Photocatalytic water splitting for hydrogen generation on cubic, orthorhombic, and tetragonal KNbO3 microcubes

Abstract

Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.

Photocatalytic hydrogen production with visible light using nanocomposites of CdS and Ni on niobium oxide

“…Given the problems observed during the synthesis of the proton-exchanged catalyst, the low amount of hydrogen production from this material was not surprising. The increased activity with Ni doping is consistent with our earlier work on KNbO 3 9 and related reports by others [27][28][29][30][31][32] . Figure 9 shows the DRIFT spectra of the starting K 4 Nb 6 O 17 material, the two bestperforming modified K 4 Nb 6 O 17 catalysts, as well as a post-reaction catalyst that was recovered after a 24-hour photolysis experiment.…”

One-pot synthesis and Nb4N5 surface modification of Nb4+ self-doped KNbO3 nanorods for enhanced visible-light-driven hydrogen production

“…[15][16][17][18] These nanoclusters can not only competently suppress the recombination of electron-hole pairs, but also act as a co-catalyst for efficient oxygen reduction to consume the photoinduced electrons. [27][28][29] Recently, Nie et al demonstrated that anchoring Au nanoparticles (NPs) onto one-dimensional (1D) KN nanowires can enhance the photocatalytic activity of KN due to the crucial role of surface plasmon resonance as well as interband transitions on Au NPs. [19][20][21][22][23][24] Potassium niobate (KNbO 3 , denoted KN) is a well-studied binary oxide system as a catalyst due to its peculiar and interesting optical and electronic properties.…”

Band gap evolution and a piezoelectric-to-electrostrictive crossover in (1 − x)KNbO3–x(Ba0.5Bi0.5)(Nb0.5Zn0.5)O3 ceramics

“…10 KN is a prototypical ferroelectric (FE) perovskite. In the classic work by Shirane et al 11 , the room-temperature spontaneous polarisation of single-domain KN was reported as 41 ± 2 µC/cm 2 . This large spontaneous polarisation was rationalised on the basis of the noncentrosymmetric position of Nb 5+ cations within the NbO 6 octahedra.…”