The function of doping nitrogen on removing fluoride with decomposing La-MOF-NH_2:Density functional theory calculation and experiments

Fluoride is an important pollutant in wastewater,and adsorption is an effective way to remove fluoride.Because nitrogen plays an important role in adsorbent materials,computational models were developed to understand the changes in work function resulting from nitrogen doping.La-N-C-800℃,was prepared by pyrolyzing La-MOF-NH_(2)to verify the influence on the performance of removing fluoride by electrosorption.Material and electrochemical performance tests were performed to characterize La-N-C-800℃.Adsorption kinetics,adsorption thermodynamics,initial concentrations,pH,and ions competition were investigated using La-N-C-800℃for fluoride removal.In addition,density functional theory was applied to evaluate the function of nitrogen.When nitrogen atoms were added,the density of states,partial density of states,populations,and different orbits of charge were calculated to discover deep changes.Nitrogen strengthened the carbon structure and La_(2)O_(3)structure to remove fluoride.In addition,nitrogen can also act as an adsorption site in the carbon structure.These results provide design ideas for improving the performance of adsorbent materials by doping elements.

Engineered nitrogen doping on VO_(2)(B)enables fast and reversible zinc-ion storage capability for aqueous zinc-ion batteries

Vanadium-based compounds with high theoretical capacities and relatively stable crystal structures are potential cathodes for aqueous zinc-ion batteries(AZIBs).Nevertheless,their low electronic conductivity and sluggish zinc-ion diffusion kinetics in the crystal lattice are greatly obstructing their practical application.Herein,a general and simple nitrogen doping strategy is proposed to construct nitrogen-doped VO_(2)(B)nanobelts(denoted as VO_(2)-N)by the ammonia heat treatment.Compared with pure VO_(2)(B),VO_(2)-N shows an expanded lattice,reduced grain size,and disordered structure,which facilitates ion transport,provides additional ion storage sites,and improves structural durability,thus presenting much-enhanced zinc-ion storage performance.Density functional theory calculations demonstrate that nitrogen doping in VO_(2)(B)improves its electronic properties and reduces the zinc-ion diffusion barrier.The optimal VO_(2)-N400 electrode exhibits a high specific capacity of 373.7 mA h g^(-1)after 100 cycles at 0.1 A g^(-1)and stable cycling performance after 2000 cycles at 5 A g^(-1).The zinc-ion storage mechanism of VO_(2)-N is identified as a typical intercalation/de-intercalation process.

MnO_(2) cathode materials with the improved stability via nitrogen doping for aqueous zinc-ion batteries

The research and exploration of manganese-based aqueous zinc-ion batteries have been controversial of cycle stability and mechanism investigation,thus improving the stability and exploring storage mechanism are still the most main issue.Defect engineering has become an effective method to improve cycle stability.Herein,a nitrogen-doped ε-MnO_(2)(MnO_(2)@N)has been prepared using electrochemical deposition and heat treatment under nitrogen atmosphere.As the cathode for zinc-ion batteries,the capacity retention rate of MnO_(2)@N cathode is close to 100%after 500 cycles at 0.5 A g^(-1),while the capacity retention rate for the initial MnO_(2) cathode is 62%.At 5 A g^(-1),the capacity retention rate of MnO_(2)@N cathode is 83%after 1000 cycles,which is much higher than the 27%capacity retention rate for the original MnO_(2) cathode.And it can be found that the oxygen vacancies increase after nitrogen doping,which can improve the conductivity of the MnO_(2)@N cathode.Also,there is Mn-N bond in MnO_(2)@N,which can enhance the electrochemical stability of MnO_(2)@N cathode.In addition,the electrochemical mechanism of MnO_(2)@N cathode has been explored by the CV,GCD and GITT tests.It is found that nitrogen doping promotes the intercalation of H^(+) and the corresponding capacity contribution.Compared with the original MnO_(2) cathode,the diffusion coefficient of H^(+) and Zn^(2+) in MnO_(2)@N cathode increases.Also,the reactions during the charging and discharging process are explored through the ex-situ XRD test.And this work may provide some new ideas for improving the stability of manganese-based zinc-ion batteries.

