Amorphous Carbon Surfaces Research Articles

Carrier gradient core-double shell structure with heterojunction transition layer for significantly enhancing dielectric properties

In this work, to prohibit the undesirable large dielectric loss and electric-field distortion of the conductive fillers/polymer with a high dielectric constant, TiO2 (TO) and Al2O3 (AO) shells were successively coated on the surface of amorphous carbon (C) to prepare the C@TO@AO core-double shell nanoparticles. This novel design of gradually varying the multilayer hierarchical interface achieved the gradient reduction of carrier concentration from the C core to the TO and AO layers. And the introduction of the multilayer hierarchical interface was advantageous to the enhancement of interface polarization. Moreover, the excellent integrated dielectric properties could be effectively achieved by adjusting the layer thickness and crystal structure of the TO layer. It was worth noting that the TO transition layer with anatase and rutile heterojunctions (HTO) had a significant enhancement in the dielectric constant of the composites induced by the strength of interfacial polarization and built-in electric field inside the HTO layer. Furthermore, the simulated electric field distribution inside the composites was further investigated to reveal the mechanism of enhanced dielectric properties. This work exerts important guiding significance for the reasonable structure design and the elaborate regulation of the shell micro-structures to improve the dielectric properties of composites.

Adsorption behaviors and mechanisms of bilirubin onto charged amorphous carbon surface with and without water by a molecular dynamics simulation

The adsorption of bilirubin onto a carbon surface holds pivotal significance in enhancing bilirubin clearance efficiency within artificial liver devices. We performed molecular dynamics simulations to reveal the adsorption behaviors and mechanisms of bilirubin onto a charged amorphous carbon surface. The hydrogen atoms are used as binding sites facilitating the adsorption of bilirubin molecules onto the uncharged amorphous carbon surface. Conversely, the oxygen atoms are used as binding sites, enhancing bilirubin adsorption on charged amorphous carbon surfaces due to their higher electronegativity. The bilirubin adsorption rate, the mean-squared displacements of bilirubin, and the interaction energy between bilirubin and amorphous carbon increase as the surface charge increases, and the adsorption amount reaches an asymptotic value as the surface charge approaches a certain threshold. In the presence of water, the competitive adsorption between bilirubin and water would occur. The hydration layer formed on charged amorphous carbon surface and the electrostatic and near-wall hydrogen-bond interactions emerge as two pivotal factors influencing bilirubin adsorption. The structured arrangement of hydration water can hinder the bilirubin adsorption, whereas the electrostatic interaction and near-wall hydrogen-bond interaction promote it. The whole competitive adsorption process unfolded in distinct stages of bilirubin adsorption and desorption, and a critical value of surface charge exists for the complete desorption of bilirubin.

Unveiling the interaction regimes between atomic oxygen and amorphous carbon surface depending on incident energy

The chemical reactions between atomic oxygen (AO) and solid surface are particularly crucial for numerous fundamental fields. However, it is lack of clearly understanding the reaction mechanisms between AO and the solid surface because the complex interaction dynamics are extremely difficult to be measured experimentally and to be modelled theoretically. In this work, the reactive molecular dynamics simulations are conducted to fully reveal the interactive mechanisms of AO irradiation on the amorphous carbon surface. As the incident energy (E) increases, our simulations demonstrate three distinct interaction regimes: (I) surface oxidation without carbon removal, (II) surface oxidation accompanied by minor material removals, and (III) continuous material removal. The first critical energy (E1) of ∼3.5 eV as the boundary between regime I and II is related to the dissociative energy of C–C bonds. The second critical energy (E2) of ∼6.5 eV as the boundary between regime II and III corresponds to the largest repulsion energy that the oxidized surface could provide. We further establish a phenomenological model to quantitatively describe how the rebound ratio varies with incident energy and surfacial oxygen density, which not only fit all simulation data perfectly but also give a very precise prediction of E2 value.

