Nitrogen Fixation Performance Research Articles

Boosting photocatalytic nitrogen fixation performance by adjusting the intramolecular D-A structure and band gap of thiophene-based COFs

Herein, we successfully synthesized two photoactive donor–acceptor (D-A) covalent organic frameworks by incorporating electric-deficient triazine and electric-rich benzotrithiophene moieties into the framework. The introduction of sulfur atom and triazine unit significantly change the intrinsic band gap of JLNU-COFs, this leads to an expanded range of light absorption, encompassing wavelengths from ultraviolet to visible. The narrow band gap of JLNU-311 allows for efficient utilization of visible light while maintaining the thermodynamic activity required for nitrogen reduction within appropriate energy bands. JLNU-311 modified with strong electron absorbing groups has higher activity to NH3 production without co-catalyst or sacrificial agent, and yield can reach 325.6 µmol/g/h. Theoretical calculation further confirm that acceptor structure can effectively regulate the band gap width, promote the adsorption, dissociation and protonation of N2 molecules on JLNU-COFs, and thus reduce the energy barrier of photocatalytic nitrogen reduction reaction (PNRR). Therefore, this study provides an effective strategy for design of active nitrogen fixing photocatalysts.

Facile method for creating frustrated Lewis pairs in g-C3N4 to enhance photocatalytic nitrogen fixation performance

Facile method for creating frustrated Lewis pairs in g-C3N4 to enhance photocatalytic nitrogen fixation performance

Strategy of constructing D-A structure and accurate active sites over graphitic carbon nitride nanowires for high efficient photocatalytic nitrogen fixation

Constructing photocatalysts for the stable and efficient production of NH3 is of excellent research significance and challenging. In this paper, the electron acceptor 5-amino-1,10-phenanthroline (AP) is introduced into the electron-donor graphitic carbon nitride (CN) framework by a simple heated copolymerization method to construct a donor–acceptor (D-A) structure. Subsequently, the phenanthroline unit is coordinated with transition metal Fe3+ ions to obtain the photocatalyst Fe(III)-0.5-AP-CN with better nitrogen fixation performance, and the average NH3 yield can reach 825.3 μmol g−1 h−1. Comprehensive experimental results and theoretical calculations show that the presence of the D-A structure can induce intramolecular charge transfer, effectively separating photogenerated electrons and holes. The Fe active sites can improve the chemisorption energy for N2, enhance the N-Fe bonding, and better activate the N2 molecule. Therefore, the synergistic effect between the construction of the D-A structure and the stably dispersed Fe active sites can enable CN to achieve high-performance N2 reduction to produce NH3.

Solar-driven photocatalytic nitrogen fixation on transition metal-doped covalent organic frameworks: First-principles study

Designing highly efficient single-atom catalysts for converting nitrogen into ammonia under ambient temperature conditions holds significant importance. Current research predominantly focuses on electrocatalytic nitrogen fixation, but compared to that, photocatalytic nitrogen fixation requires only sunlight as an energy source, making it more environmentally friendly and cost-effective. Developing efficient nitrogen reduction reaction (NRR) photocatalysts presents a promising yet highly challenging task. Two-dimensional (2D) covalent organic frameworks (COFs) have garnered interest because of their elevated surface area and regular pore structure. This study employs density functional theory calculations to investigate the potential of NRR photocatalysts using the 2D COF TMT-TFPT-COF (TT-COF) supported with 18 different transition metal atoms (TM = Rh, Nb, Os, Mo, Ru, Pt, Ni, Co, V, Cu, Fe, Re, W, Cr, Ta, Mn, Pd, Ti). Through a four-step selection process, the most promising photocatalyst is identified. The results indicate that a single Re atom loaded onto TT-COF (Re@TT-COF) displays the optimal nitrogen fixation performance, demonstrating excellent catalytic activity and selectivity with a limiting potential of only −0.30 V. Furthermore, its good light absorption efficiency, suitable band edge position, and significant photo-generated electron potential enable spontaneous nitrogen fixation. Our study provides useful guidance for the rational design of COF-based NRR photocatalysts with high activity, stability, and selectivity.

Synthesis and characterization of Ag/Cu dual-metal-functionalized porous Bi2WO6 microsphere with enhanced N2 photofixation

Semiconductor photocatalytic nitrogen reduction reaction (PNRR) stands as a promising clean technique for ammonia synthesis, yet it confronts numerous challenges. In this study, Ag nanoparticle-modified Cu-doped Bi2WO6 (ACB) porous composite materials with varying mass percentages were successfully synthesized using a solvothermal reduction approach. The incorporation of transition metal Cu effectively modulates the energy band position of Bi2WO6. Furthermore, the introduction of Ag nanoparticles significantly suppresses the recombination of photogenerated carriers. Without adding sacrificial agent, the photocatalytic nitrogen fixation yield of ACB reaches an impressive 184.93 μmol·g−1·h−1, which is 5.44 times higher than that of pristine Bi2WO6. A comprehensive analysis of the experimental results reveals that the combined effect of Cu doping and Ag nanoparticle loading endows ACB with an increased exposure of active sites, thereby significantly enhancing its photocatalytic nitrogen fixation performance. This research offers a promising approach for the design of metal nanoparticle-supported catalysts for PNRR, holding significant implications for the advancement of other material systems.

