Photocatalytic Nitrogen Fixation Research Articles

Photon driven nitrogen fixation via Ni-incorporated ZrO2/Bi2O3: p-n heterojunction

One of the promising approaches to synthesize ammonia in ambient conditions is through artificial photocatalytic nitrogen fixation. In order to overcome the hassles of charge carrier recombination and finite light response of photocatalysts, high charge separation efficiency and a wide window for optical absorption are imperative. Herein, Ni-incorporated ZrO2/Bi2O3 has been fabricated with p-n heterojunction and a bandgap aligned to absorb visible light up to 560 nm which play an important role in enhancing the production rate of ammonia. The catalyst exhibits a maximum ammonia generation rate of 9668.2 µmol h−1 g−1. Further, systematic characterization studies confirm the formation of the desired photocatalyst. This work presents a propitious strategy to configure appropriate visible light responsive photocatalyst that efficiently reduces nitrogen.

S-scheme OV–TiO2@Cu7S4 heterojunction on copper mesh for boosting visible-light nitrogen fixation

In the field of photocatalysis, the loaded photocatalyst possesses the advantages of controllable morphology, uniform preparation, low cost, and easy recovery. It can effectively avoid the secondary pollution caused by the powder catalyst and is considered a potential substitute for the powder photocatalyst. In this work, TiO2 and Cu7S4 hybrid materials with oxygen vacancies (OV) grown in situ on copper mesh (CM) were prepared by anion exchange and hydrothermal reaction. The characterization results showed that the concentration of oxygen vacancies in TiO2 increased significantly after calcination. Under the simulated visible light, the liquid film reaction was adopted. The yield of NH3 synthesized by OV–TiO2@Cu7S4/CM photocatalyst was 133.42 μmol cm−2 h−1, 5.2 and 2.2 times that of pure TiO2 and Cu7S4, respectively. The enhanced photocatalytic performance is attributed to the synergistic effect between the interfacial electric field of the S-scheme heterostructure and the abundant oxygen vacancies, which induces the efficient separation and migration of carriers. The cycle experiment showed that OV–TiO2@Cu7S4/CM heterojunction has excellent stability in photocatalytic nitrogen fixation. This work provides insight into the design of S-scheme photocatalysts with rich surface defects for green and efficient reduction of N2.

One-step fabrication of Cu-doped Bi2MoO6 microflower for enhancing performance in photocatalytic nitrogen fixation

This study enhances the photocatalytic N2 immobilization performance of Bi2MoO6 through Cu doping. Cu-doped Bi2MoO6 was synthesized via a simple solvothermal method. Various characterizations were implemented to examine the influence of Cu doping on the properties of Bi2MoO6. Results indicated that the doped Cu element had a valence state of + 2 and substituted the position of Bi3+. Cu doping exerted minimal effect on the morphology of Bi2MoO6 but largely influenced the energy band structure. The band gap was slightly narrowed, and the conduction band was raised, such that Cu-doped Bi2MoO6 could generate more electrons with stronger reducibility. Moreover, importantly, Cu doping reduced work function and improved charge separation efficiency, which was considered the major cause of enhanced photoactivity. In addition, the Cu-Bi2MoO6 catalyst exhibited higher capability in the adsorption and activation of N2. Under the combined effects of the aforementioned changes, Cu-Bi2MoO6 demonstrated considerably higher photocatalytic efficiency than Bi2MoO6. The optimized NH3 generation rate reached 302 μmol/L g−1h−1 and 157 μmol/L g−1h−1 under simulated solar light and visible light, respectively, both achieving about 2.2 times higher than that of Bi2MoO6. This work provides a successful example of improving photocatalytic N2 fixation, and it may show some light on the design and preparation of heteroatom-doped semiconductor photocatalysts for N2-to-NH3 conversion.

Bio-inspired citric acid-based bimetallic photocatalyst for nitrogen fixation from air under ambient conditions

Discovery of effective materials for photocatalytic nitrogen fixation under ambient conditions provides new opportunities for sustainable futures. Nitrogenase provides the best example of environmentally friendly nitrogen reduction. Inspired by homocitrate's specific activating effect on nitrogenase, citric acid was used instead of homocitric acid to prepare citric acid-based bimetallic organic frameworks (MOFs). Metals such as cerium and copper as bimetallic centers were coordinated with citric acid to mimic FeMo bimetallic active center in the M cluster. The results show that the morphology, structure and photocatalytic activity of the catalysts has been significantly affected by the amount of citric acid. The molar ratio of total metal to citric acid of 1.5:20 had the best ammonia evolution rate from air at a normal temperature and pressure (NTP), which was as high as 1027.6 μg g−1 h−1. It was further confirmed by the numerically study of the interactions between light and the synthesized photocatalytic particles, which can be intuitively seen that CeCu@CA-20 can support more surface charges. This work provides an effective strategy for citrate-based MOF photocatalysts and offers a new idea for nitrogenase biomimetics.