Tritium storage and release mechanism in nuclear graphite using first-principles combined thermal desorption theory

Nuclear graphite (NG) is widely applied in nuclear facilities, and its strong interaction with tritium is an essential factor for tritium transport behavior in various reactors and the treatment of radioactive NG waste. Given that NG is a polycrystalline and porous material, interactions between tritium and NG exist in various microstructures, including graphite edges, graphene basal planes, and amorphous structures. In this study, density functional theory which is integrated in Vienna ab initio simulation package (VASP) was combined with thermal desorption theory to elucidate the underlying mechanism of hydrogen isotope storage corresponding to the experimentally observed desorption peaks in NG. The four desorption temperature peaks, ranging from low to high, were mainly attributed to hydrogen isotope desorption from the graphite basal plane surface, amorphous carbon surface, unsaturated armchair and zigzag edges, respectively. The interaction between hydrogen isotopes and carbon nanostructures provides deeper insights into the understanding of tritium enrichment on the NG surface, which is primarily attributed to the adsorption of tritium on graphite basal plane-like surfaces at relatively low temperatures. This study provides a practical method to bridge the gap between the atomic binding structure and desorption temperature peaks from a kinetic perspective, providing insights into temperature-dependent hydrogen desorption in typical carbon structures and deepening our understanding of tritium transport behaviors in advanced nuclear energy systems.

Characterisation of the morphology of surface-assembled Au nanoclusters on amorphous carbon.

In this study, aberration-corrected scanning transmission electron microscopy is employed to investigate the morphology of Au clusters formed from the aggregation of single atoms sputtered onto an amorphous carbon surface. The morphologies of surface-assembled clusters of N > 100 atoms are referenced against the morphologies of size-selected clusters determined from previously published results. We observe that surface-assembled clusters (at the conditions employed here) are approximately spherical in shape. The structural isomers of the imaged clusters have also been identified, and the distribution of structural types is broadly in agreement with those from size-selected cluster deposition sources. For clusters of approximately 147 atoms, we find a preference for icosahedra over decahedra and truncated octahedra, but at this size there is a high proportion of unidentified/amorphous structures. At around 309 atoms, we find a preference for decahedra over icosahedra and truncated octahedra, but over half the structures remain unidentifiable/amorphous. For sizes above approximately 561 atoms we are able to identify most of the structures, and find decahedra are still the most favoured, although in competition with single-crystal fcc morphologies. The similarity in structure between surface-assembled and size-selected clusters from a cluster source provides evidence of the relevance of size-selected cluster studies to clusters synthesised by other, industrially relevant, methodologies.

Experimental and theoretical evidence for unprecedented strong interactions of gold atoms with boron on boron/sulfur-doped carbon surfaces.

The 16e square-planar bis-thiolato-Au(iii) complexes [AuIII(1,2-dicarba-closo-dodecarborane-1,2-dithiolato)2][NBu4] (Au-1) and [AuIII(4-methyl-1,2-benzenedithiolato)2][NBu4] (Au-2) have been synthesized and fully characterized. Au-1 and Au-2 were encapsulated in the symmetrical triblock copolymer poloxamer (Pluronic®) P123 containing blocks of poly(ethylene oxide) and poly(propylene oxide), giving micelles AuMs-1 and AuMs-2. High electron flux in scanning transmission electron microscopy (STEM) was used to generate single gold atoms and gold nanocrystals on B/S-doped graphitic surfaces, or S-doped amorphous carbon surfaces from AuMs-1 and AuMs-2, respectively. Electron energy loss spectroscopy (EELS) data suggested strong interactions of gold atoms/nanocrystals with boron in the B/S-doped graphitic matrix. Density-functional theory (DFT) calculations, also supported the experimental findings, pointing towards strong Au-B bonds, depending on the charge on the Au-(B-graphene) fragment and the presence of further defects in the graphene lattice.

