Carbon Surface Research Articles

Removal of acidic dyes; acid yellow 25 and acid red 4 from wastewater by degassed activated carbon

Abstract Activated carbon was prepared at 300 °C and 600 °C, characterized by SEM, EDX and XRD, and was then used as an adsorbent for the removal of acidic dyes; acid yellow 25 and acid red 4. The activated carbon prepared at high temperature (600 °C) due to its high carbon contents and surface area was subsequently used as adsorbent for the selected dyes adsorption using batch adsorption approaches to estimate different adsorption parameters. For the estimation of kinetics and equilibrium parameters a number of kinetics and isotherm models were employed. Dyes were adsorbed on activated carbon surface at a high rate for the first 15 min, after which it began to diffuse into the micro pores and thus the process became steady. The rate constant was estimated for first and second order kinetics models. The maximum adsorption capacities recorded were 526.32 mg g−1 for acid red 4 and 555.55 mg g−1 for acid yellow 25. The enthalpy change values recorded were; 19.44 kJ mol−1 for acid yellow 25 adsorption and 16 kJ mol−1 for acid red 4 adsorption, meant that the process is endothermic. The negative values of Gibbs free energy change (−393.28, −1,515.48, −2,634.68 J mol−1) of acid red 4 and acid yellow 25 (−251.72, −1,058.06, −2,367.84 J mol−1) at tested temperatures, confirmed the feasibility and spontaneity of the adsorption processes. The adsorption of dyes on the carbon surface was diffusion-controlled process, as demonstrated by the linear graph of intraparticle diffusion model.

Visualisation of Surface Coating Distribution Patterns on Modified CaCO3

Abstract In this work, the surface modification of calcite-type calcium carbonate using the anionic surfactant sodium stearate was studied. Various techniques were used to characterize the samples such as Fourier-transform infrared spectroscopy (FTIR), water contact angle measurements, Raman Mappingvisualisation imaging, Raman depth profiling, thermogravimetric analysis (TGA), and atomic force microscopy (AFM). The results of the Fourier Transform Infrared (FTIR) suggest the formation of a coating on the surface of the modified calcium carbonate. Water contact angle measurements, Raman Mappingvisualisation imaging, and Thermogravimetric Analysis (TGA) indicate that the optimal initial dosage of sodium stearate required for the formation of a monolayer coating is about 2 Wt%. Here, the hydrophilic heads of the sodium stearate arrange vertically on the calcium carbonate surface forming the monolayer. As the concentration of sodium stearate increases, the hydrophobic tails of the sodium stearate or calcium stearate connect each other, forming bilayer or multilayer coatings. Furthermore, the surface coating on calcium carbonate originates from the edge vertices and gradually spreads towards the central region as the amount of sodium stearate increases until complete coverage is achieved. Raman depth profiling and AFM visualization results suggest that the thickness of the monolayer coating is approximately 5.25nm.

Colloidal 2D Layered SiC Quantum Dots from a Liquid Precursor: Surface Passivation, Bright Photoluminescence, and Planar Self-Assembly.

We report the bottom-up synthesis of colloidal two-dimensional (2D) layered silicon carbide (SiC) quantum dots with a cubic structure, lateral size of 5-10 nm, ⟨110⟩ exfoliation to few atomic layers, and surface passivation with 1-dodecene. Samples shielded from oxygen and plasma-annealed for purity exhibit narrow blue photoluminescence (PL) with quantum yields (QYs) over 60% in exceptional cases, while unshielded nanocrystals (NCs) exhibit broad blue/green/white PL with 10-15% QY. The latter scenario is attributed to excess surface carbon and oxygen accrued during synthesis and processing, with size separation through ultracentrifugation revealing size-dependent impurity emission. In contrast, the shape of the bright narrow blue PL shows little variation with NC size, while in both scenarios, the maximum QY occurs near four atomic layers. When dried under heat, the disk-like NC suspensions are observed to aggregate into microscale domains, with further self-assembly into planar superlattice domains with common crystalline orientation. The results are compared with photophysical simulations and bring clarity to the broad emission commonly reported for top-down approaches, while inspiring bottom-up schemes directed at improved material quality.

Surface chemistry and catalytic activity in H2O2 decomposition of pyrolytically fluoralkylated activated carbons.

