Surface Nitrogen Content Research Articles

N-doped Porous Carbon Derived from the Pyrolysis of a Polydopamine-coated Hypercross-linked Polymer for Enhanced CO2 Adsorption.

Porous carbon materials can simultaneously capture and convert carbon dioxide, helping to reduce greenhouse gas emissions and using carbon dioxide as a feedstock for the production of valuable chemicals or fuel. In this work, a series of N-doped porous carbons (PDA@HCP(x:y)-T) was prepared; the CO2 adsorption capacity of the prepared PDA@HCP(x:y)-T was enhanced by coating polydopamine (PDA) on a hypercross-linked polymer (HCP) and then adjusting the mass ratio of PDA to HCP and the carbonization temperature. The results showed that the prepared PDA@HCP(1:1)-850 exhibited a high CO2 adsorption capacity due to abundant micropores (0.6762 cm3/g), a high specific surface area (1220.8 m²/g), and moderate surface nitrogen content (2.75%). Notably, PDA@HCP(1:1)-850 exhibited the highest CO2 uptake of 6.46 mmol/g at 0 °C and 101 kPa. Critically, these N-doped porous carbons can also be used as catalysts for the reaction of CO2 with epichlorohydrin to form chloropropylene carbonate, with chloropropylene carbonate yielding up to 64% and selectivity of the reaction reaching 94%. As a result, these N-doped porous carbons could serve as potential candidates for CO2 capture and conversion due to their high reactivity, excellent CO2 uptake, and good catalytic performance.

Relationship of CO2 adsorption performance and physicochemical property of biochar prepared by different types of biomass waste

The physicochemical property of biochar prepared by biomass waste is crucial for CO2 adsorption performance. However, the quantified relationship between the physicochemical property and CO2 adsorption capacity for biochar is still unclear. In this study, biochar samples with different physicochemical properties were prepared from six representative biomass of sewage sludge, chicken manure, apple and prickly ash branch, corn and rice straw. The quantitative investigation was conducted and the relationship between the physicochemical properties and CO2 adsorption capacity of biochar was analysed using Pearson correlation analysis method. The results showed that the biochar prepared from prickly ash branch at 800 °C pyrolysis exhibited a better CO2 adsorption capacity of 154.44mg/g and larger specific surface area of 160.83 m2/g, compared with other biochars. According to the quantitative data about physicochemical properties of twenty-four kinds of biochar samples, the correlations between CO2 adsorption capacity and microcrystalline structure, surface functional groups, nitrogen content and specific surface area were obtained. The CO2 adsorption capacity showed a significant positive correlation with the specific surface area (SBET),stacking height of aromatic layers (Lc), number of aromatic layers (N) and nitrogen content, and the correlation order was SBET >N >Lc = nitrogen content. Moreover, the CO2 adsorption capacity showed a negative correlation with diameter of aromatic planes (La), C=O, O-H and index of aromaticity (Aal/Aar), and the order of correlation was C=O > O-H >La >Aal/Aar. The effect mechanism of physicochemical properties on CO2 adsorption of biochar was that microcrystalline structure had an influence on CO2 adsorption by van der Waals force, and nitrogen, oxygen-containing functional groups, and so on by Lewis acid-base interaction and hydrogen bonding.

Machine learning assisted prediction of specific surface area and nitrogen content of biochar based on biomass type and pyrolysis conditions

Predicting and optimizing the physicochemical properties of biochar is crucial for its applications. The characteristics of biomass and pyrolysis conditions are the main factors influencing these properties. However, the numerous components of biomass and the pyrolysis conditions contribute to the substantial challenge in predicting the physicochemical properties, particularly the specific surface area and the nitrogen content of biochar. In this work, machine learning methods including random forest (RF), gradient boosting decision tree (GBDT) and extreme gradient boosting (XGB) (all with R2 exceeding 0.97) were used to predict and analyze specific surface area of biochar (SSA), N content of biochar (N-char), and yield of biochar (Yield-char). Compositions of biomass and pyrolysis conditions were selected as input variables. The partial dependence plot analysis showed the impact way of each influential factor on the target variable and the interactions among these factors in the pyrolysis process. The feature importance of these models indicated that the influencing factors toward predicting three targets (sorted by importance) were specified as follows: pyrolysis temperature, nitrogen content, and fixed carbon for Yield-char; N and ash for N-char; ash and pyrolysis temperature for SSA. This work provided new insights for understanding pyrolysis process of biomass.

