N2 Fixation Research Articles

Rhizobium acaciae and R. anhuiense are the dominant rhizobial symbionts of Pisum sativum L. from Yunnan-Guizhou Plateau.

The aim of this study is to investigate the diversity and geographic distribution of pea-nodulating rhizobia in the subtropical region of Yunnan Province from Yunnan-Guizhou Plateau. A total of 615 rhizobial isolates were obtained from root nodules of the trapping plants and characterized genetically and symbiotically. The isolates discriminated into 43 genotypes by PCR-RFLP of IGS DNA. Multiple locus sequence analysis based on 16S rRNA, recA, atpD, dnaK, and rpoB genes placed them into eight clusters corresponding to species R. acaciae, R. anhuiense, R. binae, R. bangladeshense, R. hidalgonense, and three suspected novel populations of Rhizobium genosp. I-III. R. acaciae was the dominant group (52.5%) followed by R. anhuiense (30.7%). The other species were minor groups. Based on nodC phylogeny, all of them were the symbiovar viciae. All the tested strains showed efficient symbiotic N2 fixation on pea plants, in which WLB27, WCB18, and WNY29 presented the best PGP effects. Some of the tested strains had better IAA production, with WCB18 as the best producer (64.556 mg/L). Their distribution was mainly affected by soil available phosphorus, available potassium, and effective nitrogen. According to the results of symbiotic effect and resistance tests, strains of WLB27, WCB18, and WNY29 were selected as candidates for creating inoculants. This suggests that the pea-nodulating rhizobia in Yunnan Province form a unique community. The results gave some novel information about the diversity, diversification, and biogeography of pea-nodulating rhizobia.

Nitrogen fixation by alkali and alkaline earth metal hydrides assisted by plasma.

The chemical behaviors of alkali and alkaline earth metal hydrides including LiH, KH, MgH2, CaH2, and BaH2 under nitrogen plasma differ significantly from one another, exhibiting an ammonia production trend that contrasts with that observed under thermal conditions. A prominent feature of KH is its ability to facilitate plasma-assisted N2 fixation without generating H2 byproduct, showing high atomic economy in utilization of hydride ions for N2 reduction.

A bioinspired sulfur-surrounded iron catalyst for ammonia synthesis

A nitrogenase-inspired inorganic compound consisting of iron (Fe) and molybdenum disulfide (MoS2) is designed with a promising capability of N2 fixation using first principles.

N-doped Ti3C2-reinforced porous g-C3N4 for photocatalytic contaminants degradation and nitrogen reduction.

Herein, a series of N-doped Ti3C2/porous g-C3N4 composites are ultrasonically prepared from N-doped Ti3C2 and porous g-C3N4 under N2 atmosphere. The structure, morphology, and optical characteristics of the as-prepared composites are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, etc. Moreover, photocatalytic measurements show that N-doped Ti3C2 is an excellent modifier for porous g-C3N4 to heighten its photocatalytic activity. Only 44.1% of rhodamine B can be degraded by the photocatalysis of pristine porous g-C3N4, while the photocatalytic degradation ratio of rhodamine B can reach up to 97.5% for the optimal N-doped Ti3C2 loading composites under visible light for 15 min. Moreover, the photocatalytic tests of N2 fixation confirm that the optimal composites show the highest production yield of NH4+ (11.8 μmol gcat-1 h-1), which is 2.11-folds more than that of porous g-C3N4 (5.6 μmol gcat-1 h-1). The reinforced photocatalytic properties are revealed to profit from the more photogenerated electrons and holes' separation, higher ability for light response, and more abundant active sites. This work develops the route for boosting the photocatalytic properties of porous g-C3N4 with N-doped Ti3C2.

