In-suit Growth Of Heteronanostructured Composite Photocatalysts Based On Ta₂O₅Nanofibers For The Photocatalytic Hydrogen Production

Heterostructured composite materials usually consist of two semiconductorswith different energy bands and not only maintained the performances of originallysingle materials, but also endued some special performances, such as enhanced optic,electric and magnetic performances and so an. Therefore, the heterostructuredmaterials exhibit a widely applied prospects. Tantalum-based heterostructuredmaterial has important potential applications in photocatalytic hydrogen productiondue to their orientated transfer character and excellent reduction ability. However, thiskind of materials have usually been prepared by sol-gel or co-precipitate method.This can result in more defects in the heterostructured interface and influence theinterfacial charge separation and transfer. Thereby, in this dissertation, we fabricatethe porous heterostructured NaTaO3/Ta2O5and Ta3O7F/Ta2O5nanofibers withmatched lattices through controlling the etch rate of the Ta2O5and the growth rate ofthe second phase of heterostructured. Their activities of photocatalytic hydrogenproduction have been studied. At the same time, the influence factors of preparationprocess have been discussed. The main important results are summarized as follows：(1) NaTaO3/Ta2O5heteronanostructured composites with less interface defectsand smaller interface resistance were prepared under the solvothermal condition. Thegrowth of NaTaO3nanocubes on the surface of the porous Ta2O5nanofibers wereefficiently adjusted by the dissolution of porous Ta2O5nanofibers through changingthe concentration of the NaOH. In this section, the influence of reaction time, theconcentration of NaOH and solvent species to dissolution of Ta2O5precursors werestudied in detail. The structure-evolved law of the epitaxial growth heterostructuredcomposites as well as the morphology-controlled mechanism were deeply delved. Wefound that the absorption spectrum of this kind of epitaxial growthheteronanostructured composites nanofibers have red-shift obviously and thephotocatalytic activities enhanced remarkable relative to single nano-materials. The69%NaTaO3/Ta2O5composite exhibited the highest photocatalytic activity (31.5μmol/h/0.02g), which was3.1times and10.5times larger than those of Ta2O5andNaTaO3nanofibers in pure water. This was largely attributed to the epitaxial growth heterostructured between Ta2O5and NaTaO3was beneficial to the interfacial chargetransfer of photon-generated carriers, which can effectively suppress therecombination of photogenerated charge carriers, and thus enhance the photocatalyticactivity.(2) We constructed the epitaxial growth heterostructured Ta3O7F/Ta2O5composite porous nanofibers were in-suit constructed using HF as the etching agent,Ta2O5porous nanofibers as the precursor and CH3COOH as the solvent. In thisetch-growth synchronization technology, the key is that the dissociation ofCH3COOH hindered the dissociation of HF, and thus controlled the release rate of F-,the dissolution of Ta2O5precursors, and the growth rate of HTaF6on the surface of theprecursors, which reacted with H2O to get Ta3O7F in the solution quickly. The resultsfurther confirmed that the key of the technology to prepare heterostructuredcomposites materials is to control the etch rate of the precursor which should bematched with the growth rate of the second phase, thereby to control the second phaseheterogeneous nucleation and growth along the lattice matched orientation on thesurface of the precursor. The photocatalytic activities of the as-preparedheterostructured Ta3O7F/Ta2O5porous composite nanofibers were much higher thanthat of pure Ta2O5nanofibers.