Sulfur Co-doping Research Articles

One-step synthesis of nitrogen and sulfur co-doped hierarchical porous carbon derived from acesulfame potassium as a dual-function agent for supercapacitors and lithium‑sulfur batteries

Acesulfame potassium (AK) is an artificial sweetener that contains N and S functional groups in its organic moiety and is suitable as porous carbon precursor. In this study, AK derived carbon (AKC) was obtained via direct carbonization and in situ doping without additives under the dual conditions of inert gas protection and high temperatures. The obtained AKCs exhibited high porosity structure with a specific surface area of 2043 m2 g−1 and 3.22 wt% N and 8.61 wt% S dual heteroatom doping. When applied to the supercapacitor electrode, the AKC ensured a high capacitance of 264 F g−1 at 0.5 A g−1, which maintained 86.1 % of the initial capacitance after 5000 cycles at 5 A g−1, and an ultra-high energy density of 16.3 Wh kg−1 in a full cell device. By analyzing its application in the lithium‑sulfur battery cathode, the S-loaded AKC exhibited a high capacity of 1075 mAh g−1 at 0.1C, and 490.5 mAh g−1 after 150 cycles with 66.5 % of capacity retention. The excellent performance of AKC can be attributed to its high specific surface area, pore structure, and sulfur and nitrogen co-doping combine effect. Overall, AKCs exhibited excellent electrochemical performances, thereby proposing a new synthetic strategy of preparing dual heteroatom doped porous carbon for high-performance electrode materials through a single precursor and low-cost perspective.

Synergistic Effect of Nitrogen–Sulfur Codoping on Honeycomb-like Carbon-Based High-Energy-Density Zinc-Ion Hybrid Supercapacitors

Zn-ion hybrid supercapacitors (ZHSCs) are emerging charge storage devices that inherit many of the advantages of supercapacitors and batteries. However, problems such as unsatisfactory cycling stability and low energy density need to be solved urgently, which can be accomplished by developing cathode materials with excellent properties. Herein, we report the development of performance-enhanced ZHSCs obtained by incorporating N and S heteroatoms into orange peel-based hierarchical porous carbon (NS-OPC) to facilitate Zn2+ adsorption. The results of ex situ photoelectron spectroscopy and X-ray diffraction demonstrated the presence of −OH and Zn2+ chemisorbed and Zn4SO4(OH)6·5H2O during charging and discharging, respectively. Density functional theory calculations show that double doping can promote the chemisorption/desorption kinetics of Zn2+ and thus promote the electrochemical charge storage of C materials. Impressively, when used to assemble ZHSCs, the device still has an energy density of 53.9 Wh kg–1, a high power density of 6063.75 W kg–1, and an 86.2% capacity retention after 10,000 cycles. This study not only provides a reasonable technique for developing superior C-based electrode materials but also contributes to the understanding of the charge storage process in heteroatom-doped C materials.

Ru-CoO heterostructured nanoparticles supported on nitrogen and sulfur codoped graphene nanosheets as effective electrocatalysts for hydrogen evolution reaction in alkaline media

Production of clean hydrogen energy from water splitting is vital for the future fuel industry, and nanocomposites have emerged as effective catalysts for the hydrogen evolution reaction (HER). In this study, Ru-CoO@SNG nanocomposites are prepared by controlled pyrolysis where Ru-CoO heterostructured nanoparticles are supported on nitrogen and sulfur codoped graphene oxide nanosheets. With a large surface area, the obtained composites exhibit a remarkable electrocatalytic activity toward HER in 1.0 M KOH with an overpotential of only −90 mV to reach the current density of 10 mA cm−2, in comparison to −60 mV for commercial Pt/C benchmark, along with high stability. Mechanistically, codoping of sulfur and nitrogen facilitates the dispersion of the nanoparticles, and the formation of Ru-CoO heterostructures increases the active site density, reduces the electron-transfer kinetics and boosts the catalytic performance. Results from this study highlight the unique potential of structural engineering in enhancing the electrocatalytic performance of heterostructured nanocomposites.

