Fen Sites Research Articles

Synthesis of hierarchically structured Fe3C/CNTs composites in a FeNC matrix for use as efficient ORR electrocatalysts.

Fe-N-C has a high number of FeN x active sites and has thus been regarded as a high-performance oxygen reduction reaction (ORR) catalyst, and combining Fe3C with Fe-N-C typically boosts ORR activity. However, the catalytic mechanism remains unknown, limiting further research and development. In this study, a precipitation-solvothermal process was used in conjunction with pyrolysis to produce a series of Fe-N-C catalysts derived from a zeolitic imidazolate framework (ZIF) that was composited with Fe3C. The prepared catalysts had a multiscale structure of ZIF-like carbon particles and rod-like structures, as well as bamboo-like carbon nanotubes (CNTs) and carbon layers wrapped with Fe3C particles while a series of studies revealed the origin of the rod-like structures and Fe3C phase. The hierarchical structure was beneficial to the enhanced electrocatalytic performance of catalysts for ORR. The optimal sample had the highest half-wave potential of 0.878 V vs. RHE, which was higher than that of commercial Pt/C (0.861 V vs. RHE). The ECSA of the optimal sample was 1.08 cm2 μg-1, with an electron transfer number close to 4, and functioning kinetics. The optimal sample exhibited high durability and methanol tolerance for the ORR. Finally, blocking different Fe active sites with coordination ions demonstrated that Fe(ii) was the main active site, indicating that Fe3C primarily served as a cocatalyst to optimize the electron structure of Fe-N-C, thereby synergistically improving the ORR activity.

Converting carbon black into an efficient and multi-site ORR electrocatalyst: the importance of bottom-up construction parameters.

To boost efficient energy transitions, alternatives to expensive and unsustainable noble metal-based electrocatalysts for the oxygen reduction reaction (ORR) are needed. Having this in mind, carbon black - Black Pearls 2000 (BP) was enriched in active nitrogen-containing centers, including single-atom Fe-N sites surrounded by Fe nanoclusters, through a synthesis methodology employing only broadly available precursors. The methodical approach taken to optimize the synthesis conditions highlighted the importance of (1) a proper choice of the Fe precursor; (2) melamine as an N source to limit the formation of magnetite crystals and modulate the charge density nearby the active sites, and glucose to chelate/isolate Fe atoms and thus allow the Fe-N coordination to be established, with a limiting formation of Fe0 clusters; and (3) a careful dosing of the Fe load. The ORR on the optimized electrocatalyst (Fe0.06-N@BP) proceeds mostly through a four-electron pathway, having an onset potential (0.912 V vs. RHE) and limiting current density (4.757 mA cm-2) above those measured on Pt/C (0.882 V and 4.657 mA cm-2, respectively). Moreover, the current density yielded by Fe0.06-N@BP after 24 h at 0.4 V vs. RHE was still above that of Pt/C at t = 0 (4.44 mA cm-2), making it a promising alternative to noble metal-containing electrocatalysts in fuel cells.

Forecasting the impact on endangered wildlife species affected by the planned restoration of wetlands after peat mining (Nizhny Novgorod region, Russia)

This paper is aimed to generalize and analyze information about endangered wildlife species in the disturbed fen site (comparing the state of surrounding wetlands) to predict their condition during rehabilitation and restoration of the site and subsequent monitoring during successional processes in the wetland ecosystems. The research was carried out on the territory of the Biosphere Reserve of UNESCO “Nizhegorodskoe Zavolzhye” on the example of the Kamskoe–Osinovye Kotly mire, which is a part of the Ramsar wetlands “Kama-Bakaldino Mires” (Nizhny Novgorod region). The area of the mire is about 15,000 hectares. A part of the mire with a total area of 2,770 hectares was drained and disturbed as a result of peat extraction since the 1970s to 1990s. We carried out surveys of flora and vegetation counts of small mammals, birds, amphibians and reptiles, butterflies and moths in 2021. Also for the analysis we used research data obtained in 1981-2019. A total of 58 endangered wildlife species listed in the Red Data Book of the Nizhny Novgorod region were registered in the studied territory, 14 species of which were discovered here for the first time. The location of the site which are planned to be restored, in the central part of the mire, surrounded by undisturbed communities is a condition for its successful restoration with the full biota after watering. Secondary watering of the site of former peat mining will not cause damage to endangered wildlife species. To maintain biodiversity and conserve the complex of meadow and semi-forest species we recommend carrying out the haymaking in the open spaces adjacent to the mire on the territory of the projected national park. Also we believe the succession processes in the mire and the endangered wildlife species conditions to have to be controlled.

