Photocatalytic Nitrogen Fixation Research Articles

Reinforced BiOBr for visible-light-driven nitrogen fixation: A synergistic effect of cocatalyst and oxygen vacancies

Photocatalytic nitrogen fixation is a promising long-term strategy for NH3 synthesis, with the development of effective and durable photocatalysts being crucial for achieving high-efficiency N2 to NH3 conversion. In this study, we employed vacancy and interface engineering to create bismuth (Bi) nanoparticles on hierarchical oxygen-deficient BiOBr microspheres using a one-step solvothermal approach. These Bi-decorated BiOBr microspheres, featuring oxygen vacancies, achieved a high photocatalytic ammonia synthesis rate of 222.3 μmol·g−1·h−1 in pure water under visible light irradiation, which is 3.25 times higher than that of the original BiOBr. Atomic-scale images of the interface between the defective regions of BiOBr and the Bi cocatalyst and several other material characterizations confirmed that the enhanced photoreduction activity of Bi/BiOBr is due to the synergistic effects of the metal Bi and the oxygen vacancies. These results present a straightforward and practical method for designing efficient photocatalysts for nitrogen fixation.

Rare earth-doped carbon nitride composite Ce-based metal-organic framework for visible light-driven nitrogen fixation catalysis

The utilization of visible light for photocatalytic nitrogen fixation offers a sustainable and eco-friendly strategy for the production of ammonia. The present study focuses on the synthesis of a series of rare earth-doped carbon nitride composite ultraviolet-activated Ce-UiO-66 catalysts, denoted as RECN-actMOF, for efficient nitrogen fixation. Rare earth doping modulates the band structure of carbon nitride, facilitating the formation of a type-I heterojunction with Ce-UiO-66 and promoting photocarrier generation at nitrogen fixation sites. Among these, Sm-doped SmCN-actMOF exhibits high visible-light absorption and efficient utilization of photocarriers, resulting in an apparent quantum efficiency (AQE) of 1.58% under 495 nm light irradiation. This study provides a pathway for enhancing the nitrogen fixation efficiency of photocatalysts through the incorporation of rare earth elements, and expanding the potential applications of rare earth materials in the field of photocatalysis.

Modelling Photocatalytic N2 Reduction to Ammonia: Where We Stand and Where We Are Going.

Artificial ammonia synthesis via the Haber-Bosch process is environmentally problematic due to the high energy consumption and corresponding CO emissions, produced during the reaction and before hand in hydrogen production upon methane steam reforming. Photocatalytic nitrogen fixation as a greener alternative to the conventional Haber-Bosch process enables us to perform nitrogen reduction reaction (NRR) under mild conditions, harnessing light as the energy source. Herein, we systematically review first-principles calculations used to determine the electronic/optical properties of photocatalysts, N2 adsorption and to expound possible NRR mechanisms. The most commonly studied photocatalysts for nitrogen fixation are usually modified with dopants, defects, co-catalysts and Z-scheme heterojunctions to prevent charge carrier recombination, improve charge separation efficiency and adjust a band gap to for utilizing a broader light spectrum. Most studies at the atomistic level of modeling are grounded upon density functional theory (DFT) calculations, wholly foregoing excitation effects paramount in photocatalysis. Hence, there is a dire need to consider methods beyond DFT to study the excited state properties more accurately. Furthermore, a few studies have been examined, which include higher level kinetics and macroscale simulations. Ultimately, we show there is still ample room for improvement with regard to first principles calculations and their integration in multiscale models.

Research Progress on the Application of MOF and MOF‐Based Materials in Nitrogen Reduction

AbstractElectrocatalytic and photocatalytic nitrogen fixation have become new ways to achieve green nitrogen reduction because of their environmentally friendly and cost‐effective characteristics. At present, there has been an increasing curiosity about using metal‐organic frameworks (MOFs) for photocatalysis and electrocatalysis. However, electrocatalytic and photocatalytic ammonia production is still not practical for practical applications. Having a thorough understanding of nitrogen fixation is necessary for the advancement of practical applications and the development of highly efficient catalysts in the future. The catalytic nitrogen fixation activity of MOF itself is limited. By adjusting the exposure of active sites through low‐temperature calcination and solvent addition, the photogenerated carrier recombination is inhibited, and the adsorption and activation of N2 are enhanced, improving its performance in nitrogen fixation applications. This review examines the reported photocatalysts, electrocatalysts, and photoelectrocatalysts based on MOFs and their associated materials. The underlying mechanism for photocatalysis and electrocatalysis is elucidated. Additionally, an inclusive survey of MOFs and related materials as catalysts for nitrogen reduction reaction (NRR) is presented, with representative examples discussed. Finally, the research progress of MOF‐based catalytic nitrogen fixation materials is summarized and prospected.

