Graphitic Network Research Articles

Self-Exfoliating Benzotristriazine Macrocyclic Network: A New 2D Material for High-Performance Electrochemical Energy Storage.

Aza-fused aromatic π-conjugated networks are an important class of 2D graphitic analogs, which are generally constructed using aromatic precursors. Herein, the study describes a new synthetic approach and electrochemical properties of a self-exfoliating benzotristriazine 2D network (BTTN) constructed using aliphatic precursors, under relatively mild conditions. The obtained BTTN exhibits a nanodisc-like morphology, the self-exfoliation tendency of which is ascribed to the presence of structurally different macrocycles with high electronic repulsion between the layers. The benzotristriazine repeat units of BTTN is electroactive and holds higher carbon/nitrogen ratio when compared with the conventional graphitic aza-fused π-conjugated networks. The self-exfoliated BTTN nanodiscs show excellent electrochemical energy storage of 485 and 333 F g-1 at 1 A g-1 in three-electrode and two-electrode measurements, respectively. BTTN in a symmetric coin-cell architecture exhibits a high specific energy value of 46Wh kg-1 at a power density of 1kW kg-1 and shows excellent cyclic stability of 96% for 10000 and 90% for 30000 charge-discharge cycles at a higher current density of 5 A g-1, surpassing the device performance of most of the reported all-organic pseudocapacitive 2D networks.

HZSM-5 supported with N-doped Fe for microwave catalytic pyrolysis of lignin

Microwave catalytic pyrolysis of lignin is one of emerging technologies for efficiently converting lignin into fuels and chemicals. Molecular sieves (HZSM-5) are widely used as carriers to load metallic components for biomass pyrolysis but often encounter challenges such as high diffusion resistance and insufficient acidity of acidic sites. Traditionally, HZSM-5 is directly modified to enhance the activity of the acidic sites, but this modification is ineffective in improving the metallic components’ activity. Instead, we made nitrogen doping on Fe and then supported on HZSM-5 to construct Fe-N25/HZSM-5 catalysts for microwave catalytic pyrolysis of lignin. The N-doped Fe has the effect of “killing two birds with one stone” on enhancing the catalytic activity. The characterization results indicated that N replaced C of the graphitic carbon network to form carbon nitride structure, and further combined with Fe to generate Fe-N bonds, improving the electronegativity of the metallic component. Besides, the loading of N-doped Fe increased the acidity of the catalyst. The utilization of 1.00Fe-N25/HZSM-5 obtained the greatest bio-gas yield (35.2 wt%), a hydrogen yield of 27.8 mL/min, bio-oil yield (36.4 wt%) and phenol selectivity of 46.2 %. The likely pathway of microwave catalytic pyrolysis on Fe-N25/HZSM-5 was proposed through DFT calculation, using guaiacol as a model compound. The results suggested that N-doped Fe on HZSM-5 8 T tended to break the side-chain methoxy during pyrolysis of guaiacol, with energy barrier of 0.14 eV. This paper provides a promising strategy for modification of microwave pyrolysis catalysts.

Innovative strategy for the treatment of oily wastewater by in-situ synthesis of nitrogen-doped biochar supported FeS for activation of peroxymonosulfate

ABSTRACT Disposing of oily wastewater poses a significant challenge in treating oilfield-produced wastewater treatment. This study developed a FeSNC-9/PMS system for the effective degradation of total petroleum hydrocarbons (TPHs) in oily wastewater, while increasing the value of excess sludge, thus achieving the dual purpose of waste treatment. This work involved the in-situ preparation of a porous nitrogen-doped biochar-supported iron sulphide catalyst material using surplus sludge from SBR. Compared to undoped FeS (NC-9), FeSNC-9 exhibited excellent pore structure and abundant functional groups. Fe-Nx served as an effective connecting site between FeS species and the graphite network of biochar. The FeSNC-9/PMS system significantly degraded 74.21% of TPHs within 300 min. The FeSNC-9/PMS system demonstrated remarkable TPHs degradation efficiency across a wide temperature range and under both weak acidity and near-neutral conditions The dominant reactive oxygen species were identified as SO4 •− and •OH, with O2 •− and 1O2 also confirmed as active species. Gas chromatography semi-quantitative analysis showed that the long-chain alkanes of C20-C30 in total petroleum hydrocarbons were significantly degraded into short-chain alkanes or completely mineralized. This work provides new insights for the low-cost and high-efficiency treatment of TPHs in oilfield-produced water, and delves into the activation mechanism of PMS and the degradation pathways of TPHs.

