Nitrogen-doped semiconducting oxides. Implications on photochemical, photocatalytic and electronic properties derived from EPR spectroscopy

Abstract

<p>Engineered nitrogen defects in semiconducting oxides imparts appealing photophysical and photochemical properties to the materials which can be selectively addressed through EPR spectroscopy.</p>

Comparative visible-light driven selective oxidation to aldehydes of phenylmethanol (benzyl alcohol) and 4-pyridinylmethanol (4-pyridinecarbinol) on N-TiO2 and some commercial TiO2 samples

“…However, broad the signal is, it is possible to observe a larger peak at g = 2.0045 and weaker peaks at g = 2.022 and g = 1.985, each at a distance of 32 G from the main one. This often-reported EPR triplet is seemingly a feature of nitrogen impurities in TiO 2 [1,11,18], and corresponds to a paramagnetic species N i • from interstitial nitrogen (N i ) chemically bound to a lattice [11,56]. The N i localized energy state is located a few tenths of eV above the valence band [57] and is identified as the active centre of visible light photoactivity.…”

“…[1]) while keeping in mind that high visible-light absorption alone does not necessarily imply a high photocatalytic activity. Several approaches have been explored including: (i) dye sensitization [2], (ii) doping [3][4][5][6][7][8][9][10][11], and (iii) surface complexes formation [10,12]. Some good results concerning the photocatalytic activity by visible light have been obtained with metal ion doping [3,4].…”

“…Doping by non-metals, which was a relatively later strategy, has been a flourishing research field. Especially for nitrogen-doped TiO 2 (N-TiO 2 ), the number of publications and reviews has grown extensively [5][6][7][8][9][10][11].…”

Light‐Induced Nonoxidative Coupling of Methane Using Stable Solid Solutions

“…As shown in Figure 4 b, the initially EPR‐silent SS showed an EPR signal under light irradiation in vacuum. The characteristic triplet splitting and the large hyperfine constant indicated that the photogenerated unpaired electron directly interacted with the 14 N nucleus (nuclear spin I =1, expected lines 2 I +1=3) [36, 37] . Due to the absence of a secondary hyperfine structure caused by the I =3/2 nuclear spin of 69 Ga and 71 Ga, these photogenerated unpaired electrons should be mainly located on the nitrogen atoms bonding with zinc ( I =0).…”

“…The characteristic triplet splitting and the large hyperfine constant indicated that the photogenerated unpaired electron directly interacted with the 14 N nucleus (nuclear spin I = 1, expected lines 2I + 1 = 3). [36,37] Due to the absence of a secondary hyperfine structure caused by the I = 3/2 nuclear spin of 69 Ga and 71 Ga, these photogenerated unpaired electrons should be mainly located on the nitrogen atoms bonding with zinc (I = 0). For comparison, neither pure GaN nor ZnO materials had this EPR signal under the same light irradiation (Figure S14).…”