Sandwich-Type Nitrogen and Sulfur Codoped Graphene-Backboned Porous Carbon Coated Separator for High Performance Lithium-Sulfur Batteries

Functionalized and tip-open carbon nanotubes for high-performance symmetric supercapacitors

Carbon nanotubes (CNTs) have been widely studied for use in supercapacitor electrodes because of their excellent conductivity, high aspect ratio, excellent mechanical properties, chemical stability, and large specific surface area. However, the electrochemical performance of CNTs is usually limited by their closed tips and fewer active sites. Therefore, a facile and efficient chemical-acid-etching method was employed to open the tips of CNTs and introduce functional groups. Different types of ions (Li⁺, Na⁺, and Mg²⁺) in aqueous electrolytes were investigated using the functionalized and tip-open CNTs (FTO-CNTs), and the Li⁺-based electrolyte has the best electrochemical performance. The areal capacitance when using FTO-CNTs as positive and negative electrodes could reach 542 mF cm^-2 and 410 mF cm^-2, respectively, at a scan rate of 10 mV s^-1, and the positive electrode reached the highest areal capacitance of 903 mF cm^-2 at a current density of 1 mA cm^-2. The symmetric supercapacitor-based FTO-CNTs electrode delivered a superior areal energy density of 39 μW h cm^-2 and an areal power density of 10.2 mW cm^-2, with remarkable cycling stability.

Studies on Kinetics, Isotherms, Thermodynamics and Adsorption Mechanism of Methylene Blue by N and S Co-Doped Porous Carbon Spheres

Heteroatom-doped carbon is widely used in the fields of adsorbents, electrode materials and catalysts due to its excellent physicochemical properties. N and S co-doped porous carbon spheres (N,S-PCSs) were synthesized using glucose and L-cysteine as carbon and heteroatom sources using a combined hydrothermal and KOH activation process. The physicochemical structures and single-factor methylene blue (MB) adsorption properties of the N,S-PCSs were then studied. The optimized N,S-PCSs-1 possessed a perfect spherical morphology with a 2-8-μm diameter and a large specific area of 1769.41 m2 g-1, in which the N and S contents were 2.97 at% and 0.88 at%, respectively. In the single-factor adsorption experiment for MB, the MB adsorption rate increased with an increase in carbon dosage and MB initial concentration, and the adsorption reached equilibrium within 2-3 h. The pseudo-second-order kinetic model could excellently fit the experimental data with a high R2 (0.9999). The Langmuir isothermal adsorption equation fitted well with the experimental results with an R2 value of 0.9618, and the MB maximum adsorption quantity was 909.10 mg g-1. The adsorption of MB by N,S-PCSs-1 was a spontaneous, endothermic, and random process based on the thermodynamics analyses. The adsorption mechanism mainly involved Van der Waals force adsorption, π-π stacking, hydrogen bonds and Lewis acid-base interactions.

Nitrogen and Sulfur Co-Doped Graphene as Efficient Electrode Material for L-Cysteine Detection

Two graphene samples co-doped with nitrogen and sulfur were synthesized by the hydrothermal method using thiourea as doping and reducing agent for graphene oxide (GO). An appropriate amount of thiourea was added to the aqueous dispersion of GO, previously sonicated for 30 min. The mixture was poured into an autoclave and placed in the oven for 3 h, at 120 and 200 °C. The samples were denoted NSGr-120 and NSGr-200, respectively, in agreement with the reaction temperatures. They were next morphologically and structurally characterized by advanced techniques, such as SEM/TEM, XPS, XRD, and FTIR. According to XPS analysis, the NSGr-120 sample has higher amounts of heteroatoms in comparison with NSGr-200, indicating that the reaction temperature is a crucial factor that affects the doping degree. In order to reveal the influence of the doping degree on the electrochemical performances of graphene-modified electrodes, they were tested in solutions containing L-cysteine molecules. The electrode with the best electrocatalytic performances, GC/NSGr-120, was tested to detect L-cysteine in a pharmaceutical drug, proving its applicability in real sample analysis.