Performance evaluation of different nitrogenous biomass pyrolysis chars: Physicochemical properties and ibuprofen adsorption

The preparation of high-performance porous carbons (HPPCs) using biomass as adsorbent is a viable strategy for the treatment of ibuprofen (IB) in water. In the present study, pyrolyzed carbon was prepared from duckweed (DW) and rice straw (SW) at 400, 500, and 600 °C, and subsequently mixed pyrolysis with KOH to prepare the HPPCs. The HPPCs were used for the treatment of ibuprofen (IB) in water to evaluate their absorption performance. The physicochemical properties of biochar and HPPCs were investigated using scanning electron microscopy, X-ray electron microscopy, Raman microscopy, and the Brunauer-Emmett-Taylor method. In IB adsorption experiments, adsorption equilibrium was evaluated using Langmuir and Freundlich isotherm models. The maximum adsorption capacities of DW and SW were 0.952 and 0484 g/g, respectively, at an IB concentration of 0.5 g/L. The adsorption capacity of HPPCs for IB is influenced by a multifactorial combination of the specific surface area, nitrogen content, and nitrogen-containing functional groups on the surface. Generally, the HPPCs showed great potential for the removal of the IB pharmaceutical contaminants from aqueous solutions.

Preparation and Characterization of Five Amino-Modified Hyper-Crosslinked Polymers and Performance Evaluation for Aged Transformer Oil Reclamation

Adsorption is intensively considered to be the most feasible and economical option for aged transformer oil treatment. In this work, five aminated hyper-crosslinked polymers were prepared from chloromethylated polystyrene–co-divinylbenzene (Cl-PS-DVB) through a two-stage modification of crosslinking and five different reagents aminating. After modification, the specific surface area (SBET) and nitrogen content (CN) of prepared resins were greatly improved. To evaluate the reclamation performance of resins for removing oxides and contaminants from aged transformer oils, the total acid number (TAN) and color of oils were mainly examined. The results shown that the prepared resins have superior oil reclamation capacity compared to commercial resin XAD-4 due to their higher microporous specific surface area (Smic) and surface polarity. Among them, the NHC-R3, which used dimethyltriamine (DETA) as an aminating agent, had the best deacidification and decolorization performance. A series of experiments were designed to investigate the optimal regeneration program conditions for NHC-R3, and the additional electrical characteristics of the reclaimed oil, including breakdown voltage, dielectric dissipation factor (DDF), and interfacial tension, were measured as evidence that aged oil was successfully reclaimed.

Co-production of porous N-doped biochar and hydrogen-rich gas production from simultaneous pyrolysis-activation-nitrogen doping of biomass: Synergistic mechanism of KOH and NH3

In this study, a method of simultaneous activation and nitrogen doping during biomass fast pyrolysis for co-production of porous N-doped biochar and H2-rich gas production was proposed. The effect of temperature on chemical interaction mechanism of KOH and NH3 was investigated at 500–800 °C. Results showed that KOH and NH3 had a synergistic effect on pore development and nitrogen doping, and the specific surface area and nitrogen content reached maximum values of 2008.37 m2/g and 5.05 wt%, respectively. It may be due to that NH3 entered pores generating by KOH activation for further activation, and at the same time, excessive NH3 could convert new O-containing groups to N-containing groups for more effective nitrogen doping. What's more, the H2 concentration and yield were up to 56.67 vol% and 517.95 mL/g, respectively. It indicates that the synchronization method of fast pyrolysis-activation-nitrogen doping is a promising approach, which is of great significance for the high-value utilization of biomass.