In-situ Cu mesh growth of reusable OVs-WO3/CuO heterojunction photocatalysts for enhanced nitrogen fixation efficiency

The loaded photocatalyst is an ideal material for nitrogen fixation, which does not have the problem of secondary pollution caused by powdered catalysts, and has the advantages of uniform distribution, high efficiency and easy recovery. In this paper, CuO and WO3 were grown on copper mesh (CM) by in-situ etching and solvothermal method. The photogenerated carriers and light absorption properties were synergistically promoted with the help of oxygen vacancies and S-type heterojunctions. Under simulated visible-light conditions, a liquid-membrane type reaction was employed and the nitrogen fixation performance was significantly improved. The optimal ammonia production rate of WO3/CuO/CM was 3.878 × 10−2 μmol/cm2/h, which was 9.37 and 5.16 times higher than WO3/CM and CuO/CM, respectively. This study provides ideas for the design of recyclable heterojunction catalysts with oxygen vacancies.

Sustainable nitrogen fixation by bubble discharge plasma: Performance optimization and mechanism

Sustainable nitrogen fixation driven by renewable energy sources under mild conditions has been widely sought to replace the industrial Haber-Bosch process. The fixation of nitrogen in the form of NOx− and NH4+ into aqueous solutions using electricity-driven gas–liquid discharge plasma is considered a promising prescription. In this paper, a scalable bubble discharge excited by nanosecond pulse power is employed for nitrogen fixation in the liquid phase. The nitrogen fixation performance and the mechanisms are analyzed by varying the power supply parameters, working gas flow rate and composition. The results show that an increase in voltage and frequency can result in an enhanced NO3− yield. Increases in the gas flow rate can result in inadequate activation of the working gas, which together with more inefficient mass transfer efficiencies can reduce the yield. The addition of O2 effectively elevates NO3− production while simultaneously inhibiting NH4+ production. The addition of H2O vapor increases the production of OH and H, thereby promoting the generation of reactive nitrogen and enhancing the yield of nitrogen fixation. However, the excessive addition of O2 and H2O vapor results in negative effect on the yield of nitrogen fixation, due to the significant weakening of the discharge intensity. The optimal nitrogen fixation yield was up to 16.5 μmol/min, while the optimal energy consumption was approximately 21.3 MJ/mol in this study. Finally, the mechanism related to nitrogen fixation is discussed through the optical emission spectral (OES) information in conjunction with the simulation of energy loss paths in the plasma by BOLSIG + . The work advances knowledge of the effect of parameter variations on nitrogen fixation by gas–liquid discharge for higher yield and energy production.

Synthesis and photocatalytic properties of polyaniline modified cadmium-manganese sulfide materials

In the present paper, polyaniline modification of Mn0.5Cd0.5S composite (PANI/MCS) was fabricated by a simple electrostatic adsorption method. The introduction of PANI makes PANI/MCS composites have better visible light absorption and higher photogenerated carrier segregation efficiency, thus showing better photocatalytic performance. The results show that the 50-PANI/MCS photocatalyst has the best hydrogen production capacity, which was 2.2 times greater than neat MCS. Meanwhile, the nitrogen fixation performance of the best sample 50-PANI/MCS was 4.93 times that of pure MCS. After that, a reasonable reaction mechanism was obtained through various characterization data. A cheap and readily available composite photocatalyst has been synthesized. This paper has good reference value in the area of development of efficient composite photocatalyst.

Synthesis of VO‐TiO2/VC‐g‐C3N4 Heterojunction for Improving the Photocatalytic Activity by Introducing Defect Sites