Nitrogen Fixation and Yield of Common Bean Varieties in Response to Shade and Inoculation of Common Bean

Light is not only a primary energy source, but it is also one of the environmental factors that affect plant growth and development. Common bean (Phaseolus vulgaris L.) is commonly produced in association with maize as subordinate intercrops in the Sidama region. Under such a production system, the shade effect may limit the photosynthetic and nitrogen-fixing capacity of common beans. The objective of the current study was to assess how inoculation and shade affect the ability to fix nitrogen and yield components of common beans. Three common bean varieties (Hawassa dume, Nassir, and Ibbado), two shade levels (open and 25% shade) as well as two levels of inoculation (uninoculated and inoculated) were used for these purposes. The experiment was set up in factorial randomized complete block design (RCBD) in four replications. In this experiment, Rhizobium inoculation and shade significantly (p < 0.05) affected the number of pods plant-1 and the number of seeds pod-1. The inoculated treatment produced the maximum number of pods plant-1 (14.02) and the lowest number of pods plant-1 (10.95) was obtained from uninoculated treatments. The results also showed that the inoculated Hawassa dume variety from the open treatments derived the maximum percentage of N from N2 fixation, whereas the non-inoculated Ibbado variety from the 25% shade treatments derived the lowest percentage of N. Common bean grown on full light had significantly greater N content than shade.

Double metals sites synergistically enhanced photocatalytic N2 fixation performance over Bi24O31Br10@Bi/Ti3C2Tx Ohm junctions

At present, it is a research hotspot to realize green synthetic ammonia by using solar energy. Exploring cheap and efficient co-catalysts for enhancing the performance of photocatalysts is a challenge in the field of energy conversion. In order to boost the charge separation/transfer of the photocatalyst and widen the visible light absorption, Bi24O31Br10@Bi/Ti3C2Tx with double Ohm junction is successfully fabricated by in situ growth of metal Bi and loading Ti3C2Tx MXene on the surface of Bi24O31Br10. The dual active sites of Bi and Ti3C2Tx MXene not only broaden the light adsorption of Bi24O31Br10 but also serve as excellent ‘electronic receptor’ for synergically enhancing the separation/transfer efficiency of photogenerated electrons/holes. Meanwhile, temperature programmed desorption (TPD) result revealed that MXene and Bi can promote N2 adsorption/activation and NH3 desorption over Bi24O31Br10@Bi/Ti3C2Tx. As a result, under mild conditions and without the presence of hole scavenger, the ammonia synthesis efficiency of Bi24O31Br10@Bi/Ti3C2Tx-20 % reached 53.86 μmol g-1cat for three hours which is 3.2 and 53.8 times of Bi24O31Br10 and Ti3C2Tx, respectively. This study offers a novel scheme for the construction of photocatalytic systems and demonstrates Ti3C2Tx MXene and metal Bi as a promising and cheap co-catalyst.

Au Nanoparticle-Loaded UiO-66 Metal–Organic Framework for Efficient Photocatalytic N2 Fixation

In order to achieve efficient photocatalytic N2 reduction activity for ammonia synthesis, a photochemical strategy was used in this work. UiO-66 was prepared through the solvothermal method and further loaded with Au nanoparticles (Au NPs) onto the UiO-66 (Zr) framework. The experimental results verified that there were metal–support interactions between Au NPs and UiO-66; this could facilitate charge transfer among Au NPs and UiO-66, which was beneficial to enhance the photocatalytic activity. The best N2 fixation effect of Au/UiO-66 with a loading of 1.5 wt% was tested, with a photocatalytic yield of ammonia of 66.28 μmol g−1 h−1 while maintaining good stability. The present work provides a novel approach to enhancing photocatalytic N2 fixation activity by loading NPs onto UiO-66.