Improving stability and reversibility of manganese dioxide cathode materials via nitrogen and sulfur doping for aqueous zinc ion batteries

Manganese based oxides are one of the most promising cathode materials for secondary aqueous zinc ion batteries. However, its structural instability and slow reaction kinetics have hampered its large-scale application. Here, a rational nitrogen and sulfur diatomic doping strategy is suggested to enhance the electrochemical activity and reversibility of manganese dioxide. The nitrogen and sulfur-doped manganese dioxide (N-MnxOy-S) electrode material is synthesized by a simple hydrothermal approach combined with a low temperature vulcanization treatment. The electrode exhibits an excellent initial discharge capacity of 178 mA h g−1 at 1 A g−1. Even at a high rate of 2 A g−1, the capacity retention rate exceeds 90% for 3000 cycles. The large number of oxygen defects increases the storage sites for zinc ions, resulting in the excellent electrochemical properties of N-MnxOy-S. Additionally, the Mn-S and Mn-N bonds in N-MnxOy-S boost the interfacial dynamics of manganese dioxide, which can effectively reduce the dissolution of manganese and efficiently improve the electronic conductivity. The current study demonstrates that nitrogen and sulfur co-doping is a successful method for enhancing the electrochemical performance of manganese-based oxide cathodes, which serves as an important benchmark for the development of cathode materials appropriate for aqueous zinc ion batteries.

Self-supporting network-structured MoS2/heteroatom-doped graphene as superior anode materials for sodium storage.

Layered graphene and molybdenum disulfide have outstanding sodium ion storage properties that make them suitable for sodium-ion batteries (SIBs). However, the easy and large-scale preparation of graphene and molybdenum disulfide composites with structural stability and excellent performance face enormous challenges. In this study, a self-supporting network-structured MoS2/heteroatom-doped graphene (MoS2/NSGs-G) composite is prepared by a simple and exercisable electrochemical exfoliation followed by a hydrothermal route. In the composite, layered MoS2 nanosheets and heteroatom-doped graphene nanosheets are intertwined with each other into self-supporting network architecture, which could hold back the aggregation of MoS2 and graphene effectively. Moreover, the composite possesses enlarged interlayer spacing of graphene and MoS2, which could contribute to an increase in the reaction sites and ion transport of the composite. Owing to these advantageous structural characteristics and the heteroatomic co-doping of nitrogen and sulfur, MoS2/NSGs-G demonstrates greatly reversible sodium storage capacity. The measurements revealed that the reversible cycle capacity was 443.9 mA h g-1 after 250 cycles at 0.5 A g-1, and the rate capacity was 491.5, 490.5, 453.9, 418.1, 383.8, 333.1, and 294.4 mA h g-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g-1, respectively. Furthermore, the MoS2/NSGs-G sample displayed lower resistance, dominant pseudocapacitive contribution, and faster sodium ion interface kinetics characteristic. Therefore, this study provides an operable strategy to obtain high-performance anode materials, and MoS2/NSGs-G with favorable structure and excellent cycle stability has great application potential for SIBs.

Effect of nitrogen and sulphur co-doping on the surface and diffusion characteristics of date seed-derived porous carbon for asymmetric supercapacitors

Date seeds are the by-product of date fruits, which are abundant all over the world mainly in Middle East. Herein, we report a facile transformation of waste date seeds into highly porous activated carbon (D-800) via simple one-pot hydrothermal carbonization followed by KOH activation route. The resultant date seeds derived activated carbon was then co-doped with nitrogen and sulphur (NSD-800) via effective binary heteroatom doping method. The NSD-800 material has interconnected pores like framework, which facilitate significant ion storage and fast ion transport. Heteroatom doping produces a faradaic contribution in addition to the EDLC (electric double layer capacitor) characteristics of the carbon which facilitates the faster diffusion process. Hence, NSD-800 demonstrate promising electrochemical performance achieving a high specific capacitance of 298.5 F/g at 0.5 A/g using 1 M H2SO4 electrolyte. Furthermore, symmetrical and asymmetrical supercapacitor (SC) devices were fabricated using these electrode materials for comparison purpose. It is found that D-800//NSD-800 asymmetric SC device shows superior electrochemical performance delivering high energy density of ~30 Wh/kg at a power density of 394 W/kg along with extraordinary cyclic stability of 92.7 % after 10,000 charge-discharge cycles. This intriguing performance notably bestows NSD-800 with promising prospects as electrode material for supercapacitor application.

