Strategies to achieve effective nitrogen activation

Ammonia serves as a crucial chemical raw material and hydrogen energy carrier.Aqueous electrocatalytic nitrogen reduction reaction(NRR),powered by renewable energy,has attracted tremendous interest during the past few years.Although some achievements have been revealed in aqueous NRR,significant challenges have also been identified.The activity and selectivity are fundamentally limited by nitrogen activation and competitive hydrogen evolution.This review focuses on the hurdles of nitrogen activation and delves into complementary strategies,including materials design and system optimization(reactor,electrolyte,and mediator).Then,it introduces advanced interdisciplinary technologies that have recently emerged for nitrogen activation using high-energy physics such as plasma and triboelectrification.With a better understanding of the corresponding reaction mechanisms in the coming years,these technologies have the potential to be extended in further applications.This review provides further insight into the reaction mechanisms of selectivity and stability of different reaction systems.We then recommend a rigorous and detailed protocol for investigating NRR performance and also highlight several potential research directions in this exciting field,coupling with advanced interdisciplinary applications,in situ/operando characterizations,and theoretical calculations.

The effects of phenolic acid on nitrogen metabolism in Populus 3 euramericana ‘Neva’

The declines in soil fertility and productivity in continuously cropped poplar plantations axe related to phenolic acid accumulation in the soil. Nitrogen is a vital life element for poplar and whether the accumulation of phenolic acid could influence nitrogen metabolism in poplar and thereby hinder continuous cropping is not clear. In this study, poplar cuttings of Populus × euramericana ‘Neva＇ were potted in vermiculite, and phenolic acids at three concentrations （032, 0.5X and 1.0X） were added according to the actual content （1.0X） in the soil of a second-generation poplar plantation. Each treatment had eight replicates. We measured gas exchange parameters and the activities of key enzymes related to nitrogen metabolism in the leaves. Leaf photosynthetic parameters varied with the concentration of phenolic acids. The net photosynthetic rate （PN） significantly decreased with increasing phenolic acid concentration, and non-stomatal factors might have been the primary limitation for PN- The activities of nitrate reductase （NR）, glutamine synthetase （GS） and glutamate synthase （GOGAT）, as well as the contents of nitrate nitrogen, ammonium nitrogen, and total nitrogen in the leaves decreased with increasing phenolic acid concentration. This was significantly and positively related to PN （P 〈 0.05）. The low concentration of phe- nolic acids mainly affected the transformation process of NO3- to NO2-, while the high concentration of phenolic acids affected both processes, where NO3- was transferred to NO2- and NH4＋ was transferred to glutamine （Gln）. Overall, phenolic acid had significant inhibitory effects on the photosynthetic productivity of Populus x euramericana ＇Neva＇. This was probably due to its influence on the activities of nitrogen assimilation enzymes, which reduced the amount of amino acids that were translated into protein and enzymes. Improving the absorption and utilization of nitrogen by plants could help to overcome the problems caused by continuous cropping.

Scalable fabrication and active site identification of MOF shell-derived nitrogen-doped carbon hollow frameworks for oxygen reduction

Nitrogen-doped carbon materials as promising oxygen reduction reaction(ORR) electrocatalysts attract great interest in fuel cells and metal-air batteries because of their relatively high activity, high surface area, high conductivity and low cost. To maximize their catalytic efficiency, rational design of efficient electrocatalysts with rich exposed active sites is highly desired. Besides, due to the complexity of nitrogen species, the identification of active nitrogen sites for ORR remains challenging. Herein, we develop a facile and scalable template method to construct high-concentration nitrogen-doped carbon hollow frameworks(NC), and reveal the effect of different nitrogen species on theirORRactivity on basis of experimental analysis and theoretical calculations. The formation mechanism is clearly revealed, including low-pressure vapor superassembly of thin zeolitic imidazolate framework(ZIF-8) shell on ZnO templates,in situ carbonization and template removal. The obtained NC-800 displays better ORR activity compared with other NC-700 and NC-900 samples. Our results indicate that the superior ORR activity of NC-800 is mainly attributed to its content balance of three nitrogen species. The graphitic N and pyrrolic N sites are responsible for lowering the working function, while the pyridinic N and pyrrolic N sites as possible active sites are beneficial for increasing the density of states.

Analysis of Chemical and Biological Soil Properties in Organically and Conventionally Fertilized Apple Orchards

We compared chemical and biological properties of soils in organically and conventionally fertilized apple orchards in Nagano Prefecture (one of the major apple producing regions in Japan). Five apple orchards with different fertilizer management systems were used for this study. The total carbon and total nitrogen contents were higher in the organically fertilized orchard, while the total phosphorus and total potassium were at similar levels in both organically and conventionally fertilized orchards. The bacterial biomass did not differ between the two orchards, but the N circulation activity was clearly higher in the organically fertilized orchard from April to December. Total carbon from 50,000 to 60,000 mg/kg, total nitrogen at about 3000 to 4000 mg/kg, and a C/N ratio of 15 - 20 were suggested to be suitable conditions for a high level of apple production under an organic fertilizer management system.