Construction of Co3O4 nanopolyhedra with rich oxygen vacancies from ZIF-67 for efficient photocatalytic nitrogen fixation.

Photocatalytic nitrogen fixation has attracted much attention due to the fact that it is a way of using solar energy to achieve clean and sustainable conversion of nitrogen to ammonia under mild conditions. In this paper, different proportions of Zn-doped Co3O4 nanopolyhedrons were synthesized using bimetallic ZIFs containing Co2+ and Zn2+ as precursors for the construction of photocatalytic nitrogen fixation semiconductor materials for the first time. The synthesized Co3O4 nano-polyhedron still retains the rhombic dodecahedron shape of ZIF-67 and exhibits a large specific surface area. Moreover, Zn doping results in abundant oxygen vacancies on the surface of Co3O4 polyhedron. These oxygen vacancies not only provide active sites for nitrogen adsorption and activation, but also enhance the separation ability of photocarriers, which can significantly improve the efficiency of photocatalytic nitrogen fixation of the material. When Zn-Co3O4-30 is utilized as the catalyst for photocatalytic nitrogen fixation, the nitrogen fixation rate is 96.8μmolg-1h-1, which is much higher than that of pure-Co3O4. In this study, heteroatom-doped Co3O4 polyhedron with rich oxygen vacancy was synthesized by low-temperature oxidation method, which provides a new idea for the design and synthesis of skeleton-based photocatalytic nitrogen fixation materials.

Self-Assembled Synthesis of Porous Iron-Doped Graphitic Carbon Nitride Nanostructures for Efficient Photocatalytic Hydrogen Evolution and Nitrogen Fixation

In this study, Fe-doped graphitic carbon nitride (Fe-MCNC) with varying Fe contents was synthesized via a supramolecular approach, followed by thermal exfoliation, and was then used for accelerated photocatalytic hydrogen evolution and nitrogen fixation. Various techniques were used to study the physicochemical properties of the MCN (g-C3N4 from melamine) and Fe-MCNC (MCN for g-C3N4 and C for cyanuric acid) catalysts. The field emission scanning electron microscopy (FE-SEM) images clearly demonstrate that the morphology of Fe-MCNC changes from planar sheets to porous, partially twisted (partially developed nanotube and nanorod) nanostructures. The elemental mapping study confirms the uniform distribution of Fe on the MCNC surface. The X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectroscopy (UV-DRS) results suggest that the Fe species might exist in the Fe3+ state and form Fe-N bonds with N atoms, thereby extending the visible light absorption areas and decreasing the band gap of MCN. Furthermore, doping with precise amounts of Fe might induce exfoliation and increase the specific surface area, but excessive Fe could destroy the MCN structure. The optimized Fe-MCNC nanostructure had a specific surface area of 23.6 m2 g-1, which was 8.1 times greater than that of MCN (2.89 m2 g-1). To study its photocatalytic properties, the nanostructure was tested for photocatalytic hydrogen evolution and nitrogen fixation; 2Fe-MCNC shows the highest photocatalytic activity, which is approximately 13.3 times and 2.4 times better, respectively, than MCN-1H. Due to its high efficiency and stability, the Fe-MCNC nanostructure is a promising and ideal photocatalyst for a wide range of applications.

Photocatalytic Nitrogen Fixation using Graphitic Carbon Nitride: A Review

AbstractIn this work, research articles dealing with the photocatalytic fixation of nitrogen using graphitic carbon nitride (g‐C3N4) were reviewed starting from 2015 when the first paper on this topic was published. The NH3/NH4+ production rates were adopted from these articles and statistically processed. The highest rate obtained by the composite g‐C3N4 and 1T‐MoS2 was 11120 μmol g−1 L−1 h−1. The highest reported rate provided by bulk (bare) g‐C3N4 was 5561 μmol g−1 L−1 h−1, which was higher than 90 % of the rates provided by the various composites of g‐C3N4. The quantum efficiency of the composites varied from 0.033 to 5.65 % with a median of 1.25 %. Although these results are still not competitive with the industrial Haber‐Bosh process, graphitic carbon nitride is recommended as a promising material for the future investigation of photocatalytic nitrogen fixation under visible light.

