N-doped Carbon Fibers Research Articles

Supramolecular imprinted cellulose-based N-doped biomass carbon fiber for visual detection and specific degradation of perfluorooctanoic acid

In this study, we successfully synthesized SMIP@N-CF, a nitrogen-doped biomass carbon fiber, using supramolecular imprinting technology. This material has good perfluorooctanoic acid (PFOA) adsorption properties and excellent photocatalytic ability. Therefore, it is possible to apply SMIP@N-CF to the detection system of PFOA for visual detection and to the photocatalytic process based on peroxymonosulfate (PMS) for the degradation of PFOA. The Independent Gradient Model (IGM) explains that visual detection relies on the rapid adsorption of PFOA by functional monomers, covering the catalytic site and resulting in a color change. Experimental evidence verifies its good linear response within the 0.07–90 µM range. Density Functional Theory (DFT) elucidates that charge transfer between pyridine N and C atoms activated PMS to produce reactive oxygen species to degrade PFOA, and the final degradation rate reached 94.3 %. The successful application of SMIP@N-CF provides a new idea for further understanding nitrogen-doped biomass materials and provides a scientific basis for detecting and degrading PFOA in water.

Flexible Ti3 C2 Tx MXene Bonded Bio-Derived Carbon Fibers Support Tin Disulfide for Fast and Stable Sodium Storage.

High energy density and flexible electrodes, which have high mechanical properties and electrochemical stability, are critical to the development of wearable electronics. In this work, a free-standing MXene bonded SnS2 composited nitrogen-doped carbon fibers (MXene/SnS2 @NCFs)film is reported as a flexible anode for sodium-ion batteries. SnS2 nanoparticles with high-capacity properties are covalently decorated in bio-derived nitrogen-doped 1D carbon fibers (SnS2 @NCFs) and further assembled with highly conductive MXene sheets. The addition of bacterial cellulose (BC) can further improve the flexibility of the film. The unique 3D structure of points, lines, and planes can not only offset the disadvantage of low conductivity of SnS2 nanoparticles but also expand the distance between MXene sheets, which is conducive to the penetration of electrolytes. More importantly, the MXene sheets and N-doped 1D carbon fibers (NCFs) can accommodate the large volume expansion of SnS2 nanoparticles and trap polysulfide during the cycle. The MXene/SnS2 @NCFs film exhibits better sodium storage and excellent rate performance compared to the SnS2 @NCFs. The in situ XRD and ex situ (XRD, XPS, and HRTEM) techniques are used to analyze the sodiation process and to deeply study the reaction mechanism of the films. Finally, the quasi-solid-state full cells with MXene/SnS2 @NCFs and Na3 V2 (PO4 )3 @carbon cloth (NVP@CC) fully demonstrate the application potential of the flexible electrodes.

CoS2 confined into N-doped coal-based carbon fiber as flexible anode for high performance potassium-ion capacitor

Potassium-ion capacitors (PICs), skillfully combining the features of batteries and capacitors, hold promise in energy conversion and storage. Cobalt sulfide (CoS2) anode are promising alternatives due to its high theoretical capacity and excellent potassium storage capacity. However, severe volume changes of CoS2 anode leads to capacity decline and poor cycle stability, hindering its application in PICs. Herein, we successfully confine CoS2 nanoparticles in N-doped coal-based carbon fibers (CoS2/CF). Coal-based carbon fibers with flexible characteristic elevate the conductivity and relieve the volume expansion of CoS2. Moreover, the high content of edge nitrogen as active sites further enhances the electrochemical properties. The PICs with flexible CoS2/CF-0.8 as anode exhibits superior specific capacity (331.1 mA h g−1 after 150 cycles at 0.1 A g−1) and long cycling (214.1 mA h g−1 after 900 cycles at 1.0 A g−1). Ex-situ X-ray powder diffraction (XRD) reveal that the mechanism of CoS2/CF-0.8 anode is based on reversible intercalation and conversion reaction. Importantly, CoS2/CF-0.8||activated carbon (AC) devices shows excellent energy density (101.9 W h kg−1) and long cycling (82.23% capacity maintenance rate after 1000 cycles). This work offers insights for other materials with high theoretical capacity but volume expansion problem.

ZnS/SnS2 Heterostructures Encapsulated in N-Doped Carbon Nanofibers for High-Performance Alkali Metal-Ion Batteries.