Dual-catalytic colorimetric biosensor based on double-active Fe@Co-N stellate porous carbon and DNAzyme for simultaneous detection of tetracycline antibiotics

Colorimetry can identify the detection results visually by a naked eye, but the disadvantages such as low sensitivity and high background signal seriously limit its application prospects. In this paper, we prepared Fe@Co-N stellate porous carbon nanoenzyme with a large specific surface area containing Fe-N and cobalt double peroxide active sites. A dual catalytic system of the nanoenzyme and G-quadruplex/Hemin DNAzyme was constructed, which maintained independent catalytic spaces. And a colorimetric biosensor with a low background signal and ultra-sensitive detection of tetracyclines based on a shared structure was developed. Tetracyclines could adsorb hemin from nearby G-quadruplexes to form multimers that were detached from the system by cyclic shearing of exonuclease I, achieving highly sensitive detection of low concentrations of antibiotics. The limit of detection (LOD) of 0.333 ng/mL (S/N = 3) was much lower than those of most detection methods, indicating the promising strategy could be applied for the simultaneous detection of multiple tetracyclines.

The challenge of developing ecohydrological metrics for vegetation communities in calcareous fen wetland systems

Calcareous fens are peat-wetlands fed mainly by groundwater, located in topographic hollows and served by springs or seepages of water derived by contact with base-rich mineral ground. In the European Union they are protected habitats requiring special conservation measures. To better understand the environmental supporting conditions of alkaline fen habitat found in Ireland, a 2-years hydrological and hydrochemical monitoring programme was carried out on four contrasting fen sites that covered an ecohydrological gradient representing intact to highly degraded conditions. This paper presents a methodology (and its limitations) of how the evaluation of the temporal and spatial variability of the quality and hydrological dynamics associated with different representative vegetation communities within the four fens can be used to develop ecohydrological metrics for fen habitat. The conditions supporting fen habitat in “good” ecological condition, indicative of a functioning alkaline habitat, were determined and contrasted with conditions found in habitats deemed to be in “poor” ecological condition. Results indicate that an annual water level always above the ground surface within a threshold depth envelope of between 0.030 and 0.28 m is required for at least 60% of the year for healthy fen vegetation. In terms of hydrochemistry, higher concentrations of nutrients were found in the sediments at depth and the groundwater feed compared to the phreatic water table. This suggests the fens may be incorporating the incoming nutrients into their internal biogeochemical cycles and that there is a net accumulation of nutrients within the wetlands. Although envelopes of nutrient concentrations in the surface water of the fen associated with habitat in good ecological condition can be defined (e.g., dissolved reactive phosphorus concentrations of between 6 and 37 µg-P/l for PF1 habitat), these levels should be regarded as the water quality after the fen vegetation has effectively interacted with the higher incoming nutrient levels in the groundwater. Moreover, the local hydrogeological conditions that define groundwater pathways (and associated water quality impacts) in such calcareous fens, allied to the localized nature of these measurements in these field studies, makes it difficult to define groundwater water quality threshold values with any confidence.

Post incorporation of Fe sites on defective carbon sponge with high accessibility to enhance oxygen reduction elecrocatalysis

Monodispersed Fe-N/C single-atom catalysts have excellent oxygen reduction reaction (ORR) activity in renewable energy applications. Improving the availability and stability of iron monatomic catalytic sites is challenging. Herein, an iron phthalocyanine (FePc)-based vapor deposition strategy was designed for the synthesis of monodispersed Fe-N/C single-atom catalysts. The construction of Fe-N sites with both stability and high activity on defection-rich carbon surface has been realized, ascribed to the well balance between the evaporation and decomposition of FePc on defective carbon sponge (DCS) to generate enough Fe-N active sites with full accessibility. As a result, the optimized catalyst delivered excellent ORR activity, selectivity and stability, as well promising zinc-air battery performance with good power density and discharging stability. Our results cast new insight into rational construction of easily accessible and highly active Fe-N sites.