Integrating bimetallic borides with g-C3N4 containing cyanamide defects for efficient photocatalytic nitrogen fixation

The sustainable generation of ammonia by photocatalytic nitrogen fixation under mild conditions is fascinating compared to conventional industrial processes. Nevertheless, owing to the low charge transfer efficiency, the insufficient light absorption capacity and limited active sites of the photocatalyst cause the difficult adsorption and activation of N2 molecules, thereby resulting in a low photocatalytic conversion efficiency. Herein, a novel bimetallic CoMoB nanosheets (CoMoB) co-catalyst modified carbon nitride with dual moiety defects (CN-TH3/3) Schottky junction photocatalyst is designed for photocatalytic nitrogen reduction reaction (NRR). The photocatalytic nitrogen reduction rate of the optimized CoMoB/CN-TH3/3 photocatalyst is 4.81 mM·g−1·h−1, which is 6.2 and 2.2 times higher than carbon nitride (CN) (0.78 mM·g−1·h−1) and CN-TH3/3 (2.21 mM·g−1·h−1), respectively. The excellent photocatalytic NRR performance is ascribed not only to the introduction of dual moiety defects (cyano and cyanamide groups) that extends the visible light absorption range and promotes exciton polarization dissociation, but also to the formation of interfacial electric field between CoMoB and CN-TH3/3, which effectively facilitates the interfacial charge transfer. Thus, the synergistic interaction between CN-TH3/3 and CoMoB further increases the electron numble of CoMoB active sites, which effectively strengthens the adsorption and activation of N2 and weakens the NN triple bond, thereby enhancing the photocatalytic NRR activity. This work highlights the introduced dual moiety defects and bimetallic CoMoB co-catalyst to synergistically enhance the photocatalytic nitrogen reduction performance.

Iron-doping regulated light absorption and active sites in LiTaO3 single crystal for photocatalytic nitrogen reduction

In contrast to research on active sites in nanomaterials, lithium tantalate single crystals, known for their exceptional optical properties and long-range ordered lattice structure, present a promising avenue for in-depth exploration of photocatalytic reaction systems with fewer constraints imposed by surface chemistry. Typically, the isotropy of a specific facet provides a perfect support for studying heteroatom doping. Herein, this work delves into the intrinsic catalytic sites for photocatalytic nitrogen fixation in iron-doped lithium tantalate single crystals. The presence of iron not only modifies the electronic structure of lithium tantalate, improving its light absorption capacity, but also functions as an active site for the nitrogen adsorption and activation. The photocatalytic ammonia production rate of the iron-doped lithium tantalate in pure water is maximum 26.95 μg cm−2 h−1, which is three times higher than that of undoped lithium tantalate. The combination of first-principles simulations with in situ characterizations confirms that iron doping promotes the rate-determining step and changes the pathway of hydrogenation to associative alternating. This study provides a new perspective on in-depth investigation of intrinsic catalytic active sites in photocatalysis and other catalytic processes.

Experimental and theoretical study on potentiated photocatalytic nitrogen fixation of Mo doped InVO4 nanorods

Photocatalytic nitrogen fixation is acknowledged as an eco-friendly substitute for the conventional Haber-Bosch procedure for nitrogen (N2) conversion into ammonia (NH3). Localized electron-rich oxygen vacancies (OVs) on the surface of indium-based semiconductors have been proven to possess the capacity to capture and activate N2. Herein, oxygen vacancy-enriched Mo doped InVO4 nanorods with preferred orientation have been successfully synthesized via a simple hydrothermal reaction. Doping Mo into InVO4 nanorods can not only generate numerous OVs but also simultaneously modulate their electronic structure, significantly improving the efficiency of photocatalytic nitrogen fixation. Benefiting from the optimal Mo doped content, the 5 %Mo/InVO4 sample presents the optimal photocatalytic performance with the NH3 yield of 162.00 μmol·g−1·h−1, which is 2.4 times higher than that of pristine InVO4 sample. The characterization results reveal that the introduction of OVs augments light consumption and impedes the recombination of photogenerated electrons-hole pairs. Furthermore, the effect of OVs by doping Mo on the nitrogen fixation performance is also verified by the density functional theory (DFT) theoretical calculation. This work provides a new platform for the development of promising catalysts in the photocatalytic nitrogen fixation field, and has certain theoretical and practical value.

