Fabrication Of Niobium-Based Composites And Their Photocatalytic Properties For Hydrogen Evolution

Over the past decades, semiconductor-based photocatalysts have attracted great attention due to their applications in solar energy conversion and environmental remediation. The direct conversion of solar energy to chemical energy by means of photocatalytic water splitting to produce hydrogen is considered as one of the most promising green methods. To date, a large number of semiconductor materials have been studied for such a process, however, stable and highly efficient visible-light-driven photocatalysts for hydrogen production under solar-light irradiation are still scarce. Therefore, development of efficient visible-light-driven photocatalysts for renewable energy production is highly desired. This study will contribute to the development of a novel photocatalyst with high performance, and provide a new idea in the field of solar energy conversion and basic theories of reference, the main research contents are as follows:（1） A novel heterogeneous hybrid composed of Nb₂O₅ microspheres and reduced graphene oxide has been first fabricated by a facile hydrothermal method. The as-prepared samples were systematically characterized by XRD, SEM, FTIR, Raman spectroscopy and DRS techniques. The results show that the Nb₂O₅ microspheres are well dispersed on the reduced graphene oxide（RGO） sheets and formation of Nb-O-C bond between the Nb₂O₅ microspheres and RGO results in superior interfacial contacts of the two components and promoted charges transportation and separation. The composite with optimal compositions shows an enhanced photocatalytic activity for hydrogen production from water reduction. Upon 10 h UV-vis light irradiation, ca. 8824 mmol g-1 H2 is produced over the photocatalyst consisting of 4 wt. % RGO, which is ca. 3 times as high as that of the Nb₂O₅ microspheres.（2） The visible-light-driven photocatalysts composed of Nb₂O₅ nanorods, CdS nanoparticles and N-doped graphene nanosheets for photocatalytic water reduction to produce hydrogen have been synthesized. The photocatalysts were characterized by XRD, SEM, Raman, TEM, XPS and photoelectrochemical measurements. Under visible light irradiation, the as-prepared ternay nanocomposites showed distinctly enhanced photocatalytic performance for hydrogen evolution compared to bare CdS, NbR and CdS/Nb₂O₅. The sample with 2 wt. % N-doped graphene（NGR） exhibited the highest photocatalytic activity, which is ca. 7.7 times as high as that evolved from CdS. The enhancement of photocatalytic performance may be related to the unique 1D Nb₂O₅ structure, which can provide a direct path for photoinduced charges transfer, as well as the CdS/Nb₂O₅ heterojunction structure and 2D NGR, which enhance the separation efficiency of photogenerated charge carriers. This work provides a promising and cost-effective method by combining the 0D CdS nanoparticles, 1D Nb₂O₅ nanorods and 2D N-doped graphene to form a ternary photocatalytic system for highly efficient hydrogen evolution from water without using any noble metals.（3） The Cu doped of InNbO₄ as visible-light-driven photocatalysts has been first fabricated by a facile hydrothermal method. The as-prepared samples were systematically characterized by XRD, TEM techniques. The composite with optimal compositions shows an enhanced photocatalytic activity for hydrogen production from water reduction. Upon 8 h visible light irradiation, ca. 340 mmol g-1 H2 is produced over the photocatalyst consisting of 4 wt. % Cu, which is ca. 3.5 times as high as that of the pure InNbO₄.