Nitrogen and sulfur codoped micro-mesoporous carbon sheets derived from natural biomass for synergistic removal of chromium(VI): adsorption behavior and computing mechanism

We reported the effective removal of chromium(VI) (Cr(VI)) from wastewater with nitrogen and sulfur codoped micro-mesoporous carbon sheets (N,S-MMCSs), which were fabricated by pyrolysis of natural biomass (luffa sponge) followed by chemical activation and hydrothermal treatment. N,S-MMCSs possessed a hierarchical micro-mesoporous sheet-like framework, large specific surface area (1525.45 m² g^-1), high pore volume (1.21 cm³ g^-1), and appropriate N (1.81 wt%) and S (1.01 wt%) co-doping. Batch adsorption experiments suggested that Cr(VI) adsorption by the N,S-MMCSs increased with increase the solution acidity, adsorbent dosage, Cr(VI) concentration, temperature, and time. The Cr(VI) adsorption was mainly controlled by the chemisorptions and could be well interpreted by the Langmuir isotherm and pseudo-second-order kinetic models. The maximum adsorption capacities of Cr(VI) were 217.39, 277.78, and 312.50 mg g^-1 at 298, 308, and 318 K, respectively. The Cr(VI) adsorption procedure was spontaneous, endothermic, and randomness. The Cr(VI) adsorption mechanism followed the physical adsorption, electrostatic attraction, in situ reduction, and surface chelation. Besides, the density functional theory (DFT) calculation demonstrated that the N and S co-doping could decrease the adsorption energy and enhance the attractive interaction between N,S-MMCSs and Cr(VI) through the synergistic effect, and thus significantly improve the Cr(VI) adsorption property.

Controlled drug release performance of plasma modified slab and mat matrices: A model study with "Ampicillin"

Two types of ampicillin carrier platforms were prepared with polycaprolactone (PCL) and the release behavior of a hydrophilic model drug (ampicillin sodium salt) from those matrices was investigated. Spin coating and electrospinning techniques were used to prepare slab and mat platforms, respectively. Ampicillin sodium salt (ASS) at 5% (w:w) concentration was loaded into the slab or mat structures of PCL. The thickness of the slab was measured 3.349 ± 0.345 μm and surface morphology of the slabs showed uniform PCL spherulites. On the other hand, fiber diameter of PCL and ASS loaded PCL (ASSLPCL) was measured 604 ± 176 nm and 549 ± 119 nm, respectively. The dynamic behavior of the controlled release was improved by a very thin film (<100 nm) formation of sulfur hexafluoride (SF₆) over the surface via plasma polymerization. Plasma coating was facilitated and speed up the drug diffusion, then led to 45.60 ± 6.46% and 63.67 ± 4.33% enhancement of drug from slab and mat, respectively. Transport mechanism from all matrices showed a Fickian diffusion behavior and plasma modification of the surface did not affected the mechanism. The in vitro antibacterial property of ASS loaded matrices against S. aureus and E. coli was studied through the comparison of bacterial inhibition zones and ASS showed antibacterial effect after all processes.

Cinnamon-Derived Hierarchically Porous Carbon as an Effective Lithium Polysulfide Reservoir in Lithium-Sulfur Batteries