According to the proposed pyrolytic method, granular activated carbon (AC) Norit 830 W was functionalized by thermal treatment of AC in hydrofluorocarbon (HFC) gases, pentafluoroethane and 1,1,1,2-tetrafluoroethane, at 400-800 °C. This method does not require activation by plasma and photons. Chemical and elemental analysis showed that the pyrolytic treatment provides a loading of 2.95 mmol (5.6 wt%) of fluorine per gram of AC. Nitrogen adsorption measurements indicated that the microporous structure contracted when AC was treated with HFC at temperatures above 400 °C. Thermogravimetry, Fourier transform infrared spectroscopy (FTIR) with attenuated total reflectance (ATR), and X-ray photoelectron spectroscopy (XPS) demonstrated the evolution of oxygen-containing and fluorine-containing groups to more thermostable groups with treatment temperature. The fluorine-containing groups grafted at high temperature, above 600 °C exhibited the highest thermal stability up to 1250 °C in dry argon. From the data of XPS and solid-state 19F nuclear magnetic resonance spectroscopy data, the grafted fluorine exists in several types of grafted F-containing groups, the HFC residues. By changing the thermal regime of fluorination, the composition of fluorine-containing groups on a carbon surface can be regulated. Isolated fluoroalkyl groups can be grafted at temperatures of 400-500 °C, while at 600 °C and above, the semi-ionic fluorine groups increase significantly. The hydrophobized surface demonstrated the ability to effectively decompose H2O2 in methanol solutions.

Diamond-like carbon (DLC) surface treatment decreases biofilm burden by S. aureus on titanium alloy in vitro- a pilot study.

Periprosthetic joint infection is a complication of total joint arthroplasty with treatment costs over $1.6billion dollars per year in the US with high failure rates. Therefore, generation of coatings that can prevent infection is paramount. Diamond-like carbon (DLC) is an ideal coating for implants as they are wear-resistant, corrosion-resistant, inert, and have a low friction coefficient. The purpose of this study was to test the efficacy of DLC surface treatment in prevention of biofilm on titanium discs infected with Staphylococcus aureus in vitro. Titanium alloy discs (n = 4 non-coated and n = 4 DLC-coated) were infected with 5 × 105 colony-forming units (CFU) of S. aureus for 2 weeks then analysed via crystal violet and scanning electron microscopy (SEM). Crystal violet analysis yielded differences in the appearance of biofilm on implant surface where DLC-coated had a clumpier appearance but no difference in biofilm quantification. Interestingly, this clumpy appearance did lead to differences in SEM biofilm coverage where significantly less biofilm coverage was found on DLC-coated discs (81.78% vs. 54.17%, p < 0.003). DLC-coated titanium alloy implants may have preventative properties in S. aureus infection. Observing differences in biofilm coverage does warrant additional testing including CFU titration and biofilm kinetics with eventual use in an animal model of periprosthetic joint infection.

Dark NO2 Reduction on a Graphene Surface with Implications for Soot Aging and HONO Formation.

Soot, primarily composed of elemental carbon (EC) and organic carbon (OC), is ubiquitous in PM2.5. In the atmosphere, the heterogeneous interaction between NO2 and soot is not only an important pathway driving soot aging but also of central importance to nitrous acid (HONO) formation. It is commonly believed that the surface redox reaction between reductive OC and NO2 dominates the night aging of soot and the conversion of NO2 to HONO. However, completely differing from the currently popular explanation, we find here that the redox reaction between EC and NO2 can also drive the conversion of NO2 to HONO during soot aging. By combining in situ experiments with density functional theory (DFT) calculations, we proposed that the surface carbon vacancy defects on graphite/graphene-like EC should be a type of potential primary adsorption and reactive sites inducing the heterogeneous reduction of NO2. We suggested a new mechanism that NO2 is reduced to form HONO on surface vacancy defects through the splitting of H2O molecules, and the carbon atoms adjacent to surface vacancy are simultaneously oxidized to form hydroxyl-functionalized EC. This novel finding provides insights into the chemical mechanism driving the NO2-to-HONO conversion and rapid soot aging, which expands our knowledge of the heterogeneous chemistry of soot in the atmosphere.

Cathode-Electrolyte Interphase Engineering toward Fast-Charging LiFePO4 Cathodes by Flash Carbon Coating.