Importance of carbon structure for nitrogen and sulfur co-doping to promote superior ciprofloxacin removal via peroxymonosulfate activation

Herein, five N, S-co-doped carbocatalysts were prepared from different carbonaceous precursors, namely sawdust (SD), biochar (BC), carbon-nanotubes (CNTs), graphite (GP), and graphene oxide (GO) and compared. Generally, as the graphitization degree increased, the extent of N and S doping decreased, graphitic N configuration is preferred, and S configuration is unaltered. As peroxymonosulfate (PMS) activator for ciprofloxacin (CIP) removal, the catalytic performance was in order: NS-CNTs (0.037 min−1) > NS-BC (0.032 min−1) > NS-rGO (0.024 min−1) > NS-SD (0.010 min−1) > NS-GP (0.006 min−1), with the carbonaceous properties, rather than the heteroatoms content and textural properties, being the major factor affecting the catalytic performance. NS-CNTs was found to have the supreme catalytic activity due to its remarkable conductivity (3.38 S m−1) and defective sites (ID/IG = 1.28) with high anti-interference effect against organic and inorganic matter and varying water matrixes. The PMS activation pathway was dominated by singlet oxygen (1O2) generation and electron transfer regime between CIP and PMS activated complexes. The CIP degradation intermediates were identified, and a degradation pathway is proposed. Overall, this study provides a better understanding of the importance of selecting a suitable carbonaceous platform for heteroatoms doping to produce superior PMS activator for antibiotics decontamination.

Synthesis of multiple-color emitting carbon dots by co-doping of sulfur and nitrogen

Herein, multiple color (blue, green and red) emissive carbon dots (CDs) were synthesized from the main precursor via different protocols, with emission wavelengths of 439 nm, 528 nm and 623 nm, respectively, realizing the synthesis of fluorescent CDs spanning the fluorescence emission from short to long wavelengths. Their relative PLQYs reach up to 28.9%, 31.4% and 12.3%, respectively, exceeding the PLQYs of many similar CDs. The green CDs (G-CDs) and red CDs (R-CDs) show optimal photoluminescence performance in acetone (Me2CO); while the B-CDs have a pH-dependent response in the pH 2 to 12 range. All the three CDs have excellent photostability and salt resistance. Finally, serving as fluorescent anti-counterfeiting ink was taken as an example to briefly introduce the application of multi-color CDs. This work provides a new strategy to develop low-cost multiple color phosphors for display device, biological imaging, analysis and detection and other fields.

Platinum group metal-free Fe−N−C catalysts for PEM fuel cells derived from nitrogen and sulfur doped synthetic polymers

• PGM-free Fe−N−C catalysts are produced from N or N/S co-doped porous organic gels. • S-doping alters fundamental properties of carbon materials vs S-free counterparts. • S co-doping induces extensive ultramicroporosity (pores of ∼0.6 nm) • Ultramicropores could enhance ORR via their strong adsorption potential. • S co-doped Fe−N−C catalysts achieve ∼0.15 W cm −2 peak power density in a H 2 –air FC. • Morphology dominates other Fe−N−C characteristics and determines FC performance. Fe−N−C electrocatalysts were obtained via pyrolysis of N- or N/S co-doped synthetic polymers impregnated with FeCl 3 . The influence of the presence/absence of sulfur co-doping, the initial FeCl 3 content and phenanthroline addition on the Fe−N−C–based cathode catalyst layers (CCLs) performance in H 2 -air PEM fuel cells was studied. To this end the Fe−N−C materials were first characterized concerning their chemical composition, surface chemistry, porosity and morphology. Sulfur and phenanthroline additions strongly affect these characteristics of Fe−N−C materials. This in turn determines (to various extents) the electrochemical properties as measured with a rotating ring-disk electrode and upon infusion in the cathode catalyst layer in H 2 -air PEM fuel cells. While simultaneous sulfur and phenanthroline addition yields Fe−N−C catalysts with high N-content and specific surface area, this does not translate into good electrochemical performance. We discuss the multitude of factors determining the catalysts’ and the final CCLs’ performances and conclude that the specific micro-colloidal morphology of the carbon gel-based materials dominates other Fe−N−C characteristics and determines overall FC performance. The best performing CCL provided peak power density of ∼0.15 W⋅cm −2 in a H 2 -air PEMFC.

