Diluent Gas Research Articles

Effects of flue gas recirculation on the premixed oxy-methane flames in atmospheric condition

This numerical study investigates the flame characteristics of premixed methane with various dilutions in order to simulate oxy-combustion of hydrocarbon fuels with flue gas recirculation system. In general, a recirculated flue gas consists of high concentration CO2/H2O and high gas temperature. The effect of various diluent gases on laminar burning velocity and adiabatic flame temperature is discussed via using Chemkin-pro simulation. By observing the resultant flame temperature and species concentration profiles one can identify that the flame front shifts, and the concentration profiles of major chemical reaction radicals varies, indicating the change of flame structure and flame chemical reaction paths. The dominant initial consumption reaction step of methane shifts from R53 (H + CH4CH3 + H2) to R98 (OH + CH4CH3 + H2O) when nitrogen is replaced by the recirculated gases. H and OH radical concentration would be influenced in various diluent gas cases, so that it leads to affect hydrogen formation and methane consumption. It is because that the chemical effects of the recirculated gases change the chemical reaction of the oxy-fuel combustion, and further affect reaction rate, species and radical concentrations.

Hydrate phase equilibrium of H2/CH4/CO2 ternary gas mixtures and cage occupancy percentage of hydrogen molecules

Hydrogen, methane, and carbon dioxide are co-existence in many cases such as vent gas from the steam reforming of hydrocarbons. For the purpose of H2 recovery and/or CO2 sequestration via separation technology based on hydrate, the hydrate phase equilibrium of four groups of H2/CH4/CO2 ternary gas mixtures in pure water system were determined using the isothermal pressure-search method in a temperature range of (274.7–284.5)K. During modeling hydrate formation conditions, there is little difference with experimental data no matter whether H2 works as a hydrate former or not. Hydrogen can be regarded as a kind of diluent gas for convenience when presetting the operation conditions. To meet the mass balance of each gas species, the cage occupancy percentages of hydrogen in hydrate have been evaluated. The result illustrates that the occupancy percentage of hydrogen molecules ranges from 0.3 to 2.3 percent in small cage and (2.16–13.6)×10−7 percent in large cage, which deduces that H2 molecules are indeed trapped in hydrate solid.

Simultaneous determination of three organic fluorides in workplace air by portable gas chromatography-mass spectrometer

To establish a method for rapid determination of organic fluorides in the air of a fluorine chemical plant using portable gas chromatography-mass spectrometer (GC-MS). Standard samples of monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene of different concentrations were prepared by static volumetric method with high-purity nitrogen as the diluent gas. The samples were injected into the GC-MS by a hand-held probe. Retention time and characteristic ion were used for qualitative analysis, and the area of selected ion peak was used for quantitative analysis. The standard curves were then created for quantitative determination of the three organic fluorides. The linear ranges for monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene by the method were 0.39-7.72, 0.45-8.84, and 0.61-12.20 mg/m3, respectively, the average recovery rates for the three concentrations were 102.8%, 96.0%, and 106.5%, respectively, and the average deviations were 2.1%, 5.1%, and 2.4%, respectively. The portable GC-MS can be used for the simultaneous qualitative and quantitative analysis of monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene in the workplace air, and the method is simple, fast, and accurate.

The effect of impurities on syngas combustion

The effects of chemical impurities on the combustion of syngas were investigated, focusing on CH4, a common component of syngas, and trimethylsilanol (TMS), an unstudied impurity related to those common to landfill-based syngas. Ignition properties were systematically investigated at high-pressure low-temperature conditions relevant to gas turbine combustor operation using the University of Michigan Rapid Compression Facility. Pressure time history measurements and high-speed imaging of the ignition process in this facility were used to determine auto-ignition delay times and observe ignition behaviors. The four simulated syngas mixtures used were (1) pure syngas: 30% H2, 70% CO fuel volume, (2) syngas with CH4: 27% H2, 67% CO, 6% CH4, (3 & 4) pure syngas with 10 or 100ppm TMS, all with fuel-to-O2 equivalence ratios (φ) of 0.1 at air dilution (i.e. molar O2 to inert gas ratio of 1:3.76), and N2 as the primary diluent gas. The pressures after compression were 5 & 15atm with temperatures of ∼1010–1110K respectively. The results uniquely illustrated the occurrence of two-step ignition behavior at higher pressures, with two distinct regions of heat release and pressure rise. First and second auto-ignition delay times were therefore defined and interestingly the times were affected differently by the addition of impurities. The addition of CH4 consistently increased auto-ignition delay times up to 40% at 15atm, while increasing delay times at 5atm by up to a factor of three. Conversely, the addition of 10ppm TMS impurity addition caused a consistent decrease of ∼10–30% delay times at 15atm with insignificant impact at 5atm, and 100ppm TMS impurity caused consistent decreases of 50–70% at 15atm and 20–30% decreases at 5atm. The marked pressure dependence of the auto-ignition delay time, typical for syngas at these conditions, was virtually eliminated for the 100ppm TMS mixture. Kinetic modeling suggests that the promoting effects of TMS are related to enhanced consumption and/or reduced production of HO2. The impact of TMS is remarkably similar to that for SiH4 in pure H2, suggesting a possible trend for poorly understood Si-based species to promote auto-ignition in syngas and hydrogen mixtures.