Unravelling the effect of nitrogen on the morphological evolution of thin silver films on weakly-interacting substrates

We study the effect of nitrogen on the morphological evolution of thin silver (Ag) films deposited on weakly-interacting amorphous carbon (a-C) and silicon oxide (SiOx) surfaces. Films are synthesized at a deposition rate of 0.1nm·s-1 by direct current magnetron sputtering (DCMS), high power impulse magnetron sputtering (HiPIMS), and electron-beam evaporation (EBE). We monitor growth in situ and in real time by measuring the evolution of film stress and optical properties, complemented by ex situ analyses of discontinuous-layer morphologies, film crystal structure, and film composition. We find that addition of molecular nitrogen (N2) to the plasmagenic gas (Ar) during DCMS and HiPIMS promotes a two-dimensional (2D) morphology. Concurrently, EBE-deposited films exhibit a significantly more pronounced three-dimensional morphological evolution, independently from the gas atmosphere composition. We argue that the 2D morphology in DCMS- and HiPIMS-grown films is enhanced due to incorporation of atomic nitrogen (N)—result of plasma-induced N2 dissociation—that hinders island reshaping during coalescence. This mechanism is not active during EBE due to the absence of energetic plasma electrons driving N2 dissociation. The overall results of the study show that accurate control of vapor-phase chemistry is of paramount importance when using gaseous species as agents for manipulating growth in weakly-interacting film-substrate systems.

Assessment of magnetic effects on soot characteristics in inverse diffusion ethylene flames

The magnetic effect on soot properties in ethylene inverse diffusion flames (IDF) was investigated in this study. The investigation involved the use of high-resolution transmission electron microscopy analysis (HRTEM), Raman spectroscopy analysis, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction spectroscopy (XRD) to examine the nanostructure and graphitization degree of soot collected from flame exhaust gas at various height above burner surface (HAB) under both magnetic and non-magnetic conditions. Increasing the magnetic flux density resulted in modifications to soot properties. When the sampling height was HAB = 4 cm, increasing magnetic flux density resulted in longer fringe lengths, lower fringe tortuosity, less amorphous carbon content and surface oxygen content for the collected soot from flame exhaust gas. These results indicated higher graphitization degrees, which may be attributed to longer residence time and oxidation of soot particle in flames. Moreover, when the sampling height increased from HAB = 4 cm to 6 cm under non-magnetic condition, the nanostructure of soot in the flame exhaust gas was more organized, possible due to the oxidation of soot at the region between HAB = 4 and 6 cm region. However, with the magnetic field on, the crystalline structure of soot in the flame exhaust gas became increasingly disordered as the sampling height increased. This suggested that the soot may also be affected by the magnetic effects in addition to oxidation at the region between HAB = 4 and 6 cm region. The magnetic effect could trigger the transformation of graphitic carbon to amorphous carbon in soot particles as they passed through the magnetic field. With more elaborated magnetic fields, the magnetic effect on soot could contribute to strategies controlling soot emissions and removal.

Exploring the role of surface hydrogenation in anti-friction of circular-textured amorphous carbon film from the atomic level and its dependence on textured shape

Hydrogenating the amorphous carbon (a-C) surface can achieve the ultra-low friction performance. However, the effect of surface hydrogenation on anti-friction of textured a-C surface, especially its dependence on different textured shapes, is still lack of study; the information on the complicated friction interfacial also remains unclear due to the limitation of in-situ characterization in experiment. Here, the friction behavior of circular-textured a-C film was investigated by reactive molecular dynamics simulations, and its dependence on the hydrogenated degree of textured a-C surface was mainly focused, in which the effect from textured shape was also comparatively studied. Results show that the anti-friction efficiency of the circular-textured a-C film strongly depends on the surface hydrogen content; when the surface H content is 31.0 %, the friction coefficient decreases by 97.5 %, which is attributed to the passivation effect of H atoms on the a-C surface, inhibiting the generation and crosslinking of unstable dangling bonds. Moreover, the migration of H atoms in the friction process provides a strong repulsive force, which also significantly reduces the shearing strength of the interface and the friction coefficient. In particular, further study discloses that the effect of textured shapes of a-C surface on friction behavior is also related with the surface H content; with the increase of H content, the textured shape of a-C surface, which exhibits the low-friction performance, transforms from rectangular to circular-textured one, and the corresponding low-friction mechanism also changes from the passivation of friction interface to H-induced repulsive effect. These results provide an effective way to develop an efficient a-C anti-friction system.

