Defects In Graphite Research Articles

Research on the Effect of the Graphite Defect Type and Doping Structure on Microwave Absorption Properties in Nitrogen-Doped Carbon Fiber

Research on the Effect of the Graphite Defect Type and Doping Structure on Microwave Absorption Properties in Nitrogen-Doped Carbon Fiber

Rapid preparation of N,P co-doped carbon for advanced oxidative degradation of wastewater

Heteroatom-doped porous carbon materials are highly favored as catalysts for activating persulfates in the oxidative degradation of organic pollutants due to their low metal leaching risk and cost-effectiveness. Nonetheless, the complex process of creating heteroatom-doped carbon materials often results in suboptimal doping effects. This study uses N,P-enriched plants (Eichhornia crassipes after being used for nutrient-rich water remediation) as a raw material to prepare N-P co-doped catalysts in a single step. We thoroughly investigated their performance and mechanisms in dye degradation. The findings demonstrated that the adsorbent, with its rich pore structures, surface chemical functional groups, and graphite defect structures, could completely degrade a 100 mg L−1 MB solution within 20 min. Free radical quenching experiments and EPR analysis confirmed the presence of •OH, SO4•—, O2•— and 1O2, verifying their oxidative contributions. Moreover, it was determined that the non-radical pathway (1O2 oxidation) primarily drives the oxidative degradation in this system. Additionally, tests using a small-scale fixed-bed reactor and interference resistance highlighted the practical application potential of the adsorbent developed in this study. This study not only offers a dual solution for tackling nutrient enrichment and organic pollution in water bodies but also introduces a straightforward method for preparing N, P co-doped catalysts, significantly benefiting environmental protection.

Strain-Induced Shifts in Defective Graphite Phonon Modes Predicted by Density Functional Theory

Strain-Induced Shifts in Defective Graphite Phonon Modes Predicted by Density Functional Theory

An insight into annealing mechanism of graphitized structures after irradiation

Graphite components are constantly subjected to a combined actions of annealing and irradiation due to high temperatures and thermal spike caused by irradiation when reactors are operating, resulting in complex microstructures along with matching changes in the material properties and dimensions. This study investigates the evolution process of initial irradiation defects at different annealing temperatures, which is difficult to captured by experiment. The findings indicate that 923K reactor-temperature annealing can also quickly restore isolated self-interstitial atoms and small-sized point defect clusters to intralayer locations on the nanosecond scale. However, multi-interlayer penetration damages and localized point defect aggregation from high-energy irradiation can lead to the disappearance of layered structural information, which allows these damage structures to develop into interlayer dislocations during annealing process. These interlayer dislocations further exacerbate the interlayer expansion of graphite crystal and may elucidate the mechanism behind volume expansion in nuclear graphite within reactors. Fully amorphized regions can also regain a layered structure approximately when guided by residual layered structures at 2000K, while chaotic regions or disordered layered structures form in the absence of guidance. These chaotic regions significantly exacerbate the volume expansion of graphite model, which may be related to the rapid volume increase observed in nuclear graphite components at the end of reactor life. The study provides insights into the transformation of initial irradiation defects into different types of defects under different temperatures and damage states, which serve as a critical foundation for assessing the evolution of irradiation defects in nuclear graphite for reactor applications and annealing studies.

Boosting the kinetics of bromine cathode in Zn–Br flow battery by enhancing the electrode adsorption of the droplet of bromine sequestration agent/polybromides complex

Zinc-bromine (Zn–Br) flow battery is a promising option for large scale energy storage due to its scalability and cost-effectiveness. However, the sluggish reaction kinetics of Br2/Br− have hindered further advances. In this study, we report that a nitrogen-doped carbon felt electrode derived from a metal-organic framework can facilitate the adsorption of N-methyl N-ethyl pyrrolidinium polybromide (MEP-pBr) complex droplet dispersed in aqueous electrolyte. Density functional theory (DFT) calculation and Zeta potential measurement suggest that the adsorption is primarily due to the positively charged surface induced by graphitic nitrogen defects. Electrochemical analysis indicates that the enhanced adsorption of MEP-pBr droplet significantly boosts the redox kinetics and decreases the crossover of bromine-bearing species. Consequently, the cell performance improves, achieving an energy efficiency of over 79 % during 900 cycles at a current density of 100 mA cm−2. Our work underscores the importance of providing access of MEP-pBr droplet to the electrode surface in augmenting the energy efficiency of Zn–Br flow battery.