Holocene carbon storage and testate amoeba community structure in treed peatlands of the western Hudson Bay Lowlands margin, Canada

AbstractThe Hudson Bay Lowlands (HBL) stores a significant proportion of the northern peatland carbon pool, and constraints on the factors controlling local‐scale variation are needed to better predict soil carbon stocks. We investigated two treed peatland sites, a fen and a bog, to understand how local ecohydrological factors impacted long‐term carbon storage. Ecohydrological conditions were reconstructed using quantitative water table depth reconstructions from testate amoebae (TA) and broad peat type classifications. We also linked these factors and carbon storage to changes in TA community structure through the investigation of morphological and functional traits. Both sites have high rates of peat vertical accretion during the warmer Middle Holocene. A shift to a drier, Sphagnum‐dominated habitat after 7400 cal a bp at the bog site, however, led to lower apparent carbon accumulation rates (aCARs) than at the fen site. aCARs decreased with the transition to a cooler Late Holocene climate at both sites. Both sites have higher total carbon masses (kg m−2) than other more open and younger HBL localities, demonstrating the potential importance of treed peatlands in regional carbon storage. Shifts in the frequency of TA traits corresponded to changing ecohydrological conditions and provided insights into the role of TA in carbon storage.

A Model Intercomparison Analysis for Controls on C Accumulation in North American Peatlands

AbstractPeatland biogeochemical processes have not been adequately represented in existing earth system models, which might have biased the quantification of Arctic carbon‐climate feedbacks. We revise the Peatland Terrestrial Ecosystem Model (PTEM) by incorporating additional peatland biogeochemical processes. The revised PTEM is evaluated by comparing with Holocene Peatland Model (HPM) in simulating peat physical and biogeochemical dynamics in three North American peatlands: a permafrost‐free fen site, a permafrost‐free bog site and a permafrost bog site. Peatland carbon dynamics are simulated from peat initiation to 1990 and then to year 2300. Model responses to the changes in temperature and precipitation are analyzed to identify key processes affecting peatland carbon accumulation rates. We find that the net C balance is sensitive to water table depth and nutrient availability. Future simulations to year 2300 are conducted with both models under RCP 2.6, RCP 4.5, and RCP 8.5. PTEM predicts these peatlands to be C sources or weaker C sinks when insufficient precipitation suppresses soil moisture and thereby net N mineralization and net primary production, while HPM predicts the same when drier climate leads to increasing water table depth. Our results highlight the importance of water balance and C‐N feedback on peatland C dynamics. With a warmer climate, these peatlands could become a weaker C sink or a source under drier conditions, otherwise a larger C sink if wetter. Improved understanding to peatland processes can help future quantification of peatland C dynamics in the boreal and Arctic regions.

Highly efficient adsorption and catalytic degradation of aflatoxin B1 by a novel porous carbon material derived from Fe-doped ZIF-8

The development of peroxymonosulfate (PMS) catalysts with sufficient active sites and high mass transfer capacity is a desirable but challenging aspect in advanced oxidation processes. In this work, an Fe/N-co-doped porous carbon (Fe/N-PC) material derived from silica-coated Fe-doped zeolitic imidazolate framework-8 (Fe-ZIF-8) was developed and used as catalyst for the degradation of aflatoxin B1 (AFB1). Fe-ZIF-8 introduced additional Fe-N sites with high catalytic PMS activity. Importantly, the strategy of silica coating on the surface of Fe-ZIF-8 effectively prevented the aggregation of catalyst particles during the pyrolysis process and introduced a hierarchical porous structure in Fe/N-PC, significantly improving the mass transfer of reactants on the catalyst. As a result, Fe/N-PC possessed a much higher adsorption capacity for AFB1 (202.8 mg g−1) than other reported carbon adsorbents and exhibited fast degradation of AFB1 with ultra-high removal efficiency (99.88%) within 30 min. Singlet oxygen (1O2) was proved to be the dominant reactive species for AFB1 degradation. In addition, four degradation products were identified, and two possible degradation pathways were proposed. The double bond of the terminal furan ring or the methoxy group was destroyed, which implied that the toxicity of the degradation products was significantly reduced. Based on the above results, Fe/N-PC can be considered an efficient catalyst for the removal of hard-to-degrade AFB1 in practical applications.