Temperature- and pH-Sensitive Nitrogen and Sulfur Codoped Carbon Quantum Dots for Sequential Detection of Fe3+ and H2S

In this study, nitrogen and sulfur codoped carbon quantum dot (N,S-CQD) fluorescent nanoprobes were synthesized through a one-step hydrothermal method using l-cysteine and α-methacrylic acid as raw materials, and an “on–off–on” fluorescence mechanism was designed using N,S-CQDs for sequential determination of Fe3+ and H2S in human serum. The quenching process (on–off) and mechanism of N,S-CQDs by Fe3+ were studied via fluorescence spectroscopy, zeta potential, cyclic voltammetry, and orbital energy level simulation. Meanwhile, an “off–on” strategy for the N,S-CQD/Fe3+ fluorescence sensing platform was constructed for the determination of the H2S-based “on–off” mechanism. This study not only achieved highly selective detection of Fe3+ and H2S over a wide concentration range of 0–250, 250–500, and 2.5–900 μM, respectively, but also improved our understanding on the specific identifications between N,S-CQDs, Fe3+, and H2S. What is more, it was found that N,S-CQDs also possessed pH and temperature sensing performance. Finally, N,S-CQD fluorescent nanoprobes were successfully applied for the determination of Fe3+ and H2S in spiked serum samples, which also proved their potential application in medical diagnosis and biosensors.

Nitrogen and Sulfur Codoped Porous Carbon Directly Derived from Potassium Citrate and Thiourea for High-Performance Supercapacitors.

By introducing a heteroatom into carbon material, an effective improvement in capacitance can be realized owing to surface oxidation and reduction reactions of pseudocapacitors. Herein, a simple one-pot carbonization activation method was proposed to convert potassium citrate into three-dimensional interconnected porous carbon (PC). Then, an effective double heteroatom doping method by thiourea was used to prepare nitrogen-sulfur-doped PC (N,S-PC). This porous structure facilitates the storage of a large number of ions and reduces their diffusion path. The synthesized N,S-PC nanomaterial has a capacitance of 674 F/g at 1 A/g in a 1 M H2SO4 electrolyte, can retain 94.41% of the initial capacitance after 10 000 cycles at 5 A/g, and has a long cycle life. More importantly, a symmetric supercapacitor assembled with this material can exhibit an energy density of up to 32.6 (W·h)/kg at a high-power density of 750 W/kg. This is due to the high performance of N,S-PC in supercapacitor electrode materials.

Fabrication of an Efficient N, S Co-Doped WO3 Operated in Wide-Range of Visible-Light for Photoelectrochemical Water Oxidation.

In this work, a highly efficient wide-visible-light-driven photoanode, namely, nitrogen and sulfur co-doped tungsten trioxide (S-N-WO3), was synthesized using tungstic acid (H2WO4) as W source and ammonium sulfide ((NH4)2S), which functioned simultaneously as a sulfur source and as a nitrogen source for the co-doping of nitrogen and sulfur. The EDS and XPS results indicated that the controllable formation of either N-doped WO3 (N-WO3) or S-N-WO3 by changing the nW:n(NH4)2S ratio below or above 1:5. Both N and S contents increased when increasing the nW:n(NH4)2S ratio from 1:0 to 1:15 and thereafter decreased up to 1:25. The UV-visible diffuse reflectance spectra (DRS) of S-N-WO3 exhibited a significant redshift of the absorption edge with new shoulders appearing at 470–650 nm, which became more intense as the nW:n(NH4)2S ratio increased from 1:5 and then decreased up to 1:25, with the maximum at 1:15. The values of nW:n(NH4)2S ratio dependence is consistent with the cases of the S and N contents. This suggests that S and N co-doped into the WO3 lattice are responsible for the considerable redshift in the absorption edge, with a new shoulder appearing at 470–650 nm owing to the intrabandgap formation above the valence band (VB) edge and a dopant energy level below the conduction band (CB) of WO3. Therefore, benefiting from the S and N co-doping, the S-N-WO3 photoanode generated a photoanodic current under visible light irradiation below 580 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm.