Novel Graphitic Oxynitrides as Photocatalysts for Sustainable H2 Production and CO2 Valorization. The Importance of Self-Assembly for Catalytic Activity.

The field of carbocatalysis, often portrayed by paradigmatic graphitic carbonaceous structures, has become a booming topic tailored for multiple applications. To this end, a new metal-free carbocatalyst has been constructed from simple prebiotic monomers such as cyanamide and glyoxal. The resulting material shows an excellent performance as photocatalyst for H2 production and CO2 valorization, thus unveiling its real value to tackle sustainable goals. The unique oxygen-rich carbonaceous structure has been characterized in detail, which is consistent with a graphitic layered network. The described performance in two major societal concerns along with a facile preparation from C1/C2 platforms, makes this type of overlooked oxynitride carbocatalysts promising for real-life environmental endeavors.

Hydrogen Evolution Activity of Platinum Nanoparticles Decorated on Silver Nanowire Networks and Graphite Electrodes

The catalytic activity of graphite (C) and conductive silver nanowire (AgNW) networks coated on glass and graphite substrates with low platinum content towards hydrogen evolution reaction (HER) is reported. The results exhibit that the chronoamperometric electrodeposition of platinum on AgNW substrates results in the formation of spherically shaped nanoparticle agglomerates aligned on the nanowires. Also, platinum doped graphite electrodes with a rough surface showed an efficient distribution of platinum nanoparticles (PtNPs). Studies of the electrocatalytic HER activity as a function of platinum loading indicate that the optimum loading is in the range of 60 µg/cm2 and further loading results only in a minor reduction of the overpotential. At low Pt content, a synergistic effect of the AgNW network in terms of enhancement of the HER performance was observed. Tafel analysis showed that in the low overpotential region, the Volmer reaction was the rate determining step for the graphite based electrodes. The graphite substrate in conductive connection with the nanowires was shown to significantly boost the hydrogen formation rate.

Thermally enhanced flexible phase change materials for thermal energy conversion and management of wearable electronics

The developing trend of miniaturization and integration for electronics imposes challenges of efficient heat dissipation technology, where novel materials with advanced thermal energy conversion and management are urgently needed. In this work, we propose an emerging phase change material (PCM) system with polyvinyl alcohol/expanded graphite network loading paraffin wax (PE-PW), which exhibits superb flexibility, thermal energy storage capacity and thermal conductivity. The phase change enthalpy is from 115.61 J/g to 168.93 J/g without any leakage, which can be maintained even after 500 thermal cycles. The thermal conductivity can reach 1.46 W/mK, 484% enhanced compared with that of pure PCM. Meanwhile, the thermal management test indicates that the PE-PW composites can quickly absorb and store the generated heat to achieve temperature control, thus protecting the system from overheating and indicating excellent thermal management capacity. This flexible PE-PW system has broad application prospects in the field of thermal energy conversion and management for wearable electronics.

Biomimetic mineralization coupling with seeds-induced foaming for optimizing carbon microstructure towards ultrafast sodium ion storage

Porous carbons show high surface area and capacity but suffer from uncontrollable structure, inferior initial Coulombic efficiency (ICE) and rate capability in Na+ storage. Herein, we propose a strategy of biomimetic mineralization coupling with seeds-induced foaming to optimize porous carbon sheets (CNMK) with excellent performance in ICE of 90 %, rate capability of 528 mAh g−1 at 0.05 A g−1 and 139 mAh g−1 at 50 A g−1, and capacity retention of 81 % over 5500 cycles at 20 A g−1 (half-cell); energy density of 223 Wh kg−1 (CNMK//Na3V2(PO4)3 full-cell). The reasons for such outstanding performance are as follows: (1) The “disorder-in-order” structure (rich defects/pores in graphitic network) favours Na+ storage and electrons transportation (same electrolyte). (2) The ether electrolyte shows superior Na+ storage kinetics than ester electrolyte (same anode). These results will provide an effective and practical strategy for developing advanced carbon materials and give new insights into the synergistic effect between carbon structure and ether electrolyte in Na+ storage.

