Ni₂P‐Modified Ta₃N₅ and TaON for Photocatalytic Nitrate Reduction

Abstract

Self‐sustaining photocatalytic NO3− reduction systems could become ideal NO3− removal methods. Developing an efficient, highly active photocatalyst is the key to the photocatalytic reduction of NO3−. In this work, we present the synthesis of Ni2P‐modified Ta3N5 (Ni2P/Ta3N5), TaON (Ni2P/TaON), and TiO2 (Ni2P/TiO2). Starting with a 2 mM (28 g/mL NO3−−N) aqueous solution of NO3−, as made Ni2P/Ta3N5 and Ni2P/TaON display as high as 79% and 61% NO3− conversion under 419 nm light within 12 h, which correspond to reaction rates per gram of 196 μmol g−1 h−1 and 153 μmol g−1 h−1, respectively, and apparent quantum yields of 3–4%. Compared to 24% NO3− conversion in Ni2P/TiO2, Ni2P/Ta3N5 and Ni2P/TaON exhibit higher activities due to the visible light active semiconductor (SC) substrates Ta3N5 and TaON. We also discuss two possible electron migration pathways in Ni2P/semiconductor heterostructures. Our experimental results suggest one dominant electron migration pathway in these materials, namely: Photo‐generated electrons migrate from the semiconductor to co‐catalyst Ni2P, and upshift its Fermi level. The higher Fermi level provides greater driving force and allows NO3− reduction to occur on the Ni2P surface.

Momentum-resolved electronic structure of LaTiO2N photocatalysts by resonant Soft-X-ray ARPES

“…It remains however, interstitial/chemisorbed on the surface in the form of N 2 and NO x species as corroborated by XPS data 7,32 . As the surface-lattice N and the OER intermediates (OH/O(OH)) likely react in competitive side reactions 27,[33][34][35] , it is possible that the increase in hydrophilicity and a superficial B cation-OH/O(OH) enriched surface layer, normally associated with the perovskite oxides, will have a more antagonistic role with respect to the oxynitrides.…”

Protagonists and spectators during photocatalytic solar water splitting with SrTaOxNy oxynitride

“…The photogenerated holes in the VB can then oxidise ammonia to form dinitrogen (eqn (10)), which can form NO x species according to eqn (1)-( 4). Wei et al 43 recently reported increased photocatalytic activity for nitride reduction on Ni 2 P modied tantalum nitride and tantalum oxynitride (Ta 3 N 5 and TaON, respectively). Where the photogenerated holes in the VB of the two materials are involved in the water oxidation reaction (eqn (12)) and, the photogenerated electrons in the CB transfer to the Ni 2 P states where they are involved in the photocatalytic reduction of NO 3 À .…”

“…The CB minimum and VB maximum of STON incorporate not only the redox potentials of the OER and HER, but also those for NO 3 À /NH 4 + (0.88 V), NO 3 À /HNO 2 (0.94 V) and NO 3 À /N 2 (1.24 V) at pH ¼ 0, vs. NHE. 43 This implies that all photogenerated electrons consumed in these competing reactions would no longer contribute to the HER at the Pt counter electrode (Fig. 1a), reducing the potential magnitude of the photocurrent density.…”

Reaction mechanism and selectivity regulation of photocatalytic nitrate reduction for wastewater purification: progress and challenges

“…[1][2][3][4][5][6] Nitrate is one of the most widespread pollutants in surface and underground water, which is mainly emitted from articial fertilizers in agriculture activity, factory waste disposal, and fossil fuel products of industrial effluents. 2,[7][8][9][10] Moreover, excessive nitrate emission in water has been widely recognized to pose health and environmental risks to humans, such as eutrophication and several health diseases. Especially, nitrate and its metabolic by-product nitrite are the main cause of methemoglobinemia which is also named the blue baby syndrome, tissue hypoxia and cancer.…”