A high-performance biochar produced from bamboo pyrolysis with in-situ nitrogen doping and activation for adsorption of phenol and methylene blue

Nitrogen doping is a promising method for the preparation of functional carbon materials.In this study,a nitrogen-doped porous coral biochar was prepared by using bamboo as raw material,urea as nitrogen source,and KHCO3 as green activator through in-situ pyrolysis.The structure of the obtained biochar was characterized by various techniques including nitrogen adsorption and desorption,Raman spectroscopy,X-ray photoelectron spectrometer,and etc.The adsorption properties of nitrogen-doped biochar were evaluated with phenol and methylene blue probes.The results showed that the nitrogen source ratio had a significant effect on the evolution of pore structure of biochar.Low urea addition ratio was beneficial to the development of pore structures.The optimum specific surface area of nitrogen-doped biochar could be up to 1693 m^2·g^-1.Nitrogen doping can effectively improve the adsorption capacity of biochar to phenol and methylene blue.Biochar prepared at 973.15 K with low urea addition ratio exhibited the highest adsorption capacity for phenol and methylene blue,and the equilibrium adsorption capacity was 169.0 mg·g^-1 and 499.3 mg·g^-1,respectively.By comparing the adsorption capacity of various adsorbents in related fields,it is proved that the nitrogen-doped biochar prepared in this study has a good adsorption effect.

Nitrogen doping and graphitization tuning coupled hard carbon for superior potassium-ion storage

Hard carbon material is one of the most promising anode materials for potassium ion batteries(PIBs)due to its distinct disordered and non-expandable framework.However,the intrinsically disordered microarchitecture of hard carbon results in low electric conductivity and poor rate capability.Herein,nitrogendoped and partially graphitized hard carbons(NGHCs)derived from commercial coordination compound precursor-ethylenediaminetetraacetic acid(EDTA)disodium cobalt salt hydrate are designed and prepared as high-performance PIBs anode materials.By means of a facile annealing method,nitrogen elements and graphitic domains can be controllably introduced to NGHCs.The resulting NGHCs show structural merits of mesoporous construction,nitrogen doping and homogeneous graphitic domains,which ensures fast kinetics and electron transportation.Applying in anode for PIBs,NGHCs exhibit robust rate capability with high reversible capacity of 298.8 m Ah g^-1 at 50 m A g^-1,and stable cycle stability of 137.6 mAh g^-1 at 500 m A g^-1 after 1000 cycles.Moreover,the ex situ Raman spectra reveal a mixture"adsorption-intercalation mechanism"for potassium storage of NGHCs.More importantly,full PIBs by pairing with perylenetetracarboxylic dianhydride(PTCDA)cathode demonstrate the promising potential of practical application.In terms of commercial precursor,facile synthesis and long cycle lifespan,NGHCs represent a brilliant prospect for practical large-scale applications.

Synthesis of nitrogen-doped single-walled carbon nanotubes and monitoring of doping by Raman spectroscopy

Nitrogen-doped single-walled carbon nanotubes （CNx-SWNTs） with tunable dopant concentrations were synthesized by chemical vapor deposition （CVD）, and their structure and elemental composition were characterized by using transmission electron microscopy （TEM） in combination with electron energy loss spectroscopy （EELS）. By comparing the Raman spectra of pristine and doped nanotubes, we observed the doping-induced Raman G band phonon stiffening and 2D band phonon softening, both of which reflect doping-induced renormalization of the electron and phonon energies in the nan- otubes and behave as expected in accord with the n-type doping effect. On the basis of first principles calculations of the distribution of delocalized carrier density in both the pristine and doped nanotubes, we show how the n-type doping occurs when nitrogen heteroatoms are substitutionally incorporated into the honeycomb tube-shell carbon lattice.

Full-faradaic-active nitrogen species doping enables high-energy-density carbon-based supercapacitor

Nitrogen doping is usually adopted in carbon based supercapacitor to enhance its relatively low energy density by providing extra pseudocapacity.However,the improvement of energy density is normally limited because the content of the introduced nitrogen species is not high and meanwhile only part of them is electrochemically active.Herein,we designed and fabricated a class of hierarchical nitrogen-rich porous carbons(HNPCs)possessing not only very high nitrogen content(up to 21.7 atom%)but also fully electrochemically active nitrogen species(i.e.,pyridinic N,pyrrolic N and oxidized N).Especially,in the synthesis of HNPCs,graphitic carbon nitride(g-C3N4)was used in situ not only as a nitrogen source but also as a catalyst to facilitate the polymerization of phenol and formaldehyde(as carbon precursor)and as a template to create the hierarchical porous structure.As electrodes for aqueous symmetric supercapacitor,the HNPCs with full faradaic-active nitrogen functionalities exhibit excellent supercapacitor performance:high energy density of 36.8 Wh/kg at 2.0 kW/kg(maintaining 25.7 Wh/kg at 38 kW/kg),superior rate capability with 78%capacitance retention from 1.0 to 20 A/g and excellent cycling stability with over95%capacitance retention after 10000 cycles,indicating their promising application potential in electrochemical energy storage.This novel carbon material with high-content and full electrochemically active nitrogen species may find extensive potential applications in the energy storage/conversion,catalysis,adsorption,and so on.