Natural bio-waste-derived 3D N/O self-doped heteroatom honeycomb-like porous carbon with tuned huge surface area for high-performance supercapacitor

Supercapacitor electrodes (SCs) of carbon-based materials with flexible structures and morphologies have demonstrated excellent electrical conductivity and chemical stability. Herein, a clean and cost-effective method for producing a 3D self-doped honeycomb-like carbonaceous material with KOH activation from bio-waste oyster shells (BWOSs) is described. A remarkable performance was achieved by the excellent hierarchical structured carbon (HSC-750), which has a large surface area and a reasonably high packing density. The enhanced BWOSs-derived HSC-750 shows an ultrahigh specific capacitance of 525 F/g at 0.5 A g−1 in 3 M KOH electrolyte, as well as high specific surface area (2377 m2 g−1), pore volume (1.35 cm3 g−1), nitrogen (4.70%), and oxygen (10.58%) doping contents. The SCs also exhibit exceptional cyclic stability, maintaining 98.5% of their capacitance after 10,000 charge/discharge cycles. The two-electrode approach provides a super high energy density of 28 Wh kg−1 at a power density of 250 W kg−1 in an alkaline solution, with remarkable cyclability after 10,000 cycles. The study demonstrates the innovative HSC synthesis from BWOSs precursor and cost-effective fabrication of 3D N/O self-doped heteroatom HSC for flexible energy storage.

Efficient Removal of Nickel from Wastewater Using Copper Sulfate-Ammonia Complex Modified Activated Carbon: Adsorption Performance and Mechanism.

The necessity to eliminate nickel (Ni) from wastewater stems from its environmental and health hazards. To enhance the Ni adsorption capacity, this research applied a copper sulfate-ammonia complex (tetraamminecopper (II) sulfate monohydrate, [Cu(NH3)4]SO4·H2O) as a modifying agent for a Phragmites australis-based activated carbon preparation. The physiochemical properties of powdered activated carbon (PAC) and a modified form ([Cu(NH3)4]-PAC) were examined by measuring their surface areas, analyzing their elemental composition, and using Boehm's titration method. Batch experiments were conducted to investigate the impact of various factors, such as Ni(II) concentration, contact time, pH, and ionic strength, on its substance adsorption capabilities. Additionally, the adsorption mechanisms of Ni(II) onto activated carbon were elucidated via Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The findings indicated that modified activated carbon ([Cu(NH3)4]-PAC) exhibited a lower surface area and total volume than the original activated carbon (PAC). The modification of PAC enhanced its surface's relative oxygen and nitrogen content, indicating the incorporation of functional groups containing these elements. Furthermore, the modified activated carbon, [Cu(NH3)4]-PAC, exhibited superior adsorption capacity relative to unmodified PAC. Both adsorbents' adsorption behaviors conformed to the Langmuir model and the pseudo-second-order kinetics model. The Ni(II) removal efficiency of PAC and [Cu(NH3)4]-PAC diminished progressively with rising ionic strength. Modified activated carbon [Cu(NH3)4]-PAC demonstrated notable pH buffering and adaptability. The adsorption mechanism for Ni(II) on activated carbon involves surface complexation, cation exchange, and electrostatic interaction. This research presents a cost-efficient preparation technique for preparing activated carbon with enhanced Ni(II) removal capabilities from wastewater and elucidates its underlying adsorption mechanisms.

Encapsulation of Tenebrio molitor Hydrolysate with DPP-IV Inhibitory Activity by Electrospraying and Spray-Drying.

