Surface Chemistry Of Carbon Materials Research Articles

Characterisation of the surface chemistry of carbon materials by temperature-programmed desorption: An assessment

The increasing role assumed by carbon materials in technological applications is intrinsically linked to a better understanding of carbon surface chemistry as a result of reliable methods of analysis. X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques allow to obtain qualitative and quantitative information on individual functional groups on the carbon surface. In this context, TPD has established itself as an alternative technique to the Boehm titration methodology or XPS, being especially adequate for the characterisation of oxygen functional groups on carbon materials with extended porosity. This work reviews the fundamentals and methodology to perform a correct TPD-MS analysis and assessment (qualitatively and quantitatively) of the oxygenated functional groups. The applicability of the information obtained by TPD to correlate the properties of carbon materials with their performance in practical applications is also revised.

Directional Regulation of Surface Chemistry of Graphene Using Carbon Dots for Sodium-Ion Battery Anodes

In this study, we have fabricated carbon dot/reduced graphene oxide (CDs/rGO) composites using oxygen-functionalized CDs and conductive graphene oxide (GO) by a hydrothermal method and calcination at 250 °C. The CDs can manipulate the surface functional groups of the composites by consuming C–O bonds and introducing C═O bonds. As sodium-ion battery anodes, CDs/rGO with a high C═O group content exhibits a great reversible capacity of 308 mAh g–1 at 0.05 A g–1, which is up to 1.8 times that of rGO (173 mAh g–1). It retains a capacity of 116 mAh g–1 after 2000 cycles at 2 A g–1. When assembled into a full cell, the activated anode and NVP@C display a higher initial discharge capacity of 291 mAh ganode–1 with an average working voltage of 2.5 V. The good performance of CDs/rGO is mainly due to the synergistic effects of the CDs with abundant Na storage sites and rGO with a conductive network. The improved electrochemical properties are dominated by the capacitive Na storage mechanism. This work implies that the oxygen-functionalized CDs could serve as medium to regulate the surface chemistry of carbon materials.

Influence of structural and chemical environmental factors on electrochemical hydrogen storage in carbon materials

The influences of pore size, specific surface area, and surface chemistry of carbon material as well as the pH value of electrolyte solution on the electrochemical hydrogen storage performances are investigated. Three types of carbon materials carrying micro-, meso- and macro- pores, respectively, were either commercial available or synthesized through the hard template method. Their electrochemical hydrogen storage behaviors are studied in acidic, neutral, and alkaline solutions. The results indicate that microporous carbon with a high specific surface area has great advantages in hydrogen storage capacity, stability, and cycle performance. Moreover, nitrogen-doped porous carbon can not only improve hydrogen storage capacity but also both rate and hydrogen storage stability. The neutral electrolyte provides a larger voltage window while the alkaline media exhibits positive impacts on the hydrogen storage capacity. At the same time, regardless of the pH value of the electrolytes, the larger the specific surface area of the carbon material, the higher the hydrogen storage capacity.

Bottom-Up Synthesis Strategies Enabling the Investigation of Metal Catalyst-Carbon Support Interactions

The structural versatility and vibrant surface chemistry of carbon materials offer tremendous opportunities for tailoring the catalytic performance of supported metal nanoparticles through the modulation of interfacial metal-support interactions (MSI). MSI’s geometric and structural effects are well documented for these materials. However, other potential support effects such as electronic metal-carbon interactions remain poorly understood. Such limitations are tied to constraints intrinsic to commonly available carbon materials such as activated carbon (e.g., microporosity) and the top-down approach that is often used for their synthesis. Nonetheless, it is crucial to understand the interplay between the structure, properties, and performance of carbon-supported metal catalysts to take steps toward rationalizing their design. The present study investigates promising and scalable bottom-up synthesis approaches, namely hydrothermal carbonization (HTC) and evaporation-induced self-assembly (EISA), that offer great flexibility for controlling the carbon structure. The opportunities and limitations of the methods are discussed with a particular focus on harnessing the power of oxygen functionalities. A remarkable production yield of 32.8% was achieved for mesoporous carbons synthesized via EISA. Moreover, these carbon materials present similar external surface areas of 316 ± 19 m2/g and average pore sizes of 10.0 ± 0.1 nm while offering flexibility to control the oxygen concentration in the range of 5–26 wt%. This study provides the cornerstone for future investigations of metal-carbon support interactions and the rational design of these catalysts.