Maximizing Fe-N exposure by tuning surface composition via twice acid treatment based on an ultrathin hollow nanocarbon structure for highly efficient oxygen reduction reaction

• A newly developed hollow structural Fe-N-C catalyst is synthesized by a template-free method. • Fe-N sites are embedded in an ultrasmall, ultrathin, and interconnected porous carbon structure. • The exposure and utilization of Fe-N sites was maximized by twice acid treatment. • The optimal catalyst (HNP-16) exhibited higher E 1/2 and faster ORR kinetics than Pt/C. • HNP-16 delivered a P max of 37.6 mW cm −2 in a membraneless DFFC, 140% higher than Pt/C. Fe-N-C oxygen reduction reaction (ORR) catalysts are still limited in poor ORR activity due to low Fe-N exposure and utilization. Here, we report a newly developed Fe-N-C catalyst with Fe-N sites embedded in a micro/mesopore-interconnected, ultrasmall (5–45 nm), ultrathin (1.3 nm), and hollow nanocarbon structure, which is synthesized by a facile, scalable, and template-free method by using cheap and safe reagents. Moreover, the exposure of Fe-N is maximized through twice acid treatment to tune the surface composition of the catalysts. The mass sites density of the optimal catalyst HNP-16 reached 45.0 μmol g −1 , much higher than that of untreated HNP-0 (7.4 μmol g −1 ) and common treated HNP-1 (12.2 μmol g −1 ). Benefiting from a collective contribution of abundant surface Fe-N active sites and structural advantages, HNP-16 exhibits higher half-wave potential and faster ORR kinetics than commercial Pt/C. Detailed electrochemical analysis revealed the relationships between coordination and ORR activity. The higher content of Fe-N results in faster ORR kinetics while O-related species lead to an undesired 2-electron ORR pathway. When HNP-16 was employed as the cathode catalyst in a membraneless direct formate fuel cell, it delivered an accelerated ORR current response and achieved an unprecedented maximum power density of 37.6 mW cm −2 , which was 1.4 times higher than that of Pt/C. The superior performance of HNP-16 is attributed not only to the highly exposed Fe-N sites but also to the rapid mass transfer provided by the favorable hollow structure.

Cooling Effects Revealed by Modeling of Wetlands and Land‐Atmosphere Interactions

AbstractWetlands are important ecosystems—they provide vital hydrological and ecological services such as regulating floods, storing carbon, and providing wildlife habitat. The ability to simulate their spatial extents and hydrological processes is important for valuing wetlands' function. The purpose of this study is to dynamically represent the spatial extents and hydrological processes of wetlands and investigate their feedback to regional climate in the Prairie Pothole Region (PPR) of North America, where a large number of wetlands exist. In this study, we incorporated a wetland scheme into the Noah‐MP land surface model with two major modifications: (a) modifying the subgrid saturation fraction for spatial wetland extent and (b) incorporating a dynamic wetland storage to simulate hydrological processes. This scheme was evaluated at a fen site in central Saskatchewan, Canada and applied regionally in the PPR with 13‐year climate forcing produced by a high‐resolution convection‐permitting model. The differences between wetland and no‐wetland simulations are significant, with increasing latent heat and evapotranspiration while suppressing sensible heat and runoff in the wetland scheme. Finally, the dynamic wetland scheme was applied in the Weather Research and Forecasting (WRF) model. The wetlands scheme not only modifies the surface energy balance but also interacts with the lower atmosphere, shallowing the planetary boundary layer height and promoting cloud formation. A cooling effect of 1–3°C in summer temperature is evident where wetlands are abundant. In particular, the wetland simulation shows reduction in the number of hot days for >10 days over the summer of 2006, when a long‐lasting heatwave occurred. This research has great implications for land surface/regional climate modeling and wetland conservation, especially in mitigating extreme heatwaves under climate change.

Optimizing configuration engineering of edge-hosted Fe-Nx active sites for oxygen reduction reaction

In this issue of Chem Catalysis , Fei, Ye, and Ge’s groups report a novel Fe-N/C catalyst with unique configuration of edge-hosted Fe-N 3 sites on the multiscale porous carbon framework, which presents an outstanding ORR activity. This work provides a unique strategy for designing a high-performance catalyst by optimizing chemical coordination of Fe-N x active sites. In this issue of Chem Catalysis , Fei, Ye, and Ge’s groups report a novel Fe-N/C catalyst with unique configuration of edge-hosted Fe-N 3 sites on the multiscale porous carbon framework, which presents an outstanding ORR activity. This work provides a unique strategy for designing a high-performance catalyst by optimizing chemical coordination of Fe-N x active sites.