Lithium iron phosphate (LiFePO4, LFP) batteries are widely used in electric vehicles and energy storage systems due to their excellent cycling stability, affordability and safety. However, the rate performance of LFP remains limited due to its low intrinsic electronic and ionic conductivities. In this work, an ex situ flash carbon coating method is developed to enhance the interfacial properties for fast charging. A continuous, amorphous carbon layer is achieved by rapidly decomposing the precursors and depositing carbon species in a confined space within 10 s. Simultaneously, different heteroatoms can be introduced into the surface carbon matrix, which regulates the irregular growth of cathode-electrolyte interphase (CEI) and selectively facilitates the inorganic region formation. The inorganic-rich, hybrid conductive CEI not only promotes electron and ion transport but also restricts parasitic side reactions. Consequently, LFP cathodes with fluorinated carbon coatings exhibited the highest capacity of 151 mAh g-1 at 0.2 C and 96mAhg-1 at 10 C, indicating their excellent rate capability over commercial LFP (58mAh g-1 at 10 C). This solvent-free, versatile surface modification is shown for other electrode materials, providing an efficient platform for electrode-electrolyte interphase engineering through a surface post-treatment.

Stabilized Cu0 -Cu1+ dual sites in a cyanamide framework for selective CO2 electroreduction to ethylene

Electrochemical reduction of carbon dioxide to produce high-value ethylene is often limited by poor selectivity and yield of multi-carbon products. To address this, we propose a cyanamide-coordinated isolated copper framework with both metallic copper (Cu0) and charged copper (Cu1+) sites as an efficient electrocatalyst for the reduction of carbon dioxide to ethylene. Our operando electrochemical characterizations and theoretical calculations reveal that copper atoms in the Cuδ+NCN complex enhance carbon dioxide activation by improving surface carbon monoxide adsorption, while delocalized electrons around copper sites facilitate carbon-carbon coupling by reducing the Gibbs free energy for *CHC formation. This leads to high selectivity for ethylene production. The Cuδ+NCN catalyst achieves 77.7% selectivity for carbon dioxide to ethylene conversion at a partial current density of 400 milliamperes per square centimeter and demonstrates long-term stability over 80 hours in membrane electrode assembly-based electrolysers. This study provides a strategic approach for designing catalysts for the electrosynthesis of value-added chemicals from carbon dioxide.

Effect of surface carbon of iron carbide on Fischer-Tropsch synthesis: A density functional theory study

The surface iron of iron carbide has been identified as active in Fischer-Tropsch synthesis (FTS), but the effect of surface carbon remains a topic of debate. Herein, to clarify the effect of surface carbon of iron carbide on FTS, we conducted a density functional theory (DFT) study on CO adsorption, H2 activation and CO hydrogenation over ε-Fe2C and θ-Fe3C. Compared to Fe3C(111), the Fe2C(111) facet exhibits more low-coordinated carbon, benefiting for CO adsorption and H2 activation. Because of the low-coordinated carbon, the Fe2C(111) is more active for FTS than Fe3C(111), not only through the formation of CH2 species with H atoms, but also through the direct C–C coupling for the carbon chain growth. The consumed carbon on Fe2C(111) can be recovered timely by absorption and direct dissociation of CO, ensuring the sustainability of the carbon chain growth. This work contributes to a comprehensive understanding of the FTS mechanism over iron carbide surface.

Unveiling the porosity effect of superbase ionic liquid-modified carbon sorbents in CO2 capture from air

Direct air capture (DAC) of CO2 represents one of the most promising technologies to achieve negative carbon emissions. Herein, the superbase ionic liquids (ILs)-modified carbon substrates were developed towards DAC of CO2 by harnessing the strong CO2 binding capability of IL and the ordered porous channels provided by the carbon supports. Detailed porosity analysis revealed that the IL with aromatic cation and oxygenate anion preferred to fill the micropores, and a thin layer was created on the surface of the mesopores. Strong π-π interaction between the IL layer and the carbon surface was disclosed by wide-angle X-ray scattering (WAXS) analysis, leading to enhanced thermal stability of the IL phase. With the same lL coating amount, the DAC of CO2 evaluation revealed that larger mesopore size and pore volume in the carbon/IL composite materials led to higher CO2 uptake capacity by exposing more active sites to integrate CO2 from diluted sources. The thermodynamic analysis confirmed the critical role of IL coating in providing strong chemisorption sites and significantly improved selectivity to enrich the diluted CO2 from the air atmosphere. This work provides guidance on leveraging the scaffolds' surface properties and porosities of the scaffolds to tune the DAC of CO2 behaviour.