Construction of Fe(III) Active Sites on Phenanthroline-Grafted g-C3N4: Reduced Work Function and Enhanced Intramolecular Charge Transfer for Efficient N2 Photofixation.

Photocatalytic nitrogen fixation is one of the important pathways for green and sustainable ammonia synthesis, but the extremely high bonding energy of the N≡N triple bond makes it difficult for conventional nitrogen fixation photocatalysts to directly activate and hydrogenate. Given this, we covalently grafted the phenanthroline unit onto graphitic carbon nitride nanosheets (CN) by the simple thermal oxidation method and complexed it with transition metal Fe3+ ions to obtain stable dispersed Fe active sites, which can significantly improve the photocatalytic activity. The Fe(III)-4-P-CN photocatalyst morphology consists of porous lamellar structures internally connected by nanowires. The special morphology of the catalysts gives them excellent nitrogen fixation performance, with an average NH3 yield of 492.9 μmol g-1 h-1, which is 6.5 times higher than that of the pristine CN, as well as better photocatalytic cycling stability. Comprehensive experiments and density-functional theory results show that Fe(III)-4-P-CN is more favorable than pristine CN for *N2 activation, effectively lowering the reaction energy barrier. Moreover, other byproducts (such as nitrate and H2O2) are also produced during the photocatalytic nitrogen fixation process, which also provides a new way for nitrogen-fixing photocatalysts to achieve multifunctional applications.

Modulation of cationic vacancies in Co3O4 for promoted photocatalytic nitrogen fixation and electrocatalytic nitrate reduction to ammonia

Defect engineering offers a powerful approach to tune the local surface microstructure, electron band structure and chemistry of photo- and electro-catalysts, to thereby enhancing their performance in nitrogen reduction reaction (NRR) and electrocatalytic nitrate reduction to ammonia (NO3-RR). The present study has successfully synthesized cobalt-rich vacancy (VCo) Co3O4 through a two-step method, allowing for controlled manipulation of the concentration of cobalt vacancies through heat treatment. The impact of varying concentrations of cobalt vacancies on the performance of photocatalytic nitrogen reduction reaction and electrocatalytic nitrate ammonia production was investigated. Remarkably, the catalysts heat-treated at 500 °C, exhibited a significantly enhanced photocatalytic nitrogen fixation performance with a rate of 67.5 μmol·g-1·h-1. The catalysts heat-treated at 300 °C, exhibited an ammonia yield of 339.05 mmol·g-1·h-1 at -1.1 V (vs. RHE), while achieving a maximum Faraday efficiency of 84.3 % at -0.9 V (vs. RHE). The enhanced activity can be attributed to the presence of cobalt vacancies, which synergistically modulate both the structural and electronic properties. This dual functionality of cobalt-rich vacancy Co3O4 not only underscores its potential as a highly efficient photocatalyst for NRR and an electrocatalyst for NO3-RR but also highlights the intricate interplay between defect engineering, microstructural tuning, and electronic structure in promoting diverse catalytic activities. Our findings not only advance the fundamental understanding of defect-induced enhancements but also pave the way for the rational design of multifunctional catalysts capable of excelling in both photo- and electro-catalytic applications.

Photocatalytic Nitrogen Fixation Coupled with the Generation of Value-Added Chemicals from N2 and Cellulose over MoO3 Nanosheets.