Proteome profiling of Paenibacillus sonchi genomovar Riograndensis SBR5T under conventional and alternative nitrogen fixation

Paenibacillus sonchi SBR5T is a Gram-positive, endospore-forming facultative aerobic diazotrophic bacterium that can fix nitrogen via an alternative Fe-only nitrogenase (AnfHDGK). In several bacteria, this alternative system is expressed under molybdenum (Mo)-limiting conditions when the conventional Mo-dependent nitrogenase (NifHDK) production is impaired. The regulatory mechanisms, metabolic processes, and cellular functions of N2 fixation by alternative and/or conventional systems are poorly understood in the Paenibacillus genus. We conducted a comparative proteomic profiling study of P. sonchi SBR5T grown under N2-fixing conditions with and without Mo supply through an LC-MS/MS and label-free quantification analysis to address this gap. Protein abundances revealed overrepresented processes related to anaerobiosis growth adaption, Fe-S cluster biosynthesis, ammonia assimilation, electron transfer, and sporulation under N2-fixing conditions compared to non-fixing control. Under Mo limitation, the Fe-only nitrogenase components were overrepresented together with the Mo-transporter system, while the dinitrogenase component (NifDK) of Mo‑nitrogenase was underrepresented. The dinitrogenase reductase component (NifH) and accessory proteins encoded by the nif operon had no significant differential expression, suggesting post-transcriptional regulation of nif gene products in this strain. Overall, this was the first comprehensive proteomic analysis of a diazotrophic strain from the Paenibacillaceae family, and it provided insights related to alternative N2-fixation by Fe-only nitrogenase. SignificanceIn this work, we try to understand how the alternative nitrogen fixation system, presented by some diazotrophic bacteria, works. For this, we used the SBR5 lineage of P. sonchi, which presents the alternative system in which the nitrogenase cofactor is composed only of iron. In addition, we tried to unravel the proteome of this strain in different situations of nitrogen fixation, since, for Gram-positive bacteria, these systems are little known. The results achieved, through LC-MS/MS and label-free quantitative analysis, showed an overrepresentation of proteins related to different processes involved with growth under stressful conditions in situations of nitrogen deficiency, in addition to suggesting that some encoded proteins by the nif operon may be regulated at post-transcriptional levels. Our findings represent important steps toward the elucidation of nitrogen fixation systems in Gram-positive diazotrophic bacteria.

Enhancing electrochemical N2 reduction at mild conditions with FexOy co-deposited on amorphous MoS2

Electrochemical reduction of N2 can lead to the clean and sustainable production of NH3 under environmental conditions. However, limited progress has been made as most catalysts lack efficient activity for N2 fixation. Here, we report FexOy co-deposited on amorphous MoS2 supported on a gas diffusion layer electrode (GDL) as an effective catalyst for N2 reduction. The catalysts were prepared by electrodeposition, a simple and low-cost method. Physical characterizations revealed the amorphous nature of MoS2 and while FexOy was evenly distributed over MoS2. In 0.1 M Na2SO4, GDL/MoS2-Fe-1 exhibited an NH3 yield of 7.38 µmol h−1 cm−2, a value almost 2 times greater than that obtained for MoS2/GDL and a faradaic efficiency of 54.9 % at ˗0.2 V vs. reversible hydrogen electrode (RHE) at 25 ℃. Also, the catalyst displayed high stability and durability, retaining almost 93 % of its original values after recycling tests. The amorphous MoS2-FexOy provides new insight into designing efficient and robust catalysts for nitrogen reduction.

(Invited) In Situ Characterization during Electrode Processing: The Role of Hidden Parameters