Rare earth oxide promoted Ru/Al2O3 dual function materials for CO2 capture and methanation: An operando DRIFTS and TGA study

Dual-function materials (DFMs) combine sorbent and catalytic components to perform selective CO2 capture and subsequent hydrogenation. This study explores the performance of rare-earth oxides (REOs) as CO2 adsorption sites on Ru/Al2O3. REOs increase CO2 uptake by upwards of +60 % by enhancing the overall catalyst surface basicity and favoring metal–support interactions. Thermogravimetric analysis during CO2 adsorption-hydrogenation cycles exhibited significant catalytic activity and enhanced stability of Ru-REO/Al2O3 at temperatures as low as 200 °C. This leads to methane production of 50–85 µmol g−1, surpassing recently reported values obtained for alkali and alkali-earth promoted Ru-based materials operated at 250 °C. The highest performing studied DFM, RuNd2O3/Al2O3, achieved 85 % CO2 capture efficiency and steadily produced methane in cyclic operation (+120 % CO2 uptake relative to Ru/Al2O3). Operando DRIFTS revealed that the dominant mechanism for methane formation is the hydrogenation of ruthenium carbonyls, which are stabilized by REOs. Upon CO2 exposure, surface carbonates and bicarbonate species form more abundantly on DFMs than on Ru/Al2O3. This confirms that REOs enhance the adsorption and retention of carbonates, which generate additional promoter-related reaction pathways during low-temperature hydrogenation. These findings are crucial in the advancement of sustainable, wider operation range carbon capture and utilization technologies.

N-doped carbon dots-modulated interfacial charge transfer and surface structure in FeNbO4 photocatalysts for enhanced CO2 conversion selectivity to CH4

The photocatalytic carbon dioxide reduction reaction (CO2RR) is an innovative and reliable technology to address the issues of energy shortage and climate change simultaneously. However, issues such as insufficient light absorption, rapid electron-hole recombination and low surface activity during CO2RR severely limit the catalysts’ efficiency for photocatalysis. In this study, we present nanohybrid N-CDs/FeNbO4 catalysts to overcome these challenges and achieve high-efficient photocatalytic conversion of CO2 to CH4. The enhancement process starts with the introduction of modified N-CDs, which have a broad light absorption capability. These N-CDs also help to modulate the interfacial charge transfer kinetics, leading to improved charge separation and transfer. This, in turn, enhances the multielectron transfer conversion selectivity of CO2 to CH4. Meanwhile, CO2 adsorption on the photocatalysts is increased due to the creation of oxygen vacancies and lattice stresses resulting from the introduction of N-CDs. This work presents a new approach for improving the photocatalytic performance by adjusting surface structure and interfacial behaviors.

Identification of mechanisms and experimental implementation for enhancing the interfacial force between oxygen functionalized waste carbon fibers and polyamide resin

To recycle waste carbon fibers (CFs) and utilize them as a composite material with polyamide–6 (PA–6), the oxidation of the carbon surface is crucial for enhancing its bonding with PA–6 without damaging the waste CFs. However, the most effective oxygen-containing functional group (O–group) was hitherto unknown. In this study, computational simulations demonstrated that incorporating O–groups enhanced the interfacial bonding force via hydrogen bonding between the oxygen of the O–groups and hydrogen (N–H) of PA–6. Among various O–groups, the bonding of lactone groups to PA–6 was energetically most favorable, corroborated by different oxidation treatments such as acid, heat, and plasma. As the reaction time or temperature increased, the amount of O–groups, such as lactones, increased. Regardless of the oxidation treatment type, an increase in the amount of O–groups increased the interfacial force, and this tendency was predominantly observed in lactone groups. However, excessive surface oxidation introduced defects on the surface of CFs, which reduced the interfacial force. The modification of waste CFs by identifying the proposed mechanisms lays the groundwork for synthesizing high-quality waste CF composites.