S-scheme enhanced photocatalysis on graphitic carbon nitride functionalized with perylene tetracarboxylic diimide

It is a challenge to realize the catalytic conversion of ammonia by photocatalysis under mild conditions, because it is limited by the high photoinduced carrier recombination rate and low photo-absorption efficiency. Herein, we perform the condensation reaction of 3,4,9,10-perylenetetracarboxylic diimide (PTCDA) with graphitic carbon nitride (g-C3N4) nanosheets to obtain a novel organic semiconductor perylene tetracarboxylic diimide (PTCDI) modified g-C3N4 S-scheme heterostructure (named PTCDI@g-C3N4) via thermal-etching and bath process. The obtained PTCDI@g-C3N4 composite shows an obvious improvement in photocatalytic nitrogen reduction rate of 7308.9 μmol L−1 g−1h−1 with methanol under the Xe lamp irradiation, higher than g-C3N4 nanosheets (1215.3 μmol L−1 g−1 h−1). The excellent photocatalytic performance of PTCDI@g-C3N4 heterostructure is ascribed to two advantages: (1) The S-scheme heterojunction between organic semiconductor PTCDI and g-C3N4 nanosheets is profit to suppress carrier recombination and enhance electron utilization efficiency; (2) The utilization rate of g-C3N4 nanosheets to light was promoted due to the existence of PTCDI with broad visible light absorption. This work may help to provide a possibility to realize efficient photocatalytic nitrogen fixation by preparing organic-nonmetallic heterostructure through facile methods.

The order of loading affects photocatalytic nitrogen fixation activity of the ternary composites of PdO/Au–TiO2

We applied PdO/Au–TiO2 to photocatalytic nitrogen fixation and found that Au, as electron transport channel, is conducive to N2 fixation.

Cationic vacancy engineering of p-TiO2 for enhanced photocatalytic nitrogen fixation.

Defect engineering is one of the effective strategies to regulate and control catalyst properties. Constructing appropriate catalytically active centers effectively tunes the electronic and surface properties of the catalyst to achieve further enrichment of photogenerated electrons, enhances the electronic feedback of the catalytically active center to the anti-bonding orbitals of the nitrogen molecule, and enhances N2 adsorption while weakening the NN bond. In this study, titanium vacancy (VTi)-rich undoped anatase p-TiO2 was successfully synthesized to investigate the effect of its metal vacancies on photocatalytic nitrogen reduction reaction (NRR) performance. The cation vacancies of VTi-rich p-TiO2 lead to local charge defects that enhance carrier separation and transport while trapping electrons to activate N2, allowing effective reduction of the excited electrons to NH3. This work provides a viable strategy for driving the efficiency of photocatalytic nitrogen fixation processes by altering the structural properties of semiconductors through cationic vacancies, offering new opportunities and challenges for the design and preparation of titanium dioxide-based materials.

Photon localization effect and surface oxygen vacancy enhanced photocatalytic nitrogen fixation performance for nanocrystalline titanium dioxide films

The synergistic enhancement effect of photonic crystals and surface oxygen vacancies was achieved. A possible nitrogen reduction reaction mechanism was proposed through DFT calculations.

Ag nanoparticles in the cages of MIL-101(Cr) as an efficient and stable photocatalyst for nitrogen reduction reaction

Ligand–metal charge transfer mechanism and localized surface plasmon resonance effect mechanism synergize efficient photocatalytic nitrogen fixation.

The construction of a vanadium-doped polysulfide iron bimetallic active center for enhanced photocatalytic nitrogen fixation

Inspired by natural nitrogen fixation, we constructed a metal–S mimetic biocatalyst using vanadium-doped iron polysulfide as the active center combined with g-C3N5, which is rich in nitrogen vacancies.