Comments on the XPS Analysis of Carbon Materials

The surface chemistry of carbon materials is predominantly explored using x-ray photoelectron spectroscopy (XPS). However, many published papers have critical failures in the published analysis, stemming from an ill-informed approach to analyzing the spectroscopic data. Herein, a discussion on lineshapes and changes in the spectral envelope of predominantly graphitic materials are explored, together with the use of the D-parameter, to ascertain graphitic content, using this information to highlight a simple and logical approach to strengthen confidence in the functionalization derived from the carbon core-level spectra.

New Insights into the Quantitative Relationship between Surface Chemistry of Fullerene (C60) and Solubility Parameters and Compatibility with Polymers.

The quantitative relationship between the surface chemistry of carbon materials and the compatibility with polymers is a fundamental and vital physical chemistry problem in the field of polymer nanocomposites. Traditional experimental methods are difficult to solve this problem, so no theory has been formed to guide the functionalization of carbon materials. In this work, the quantitative relationship between functional groups and Hildebrand (δT) and transformed Hansen (δvdW and δele) solubility parameters of fullerene (C60) was determined by molecular dynamics simulation. Besides, which solubility parameter can more accurately predict the compatibility between C60 and three typical polymers with different polarity as a function of grafting ratio is investigated. Very interestingly, no matter which group is grafted, δT and δvdW of C60 show a slight increase first and then a decrease with the grafting ratio, whereas δele first increases abruptly and then decreases slightly. The introduction of polar groups (-OH, -COOH, and -NH2) is conducive to improving the compatibility between C60 and polymers, whereas the introduction of the nonpolar group (-CH3) is not. In terms of predicting compatibility, the Hildebrand solubility parameter is better than the Hansen solubility parameter due to the nonpolar nature of the polymers, even for nitrile butadiene rubber. Finally, the optimum grafting ratios corresponding to the maximum binding energies of C60/polymers mixtures were obtained. This study provides a new understanding of the functionalization of C60 at the molecular level and promotes the development of the theory of the thermodynamics of mixing.

Insight into the difference in activation of peroxymonosulfate with nitrogen-doped and non-doped carbon catalysts to degrade bisphenol A

Heteroatom-modified carbon-based catalysts (especially nitrogen-doped) have been reported to be effective in activating peroxymonosulfate (PMS). Nevertheless, here our study found that graphitized carbon nanomaterial (GC800) exhibited a similar catalytic capacity as the nitrogen-doped graphitized carbon nanomaterial (NGC800) in the degradation of bisphenol A (BPA) via activating PMS, however, the degradation rate constant of the former was approximately 1.72-times greater than that of the latter. Meanwhile, GC800 showed admirable versatility, wide application range of pH value and excellent stability. Furthermore, the connection between the difference in surface chemistry (surface functional groups, electronic properties) and reaction rate between GC800 and NGC800 was discussed. Quenching experiments combined with electron paramagnetic resonance (EPR) and electrochemical measurements revealed the existence of a multi-pathway synergy in GC800/PMS system dominated by the non-radical electron-transfer pathway and complemented by radical (O2•−)/non-radical (1O2) pathway. The high proportion of carbonyl groups and sp2-hybridized carbon as the main parameters affected the electron density of GC800 in the process of non-radical electron transfer. In contrast, NGC800/PMS system only followed the non-radical oxidation pathway with singlet oxygen being the predominant ROS. Pyrrolic N affected the non-radical oxidation pathway of NGC800. This work verifies the significant role of surface chemistry of carbon materials and the synergy between non-radical electron transfer and radical/non-radical oxidation on the catalytic velocity. And it presents a novel thought in the design of high-efficiency carbon-based catalysts toward green and sustainable ecological restoration.

Electrochemical performance of N‐doped superporous activated carbons in ionic liquid‐based electrolytes

The electrochemical performance of nitrogen-doped and non-doped superporous activated carbons as electrodes for supercapacitors was assessed in organic and ionic liquid-based electrolytes. The nitrogen functionalization was carried out through post-modification treatments at mild conditions to produce N-doped activated carbons that preserve the microporosity of the pristine carbon material. The electrodes based on these materials provide large capacitance values (up to 150–180 F/g) in both 1 M Pyr14TFSI/PC and 1 M Pyr14BF4/PC due to their tailored porous texture, given by their well-developed microporosity and low mesopore volume. The electrochemical double layer capacitors based on these materials displayed outstanding capacitance (37–40 F/g and 14 F/cm3) and energy values (44–48 Wh/kg and 16–17 Wh/L). The nitrogen-doped activated carbons evidence high stability at positive and negative polarization potentials due the presence of specific N functionalities. The results prove that surface chemistry of carbon materials plays a key role on their degradation under high operation voltage conditions. The durability of the devices can be improved by doping carbon electrodes with selected nitrogen groups, such as nitrogen heterocycles and amine-like surface functionalities.