Highly conductive solid-solid phase change composites and devices enhanced by aligned graphite networks for solar/electro-thermal energy storage

Phase change materials (PCMs) are widely considered as promising energy storage materials for solar/electro-thermal energy storage. Nevertheless, the inherent low thermal/electrical conductivities of most PCMs limit their energy conversion efficiencies, hindering their practical applications. Herein, we fabricate a highly thermally/electrically conductive solid-solid phase change composite (PCC) enabled by forming aligned graphite networks through pressing the mixture of the trimethylolethane and porous expanded graphite (EG). Experiments indicate that both the thermal and electrical conductivities of the PCC increase with increasing mass proportion of the EG because the aligned graphite networks establish highly conductive pathways. Meanwhile, the PCC4 sample with the EG proportion of 20 ​wt% can achieve a high thermal conductivity of 12.82 ​± ​0.38 ​W·m−1·K−1 and a high electrical conductivity of 4.11 ​± ​0.02 ​S·cm−1 in the lengthwise direction. Furthermore, a solar-thermal energy storage device incorporating the PCC4, a solar selective absorber, and a highly transparent glass is developed, which reaches a high solar-thermal efficiency of 77.30 ​± ​2.71% under 3.0 suns. Moreover, the PCC4 can also reach a high electro-thermal efficiency of 91.62 ​± ​3.52% at a low voltage of 3.6 ​V, demonstrating its superior electro-thermal storage performance. Finally, stability experiments indicate that PCCs exhibit stabilized performance in prolonged TES operations. Overall, this work offers highly conductive and cost-effective PCCs, which are suitable for large-scale and efficient solar/electro-thermal energy storage.

In-vivo blood pressure sensing with bi-filler nanocomposite

Conductive elastomers present desirable qualities for sensing pressure in-vivo, such as high piezoresistance in tiny volumes, conformability and, biocompatibility. Many electrically conductive nanocomposites however, are susceptible to electrical drift following repeated stress cycles and chemical aging. Here we propose an innovative approach to stabilize nanocomposite percolation network against incomplete recovery to improve reproducibility and facilitate sensor calibration. We decouple the tunnelling-percolation network of highly-oriented pyrolytic graphite (HOPG) nanoparticles from the incomplete viscoelastic recovery of the polydimethylsiloxane (PDMS) matrix by inserting minute amounts of insulating SiO2 nanospheres. SiO2 nanospheres effectively reduce the number of nearest neighbours at each percolation node switching off the parallel electrical pathways that might become activated under incomplete viscoelastic relaxation. We varied the size of SiO2 nanospheres and their filling fraction to demonstrate nearly complete piezoresistance recovery when SiO2 and HOPG nanoparticles have equal diameters (≈400 nm) and SiO2 and HOPG volume fractions are 1 % and 29.5 % respectively. We demonstrate an in-vivo blood pressure sensor based on this bi-filler composite.

Low-crystallinity conductive multivalence iron sulfide-embedded S-doped anode and high-surface area O-doped cathode of 3D porous N-rich graphitic carbon frameworks for high-performance sodium-ion hybrid energy storages