Micron and nano-sized functional materials play a key role for future technologies that are currently developed in the field of energy conversion (electrolysers, fuel cells) and electrocatalysis (N2 fixation, CO2 reduction reaction). While new materials with outstanding properties are continuously developed, they rarely find their way into – urgently needed – large scale production and industrial applications.1 One reason for this are hidden parameters that occur during ink formulation, coating (and decal transfer), cell assembly, and operation. We propose the development of coherent workflows that help us to identify reliable correlations. These should be developed for each electrocatalyst, bridging synthesis, electrode and gas diffusion electrode (GDE) / membrane electrode assembly (MEA) fabrication, and testing. All information, including “negative” results like crack formation, delamination, structural ageing and dissolution, must be reported until the relevant hidden parameters are deciphered, and the design chain is understood. Then, materials and electrodes derived from complementary processes and exhibiting subtle variations in composition and structure, can be evaluated against each other.However, this implies to fill the “blackbox” between technical catalysts and electrochemical testing in flow cells, GDEs or MEAs, with quantitative data on powders, ink formulations and coating properties. In the past years, we developed a toolbox of methods that starts from key control characteristics for technical catalysts, i.e., Pt/C for polymer electrolyte membrane fuel cells, that thereon enable the in situ analysis of ink formulations and pastes during the dispersion process and at application concentration.2,3 This is followed by the assessment of the resulting coatings from large-area crack analysis down to the level of surface roughness and pore size characteristics.4 Finally, this input is connected with performance and stability testing results to enable the comparison of different materials, the assessment of structure property relations, and ultimately to establish inline process control during electrode manufacturing. In this contribution, the developed methods will be summarized and related to their current limitations and prospects, in particular for unraveling hidden parameters during electrode fabrication and MEA assembly as well as in line process control. Literature [1] Siegmund, Daniel; Metz, Sebastian; Peinecke, Volker; Warner, Terence E.; Cremers, Carsten; Grevé, Anna; Smolinka, Tom; Segets, Doris; Apfel, Ulf-Peter; Crossing the Valley of Death : From Fundamental to Applied Research in Electrolysis, JACS Au 1 (2021), 527 – 535.[2] Bapat, Shalmali; Segets, Doris; Sedimentation Dynamics of Colloidal Formulations through Direct Visualization : Implications for Fuel Cell Catalyst Inks, ACS Applied Nano Materials 3 (2020), 7384 – 739.[3] Bapat, Shalmali; Giehl, Christopher; Kohsakowski, Sebastian; Peinecke, Volker; Schäffler, Michael; Segets, Doris; On the state and stability of fuel cell catalyst inks, Advanced Powder Technology 32 (2021), 3845 – 3859.[4] Jaster, Theresa; Albers, Simon; Leonhard, Armin; Kräenbring, Mena-Alexander; Lohmann, Heiko; Zeidler-Fandrich, Barbara; Özcan, Fatih; Segets, Doris; Apfel, Ulf-Peter; Enhancement of CO₂RR product formation on Cu-ZnO-based electrodes by varying ink formulation and post-treatment methods, JPhys Energy 5 (2023), 024001.

Contrasting potential for biological N2 fixation at three polluted central European Sphagnum peat bogs: combining the 15N2-tracer and natural-abundance isotope approaches

Abstract. Availability of reactive nitrogen (Nr) is a key control on carbon (C) sequestration in wetlands. To complement the metabolic demands of Sphagnum in pristine rain-fed bogs, diazotrophs supply additional Nr via biological nitrogen fixation (BNF). As breaking the triple bond of atmospheric N2 is energy-intensive, it is reasonable to assume that increasing inputs of pollutant Nr will lead to BNF downregulation. However, recent studies have also documented measurable BNF rates in Sphagnum-dominated bogs in polluted regions, indicating the adaptation of N2 fixers to changing N deposition. Our aim was to quantify BNF in high-elevation peatlands located in industrialized central Europe. A 15N2-tracer experiment was combined with a natural-abundance N-isotope study at three Sphagnum-dominated peat bogs in the northern Czech Republic in an attempt to assess the roles of individual BNF drivers. High short-term BNF rates (8.2 ± 4.6 g N m2 d−1) were observed at Malé mechové jezírko, which receives ∼ 17 kg Nr ha−1 yr−1. The remaining two peat bogs, whose recent atmospheric Nr inputs differed from Malé mechové jezírko by only 1–2 kg ha−1 yr−1 (Uhlír̆ská and Brumiště), showed zero BNF. The following parameters were investigated to elucidate the BNF difference: the NH4+-N / NO3--N ratio, temperature, wetness, Sphagnum species, organic-N availability, possible P limitation, possible molybdenum (Mo) limitation, SO42- deposition, and pH. At Malé mechové jezírko and Uhlír̆ská, the same moss species (S. girgensohnii) was used for the 15N2 experiment; therefore, the host identity could not explain the difference in BNF at these sites. Temperature and moisture were also identical in all incubations and could not explain the between-site differences in BNF. The N : P stoichiometry in peat and bog water indicated that Brumiště may have lacked BNF due to P limitation, whereas non-detectable BNF at Uhlír̆ská may have been related to the 70-fold higher SO42- concentration in bog water. Across the sites, the mean natural-abundance δ15N values increased in the following order: atmospheric deposition (−5.3 ± 0.3 ‰) < Sphagnum (−4.3 ± 0.1 ‰) < bog water (−3.9 ± 0.4 ‰) < atmospheric N2 (0.0 ‰). Only at Brumiště was N in Sphagnum significantly isotopically heavier than in atmospheric deposition, possibly indicating a longer-term BNF effect. Collectively, our data highlight spatial heterogeneity in BNF rates under high Nr inputs as well as the importance of environmental parameters other than atmospheric Nr pollution in regulating BNF.