AbstractDefect engineering is a proven strategy for enhancing the performance of photocatalysts. Herein, we present a new method for preparing heterojunction photocatalytic materials, VO‐TiO2/VC‐g‐C3N4, with enhanced activity. The presence of defect sites and a heterojunction structure in the catalyst gives rise to exceptional charge separation efficiency and light absorption capabilities. The synergistic effect of the heterojunction interface and activated defect sites, which act as active sites, significantly enhanced the overall photocatalytic performance of VO‐TiO2/VC‐g‐C3N4. The catalyst VO‐TiO2/VC‐g‐C3N4 exhibits superior photocatalytic activity in the NO degradation reaction: displaying 3.5‐ and 2.2 times higher degradation efficiency than VO‐TiO2 and VC‐g‐C3N4, respectively. Moreover, the nitrogen fixation performance of VO‐TiO2/VC‐g‐C3N4 is 3.8‐ and 3.1 times higher than that of VO‐TiO2 and VC‐g‐C3N4, respectively. Electron paramagnetic resonance (EPR) spectroscopy capture experiments revealed that 1O2 and ⋅ OH are the primary active species in the photocatalytic reaction. The collaboration of carbon vacancy defects, oxygen vacancy defects, and the heterojunction structure created additional active sites for VO‐TiO2/VC‐g‐C3N4. The insights gained from this study offer valuable guidance for the efficient design and synthesis of VO‐TiO2/VC‐g‐C3N4 heterojunction photocatalysts, and lay a solid foundation for further research and development of such systems for large‐scale environmental remediation.

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.

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.

General corrosion endowed by electrolyte engineering enhancing Lithium-Mediated nitrogen fixation

Lithium-mediated ammonia electrochemical synthesis (LMAES) holds promise for approximating and superseding the capacity of Haber-Bosch technology. However, currently used tetrahydrofuran electrolyte in such system hinders the further enhancement of nitrogen fixation performance greatly due to the over-passivation of the reaction interface suppressing the corrosion rate of the active species on metallic lithium. Here, we develop a remarkably 1,2-diethoxyethane (DEE) electrolyte to enhance the performance of LMAES. Systematic simulations combined with experimental results jointly elucidate that the unique Li+ solvation environment in DEE electrolyte significantly weakens the passivation of the electrode interface and triggers the general corrosion behavior of active species to electrodeposited lithium. Compared with conventional tetrahydrofuran electrolyte, this DEE electrolyte brings nearly twice the improvement of Faradaic efficiency (from 33.4 % to 61.7 %). This work offers a progressive insight into advanced electrolyte designs for LMAES.

Directional design of the pyridine ligand functional block fine-tuned hydrophobicity to improve the electrocatalytic nitrogen fixation performance of the Co/Ni based MOFs-derived materials

A series of isostructural Co/Ni-MOFs with different linearly bridged bipyridines as organic linkers has been designed and synthesized. Experimental studies reveal that linker engineering by tuning the functional block of the pyridine-bridging units renders these MOFs derived materials with significantly improved electrocatalytic nitrogen reduction reactions (eNRR) to NH3. Among them, at −0.4 V vs reversible hydrogen electrode the one containing a 1,3,4-thiadiazole unit exhibits the best eNRR performance in 0.1 M Na2SO4 with the highest NH3 yield (39.7 μg h−1 mg−1) and Faraday efficiency (33.3 %). This excellent nitrogen fixation performance comes from the synergistic effect of the heterojunction formed by the Co2N component that is conducive to nitrogen fixation and the Co9S8 component that inhibits hydrogen evolution in the derived material. Significantly, the systematic tuning of the bridging ligands in MOFs provides a new pathway to develop eNRR electrocatalysts.

Effective 1D/2D nanostructured S-scheme W18O49/g-C3N4 heterojunction photocatalyst fabrication for improved photocatalytic nitrogen fixation performance

The fundamental insights into the reaction mechanism, especially the electron transfer mechanism, are highly promising yet challenging for W18O49/g-C3N4 heterojunction catalysts during photocatalytic nitrogen fixation. Herein, the 1D/2D nanostructured S-scheme heterojunctions were designed by in situ growth of 1D W18O49 nanowires on 2D g-C3N4 nanosheets through solvothermal method using methanol as solvent. In situ XPS analysis revealed that electrons in the conduction band of W18O49 recombine with holes in the valence band of g-C3N4 under the conduction effect of internal electric field, band bending, and Coulombic attraction in the W18O49/g-C3N4 heterojunction. The photogenerated electrons are retained in g-C3N4, where the negative reduction potential of its conduction band enhances the activation of N2. As a result, the ammonia generation rate employing the optimal W18O49/g-C3N4 heterojunction is 64.8 μmol gcat−1 h−1, approximately double that of W18O49 alone and 2.3 times higher than that of g-C3N4. The enhanced activity and facile methodology make the current material exceedingly appealing for implementation in photocatalytic nitrogen fixation for the synthesis of ammonia.

Enhanced photocatalytic nitrogen fixation performance via in situ constructing BiO2–x/NaNbO3 heterojunction

The fabrication of heterojunction catalysts is an effective strategy to enhance charge separation efficiency, thereby boosting the performance of photocatalysts. In this study, BiO2–x nanosheets were synthesized through a hydrothermal process and loaded onto NaNbO3 microcube to construct a series of BiO2–x/NaNbO3 heterojunctions for photocatalytic N2 fixation. Results indicated that 2.5% BiO2–x/NaNbO3 had the highest photocatalytic performance. The NH3 production rate under simulated solar light reached 406.4 μmol·L−1·g−1·h−1, which reaches 2.6 and 3.8 times that of NaNbO3 and BiO2–x, respectively. BiO2–x nanosheets primarily act as electron trappers to enhance the separation efficiency of charge carriers. The strong interaction between BiO2–x and NaNbO3 facilitate the electron migration between them. Meanwhile, the abundant oxygen vacancies in BiO2–x nanosheets may facilitate the adsorption and activation of N2, which may be another possible reason of the high photocatalytic activity of the BiO2–x/NaNbO3. This study may offer new insights for the development of semiconductor materials in photocatalytic nitrogen fixation.

