Surface Of Carbon Substrate Research Articles

Mechanisms of N2 molecule adsorption and accumulation on surfactant-modified substrates: A molecular dynamics simulation

In flotation processes, gas molecules adhere to and accumulate on the target mineral surface, forming micro-nanobubbles, which can significantly enhance the efficiency of particle-bubble adhesion. Surfactants are commonly employed as auxiliary agents and play pivotal roles in flotation. However, the effect of surfactant pre-adsorption at the solid–liquid interface on the microscopic process of gas molecule adsorption and accumulation remains unclear. In this study, varying degrees of roughness surface in carbon substrates, the fatty alcohol polyoxyethylene ether (C12EO15), nitrogen molecules (N2), and water molecules (H2O) were employed to construct a gas–liquid–solid model for molecular dynamics simulations aimed at elucidating the underlying mechanisms of N2 molecule adsorption and accumulation on surfactant-modified substrates at the molecular level. The research findings revealed that N2 molecules preferred adsorption in close proximity to carbon atoms along the alkyl chain of the C12EO15 molecule. C12EO15 molecules exhibit a bending and intertwining behaviour on the hydrophobic carbon substrate surface, thereby forming a “network” adsorption layer. An increase in the quantity of surfactants provides abundant adsorption sites for N2 molecules at the solid–liquid interface, consequently augmenting the adsorption capacity of N2 molecules. Nonetheless, the presence of interstitial gaps between the surfactant-formed adsorption sites impedes the diffusion of the N2 molecules at each adsorption locus. This hindrance may obstruct the subsequent generation of micro-nano bubbles at the solid–liquid interface.

Tetrahydrofuran aided self-assembly synthesis of nZVI@gBC composite as persulfate activator for degradation of 2,4-dichlorophenol

• nZVI@gBC were synthesized by one-step carbothermal reduction method aided by Tetrahydrofuran. • The formation of graphene nano-shells greatly enhanced the stability of nZVI in the air environment. • The nZVI@gBC exhibited superior degradation performance to 2,4-DCP by activating PS. • Four active free radicals (SO 4 •− , •OH, O 2 •− and 1 O 2 ) were produced and participated in the degradation of 2,4-DCP. The defects of easy agglomeration and oxidation of nano zero valent iron (nZVI) limit its large-scale application in industry, especially in the field of environmental remediation. In this study, the iron nanoparticles encapsulated by graphene nano-shells which anchored on the surface of carbon substrate (nZVI@gBC) were synthesized by a one-step carbothermal reduction method aided by Tetrahydrofuran. When the mass ratio of carbon source to iron source is 2:3 and the carbothermic reduction temperature is 700 °C, stabilized nZVI @gBC can be successfully synthesized with a high iron loading rate of 32.5%. The multilayer graphene shell can effectively prevent the rapid passivation and agglomeration of the nZVI core, and the electronic interaction between the iron nanoparticles core and the graphene carbon shell further enhances the catalytic activity and stability of nZVI@gBC. Therefore, due to the unique structure of graphene nano-shells, nZVI@gBC can be stably stored in the air for more than 80 days. In addition, nZVI@gBC exhibited superior catalytic activity in the experiment of removing 2,4-dichlorophenol (2,4-DCP) in groundwater as a persulfate activator. Notably, both the electron paramagnetic resonance (EPR) and quenching tests showed that SO 4 •− , •OH, O 2 •− and 1 O 2 were both involved in the degradation process of 2,4-DCP, and SO 4 •− were the major active species. Simultaneously, three possible degradation pathways of 2,4-DCP were deduced by GC/MS, which were caused by dechlorination, dehydrogenation or carbon–carbon bond cleavage under the attack of SO 4 •− , •OH, O 2 •− and 1 O 2 . Besides, nZVI@gBC can use the dissolved oxygen in the liquid to generate hydroxyl radicals to effectively remove 2,4-DCP without persulfate. This kind of multifunctional nZVI@gBC may become a promising iron-carbon catalyst for large-scale applications in the field of environmental remediation.