Mesoporous structure and amorphous Fe-N sites regulation in Fe-g-C3N4 for boosted visible-light-driven photo-Fenton reaction

Heterogeneous photo-Fenton catalysts prepared by doping metal ions in g-C3N4 are promising alternatives to traditional homogeneous Fenton catalysts, but are restricted by poor mesoporous structure and agglomerate of metal species. Recently, the highly uniformly dispersed metal-N active sites in various photocatalysts have been proved to be the critical reason for their enhanced catalytic activity. In this study based on reasonable control of mesoporous structure and metal-N active sites, mesoporous Fe-g-C3N4 was synthesized using a simple one-step thermal shrinkage polymerization method using ferrous oxalate as iron source and pore-forming agent. The Fe and N elements in the triazine ring skeleton of Fe-g-C3N4 form a σ-π bond, thus the photogenerated electrons can be quickly transferred to Fe3+ to form Fe2+ under the interaction of chemical bonds, accelerating the Fenton reaction rate. Density functional theory calculations results demonstrate that the energy band structure and electron cloud density distribution of Fe-Nx active structure are better than that of routine FeOx crystal structure with metal species agglomeration. In addition, the excellent mesoporous structure of Fe-g-C3N4 creates conditions for the high exposure of Fe-Nx active sites in the photo-Fenton reaction under visible light. The as-developed Fe-g-C3N4 system shows high recyclability and excellent photo-Fenton performance for removal of typical intractable pollutants (The degradation rate of dye and tetracycline reaches 98.2% and 98.7% at 60 and 120 min, respectively). This work provides a facile and sustainable route to develop mesoporous highly-active heterogeneous Fenton-like catalysts and even further general the design of general catalyst with ideal metal-N active sites, thereby promoting a feasible and efficient wastewater remediation solution.

Electrochemical Investigation of Pt/Fe-N-C Catalysts as a Promising Low Pt-Loading Catalyst for Polymer Electrolyte Membrane Fuel Cells

Nowadays polymer electrolyte membrane fuel cells (PEMFC) become commercially established systems used in automobile, stationary and portable power generation industry which provide an improved kinetic, high efficiency, zero emission and high tolerance to the impurities. A standard catalyst used in PEMFC is based on Pt nanoparticles on carbon support materials. However, high cost of this critical raw material stimulates interest in the development of platinum group metals-free electrocatalysts (1). Fe-N-C materials are one of the promising non-precious metal electrocatalysts for these fuel cells which have recently reached outstanding performance in terms of oxygen reduction reaction (ORR) activity (2). However, the volumetric activity and durability of Fe-N-C catalyst is still significantly lower compared to Pt/C in PEMFC mainly due to their lower turnover frequency and active sites density (3).Therefore, in this work, a Black Pearl (BP) based Fe-N-C catalyst is used as ORR active support material for Pt-nanoparticles to investigate synergetic effects of active Pt and Fe-N sites towards stability and volumetric activity. We present a comparative electrochemical characterization of Pt/Fe-N-C and Pt/BP electrocatalysts with loadings of 0.01, 0.1 and 1 wt.% Pt. The measurements were done in terms of rotating ring-disk electrode experiments in 0.1 M HClO4 electrolyte under accelerated stress test (AST) during 5000 cycles in potential range 0.6 – 1.5 V vs RHE in N2-saturated electrolyte, in order to provoke Pt as well as carbon support degradation. The electrochemical surface area (ECSA) of the Pt was determined by hydrogen underpotential deposition (HUPD) and CO stripping methods before and after AST for Pt/BP catalysts. However, for Pt/Fe-N-C the ECSA determination was impossible because for metal-oxide supported Pt catalysts, a straightforward analysis of HUPD and CO methods fails to give meaningful values. The RRDE experiments revealed that ORR mass and specific activities were significantly decreased after AST especially for Pt/BP (Fig. 1) which was attributed to the platinum dissolution as well as carbon support degradation during cycling.1. E. Eren, N. Özkan, Y. Devrim, Int J Hydrogen 2020, 45 (58), 33957-33967.2. Y. He, S. Liu, C. Priest, Q.Shi , G. Wu, Chem. Soc. Rev., 2020, 11, 3484–3524.3. T. Reshetenko, A. Serov, M. Odgaard, G. Randolf, L. Osmieri, A. Kulikovsky, Electrochem Commun 2020, 118, 106795.Figure 1. Cathodic scan of ORR curves of 0.1 wt.% Pt/BP catalyst with 40 µg cm-2 Pt loading in O2-saturated 0.1 M HClO4 at scan rate 5 mV s-1 by 1600 rpm before and after AST. Figure 1