Investigation of Iron Based Di-Atomic Catalysts to Identify Active Sites for Coupled Reduction Reactions of CO2 and N2

Urea is a valuable chemical feed stock that is commonly used in fertilizers and other industrial applications, including for the production of plastics and resins. Conventionally, industrial urea is produced through the reaction of ammonia and carbon dioxide under high pressure and temperature, resulting in intensive energy inputs and inefficiencies. In contrast, electrochemical synthesis of urea under mild conditions has been shown to be possible by coupled electrochemical reduction of CO2 (CO2RR) and N2 (NRR)1. While finding active and efficient catalysts remains a major challenge, rational design can be advanced by identification of the favourable atomic arrangements that facilitate C-N bond formation. For this purpose, carbon-supported and nitrogen-coordinated metal single atom catalysts (SACs) are a promising class of electrocatalysts2. Given their well-defined atomic structure, these material systems are valuable model systems for identifying active sites for specific reactions.Cu and Ni are well-known as efficient CO2RR catalysts3,4, whereas Fe-based catalysts are traditionally used for N2 fixation to produce NH3 via the thermochemical Haber-Bosch method5. This background knowledge served as motivation for fabrication of two types of di-atomic catalysts (DACs), containing Cu-Fe and Ni-Fe components anchored in an electrochemically inert carbon framework. A wet-chemical method was used for synthesizing these materials. While no crystalline metallic reflections were observed in X-ray diffraction patterns, X-ray photoelectron spectroscopy confirmed the presence of constituent metals along with lattice N, O, and C. The X-ray absorption near edge structure (XANES) measurements of Fe, Ni and Cu edges show significantly different spectra when compared to corresponding metal foils and oxides. Importantly, a nitrogen-coordinated ‘single atom’ morphology with inter-metal interactions is confirmed by extended X-ray absorption fine structure (EXAFS). Electrochemical reduction reactions in the presence of CO2 and N2 showed formation of 2e- CO2RR products, with CO dominant for the case of Ni-Fe DACs. In contrast, for the case of Cu-Fe DACs, formic acid generation was significantly more pronounced than CO. For the case of isolated NRR, NH3 was observed for both DACs. The production of urea, however, was only observed for Cu-Fe DACs. While mechanistic investigations are underway, the primary difference in these activities is hypothesized to be due to formation of different intermediates and reaction paths followed during CO2RR. Previous studies6 have suggested that the choice of reaction path, CO2→*OCHO→formic acid or CO2→*COOH→CO, could be dependent on oxophilicity of the reaction site. Our observations indicate that C-N coupling is promoted by oxophilic CO2RR catalysts. Since the direct identification of active sites for coupled CO2RR and NRR has rarely been reported using simple ‘single atom’ based catalyst systems, our work opens up a new direction for designing catalysts capable of C-N coupling for the efficient generation of the valuable chemical, urea, under ambient conditions.References Chen, C., Zhu, X., Wen, X., Zhou, Y., Zhou, L., Li, H., Tao, L., Li, Q., Du, S., Liu, T. and Yan, D., Nat. Chem. 12, 717–724 (2020).Chen, Y., Ji, S., Chen, C., Peng, Q., Wang, D. and Li, Y., Joule 2, 1242–1264, (2018).Ferri, M., Delafontaine, L., Guo, S., Asset, T., Cristiani, P., Campisi, S., Gervasini, A. and Atanassov, P., ACS Energy Lett. 7, 2304–2310, (2022).Leverett, J., Yuwono, J.A., Kumar, P., Tran-Phu, T., Qu, J., Cairney, J., Wang, X., Simonov, A.N., Hocking, R.K., Johannessen, B. and Dai, L., ACS Energy Lett. 7, 920–928 (2022).Fuller, J., An, Q., Fortunelli, A. and Goddard III, W.A., Acc. Chem. Res. 55, 1124–1134 (2022).Feaster, J.T., Shi, C., Cave, E.R., Hatsukade, T., Abram, D.N., Kuhl, K.P., Hahn, C., Nørskov, J.K. and Jaramillo, T.F., ACS Catal. 7, 4822–4827 (2017).