Electroplating sludge-derived metal and sulfur co-doping catalyst and its application in methanol production by CO2 catalytic hydrogenation

Electroplating sludge is a hazardous waste and its recycling is a hot topic. Electroplating sludge usually contains plenty of transition metals and multi-hetero atoms, which are potential resources. For the first time, this work synthesized spinel catalyst from Zn- and Cr-containing electroplating sludges by a simple calcination method, and applied the obtained catalysts in CH3OH production by CO2 catalytic hydrogenation. The spinel was doped by various heteroatoms, including Fe, Mn, Cu, and even S. According to detailed characterizations, the metal doping increased the low-temperature conversion efficiency of CO2 but decreased the CH3OH selectivity at the same time. After a further doping of S, although CO2 conversion efficiency was slightly decreased, the selectivity of CH3OH was significantly increased. After all, the optimized catalyst attained a conversion efficiency of 8.6% (CO2) as well as a selectivity of 73.3% (CH3OH) at 250 °C and 3 MPa. As a result, above results realized high-value-added utilization of hazardous waste and producing valuable product at the same time, which was in favor of circular development.

Influence of carbonaceous materials supported nanostructured nickel phosphide as an electrocatalyst for the hydrogen evolution reaction

A promising hydrogen evolution reaction performance is achieved in this work by Ni2P nanoparticles supported on Nitrogen, Sulphur co-doped reduced graphene oxide (N,S-rGO) synthesized via hydrothermal method. The enhanced electrochemical activity of the electrocatalyst can be attributed to the presence of more defect sites in the graphitic carbon as well as the synergistic effect between both N and S co-doped reduced graphene oxide. Ni2P–N, S-rGO showed the comparative intensity ratio ID/IG value of 1.96, which is higher compared to other carbon materials. It shows that the defect was increased when nitrogen and sulphur co-doping occurs on reduced graphene oxide sheets which in turn leads to an increase in both active doping sites and improve conductivity. Ni2P incorporated with N, S-rGO was found to be the best for attaining a current density of 10 mA/cm2 at an overpotential of 179 mV in 0.5 M H2SO4. As well, the Tafel slope of 71 mV/dec confirms that the Ni2P incorporated with N, S-rGO proceeds through the Volmer-Heyrovsky mechanism.

Highly Efficient Sulfur and Nitrogen Codoped Graphene Quantum Dots as a Metal-Free Green Photocatalyst for Photocatalysis and Fluorescent Ink Applications.

The demand for modern organic pollutant treatment has prompted the development of environmentally acceptable photocatalytic processes. In this work, we report novel nitrogen and sulfur codoped graphene quantum dot (S,N-GQD) based photocatalysts and fluorescent ink for the first time. For the degradation of organic dyes under visible irradiation, a hydrothermal technique was employed to generate S,N-GQD green nanomaterials. The synthesized samples were examined using XRD, HR-TEM, EDX, FT-IR, PL, and UV–vis spectroscopy. UV-DRS was used to determine the energy band gap of S,N-GQDs, and it was obtained to be around ∼2.54 eV. To explore the catalytic behavior of the produced S,N-GQDs as green nanomaterials, organic dyes (i.e., crystal violet and Alizarin yellow) have been used as a reference dye in this study. Using several radical scavenging agents, the photocatalytic mechanism was examined. This novel photocatalyst offers a promising alternative for the breakdown of organic pollutants. Moreover, these S,N-GQDs can also be used as fluorescent ink for imaging purposes and security reasons.