Heterogeneous composite ZnS/SnS2 is designed to meet various requirements for alkali metal-ion batteries. The composite is prepared using an electrostatic spinning method and encapsulated in N-doped carbon fibers after high-temperature vulcanization. The special structure of the composite provides a dependable interconnection and fast conductive network for alkali metal ions. The conductive carbon network shortens the diffusion path and greatly improves the migration efficiency of the alkali metal ions in the electrode. As expected, when the current density is 0.1 A g-1, the ZnS/SnS2@NCNFs maintain a high discharge capacity of more than 1437.5, 1321.2, and 861.6 mA h g-1 for lithium-ion, sodium-ion, and potassium-ion batteries, respectively. What is more, a full cell using a prelithiated composite anode and a LiFePO4 cathode is tested and shows excellent electrochemical performance. This work provides new perspectives for the development of novel anodes that can efficiently store alkali metal ions, as well as for the fine-structure design of materials.

Optimizing oxygen vacancies through grain boundary engineering to enhance electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction is a challenging process that requires achieving high ammonia yield rate and reasonable faradaic efficiency. To address this issue, this study developed a catalyst by in situ anchoring interfacial intergrown ultrafine MoO2 nanograins on N-doped carbon fibers. By optimizing the thermal treatment conditions, an abundant number of grain boundaries were generated between MoO2 nanograins, which led to an increased fraction of oxygen vacancies. This, in turn, improved the transfer of electrons, resulting in the creation of highly active reactive sites and efficient nitrogen trapping. The resulting optimal catalyst, MoO2/C700, outperformed commercial MoO2 and state-of-the-art N2 reduction catalysts, with NH3 yield and Faradic efficiency of 173.7 μg h-1 mg-1cat and 27.6%, respectively, under - 0.7 V vs. RHE in 1 M KOH electrolyte. In situ X-ray photoelectron spectroscopy characterization and density functional theory calculation validated the electronic structure effect and advantage of N2 adsorption over oxygen vacancy, revealing the dominant interplay of N2 and oxygen vacancy and generating electronic transfer between nitrogen and Mo(IV). The study also unveiled the origin of improved activity by correlating with the interfacial effect, demonstrating the big potential for practical N2 reduction applications as the obtained optimal catalyst exhibited appreciable catalytic stability during 60 h of continuous electrolysis. This work demonstrates the feasibility of enhancing electrocatalytic nitrogen reduction by engineering grain boundaries to promote oxygen vacancies, offering a promising avenue for efficient and sustainable ammonia production.

Construction of lotus stem-like Li3VO4 wrapped on carbon fibers via chemical lithiation promoting interfacial dynamics for capacitive lithium storage

Oxides based on vanadium redox couple, such as orthorhombic Li3VO4, has drawn great attentions due to its high theoretical capacity and moderate operating voltage. However, the rate property is largely hindered by the slow interfacial dynamics of Li3VO4. Here we synthesized the lotus stem-like Li3VO4 wrapped in N-doped carbon fibers (Li3VO4/C NF) stemmed from the chemical lithiation of V2O3/C NF. The knobbly Li3VO4 rooted in the interconnected carbon fibers provides abundant active sites and well-developed conductive networks. Thus, this anode delivers high specific capacity of 558.9 mAh g−1 at 0.2 A g−1 and excellent rate capacity of 419 mAh g−1 at 2 A g−1 sustaining 900 cycles with an average potential of 0.7 V vs. Li+/Li. Furthermore, the kinetic analysis reveals that the pseudocapacitance dominants the lithium storage process and the favorable interfacial ion and electronic transport is responsible for the enhanced rate performance. The full cell (Li3VO4/C NF||LiFePO4) also shows a competitive performance for commercialization. This work boosts the development of vanadium-based anode materials with desired electrochemical properties meeting devices requirements.

A novel in-situ fabrication of N-doped carbon fibers wrapped nano-LiFePO4 composites as cathode of advanced Li-ion batteries

In this work, we first report a novel in-situ fabrication of N-doped carbon fibers-wrapped nano-LiFePO4 composites by reducing low- cost FePO4 with nitrilotriacetic acid (NTA). The crystallization temperature, particle morphology, composition, phase have been investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS) and scanning electron microscopy (SEM). The proper content of NTA is 10 wt%. As cathode of lithium-half batteries, the LiFePO4 composites with 10 wt% NTA deliver superior lithium storage performance to the previously reported LiFePO4. Specifically, the composites approach a capacity of 155.5 mA h g−1 after 500 cycles at 0.1C, 98 mAh g−1 after 2000 cycles at 10C, and good rate capability, which is suitable for the development of power batteries.