Creation of N-C=O active groups on N-doped CNT as an efficient CarboCatalyst for solvent-free aerobic coupling of benzylamine

The creation of specific catalytic functionalities in the nanocarbon materials is an important approach to develop the metal-free nanocarbon materials (carbocatalysts). We report herein a functionalization strategy by treatment of N-doped carbon nanotubes (NCNT) with ozone/water to create oxygen groups nearby the N groups (N-C=O). These groups, different from those present in conventionally oxidized NCNT, show peculiar catalytic behavior. The N atom adjacent to carbonyl group (N-C=O) modifies the reactivity of carbonyl towards C-H activation and simultaneously activate O2 molecule for bifunctionality. Efficient performance for oxidative coupling of benzylamine to imine (>99% imine selectivity) can be obtained under solvent-free conditions at ambient pressure. The benzylamine productivity reaches as high as 131.3 μmol m−2 h−1, which is the highest among any other reported carbon-based catalysts. This work not only highlights a sustainable strategy for tuned surface chemistry of carbon materials by using mild ozonation process, but also reports a novel green aerobic synthesis method of benzylamine using tailored metal-free carbon nanomaterials.

(Invited) The Essential Role of Carbon in Battery Applications: Several Examples from Li/Na-Based Batteries

Carbon with different structures and properties is almost indispensable as active or assisting materials in battery devices. In this presentation, I will share several examples of controlling the structure and surface chemistry of carbon materials for active anode materials, surface coating layers, and conducive and/or mechanical frameworks in different kinds of battery applications. Si-based anodes for Li-ion batteries, Na-ion batteries and Li-S batteries will be discussed.

New insights into oxygen surface coverage and the resulting two-component structure of graphene oxide

Abstract Elucidating the essential details of the structure of graphene oxide (GO) is still a challenge. There is no consensus in the increasingly abundant literature, especially relating to the epoxy groups as the main surface complexes in the basal plane, as well as the simultaneous presence of GO sheets and oxidative debris (OD), with a large difference in their oxygen content. In the present work we characterized the base-washed GO (bwGO) sheets, the OD and the humic fraction of the OD obtained by base digestion, when the parent GO was dispersed by applying sonication, a routine procedure when starting from dried graphite oxide. When sonication is not applied, the amount of OD detected is considerably lower, indicative of its formation before base digestion. The presence of lactols and carboxylic anhydrides as the dominant surface complexes at graphene edges is consistent with all the characterization results, as well as with the general knowledge of surface chemistry of carbon materials ranging from coal to graphite. These findings suggest that the Hummers-Offeman reaction produces a chemical scissor effect during the water/hydrogen peroxide quenching step, yielding a broad size distribution of GO sheets, with little in-plane oxidation and the vast majority of edges being oxidized to form oxepinone-type functionalities.

Unraveling the structural properties and dynamics of sulfonated solid acid carbon catalysts with neutron vibrational spectroscopy

Last year, nearly 1 billion waste tires were disposed of globally, a number that continues to grow with the deployment of more automobiles. Recycling this hazardous waste to produce useful products is paramount towards sustainability that has a direct impact on society. In an effort to alleviate the impact of this waste, we have shown that scrap tire crumb rubber can be turned into value-added sulfonated carbon catalysts that can be used for a number of applications. Here, we analyze the sulfonated carbon catalysts with several techniques in order to elucidate the structural properties as well as the impact of pre- and post-sulfonation on the surface functionalities. Most notably, we applied neutron vibrational spectroscopy in order to better understand the surface chemistry of carbon material and resolve the role of protons in tire-derived carbon. Our results suggest that tuning the surface chemistry and the content of sulfur and hydrogen will promote Lewis-acid catalysis, which allows for important heterogeneous reactions such as esterification.

Structural Evolution of Phosphorus Species on Graphene with a Stabilized Electrochemical Interface.