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis:A Strategy for Ammonia Synthesis under Mild Conditions

The activation and reduction of N_(2)to produce ammonia under mild conditions is of great interest,but challenges remain.Here,we report a breakthrough in efficient dinitrogen cleavage by employing small Ptn+(n=1–4)clusters and convenient plasma assistance.The reactivity of Pt3+is found to be substantially higher than that of other clusters,and the formed Pt3N7+shows prominent mass abundance among the odd-nitrogen products.We illustrate that a chain reaction path within dual cluster cooperation,especially via a“3+2”mode,is beneficial to N≡N triple bond dissociation,embodying efficient synergistic catalysis.A key intermediate containing a bridged N_(2)of binding with two Pt clusters facilitates N_(2)activation with significantly enhanced interactions between the d orbitals of Pt and the antibondingπ*-orbitals of N_(2).Furthermore,by reacting the Pt_(n)N_(m)+clusters with H_(2),we observed hydrogenation products of both evenand odd-hydrogen species,indicative of ammonia release.The in situ synthesized platinum nitride clusters,typically Pt_(3)N_(7)+,induce a highly active N site for hydrogen anchoring,enabling a cost-effective hydrotreating process for ammonia synthesis.

Alloying cobalt with ruthenium in nitrogen doped graphene layers for developing highly active hydrogen evolution electrocatalysts in alkaline media

Subject Code:B01With the support by the National Natural Science Foundation of China,a creative study by the research group led by Prof.Chen Qianwang(陈乾旺)from the University of Science and Technology of China and High Magnetic Field Laboratory,Hefei Institutes of Physical Science,Chinese Academy of

Multi-endpoint assays reveal more severe toxicity induced by chloraminated effluent organic matter than chloraminated natural organic matter

Disinfection by chloramination produces toxic byproducts and the difference in toxicity of reclaimed and drinking water treated by chloramination remains unclear.This study investigated cytotoxic effects at the same concentrations of dissolved organic matter and showed that chloraminated effluent organic matter(EfOM)induced 1.7 times higher cytotoxicity than chloraminated natural organic matter(NOM)applied to simulate drinking water.Chloraminated EfOM induced more reactive nitrogen species than chloraminated NOM,and chloraminated EfOM and NOM induced similar and higher levels of reactive oxygen species than the negative control,respectively.Consequently,intracellular macromolecule damage indicated by DNA/RNA damage marker 8–hydroxy-(deoxy)guanosine and the intracellular protein carbonyl concentration induced by chloraminated EfOM was higher and slightly more than that induced by chloraminated NOM,respectively.These data were consistent with the effects on cell physiological processes.Cell cycle arrest mainly occurred in G2 phase by chloraminated EfOM and NOM.Early apoptotic cells,which could return to normal,increased upon exposure to high concentrations of chloraminated EfOM and NOM.Moreover,necrotic cells were significantly increased from 0.5%to 2.5%when the concentration increased from 20-to 60-fold chloraminated EfOM,but were not obviously changed by chloraminated NOM.These results indicated that the comprehensive intracellular changes induced by toxic substances in chloraminated EfOM were more irreversible and induced more cell death than chloraminated NOM.

Divergent responses of soil carbon and nitrogen pools to short-term nitrogen addition between two plantations in Northeast China

Nitrogen(N)deposition has a profound influence on forest soil carbon(C)and N pools,but there was no consensus on the responses of different C and N components in different forest types.In this study,a two-year simulated N deposition experiment with four levels of N(NH4NO3)-addition treatments(0,50,100,and 150 kg N/hm^(2)·a)were conducted in Larix gmelinii(LG)and Quercus mongolica(QM)plantation in Northeast China,in order to investigate the C and N pool dynamics under continuously enhanced N deposition.Soil organic carbon(SOC),soil total N(STN)and their active components(readily oxidizable C,ROC;dissolved organic C,DOC;microbial biomass C,MBC,dissolved organic N,DON;microbial biomass N,MBN)of the forest soil were measured monthly from May to October 2017.C and N contents in LG were observed higher than in QM.N addition had no effect on SOC and STN of LG,but significantly increased SOC and STN of QM at low N addition level.Low N addition generally raised active C components(ROC,DOC,and MBC)in both plantations,whereas high N addition did not significantly affect these components,or even decreased ROC in LG soil.Low N addition also increased STN and MBN of QM,while no significant change in STN and MBN of LG was observed.DON was directly affected by N addition and increased significantly with elevated N addition levels.The results indicated that N addition,especially of low rate,might enhance the C sequestration capacity of the forest soils and mitigate climate change.

Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China

It is of great significance to explore the effects of different tillage practices on total nitrogen and its components in rice-wheat rotation farmland.The experiment was carried out in Jiangyan County,Jiangsu Province of China,and a total of four treatments were set up:minimum tillage(MT),rotary tillage(RT),conventional tillage(CT),and conventional tillage without straw retention(CT0).The total nitrogen(TN),light fraction nitrogen(LFN),heavy fraction nitrogen(HFN),particulate nitrogen(PN),and mineral-associated nitrogen(MN)in 0-20 cm soil were determined.The results show that MT increased TN concentration by2.26%-27.57%compared with the other treatments in 0-5 cm soil,but it lost this advantage in 5-10 cm and 10-20 cm soil.MT altered the concentration of LFN by 6.03%-95.86%,of HFN by 1.68%-20.75%,of PN by 12.58%-96.83%,and of MN by−1.73%-9.83%as compared to RT,CT,and CT0 in 0-5 cm soil,respectively.With the deepened of soil depth,the concentration of TN,LFN,HFN,PN,and MN decreased quickly in MT,which was lower than that in RT and CT at 10-20 cm soil depth.Straw return increased the concentration of TN and its components in 0-20 cm soil.The concentration of TN was extremely significantly positively correlated with that of LFN,HFN,PN,and MN(p<0.01).The variation of TN was significantly positively correlated with that of LFN,HFN,PN,and MN(p<0.01),and LFN showed the highest sensitivity to tillage practice.In general,minimum tillage combined with straw retention increased the concentration of soil TN and its components in topsoil.LFN was the best indicator to indicate the change in soil total nitrogen affected by tillage practice.

The first metagenome of activated sludge from full-scale anaerobic/anoxic/oxic(A2O) nitrogen and phosphorus removal reactor using Illumina sequencing

The anaerobic/anoxic/oxic（A2O） process is globally one of the widely used biological sewage treatment processes. This is the first report of a metagenomic analysis using Illumina sequencing of full-scale A2O sludge from a municipal sewage treatment plant.With more than 530,000 clean reads from different taxa and metabolic categories, the metagenome results allow us to gain insight into the functioning of the biological community of the A2O sludge. There are 51 phyla and nearly 900 genera identified from the A2O activated sludge ecosystem. Proteobacteria, Bacteroidetes, Nitrospirae and Chloroflexi are predominant phyla in the activated sludge, suggesting that these organisms play key roles in the biodegradation processes in the A2O sewage treatment system.Nitrospira, Thauera, Dechloromonas and Ignavibacterium, which have abilities to metabolize nitrogen and aromatic compounds, are most prevalent genera. The percent of nitrogen and phosphorus metabolism in the A2O sludge is 2.72% and 1.48%, respectively. In the current A2O sludge, the proportion of Candidatus Accumulibacter is 1.37%, which is several times more than that reported in a recent study of A2O sludge. Among the four processes of nitrogen metabolism, denitrification related genes had the highest number of sequences（76.74%）, followed by ammonification（15.77%）, nitrogen fixation（3.88%） and nitrification（3.61%）. In phylum Planctomycetes, four genera（Planctomyces, Pirellula, Gemmata and Singulisphaera） are included in the top 30 abundant genera, suggesting the key role of ANAMMOX in nitrogen metabolism in the A2O sludge.

Nitrogen removal from coal gasification wastewater by activated carbon technologies combined with short-cut nitrogen removal process

A system combining granular activated carbon and powdered activated carbon technologies along with shortcut biological nitrogen removal （GAC-PACT-SBNR） was developed to enhance total nitrogen （TN） removal for anaerobically treated coal gasification wastewater with less need for external carbon resources. The TN removal efficiency in SBNR was significantly improved by introducing the effluent from the GAC process into SBNR during the anoxic stage, with removal percentage increasing from 43.8%49.6% to 68.8%-75.8%. However, the TN removal rate decreased with the progressive deterioration of GAC adsorption. After adding activated sludge to the GAG compartment, the granular carbon had a longer service-life and the demand for external carbon resources became lower. Eventually, the TN removal rate in SBNR was almost constant at approx. 43.3%, as compared to approx. 20.0% before seeding with sludge. In addition, the production of some alkalinity during the denitrification resulted in a net savings in alkalinity requirements for the nitrification reaction and refractory chemical oxygen demand （COD） degradation by autotrophic bacteria in SBNR under oxic conditions. PACT showed excellent resilience to increasing organic loadings. The microbial community analysis revealed that the PACT had a greater variety of bacterial taxons and the dominant species associated with the three compartments were in good agreement with the removal of typical pollutants. The study demonstrated that pre-adsorption by the GAC-sludge process could be a technically and economically feasible method to enhance TN removal in coal gasification wastewater （CGW）.

