S-Scheme TiO₂/CuNb₂O₆ Nanocomposite Photocatalyst with Enhanced H₂ Evolution Activity from Aqueous Glycerol Solution

Abstract

Steering of photoexcitons via interface engineering of semiconductor photocatalysts is key to achieving a stable and efficient photocatalyst for continuous hydrogen production. Among them, the development of 1D nanostructures with several advantageous properties such as wide surface area, effective light harvesting, and increased electron moving kinetics has received special attention. In this work, 1D titania nanobars were successfully synthesized via the methanol-assisted solvothermal method, in which alcohol formed hydrogen bonds with nuclei, which consequently encouraged the growth of nanobars. Following this, the titania nanobars were integrated with solvothermally synthesized monoclinic CuNb 2 O 6 nanoparticles. TEM analysis revealed the formation of TiO 2 nanobars and their uniform interaction with CuNb 2 O 6 nanoparticles. A S-scheme heterojunction is formed at the interface of TiO 2 nanobars and CuNb 2 O 6 nanoparticles. 1D morphology of titania and CuNb 2 O 6 plays a key role in light absorption and boosts the photocatalytic activity by promoting the separation and transfer of photoexcited charge carriers. The electrons at the TiO 2 conduction band and holes at the valance band of CuNb 2 O 6 facilitated recombination at the heterojunction. The remaining electrons at the conduction band of CuNb 2 O 6 and holes at the valance band of TiO 2 tend to participate in redox reactions at their terminals. As the loading of CuNb 2 O 6 increases, the rate of activity initially increases and then decreases, which is consistent with the trend for light penetration-dependent photocatalytic hydrogen evolution. The band edge potentials of TiO 2 and CuNb 2 O 6 were also revealed using VB-XPS and UPS analysis. In addition to catalytic stability, the effect of glycerol concentration, catalyst loading, time on stream, recyclability, and parametric analysis which aided in the discovery of ideal experimental conditions is revealed. Under optimal conditions, the photocatalyst showed an enhanced rate of H 2 generation (146 mmol h −1 g cat −1) under simulated solar light irradiation. The solar to H 2 conversion efficacy is also discussed with comparison.

Metal-doped niobate pyrochlores and double-perovskites for glycerol valorization: structural and electronic properties and DFT calculations

“…The peaks are accompanied by two satellites at 936.3 and 940.6 eV, matching well with those of Cu 2+ ions in both CuNb 2 O 6 and Cu 3 Nb 2 O 8 materials. 29,49–52 This result agrees with the XRD and Raman measurements that suggest the existence of the aforesaid phases. As with most of the observed surface properties of Cu-based materials, 51,52 the Cu LMM Auger line also appears as a broad peak in the 578–574 eV range, which is readily attributable to the divalent and monovalent copper species.…”

“…The bindings energies and metal to niobium surface atomic ratios are listed in Table S 4 (ESI †) Two broad and asymmetric Nb 3d peaks appear at 209.1 and 206.2 eV (Table S4 †), which is associated with the doublet Nb 3d 3/2 -Nb 3d 5/2 . This reveals the coordination environment of Nb octahedra bonded with six oxygen atoms and represents the pentavalent oxidation state of Nb, 29,49 independently of the A site of the ANb 2 O 6 niobate columbite phase.…”