A comparison between physically and chemically driven etching in the oxidation of graphite surfaces

AgIn5S8/g-C3N4 Composite Photocatalyst Coupled with Low-Temperature Plasma-Enhanced Degradation of Hydroxypropyl-Guar-Simulated Oilfield Wastewater

The effective treatment and recovery of fracturing wastewater has always been one of the difficult problems to be solved in oilfield wastewater treatment. Accordingly, in this paper, photocatalytic-coupled low-temperature plasma technology was used to degrade the simulated wastewater containing hydroxypropyl guar, the main component of fracturing fluid. Results indicated that hydroxypropyl-guar wastewater could be degraded to a certain extent by either photocatalytic technology or plasma technology; the chemical oxygen demand and viscosity of the treated wastewater under two single-technique optimal conditions were 781 mg·L-1, 0.79 mPa·s-1 and 1296 mg·L-1, 1.01 mPa·s-1, respectively. Furthermore, the effective coupling of AgIn5S8/gC3N4 photocatalysis and dielectric-barrier discharge-low-temperature plasma not only enhanced the degradation degree of hydroxypropyl guar but also improved its degradation efficiency. Under the optimal conditions of coupling treatment, the hydroxypropyl-guar wastewater achieved the effect of a single treatment within 6 min, and the chemical oxygen demand and viscosity of the treated wastewater reduced to below 490 mg·L-1 and 0.65 mPa·s-1, respectively. In the process of coupled treatment, the AgIn5S8/gC3N4 could directly absorb the light and strong electric field generated by the system discharge and play an important role in the photocatalytic degradation, thus effectively improving the energy utilization rate of the discharge system and enhancing the degradation efficiency of hydroxypropyl guar.

Enhanced Catalytic Hydrodeoxygenation of Activated Carbon-Supported Metal Catalysts via Rapid Plasma Surface Functionalization

We employ a nonthermal, He/O₂ atmospheric plasma as an efficient surface functionalization method of activated carbons. We show that plasma treatment rapidly increases the surface oxygen content from 4.1 to 23.4% on a polymer-based spherical activated carbon in 10 min. Plasma treatment is 3 orders of magnitude faster than acidic oxidation and introduces a diverse range of carbonyl (C═O) and carboxyl (O-C═O) functionalities that were not found with acidic oxidation. The increased oxygen functionalities reduce the particle size of a high 20 wt % loading Cu catalyst by >44% and suppress the formation of large agglomerates. Increased metal dispersion exposes additional active sites and improves the yield of hydrodeoxygenation of 5-hydroxymethyl furfural to 2,5-dimethyl furan, an essential compound for biofuel replacement, by 47%. Surface functionalization via plasma can advance catalysis synthesis while being rapid and sustainable.

Molecular Dynamics Simulations and Theoretical Model for Engineering Tensile Properties of Single-and Multi-Walled Carbon Nanotubes

To apply carbon nanotubes (CNTs) as reinforcing agents in next-generation composites, it is essential to improve their nominal strength. However, since it is difficult to completely remove the defects, the synthesis guideline for improving nominal strength is still unclear, i.e., the effective strength and the number of nanotube layers required to improve the nominal strength has been undermined. In this study, molecular dynamics simulations were used to elucidate the effects of vacancies on the mechanical properties of CNTs. Additionally, the relationships between the number of layers and effective and nominal strengths of CNTs were discussed theoretically. The presence of extensive vacancies provides a possible explanation for the low nominal strengths obtained in previous experimental measurements of CNTs. This study indicates that the nominal strength can be increased from the experimentally obtained values of 10 GPa to approximately 20 GPa by using six to nine nanotube layers, even if the increase in effective strength of each layer is small. This has advantages over double-walled CNTs, because the effective strength of such CNTs must be approximately 60 GPa to achieve a nominal strength of 20 GPa.