This study investigates the encapsulation of Tenebrio molitor hydrolysate exhibiting DPP-IV inhibitory activity by spray-drying and electrospraying techniques. First, we optimized the feed formulation and processing conditions required to obtain nano-microcapsules by electrospraying when using Arabic gum as an encapsulating agent and pullulan and Tween 20 as additives. The optimum formulation was also dried by spray-drying, where the removal of the additives was also assayed. Morphology analysis reveals that electrosprayed capsules have a smaller size (1.2 ± 0.5 µm vs. 12.4 ± 8.7 µm) and greater uniformity compared to those obtained by spray-drying. Regarding the surface nitrogen content and DPP-IV inhibitory activity, our results show no significant difference between the electrosprayed capsules and spray-dried capsules containing additives (IC50 of ~1.5 mg protein/mL). Therefore, it was concluded that adding additives during spray-drying allows for a similar encapsulation efficiency and reduced degradation during processing, as achieved by electrospraying technique but providing higher productivity. On the other hand, spray-dried capsules without additives displayed a higher surface nitrogen content percentage, which was mainly due to the absence of Tween 20 in the feed formulation. Consequently, these capsules presented a higher IC50 value (IC50 of 1.99 ± 0.03 mg protein/mL) due to the potential degradation of surface-exposed peptides.

Efficient Alkyne Semihydrogenation Catalysis Enabled by Synergistic Chemical and Thermal Modifications of a PdIn MOF.

Recently, there has been a growing interest in using MOF templating to synthesize heterogeneous catalysts based on metal nanoparticles on carbonaceous supports. Unlike the common approach of direct pyrolysis of PdIn-MOFs at high temperatures, this work proposes a reductive chemical treatment under mild conditions before pyrolysis (resulting in PdIn-QT). The resulting material (PdIn-QT) underwent comprehensive characterization via state-of-the-art aberration-corrected electron microscopy, N2 physisorption, X-ray absorption spectroscopy, Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. These analyses have proven the existence of PdIn bimetallic nanoparticles supported on N-doped carbon. In situ DRIFT spectroscopy reveals the advantageous role of indium (In) in regulating Pd activity in alkyne semihydrogenation. Notably, incorporating a soft nucleation step before pyrolysis enhances surface area, porosity, and nitrogen content compared to direct MOF pyrolysis. The optimized material exhibits outstanding catalytic performance with 96% phenylacetylene conversion and 96% selectivity to phenylethylene in the fifth cycle under mild conditions (5 mmol phenylacetylene, 7 mg cat, 5 mL EtOH, R.T., 1 H2 bar).

Cycles of solar ultraviolet radiation favor periodic expansions of cyanobacterial blooms in global lakes

Global warming and eutrophication are known to increase the prevalence of cyanobacterial blooms, posing a severe threat to the ecological stability and sustainability of water bodies. The long-term (over an annual time frame) effect of UV radiation on cyanobacterial blooms in lakes are rarely discussed though the substantial effects of high-intensity UV radiation on the growth inhibition of marine phytoplankton were studied. Here, we employed the datasets on surface solar UV radiation, nitrogen and phosphorus concentrations, and the annual scales and frequencies of cyanobacterial blooms in lakes across long-term spatial scales to probe the relationship of UV radiation with cyanobacterial blooms. The results indicated that enhanced solar UV radiation may unintentionally stimulate cyanobacterial growth and favor the expansions of cyanobacterial blooms in lakes around the world. The fluctuating UV radiation significantly affects the annual scales of cyanobacterial blooms in both eutrophic and oligotrophic lakes. Solar UV radiation enhances the positive impact of rising phosphorus levels on cyanobacterial blooms because UV radiation prompts the synthesis of polyphosphate in cyanobacteria cells, which helps cyanobacteria to alleviate the stress of UV light. The scales of cyanobacterial blooms are significantly impacted by solar UV radiation intensities as opposed to the annual frequency of cyanobacterial blooms. Furthermore, solar UV radiation fluctuation with a 9-year period over a 14-year main cycles significantly affects the periodicities of cyanobacterial blooms in global lakes, which provides a basis for predicting the peak value of the scales of cyanobacterial blooms in lakes. These findings opened up new avenues of inquiry into the mechanism and management strategies of cyanobacterial blooms in lakes worldwide.