Phosphorus doping is an effective approach to tailor the surface chemistry of carbon materials. In this work, two-dimensional graphene, as a simplified model for all sp2 hybrid carbon allotropes, is employed to explore the surface chemistry of P-doped carbon materials. Thermally reduced graphene oxide, with abundant residual oxygen functionalities, is doped by phosphorus heteroatoms through H3PO4 activation, followed by passivation in an inert atmosphere. The structural evolution of the phosphorus species in the carbon lattice during the thermal treatment is systematically studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy with the assistance of first-principles calculations. The C3-P═O configuration is identified as the most stable structure in the graphene lattice and plays a key role in stabilizing the electrochemical interface between the electrode and electrolyte. These features enable an electrode based on P-doped graphene to exhibit an enlarged potential window of 1.5 V in an aqueous electrolyte, a remarkable improved cycling stability, and an ultralow leak current. Therefore, this contribution provides insights for designing phosphorus-doped carbon materials toward electrocatalysis, energy-related applications, and so forth.

Carbon microspheres with micro- and mesopores synthesized via spray pyrolysis for high-energy-density, electrical-double-layer capacitors

The graphitic properties, optimized pore structure, and surface chemistry of carbon materials are important factors for developing high-performance supercapacitors. In this study, we synthesized partially graphitic carbon microspheres with large surface area and multimodal pore-size distribution (high amount of micropores and small amount of mesopores) using a facile spray pyrolysis process. Vanadium oxide-carbon microspheres were synthesized via spray pyrolysis at 1000 °C. Subsequently, selective etching of vanadium oxide using NH4OH solution resulted in porous carbon (PC) microspheres with large surface area and multimodal pore structure. The post-treatment process of PC microspheres at 900 °C in Ar atmosphere enabled not only the synthesis of partially graphitic carbon microsphere via graphitization, but also the elimination of organic functional groups at the carbon surface. The supercapacitor fabricated with post-treated PC microspheres (PC-900) with a voltage window of 2.5 V exhibited high specific capacitance (110 F g−1 at 30 A g−1) and excellent rate capability in an organic electrolyte. The PC-900 supercapacitor could also produce high energy density (23 Wh kg−1) even at high power density (42 kW kg−1). In addition, the PC-900 supercapacitor exhibited excellent cyclability with capacitance reduction of approximately 5% after 10,000 cycles.

The correlation between carbon structures and electrochemical properties of sulfur/carbon composites for Li-S batteries

Abstract The structures of carbon materials greatly affect the electrochemical properties of sulfur/carbon composites for lithium-sulfur (Li-S) batteries. Understanding the effect of carbon structure factors on the electrochemical properties of sulfur/carbon composites helps in rational designing of the cathode material for optimized battery performance. We prepare reduced graphene oxide (RGO), cysteine-modified RGO (RGO-CYS), microwave-expanded graphite oxide (MEGO) and activated-MEGO (aMEGO) with specific surface areas (SSA) of 58–3010 m 2 g −1 , C/O atomic ratios of 2.41–10.81, pore sizes of 0.9–5.6 nm and pore volumes of 0.14–2.03 cm 3 g −1 . The electrochemical performance researches S/RGO-CYS > S/RGO > S/MEGO > S/aMEGO when it is listed in the order of their specific capacity, rate capability and cyclic life. And the S/RGO-CYS delivers a high reversible capacity of 455 mA h g −1 at 8 C. The excellent performance of S/RGO-CYS composite is ascribed to the sulfur-containing functional groups of the RGO-CYS, which helps the sulfur dispersion and stabilizes the dissoluble lithium polysulfides. Our results demonstrate that the surface chemistry of carbon materials plays a more important role than the SSA, pore size and pore volume for the electrochemical properties of sulfur/carbon composites for Li-S batteries.

Oxidative dehydrogenation of isobutane catalyzed by an activated carbon fiber cloth exposed to supercritical fluids

Modifications that supercritical fluids promote in the surface chemistry of carbon materials are scarcely investigated. Due to this lack of knowledge, carbon materials exposed to supercritical fluids have not been tested in any catalytic application. Here, we present the oxidative dehydrogenation of isobutane catalyzed by an activated carbon fiber cloth previously exposed to supercritical carbon dioxide, supercritical water and nitric acid. The role of carbonyl–quinone groups as active sites is confirmed by their direct correlation with catalytic activity. The ability of the active sites to produce isobutene is hindered by the presence of acidic groups. Supercritical treatments develop microporosity, while removing acidic oxygen surface groups and incorporating carbonyl–quinone groups, so they are appropriate methods to develop efficient carbon catalysts for this reaction. Coke deposits formed during reaction modify the surface chemistry and porosity of the catalysts. Samples presenting high surface areas are deactivated by coke deposition more slowly. Thanks to it, fibers exposed to supercritical water showed the best performance.