Regulation of reactive oxygen species generation by graphitization and defect degree of Co-loaded carbon in peroxymonosulfate activation

The designing of functional groups and structured active sites is a vital strategy for efficient Peroxymonosulfate (PMS)-based advanced oxidation processes (PMS-AOPs). However, the regulation mechanism and correlation of graphitization/defect degree and reactive oxygen species (ROS) are still not fully understood for a composite catalyst. Herein, a family of metal–organic framework (MOF)-derived cobalt-nitrogen-carbon with different graphitization/defect degrees was designed and synthesized successfully to activate PMS for carbamazepine (CBZ) degradation. NC-0.6/PMS system exhibited efficient performance for several contaminants, but NC-10/PMS system preferred to remove contaminants with low electrophilicity. The correlation analysis and Fukui index calculation revealed that high graphitization and low defect degree of catalysts stimulated diverse ROS generation (•OH and 1O2) and the decreasing of graphitization was beneficial to form a single 1O2 oxidation system. The regulation of ROS was a potential approach for the selective removal of contaminants. This work provides a new insight into the mechanism transformation of ROS-oriented degradation of pollutants in PMS-AOPs.

Miniaturized Hard Carbon Nanofiber Aerogels: From Multiscale Electromagnetic Response Manipulation to Integrated Multifunctional Absorbers

AbstractThe multiscale structural engineering strategy presents a powerful method for tailoring the structural attributes of materials at various levels, enabling the flexible control and manipulation of their electromagnetic properties. Nonetheless, orchestrating the multiscale architecture of polymer‐derived carbon aerogels specifically for microwave absorption poses significant challenges. Herein, aramid‐derived hard carbon nanofiber aerogel microspheres (CNFAMs) featuring a hierarchical skin‐core structure are fabricated through a wet‐spinning technique, combined with reprotonation‐mediated self‐assembly and carbonization processes. The presence of large‐scale voids between neighboring microspheres and the microscale porosity within the microspheres themselves improves impedance matching and promotes microwave reflection and scattering. The distinct graphitic domains and defects serve as pivotal elements for conduction and polarization losses, significantly impacting microwave attenuation. By meticulously tailoring the macroscale dimensions, microscale porous architecture, and nanoscale domains, the optimized CNFAMs demonstrate a remarkable absorption bandwidth of 9.62 GHz at an ultralow filling of 0.97 wt%. Additionally, the implementation of application‐oriented microwave absorption through the innovative integration of polysilsesquioxane‐CNFAMs in a host–guest aerogel is explored. This composite system brings together broadband absorption, superhydrophobicity, thermal insulation, resistance to freezing, and robust tolerance to harsh environments. Such a multifaceted approach is designed to tackle the growing challenges associated with complex electromagnetic environments effectively.

A simple and feasible method for preparing chromium carbide coating on graphite through binary NaCl-KCl molten salt

Due to excellent high temperatures resistance and wear resistance, graphite showed great potential apply in refractory materials. However, the porosity defects caused by the layered stacked structure of graphite would lead to easy permeability, which would result in reducing material’s lifetime. Surface coating technology was considered to be an ideal method to solve the problems through a stable coating on the surface of graphite. But existing methods have some disadvantages, such as high-cost and complex processes. In this work, a simple, low-cost and green molten salt method was designed. This method successfully prepared a Cr7C3 coating on the graphite surface. The effect of reaction time and temperatures on the chromium carbide coating was investigated by SEM and EDS. The results showed that the thickness of the coating layer increased gradually with the increase in reaction time or reaction temperature, and finally stabilized at about 8 μm. In addition, the reasons behind the formation of Cr7C3 coatings were discussed in terms of both the molten salt reaction and Gibbs free energy, as well as the effect of the coating structure on adhesion. Based on this method, it could not only effectively address the structure defects of graphite, but also showed simple preparation processes and low cost, which would promote the development of graphite materials in high-temperature resistant materials.

Enhancing insight into sorption-degradation interplay: A comparative study on the removal of organics by biochar through experiments and theoretical calculations

Sorption and degradation occur simultaneously during the removal of aromatic organics by biochar. However, the unclear association between sorption and degradation limited our understanding of the underlying mechanisms of organic removal by biochars. Herein, the removal of monocyclic 2,6-dimethylphenol (DMP) and bicyclic bisphenol A (BPA) by raw and potassium hydroxide modified biochars was comparatively investigated by batch removal experiments and theoretical calculations. Under identical initial concentrations, biochar displayed lower sorption but higher degradation for DMP compared to BPA, whilst higher sorption corresponded to greater degradation for the same chemical. Sorption mechanisms revealed by molecular dynamic simulations include π-π, hydrophobic, and hydrogen bonding interactions. Density functional theory calculations identified the preferred degradation sites on biochar for adsorbed organics are graphitic nitrogen, defects, carboxyl, and hydroxyl functional groups. Analysis of free radicals and degradation intermediates concluded that the degradation pathways involve both free radical pathways and electron transfer processes for DMP, while only free radicals for BPA. Experimental and computational results indicated an increase in ring quantity can lead to higher sorption affinity but lower degradability of aromatic organics by biochar. Findings of this research provide theoretical support for the advancement of biochar based aromatic contaminant mitigation strategies.