Protein Adsorption and Its Effects on Electroanalytical Performance of Nanocellulose/Carbon Nanotube Composite Electrodes.

Protein fouling is a critical issue in the development of electrochemical sensors for medical applications, as it can significantly impact their sensitivity, stability, and reliability. Modifying planar electrodes with conductive nanomaterials that possess a high surface area, such as carbon nanotubes (CNTs), has been shown to significantly improve fouling resistance and sensitivity. However, the inherent hydrophobicity of CNTs and their poor dispersibility in solvents pose challenges in optimizing such electrode architectures for maximum sensitivity. Fortunately, nanocellulosic materials offer an efficient and sustainable approach to achieving effective functional and hybrid nanoscale architectures by enabling stable aqueous dispersions of carbon nanomaterials. Additionally, the inherent hygroscopicity and fouling-resistant nature of nanocellulosic materials can provide superior functionalities in such composites. In this study, we evaluate the fouling behavior of two nanocellulose (NC)/multiwalled carbon nanotube (MWCNT) composite electrode systems: one using sulfated cellulose nanofibers and another using sulfated cellulose nanocrystals. We compare these composites to commercial MWCNT electrodes without nanocellulose and analyze their behavior in physiologically relevant fouling environments of varying complexity using common outer- and inner-sphere redox probes. Additionally, we use quartz crystal microgravimetry with dissipation monitoring (QCM-D) to investigate the behavior of amorphous carbon surfaces and nanocellulosic materials in fouling environments. Our results demonstrate that the NC/MWCNT composite electrodes provide significant advantages for measurement reliability, sensitivity, and selectivity over only MWCNT-based electrodes, even in complex physiological monitoring environments such as human plasma.

Surface wettability control and fluorination modeling of amorphous carbon films fluorinated with CF4 plasma

In this study, the wettability of amorphous carbon films was tuned by controlling the degree of plasma fluorination, and the degree of fluorination on the surface was characterized by varying the process variables in inductively coupled CF4 plasmas. Surface wettability was characterized in terms of the contact angle, whereas the degree of surface fluorination was estimated by measuring the F/C atomic ratio using X-ray photoelectron spectroscopy. The relationship between the contact angle and F/C atomic ratio was investigated. The contact angle decreased from 59° to 20° as the F/C atomic ratio increased from 0 to 0.1 with a low degree of fluorination. The contact angle subsequently increased to 114° as the F/C atomic ratio increased to 0.46 with increased surface fluorination. The hydrophilicity, represented by a low contact angle, can be attributed to the large fraction of polar CF bonds on the surface at low fluorination, whereas the hydrophobicity, represented by a high contact angle, can be attributed to the CF2 bonds on the surface at high fluorination. The effect of ions on surface fluorination was investigated in CF4 plasma. The surface fluorine fraction increased from 0.026 to 0.31 as the ion density increased from 2.6 × 109 to 1.3 × 1010 cm−3, while it increased from 0.026 to 0.30 with an increase in ion energy from 15 to 140.5 eV. The degree of surface fluorination was modeled in terms of the adsorption and desorption rates of fluorine atoms with different radical densities, ion densities, and ion energies. Ion bombardment can increase fluorine adsorption by creating active sites on the surface. The average number of active sites for F radical adsorption per ion bombardment was estimated from the surface fluorination model. The modeled surface fluorine fraction demonstrated favorable agreement with our experimental results for CF4 plasma fluorination at various ion densities and energies. This model indicates that the contribution of ions to the fluorination of the amorphous carbon surface is considerably larger than that of the F radicals.

ZnO-decorated SiC@C hybrids with strong electromagnetic absorption.

