 nucleus are formed on lead oxide sheets heterogeneously. Then, the nucleus grow into single-crystal cubic-like perovskite PbTiO3 nanoparticles with a size of 100-150nm via an Ostwald Ripening process. With increase of NaOH concentration (3g), amounts of single-crystal cubic-like perovskite PbTiO3 nanoparticles are rapidly formed. Then some of them aggregate into plates via an Oriented Attachment process and melt into a whole PbTiO3 nanoplate with an average width of 359nm. When the concentration of NaOH (4-5g) is high, lead oxide sheets act as templets. Titanium precursor absorb onto the lead oxides and decompose into titanium oxide nanocrystals, which react with the lead oxide sheets in-situ and form thin PbTiO3 nanosheets. Then the sheets form PbTiO3 nanoplates with a thickness of 150-250nm and a width between 400-1500nm via an OA process.(2) Ag2O nanoparticles are selectively deposited on the positive polar surface of PTO nanoplates under visible light with a wavelength more than 420nm. The possible mechanism is proposed. PTO nanoplate could produce electrons and holes on the surface under visible illumination. With the effect of ferroelectric polarization, photogenerated electrons are concentrated on the positive polar surface of PTO nanoplate, reducing the absorbed silver ions into silver nanocrystals, while oxygen is demonstrated to be able to be produced with the existence of silver nitrate. Given that the electron affinity of oxygen is stronger than silver and the redox potential of oxygen is more positive than that of silver, the saturated dissolved oxygen and the formed intermediate oxidants could oxidize the freshly formed silver nanocrystals into silver oxide.(3) Photodegradation experiments of MB, MO, RhB and salicylic acid are conducted under visible light illumination with Ag2O/PbTiO3 (S25). Results show that the composite has highly efficient photoactivity and excellent stability. This could be explained by two reasons:firstly, there exists a large difference in the position of the conduction bands of PTO and Ag2O, making the photogenerated electrons flow towards Ag2O under illumination; secondly, the ferroelectric polarization effect of PTO nanoplate could induce the concentration of photogenerated electrons at interface, which is favorable to the separation of photogenerated carriers, and thus promotes the photocatalytic efficiency of Ag2O. In addition, it is found that ammonia could protect silver from being oxidized during illumination by forming complex. |
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