Facile grafting strategy synthesis of single-atom electrocatalyst with enhanced ORR performance

Single-atom catalysts (SACs) have become one of the most considered research directions today, owing to their maximum atom utilization and simple structures, to investigate structure-activity relationships. In the field of non-precious-metal electrocatalysts, atomically dispersed Fe-N4 active sites have been proven to possess the best oxygen reduction activity. Yet the majority of preparation methods remains complex and costly with unsatisfying controllability. Herein, we have designed a surface-grafting strategy to directly synthesize an atomically dispersed Fe-NVC electrocatalyst applied to the oxygen reduction reaction (ORR). Through an esterification process in organic solution, metal-containing precursors were anchored on the surface of carbon substrates. The covalent bonding effect could suppress the formation of aggregated particles during heat treatment. Melamine was further introduced as both a cost-effective nitrogen resource and blocking agent retarding the migration of metal atoms. The optimized catalyst has proven to have abundant atomically dispersed Fe-N4 active sites with enhanced ORR catalytic performance in acid condition. This method has provided new feasible ideas for the synthesis of SACs.

Performance improvement of oxygen on the carbon substrate surface for dispersion of cobalt nanoparticles and its effect on hydrogen generation rate via NaBH4 hydrolysis

Carbon substrates, as previously reported, are colloidal carbon spheres (CCS) that contain oxygen-rich functional groups on the surface could that provide a suitable support for Co catalysts used for the hydrolysis of NaBH4. Our results show that the unmodified CCS substrate does not adequately interact with the Co2+ precursor to decrease the cobalt ion concentration in solution. However, after successful modification of the oxygen groups on the CCS substrate's surface, the Co ion concentration in solution decreased by 30% indicating interaction of the Co ions with the substrate surface. Also the cobalt dispersion and the hydrogen generation rate (HGR) for the catalysts supported on the modified substrate is much better than for the Co catalyst supported on the unmodified substrate. Therefore, the presence of oxygen on the substrate surface is not sufficient to provide a suitable dispersion and performance for nanocatalysts and modification of the surface leads to an improved catalyst.

Nanoparticles and Single Atoms in Commercial Carbon-Supported Platinum-Group Metal Catalysts

Nanoparticles of platinum-group metals (PGM) on carbon supports are widely used as catalysts for a number of chemical and electrochemical conversions on laboratory and industrial scale. The newly emerging field of single-atom catalysis focuses on the ultimate level of metal dispersion, i.e. atomically dispersed metal species anchored on the substrate surface. However, the presence of single atoms in traditional nanoparticle-based catalysts remains largely overlooked. In this work, we use aberration-corrected scanning transmission electron microscope to investigate four commercially available nanoparticle-based PGM/C catalysts (PGM = Ru, Rh, Pd, Pt). Annular dark-field (ADF) images at high magnifications reveal that in addition to nanoparticles, single atoms are also present on the surface of carbon substrates. Scanning electron microscopy, X-ray diffraction and size distribution analysis show that the materials vary in nanoparticle size and type of carbon support. These observations raise questions about the possible ubiquitous presence of single atoms in conventional nanoparticle PGM/C catalysts and the role they may play in their synthesis, activity, and stability. We critically discuss the observations with regard to the quickly developing field of single atom catalysis.

Preparation of Hybrid Composite Materials on the Basis of Vanadium and Molybdenum Oxide Compounds

Hybrid composite oxide material is obtained by transient electrolysis method on the surface of carbon fiber substrate having the ability to reverse electrochemical intercalation of lithium. It is established that electrochemical characteristics of the hybrid composite oxide material depend on the concentration of sodium metavanadate in the solution of cathodic degreasing electrolyte during the preparation of carbon substrate surface.