Ab Initio Study of the Vibrational Signatures for the Covalent Functionalization of Graphene

The present work reports a theoretical study of the infrared (IR) and Raman spectra of chemical structures that are useful for the description of the surface chemistry of carbon materials. There has been a recent demand in materials science and surface functionalization to couple organic entities with sp2 carbon nanostructures. A slab model of single-layer graphene with its edges terminated by hydrogen atoms containing 82 atoms per unit cell was used in our study. The organic coupling agent, perfluorophenylazide (PFPA), was used according to a recent experiment [Liu, L.-H.; et al. Nano Lett. 2010, 10, 3754]. Two ab initio DFT functionals, B3LYP and ωB97XD, were adopted to calculate the IR and Raman spectra. The computational approach was tested by comparing the calculated IR spectra to those obtained experimentally for various reference compounds. The vibrational features were probed before and after the reaction, and the changes, arising in both PFPA and graphene spectra as a result of the coupling, were...

The influence of structure and surface chemistry of carbon materials on the decomposition of hydrogen peroxide

Carbon materials with different structural and chemical properties, namely activated carbons, carbon xerogels, carbon nanotubes, graphene oxide, graphite and glycerol-based carbon materials, were tested under different operating conditions for their ability to catalyse hydrogen peroxide (H2O2) decomposition in aqueous solutions. Activated carbons treated with concentrated sulphuric acid (ACS) are the most active catalytic materials for H2O2 decomposition in most of the conditions studied, due to the presence of sulphur containing functional groups at their surface. In addition, ACS proved to be a stable catalyst in reutilization tests for H2O2 decomposition. Methanol was used as selective scavenger of hydroxyl radicals (HO), to show that activated carbons with a markedly basic character lead to the highest yield of HO formed during the H2O2 decomposition process (14%, after 150min of reaction). Overall, from the mechanistic interpretation of H2O2 decomposition, it is concluded that the presence of sulphur containing functional groups at the surface of the activated carbons improves the removal of H2O2 in aqueous solutions, but, on the other hand, the selective decomposition of H2O2 via HO formation is enhanced by the presence of basic active sites on the carbon surface.

Changes in Surface Chemistry of Carbon Materials upon Electrochemical Measurements and their Effects on Capacitance in Acidic and Neutral Electrolytes

Four porous carbon samples with very similar porosities but visible differences in their surface chemistry are investigated as supercapacitor electrodes in 1 M H₂SO₄ and 3 M NaCl. The key objective is to monitor the changes to the oxygen- and nitrogen-containing functionalities in oxygen- and nitrogen+oxygen-rich carbons upon a three-electrode test and the effect of these changes on the energy storage capacity in a real two-electrode supercapacitor setup. The carbon samples are thoroughly characterized by nitrogen sorption measurements, Raman spectroscopy, potentiometric titrations, elemental analysis, and synchrotron XPS. The findings presented in this work imply that the pretreatment of the oxygen- and nitrogen+oxygen-rich carbons under the conditions of the three-electrode test in an acidic electrolyte are beneficial to the overall energy storage capacity as the pores become more accessible to the electrolyte ions and the contribution of pseudocapacitive oxygen-containing groups increases in the oxygen-rich carbons, whereas favorable changes to the electronic structure take place in the nitrogen+oxygen-rich carbons. Thus, the total capacitance increases as a result of the improved double-layer capacitance as well as pseudocapacitance. Greater capacitance after the three-electrode test is also measured in a neutral electrolyte for both sets of samples, which is a result of improved double-layer capacitance upon the removal of some oxygen-containing functional groups that leads to better accessibility of the pores.

Characterization of Carbon Surface Chemistry by Combined Temperature Programmed Desorption with in Situ X-ray Photoelectron Spectrometry and Temperature Programmed Desorption with Mass Spectrometry Analysis

The analysis of the surface chemistry of carbon materials is of prime importance in numerous applications, but it is still a challenge to identify and quantify the surface functional groups which are present on a given carbon. Temperature programmed desorption with mass spectrometry analysis (TPD-MS) and X-ray photoelectron spectroscopy with an in situ heating device (TPD-XPS) were combined in order to improve the characterization of carbon surface chemistry. TPD-MS analysis allowed the quantitative analysis of the released gases as a function of temperature, while the use of a TPD device inside the XPS setup enabled the determination of the functional groups that remain on the surface at the same temperatures. TPD-MS results were then used to add constraints on the deconvolution of the O1s envelope of the XPS spectra. Furthermore, a better knowledge of the evolution of oxygen functional groups with temperature during a thermal treatment could be obtained. Hence, we show here that the combination of these two methods allows to increase the reliability of the analysis of the surface chemistry of carbon materials.