Managing the Scaling Relationship for Plasma-Activated Electrolysis Toward Nitrogen Fixation

To substitute fossil feedstock, storing renewable electricity in chemical bonds has become one of the tremendous and attractive approaches. This approach enables the transformation of base molecules (i.e., H2O, N2, CO2) into energy or chemical-rich molecules. The energy stored in the nitrogen-based compound is a critical biogeochemical cycle in nature due to its essential nutrient for living organisms in the forms of ammonia, nitrates, urea, amino acids, and DNA/RNA nucleotides as well as the high atmospheric volume of 78%. Artificial nitrogen fixation via a catalytic approach powered by sustainable renewables (e.g. wind, solar) provides an alternative as well as promising route to resource the value-added chemicals.N2 is a nonreactive base molecule due to its non-polarity and a strong triple bond between the atoms. Subsequently, even with an active catalyst, a substantial amount of energy is needed to activate N2 [1]. This Account covers our group’s recent advances in solid oxide electrolysis cells (SOECs) for providing reacting species on catalysts in a controllable manner while a radio frequency (RF) plasma is used to increase the reactivity of nitrogen [2,3]. Using oxygen ion or proton conducting SOECs we can produce either ammonia or nitric oxide (via reacting with plasma-activated N2) by suppressing oxygen or hydrogen evolution, respectively. The spatial separation of nitrogen dissociation and catalytic formation of the target molecules provides true independent parameters to optimize the electrocatalytic reactions. In both cases, the concentration of products is orders of magnitude higher than equilibrium (in the absence of plasma) while very high selectivity to nitrogen fixation is observed.To date most of the studies have focused on the material axis, however, recent theoretical studies have revealed that large-scale N2 fixation necessitates the rational design of the reactor, catalyst selectivity, reaction kinetics, and fluid dynamics and thus it keeps the processes far from the optimum performance. In this contribution, we investigate several aspects including flow dynamics, nature of the catalyst, activation energy of the catalytic process, catalyst surface-to-volume ratio, catalyst selectivity, and residence time of plasma-activated nitrogen to reach the catalyst surface, toward solving the aforementioned limitations.