Source and Control of Nitrogen for X70 Pipeline Steel

The effects of some key factors on nitrogen absorption during the smelting process of X70 pipeline steel were studied,and the source of nitrogen pick-up was analyzed to find the bottleneck for nitrogen control.A series of measures were put forward to decrease the nitrogen pick-up.The results indicated that an exponential relationship existed between the nitrogen absorption index and the free oxygen in molten steel.Nitrogen absorption index could decrease below 0.3when free oxygen in molten steel was above 100×10^（-6） after tapping.For low sulfur killed steel,the nitrogen absorption ratio and sulfur content satisfied a linear relationship with a slope of-0.007.Low free-oxygen and sulfur were beneficial to the deep desulfurization during vacuum treatment.The contradiction of high desulfurization ratio and low nitrogen pick-up during LF process could be resolved by skimming oxidizing slag after tapping and making new high basicity top slag.After optimization,the average content of nitrogen in final product decreased from 46×10（-6）to 35×10（-6）.

Biochemical and microbial soil functioning after application of the insecticide imidacloprid

Imidacloprid is one of the most commonly used insecticides in agricultural practice, and its application poses a potential risk for soil microorganisms. The objective of this study was to assess whether changes in the structure of the soil microbial community after imidacloprid application at the field rate（FR, 1 mg/kg soil） and 10 times the FR（10 × FR, 10 mg/kg soil）may also have an impact on biochemical and microbial soil functioning. The obtained data showed a negative effect by imidacloprid applied at the FR dosage for substrate-induced respiration（SIR）, the number of total bacteria, dehydrogenase（DHA）, both phosphatases（PHOS-H and PHOS-OH）, and urease（URE） at the beginning of the experiment. In 10 × FR treated soil, decreased activity of SIR, DHA, PHOS-OH and PHOS-H was observed over the experimental period. Nitrifying and N2-fixing bacteria were the most sensitive to imidacloprid. The concentration of NO3-decreased in both imidacloprid-treated soils,whereas the concentration of NH4＋in soil with 10 × FR was higher than in the control.Analysis of the bacterial growth strategy revealed that imidacloprid affected the r- or K-type bacterial classes as indicated also by the decreased eco-physiological（EP） index.Imidacloprid affected the physiological state of culturable bacteria and caused a reduction in the rate of colony formation as well as a prolonged time for growth. Principal component analysis showed that imidacloprid application significantly shifted the measured parameters, and the application of imidacloprid may pose a potential risk to the biochemical and microbial activity of soils.

In-situ anion exchange based Bi_(2)S_(3)/OV-Bi_(2)MoO_(6)heterostructure for efficient ammonia production:A synchronized approach to strengthen NRR and OER reactions

Photocatalytic ammonia generation via nitrogen reduction reaction(NRR)is a green and prospective nitrogen fixation technique.However,NRR is often hampered by the high N_(2) adsorption/activation energies and is accompanied by a slow kinetics oxygen evolution reaction(OER).Herein,a robust Bi_(2)S_(3)/OVBi_(2)MoO_(6)S-scheme heterojunction is constructed using a simple in-situ anion exchange process,which enables oxygen vacancy(OVs)abundant Bi_(2)Mo O_(6) microspheres with surface deposited Bi_(2)S_(3).The asfabricated Bi_(2)S_(3)/OVBi_(2)MoO_(6) functioned as an effective photocatalyst to convert N_(2)-to-NH_(3) under mild conditions.The photocatalytic NH_(3)/NH_(4)^(+) production rate reached 126μmol g_(cat)^(-1)under visible light for2.5 h with 2%of Bi_(2)S_(3)/OVBi_(2)MoO_(6)photocatalyst,which was 8-fold higher than pristine Bi_(2)MoO_(6).Furthermore,the as-fabricated Bi_(2)S_(3)/Bi_(2)MoO_(6)heterojunction exhibited good selectivity,high stability and reproducibility.The excellent photocatalytic NRR performance was ascribed to the Bi_(2)S_(3)/Bi_(2)MoO_(6)heterojunction formed subsequent to the strong interaction between Bi_(2)S_(3)and Bi_(2)MoO_(6).The OVs facilitated the chemical adsorption process allowing activation of N_(2)molecule on the Bi_(2)S_(3)/Bi_(2)MoO_(6).Simultaneously,the S-scheme heterojunction prolonged the lifetime of photogenerated carriers,accelerated the electrons/holes spatial separation and accumulation on the Bi_(2)S_(3)(reduction)and Bi_(2)MoO_(6)side(oxidation),respectively,thus strengthening both OER and NRR half-reactions.This simple in-situ anion exchange method offers a novel technique for strengthening OER and NRR half-reactions in Bi-based photocatalysts for effective photocatalytic ammonia generation.