Atomically dispersed iron atoms on nitrogen-doped porous carbon catalyst with high density and accessibility for oxygen reduction

• AD-Fe-NPC was successfully developed as oxygen reduction catalysts. • HAADF-STEM images confirmed the atomic dispersion of Fe on AD-Fe-NPC catalysts. • The optimized AD-Fe-NPC structure exhibited superior ORR activity to Pt/C. The development of high-performance, low-cost and high-stability oxygen reduction reaction (ORR) non-platinum catalysts has become one of the main research directions on fuel cells and metal-air batteries. Here, we developed porous carbon catalysts with atomically dispersed nitrogen coordinated iron atoms (Fe-N x ) as the active sites (AD-Fe-NPC) using Fe-doped ZIF-8 and 1,10-phenanthroline as precursors. The additional nitrogen coordinated sites from 1,10-phenanthroline, together with a special structure of ZIF-8 can suppress the agglomeration of Fe atoms, leading to isolated Fe atoms with high density on graphitic carbon during the pyrolysis. As a result, the sample prepared using 50 mg of 1,10-phenanthroline (AD-Fe-NPC-50) exhibited a high activity towards oxygen reduction with a half-wave potential of 0.91 V versus reversible hydrogen electrode in 0.1 M KOH, which is attributed to the high porosity (1011.2 m 2 g −1 ) and density of Fe-N x active sites (1.1 at%). Furthermore, as an air electrode in zinc-air batteries, the AD-Fe-NPC-50 demonstrated a maximum power density of about 201 mA cm −2 and a specific capacity of 782 mA h g Zn −1 at 10 mA cm −2 , which outperformed commercial Pt/C and many state-of-the-art non-precious metal catalysts.

Boosting the ORR active and Zn-air battery performance through ameliorating the coordination environment of iron phthalocyanine

Iron phthalocyanine (FePc) with unique iron-pyrrolic nitrogen (Fe-N) structure has attracted an increasing attention on the oxygen reduction reaction (ORR). Unfortunately, the Fe-N site is not “active” because of its symmetry in the plane and always exhibits unsatisfactory ORR activity. Herein, we design a non-contact scheme of axial carbon substrate induced Fe-N electron localization to improve its ORR performance. Theoretical calculation indicates that the addition of MWCNTs causes the aggregation of electron cloud around Fe-N, enhances the oxygen adsorption capacity and accelerates the ORR rate. The obtained catalyst shows a Tafel slope of 35.8 mV·dec−1, an initial potential of 0.979 V vs. RHE, a half-wave potential of 0.902 V vs. RHE and a limiting current density of 5.42 mA·cm−2 in alkaline medium. The Zn-air battery assembled by this catalyst also demonstrates a large discharge voltage of 1.296 V, considerable power density of 102 mW·cm−2 and superior cycling stability (500 cycles). This work not only simplifies the process of preparing high efficiency transition metal catalysts but also does some tentative explore for realizing the practical use of Zn-air battery.

Synergistic desulfurization over graphitic N and enzyme-like Fe-N sites of Fe-N-C

By coupling P450 enzyme-like single-atom Fe-N center and graphitic N into N-doped carbon matrix, we precisely fabricated a robust Fe-N-C adsorbent for efficient, stable and reversible desulfurization, notably exceeding the counterparts of commercial carbon black, iron porphyrin and its hybrid. Our results disclosed that the adsorptive desulfurization mainly occurred in the atomic Fe-N and graphitic N sites via the formation of Fe-S bond between Fe3d and S3p orbitals, and N/S electrostatic interaction, respectively. The excellent desulfurization capability (34.03 mg S/g) of Fe-N-C not only originated from its effective adsorption sites, large surface area and abundant porosity, but also relied on the moderate binding strength between adsorption sites and organosulfur, which could be well optimized by modulating the pyrrolic/pyridinic N and graphitization structure, enabling its outstanding recyclability via a feasible cleavage of formed Fe-S and N-S bonds without obvious loss of activity. Moreover, Fe-N-C still maintained the 91.20% and 84.56% desulfurization selectivity, even in the presence of the interfacing substrates such as thiophene and 4,6-dimethyldibenzothiophene, respectively. This work would provide a new opportunity to metal-N-C with tunable site configuration and density for various selective adsorption and separation.

