Fabrication And Properties Of The Functional Assemblies Based On Potasiuum Niobate With Varied Morphologies

The photocatalytic hydrogen evolution from water reduction is an ideal way to convert solar energy into clean and renewable hydrogen energy. It has become a hot research topic in the field of photocatalysis. As a kind of stable, cheap, morphology controllable and easy to be modified semiconductor, potassium niobate shows potential applications in the fields of photocatalysis and sensors. In this paper, the reduced graphene oxide (RGO) instead of noble metal Pt was loaded onto the potassium niobates with varied morphologies, and prepared two kinds of potassium niobate photocatalysts for photocatalytic hydrogen evolution. In addition, the controllable and orderly potassium niobate nanosheets/Ag2O composite films were fabricated by layer-by-layer self-assembly method. The films showed sensitive and fast SERS response for the detection of crystal violet with low concentration, and the mechanism of electron transfer were also studied. The main contents are summarized as follows:A new type of potassium niobate/reduced graphene oxide (RGO) composite nanoscrolls was prepared by the intercalation of RGO in the process of curling of the potassium niobate nanosheets. The as-prepared potassium niobate/RGO composite nanoscrolls were characterized with powder X-ray diffraction, transmission electron microscopy, Raman spectroscopy, solid diffuse reflectance UV-visible spectroscopy and fluorescence spectroscopy. The photocatalytic activity of the composite nanoscrolls was evaluated by hydrogen evolution from aqueous methanol under UV irradiation. It was found that the photocatalytic activity was enhanced as 3.1 times after introducing 2% RGO, compared with the pure potassium niobate nanoscrolls. It was ascribed to the enhanced separation efficiency of electron/hole pairs as testified by electrochemical impedance spectrum and fluorescence spectrum. Moreover, the composite photocatalyst was stable and easy to be recycled.A facile approach to synthesize reduced graphene oxide (RGO) loaded potassium niobate microspheres was reported. The composition, microstructure and electron-transfer properties of the obtained product were characterized. Compared to pure potassium niobate microspheres and commercial P25 TiO2, the as-prepared potassium niobate microspheres/RGO composite showed much higher photocatalytic activity for generating hydrogen under UV irradiation. It was ascribed to the enhanced separation efficiency of electron/hole pairs as testified by electrochemical impedance spectrum and fluorescence spectrum. Importantly, the composite photocatalyst was stable and easy to recycle, and the amount of hydrogen evolution did not decrease after six recycles.The orderly potassium niobate nanosheets/Ag2O composite films with uniform morphology were achieved by layer-by-layer self-assembly combined with ultraviolet light reduction. The composition, structure and morphology of potassium niobate nanosheets/Ag2O composite films were studied by XPS, XRD and SEM. The films were used as a SERS probe to detect crystal violet with low concentration. The results showed that the potassium niobate nanosheets/Ag20 composite films were an active substrate for fast and sensitive detection of crystal violet with low concentration, and the quick electron transfer between potassium niobate nanosheets and Ag2O was the key factor.