Fabrication of High-Recognition Self-Driven Protein Surface Imprinted Mesoporous N-Doped Carbon Fiber

Fabrication of High-Recognition Self-Driven Protein Surface Imprinted Mesoporous N-Doped Carbon Fiber

One dimensional pea-shaped NiSe2 nanoparticles encapsulated in N-doped graphitic carbon fibers to boost redox reversibility in sodium-ion batteries

In recent years, sodium-ion batteries (SIBs) have emerged as a promising technology for energy storage systems (ESSs) because of the abundance and affordability of sodium. Recently, metal selenides have been studied as promising high-performance conversion-type anode materials in SIBs. Among them, nickel selenide (NiSe2) has received considerable attention due to its high theoretical capacity of 495 mAh g–1 and conductivity. However, it still suffers from poor cycling stability because of the low electrochemical reactivity, large volume expansion, and structural instability during cycles. To address these challenges, NiSe2 nanoparticles encapsulated in N-doped graphitic carbon fibers (NiSe2@NGCF) were synthesized by using ZIF-8 as a template. NiSe2@NGCF showed a high discharge capacity of 558.3 mAh g–1 with a fading rate of 0.14% per cycle after 200 cycles at 0.5 A g–1 in 0.01–3.0 V. At a very high current density of 5 A g–1, the capacity still displayed excellent long-term cycle life with a discharge capacity of 406.1 mAh g–1 with a fading rate of 0.016% per cycle after 3000 cycles. The mechanism of the excellent electrochemical performance of NiSe2@NGCF was thoroughly investigated by ex-situ XRD, TEM, and SEM analyses. Furthermore, NiSe2@NGCF//Na3V2(PO4)3 full-cell also delivered an excellent reversible capacity of 378.7 mAh g−1 at 0.1 A g−1 after 50 cycles, demonstrating its potential for practical application in SIBs.

Free-standing N-doped hollow carbon fiber encapsulate P/GeP hybrid anode for rechargeable Li-ion battery

Red phosphorus (RP) with appropriate working voltage and high lithium storage specific capacity has been considered as high-performance anode for Li-ion battery (LiB). However, the volume expansion of the RP anode reached 350 % during the intercalation/deintercalation of Li-ion processes, resulting in the detachment of active material and poor specific capacity. Herein, flexible hollow nanochannel carbon nanofiber was prepared through simple electrospinning, then P/GeP nano powder were encapsulated in the N-rich carbon nanofiber using a facile in situ synthesis method, where the introduction of GeP not only innovatively served as the high conductive dispersant for P, but simultaneously acted as the active component in reacting with Li-ion. The unique designed nanoarchitecture not only boosted the structural stability and electronic conductivity of the hybrid composite, but also facilitated the transport of electrons and Li-ion. Upon served as free-standing LiB anode, the N-doped hollow carbon fiber encapsulate P/GeP (P/GeP/C) anode displayed remarkably reversible capacities, superior rate performances, and long-term cycle stability for lithium storage. For instance, P/GeP/C of only 10.6 wt% GeP and 28.5 wt% P delivered 290.2 mA h g−1 under a high current density of 5 A g−1 and showed a high capacity of 575.6 and 436.9 mA h g−1 at a current density of 0.1 A g−1 and 1.0 A g−1 after 50 cycles, respectively.

Coupling MnS and CoS Nanocrystals on Self-Supported Porous N-doped Carbon Nanofibers to Enhance Oxygen Electrocatalytic Performance for Flexible Zn-Air Batteries.

Seeking highly efficient, stable, and cost-effective bifunctional electrocatalysts of rechargeable Zn-air batteries (ZABs) is the top-priority for developing new generation portable electronic devices. For this, the rational and effective structural design, interface engineering, and electron recombination on electrocatalysts should be taken into account to reduce the reaction overpotential and expedite the kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we construct a MnCo-based metal organic framework-derived heterogeneous MnS-CoS nanocrystals, which are anchored on free-standing porous N-doped carbon fibers (PNCFs) by the in situ growth method and vulcanization process. Benefiting from the abundant vacancies and active sites, strong interfacial coupling as well as favorable conductivity, the MnS-CoS/PNCFs composite electrode delivers a mentionable oxygen electrocatalytic activity and stability with a half-wave potential of 0.81 V for ORR and an overpotential of 350 mV for OER in the alkaline medium. Of note, the flexible rechargeable ZAB using MnS-CoS/PNCFs as binder-free air cathode offers high power density of 86.7 mW cm-2, large specific capacity of 563 mA h g-1, and adapts to different bending degree of operation. In addition, the density functional theory calculation clarifies that the heterogeneous MnS-CoS nanocrystals reduces the reaction barrier and enhances the conductivity of the catalyst and the adsorption capacity of the intermediates during the ORR and OER process. This study opens up a new insight to the design of the self-supported air cathode for flexible electronic devices.

