Preparation And Photocatalytic Activity Of AgNbO₃Composites

As world demand for energy continues to rise, considerable efforts has been devoted to thedevelopment of renewable energy in recent years. Photocatalytic materials has received increasing attentionfor its broad application prospects in renewable resources developing and environmental conditioning.Over the past few decades, many semiconductor materials have been developed for use as photocatalysts orphotoelectrodes driven at ultraviolet （UV） wavelengths. As the largest proportion of the solar energyspectrum lies in the visible range, more efficient photocatalytic conversion of solar energy could beachieved using a suitable material that is active under visible light. Development of new visible-lightphotocatalysts has gained more and more attention in recent years. Among them, solid-solutionsemiconductors are of particular interest for the tunable energy band structures and the derivedadvantageous performances that are unattainable by the individual end material. AgNbO₃is a goodantiferroelectric compound which belongs to the perovskite family. Silver niobate AgNbO₃has beenreported to be promising visible light sensitive photocatalysts with the band-gap of less than3.1eV. Thecovalent character is ascribed to the Nb4d-O2p and Ag4d-O2p hybridizations in AgNbO₃. The Nb-O andAg-O hybridization would be a key factor of the off-center displacements of Nb and Ag cations along the caxis, which induces the ferrielectricity in AgNbO₃. The covalent bonds and the existence of Ag atom areresponsible for the visible-light response of AgNbO₃photocatalyst. Thus, AgNbO₃serve as basecompounds for a variety of solid solutions showing a combination of electrical and mechanical properties.Recently, AgNbO₃-based solid solutions, such as AgNbO₃-NaNbO₃and AgNbO₃-SrTiO₃, were reported asa series of new photocatalysts for air purification with higher activities in comparison with pristineAgNbO₃.In order to improve the photoelectrochemical and photocatalytic properties of silver niobate, powdersand thin films were prepared. Then we investigate the photoelectrochemical and photocatalytic properties.The main contents and achievements in this thesis are as follows:1. AgNbO₃、NaNbO₃/AgNbO₃10、NaNbO₃/AgNbO₃30、NaNbO₃/AgNbO₃50on FTOconducting glass substrates were fabricated by pulsed laser deposition. The crystal structures andtransmittance spectrum were determined by an X-ray diffractometer and UV-vis spectrophotometer. The photoelectrochemical measurements were performed in a three-electrode glass cell. These investigationsreveal that the sodium niobate layer plays a role in preventing recombination of electrons and holes. Thequantum efficiency was improved.2. AgNbO₃has attracted increasing attention as a practical photocatalytic material. AgNbO₃andAg2Nb4O11-AgNbO₃on FTO conducting glass substrates were fabricated by pulsed laser deposition. Thecrystal structures, morphology and transmittance spectrum were determined by an X-ray diffractometer,UV-vis spectrophotometer and Atomic Force Microscope respectively. The indirect band gap of AN andAN01are2.85and2.96eV respectively. Ag2Nb4O11has a higher efficiency of electron-cavity separated atthe surface states. The RIp/Isof AN film approximately1.5times higher than that for the AN01film. Thisillustrates that the second phase Ag2Nb4O11will inhibits the recombination of electrons and holes at thesurface states.3. A series of AgNbO₃powders with AL2O₃as inhibitor were prepared by solid state method. Theresults show that inhibitor of AL2O₃improves the degradation of silver niobate. The inhibitor plays a role inpreventing crystal growth of silver niobate. This leads to surface area of silver niobate increased. Then thedegradation rate of silver niobate was improved.