Nitrogen fixation of lablab and finger millet in South‐India

AbstractBackgroundIn a long‐term rotation experiment (2016–2022) with different nitrogen (N) fertilizer levels in subtropical South‐India, crop yields of low N plots were unexpectedly high. We therefore hypothesized that in the absence of mineral N application, these yields are largely due to N inputs by N2 fixation in the component crops. To assess the diazotrophic N2‐fixation of lablab (Lablab purpureus L. Sweet) and possible associative N2‐fixation of finger millet (Eleusine coracana L. Gaertn), a controlled experiment was conducted during the 2021 monsoon season within the above‐mentioned long‐term field study. Two approaches were used to estimate the quantity of N derived from the atmosphere (Ndfa): the dilution method using a 15N‐labeled fertilizer and the natural abundance method.MethodFor the 15N dilution method irrigated maize (Zea maize L.), finger millet and lablab were labeled with two split applications of 10% 15N fertilizer (50:50 15N‐urea and 15N‐ammonium sulfate) amounting to a total of 15 kg N ha−1. Maize was selected as the non‐fixing reference plant to estimate diazotrophic N2‐fixation. The entire aboveground biomass of the labeled plants was harvested at maturity and analyzed for total DM, N concentration, and the 15N isotope ratio.ResultsN2 fixation efficiency for lablab was 52%–69% depending on the calculation method, corresponding to 40–53 kg N ha−1. For finger millet, the natural abundance method resulted in an estimated N2‐fixation of 5 kg N ha−1, which was suggested by the results of the dilution method whereby the reference plant maize was only poorly labeled.ConclusionLabeling of maize might have been diluted due to unexpected associative N2‐fixation or N‐uptake from unlabeled deep soil N pools. The data underline the importance of symbiotic N2‐fixation in crop rotation systems of South‐India.

Fixation of air nitrogen to ammonia and nitrate using cathodic plasma and anodic plasma in the air plasma electrolysis method

AbstractThe fixation of nitrogen (N2) from the air into ammonia (NH3) and nitrate (NO3−) is usually conducted using the Haber–Bosch process, which requires the raw material of hydrocarbons for hydrogen (H2), which has a large amount of energy but produces high CO2 emissions. An environmentally friendly and energy‐saving alternative is the air plasma electrolysis method, which can be used to synthesize NH3 and NO3− under ambient conditions. In this study, this method was used to inject air into the plasma zone in a K2SO4 electrolyte solution to produce N2 fixation compounds. The results showed that the use of cathodic plasma promoted the formation of NH3 but suppressed NO3− production. The optimal air injection rate was achieved at 0.6 L.min−1 and an electrical power of 452 W, with a total fixed N2 of 51.66 mmol. The highest formation of NO3− in cathodic plasma was obtained in 35 min, with a value of 29.92 mmol, and 2.57 mmol NH3 was achieved at 60 min. The high concentration of H2 gas, which is a by‐product of this process, can contribute to increasing the use of Haber–Bosch green technology in the production of NH3.

Facile synthesis of Sn-doped MOF-5 catalysts for efficient photocatalytic nitrogen fixation

The utilization of Zn4O(1,4-benzenedicarboxylate)3 metal-organic framework (MOF-5) as a photocatalyst remains a substantial challenge owing to the limited stability under humid conditions and the low photocatalysis efficiency. Herein, a series of Sn-doped MOF-5 (Sn-MOF-5) were designed and fabricated for the photocatalytic N2 fixation using the specific T-tube photocatalysis reactor. Detailed characterization results illustrates that an appropriate amount of Sn4+ doping can not only enhance the specific surface area and reducing capacity of MOF-5, but also decrease the bandgap width and promote the separation of photogenerated carriers. Therefore, at a Zn:Sn ratio of 6, Sn-MOF-5 with the highest Sn4+ ratio shows superior catalytic performance with the ammonia (NH3) yield achieved 3912.76 μmol L−1 g−1 after 5 h, and the chemical stability is almost no decay after 15 h of continuous photocatalysis. This may offer a new strategy for improving catalytic performance and stability of MOF through doping Sn4+.

Synergistic Effect of Oxygen Vacancy and High Porosity of Nano MIL‐125(Ti) for Enhanced Photocatalytic Nitrogen Fixation

AbstractThis work reports that a low‐temperature thermal calcination strategy was adopted to modulate the electronic structure and attain an abundance of surface‐active sites while maintaining the crystal morphology. All the experiments demonstrate that the new photocatalyst nano MIL‐125(Ti)‐250 obtained by thermal calcination strategy has abundant Ti3+ induced by oxygen vacancies and high specific surface area. This facilitates the adsorption and activation of N2 molecules on the active sites in the photocatalytic nitrogen fixation. The photocatalytic NH3 yield over MIL‐125(Ti)‐250 is enhanced to 156.9 μmol g−1 h−1, over twice higher than that of the parent MIL‐125(Ti) (76.2 μmol g−1 h−1). Combined with density function theory (DFT), it shows that the N2 adsorption pattern on the active sites tends to be from “end‐on” to “side‐on” mode, which is thermodynamically favourable. Moreover, the electrochemical tests demonstrate that the high atomic ratio of Ti3+/Ti4+ can enhance carrier separation, which also promotes the efficiency of photocatalytic N2 fixation. This work may offer new insights into the design of innovative photocatalysts for various chemical reduction reactions.