Photocatalytic nitrogen fixation from N2 provides an alternative strategy for ammonia (NH3) production, but it was limited by the consumption of a sacrificial electron donor for the currently reported half-reaction system. Here, we use naturally abundant and renewable cellulose as the sacrificial reagent for photocatalytic nitrogen fixation over oxygen-vacancy-modified MoO3 nanosheets as the photocatalyst. In this smartly designed photocatalytic system, the photooxidation of cellulose not only generates value-added chemicals but also provides electrons for the N2 reduction reaction and results in the production of NH3 with a maximum rate of 68 μmol·h-1·g-1. Also, the oxygen vacancies provide efficient active sites for both cellulose oxygenolysis and nitrogen fixation reactions. This work represents useful inspiration for realizing nitrogen fixation coupled with the generation of value-added chemicals from N2 and cellulose through a photocatalysis strategy.

Boosting photocatalytic nitrogen fixation over Ni/Fe co-doped BiOBr in pure water under the synergistic effect of enhanced internal electric field and oxygen vacancies

To improve energy and environmental problems, the green and energy-saving photocatalytic ammonia synthesis reaction has received extensive research. The production of photocatalysts that possess high electron-hole separation rates has become an urgent problem. In this paper, we successfully synthesized Ni/Fe bimetallic co-doped nanoflower-like BiOBr materials enriched with oxygen vacancies through a simple one-step hydrothermal strategy. The effects of the introduction of transition metals Ni and Fe on the photocatalytic performance of BiOBr were examined using a variety of test methods. The findings demonstrated that Ni/Fe doping induced BiOBr lattice distortion and enhanced the internal electric field (IEF) and oxygen vacancy (OV) concentration of BiOBr. Furthermore, the Fe3+/Fe2+ redox pathway can be utilized as a photocatalytic active site to improve charge aggregation and accelerate the reaction process. The metal doping and vacancy defects assist in the adsorption and activation of nitrogen, synergistically promoting the photocatalytic performance of BiOBr. In purified water without any organic scavengers, the Ni/Fe-BiOBr exhibiting optimal nitrogen fixation efficiency generated a production of ammonia of 433.8 μmol g−1 h−1, which surpasses the unmodified BiOBr by about 5.7 times. This paper offers new perspectives into how extremely effective photocatalysts for nitrogen fixation might be developed in the future.

Synergistic effect of bimetallic active sites on Ce doped NH2–MIL-125 for promoting photocatalytic conversion of nitrogen to NH3

Ammonia (NH3), one of the most abundant inorganic compounds in the world, is highly demanded in the international market. NH3 is mainly synthesized using Haber-Bosch technology, which severely pollutes the environment and consumes high quantities of energy. In this study, a series of Ce doped NH2–MIL-125 (Ce–NH2–MIL-125) was prepared using a one-step solvothermal method to assess the activity of photocatalytic nitrogen fixation. The applied light energy interval of Ce–NH2–MIL-125 was widened, and the establishment of a Ce–O–Ti chemical bond optimized the transport path of the photogenerated carriers. This excellent photoelectric performance represents a significant improvement in the separation capacity of the photogenerated electrons and holes in Ce–NH2–MIL-125. Doping with Ce resulted in the generation of dual active sites, Ti4+/Ti3+ and Ce4+/Ce3+, in NH2–MIL-125; additionally, the increase in the amount of Ti3+ was significantly higher than that of the initial NH2–MIL-125. The synergistic effect of the bimetallic active sites in Ce–NH2–MIL-125 accelerated the photocatalytic nitrogen fixation reaction. Under full spectrum radiation, the ammonia generation rate of NH2–MIL-125 was 10.6 µmol g−1 h−1. Ce–NH2–MIL-125–1.0 exhibited the highest capacity for nitrogen fixation; the highest ammonia formation rate was 39.4 µmol g−1 h−1. The photocatalytic activity of Ce–NH2–MIL-125–1.0 was 3.7 times higher than that of NH2–MIL-125. This study provides a reference for catalytic research on modified NH2–MIL-125.

Efficient photocatalytic nitrogen fixation via oxygen vacancies in Zr-MOFs at ambient conditions