In Situ Thermal Atomization To Convert Supported Nickel Nanoparticles into Surface‐Bound Nickel Single‐Atom Catalysts

AbstractThe arrangement of the active sites on the surface of a catalysts can reduce the problem of mass transfer and enhance the atom economy. Herein, supported Ni metal nanoparticles can be transformed to thermal stable Ni single atoms, mostly located on the surface of the support. Assisted by N‐doped carbon with abundant defects, this synthetic process not only transform the nanoparticles to single atoms, but also creates numerous pores to facilitate the contact of dissolved CO2 and single Ni sites. The proposed mechanism is that the Ni nanoparticles could break surface C−C bonds drill into the carbon matrix, leaving pores on the surface. When Ni nanoparticles are exposed to N‐doped carbon, the strong coordination splits Ni atoms from Ni NPs. The Ni atoms are stabilized within the surface of carbon substrate. The continuous loss of atomic Ni species from the NPs would finally result in atomization of Ni NPs. CO2 electroreduction testing shows that the surface enriched with Ni single atoms delivers better performance than supported Ni NPs and other similar catalysts.

In Situ Thermal Atomization To Convert Supported Nickel Nanoparticles into Surface-Bound Nickel Single-Atom Catalysts.

The arrangement of the active sites on the surface of a catalysts can reduce the problem of mass transfer and enhance the atom economy. Herein, supported Ni metal nanoparticles can be transformed to thermal stable Ni single atoms, mostly located on the surface of the support. Assisted by N-doped carbon with abundant defects, this synthetic process not only transform the nanoparticles to single atoms, but also creates numerous pores to facilitate the contact of dissolved CO2 and single Ni sites. The proposed mechanism is that the Ni nanoparticles could break surface C-C bonds drill into the carbon matrix, leaving pores on the surface. When Ni nanoparticles are exposed to N-doped carbon, the strong coordination splits Ni atoms from Ni NPs. The Ni atoms are stabilized within the surface of carbon substrate. The continuous loss of atomic Ni species from the NPs would finally result in atomization of Ni NPs. CO2 electroreduction testing shows that the surface enriched with Ni single atoms delivers better performance than supported Ni NPs and other similar catalysts.

Insight into the effect of boron doping on sulfur/carbon cathode in lithium-sulfur batteries.

To exploit the high energy density of lithium-sulfur batteries, porous carbon materials have been widely used as the host materials of the S cathode. Current studies about carbon hosts are more frequently focused on the design of carbon structures rather than modification of its properties. In this study, we use boron-doped porous carbon materials as the host material of the S cathode to get an insightful investigation of the effect of B dopant on the S/C cathode. Powder electronic conductivity shows that the B-doped carbon materials exhibit higher conductivity than the pure analogous porous carbon. Moreover, by X-ray photoelectron spectroscopy, we prove that doping with B leads to a positively polarized surface of carbon substrates and allows chemisorption of S and its polysulfides. Thus, the B-doped carbons can ensure a more stable S/C cathode with satisfactory conductivity, which is demonstrated by the electrochemical performance evaluation. The S/B-doped carbon cathode was found to deliver much higher initial capacity (1300 mA h g(-1) at 0.25 C), improved cyclic stability, and rate capability when compared with the cathode based on pure porous carbon. Electrochemical impedance spectra also indicate the low resistance of the S/B-doped C cathode and the chemisorption of polysulfide anions because of the presence of B. These features of B doping can play the positive role in the electrochemical performance of S cathodes and help to build better Li-S batteries.

Syntheses of hyperbranched liquid-crystalline biopolymers with strong adhesion from phenolic phytomonomers

A novel thermotropic liquid-crystalline (LC) biocopolymer, poly{trans-3-methoxyl-4-hydroxycinnamic acid (MHCA: ferulic acid)-co-trans-3,4-dihydroxycinnamic acid (DHCA: caffeic acid)}, was synthesized by a thermal acidolysis-polycondensation of MHCA and DHCA, efficiently catalyzed by Na2HPO4. When the MHCA composition of poly(MHCA-co-DHCA) was 60, 75, and 90 mol %, the copolymers showed a nematic LC phase although individual homopolymers such as polyMHCA and polyDHCA did not exhibit LC phase. Poly(MHCA-co-DHCA)s showed high molecular weight (M w) ranged between M n 2.6 × 104 to 3.7 × 104 and M w 8.2 × 104 to 13.1 × 104, respectively, high glass-transition temperature (T g) with the range of 115 to 140 °C and high degradation temperature T 10, from 315 to 356 °C. In the adhesive test of copolymers against the surface of carbon substrate, the copolymers showed high shear strength at fracture.