SnCo Nanoparticles Loaded in Hollow Carbon Spheres Interlinked by N-Doped Carbon Fibers for High-Performance Sodium-Ion Batteries.

The development of Sn-based materials with electrochemically inactive matrices is a novel strategy to alleviate the volume expansion and giant structure strain/stress during the sodiation/desodiation process. In this work, a freestanding membrane based on the unique bean pod-like host composed by nitrogen-doped carbon fibers and hollow carbon spheres (HCSs) encapsulated with SnCo nanoparticles is synthesized by electrospinning (B-SnCo/NCFs). In this unique bean pod-like structure, Sn acts as a host for Na+ storage, while the Co plays the important role of an electrochemically inactive matrix that can not only buffer the volume variations but also inhibit aggregation and particle growth of the Sn phase during the electrochemical Na-Sn alloying process. Meanwhile, the introduction of hollow carbon spheres can not only provide enough sufficient void space to withstand the volume expansion during the (de)sodiation processes but also improve the conductivity of the anode along the carbon fibers. Furthermore, the B-SnCo/NCF freestanding membrane can increase the contact area between the active material and the electrolyte, which can provide more active sites during the cycling process. When used as an anode material for Na-ion batteries, the freestanding B-SnCo/NCF anode exhibits an outstanding rate capacity of 243.5 mA h g-1 at 1.6 A g-1and an excellent specific capacity of 351 mA h g-1 at 0.1 A g-1 for 300 cycles.

WS2 nanosheets anchored on N-doped carbon fibers for superior electromagnetic wave absorption

The carbon fiber three-dimensional (3D) network structure causes conduction loss due to the induced current under an electromagnetic (EM) field, while it can serve as a substrate for the growth of other materials to construct carbon fiber-based composites. Usually, introducing other dielectric loss materials on the carbon fiber surface can adjust the EM parameters and impedance matching, and enhance the loss ability. N-doped carbon fibers anchored by WS2 nanosheets (NCFs@WS2) are reported in this work. When the filling ratio in paraffin is 10 wt%, the maximum reflection loss (RL) value reaches −81.1 dB at 3.5 mm. Additionally, the maximum effective absorption bandwidth (EAB) value reaches 6.24 GHz (9.44 ∼ 15.68 GHz) when the thickness is 3.0 mm. The introduction of WS2 nanosheets not only enhances the multiple scattering of EM waves, but also improves the interfacial polarization loss and dipole polarization loss. Therefore, the superior EM wave absorption performance of NCFs@WS2 is attributed to the good impedance matching, as well as the synergistic effect of conduction loss and polarization loss. This work enriches the research on carbon fiber-based composites and their EM wave absorption performance.

N-Doped Carbon Fibers Derived from Porous Wood Fibers Encapsulated in a Zeolitic Imidazolate Framework as an Electrode Material for Supercapacitors

Developing highly porous and conductive carbon electrodes is crucial for high-performance electrochemical double-layer capacitors. We provide a method for preparing supercapacitor electrode materials using zeolitic imidazolate framework-8 (ZIF-8)-coated wood fibers. The material has high nitrogen (N)-doping content and a specific surface area of 593.52 m2 g-1. When used as a supercapacitor electrode, the composite exhibits a high specific capacitance of 270.74 F g-1, with an excellent capacitance retention rate of 98.4% after 10,000 cycles. The symmetrical supercapacitors (SSCs) with two carbon fiber electrodes (CWFZ2) showed a high power density of 2272.73 W kg-1 (at an energy density of 2.46 W h kg-1) and an energy density of 4.15 Wh kg-1 (at a power density of 113.64 W kg-1). Moreover, the SSCs maintained 81.21% of the initial capacitance after 10,000 cycles at a current density of 10 A g-1, which proves that the SSCs have good cycle stability. The excellent capacitance performance is primarily attributed to the high conductivity and N source provided by the zeolite imidazole framework. Because of this carbon material's unique structural features and N-doping, our obtained CWFZ2 electrode material could be a candidate for high-performance supercapacitor electrode materials.