Valorising lignocellulosic biomass to high-performance electrocatalysts via anaerobic digestion pretreatment

AbstractAnaerobic digestion (AD) was initially evaluated as a potential preprocessing method for preparing biomass-based carbon electrocatalysts in this study. The AD pretreatment succeeded in the structural depolymerization and nitrogen enrichment of Hybrid Pennisetum, which provided favorable conditions to achieve efficient and homogeneous nitrogen introduction due to microorganism community enrichment and provided a porous structure by degradation of the biodegradable components. The resulted biochar exhibited improved physiochemical properties including higher specific surface areas, nitrogen content and graphitization degree than that obtained from pyrolyzing raw biomass. These improvements were positively correlated with the AD time and showed to have enhanced the performance in oxygen reduction reaction and practical microbial fuel cell applications. Amongst the investigated samples, the obtained biochar pretreated by AD for 15 days exhibited the most excellent performance with an onset potential of 0.17 V (VS. saturated calomel electrode) and the maximal power density of 543.2 mW cm−2 assembled in microbial fuel cells. This study suggested applying AD as a new biological pretreatment in the preparation of biomass-based electrocatalysts, and provided a unique pathway for fabricating high-performance biochar-based catalysts by structure optimization and N-containing active sites construction via gentle biological method, thereby providing a cost-effective method to fabricate metal-free catalysts for oxygen reduction reaction. Graphical Abstract

Tailoring Nitrogen‐Doped Activated Carbons: Central Composite Design for Enhanced CO2 Adsorption

AbstractIn a single step, nitrogen‐doped activated carbons have been synthesized using walnut shells and urea as precursors by chemical activation with K2CO3. The textural and elemental properties such as surface area, micropore volume, nitrogen content, and yield were optimized in a multivariable way using a central composite design of experiments 23, varying the urea‐nutshell ratio, K2CO3 ratio, and activation temperature. Activated carbon doped with the highest nitrogen presented a surface area of 895 m2 g−1, a micropore volume of 0.22 cm3 g−1, and a nitrogen content of 4.11 %. Furthermore, the yield of 13.85 % at urea impregnation ratio 1.56 gUrea gNutshell−1, activating agent ratio 1.4 gK2CO3 gCarbon−1, and temperature of 591 °C, being the temperature and the urea impregnation ratio the significant variables in the responses evaluated. The best‐activated carbon doped with nitrogen presented a CO2 adsorption capacity of 2.78 mol kg−1, reversible adsorption‐desorption, and selectivity against nitrogen of 33.2 molCO2/molN2, superior to a commercial activated carbon with similar textural properties at the same experimental conditions and being in the order of magnitude as activated carbons synthesized under similar conditions.

Lignin-derived nitrogen doped hierarchical porous carbon spheres for highly efficient dichloromethane adsorption

Biomass-prepared porous carbon materials are promising solid adsorbents for the removal of volatile organic compounds (VOCs). However, their application is hindered due to the insufficient number of pores and poor surface activity. In this study, a lignin-derived nitrogen-doped hierarchical porous carbon sphere (NHPCS-0.5) with abundant surface active sites was synthesised through spray drying and carbonisation–activation methods. The optimised NHPCS-0.5 displayed a high BET specific surface area (2961 m2·g−1) and total pore volume (1.57 cm3·g−1), developed hierarchical porous distribution with micro-/meso-/macropores and satisfactory surface nitrogen content. Moreover, it exhibited an excellent dichloromethane adsorption capacity of 156 mg·g−1 and maintained 86% of initial capacity after five regeneration cycles, indicating an outstanding regenerative ability. The nitrogen introduction improved the micropore volume and adsorption capacity. Adsorption mechanism reveals that micropore filling and enhanced van der Waals interaction of carbon surface with dichloromethane molecule by N-containing functional groups played a vital role in adsorption, and mesopores contributed to the high adsorption rates. The above results indicate the potential of NHPCS-0.5 as an adsorbent for VOC removal and provide new ideas for the utilisation of lignin and design of carbon sphere materials.

