Formation of Sol–Gel-Derived TaO_xN_y Photocatalysts

Abstract

Tantalum oxynitride (TaON) is a visible photocatalyst (λ < 520 nm) that has been investigated for green energy applications, specifically, the solar production of hydrogen gas. Metal oxynitrides are often generated by the ammonolysis of metal oxides at very high temperatures. We have investigated an alternative synthetic procedure to produce gram-scale quantities of photocatalytically active TaO x N y materials using room-temperature sol–gel chemistry. X-ray photoelectron spectroscopy (XPS) results confirm that nitrogen was incorporated into materials with a Ta2O5 crystal structure. Optical characterization reveals that sol–gel-synthesized TaO x N y has a 2.3 eV bandgap, in agreement with bulk TaON. Furthermore, photoluminescence experiments reveal that two distinct material systems are being created during the initial sol phase of the synthesis: one species is primarily metal oxide, while the other is a N-doped species. This observation may lead to synthetic methods that improve the doping content of sol–gel-derived materials.

Theoretical Investigation of Ta2O5, TaON, and Ta3N5: Electronic Band Structures and Absolute Band Edges

“…In this work, we mainly focus on three tantalum-based compounds, namely, Ta 2 O 5 , TaON, and Ta 3 N 5 . The latter two compounds have been verified experimentally to have smaller band gaps than common oxides and to exhibit visible-light photocatalytic activity. − A series of studies on the electronic structures of the three compounds based on DFT have been published. − Compared with pure metal oxides and nitrides, metal oxynitrides have the attractive feature that they often combine the small band gap of nitrides with the good stability of oxides. − ,, By systematically considering the oxide, nitride, and oxynitride of the same transition metal element (i.e., Ta), our purpose in this work is to investigate the band gaps and the absolute band positions of these compounds using state-of-the-art first-principles approaches and to further clarify the origin of the differences among them.…”

Fabrication of tantalum oxyfluoride and oxynitride thin films via ammonolysis of sol–gel processed tetraethoxo (β-diketonato) tantalum (V) precursors for enhanced photocatalytic activity

“…This lowering of band gap may be attributed to the fact that substitution of ethoxide ligands with differen β-diketones increased the steric hinderence offered to the substitution of hydroxyl group leading to reduced rate of hydrolysis to an extent that only small oligomeric units are formed. It is reasonable to conceptualize that this will lead to elimination of defects in Ta 2 O 5 upon calcination at 500 °C [36,54]. From the observed band gap values, it is believed that the rate of hydrolysis in complex is faster that of 1 and 2 resulting in the formation of small oligomeric units, forming short cross-linked matrix in the gel of precursor during polycondensation reaction.…”

A Selective Synthesis of TaON Nanoparticles and Their Comparative Study of Photoelectrochemical Properties

“…Tantalum oxide has a bandgap that straddles the redox potential of water making it a viable candidate, if properly optimized to absorb visible light, that would facilitate production of solar fuels [13]. For example, they can be integrated with the most earth abundant and eco-friendly element-nitrogen-to form oxynitrides: TaO x N y (y = 1 − x) [14,15]. This singular option allows for tuning the optical bandgap (E g ) over a wide range of 1.6-4.0 eV solely based on Ta: O: N ratio.…”