Shape‐Dependent Acidity and Photocatalytic Activity of Nb₂O₅ Nanocrystals with an Active TT (001) Surface

Abstract

The search for new low carbon and clean energy technologies is prominent on the research agendas of many governments, universities, and industrial sectors. In particular, the possibility of using solar energy for hydrogen production, fine chemicals manufacture, and water cleansing is currently under intense research. The use of semiconducting oxides, such as TiO 2 and ZnO, as photoactive materials has been receiving much attention. Recent work indicates that nanoparticles of these compounds show strong shape-dependent (surface-dependent) photocatalytic properties. [1,2] Spherical nanoparticles with high specific surface area to volume ratios are generally preferred. However, the high electron-hole recombination rate sometimes seen on their defect-rich nonplanar surfaces can be problematic. [1] As an n-type transition metal oxide semiconductor, Nb 2 O 5 has attracted a great deal of interest owing to remarkable applications in gas sensing, acid catalysis, electrochromics, field emission displays, and microelectronics. [3][4][5][6][7] Despite having high photocatalytic activity and well-documented water-tolerant acidic surfaces, at present there are few studies concerning the use of Nb 2 O 5 -based materials for photocatalytic applications. [8,9] Herein we report that the (100) surface lying along the axis of pseudo-hexagonal TT Nb 2 O 5 nanorod crystals offers enhanced photocatalytic activity over nanospheres for methylene blue decomposition in aqueous solution. We also reveal for the first time that the strong acidic sites on the exposed crystallographic planes of the nanorods readily bind methylene blue molecules from solution. In the presence of a typical radical scavenger (DMSO), Nb 2 O 5 nanorods show only a marginal decrease in decomposition rate. This is in contrast to ZnO, which adopts the classical mechanism of holeinduced hydroxyl radical attack on organic molecules in solution. The unique combination of adsorption and preconcentration of organic contaminants followed by direct surface decomposition driven by photocarriers gives rise to improved efficiency in this nonclassical mechanism for photomineralization on a Nb 2 O 5 surface.Details on materials synthesis, testing, and characterization can be found in the Supporting Information. As seen from the TEM image in Figure 1 a, Nb 2 O 5 nanospheres of 20-50 nm diameter were obtained by our precipitation method. Selected area electron diffraction (SAED) (see the Supporting Information) gave ring patterns indicative of the poor long-range crystallinity of the Nb 2 O 5 nanospheres. This is not surprising given the fact that the rapid non-equilibrium precipitation conditions do not allow for the extended growth of a particular phase. Thus, spherically shaped particles that offer a decrease in overall surface energy are anticipated. However, in the case of Nb 2 O 5 nanorod synthesis, we employed the solvothermal technique over a lengthy growth period in the presence of a structure-directing agent, oleic acid in trioctylamine. The TEM image in Figure 1 b clearl...

Hexagonal-like Nb2O5 Nanoplates-Based Photodetectors and Photocatalyst with High Performances

“…However, the Nb peak can be deconvoluted into two peaks with binding energies of 207.2 eV and 205.8 eV, and are assigned to Nb 5+ and Nb 4+ , respectively. This agrees well with the reported literature values (207.0 to 207.6 eV for Nb 3d5/2 in Nb 2 O 5 and 205.2 to 206.1 eV for Nb 3d5/2 in NbO 2 according to the NIST database)3243. Furthermore, these results also suggest that there are small amounts of suboxide species such as NbO 2 in the Nb 2 O 5 , in accordance with the EDS stoichiometric Nb 2 O 4.8 composition.…”

“…It has been reported that Nb 2 O 5 exhibits a different decomposition mechanism from the conventional radical-produced process. With regard to the strong adsorption of dye molecules, it seems that the dye molecules are immobilized at the solid acid sites, where the photoinduced electrons and holes on the surface can attack dye species without producing any radicals32. Therefore, the higher adsorbed amounts of dye molecules as well as the bigger surface-to-volume ratio of Nb 2 O 5 nanoplates lead to the higher degree decomposition of dyes than commercial Nb 2 O 5 .…”

“…Up to now, various interesting morphologies of Nb 2 O 5 nanostructures, such as nanowires18, nanobelts19, nanorods20, nanotubes2122, opal nanostructure23, mesoporous2425, hollow nanospheres26, nanosheets27, and nanoparticles28, have been synthesized. These nanostructures offer Nb 2 O 5 several unique features for a variety of device applications, involving field emitters29, lithium ion batteries30, photodetectors31, photocatalyst32, biosensors33, gas sensors34, etc. Owing to its bandgap, which rests in a relatively wide range from about 2.8 to 3.8 eV depending on the preparation methods353637, Nb 2 O 5 is a potential candidate for UV-A light (wavelengths ranging from 400 nm to 320 nm) detection.…”

CNTs-Modified Nb3O7F Hybrid Nanocrystal towards Faster Carrier Migration, Lower Bandgap and Higher Photocatalytic Activity

“…5b). The two peaks could be ascribed to Nb–F chemical bonding20. The peaks of NOF at around 529.54 and 683.74 eV can be ascribed to O1s corresponding to typical Nb-O band and F1s corresponding to typical Nb-F band (Fig.…”

Single-Pot Synthesis of ⟨001⟩-Faceted N-Doped Nb2O5/Reduced Graphene Oxide Nanocomposite for Efficient Photoelectrochemical Water Splitting

“…[18][19][20] Recently, the activity of Nb 2 O 5 was shown to be closely associated with its shape and surface structure. [21][22][23][24][25] In particular, nanorods of Nb 2 O 5 were prepared and shown to possess superior properties in various applications including humidity sensor, 21 powerful catalysts for vanadium redox flow battery, 22 high performance dye-sensitized solar cells, 23 biosensor, 24 etc. However, Nb 2 O 5 nanocrystals remain less explored as a photocatalyst presumably due to its rather wide band gap that makes it active in the UV region alone, therefore restraining the practical use of Nb 2 O 5 to ≤5%.…”