Facile synthesis of dense SiBCN coatings with excellent compactness, smoothness, and high-temperature inertness on defective graphite surfaces

SiBCN ceramics possess extreme high-temperature stability among engineering ceramics; however, their application is constrained by the difficulty in achieving large continuous products at low cost. This work exhibits the possibility of fabricating SiBCN continuous coatings on graphite substrates to improve their surface integrity, hardness, and inertness. The ceramic coatings were fabricated simply by spin coating, curing, and pyrolysis. The key innovations are the synthesis of the precursor, polyborosilazane (PBSZ), that derives continuous ceramic films after pyrolysis, and the finding that the xylene solution of PBSZ can achieve a very good spinning performance on various surfaces, especially the low-quality graphite surfaces with holes. The fabricated SiBCN coatings, characterized to be networks of Si–C, Si–N, C–C, and B–N bonds, possessed smooth and hard surfaces with roughness below 9 nm and a hardness of 7.3 GPa. The coating thickness can be well controlled in the range of 1.4 – 2.1 μm as the latter is linearly dependent on the concentration of PBSZ in the solution. Detailed observations of surface morphologies and physisorption experiments reveal that the coating surfaces are crack-free and highly dense, rendering a significant reduction in specific surface areas when a defective graphite face is coated.

Irregular network of extended defects in graphene and a new criterion of the crystal lattice melting

Investigation of graphite defects has long and rich history. However, it turned out, that most point defects in graphene, such as vacancies or topological Stone-Wales defect, have high formation energies, preventing them from formation in large quantities. Recently, we have proposed a new type of extended defects in graphene, with formation energy per atom only slightly above the melting temperature. This means, that these planar defects may occur near the melting temperature in sufficient quantities to influence the thermodynamic properties of graphene. Still, there is discrepancy between thermodynamic properties of these defects and their topology, which can be successfully resolved by proposition of a new defects' type – irregular network of extended defects, which will be described in this paper. The study of network stability from these defects enables us to formulate a new criterion of crystal lattice melting, which supersedes the Lindemann/Born criteria.

A facile approach for regeneration of graphite anodes from spent lithium-ion battery

Recycling of lithium-ion battery anodes has become a topic of interest due to the retirement of batteries. However, existing recycling methods have either been environmentally unfriendly or lacked high purity levels. Here, a simple and low-cost recycling method is developed. Firstly, organic matter in graphite is eliminated through heat treatment. The removal of metal impurities in graphite is then carried out by utilizing sulfuric acid (H2SO4) leaching. Lastly, potassium hydroxide (KOH) etching is utilized to restore the structural defects of graphite. This comprehensive process enhances the cycling stability and rate capability of graphite. The initial discharge capacity at 0.1 C can reach a specific capacity of 422.42 mAh/g, and the specific capacity of the discharge after 100 cycles is 365.97 mAh/g, which reaches the standard of commercial graphite (CG). The results demonstrate that the method effectively purifies and regenerates waste graphite (WG). This process can alleviate resource pressure while being suitable for industrial applications due to its simplicity and low cost.

Novel cow dung-doped sludge biochar as an efficient ozone catalyst: Synergy between graphitic structure and defects induces free radical pathways

A composite material, cow dung-doped sludge biochar (Zn@SBC-CD), was synthesized by one-step pyrolysis using ZnCl2 as an activating agent and applied to a catalytic ozonation process (COP) for methylene blue (MB) removal. SEM, XRD, FTIR, XPS and BET analyses were performed to characterize the biochar (BC) catalysts. Zn@SBC-CD had high graphitization degree, abundant active sites and uniform distribution of Zn on its surface. Complete removal of MB was achieved within 10 min, with a removal rate much higher than that of ozone alone (32.4%), implying the excellent ozone activation performance of Zn@SBC-CD. The influence of experimental parameters on MB removal efficiency was examined. Under the optimum conditions in terms of ozone dose 0.04 mg/mL, catalyst dose 400 mg/L and pH 6.0, COD was completely removed after 20 min. Electron paramagnetic resonance (EPR) analysis revealed radical and non-radical pathways were involved in MB degradation. The Zn@SBC-CD/O3 system generated superoxide anion radicals (•O2−), which were the main active species for MB removal, through adsorption, transformation, and transfer, Furthermore, Zn@SBC-CD exhibited good reusability and stability in cycling experiments. This study provides a novel approach for the utilization of cow dung and sludge in synthesis of functional biocatalysts and application in organic wastewater treatment.