Methane sulfonic acid-assisted synthesis of g-C3N4/Ni2P/Ni foam: Efficient, stable and recyclable for photocatalytic nitrogen fixation under visible light

Photocatalytic nitrogen fixation is of great significance for solving the energy crisis and healthy development of the environment. However, photocatalysts have problems such as low activity, poor stability and difficult recovery, which seriously limit their application. Herein, we in situ synthesized g-C3N4/Ni2P/Ni three-dimensional reticulated foam photocatalysts (CNNPF) with excellent photocatalytic nitrogen fixation performance under visible light by a two-step methane sulfonic acid-assisted carbon nitride loading-calcined phosphatisation method, using nickel foam as the carrier and raw material. The results showed that the CNNPF had a stable three-dimensional network structure, and g-C3N4 was stably immobilized to the nickel foam skeleton with Ni2P. The best performance of CNNPF with ultrasonication for 2 h and phosphatisation for 1 h showed a high photocatalytic nitrogen fixation efficiency of up to 373 μmol·h−1·g−1, which was attributed to the Ni2P co-catalyst modification of g-C3N4 that led to the improvement of photogenerated electron-hole pair separation efficiency. Meanwhile, the three-dimensional network structure is favorable to provide more active sites for N2 adsorption and activation. In addition, the prepared material also has good stability and recyclability, and its nitrogen fixation efficiency was still maintained at 350 μmol·h−1·g−1 after five cycles. The present work provides a direction for the design of efficient and recyclable photocatalytic systems that show great potential in the field of economically sustainable nitrogen fixation.

In-MOF derived In2S3-X@ZnS heterojunction with rich sulfur vacancies for enhanced performance in photocatalytic nitrogen fixation

Photocatalytic nitrogen fixation has the characteristics of green, energy-saving and environment-friendly. Herein, the hollow microtube-flower In2S3-X@ZnS with rich sulfur vacancies was synthesized by the one-step solvothermal method of sulfurization from the precursor MIL-68(In). In-MOF derived sulfur-vacancy modulation and the construction of the In2S3-X@ZnS heterojunction had been proved to be the desirable strategies to dramatically enhance the ammonia production rate. One the one hand, the characterizations of HRTEM, ESR and the transient photocurrent responses (TPR) in N2, Air and Ar saturated solution directly and indirectly proved the existence of rich sulfur-vacancy, which could be the active sites for the chemisorption and activation of N2. On the other hand, the results of EIS, PL and band analysis demonstrated that the established Type-п heterojunction promoted the photogenerated carriers to separate and clarified the enhanced photocatalytic mechanism, the corresponding nitrogen fixation performance had been greatly improved with a high yield rate of 58.988 µmol∙gcat−1∙h−1, which was evidently much higher than that of pristine In2S3-X and pure ZnS. This work provided a new insight for developing functional photocatalysts with the synergy effect of sulfur-vacancy and heterojunction for highly efficient nitrogen fixation.

Construction of a direct Z-scheme Mn0.5Cd0.5S/CoTiO3 heterojunction with enhanced photocatalytic nitrogen fixation performance

The exploration and design of highly efficient and robust photocatalysts composed of earth-abundant materials for ambient photocatalytic N2 fixation to ammonia remains a significant challenge. Here, we have fabricated a stable and highly efficient direct Z-scheme Mn0.5Cd0.5S/CoTiO3 heterostructure for N2 fixation by depositing Mn0.5Cd0.5S nanoparticles on CoTiO3 surface. Under ambient conditions, the optimized Mn0.5Cd0.5S/CoTiO3 heterojunction achieved a significant NH3 production rate of 121.9 μmol g-1h−1 without cocatalyst modification, representing a 5.1- and 5.9-fold increase over pristine Mn0.5Cd0.5S and CoTiO3, respectively, and also exceeding most previously reported photocatalytic systems. The significant improvement in ammonia production primarily results from the Z-scheme charge transfer path between the Mn0.5Cd0.5S and CoTiO3 components, which enables effective separation of photoinduced carriers while maintaining their robust redox capacity, thus dramatically boosting ammonia generation performance. This research may provide new insights for advancing other alternative Z-scheme photocatalytic systems with remarkable stability and exceptional efficiency in N2 fixation.