Si nanoparticles embedded in porous N-doped carbon fibers as a binder-free and flexible anode for high-performance lithium-ion batteries

Si has attracted more attention as an ideal anode for next-generation Li-ion batteries (LIBs), due to its large theoretical capacity and low de-lithiation voltage. However, extreme volume change (about 300%) and low electronic conductivity severely hinder its practical application. Herein, to overcome these problems, via the electrospinning and pyrolysis processes, Si nanoparticles are embedded in porous N-doped carbon fibers (Si/P-NCFs) and interwoven into a flexible film. The binder-free and flexible Si/P-NCFs can significantly enhance the Li-ion storage capacity (1386 mAh g−1 after 100 cycles at 0.1 A g–1), cycling stability (942 mAh g−1 over 1000 cycles at 1 A g−1), as well as rate capability (381 mAh g−1 at 10 A g−1). These improvements are ascribed to the spatial confinement of carbon fibers and buffering effect of porous structure, which synergistically prevent the harm caused by the volume change. Additionally, porous N-doped carbon networks and binder-free structure can significantly enhance electron/ion conductivities. This work demonstrates an effective design to address the volume change and low electronic conductivity of Si towards advanced flexible Si-based anodes, as well as exhibits promising potential in practical use.

Fabrication of N−doped carbon nanotube/carbon fiber dendritic composites with abundant interfaces for electromagnetic wave absorption

Three−dimensional (3D) hierarchical nano−microstructures have shown unprecedented physicochemical properties. However, it still remains great challenge to construct well−defined architectures with 3D hierarchical feature. Herein, we develop an electrospinning technique followed by a high−temperature carbonization process to fabricate N−doped carbon fibers (NCF) with N−doped carbon nanotubes (NCNTs) vertically grown on the surface of NCF using the Fe species as catalysts. In the 3D hierarchical structures, the Fe3C nanoparticles (NPs) are embedded within NCF matrix, while the Fe NPs are encapsulated within NCNT. Due to the unique structural feature, the as−prepared hierarchical structure exhibits excellent electromagnetic wave absorption performance with an absorption bandwidth of 4.0 GHz and a minimum reflection loss of −49.56 dB with a thickness as low as 1.50 mm. Experimental and theoretical studies indicate that the enhanced electromagnetic wave absorption performance of the hierarchical structure can be explained by the increased conduction loss induced by the introduction of metallic NPs and formation of 3D conductive networks, and the enhanced polarization loss caused by the additional interfaces and defects in the hierarchical structure. This work provides an efficient way to fabricate 3D architecture for high−efficiency electromagnetic wave absorption.

Hierarchically porous Co@N-doped carbon fiber assembled by MOF-derived hollow polyhedrons enables effective electronic/mass transport: An advanced 1D oxygen reduction catalyst for Zn-air battery

Developing advanced oxygen reduction reaction (ORR) electrocatalysts with rapid mass/electron transport as well as conducting relevant kinetics investigations is essential for energy technologies, but both still face ongoing challenges. Herein, a facile approach was reported for achieving the highly dispersed Co nanoparticles anchored hierarchically porous N-doped carbon fibers (Co@N-HPCFs), which were assembled by core-shell MOFs-derived hollow polyhedrons. Notably, the unique one-dimensional (1D) carbon fibers with hierarchical porosity can effectively improve the exposure of active sites and facilitate the electron transfer and mass transfer, resulting in the enhanced reaction kinetics. As a result, the ORR performance of the optimal Co@N-HPCF catalysts remarkably outperforms that of commercial Pt/C in alkaline solution, reaching a limited diffusion current density (J) of 5.85 mA cm−2 and a half-wave potential (E1/2) of 0.831 V. Particularly, the prepared Co@N-HPCF catalysts can be used as an excellent air-cathode for liquid/solid-state Zn-air batteries, exhibiting great potentiality in portable/wearable energy devices. Furthermore, the reaction kinetic during ORR process is deeply explored by finite element simulation, so as to intuitively grasp the kinetic control region, diffusion control region, and mixing control region of the ORR process, and accurately obtain the relevant kinetic parameters. This work offers an effective strategy and a reliable theoretical basis for the engineering of first-class ORR electrocatalysts with fast electronic/mass transport.