The Effect of Carbon Structure of DLC Coatings on Friction Characteristics of MoDTC-Derived Tribofilm by Using an In Situ Reflectance Spectroscopy

In this study, six types of DLC coatings were prepared, featuring different carbon structures (including amorphous ta-C coatings and GNC coatings with nanocrystallites) and different doped Ta amounts, to investigate friction characteristics. The results of friction tests with MoDTC-added lubricant revealed a consistent trend: DLC coatings with a higher ID/IG ratio exhibited lower friction coefficients. In addition, in situ observations using reflectance spectroscopy highlighted that the tribofilm formed on DLC coatings with a higher ID/IG ratio maintained a higher MoS2/(MoS2+MoO3)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{MoS}}}_{2}/({{\ ext{MoS}}}_{2}+{{\ ext{MoO}}}_{3})$$\\end{document} ratio, which exhibited a strong correlation with the friction coefficient. Measurements of a work function of each DLC coating indicated that those with a higher ID/IG ratio had a higher work function, suggesting the inclusion of a larger amount of graphite structure defects. These active defects in the graphite structure were deemed responsible for enhancing the friction reduction effect of MoDTC. The outcomes of this study propose a material design approach for DLC coatings that amplifies the effectiveness of lubricant additives in friction reduction.Graphical abstract

The coupling mechanism of shrinkage defects and graphite on the corrosion resistance of ductile iron

This study investigated the coupling mechanism of shrinkage defects and graphite on the corrosion resistance of ductile iron by electrochemical measurements, quasi-in-situ immersion tests and numerical simulations. The detrimental impact of shrinkage defects was confirmed by elevated corrosion current density and the formation of a porous corrosion product layer. Multiple-galvanic coupling effect among the matrix, graphite, and shrinkage defects serves as corrosion triggers, which is verified by scanning Kelvin probe force microscopy (SKPFM) and numerical simulations. Additionally, quasi-in-situ observations corroborate the deposition of corrosion products and Cl enrichment at defect bottoms, expediting occluded cell formation and corrosion propagation.

A novel carbon-based solid acid catalyst with high acidity for the hydration of α-pinene to α-terpineol: Effect of graphite crystallite size and synergistic effect of defects

This work, for the first time, highlights that small-sized graphite crystallite and highly defective carbon-based catalysts can effectively increase the −SO3H density of the catalysts and modulate the surface electronic properties of the catalysts, which further facilitates the α-pinene hydration reaction. Hydrothermal phosphoric acid modulation of graphite crystallite size and defects in carbon-based catalysts systematically revealed the correlation between −SO3H density, catalytic activity, graphite crystallite size, and defects in biomass carbon. The characterization results demonstrate that small-size graphite crystallites and high structural defects provide more sp2 hybridized carbon edges, contributing to the catalyst's increase of −SO3H density. The −SO3H group density of the catalyst increased from 0.89 to 1.20 mmol/g after hydrothermal phosphoric acid treatment. The catalyst has the highest efficiency in the α-pinene hydration to α-terpineol among the reported catalysts, in which 87.06 % of α-pinene was converted and reached a maximum α-terpineol selectivity (55.38 %) time only 22 h. Density functional theory calculations show that the lattice defects of graphite crystallites in catalysts lead to the polarization of the electron cloud around the catalyst, which further leads to the reduction of electrostatic resistance between α-pinene and the active catalytic sites. The apparent activation energy of hydration by the catalyst is 1.74 times lower than that of conventional biomass carbon-based solid acids. The reduction of graphite crystallite size is considered a critical step in improving the selectivity of α-terpineol attributed to the effective reduction of α-terpineol adsorbed on the catalyst.