Photocatalytic nitrogen fixation is seen to be a potential technology for nitrogen reduction due to its eco-friendliness, low energy consumption, and environmental protection. In this study, photocatalysts with abundant oxygen vacancies (Zr-naphthalene dicarboxylic acid (Zr-NDC) and Zr-phthalic acid (Zr-BDC)) were designed using 1,4-naphthalene dicarboxylic acid (H2NDC) and 1,4-phthalic acid (H2BDC) as ligands. Since the structure of H2NDC includes one extra benzene ring than H2BDC, the charge density differential of the organic ligand is probably altered. The hypothesis is proved by density function theory (DFT) calculation. The abundant oxygen vacancies of the catalyst offer numerous active sites for nitrogen fixation. Concurrently, the process of ligand–metal charge transfer facilitates photo-electron transfer, creating an active center for nitrogen reduction. Additionally, the functionalization of ligand amplifies another pathway for charge transfer, broadening the light absorption range of Metal-organic framework (MOF) and increasing its capacity for nitrogen reduction. In contrast to H2BDC, the benzene ring added in H2NDC structure acts as an electron energy storage tank with a stronger electron density difference favorable for photogenerated electron-hole separation resulting in higher photocatalytic activity in Zr-NDC. The experimental results show that the nitrogen fixation efficiency of Zr-NDC is 163.7 µmol g−1h−1, which is significantly better than that of Zr-BDC (29.3 µmol g−1h−1). This work utilizes cost-effective and non-toxic ingredients to design highly efficient photocatalysts, thereby significantly contributing to the practical implementation of green chemistry principles.

Experimental Protocols for Sustainable Ammonia Production by Photocatalytic Nitrogen Fixation: Pitfalls and Remedial Measures

AbstractThe synthesis of ammonia (NH3) by photocatalytic nitrogen (N2) fixation has gained tremendous attention from researchers worldwide. The number of reports on different materials for photocatalytic N2 fixation is increasing year by year in the quest for developing breakthrough and sustainable photocatalysts in this field. However, there are several pitfalls (nitrogenous impurities in feed gas and on the surface of the catalyst, reaction conditions, use of scavengers, NH3 quantification methods, etc.) in the path of photocatalytic N2 fixation experiments, which can lead to the reporting of bogus NH3 production rates. Therefore, the use of accurate experimental protocols for the quantification of photogenerated NH3 requires immediate attention and focus of the researchers so that reliable data can be reported in the literature. This perspective article mainly focuses on generating awareness in the photocatalytic N2 fixation research community about the recent establishments for reporting experimental results in this field. Several pitfalls that may lead to the wrong data reporting and remedial measures to avoid them are discussed in detail. Finally, a summary of the recent advancements in this field and recommendations on future directions is provided.

Cerium-based metal-organic framework-modified natural mineral vermiculite for photocatalytic nitrogen fixation under visible-light irradiation

Cerium-based metal-organic framework-modified natural mineral vermiculite for photocatalytic nitrogen fixation under visible-light irradiation

Synergistic effects of MoFe bimetallic carbon dots for enhanced photocatalytic nitrogen fixation

The fixation of nitrogen to ammonia by photocatalysis displays great prospects. To this end, designing efficient catalysts is vital. As a type of graphitic carbon nitride, g-C3N5 is rich in N atoms, which endows it with a superior energy band structure. To compensate for the lack of active sites and the fast recombination of photogenerated carriers, we constructed MoFe bimetallic carbon dots loaded g-C3N5, with an NH3 yield of 812.9 μmol h−1 gcat−1. The introduction of metal carbon dots facilitates charge transfer. Through further study, it was found that Fe sites are mainly responsible for activating nitrogen, while Mo sites tend to split water to produce protons. Bimetallic carbon dots showed a synergistic effect on the enhancement of nitrogen fixation performance. This work offers some insights for the construction of efficient nitrogen fixation catalysts with novel carbon dots types of active centers.

Recent Advances in Application of 1D Nanomaterials for Photocatalytic Nitrogen Fixation

Ammonia, as the second most-produced chemical worldwide, serves diverse roles in the industrial and agricultural sectors. However, its conventional production via the Haber–Bosch process poses significant challenges, including high energy consumption and carbon dioxide emissions. In contrast, photocatalytic nitrogen (N2) fixation, utilizing solar energy with minimal emissions, offers a promising method for sustainable ammonia synthesis. Despite ongoing efforts, photocatalytic nitrogen fixation catalysts continue to encounter challenges such as inadequate N2 adsorption, limited light absorption, and rapid photocarrier recombination. This review explores how the electronic structure and surface characteristics of one-dimensional nanomaterials could mitigate these challenges, making them promising photocatalysts for N2 fixation. The review delves into the underlying photocatalytic mechanisms of nitrogen fixation and various synthesis methods for one-dimensional nanomaterials. Additionally, it highlights the role of the high surface area of one-dimensional nanomaterials in enhancing photocatalytic performance. A comparative analysis of the photocatalytic nitrogen fixation capabilities of different one-dimensional nanomaterials is provided. Lastly, the review offers insights into potential future advancements in photocatalytic nitrogen fixation.