One-Pot Hydrothermal Synthesized Nitrogen and Sulfur Codoped Carbon Dots for Acid Corrosion Inhibition of Q235 Steel.

N and S codoped carbon dots having good water solubility have been successfully made by a novel hydrothermal method and characterized by FTIR, XPS, and TEM. The as-synthesized CDs were carbon particles rich in polar functional groups less than 10 nm in size. Electrochemical measurements, gravimetry, and surface analysis methods were utilized to examine the inhibition characteristics and adsorption mechanism of CDs on the carbon steel in acid pickling solutions. Electrochemical measurements verified that the CDs displayed adequate protection with high inhibition efficiency of 97.8%. The long-term weight-loss experiments up to 72 h further confirmed the excellent corrosion inhibition at room temperature and 313 K. The results presented are helpful for the formulation of more effective acid pickling corrosion inhibitors.

Nitrogen and sulfur co-doping strategy to trigger the peroxidase-like and electrochemical activity of Ti3C2 nanosheets for sensitive uric acid detection

The development of functional nanomaterials based on the unique structure and morphology of MXene for biosensing has aroused great interest. In this work, using thiourea as the doping source, a new structure composed of nitrogen and sulfur co-doped on the surface of Ti3C2 nanosheets was synthesized through a simple one-step synthesis method. Fortunately, the obtained nitrogen and sulfur co-doped Ti3C2 nanosheets (NS–Ti3C2 NSs) showed excellent peroxidase-like activity and electrochemical activity. The catalytic mechanism of modified Ti3C2 nanosheets was explored. It is revealed that the catalytic mechanism of NS-Ti3C2 NSs is composed of two important parts: the dissociation and adsorption of H2O2 and the protonation of TMB. In addition, the fabricated NS-Ti3C2 NSs-based electrochemical biosensor is superior to the counterpart from Ti3C2 nanosheets, indicating that the doping of nitrogen and sulfur elements provides more active sites and promotes electron transport efficiency. Combining the unique advantages of colorimetry and electrochemical technology, we have developed a fast, accurate, intuitive and efficient UA detection method for uric acid in the range of 2 μM–400 μM with a detection limit (LOD) of 0.19 μM. The established sensing platform in this study prove the possibility of the doping method for the development of MXene-based biosensors with high sensitivity and high performance, and pave the way for the future development of biosensors for biomedical fields.

Engineering a heteroatom-doped multidimensional carbon network for dendrite-free lithium metal anode

Lithium metal anode (LMA) has attracted widespread attention on account of its highest theoretical capacity and low reduction potential. However, the practical application of LMA has been long hindered by safety concerns and huge volume change resulting from the inevitable lithium dendrites growth. Herein, a multidimensional framework consisting of commercial carbon cloth (CC) and N, S-codoped porous carbon (PNSC) net (CC@PNSC) is fabricated and applied for LMA. This CC@PNSC skeleton has a large specific surface area, and the local current density can be significantly decreased. In addition, the synergetic effect of nitrogen and sulfur codoping endows CC with enhanced lithiophilicity and even lithium plating behavior. More importantly, the in-situ formed Li3N and Li2S during the molten lithium infusion process facilitate Li+ transfer kinetics and effectively homogenize the Li+ flux diffusion. The as-prepared CC@PNSC-Li composite anode exhibits high specific capacity (3 mA h cm−2, 500 h) and impressive cycling stability with a flat voltage profile at a current density of 1 mA cm−2 (750 h). When paired with LiFePO4 (LFP), the LFP||CC@PNSC-Li cell delivers an extraordinary rate capacity (especially at 5C) and a long-term cycling lifespan at 1C (600 cycles and capacity retention of 89.06%).