Tuning intrinsic defects of Pt-based carbon supports by high-energy ball-milling for enhanced alkaline hydrogen evolution

Carbon materials are significant supports for catalysts, in which surface properties play a crucial role in catalytic performances. However, the correlation between the intrinsic defects of carbon supports and the alkaline hydrogen evolution reaction (HER) performance of catalysts is still unclear. Herein, graphite (G) was used as a model support to study the effect of intrinsic defects of carbon support on the HER performance. To this end, defect-enriched graphite supports were obtained by a simple high-energy ball-milling process. The affluent intrinsic defects (edge surfaces) in graphite supports served as active sites for the dispersion and anchoring of Pt nanoparticles for better electron transfer from Pt species to the support, leading to strong metal-support interactions. The resulting Pt-loaded on defect-enriched DG-30 (Pt/DG-30) delivered a lower overpotential of 46 mV at 10 mA cm−2 when compared to undecorated Pt/G (177 mV), indicating an excellent HER activity. Pt/DG-30 also showed superior stability due to the strong metal-support interactions between Pt nanoparticles and carbon support. In sum, significant insights into the rational optimization and regulation of intrinsic defects of carbon supports were provided for the preparation of new catalysts-modified carbon supports with enhanced HER performances.

N-doped carbon derived from thermoplastic and thermosetting polyimides toward electromagnetic waves absorption

Due to stronger tunability, higher stability, and low production costs, polymeric material-based carbon materials are considered to have the potential to become high-performance electromagnetic wave absorbing (EWA) materials. In this work, polymer-derived carbon is made by pyrolyzing thermoplastic polyimide (TPPI) and thermosetting polyimide (TSPI) at different temperatures. Using Raman and XPS analysis, the graphitization degree and defect content of carbonized TPPI and TSPI are obtained. The reflection loss is calculated by through their electromagnetic parameters. The prepared carbonaceous materials exhibit excellent EWA performance. Specifically, the maximum effective absorption band (EABmax) of carbonized TSPI at 1500 C can reach 4.1 GHz with thickness of 1.8 mm, and that of carbonized TPPI at 900 C can reach 4 GHz at lower thickness of 1.6 mm. The different structures of TPPI and TSPI result in different degrees of graphitization and defect content at the same temperature, which further leads to differences in their EWA performance. This work provides inspiration for studying the influence of precursor structure on the EWA preformation of carbon materials obtained through pyrolysis.

Effect of pretreatment synergistics on Shenfu low-rank coal pyrolysis in molten metal

The two key factors that significantly impact coal pyrolysis are its structural composition and the medium in which it is carried out. In this study, effects of acid pretreatment (AP), hydrothermal pretreatment (HTP), and acid-hydrothermal synergistic pretreatment (AP-HTP) on Shenfu Low-rank coal (SF) structure were investigated. In molten metals (MM), the distribution and composition of coal pyrolysis products were investigated to evaluate the impact of pretreatment synergistics. The results showed that changing the structure of the coal had a significant effect on the pyrolysis behavior. The molten metal stimulated the pyrolytic conversion of the coal. Pyrolysis in molten metal with AP-HTP synergistic pretreatment coal (SF-AH/MM) increased the tar yield and reduced the water yield. The tar of SF-AH/MM increased aromatic and phenolic compounds, while decreased the aliphatic and oxygen compounds. The H2 increased by 19.48 % and carbon oxides decreased for the gas of SF-AH/MM. Moreover, the char of SF-AH/MM enriched the aromatic structure and the content of the perfect graphite crystal structure, while reduced the degree of graphite lattice defects. The pretreatment synergistics affected the structure of coal and the molten metals enhanced the pyrolysis process, the distribution of products was optimized. Pyrolysis of synergistic pretreatment coal in molten metals is promising to enhance the tar yield, the H2 yield and improved the quality of the char.

Improved thermolytic dehydrogenation of LiBH4 nanoconfined in few-layer graphene with different functionalities

In this work, lithium borohydride (LiBH4) was loaded into plasma-activated nanoporous few-layer graphene (FLG) powders with different specific surface areas (∼400–800 m2/g) and functional groups (carboxyl and amine) to investigate the effect of LiBH4@FLG nanoconfinement on the dehydrogenation properties. It was observed that the dehydrogenation temperature dropped significantly from 463 °C for pure LiBH4 to ∼120 °C for all LiBH4@FLG nanocomposites. This was attributed to the nano-sized pores of the FLG materials that can constrain LiBH4 by nanoconfinement and thus decrease the dehydrogenation temperature. The highest dehydrogenation yield of 83% occurred in LiBH4@FLG with 400 m2/g surface area and amine groups, possibly due to Lewis basic amino groups and better graphitic structure. Moreover, it was found that both the surface area and the graphitic defects on the FLG host materials have an influence on the dehydrogenation kinetics. LiBH4@FLG with 800 m2/g surface area and carboxyl groups possesses the lowest activation energy due to its high surface area and high concentration of graphitic defects.