Electrocatalysts for fuel cells synthesized in supercritical carbon dioxide

We applied the method of directly depositing an organometallic precursor from a solution in supercritical carbon dioxide on a dispersed carbon substrate surface followed by reduction to obtain a number of electrocatalytic materials in the form of nanoscale platinum particles on dispersed carbon supports (Vulcan XC72r carbon black, acetylene black, nanotubes). The synthesized materials persistently showed a monodisperse size distribution of platinum particles with an average diameter of 2–3 nm, regardless of the substrate nature, and a uniform distribution over the support surface. The synthesized electrocatalysts (ECs) were tested as part of an operating cathode electrode of a phosphoric acid fuel cell (FC) with a PBI matrix. In this case, the membrane-electrode assembly with this cathode showed current-voltage characteristics as good as the reference characteristics achieved with electrodes produced by BASF.

Hydrophilic-hydrophobic and sorption properties of the catalyst layers of electrodes in a proton-exchange membrane fuel cell: A stage-by-stage study

In the electrodes of a proton-exchange membrane fuel cell, the hydrophilic-hydrophobic properties of the catalyst layers (CL), which contain a carbon substrate (CS), an ionomer in the form of Nafion resin, and a platinum catalyst, are investigated with standard contact porosimetry. Regularities in the influence of ionomer on the hydrophilic-hydrophobic properties of ten different CS, including Vulcan XC-72 carbon black, are investigated. The following plots are obtained: pore distribution curves with respect to radii, water desorption isotherms, moisture content distribution curves with respect to capillary pressure and to the free energy of binding water to material, and the wetting angle of water for the samples under investigation as a function of pore radius. It is established that both a hydrophobic effect and a hydrophilic effect occur in CL as a result of ionomer application to the CS under investigation. It is concluded that these different effects are determined by the orientation of the sulfonate groups (inside and outside) in the resin particles. This orientation depends on the extent of the binding of sulfonate groups to the CS surface by adsorption. CS surface properties are determined by the type and concentration of surface groups. Thus, the phenomenon of ionogenic-group inversion is established. When platinum is applied to CS, the CL become partially hydrophilic.

Porous structure of the catalyst layers of electrodes in a proton-exchange membrane fuel cell: A stage-by-stage study

Porous structure is studied by standard contact porosimetry after each stage in the preparation of a catalyst layer, which contains a carbon substrate (CS), an ionomer in the form of Nafion resin, and a platinum catalyst. The influence of the ionomer on the porous structure of ten different CS is investigated. The structure of these samples is studied over the maximum range of their pore radii r ∼ 0.3–105 nm. Pores of main volume within particles of the CS under investigation are mainly distributed over the maximum range of their radii from r ≤ 1 to ∼ 50 nm. Ionomer introduction into all the CS under investigation leads to an increase in the integral porosity due to the porosity of the intergranular structure. The change in porosity of the intragranular structure is caused by ionomer blocking small pores in the CS. In most CS, ionomer blocks pores of different sizes, from micropores with radii r ≤ 1 nm and up to r ∼ 1000 nm. It is concluded that the extent of blockage of CS pores is largely determined by the surface properties of the CS and Nafion resin and, more precisely, by the difference in resin adhesion to the CS surface because of the presence of different surface groups on the CS surface. When platinum is applied to CS, this leads to an increase in the specific volume of the micropores. The smallest dimensions of platinum particles are estimated to be on the order of 1 nm.