Porous carbon materials derived from discarded COVID-19 masks via microwave solvothermal method for lithium‑sulfur batteries

With the spread of COVID-19, disposable medical masks (DMMs) have become a significant source of new hazardous solid waste. Their proper disposal is not only beneficial to the safety of biological systems but also useful to achieve considerable economic value. The first step of this study was to investigate the chemical composition of DMMs. It is primarily composed of polypropylene, polyethylene terephthalate and iron, with fibrous polypropylene accounting for approximately 80% of the total weight. Then, DMMs were sulfonated and oxidised by the microwave-driven concentrated sulfuric acid within 8 min based on the fact that the concentrated sulfuric acid exhibits a good microwave absorption capacity. The co-doping of sulfur and oxygen was achieved while improving the thermal stability of DMMs. Subsequently, the self-activation pyrolysis of sulfonated and oxidised DMMs (P-SO@DMMs) was further realized in low-flow-rate argon. The specific surface area of P-SO@DMMs increased from 2.0 to 830.9 m2·g−1. P-SO@DMMs sulfur cathodes have promising electrochemical properties because of their porous structures and the synergistic effect of sulfur and oxygen co-doping. The capacity of the samples irradiated by microwave for 10 min at 0.1, 0.2, 0.5, 1, 2 and 5 C were 1313.6, 1010.9, 816.5, 634.4, 513.4 and 453.1 mAh·g−1, respectively, and after returning to 0.2 C and continuing the cycle for 50 revolutions, maintained 50.5% of the initial capacity. After 400 cycles, its capacity is 38.1% of the initial capacity at 0.5 C. It is slightly higher than the electrochemical performance of the sample treated by microwave for 8 min and significantly higher than the sample treated by 6 min. This work converts structurally complex, biohazardous DMMs into porous carbon with high specific surface area by clean and efficient microwave solvothermal and self-activating pyrolysis, which facilitates the development of carbon based materials at low cost and large scale.

Nitrogen and sulfur co-doped Nb2C-MXene nanosheets for the ultrasensitive electrochemical detection dopamine under acidic conditions in gastric juice

Nitrogen and sulfur co-doped Nb 2 C MXene (NS-Nb 2 C) which successfully synthesized in a one-step treatment of Nb 2 C using thiourea as N,S resource is used as a stable and high-performance sensing material for highly sensitive detection of dopamine (DA) in gastric juice under acidic conditions. The NS-Nb 2 C is more electrochemically active than multilayered Nb 2 C nanosheets (ML-Nb 2 C) and delaminated Nb 2 C nanosheets (DL-Nb 2 C) under acidic conditions due to the provision of active sites, high surface area and enhanced conductivity caused by the heteroatom doping strategy. • A novel electrochemical sensor based on nitrogen and sulfur co-doped Nb 2 C MXene is proposed for DA detection in gastric juice. • NS-Nb 2 C is more electrochemically active than multilayered Nb 2 C nanosheets and delaminated Nb 2 C nanosheets. • This work provides a new direction for the application of Nb-based MXene in the electrochemical sensing applications. • Nitrogen and sulfur co-doping is an effective method to improve the electrochemical performance of MXene. This work reports the synthesis and application of nitrogen and sulfur co-doped Nb 2 C MXene (NS-Nb 2 C) for the sensing of dopamine (DA) in gastric juice. NS-Nb 2 C MXene was successfully synthesized in a one-step treatment of Nb 2 C using thiourea as N,S resource. The heteroatom doping strategy enables introduction of N,S into MXene nanosheets and simultaneously induces the increased interlayer spacing, high surface area, and enhanced electrical conductivity. It was found that NS-Nb 2 C is more electrochemically active than multilayered Nb 2 C nanosheets (ML-Nb 2 C) and delaminated Nb 2 C nanosheets (DL-Nb 2 C). Based on this, the as-prepared NS-Nb 2 C/Nafion/GCE was used to study the electrochemical behavior of dopamine in pH = 3.0. The sensing interface not only utilizes the unique two-dimensional (2D) nanosheet morphology of Nb 2 C that has a larger surface area and conductive network, but also takes advantage of the more active sites provided by doping. This enables the sensor to achieve ultra-sensitive detection of dopamine (S/N = 3) with a low limit of detection (LOD) of 0.12 µM. In addition, the prepared sensor has good stability and selectivity, and the results of detecting DA in simulated gastric juice is satisfactory. The results indicated that the Nb-based MXenes provided a promising tool for acidic electrochemical sensing applications.