Sb Nanoparticles Embedded in the N-Doped Carbon Fibers as Binder-Free Anode for Flexible Li-Ion Batteries.

Antimony (Sb) is considered a promising anode for Li-ion batteries (LIBs) because of its high theoretical specific capacity and safe Li-ion insertion potential; however, the LIBs suffer from dramatic volume variation. The volume expansion results in unstable electrode/electrolyte interphase and active material exfoliation during lithiation and delithiation processes. Designing flexible free-standing electrodes can effectively inhibit the exfoliation of the electrode materials from the current collector. However, the generally adopted methods for preparing flexible free-standing electrodes are complex and high cost. To address these issues, we report the synthesis of a unique Sb nanoparticle@N-doped porous carbon fiber structure as a free-standing electrode via an electrospinning method and surface passivation. Such a hierarchical structure possesses a robust framework with rich voids and a stable solid electrolyte interphase (SEI) film, which can well accommodate the mechanical strain and avoid electrode cracks and pulverization during lithiation/delithiation processes. When evaluated as an anode for LIBs, the as-prepared nanoarchitectures exhibited a high initial reversible capacity (675 mAh g−1) and good cyclability (480 mAh g−1 after 300 cycles at a current density of 400 mA g−1), along with a superior rate capability (420 mA h g−1 at 1 A g−1). This work could offer a simple, effective, and efficient approach to improve flexible and free-standing alloy-based anode materials for high performance Li-ion batteries.

The intercalation cathode materials of heterostructure MnS/MnO with dual ions defect embedded in N-doped carbon fibers for aqueous zinc ion batteries

Manganese-based materials are often used as cathode materials for aqueous zinc ion batteries (AZIBs), which have the advantages of high theoretical capacity, low cost, low toxicity and various valence states. However, the inherent poor conductivity, sluggish zinc ion diffusion kinetics and terrible rate performance limit their practical application. Herein, MnS/MnO@NCF composite was synthesized by a simple electrospinning method. The N-doped carbon fibers (abbreviated as NCF) is produced during the carbonization process of PVP, which greatly improves the electronic conductivity of materials, and the formation of heterostructure MnS/MnO create abundant heterointerfaces with plentiful reaction active sites, which further improve the surface reaction kinetics. Meanwhile, an in-situ electrochemical approach inducing dual ions defect of Mn-defect and S-defect is used to unlock the electrochemical activity of MnS/MnO@NCF through the initial charge process for the first time, which can convert terrible electrochemical characteristic of MnS/MnO@NCF towards Zn2+ and H+ into high electrochemically active cathode for AZIBs. Finally, it exhibits a considerable capacity and superior cycleability with the specific discharge capacity of 151 mAh g−1 even after 400 cycles when used as the cathode material for AZIBs. Remarkably, it can even achieve a reversible capacity as high as 128.7 mAh g−1 at current density of 2 A g−1. Ex situ characterizations reveal the main co-insertion/extraction mechanism for H+ and Zn2+ without structural collapse, and the vacancy formation energies and the diffusion energy barrier of Zn2+calculated by density functional theory further explain the excellent rate performance and the energy storage mechanism of the MnS/MnO@NCF material.

N-doped carbon fibers in situ prepared by hydrothermal carbonization of Camellia sinensis branches waste for efficient removal of heavy metal ions.

N-doped carbon fibers (NCFs) were in situ prepared by Camellia sinensis branches waste through hydrothermal carbonization with urea/ZnCl2 at 160-280 °C under 0.8-8.9 MPa. The structural characteristics of NCFs were investigated by elemental analysis, SEM, TEM, XRD, XPS, Raman spectra, and BET surface area. The highest N content of NCFs obtained at 280 °C was 8.96%, and the main forms of doped N were pyridinic N, pyrrolic N, and graphitic N. Moreover, NCFs were applied to remove metal ions successfully. The results showed that NCF-240 had the maximum adsorption amounts of 106.52, 125.23, and 153.49 mg/g for Cu2+, Pb2+, and Zn2+, respectively, while NCF-280 had the best removal ability on Cr6+ (145.67 mg/g). Finally, it demonstrated that the adsorption behavior of NCFs was well fitted by the pseudo-second-order kinetic and the Langmuir adsorption isotherm models.