Interface modification of TiAlN coated TiCN-based cermet through plasma nitriding

This study aimed to enhance the comprehensive properties of coated TiCN-based cermets through a combination of plasma nitriding (PN) and physical vapor deposition (PVD) of TiAlN. Varied N2/Ar ratio gas mixtures were utilized as the plasma discharge atmosphere. The investigation focused on the structure and characteristics of the coated TiCN-based cermets. Results indicated an increase in surface hardness and nitrogen content on the substrate, along with a refinement in the grain structure of the TiAlN coating following plasma nitriding by adjusting the N2/Ar ratio. The coatings predominantly exhibited the (200) orientation. When the N2/Ar ratio varied, there was a nitrided layer on the substrate surface with a thickness of 1 to 1.5 μm. Moreover, optimal outcomes, including the highest H/E ratio (0.094) for the TiAlN coating, and improved cutting performance of the coated TiCN-based cermet insert, were achieved under the condition of N2:Ar = 1:1.

Development of Fe-13.8Cr-8.9Mn alloy for steel biomaterials

Traumatic, osteoarthritic, tumoral, and congenital bone issues impact human lives and health. The next generation of bone implants is made from biodegradable materials, including Fe-based materials with superior mechanical properties and high biocompatibility. However, efforts to inhibit the risk of inflammation and bacterial infection due to the biological response and corrosion properties of metals are a significant challenge. This study aims to develop biomaterials based on Fe-Cr-Mn alloys to obtain superior physical and mechanical properties through plasma nitriding. Each sample was plasma-nitridated in a vacuum chamber at various temperatures of 250–450 °C for 3 hours at a pressure of 1.8 kPa. Several main tests were performed to investigate the effects of plasma nitriding, such as the chemical compositions of raw material, surface nitrogen contents, phase changes, thickness, hardness, and corrosion. Those parameters were then used to evaluate plasma nitriding's effectiveness, including observing the change in phenomena at each temperature treatment. The results indicated that forming the S phase on the surface of Fe-13.8Cr-8.9Mn alloy is a saturated solution of nitrogen in ɣ-Fe, where the nitrogen content on the surface increases with increasing nitriding temperature. The layer's surface hardness is uniform across its whole thickness, which reduces as the grade of raw material passes through the nitride layer. The highest hardness at a nitriding temperature of 450 °C reached 625.3 VHN. The findings showed that the corrosion rate decreased significantly, reaching the lowest value, 0.0018 mm/year, at a plasma nitriding temperature of 450 °C. Plasma nitriding could enhance the physical and mechanical properties of Fe-Cr-Mn alloy

A three-step process to produce biochar with good magnetism, high specific surface area, and high levels of nitrogen doping for the efficient removal of sulfamethoxazole

Efficient sorbents that have high sorption capacity and suitable separability are promising and are urgently needed to remove diverse contaminants from water environments. In this study, nitrogen-doped magnetic porous biochars (NMPBs) were synthesized from marine algae by a three-step process consisting of prepyrolysis, copyrolysis and coprecipitation. For NMPBs, the surface area was up to 1531 m2/g, the magnetization strength was up to 31 emu/g, and the surface nitrogen content was up to 3 %. The NMPBs showed the expected sorption capability for sulfamethoxazole, with the removal quantity reaching 502 mg g−1 based on the sorption isotherm model. NMPBs also showed excellent separability and reusability, and the removal rate remained at 87 % after seven cycles. Partitioning and adsorption, including pore filling, hydrogen bonding, π-π stacking, partitioning and electrostatic interactions, were the sorption processes in removing sulfamethoxazole. In this work, marine algae were converted into an engineered biochar that is promising for environmental remediation.