Synergistic Effect of Oxygen Vacancy and High Porosity of Nano MIL-125(Ti) for Enhanced Photocatalytic Nitrogen Fixation.

This work reports that a low-temperature thermal calcination strategy was adopted to modulate the electronic structure and attain an abundance of surface-active sites while maintaining the crystal morphology. All the experiments demonstrate that the new photocatalyst nano MIL-125(Ti)-250 obtained by thermal calcination strategy has abundant Ti3+ induced by oxygen vacancies and high specific surface area. This facilitates the adsorption and activation of N2 molecules on the active sites in the photocatalytic nitrogen fixation. The photocatalytic NH3 yield over MIL-125(Ti)-250 is enhanced to 156.9 μmol g-1 h-1 , over twice higher than that of the parent MIL-125(Ti) (76.2 μmol g-1 h-1 ). Combined with density function theory (DFT), it shows that the N2 adsorption pattern on the active sites tends to be from "end-on" to "side-on" mode, which is thermodynamically favourable. Moreover, the electrochemical tests demonstrate that the high atomic ratio of Ti3+ /Ti4+ can enhance carrier separation, which also promotes the efficiency of photocatalytic N2 fixation. This work may offer new insights into the design of innovative photocatalysts for various chemical reduction reactions.

Effects of nitrogen supply on hydrogen-oxidizing bacterial enrichment to produce microbial protein: Comparing nitrogen fixation and ammonium assimilation

To investigate the effects of nitrogen source supply on microbial protein (MP) production by hydrogen-oxidizing bacteria (HOB) under continuous feed gas provision, a sequencing batch culture comparison (N2 fixation versus ammonium assimilation) was performed. The results confirmed that even under basic cultivation conditions, N2-fixing HOB (NF-HOB) communities showed higher levels of CO2 and N2 fixation (190.45 mg/L Δ CODt and 11.75 mg/L Δ TNbiomass) than previously known, with the highest biomass yield being 0.153 g CDW/g COD-H2. Rich ammonium stimulated MP synthesis and the biomass accumulation of communities (increased by 7.4 ～ 14.3 times), presumably through the enhancement of H2 and CO2 absorption. The micro mechanism may involve encouraging the enrichment of species like Xanthobacter and Acinetobacter then raising the abundance of nitrogenase and glutamate synthase to facilitate the nitrogen assimilation. This would provide NF-HOB with ideas for optimizing their MP synthesis activity.

Photocatalytic Enhancement Strategy with the Introduction of Metallic Bi: A Review on Bi/Semiconductor Photocatalysts.

Semiconductor photocatalysis has great potential in the fields of solar fuel production and environmental remediation. Nevertheless, the photocatalytic efficiency still constrains its practical production applications. The development of new semiconductor materials is essential to enhance the solar energy conversion efficiency of photocatalytic systems. Recently, the research on enhancing the photocatalytic performance of semiconductors by introducing bismuth (Bi) has attracted widespread attention. In this review, we briefly overview the main synthesis methods of Bi/semiconductor photocatalysts and summarize the control of the micromorphology of Bi in Bi/semiconductors and the key role of Bi in the catalytic system. In addition, the promising applications of Bi/semiconductors in photocatalysis, such as pollutant degradation, sterilization, water separation, CO2 reduction, and N2 fixation, are outlined. Finally, an outlook on the challenges and future research directions of Bi/semiconductor photocatalysts is given. We aim to offer guidance for the rational design and synthesis of high-efficiency Bi/semiconductor photocatalysts for energy and environmental applications.