Atomically Dispersed Iron Metal Site in a Porphyrin-Based Metal-Organic Framework for Photocatalytic Nitrogen Fixation.

The rational design of photocatalysts for efficient nitrogen (N2) fixation at ambient conditions is important for revolutionizing ammonia production and quite challenging because the great difficulty lies in the adsorption and activation of the inert N2. Inspired by a biological molecule, chlorophyll, featuring a porphyrin structure as the photosensitizer and enzyme nitrogenase featuring an iron (Fe) atom as a favorable binding site for N2via π-backbonding, here we developed a porphyrin-based metal-organic framework (PMOF) with Fe as the active center as an artificial photocatalyst for N2 reduction reaction (NRR) under ambient conditions. The PMOF features aluminum (Al) as metal node imparting high stability and Fe incorporated and atomically dispersed by residing at each porphyrin ring promoting the adsorption and the activation of N2, termed Al-PMOF(Fe). Compared with the pristine Al-PMOF, Al-PMOF(Fe) exhibits a substantial enhancement in NH3 yield (635 μg g-1cat.) and production rate (127 μg h-1 g-1cat.) of 82% and 50%, respectively, on par with the best-performing MOF-based NRR catalysts. Three cycles of photocatalytic NRR experimental results corroborate a stable photocatalytic activity of Al-PMOF(Fe). The combined experimental and theoretical results reveal that the Fe-N site in Al-PMOF(Fe) is the active photocatalytic center that can mitigate the difficulty of the rate-determining step in photocatalytic NRR. The possible reaction pathways of NRR on Al-PMOF(Fe) were established. Our study of porphyrin-based MOF for the photocatalytic NRR will provide insight into the rational design of catalysts for artificial photosynthesis.

Selective Capacitive Removal of Heavy Metal Ions from Wastewater over Lewis Base Sites of S-Doped Fe–N–C Cathodes via an Electro-Adsorption Process

The pollution of toxic heavy metals is becoming an increasingly important issue in environmental remediation because these metals are harmful to the ecological environment and human health. Highly efficient selective removal of heavy metal ions is a huge challenge for wastewater purification. Here, highly efficient selective capacitive removal (SCR) of heavy metal ions from complex wastewater over Lewis base sites of S-doped Fe-N-C cathodes was originally performed via an electro-adsorption process. The SCR efficiency of heavy metal ions can reach 99% in a binary mixed solution [NaCl (100 ppm) and metal nitrate (10 ppm)]. Even the SCR efficiency of heavy metal ions in a mixed solution containing NaCl (100 ppm) and multicomponent metal nitrates (10 ppm for each) can approach 99%. Meanwhile, the electrode also demonstrated excellent cycle performance. It has been demonstrated that the doping of S can not only enhance the activity of Fe-N sites and improve the removal ability of heavy metal ions but also combine with heavy metal ions by forming covalent bonds of S- clusters on Lewis bases. This work demonstrates a prospective way for the selective removal of heavy metal ions in wastewater.

Field studies on breeding sites of CulicoidesLatreille (Diptera: Ceratopogonidae) in agriculturally used and natural habitats

Culicoides are vectors of pathogens mainly of veterinary importance. To establish targeted vector control measures, it is paramount to comprehend the ecological factors determining their distribution. Therefore, we used emergence traps to sample eight biotopes and assess their potential as breeding sites. Part one of the study investigates agricultural habitats, part two compares four biotopes of a forest-dominated area with less anthropogenic influence, including a physicochemical analysis of soil moisture, pH value and organic content. Thirteen culicoid species were collected, with a strong dominance of the Obsoletus Complex on meadows, and with Culicoides punctatus (Meigen), Culicoides pictipennis (Staeger) and the Obsoletus Complex, to be the most abundant species in the natural habitats. Several co-existing species were found, some of them not having been described before. Our results suggest that ungrazed meadows seem unsuitable as breeding sites. Only the influence of livestock creates adequate conditions for certain midge species. The alder on fen site contained most culicoid species with the highest species diversity. Our study clearly indicates that knowledge of species-specific preferences for environmental habitat conditions (choice of breeding site) in connection to soil conditions is crucial to understand the biology and phenology of midges and their role as vectors of pathogens.