Photocatalytic reduction of nitrogen to ammonia with coprecipitated Fe(III) and Ti(IV) hydrous oxides

Fundamentals and Recent Progress of Photocatalytic Nitrogen‐Fixation Reaction over Semiconductors

“…Although only a small amount of NO can be detected, the authors predicted that other semiconductors may also have the ability of photocatalytic N 2 oxidation and the adsorbed nitrogen species formed during the process may itself undergo further oxidation to a more stable substance, such as the NO 2 − ion, because this photocatalytic process already happens in the nature. [ 35 ] Actually, it was found that nitrate ions was one of the products when TiO 2 (H 2 O) n •Fe 2 O 3 (H 2 O) n and ultrafine FeOOH were applied as nitrogen‐fixation photocatalysts, [ 38,39,69 ] which confirmed the aforementioned prediction.…”

“…In fact, only NRR products (NH 3 or NH 4 + ) were found in the most photocatalytic nitrogen‐fixation systems. However, in a few situations, both the reductive product (NH 3 ) and the oxidative one (NO 3 − ) were observed simultaneously, [ 38,39,69 ] which means it is possible that photocatalytic NRR and NOR occur in the same system. Currently, it is hard to confirm whether the nitrogen‐fixation process between these interconnected pathways carried out by oxidation or reduction reaction as the mutual conversion of those redox products is a complicated process.…”

“…[ 132 ] Similarly, Tennakone et al synthesized a hydrated oxide containing Ti(IV) and Fe(III) as composite photocatalyst (Ti/Fe ratio is 8%) for N 2 reduction to NH 3 under visible light irradiation, and found that the NNR activity of the composite is higher than that of the single hydrous Fe 2 O 3 which also photocatalyzes the NRR reaction. [ 38 ] In the composite photocatalyst, the electron−hole separation is more effective, and consequently making multielectron transfers more probable. [ 38 ] Furthermore, oxidations and reductions occur at distinctly separated regions of the composite particle.…”

“…[ 38 ] In the composite photocatalyst, the electron−hole separation is more effective, and consequently making multielectron transfers more probable. [ 38 ] Furthermore, oxidations and reductions occur at distinctly separated regions of the composite particle. For instance, TiO 2 containing water was used as the hole aggregation center and water oxidation sites, and the NRR was carried out on Fe 2 O 3 with very negative flatband potential and strong N 2 chemical adsorption, and therefore causing the enhanced visible‐light‐driven NRR activity.…”

“…In 1977, Schrauzer and Guth first reported that N 2 can be photocatalytically reduced to NH 3 and N 2 H 4 over TiO 2 , and Fe 2 O 3 loading can improve the nitrogen‐fixation ability of TiO 2 . [ 27 ] Since then, various semiconducting materials, such as oxides, [ 11,28–35 ] sulfides, [ 12–14,36,37 ] hydroxides, [ 38–40 ] and bismuth halides, [ 41–45 ] have been used as the nitrogen‐fixation photocatalysts. Also, many strategies including manufacturing defects, supporting cocatalysts, and constructing heterojunctions have been developed to improve the nitrogen‐fixation performance.…”