A novel strategy is provided to improve the absorption of SiC nanomaterials through surface carbonization of SiC nanowires and hydrolysis. SiC@C-ZnO composites were synthesized with different dosages of ZnNO3·6H2O. Composition, microstructure, and electromagnetic properties of the composites were characterized and analyzed. Results from TEM and XRD show that crystalline ZnO particles adhere to the surface of amorphous carbon, and the ZnO content increases as a function of a dosage of ZnNO3·6H2O. The as-prepared SiC@C-ZnO hybrids exhibit effective electromagnetic absorption, which is related to a synergy effect of different dielectric loss processes. The minimum reflection loss reached -65.4 dB at 11 GHz at a sample thickness of 3.1 mm, while the effective absorption bandwidth (EAB) reached 7 GHz at a sample thickness of 2.56 mm. Furthermore, the EAB of the samples can also cover the whole X band and Ku band at small sample thicknesses (2.09-3.47 mm). The excellent properties of the materials suggest great prospect as electromagnetic absorbers.

Effect of Na+ on the Adsorption Behavior of Polystyrene Nanoparticles onto Coal and Quartz Surfaces

The recovery of difficult-to-float coal using traditional nonpolar hydrocarbon oil collectors can be challenging, particularly for low-rank or oxidized coal. Thus, there is a need for more efficient flotation agents. Nanoparticle flotation collector technology has become increasingly popular in the field of mineral processing, and the presence of various ions in the slurry can significantly affect the interaction between collectors and mineral surfaces. In this study, cationic polystyrene (PS) nanoparticles were prepared using an emulsion polymerization method, and the effects of Na+ ion concentration on the in situ adsorption and desorption processes, adsorption layer configuration, and adsorption kinetics of PS particles on amorphous carbon (coal model) and SiO2 sensors (quartz mineral model) were analyzed using the quartz crystal microbalance with dissipation (QCM-D) technique. Our results showed that the hydrophobic PS nanoparticles irreversibly adsorbed onto both amorphous carbon and SiO2 sensors under different environmental conditions, and their adsorption capacity decreased gradually with increasing Na+ ion concentration. Increasing Na+ ion concentration from 0 M to 1.0 M resulted in a 24.4% and 30.9% decrease in equilibrium adsorption capacities of PS nanoparticles onto amorphous carbon and SiO2 surfaces, respectively. The adsorption rate of PS nanoparticles onto the SiO2 surface was much greater than that on the amorphous carbon surface. The adsorption rate constant of PS nanoparticles onto SiO2 surfaces was 0.782 at 0.1 M Na+ ion concentration, while its adsorption rate constant onto amorphous carbon surfaces was only 0.060. Moreover, the adsorption process was found to be more in line with the quasi-primary kinetic model. These findings suggest that PS nanoparticles may serve as promising flotation collectors for the recovery of difficult-to-float coal, and highlight the importance of considering the effect of dissolved ions on the adsorption properties of flotation collectors.

Lubricity of chelated orthoborate-phosphonium ionic liquids on tetrahedral amorphous carbon and steel surfaces

In boundary lubrication, formation of tribofilms and subsequent friction and wear properties are strongly influenced by lubricant affinity to the lubricating surfaces. Ionic liquids (ILs), which are composed of ions, are expected to provide enhanced surface affinity compared to molecular liquids. This is also of interest for non-ferrous surfaces such as diamond-like carbon (DLC) coatings. DLC technology is widely utilised for sliding components, but DLC performance with conventional lubricants does not always fulfil the requirements. In this study, we compare lubricating performance of two non–halogenated ILs with a common cation, trihexyl(tetradecyl)phosphonium, but different anions, bis(oxalato)borate and bis(mandelato)borate, in the steel/steel and steel/DLC contacts. The tribofilms formed and their lubrication mechanism are investigated using a wide range of surface analysis techniques: Atomic Force Microscopy (AFM), nano-indentation, SEM-EDX and X-ray Photoelectron Spectroscopy (XPS). It is demonstrated that both ILs exhibited better lubricating performance than PAO oils of similar viscosity. It is also shown that the lubricating performance is controlled by the chemical stability of ILs, surface hardness and topography. The phosphonium bis(oxalato)borate IL exhibited excellent lubricity but its performance was adversely affected by the rough and very hard DLC surface that disrupted a delicate balance between the rates of tribofilm formation and removal. A higher chemical stability of the phosphonium bis(mandelato)borate IL facilitated formation of a non-sacrificial ionic tribofilm that reduced friction to a lower extent than the phosphonium bis(oxalato)borate IL but without accelerated tribochemical wear. The results demonstrate the potential for controlling lubrication properties by tuning functional groups of anion structure and subsequent chemical reactivity of ILs with lubricated surfaces.