甘露醇与酸碱度协同调控氧空位修饰钼酸铋纳米棒的合成及其高效光催化固氮活性

Oxygen vacancies (Ovs) in semiconductors, which can adsorb and activate N2 molecules, are active sites for photocatalytic nitrogen reduction to ammonia. However, simple and effective methods for creating Ovs still need to be explored. Herein, mannitol was used to selectively create Ovs at Mo in Bi2MoO6 (BMO) and form BMO short nanorods (SNRs) through a hydrothermal process, with the Ov content, SNR size, and surface area of the sample effectively tuned by pH. BMO SNRs containing the most Ovs exhibit the highest visible light absorption, fastest photoexcited charge separation, and best photocatalytic nitrogen fixation performance, with an N2 reduction reaction rate in pure water reaching approximately 107-fold that of BMO nanosheets synthesized in the absence of mannitol, and an apparent quantum yield of 2.78% at 420 nm, superior to all of the reported BMO-based photocatalysts. This work provides a new and simple method for selective Ov creation and the morphological tuning of BMO to expedite the photocatalytic N2 reduction.

Electron transfer bridge inducing polarization of nitrogen molecules for enhanced photocatalytic nitrogen fixation.

Ammonia (NH3) plays a crucial role in the production of fertilizers, medicines, fibers, etc., which are closely relevant to the development of human society. However, the inert and nonpolar properties of NN seriously hinder artificial nitrogen fixation under mild conditions. Herein, we introduce a novel strategy to enhance the photocatalytic efficiency of N2 fixation through the directional polarization of N2 by rare earth metal atoms, which act as a local "electron transfer bridge." This bridge facilitates the transfer of delocalized electrons to the distal N atom and redirects the polarization of adsorbed N2 molecules. Taking cerium doped BiOCl (Ce-BiOCl) as an example, our results reveal that the electrons transfer to the distal N atom through the cerium atom, resulting in absorbed nitrogen molecular polarization. Consequently, the polarized nitrogen molecules exhibit an easier trend for NN cleavage and the subsequent hydrogenation process, and exhibit a greatly enhanced photocatalytic ammonia production rate of 46.7 μmol g-1 h-1 in cerium doped BiOCl, nearly 4 times higher than that of pure BiOCl. The original concept of directional polarization of N2 presented in this work not only deepens our understanding of the N2 molecular activation mechanism but also broadens our horizons for designing highly efficient catalysts for N2 fixation.

Tailoring defects in SrTiO3 by one step nanoarchitectonics for realizing photocatalytic nitrogen fixation in pure water.

Surface contamination of materials by nitrogenous impurities is a major problem that can bias the quantification of ammonia in photocatalytic N2 fixation reactions. In this work, SrTiO3 nanocubes were prepared by using a nitrogenous precursor and engineered with Ti3+ sites and oxygen vacancy defects in a one-step solvothermal approach. It was observed that the synthesized materials were containing surface nitrogenous impurities and therefore a rigorous cleaning procedure was adopted to eliminate them to the best extent. The contribution of unavoidable surface impurities was deduced in the form of adventitious NH3 by employing control experiments and a realistic photocatalytic NH3 generation was achieved. It was found that pristine SrTiO3 showed no photocatalytic activity, whereas one of the defected SrTiO3 materials showed the highest NH3 formation under natural sunlight in pure water, which was ascribed to the tuned defect sites, enhanced surface area and efficient separation of photogenerated charges. Based on the experimental results, a stringent protocol has been suggested for materials synthesis while working with nitrogenous precursors and for subsequent photocatalytic N2 fixation experiments. Thus, the present study provides a simple and affordable procedure for catalyst synthesis for the studied application and expands the scope of perovskite oxide materials to fabricate efficient photocatalysts for sustainable NH3 production.

Enhancement of the properties of ZnAl-LDHs for photocatalytic nitrogen reduction reaction by controlling anion intercalation

The anion regulated channel of LDHs blocked by carbonate was opened by controlling the suberate intercalation, thus discussing the effect of different anions of PMo12−XVX, X = 0, 1, 2, 3, 8) intercalation on the photocatalytic nitrogen fixation performance of ZnAl-LDH.

2d Boron Nitride Supported Cu2o Promotes Photocatalytic Nitrogen Fixation at Normal Temperature and Pressure

2d Boron Nitride Supported Cu2o Promotes Photocatalytic Nitrogen Fixation at Normal Temperature and Pressure

Constructing asymmetric active sites on defective Ru/W18O49for photocatalytic nitrogen fixation

Boosting photocatalytic N2fixation can be achieved on Ru/W18O49by tuning defect states by constructing asymmetric active sites.

2D boron nitride supported Cu2O promotes photocatalytic nitrogen fixation at normal temperature and pressure

Boron nitride (BN) semiconductors, as graphene analogues, have attracted extensive attention in the field of photocatalysis due to their unique physical and chemical properties.