Surface chemical composition of single WNh stars

Context. Wolf–Rayet (WR) stars of the WNh category contain a significant fraction of hydrogen at their surface. They can be hydrogen-burning, very massive stars or stars in a post-main sequence phase of evolution. Also, WNh stars are sometimes not included in population synthesis models. Aims. We aim to better characterise the properties of single WNh stars in the Galaxy and the Magellanic Clouds. In particular, we want to constrain their surface chemistry beyond the hydrogen content by determining the helium, carbon, and nitrogen surface abundances. Methods. We perform a spectroscopic analysis of 22 single WNh stars. We fit their ultraviolet and/or optical spectra using synthetic spectra computed with the code CMFGEN. We determine the main stellar parameters (temperature, luminosity, mass-loss rates) and the surface H, He, C, and N mass fractions. We investigate the ability of current evolutionary models to reproduce all parameters at the same time. Results. We find that all WNh stars show the signatures of CNO-cycle material at their surface: they are carbon-depleted and nitrogen-rich. A clear trend of higher nitrogen content at higher metallicity is observed, as expected. The amount of hydrogen (X) varies significantly from one star to another, independently of luminosity. Values of X larger than 0.4 are not exceptional. The majority of Galactic WNh stars can be explained by evolutionary models, provided sufficient fine-tuning of the input parameters of evolutionary calculations. At lower metallicity, most stars escape predictions from evolutionary models. This has been noted in the literature but constraints on the surface nitrogen content exacerbate this severe issue. Conclusions. Our study highlights the need to refine the treatment of WR stars in both stellar evolution and population synthesis models.

Preparation of amine-incorporated hydroxyapatite through a single-step hydrothermal reaction

We report on the preparation of an amine-incorporated hydroxyapatite (NH2-HAP) by applying o-phosphorylethanolamine (PEA) as a phosphate source. By changing the ratio of PEA to normal phosphate source, three samples of NH2-HAPs having different contents of amine are synthesized. The TEM analysis confirmed that NH2-HAP exhibits elongated rod shape which is similar to the hexagonal rod of pure hydroxyapatite (HAP). As the concentration of PEA increases, the average size of NH2-HAP along (001) direction decreases approximately from 55.4(±10.39) to 31.2(±8.3) nm. The XRD patterns of NH2-HAPs are well matched with typical HAP patterns. Line broadening of XRD peaks in NH2-HAP seems to originate from low crystallinity and smaller size compared to pure HAP. Primary amine group on the surface of NH2-HAP is confirmed by both surface elemental analysis (XPS) and the ninhydrin test. The nitrogen content of NH2-HAP surface is approximately 0.6 ∼ 1.1 at.% based on XPS experiment.

Boosting the electrochemical performance of NiFe2O4/Carbon composite materials by nitrogen doping for supercapacitors application

The development of high-performance anode materials is of great importance for improving the electrochemical performance of asymmetric supercapacitors. Here, nickel ferrite/porous carbon composite is synthesized via hydrothermal approach and the electrochemical properties are improved by nitrogen doping process. As the surface nitrogen content of the porous carbon precursor increased from 2.40 at.% to 9.53 at.%, the nickel ferrite/porous carbon composite exhibited substantial improvement in specific capacitance (increased from 136.4 to 201.4 F g−1 at 1 A g−1) in an alkaline aqueous electrolyte. The energy density of the assembled asymmetric supercapacitor was increased from 17.7 W h kg−1 to 11.2 W h kg−1, and the cycle retention rate after 10,000 cycles at 2 A g−1 was increased from 16.5 % to 85.7 %. Nitrogen atoms on the carbon surface provide active sites for the growth of nickel ferrite nanoparticles and enhance the interfacial effect between nickel ferrite nanoparticles and porous carbon materials, enhancing the charge transfer and preventing particle aggregation during charge and discharge processes. The fabricated nickel ferrite/nitrogen-doped porous carbon composite exhibits excellent capacitance and cycling stability, providing a new option for asymmetric supercapacitor anode materials.