Sodium-ion hybrid energy storages (SIHESs) are promising electrochemical energy storages for many applications, but their low energy and power densities are yet to be overcome. Herein, we report a strategy to realize ultrahigh-energy density and fast-rechargeable SIHESs. Ultrafine iron sulfide-embedded S-doped carbon/graphene (FS/C/G) anode materials are synthesized from iron-based metal-organic framework (MOF)/graphene oxide heterostructures via graphitic carbon formation and sulfidation. Operando and ex-situ analyses reveal that cycled iron sulfides are rescaled into low-crystallinity conductive fragments with Fe vacancies and multivalence Fe2+/Fe3+ states. Size reduction to fragments inside a 3D porous S-doped N-rich graphitic carbon framework induces high-capacity/high-rate FS/C/G performance. Moreover, 3D porous O-doped carbon cathode materials are synthesized from zeolitic imidazolate frameworks (ZIFs) via pyrolysis-assisted micropore and KOH-assisted mesopore formations. This ZIF-derived porous carbon (ZDPC) has a ∼20-fold higher surface area (3972 m2/g) than conventional ZDCs, O-induced micropores/N-rich sites for high capacity, heteroatom-induced ion-accessible defects/mesopores, and N-rich conductive graphitic carbon networks. Additionally, FS/C/G//ZDPC SHHES benefits from diffusion-controlled and capacitive reactions, as demonstrated by its hitherto highest energy density of 247 Wh kg-1 outperforming state-of-the-art SIHESs, fast-rechargeable power density (up to 34,748 W kg-1) exceeding battery-type reactions by more than 100 folds, and cycle stability with ∼100 % Coulombic efficiency over 5000 charge-discharge cycles.

A novel method for exploring the wear resistance characteristics of ethylene propylene diene monomers‐polyamide elastomers with nano‐graphite

AbstractHansen solubility parameter theory and rheological laws were employed to investigate the microscopic cross‐linked network structure of the wear‐resistant elastomer based on ethylene propylene diene monomers (EPDM)‐polyamide elastomers (PAE)/graphite. With the condition of the same carbon black content, the wear volume of EPDM‐PAE increased after added wax powder and decreased by adding five percent graphite. The role of microscopic cross‐linked network on the wear‐resistant properties was specifically characterized by a highly linear synergistic relationship between wear volume and cross‐link density. The motion ability of micro chain segments has been characterized by the frequency sweep and the influence of the filler network has been represented by the strain sweep. Scanning electron microscope was used to characterize the micro filling structure, while stereomicroscope view was used to explore the wear interface. It was noteworthy that the graphite network layer formed on the abrasive surface on top of the abrasive grit wear transformed the wear mechanism into composite wear. This work was an innovative perspective to study rubber‐plastic/solid lubricant‐based wear‐resistant elastomers, based on microscopic network structures, which could help to obtain new wear‐resistant elastomers with specific properties.

Interfacial MoO2 nanograins assembled over graphitic carbon nanofibers boosting efficient electrocatalytic reduction of nitrate to ammonia

Electrocatalytic nitrate reduction reaction (NO3-RR) for sustainable carbon-free hydrogen carrier (NH3) production from polluted NO3- sources of industrial wastewater is very promising. Mo-based catalysts are defined as popular electrocatalytic materials, but the rational performance achievement of Mo-based catalysts in the NO3-RR remains limited. In this study, to overcome the NO3-RR activity limitation, the interfacial MoO2 nanograins assembled on the N-functional carbon nanofibers (defined as MoO2/C) were constructed by electrospun and controlled graphitizing process. The comparative catalysts dominated by molybdenum oxides namely MoO2/MoO3 were synthesized by controlled calcination in air atmosphere. The MoO2 nanograins anchored in situ on carbon nanofibres could afford more interfacial active regions and accelerate the electron transfer efficiency of the electrocatalytic process by graphitic carbon fiber network. More importantly, MoO2/C was endowed with more oxygen vacancy sites which can trap the free NO3- ions over the reactive sites to enhance the surface interaction of NO3- with catalytic sites during the reaction process. The experimental results showed that the electrocatalytic nitrate reduction performance of the catalyst MoO2/C obviously outperformed that of MoO2/MoO3 in the light of the atomic activity efficiency with a near 7.5 folds enhancement. The MoO2/C affords the highest NH3 yield of 4838.5 µg h−1 mgcat−1 and Faraday efficiency of 30 % at –0.9 V vs.RHE and was endowed with 50 h of continuous reaction stability, proving the potential in practical electrochemical water treatment involving nitrate contamination.

Scalable nanoarchitectonics with microporous polymer composite for methanol-tolerant ORR electrocatalysts

We report an efficient ORR electrocatalyst containing cobalt single atom and cobalt nanoparticle active sites embedded in a porous nitrogen-doped graphitic carbon network.