Unraveling the friction response from selective hydrogenation of textured amorphous carbon surface

Ultra-low friction of amorphous carbon (a-C) film can be achieved by binding to hydrogen atoms or texturing conformations. However, it remains unclear how selective surface hydrogenation affects the friction behavior of textured a-C film. In particular, the corresponding transformation of interfacial structure and the movement of hydrogen atoms have not yet been reported because of the limitation of in-situ experimental characterization. Here, textured a-C films with selective hydrogenated surfaces were prepared, and the corresponding friction response and the transformation of interfacial structure were investigated systematically using reactive molecular dynamics simulation. Results showed that introducing hydrogen atoms to the selective bump sites of textured a-C surfaces significantly reduced the friction coefficient; however, its efficiency was closely sensitive to the hydrogen content, which was related to the interfacial passivation and the repulsion effect induced by H atoms. Most importantly, the separation of –CH clusters from textured a-C surface during sliding process and their re-bonding with the naked mating a-C surface played a key role in further enhancing the repulsive effect between contacted a-C surfaces, thereby improving the anti-friction behavior, which has not been mentioned in previous studies. These results suggest a new approach to develop the high-efficient a-C friction system for applications.

Designing high efficiency graphite felt electrode via HNO3 vapor activation towards stable vanadium redox flow battery

A new method of preparing nitric acid vapor treated graphite felt for vanadium redox flow battery (VRFB) is developed. This method outperforms traditional impregnation methods in convenience, efficacy and controllability of fabrication process. A sequence reaction mechanism is proposed for nitric acid vapor treated graphite felt reactions occurring at 200 °C. The modified-graphite felt (m-GF) with excellent electrocatalytic redox reversibility toward VO2+/VO2+ and V2+/V3+ redox couples is prepared in the conditions of VHNO3/mpGF=0.45 mL g−1 at 200 °C in 300 min (m-GF-0.45). The nitric acid vapor reaction with graphite felts occurs preferentially on the surface of amorphous carbon and at defect sites in the graphitic structure, yields N2 and carbon-oxygen surface complexes, resulting in a higher double layer capacity (DLC) from 146 μF mg−1 (p-GF) to 1514 μF mg−1 (m-GF-0.45). Thus, the energy efficiency and discharge capacity of m-GF-0.45 electrode increases significantly by 8.7% and 100% at 150 mA cm−2, respectively.

Friction dependence on the textured structure of an amorphous carbon surface: A reactive molecular dynamics study

Amorphous carbon (a-C) film provides ultralow friction when combined with lubricating oil. However, it is unclear how textured surfaces affect the friction behavior of a-C at atomic scale, specifically the transformation of interfacial structure and the flow of lubricating oil, owing to the limitations of experimental characterization. Here, a-C films with different textured surfaces were fabricated, and the friction behaviors of mating a-C surfaces with textured parameters, including nanoscale depth and width, were examined by reactive molecular dynamics simulation. Results indicate that compared to that under dry condition, the introduction of a textured surface reduces the friction coefficient of a-C under oil lubrication condition. However, its efficiency highly depends on the depth and width of textured surface, exhibiting different effects on hydrodynamic lubrication. The increase in textured depth causes the friction coefficient decreased first and then increased, attributing to the lubrication from hydrodynamic to boundary state as primary mechanism. The regional aggregation of lubricant atoms with a textured width on the a-C surface occurs at the friction interface following the increased friction coefficient. These results provide insights into the underlying friction mechanism of a-C films induced by surface texturing and enable the development of highly efficient lubrication systems for applications.