3D Co-doped carbon nanosheets as high-performance electrodes for Li-S batteries

3D petal-shaped Cobalt-doped carbon nanosheets (PCoCNS) were synthesized as excellent sulfur hosts for lithium-sulfur (Li-S) batteries. Co doping enhanced the affinity of the carbon surface for lithium polysulfides (LiPSs), inhibiting the shuttle effect. The electrocatalytic effect of the PCoCNS electrode exhibited enhanced polysulfide conversion kinetics. thereby promote Li2S formation. Owing to the above advantages, the PCoCNS cathode exhibited satisfactory reversibility of 841 mAh/g with a high capacity retention of 91 %. Additionally, it displayed high coulombic efficiency (CE) values exceeding 97 % over 100 cycles at a current rate of 0.5C. Furthermore, the electrode demonstrated low polarization and exhibited an excellent rate performance, delivering a capacity of 575 mAh/g at the high rate of 3C. This study synthesized a promising sulfur cathode for enhancing the electrochemical performance of Li-S batteries.

Insights into the effect of Fe-Zn interaction on tunable reactivity in Fischer–Tropsch synthesis

In the Fischer–Tropsch synthesis (FTS) reaction, the intricate reaction conditions are prone to induce phase transitions in iron carbides, which markedly affect catalytic performance. Manipulating and stabilizing the active phase is paramount for ensuring the catalyst efficiency. In this study, we regulated the Fe-Zn interaction to investigate the influence of iron carbides and the characteristics of surface carbon species. The strong interaction significantly enhanced the adsorption and dissociation of CO on the catalyst surface, thereby facilitating the formation of carbon-rich Fe2(.2)C. Consequently, the FeZn-s catalyst exhibited the highest iron time yield (FTY) of 959 μmolCO·gFe-1·s-1. But meanwhile, the stronger Fe-Zn interaction also accelerated the carbon deposition rate and elevated the graphitization degree of the surface carbon, expediting the catalyst deactivation. These results provide an insight into the modulation and stabilization of iron carbides by adjusting the interaction between the Fe and supports, which inspires the further development of Fe-based catalysts for FTS applications.

Electrowetting on glassy carbon substrates.

The wetting properties of carbon surfaces are important for a number of applications, including in electrochemistry. An under-studied area is the electrowetting properties of carbon materials, namely the sensitivity of wetting to an applied potential. In this work we explore the electrowetting behaviour of glassy carbon substrates and compare and contrast the observed response with our previous work using highly oriented pyrolytic graphite. As with the graphite substrate, "water-in-salt" electrolytes are found to suppress faradaic processes, thereby enlarging the electrochemical potential window. A notable difference in response to positive and negative polarity was seen for the graphite and glassy carbon substrates. Moreover, whereas graphite has previously been shown to give a reversible electrowetting response over many cycles, an irreversible wetting was observed for glassy carbon. Similarly, the timescales of the wetting process were much faster on the graphitic substrate. Reasons underlying these marked changes in behaviour on the different carbon surfaces are suggested.

Effect of rGO synthesis on Mg-C interaction-induced hydrogen uptake by Mg-rGO nanocomposites

Reduced graphene oxide (rGO) is synthesized electrochemically (erGO), chemically (crGO) and thermally (trGO). These are eventually used for synthesizing Mg-erGO, Mg-crGO and Mg-trGO nanocomposites by ball-milling (ball:powder = 40:1, 20 h, 450 rpm) for hydrogen storage. Upon H-uptake (PH2 = 15 bar, 320 °C), Mg-erGO exhibits fastest and highest H-uptake (∼6 wt%) with lowest incubation time (∼2h). Mg-crGO and Mg-trGO yield lower H-uptake (∼5 wt%) and larger incubation times (∼7, ∼20 h). The erGO is highly wrinkled offering easy access to its surface and highest extent of sp2 carbon (XPS). Contrarily, crGO and trGO possess lower wrinkling and heavy stacking, respectively. Mg-erGO is least defective as estimated from Raman (ID/IG∼1.11) versus Mg-crGO and Mg-trGO (ID/IG∼1.22, 1.46). This least defective erGO enhances Mg → C electron transfer in Mg-erGO, inducing H-H bond polarization and subsequent Mg-H bond formation. Thus, it leads to the best H-uptake performance.