Laser-Induced Ignition and Combustion Behavior of Individual Graphite Microparticles in a Micro-Combustor

Microscale combustion has potential application in a micro power generator. This paper studied the ignition and combustion behavior of individual graphite microparticles in a micro-combustor to explore the utilization of carbon-based fuels at the microscale system. The individual graphite microparticles inside the micro-combustor were ignited by a highly focused laser in an air flow with natural convection at atmospheric temperature and pressure. The results show that the ignition of graphite microparticles was heterogeneous. The particle diameter had a small weak effect on ignition delay time and threshold ignition energy. The micro-combustor wall heat losses had significant effects on the ignition and combustion. During combustion, flame instability, photophoresis, repetitive extinction and reignition were identified. The flame structure was asymmetric, and the fluctuation of flame front and radiation intensity showed combustion instability. Photophoretic force pushed the graphite away from the focal point and resulted in extinction. Owing to large wall heat loss, the flame quickly extinguished. However, the graphite was inductively reignited by laser.

Reaction Mechanism of the Reduction of Ozone on Graphite

The kinetics of the ozonation of graphite with different particle sizes (106 μm, G₁₀₆; 6.20 μm, G_6.2) was studied at several temperatures under a flow of O₃ diluted in O₂. The reaction was first-order with respect to graphite and to the consumption of ozone. X-ray photoelectron spectrum (XPS) showed that the reactions occurring in the solid under steady-state conditions maintain the original stoichiometry, as predicted by the postulated mechanism for SO₂. The deoxygenation reaction occurred along with the ozonation reaction at 100 °C. The rate of oxygen elimination in the flow system has the same rate-determining kinetic barrier as ozone insertion. Ozonation and deoxygenation reactions are sequentially related. Ozonation occurs with the insertion of O₃, forming a 1,2,3-trioxolane followed by an oxygen transfer that produces a peroxide valence tautomer in equilibrium with 1,3-dicarbonyl, [peroxide ↔ dicarbonyl], and an oxirene that eliminates atomic oxygen. The decarboxylation reaction was studied at 600 °C from the ozonated G₁₀₆ (ΔG^≠ = 83.60 ± 0.08 kcal·mol^-1). Total decarboxylation at 600 °C matched the number of moles of CO₂ removed and the oxygen content after ozonation, showing that the reduction of ozone on graphite was essentially a clean reduction with no secondary oxidations. When ozonized graphite was heated to 600 °C, only [peroxide ↔ dicarbonyl] species remained in the matrix. The peroxide tautomer isomerized to dioxirane and eliminated CO₂ as a dioxicarbene. Total deoxygenation of decarboxylated graphite G₁₀₆ was obtained by pyrolysis. There was residual oxygen that arose from the atomic oxygen eliminated from the oxirene, intercalated in graphite layers, and formed basal epoxy groups. Also, incoming O atoms reacted with the intercalated O atoms to produce O₂ molecules. Thermal annealing deintercalated molecular oxygen (600-900 °C).

Novel Methods for Efficacy Testing of Disinfectants – Part I

The pathogens which are the effective transmitters of various infections pose a serious problem in restraining their interference in maintaining a sterile environment. The practical applicability of traditional methods of disinfection is restricted due to their cumbersomeness, toxic product generation, and cost-effectiveness. Therefore, the objective of the current review is to elaborate the efficacies and limitations of various novel disinfectants that can show their activity in a few minutes of treatment. The expected outcome would be feasibility for selection of a favorable disinfectant through various technologies that can generate uniform results and form a basis for the true estimation required parameters. Hence, the current paper ends with the consideration of unique new techniques that distinguishes their simplicity, safety, and efficacy in generating a sterile environment.