Mechanochemical Synthesis of Visible-light Induced Photocatalyst with Nitrogen and Carbon Doping

Nitrogen and/or carbon doped titania photocatalysts were prepared by a novel mechanochemical method. The prepared powders possessed two absorption edges around 400 and 540 nm wavelengths and showed excellent photocatalytic ability for nitrogen monoxide oxidation under visible light irradiation. Under the irradiation of visible light of wavelength >510 nm,37% of nitrogen monoxide could be continuously removed by the carbon and nitrogen co-doped titania prepared by planetary ball milling of P-25 titania–10% hexamethylenetetramine mixture followed by calcination in air at 400-C.

Successful Nitrogen Doping of 1.3 GHz Single Cell Superconducting Radio-Frequency Cavities

A high intrinsic quality factor （Q0） of a superconducting radio-frequency cavity is beneficial to reducing the oper- ation costs of superconducting accelerators. Nitrogen doping （N-doping） has been demonstrated as a aseful way to improve Q0 of the superconducting cavity in recent years. N-doping researches with 1.3 GHz single cell cavities are carried out at Peking University and the preliminary results are promising. Our recipe is slightly different from other laboratories. After 250μm polishing, high pressure rinsing and 3 h high temperature annealing, the cavities are nitrogen doped at 2.7-4.0Pa for 20rain and then followed by 15μm electropolishing. Vertical test results show that Q0 of a 1.3 GHz single cell cavity made of large grain niobium has increased to 4 ×10 10 at 2.0K and medium gradient.

Effects of Nitrogen Doping on Microstructure and Photocatalytic Activity of Nanocrystalline TiO_2 Powders

Nitrogen-doped TiO2 nanocrystalline powders were prepared by hydrolysis of tetrachloride titanium （TiCl4） in a mixed solution of ethanol and ammonium nitrate （NH4NO3） at ambient temperature and atmosphere followed by calcination at 400 ℃ for 2 h in air. FTIR spectra demonstrate that amine group in original gel is eliminated by calcination, and the TiO2 powder is liable to absorb water onto its surface and into its capillary pore. XRD and SEM results show that the average size of nanocrystalline TiO2 particles is no more than 60 nm and with increasing the calcination temperature, the size of particles increases. XPS studies indicate the nitrogen atom enters into the TiO2 lattice and occupies the position of oxygen atom. The nitrogen doping not only depresses the grain growth of TiO2 particles, but also reduces the phase transformation temperature of anatase to futile. The photocatalytic activity of the nitrogen-doped TiO2 powders has been evaluated by experiments of photocatalytic degradation aqueous methylene blue.

Doping sites modulation of T-Nb_(2)O_(5) to achieve ultrafast lithium storage

Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials,in which the doping sites greatly influence the electrochemical performances.However,very few reports focus on enhancing the lithium storage performances of Nb_(2)O_(5) via heteroatoms doping,yet the effect of different doping sites remains unclear.Herein,nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))via a urea-assisted annealing process.Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb_(2)O_(5) can be tuned by the heating rate,in which substitutional N can increase the spacing of the Li^(+)transport layer as well as reduce the band gap,while interstitial N can provide an electron-rich environment for Li^(+)transport layer and then reduce the Li^(+)diffusion barrier.Arising from the synergistic effect of N doping at different sites,the N-doped T-Nb_(2)O_(5) without carbon coating delivers impressive rate performance(104.6 mA h g^(-1) at 25 C)as well as enhanced cycle stability with a retention of 70.5%over1000 cycles at 5 C.In addition,the assembled lithium ion capacitor exhibits a high energy density of46.6 Wh kg^(-1) even at high power density of 8.4 kW kg^(-1).

Anchoring nitrogen-doped Co_(2)P nanoflakes on NiCo_(2)O_(4)nanorod arrays over nickel foam as high-performance 3D electrode for alkaline hydrogen evolution

Effective and robust electrocatalysts are mainly based on innovative materials and unique structures.Herein,we designed a flakelike cobalt phosphide-based catalyst supporting on NiCo_(2)O_(4)nanorods array,which in-situ grew on the nickel foam(NF)current collector,referring as NCo_(2)P/NiCo_(2)O_(4)/NF electrode.By optimizing the microstructure and electronic structure through 3D hierarchy fabrication and nitrogen doping,the catalyst features with abundant electrochemical surface area,favorable surface wettability,excellent electron transport,as well as tailored d band center.Consequently,the as-prepared N-Co_(2)P/NiCo_(2)O_(4)/NF electrode exhibits an impressive HER activity with a low overpotentials of58 mV at 10 mA cm^(-2),a Tafel slop of 75 mV dec^(-1),as well as superior durability in alkaline medium.This work may provide a new pathway to effectively improve the hydrogen evolution performance of transition metal phosphides and to develop promising electrodes for practical electrocatalysis.