Lithium-sulfur batteries are attractive candidates for next generation high energy applications, but more research works are needed to overcome their current challenges, namely: (a) the poor electronic conductivity of sulfur, and (b) the dissolution and migration of long-chain polysulfides. Inspired by eco-friendly and bio-derived materials, we synthesized highly porous carbon from cinnamon sticks. The bio-carbon had an ultra-high surface area and large pore volume, which serves the dual functions of making sulfur particles highly conductive and acting as a polysulfide reservoir. Sulfur was predominantly impregnated into pores of the carbon, and the inter-connected hierarchical pore structure facilitated a faster ionic transport. The strong carbon framework maintained structural integrity upon volume expansion, and the unoccupied pores served as polysulfide trapping sites, thereby retaining the polysulfide within the cathode and preventing sulfur loss. These mechanisms contributed to the superior performance of the lithium-sulfur cell, which delivered a discharge capacity of 1020 mAh g^-1 at a 0.2C rate. Furthermore, the cell exhibited improved kinetics, with an excellent cycling stability for 150 cycles with a very low capacity decay of 0.10% per cycle. This strategy of combining all types of pores (micro, meso and macro) with a high pore volume and ultra-high surface area had a synergistic effect on improving the performance of the sulfur cathode.

Nature of the Synergistic Effect of N and S Co-Doped Graphene for the Enhanced Simultaneous Determination of Toxic Pollutants

N-doped graphene (NG), S-doped graphene (SG), and N and S co-doped graphene nanocatalysts with different doping sequences (N-SG and S-NG) are successfully synthesized by a facile low-temperature hydrothermal method. By changing the synthetic sequence, S-NG significantly increases the electron transport rate of the sensor and the electrocatalytic ability compared to NG, SG, and N-SG due to the optimal proportion of doping element content and suitable N- and S-bonding configurations. The origin of the synergistic effect of N and S co-doped graphene is confirmed. Traces of S doping greatly enhance the electrochemical performance. The large volume of S-O_x groups may prevent the analytes from approaching the catalytic sites of the sensing materials due to a steric hindrance effect. S-NG, which possesses less S-O_x groups, exhibits better performance than N-SG. Pyridinic N plays an important role in enhancing the electrochemical activity and conductivity. The simultaneous determination of aniline (AN), p-phenylenediamine (PPD), and nitrobenzene (NB) as typical toxic pollutants is performed by employing the S-NG nanoarchitecture. The detection limits (S/N = 3) for AN, PPD, and NB are 0.023, 0.051, and 0.216 μM, respectively. In addition, the S-NG sensors also have excellent anti-interference, stability, and reproducibility. The precise control and synthesis of multiheteroatoms into graphene represent a promising strategy to enhance the electrocatalytic performance in energy and environmental fields.

Wheat Straw-Derived N-, O-, and S-Tri-doped Porous Carbon with Ultrahigh Specific Surface Area for Lithium-Sulfur Batteries

Recently, lithium-sulfur (Li-S) batteries have been greeted by a huge ovation owing to their very high theoretical specific capacity (1675 mAh·g⁻¹) and theoretical energy density (2600 Wh·kg⁻¹). However, the full commercialization of Li-S batteries is still hindered by dramatic capacity fading resulting from the notorious “shuttle effect” of polysulfides. Herein, we first describe the development of a facile, inexpensive, and high-producing strategy for the fabrication of N-, O-, and S-tri-doped porous carbon (NOSPC) via pyrolysis of natural wheat straw, followed by KOH activation. The as-obtained NOSPC shows characteristic features of a highly porous carbon frame, ultrahigh specific surface area (3101.8 m²·g⁻¹), large pore volume (1.92 cm³·g⁻¹), good electrical conductivity, and in situ nitrogen (1.36 at %), oxygen (7.43 at %), and sulfur (0.7 at %) tri-doping. The NOSPC is afterwards selected to fabricate the NOSPC-sulfur (NOSPC/S) composite for the Li-S batteries cathode material. The as-prepared NOSPC/S cathode delivers a large initial discharge capacity (1049.2 mAh·g⁻¹ at 0.2 C), good cycling stability (retains a reversible capacity of 454.7 mAh·g⁻¹ over 500 cycles at 1 C with a low capacity decay of 0.088% per cycle), and superior rate performance (619.2 mAh·g⁻¹ at 2 C). The excellent electrochemical performance is mainly attributed to the synergistic effects of structural restriction and multidimensional chemical adsorptions for cooperatively repressing the polysulfides shuttle.