Atomic covalent functionalization of graphene

Although graphene's physical structure is a single atom thick, two-dimensional, hexagonal crystal of sp(2) bonded carbon, this simple description belies the myriad interesting and complex physical properties attributed to this fascinating material. Because of its unusual electronic structure and superlative properties, graphene serves as a leading candidate for many next generation technologies including high frequency electronics, broadband photodetectors, biological and gas sensors, and transparent conductive coatings. Despite this promise, researchers could apply graphene more routinely in real-world technologies if they could chemically adjust graphene's electronic properties. For example, the covalent modification of graphene to create a band gap comparable to silicon (∼1 eV) would enable its use in digital electronics, and larger band gaps would provide new opportunities for graphene-based photonics. Toward this end, researchers have focused considerable effort on the chemical functionalization of graphene. Due to its high thermodynamic stability and chemical inertness, new methods and techniques are required to create covalent bonds without promoting undesirable side reactions or irreversible damage to the underlying carbon lattice. In this Account, we review and discuss recent theoretical and experimental work studying covalent modifications to graphene using gas phase atomic radicals. Atomic radicals have sufficient energy to overcome the kinetic and thermodynamic barriers associated with covalent reactions on the basal plane of graphene but lack the energy required to break the C-C sigma bonds that would destroy the carbon lattice. Furthermore, because they are atomic species, radicals substantially reduce the likelihood of unwanted side reactions that confound other covalent chemistries. Overall, these methods based on atomic radicals show promise for the homogeneous functionalization of graphene and the production of new classes of two-dimensional materials with fundamentally different electronic and physical properties. Specifically, we focus on recent studies of the addition of atomic hydrogen, fluorine, and oxygen to the basal plane of graphene. In each of these reactions, a high energy, activating step initiates the process, breaking the local π structure and distorting the surrounding lattice. Scanning tunneling microscopy experiments reveal that substrate mediated interactions often dominate when the initial binding event occurs. We then compare these substrate effects with the results of theoretical studies that typically assume a vacuum environment. As the surface coverage increases, clusters often form around the initial distortion, and the stoichiometric composition of the saturated end product depends strongly on both the substrate and reactant species. In addition to these chemical and structural observations, we review how covalent modification can extend the range of physical properties that are achievable in two-dimensional materials.

Photochemical oxidation of CVD-grown single layer graphene

CVD-grown single layer graphene undergoes rapid photochemical oxidation in the presence of ultraviolet light and oxygen. The oxidation results in a homogeneous decay of the graphitic material; no nanoscale line cracks or pits were observed with an atomic force microscope. The conductivity of the graphene film decreases with an increasing degree of oxidation. It is crucial to understand and enhance the photochemical stability of graphene for its long term use as a transparent conducting material.

Identification of structural defects in graphitic materials by gas-phase anisotropic etching

We developed a method of identifying the structural defects in graphitic materials by an anisotropic etching technique. Intrinsic and oxygen- or argon- plasma induced artificial defects' density and domain size can be obtained easily and precisely. It was inferred, through our investigations, that the grade ZYA highly oriented pyrolytic graphite (HOPG) sample has a better crystal quality, with a lower defect density, while the Kish graphite has a larger grain size and higher defect density. Defect types and lattice orientations can also be extracted by this technique. Furthermore, this method could apply to various graphitic materials including graphene.

Nonthermal atmospheric plasma rapidly disinfects multidrug-resistant microbes by inducing cell surface damage

Plasma, a unique state of matter with properties similar to those of ionized gas, is an effective biological disinfectant. However, the mechanism through which nonthermal or "cold" plasma inactivates microbes on surfaces is poorly understood, due in part to challenges associated with processing and analyzing live cells on surfaces rather than in aqueous solution. Here, we employ membrane adsorption techniques to visualize the cellular effects of plasma on representative clinical isolates of drug-resistant microbes. Through direct fluorescent imaging, we demonstrate that plasma rapidly inactivates planktonic cultures, with >5 log(10) kill in 30 s by damaging the cell surface in a time-dependent manner, resulting in a loss of membrane integrity, leakage of intracellular components (nucleic acid, protein, ATP), and ultimately focal dissolution of the cell surface with longer exposure time. This occurred with similar kinetic rates among methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Candida albicans. We observed no correlative evidence that plasma induced widespread genomic damage or oxidative protein modification prior to the onset of membrane damage. Consistent with the notion that plasma is superficial, plasma-mediated sterilization was dramatically reduced when microbial cells were enveloped in aqueous buffer prior to treatment. These results support the use of nonthermal plasmas for disinfecting multidrug-resistant microbes in environmental settings and substantiate ongoing clinical applications for plasma devices.