Nitrogen doping/infusion of 650 MHz cavities for CEPC

The nitrogen doping/infusion of 650 MHz cavities for the circular electron positron collider(CEPC)is investigated in this study.Two 650 MHz 1-cell cavities are first treated via buffered chemical polishing(BCP),followed by nitrogen doping.A"2/6"condition is adopted,similar to that for 1.3 GHz cavities of Linear Coherent Light Source II.The quality factor of both cavities improved to 7×10^(10)in low fields,i.e.,higher than that obtained from the baseline test.One 650 MHz two-cell cavity is nitrogen infused at 165℃for 48 h with a BCP surface base.The intrinsic quality factor(Q0)reached6×10^(10)at 22 MV/m in the vertical test,and the maximum gradient is 25 MV/m,which exceeds the specification of the CEPC(4×10^(10)at 22 MV/m).

Impact of nitrogen doping on growth and hydrogen impurity incorporation of thick nanocrystalline diamond films

A much larger amount of bonded hydrogen was found in thick nanocrystalline diamond （NCD） films produced by only adding 0.24% N2 into 4% CH4/H2 plasma, as compared to the high quality transparent microcrystalline diamond （MCD） films, grown using the same growth parameters except for nitrogen. These experimental results clearly evidence that defect formation and impurity incorporation （for example, N and H） impeding diamond grain growth is the main formation mechanism of NCD upon nitrogen doping and strongly support the model proposed in the literature that nitrogen competes with CHx （x = 1, 2, 3） growth species for adsorption sites.

Enhancing water splitting via weakening H_(2) and O_(2) adsorption on NiCo-LDH@CdS due to interstitial nitrogen doping: A close look at the mechanism of electron transfer

This paper is a report on the development of a convenient approach to fabricating a very efficient hybrid photoelectrocatalyst for water splitting.This photoelectrocatalyst consists of nickel-cobalt layered double hydroxide as the core,cadmium sulfide as the shell,and nitrogen,hence NiCo-LDH@CdS-N.For the electrocatalytic activity to be improved,the H_(2) and O_(2) binding energy needs to be weakened.The interstitial nitrogen doping on NiCo-LDH@CdS can increase electrocatalytic activity to a great extent.NiCoLDH@CdS nanoparticles are obtained by subjecting to nitriding the NiCo-LDH@CdS electrode coated with polyvinylpyrrolidone nanosheets.This electrode has a large specific surface area,allows fast transfer of electrons,and exhibits long-term stability.The experimental results presented in this paper reveal that interstitial nitrogen doping largely reduces H_(2) and O_(2) binding energy and lowers the activation barrier for the formation and splitting of water.

Electronic Transport Properties of Diblock Co-Oligomer Molecule Devices Sandwiched between Nitrogen Doping Armchair Graphene Nanoribbon Electrodes

We investigate the electronic transport properties of dipyrimidinyl-diphenyl sandwiched between two armchair graphene nanoribbon electrodes using the nonequilibrium Green function formalism combined with a first-principles method based on density functional theory. Among the three models M1–M3, M1 is not doped with a heteroatom. In the left parts of M2 and M3, nitrogen atoms are doped at two edges of the nanoribbon. In the right parts, nitrogen atoms are doped at one center and at the edges of M2 and M3, respectively. Comparisons of M1, M2 and M3 show obvious rectifying characteristics, and the maximum rectification ratios are up to 42.9 in M2. The results show that the rectifying behavior is strongly dependent on the doping position of electrodes. A higher rectification ratio can be found in the dipyrimidinyl-diphenyl molecular device with asymmetric doping of left and right electrodes, which suggests that this system has a broader application in future logic and memory devices.