Alveoli-Mimetic Synergistic Liquid and Solid Thermal Conductive Interface as a Novel Strategy for Designing High-Performance Thermal Interface Materials.

Thermal interface materials (TIMs) are in desperate desire with the development of the modern electronic industry. An excellent TIM needs desired comprehensive properties including but not limited to high thermal conductivity, low Yong's modulus, lightweight, as well as low price. However, as is typically the case, those properties are naturally contradictory. To tackle such dilemmas, a strategy of construction high-performance TIM inspired by alveoli is proposed. The material design includes the self-alignment of graphite into 3D interconnected thermally conductive networks by polydimethylsiloxane beads (PBs) -the alveoli; and a small amount of liquid metal (LM) - capillary networks bridging the PBs and graphite network. Through the delicate structural regulation and the synergistic effect of the LM and solid graphite filler, superb thermal conductivity (9.98 ± 0.34W m-1 K-1) can be achieved. The light emitting diode (LED) application and their performance in the central processing unit (CPU) heat dispersion manifest the TIM developed in the work has stable thermal conductivity for long-term applications. The thermally conductive, soft, and lightweight composites are believed to be high-performance silicone bases TIMs for advanced electronics.

Enhanced thermal conductivity of phase change composites with novel binary graphite networks

The thermal conductivity and porous structure of carbon-based networks significantly affect the heat exchange efficiency in phase change composites. However, simultaneously improving its thermal conductivity and controlling the formation of micrometer-scale open pores remains a significant challenge. In this study, a binary graphite network is constructed by both high-thermal-conductivity mesophase-pitch carbon fibers and high-textured pyrolysis carbon through chemical vapor deposition and ultra-high temperature graphitization, then embed paraffin to form high-performance phase change composites. The characteristic hierarchical pore structure in the binary graphite network facilitating the paraffin impregnation and its heat exchange efficiency is greatly improved by showing an optimum thermal conductivity of 144.78 W·m−1·K−1 and a phase change enthalpy of 87.4 J·g−1 at 0.6 g·cm−3 graphite skeleton and 51 wt% paraffin. The developed phase change composites hold great application potential in thermal control for space optical-mechanical systems and other critical aerospace components.

Nitrogen Radiofrequency Plasma Treatment of Graphene

AbstractThe incorporation of nitrogen (N) atoms into a graphitic network such as graphene (Gr) remains a major challenge. However, even if the insertion mechanisms are not yet fully understood, it is certain that the modification of the electrical properties of Gr is possible according to the configuration adopted. Several simulations work, notably using DFT, have shown that the incorporation of N in Gr can induce an increase in the electrical conductivity and N acts as an electron donor; this increase is linked to the amount of N, the sp2/sp3 carbon configuration, and the nature of C−N bonding. Nitrogen radiofrequency (RF) plasma has been used to incorporate N into Gr materials. The RF plasma method shows the possibility to incorporate N‐graphitic nitrogen into Gr after a pre‐treatment with nitric acid. X‐ray photoelectron spectroscopy and Raman spectrometry were used to quantify the functionalized groups. The modifications of the graphene surface chemistry along the amount of N inside the Gr change the chemical environment of N. This method, enabling the incorporation of N inside Gr matrix, opens up a route to a broad range of applications.

Modification of the electronic structure of g-C3N4 using urea to enhance the visible light-assisted degradation of organic pollutants.

Graphitic carbon nitride has been proven to be a good candidate for using solar energy for photo-induced pollutant degradation. However, the high photo-induced holes-electron recombination rate, unfavorable morphology, and textural properties limited their application. In this study, we present a novel g-C3N4 with a novel electronic structure and physiochemical properties by introducing a single nitrogen in the graphitic network of the g-C3N4 through a novel method involving step-by-step co-polycondensation of melamine and urea. Through extensive characterization using techniques such as XPS, UPS-XPS, Raman, XRD, FE-SEM, TEM, and N2 adsorption-desorption, we analyze the electronic and crystallographic properties, as well as the morphology and textural features of the newly prepared g-C3N4 (N-g-C3N4). This material exhibits a lower C/N ratio of 0.62 compared to conventional g-C3N4 and a reduced band gap of 2.63 eV. The newly prepared g-C3N4 demonstrates a distinct valance band maxima that enhances its photo-induced oxidation potential, improving photocatalytic activity in degrading various organic pollutants. We thoroughly investigate the photocatalytic degradation performance of N-g-C3N4 for Congo red (CR) and sulfamethoxazole (SMX), and removal of up to 90 and 86% was attained after 2 h at solution pH of 5.5 for CR and SMX. The influence of different parameters was examined to understand the degradation mechanism and the influence of reactive oxygenated species. The catalytic performance is also evaluated in the degradation of various organic pollutants, and it showed a good performance.