Dry cleaning of InSb surfaces by hydrogen molecule exposure in ultrahigh vacuum

Cleaning semiconductor surfaces by atomic hydrogen or hydrogen plasma has gained significant interest because such a dry-cleaning method enables to reduce consumption of chemicals and pure water, and to treat challenging surfaces of three-dimensional semiconductor nanostructures. We have studied effects of mere H2 molecule exposures on (111)B and (110) surfaces of InSb with native oxides in an ultrahigh-vacuum (UHV) chamber. Without any hydrogen cracking, exposure of native-oxide covered InSb(111)B, heated simultaneously at 350 °C, to H2 with a partial pressure of 5∙10−5 mbar decreases amount of surface oxides and carbon, according to x-ray photoelectron spectroscopy, and provides (2×2) low-energy electron diffraction (LEED) pattern. Scanning tunneling microscopy indicates that this InSb(111)B(2×2) surface contains still extra Sb. When the InSb temperature increases to 400 °C during the H2 exposure, LEED changes to (3×3) pattern, which is known to arise from a less Sb-rich surface compared to InSb(111)B(2×2). When InSb(111)B(3×3) is exposed to H2 at the lowered temperature of 300 °C, LEED changes back to (2×2), which is discussed to arise from that InSb(111)B(3×3) contains still oxygen. Experiments for InSb(110) support that the found H2 exposure effects apply to different crystal faces of InSb.

Carbon coating engineering enhances the stability of graphite anode in potassium ion batteries

Graphite forms reversible potassium-graphite intercalation compounds electrochemically. Graphite anode possesses a high reversible specific capacity (279 mAh g−1) and an optimal low potential platform, rendering it an ideal anode material for potassium-ion batteries. However, the intercalation of K+ ions in graphite causes a bulk volume expansion of up to 61%, resulting in irreversible damage to the structure of graphite, which leads to inferior cycling stability. In this paper, surface-oxidized graphite (OG) with reduced particle size and increased defect densities was obtained by mechanical ball milling and chemical oxidation. Composites of soft carbon-coated OG (OG@PC) were prepared by soft carbon coating. The soft carbon coating can alleviate the bulk expansion caused by K+ intercalation/deintercalation in OG, thus slowing down the destruction of the crystalline structure of graphite after multiple charging/discharging cycles. OG@PC exhibits increased reversible specific capacity from 267 mAh g−1 to 314 mAh g−1 compared with pristine graphite at a current density of 0.05 A g−1. Moreover, at a high current density of 0.5 A g−1, a reversible specific capacity of 213 mAh g−1 was achieved after 200 cycles. This work investigates simple surface carbon coating strategies to improve the cycling stability of a graphite anode of potassium-ion batteries.

Unraveling the Role of Intrinsic Carbon Defects for the Heterogeneous Reduction of NO with NH3

ABSTRACT This study investigates the impact of intrinsic carbon defects on the reduction of nitrogen oxides (NOx) during coal combustion, with a focus on the synergistic effect of ammonia (NH3) and pulverized coal. Two representative computational models containing intrinsic carbon defects are described, and their influence on NH3 reduction of NO is studied. Stable species and transition states present in the pathways are calculated using B3LYP/6-31 G(d). Results indicate that exposed edge carbon atoms exhibit higher charge density distribution, affecting NH3 adsorption and NO reduction. The maximum energy barriers for both pathways do not exceed 45 kcal/mol, achievable in practical coal combustion systems. This paper also calculates the heterogeneous reduction process of a model without intrinsic carbon defects (Char model), with the aim of observing the specific effects of intrinsic carbon defects on the processes of migration of H/O atoms, migration and recombination of N atoms, and formation and desorption of N2 molecules. Furthermore, the analyses demonstrated an increase in the rate of heterogeneous reduction of NH3 and NO on defective carbon surfaces in comparison to the Char/NH/NO system, indicating that the intrinsic defects of the carbon have a contributory effect on the catalytic activity. With regard to the magnitude of the increase in reaction rate with increasing temperature, the presence of intrinsic defects in the carbon base serves to reinforce the role of temperature in the rate-determining step. Overall, this study provides insights into the role of intrinsic defects in carbon-based catalysis and offers implications for nitrogen oxide emission control strategies.