Fabrication of an Fe‐Doped SrTiO₃ Photocatalyst with Enhanced Dinitrogen Photofixation Performance

Abstract

SrTiO3 as semiconducting photocatalyst has been extensively investigated due to its band edges meeting the thermodynamic requirements for water splitting, but a few attention has been concentrated on its application in the NH3 synthesis via N2 photofixation process. Herein, Fe‐doped SrTiO3 (FexSr1–xTiO3) products (0 ≤ x ≤ 0.20) were synthesized via a hydrothermal process followed by calcination at 700 °C. All FexSr1–xTiO3 products (0.03 ≤ x ≤ 0.20) deliver an enhanced N2 fixation ability, and FexSr1–xTiO3 (x = 0.10) achieves the best NH3 production activity of 30.1 µmol g–1 h–1, which is 3.2‐hold higher than that of SrTiO3 alone. Once the x value is higher than 0.10, FexSr1–xTiO3 will transform into composites containing Fe‐doped SrTiO3 and α‐Fe2O3, which acts as charge recombination sites, thus causes a decreased N2 fixation activity. Further investigations demonstrate that the surface Fe3+‐doped sites can not only chemisorb and activate N2 molecules, but also promote the interfacial electron transfer from Fe‐doped SrTiO3 to N2 molecules, and thus significantly improve the N2 fixation ability. The present Fe‐doped SrTiO3 products exhibit characteristic features such as stable and efficient N2 fixation ability as well as simultaneous realization of N2 reduction and H2O oxidation without co‐catalyst, which are of significance in artificial photosynthesis with H2O as electron and proton sources.

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

“…Theoretically, some reductive substances (such as ethylene diamine tetraacetic acid (EDTA), methanol, ethanol, and Na 2 SO 3 ) can be used as hole sacrificial reagents. [ 31,52–55 ] In view of the risk of interference with the subsequent NH 3 detection and the corrosion of photocatalyst, however, the sacrificial reagent should be carefully considered. Unquestionably, the ideal hole sacrificial reagent is water.…”

“…Hitherto, many efforts have been made on the choice and modification of semiconductors, such as doping, introducing vacancy, supporting cocatalyst, morphology regulation, and constructing heterojunction, to accelerate the nitrogen‐fixation processes. Based on the elemental compositions, the various nitrogen‐fixation photocatalysts can be will be classified into the following categories: TiO 2 and other metal oxides, [ 30–32,52–54,83–91,96–99,103,104 ] bismuth oxyhalides, [ 41–45,105–111 ] metal sulfides and biomimetic materials, [ 12–14,36,37,112–116 ] graphitic nitride carbon, [ 99,117–123 ] and the relative composites or heterojunctions. [ 55,62,78,88,99,114,121–124 ] In the subsequent sections, the photocatalysts will be classified based on their elemental compositions and nitrogen‐fixation reactions (NRR and NOR).…”

“…To overcome these problems, a number of feasible strategies were developed to enhance the NRR activity, which include introducing vacancy by doping, loading noble metal cocatalysts, and establishing heterojunctions. [ 52,53 ] In the early studies, TM elements (such as Co, Mo, Ni, Mg, Cr, V, Ce, and Fe) were doped into TiO 2 lattice for improving the N 2 adsorption and activation as well as the spectral response range, but the photoactivity was not satisfactory. [ 27,29,32,86,98,125,126 ] Also, TM nanoparticles as cocatalysts have been supported on TiO 2 to promote the photoinduced charge separation.…”

“…Although SrTiO 3 is also an extensively investigated photocatalyst in the field of water splitting, a few attention has been paid on its application in NH 3 synthesis Peng and coworkers synthesized Fe‐doped SrTiO 3 (Fe x Sr 1– x TiO 3 , 0 ≤ x ≤ 0.20) via a hydrothermal process ( Figure a). [ 53 ] The Fe x Sr 1– x TiO 3 (0.03 ≤ x ≤ 0.20) products delivered enhanced NNR ability, and Fe x Sr 1– x TiO 3 ( x = 0.10) achieved the best NH 3 yield of 30.1 μmol g −1 h −1 , 3.2‐fold higher than that of SrTiO 3 alone (Figure 16b). [ 53 ] Once the x value is higher than 0.10, Fe x Sr 1– x TiO 3 transformed into composite containing Fe‐doped SrTiO 3 and α‐Fe 2 O 3 , which acts as charge recombination sites, and thus causing a decreased NNR activity.…”

“…[ 53 ] The Fe x Sr 1– x TiO 3 (0.03 ≤ x ≤ 0.20) products delivered enhanced NNR ability, and Fe x Sr 1– x TiO 3 ( x = 0.10) achieved the best NH 3 yield of 30.1 μmol g −1 h −1 , 3.2‐fold higher than that of SrTiO 3 alone (Figure 16b). [ 53 ] Once the x value is higher than 0.10, Fe x Sr 1– x TiO 3 transformed into composite containing Fe‐doped SrTiO 3 and α‐Fe 2 O 3 , which acts as charge recombination sites, and thus causing a decreased NNR activity. Moreover, the Fe x Sr 1– x TiO 3 bearing suitable band edges implemented the N 2 reduction and H 2 O oxidation at the same time (Figure 16c).…”