Enhanced Visible Light Photocatalytic Activity of Exfoliated Boron‐TiO2 Composite for Degradation of Rhodamine B and Nitrogen Fixation

AbstractThe design of an efficient, recyclable, visible light photocatalytic system was examined as a viable new green way to address environmental challenges such as removal of pollutants from wastewater and N2 fixation. The exfoliated boron (Bexf)‐Titanium oxide (TiO2) composite visible light active photocatalysts were successfully constructed via a simple wet chemical method by utilizing acetone as a solvent. The composite was evaluated for the photodegradation of Rhodamine B (RhB) dye and reduction of N2, which exhibits improved photocatalytic activity for degradation of RhB as well as for reduction of N2. Experiments with different quenchers indicate that the photogenerated superoxide radical anion (O2⋅−) plays a significant role in the degradation of RhB as well as for N2 reduction reactions. The composite catalyst shows good photostability and there is no significant reduction of the catalyst activity for dye degradation up to 4 cycles of reaction. This work affords a significant view into the design of reusable TiO2 composite materials for photocatalytic RhB degradation and nitrogen fixation.

Incorporation of Cu5FeS4 QDs with Abundant Oxygen Vacancy TiO2 QDs/TiO2 OVs: Double S-Scheme Photocatalysts for Effectual N2 Conversion to NH3 under Simulated Solar Light.

Photocatalytic N2 conversion to NH3 is a green, sustainable pathway with renewable energy sources and carbon neutrality. In this research, ternary TiO2 QDs/TiO2 OVs/Cu5FeS4 nanocomposites were prepared by an easy and affordable procedure and utilized to produce clean ammonia energy without a sacrificial agent. The amount of produced green ammonia by the optimum nanocomposite achieved was 17,274 μmol L-1 g-1, which was approximately 20.9, 6.48, 4.45, 2.26, and 1.45 times higher than those of commercial TiO2, TiO2 QDs, TiO2 OVs, Cu5FeS4, and TiO2 QDs/TiO2 OVs photocatalysts, respectively. Lattice compatibility through the developed homojunction within TiO2 QDs/TiO2 OVs and the integration of Cu5FeS4 nanoparticles led to the establishment of a double S-scheme homo/heterojunction system, which improved the photocatalytic activity by maintaining electrons and holes with high oxidation and reduction power and greatly reduced the recombination of charges, which led to the acceleration of charge transfer and migration. Besides, the promoted surface area compared to the pure components, introducing oxygen vacancies, and reducing the particle size boosted the photocatalytic N2 conversion to NH3. The results of this research are a basis for the rational design of homojunction/heterojunction visible-light-responsive systems for photocatalytic nitrogen fixation reactions.

Promoting nitrogen photofixation for the synthesis of ammonia using oxygen-vacant Fe2O3/ZrO2 visible light photocatalyst with straddling heterojunction and enhanced charge transfer

Photocatalytic nitrogen (N2) fixation is a promising and environmentally friendly alternative approach to the energy-intensive Haber-Bosch process to produce green ammonia (NH3) with zero carbon emissions. However, the unique setbacks rest on developing an active photocatalyst with an accelerated charge transfer that could efficiently adsorb and activate the chemically inert N2 into useful NH3. Herein, an oxygen-vacant Fe2O3/ZrO2 photocatalyst with straddling heterojunction was successfully synthesised by the hydrothermal method followed by calcination at 450 °C. The addition of oxygen vacancy-inducing ferromagnetic material on ZrO2 increased the adsorption and activation of N2, broadened the solar absorption window (680 nm extending to 910 nm). It also accelerated light-induced charge separation of the photocatalyst thereby greatly enhancing the production of NH3 (1.301 mmol h−1 g−1) with about a 7-fold increase in comparison to ZrO2 at ambient conditions under sunlight irradiation. This work therefore sheds light on the effect of oxygen vacancies and the flow of charge carriers in the effective photofixation of N2 to NH3 synthesis through a sustainable route.