In-situ strain characterization and stress analysis of SnO2@graphite@CNT electrodes for lithium-ion batteries by digital image correlation method

In this study, SnO2@graphite@CNT composite was synthesized by growing SnO2 nanoparticles within the interconnected three-dimensional network of graphite and carbon nanotubes using an acoustic chemistry method and a followed annealing treatment. As anode material for lithium-ion batteries, the composite exhibits high specific capacity and excellent cycling stability. The deformation behavior of the SnO2@graphite@CNT electrodes was in-situ monitored and recorded during discharge-charge process, and the strain fields onto the electrode surface was analyzed using digital image correlation technique. The dynamic evolution of plane stress in the electrode was evaluated by combining strain data with a mechano-electrochemical constitutive equation, and the contributions of mechanical and electrochemical parts to the plane stress also be discussed, respectively. The results provide valuable insights into the volume deformation behavior and mechano-electrochemical failure mechanism of SnO2-based electrodes for lithium-ion batteries.

A self-supporting graphitic carbon nanocage network confining high-loading sulfur for high performance potassium-sulfur batteries

Potassium-sulfur (K-S) battery is a promising candidate for high-energy and low-cost energy storage system. However, the development of K-S battery is challenged by the sluggish kinetics, low utilization of sulfur and serious shuttle effect. Herein, a novel self-supporting carbon/sulfur composite cathode (S@GCNs) was developed by infusing sulfur into an interconnected graphitic carbon nanocage (GCNs) network. Typically, the small GCNs (<10 nm) provide a large amount of space for sulfur storage, the sulfur content could reach more than 80 wt%. In addition, the interconnected GCNs network with high conductivity provide fast transport pathways for electrons/ions, and the strong confinement of GCNs on sulfur will buffer the volume expansion of sulfur and alleviate shuttle effect. The unique microstructure of S@GCNs boosts the rate capability and cycle stability of K-S battery, the initial capacity was 452.7 mAh/g, which remained 270.6 mAh/g and 205.9 mAh/g after 10 and 20 cycles, the capacity can reach 97.7 mA h g−1 even at 2000 mA g−1. Characterizations of the phase and structural evolution of S@GCNs revealed the reversible conversion mechanism of sulfur: S0↔ K2Sx (x = 5, 6)↔ K2Sx (x = 4)↔ K2S3.

Monotropic type transformations of diamond below the Berman-Simon line

We construct the phase diagram of a monotropic type for carbon under the Berman-Simon line. It describes metastable phase transformations occurring in diamond when the graphitization is delayed. However, thus far, monotropic phase transition of metastable diamond could not be experimentally observed. To produced delay conditions, we introduced at diamond surface a droplet of graphite melt with a temperature of about 4800K. We demonstrate that thermal shock provided mechanical stress and competition between phase transformations occurring at two high temperature and high pressure branches. At the so called “fast graphitization line” (reported by F.P. Bundy et al., Carbon 34 (1996) 141) the transformations take place tending to the spontaneous diamond graphitization, whereas at the line of monotropic phase diagram, they tend toward the melting of diamond. The transition can start as the graphitization, whereas change-over to the second branch can occur as a result of rapid unloading of mechanical stresses. The melting wins this is competition due to its faster kinetics. We have also found out the characteristic features underlying the initiation of processes near the “fast graphitization line” as are dealing with the spontaneous formation in diamond of a network of compressed graphite, and with the melting of such graphite in the course of its expansion taking place owing to the loss of mechanical stability of diamond caused by the network. This mechanism, apparently reveals a liquid-like nature of the transformations at the “fast graphitization line”.