Toughness enhancement of single-crystal diamond by the homoepitaxial growth of periodic nitrogen-doped nano-multilayers

Periodic nitrogen-doped homoepitaxial nano-multilayers were grown by microwave plasma chemical vapor deposition. The residual time of gases(such as CH4and N2) in the chamber was determined by optical emission spectroscopy to determine the nano-multilayer growth process, and thin, nanoscale nitrogen-doped layers were obtained. The highest toughness of 18.2 MPa·m^(1/2)under a Young’s modulus of1000 GPa is obtained when the single-layer thickness of periodic nitrogen-doped nano-multilayers is about 96 nm. The fracture toughness of periodic nitrogen-doped CVD layer is about 2.1 times that of the HPHT seed substrate. Alternating tensile and compressive stresses are derived from periodic nitrogen doping;hence, the fracture toughness is significantly improved. Single-crystal diamond with a high toughness demonstrates wide application prospects for high-pressure anvils and single-point diamond cutting tools.

Preparation and Electrochemical Performance of Si@void@NC Composite with a Tunable Nitrogen Doping Content in the Carbon Layer

A strategy for the preparation nitrogen-doped carbon encapsulated Si nanocomposite with a void layer(Si@void@NC)is proposed,in which the nitrogen doping content in the carbon layer is tunable.Aniline and ortho-phenylenediamine are both selected as the nitrogen,carbon sources and co-polymerized on Si@SiO_(2),in which SiO_(2)is functionalized as a void template.SEM and TEM observation show that Si nanoparticles are encapsulated in a hollow and interconnected carbon cages with a thickness of less than 10 nm,which is inclined to agglomerate together to form larger particles in micrometer scale.The variation of mole ratio of aniline and ortho-phenylenediamine will enable the change of nitrogen doping level in the carbon layer and ranges from 3.2%to 8.4%.The nitrogen is doped into the carbon framework in the form of pyridinic,pyrrolic and graphitic nitrogen.Electrochemical tests indicate that the nitrogen content influences the SEI formation and the lithiation of Si nanoparticles.The potential for the decomposition of electrolyte to form SEI film and the alloying of Si-Li negatively shift when the nitrogen doping content is increased.Furthermore,the cycling performance of Si@void@NC is improved when raising the nitrogen content in the carbon.And the optimal nitrogen content is 7.5%,which is corresponding to the mole ratio of aniline to ortho-phenylenediamine is 5:5.

Effects of Nitrogen Doping on Microstructures and Irradiation Resistance of Ti-Zr-Nb-V-Mo Refractory High-Entropy Alloy

Interstitial strengthening with nitrogen(N)is one of the effective ways to improve the mechanical properties of HEAs,but the effects of N on the microstructures and mechanical properties of the irradiated HEAs have not been studied extensively.Here,the microstructures and mechanical properties of N-free and N-doped Ti_(2)ZrNbV_(0.5)Mo_(0.2)HEAs before and after He irradiation were investigated.The results showed that the solid solution strengthening caused by interstitial N improved the yield strength at room temperature and 1023 K without significantly reducing plasticity.N doping significantly promoted the growth,aggregation and wider spatial distribution of He bubbles by enhancing the mobility of He atoms/He-vacancy complexes,with the average size of He bubbles increasing from 10.4 nm in N-free HEA to 31.0 nm in N-doped HEA.In addition,N-doped HEA showed a much higher irradiation hardness increment and hardening fraction than N-free HEA.Contrary to conventional materials doped with N,the introduction of N into Ti_(2)ZrNbV_(0.5)Mo_(0.2)HEA had adverse effects on its resistance to He bubble growth and irradiation hardening.The results of this study indicated that N doping may not improve the irradiation resistance of HEAs.

Multiscale confinement nitridation in molybdenum carbide for efficient hydrogen production

The molybdenum carbide(Mo_(2)C)has been regarded as one of the most cost-efficient and stable electrocatalyst for the hydrogen evolution reaction(HER)by the virtue of its Pt-like electronic structures.However,the inherent limitation of high density of empty valence band significantly reduces its catalytic reactivity by reason of strong hydrogen desorption resistance.Herein,we propose a multiscale confinement synthesis method to design the nitrogen-rich Mo_(2)C for modulating the band structure via decomposing the pre-coordination bonded polymer in a pressure-tight tube sealing system.Pre-bonded c/N-Mo in the coordination precursor constructs a micro-confinement space,enabling the homogeneous nitrogenization in-situ happened during the formation of Mo_(2)C.Simultaneously,the evolved gases from the precursor decomposition in tube sealing system establish a macro-confinement environment,preventing the lattice N escape and further endowing a continuous nitridation.Combining the multiscale confinement effects,the nitrogen-rich Mo2C displays as high as 25%N-Mo concentration in carbide lattice,leading to a satisfactory band structure.Accordingly,the constructed nitrogen-rich Mo_(2)C reveals an adorable catalytic activity for HER in both alkaline and acid solution.It is anticipated that the multiscale confinement synthesis strategy presents guideline for the rational design of electrocatalysts and beyond.