Microstructure and property of SiC coating for carbon materials

SiC coating has been developed on four kinds of carbon substrates using a slurry-sintering method. The relationship between the microstructure and property of SiC coating and carbon substrates was investigated experimentally and theoretically. It was found that the pore radius of carbon substrates has marked effect on the microstructure and property of SiC coating. SiC gradient coating which is beneficial to improve the oxidation resistance for carbon materials, is expected to form on the surface of carbon substrate with the pore radius mainly over the range of 100–500 nm.

Quantum dot-based immunosensor for the detection of prostate-specific antigen using fluorescence microscopy

A sensitive optical method based on quantum dot (QD) technology is demonstrated for the detection of an important cancer marker, total prostate-specific antigen (TPSA) on a disposable carbon substrate surface. Immuno-recognition was carried out on a carbon substrate using a sandwich assay approach, where the primary antibody (Ab)-protein A complex covalently bound to the substrate surface, was allowed to capture TPSA. After the recognition event, the substrate was exposed to the biotinylated secondary Abs. After incubation with the QD streptavidin conjugates, QDs were captured on the substrate surface by the strong biotin-streptavidin affinity. Fluorescence imaging of the substrate surface illuminated the QDs, and provided a very sensitive tool for the detection of TPSA in undiluted human serum samples with a detection limit of 0.25 ng/mL. The potential of this method for application as a simple and efficient diagnostic strategy for immunoassays is discussed.

An activated carbon substrate surface for laser desorption mass spectrometry

A method to obtain laser desorption/ionization mass spectra of organic compounds by depositing sample solutions onto a carbon substrate surface is demonstrated. The substrate consists of a thin layer of activated carbon particles immobilized on an aluminum support. In common with the porous carbon suspension samples used in previous “surface-assisted laser desorption/ionization” (SALDI) work, the mass spectra contain only a few “matrix” background ion peaks, minimizing interference with analyte ion peaks. The presence of glycerol ensured that the ion signals were stable over hundreds of laser shots. In addition, the carbon substrate surface has several advantages over the suspension samples. The use of a very thin layer of carbon significantly improves the sensitivity. Detection limits range from attomoles for crystal violet to femtomoles for bradykinin. Very little sample preparation is required as the analyte solution is simply pipetted onto the substrate surface and glycerol added. When using an alternate sample deposition method, a mass resolution for bradykinin of 1800 is achieved in linear time-of-flight mode. This is close to the resolution limit set by the detector system and above instrument specification for matrix-assisted laser desorption/ionization mass spectra.

Atom assisted sputtering yield amplification

At first sight one might assume that it is unlikely to influence the sputtering yield of a specific ion/substrate combination by any external means. However, we have found that such an influence may well be introduced. The sputtering yield is predominantly determined by the ion/substrate momentum transfer efficiency and the energy of the incoming ion. Sputter erosion of, e.g., carbon atoms by argon ions from a carbon substrate exhibits a very low sputtering yield. Due to the difference in masses between carbon and argon much of the momentum is transferred into the bulk of the carbon substrate. This situation could be changed by simultaneous codeposition of Pt atoms onto the carbon substrate surface during the argon sputtering. Keeping the argon flux at a level well above what is needed to sputter remove all the deposited Pt atoms the following effect occurs. Some of the deposited Pt atoms will be forward implanted by the energetic argon ions into the near surface region of the carbon substrate. Collision between both argon (M=40) and carbon (M=12) atoms with the implanted Pt atom (M=195) can result in reflection of some of the light atoms. Therefore implanted Pt atoms will act as effective reflection centers pushing the collision cascade to take place closer to the surface region, thereby contributing to an effective increase of the number of collision cascades in this region. This reflection effect will result in a substantial increase of the sputtering yield of carbon atoms. Experimental verification of this effect for the (Ar+C+Pt) and the (Ar+Si+Pt) systems will be presented. It will be also shown that this sputter amplification process can be predicted from computer simulations using the t-dyn version of the Monte Carlo trim code.