Rational design of MWCNTs@amorphous carbon@MoS2: Towards high performance cathode for aqueous zinc-ion batteries

The sluggish diffusion kinetics of divalent Zn2+ in cathode and the limited availability of active material have seriously hindered the practical application of aqueous zinc ion batteries (AZIBs). Herein, multi-walled carbon nanotubes modified by amorphous carbon layer successfully compounded with MoS2 (MWCNTs@a-C@MoS2) are designed as the cathode for AZIBs. Benefiting from the large number of oxygenous groups on the loose surface of amorphous carbon, MoS2 can uniformly nucleate and grow on the MWCNTs, thus avoiding the agglomeration of MoS2 and improving the utilization of active materials. Therefore, this nanocomposite exhibits long-term cycling stability (78% capacity retention after 1000 cycles at 5 A g-1) and glorious high-rate capability (110 mAh g-1 at 12 A g-1). The electrochemical reaction kinetics of MWCNTs@a-C@MoS2 electrode were investigated by galvanostatic intermittent titration (GITT), cyclic voltammetry (CV) measurements and molecular dynamics (MD) simulations, indicating its desirable pseudocapacitive behaviors and low Zn2+ diffusion energy barrier. By ex-situ characterizations, the Zn-intercalation mechanism of MWCNTs@a-C@MoS2 was revealed. This electrode also exhibits stable performance in flexible quasi-solid-state AZIBs even under extreme bending conditions, demonstrating its practicality.

Magnetic amorphous carbon@manganese ferrite hybrid materials as a heterogeneous persulfate activator for catalytic oxidation of tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA), a typical brominated flame retardant in industry, has been recognized as a toxic chemical and an endocrine disruptor. Hence, it’s urgently required to remove it from aquatic environment. In this work, the magnetic amorphous carbon@manganese ferrite (C@MnFe2O4) hybrid materials have been fabricated by hydrothermal method with high temperature annealing method to serve as catalyst for the activation of persulfate (PS) to degrade the TBBPA. The structure characterization results manifest that the synthesized MnFe2O4 particles are evenly distributed on the surface of amorphous carbon in the C@MnFe2O4 hybrid. The factors to affect the catalytic degradation of TBBPA by C@MnFe2O4 hybrid/PS system including type of C@MnFe2O4 hybrid materials, PS dosage, concentration of C@MnFe2O4 and reaction time are investigated systematically. The results show that the highest removal ratio of TBBPA could reach 91.9% after treatment of 90 min by C@MnFe2O4 hybrid/PS system. Furthermore, the C@MnFe2O4 hybrid demonstrates a high stability and recyclability. The electron paramagnetic resonance (EPR) verifies that the introduction of C@MnFe2O4 hybrid into PS system could facilitate the generation of ⋅OH and SO4⋅- radicals for degradation of TBBPA. The degradation intermediates are detected and two possible degradation pathways are proposed. This work provides a new insight for the design and development of novel catalyst for the activation of PS to degrade organic pollutants.

Relating Dry Friction to Interdigitation of Surface Passivation Species: A Molecular Dynamics Study on Amorphous Carbon.

Friction in boundary lubrication is strongly influenced by the atomic structure of the sliding surfaces. In this work, friction between dry amorphous carbon (a-C) surfaces with chemisorbed fragments of lubricant molecules is investigated employing molecular dynamic simulations. The influence of length, grafting density and polarity of the fragments on the shear stress is studied for linear alkanes and alcohols. We find that the shear stress of chain-passivated a-C surfaces is independent of the a-C density. Among all considered chain-passivated systems, those with a high density of chains of equal length exhibit the lowest shear stress. However, shear stress in chain-passivated a-C is consistently higher than in a-C surfaces with atomic passivation. Finally, surface passivation species with OH head groups generally lead to higher friction than their non-polar analogs. Beyond these qualitative trends, the shear stress behavior for all atomic- and chain-passivated, non-polar systems can be explained semi-quantitatively by steric interactions between the two surfaces that cause resistance to the sliding motion. For polar passivation species electrostatic interactions play an additional role. A corresponding descriptor that properly captures the interlocking of the two surfaces along the sliding direction is developed based on the maximum overlap between atoms of the two contacting surfaces.