Investigation of thermal and carbothermal reduction of volatile oxides (ZnO, SnO2, GeO2, and MgO) via solar-driven vacuum thermogravimetry for thermochemical production of solar fuels

This study addresses the solar thermogravimetry analysis of high-temperature reduction reactions involving volatile metal oxides for application in solar thermochemical fuel production via two-step H2O and CO2 splitting. The redox cycles encompass the thermal or carbo-thermal reduction of a metal oxide using concentrated solar energy followed by its oxidation with CO2 and/or H2O to produce solar-derived fuels (CO and/or H2). A new solar-driven vacuum thermogravimeter has been developed for the investigation of the high-temperature thermochemical reactions. The system is designed for reduced pressure operation down to a few mbar with flowing purge gas for studying low-pressure conditions, while the weight change of the solid reactants is continuously monitored during high-temperature solar heating under non-linear heating profile. The method was applied to investigate the kinetic rates of the thermochemical solid/gas reactions involving ZnO, SnO2, GeO2, and MgO volatile oxides in a controlled atmosphere. The reaction rates were determined as a function of the temperature for different pressures in the system. Metal oxides reduction under low pressure was shown to be of special interest because the reaction rate is greatly enhanced and the required temperature to achieve a given reduction rate is significantly lowered. In contrast to inert gas dilution, a total pressure decrease also reduces the need for a diluent gas, thus simplifying the process and avoiding energy penalties associated with inert gas recycling.

Experimental and computational investigation on the gas phase reaction of p-cymene with Cl atoms.

The rate coefficient for the gas-phase reaction of Cl atoms with p-cymene was determined as a function of temperature (288-350 K) and pressure (700-800 Torr) using the relative rate technique, with 1,3-butadiene and ethylene as reference compounds. Cl atoms were generated by UV photolysis of oxalyl chloride ((COCl)2) at 254 nm, and nitrogen was used as the diluent gas. The rate coefficient for the reaction of Cl atoms with p-cymene at 298 K was measured to be (2.58 ± 1.55) × 10(-10) cm(3) molecule(-1) s(-1). The kinetic data obtained over the temperature range 288-350 K were used to derive an Arrhenius expression: k(T) = (9.36 ± 2.90) × 10(-10) exp[-(488 ± 98)/T] cm(3) molecule(-1) s(-1). Theoretical kinetic calculations were also performed for the title reaction using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) between 250 and 400 K. The calculated rate coefficients obtained over the temperature range 250-400 K were used to derive an Arrhenius expression: k(T) = 5.41 × 10(-13) exp[1837/T] cm(3) molecule(-1) s(-1). Theoretical study indicated that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected. The atmospheric lifetime (τ) of p-cymene due to its reactions with various tropospheric oxidants was estimated, and it was concluded that the reactions of p-cymene with Cl atoms may compete with OH radicals in the marine boundary layer and in coastal urban areas where the concentration of Cl atoms is high.

Dependence of the Texture on the Thermoelectric Properties of C/C Composites

C/C composites with different microstructures were fabricated by microwave chemical vapor infiltration (MCVI) using carbon felt as fiber preform, CH4 as precursor gas and N2 as diluent gas. The different microstructures of C/C composites were characterized by polarizing microscope (PLM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectra. Thermoelectric properties were systematically investigated via thermoelectric performance testing instrument (ZEM-2) and laser thermal conductivity instrument (TC-9000H). The results reveal that positive Seebeck coefficient is obtained from C/C composites with different micro- structures and an important relationship is existed between thermoelectric property and orientation of pyrocarbon. See- beck coefficient, electrical conductivity and thermal conductivity are increased gradually with the texture of pyrocarbon evolved from isotropy, low texture and middle texture to high texture. With the texture being reinforced, it has a more important influence on carriers than on phonons. As a result, the merit ZT is increased with the reinforce of the texture.

Gas–liquid dielectric barrier discharge falling film reactor for the decoloration of dyeing water

AbstractBACKGROUNDDecoloration of dyes is a top priority to enhance biodegradability in color‐free wastewater post‐treatment. A gas–liquid dielectric barrier discharge (DBD) falling film reactor has been developed as a promising approach to the decoloration of dyes.RESULTSRhodamine B was employed as a model compound. The effects of residence time of the liquid film with different initial concentrations, oxygen flow rates and oxygen concentrations (using different diluent gases, e.g. argon and nitrogen) were investigated. Longer liquid film residence time and lower oxygen flow rate resulted in higher decoloration efficiency. The decoloration efficiency in oxygen and nitrogen discharge was slightly higher than that in oxygen and argon discharge at the same oxygen concentration. The mechanisms of decoloration and the production of oxidative species are clearly revealed. The highest decoloration efficiency (up to 97.4%) with initial concentration of 50 mg L−1 was obtained in pure oxygen discharge with liquid residence time of 1.9 s at an oxygen flow rate of 100 mL min−1.CONCLUSIONThe proposed gas–liquid DBD falling film reactor is a promising alternative to advanced oxidation processes (AOPs) for effective treatment of dyes. These results are helpful for further real plasma wastewater treatment. © 2014 Society of Chemical Industry

The Influence of a Second Metal on the Ni/SiC Catalyst for the Methanation of Syngas

The catalytic performance of silicon carbide supported nickel catalysts modified with or without second metal (Co, Cu and Zn) for the methanation of CO has been investigated in a fixed-bed reactor using a feed consisting of 25% CO and 75% <TEX>$H_2$</TEX> without any diluent gas. It has been found that the introduction of Co species can clearly improve the catalytic activity of Ni/SiC catalyst, whereas the addition of Cu or Zn can result in a significant decrease in the catalytic activity. The characterizations by means of XRD, TEM, XPS, CO-TPD and <TEX>$H_2$</TEX>-TPR indicate that the addition of Co could decrease the particle size of active metal, increase active sites on the surface of methanation catalyst, improve the chemisorption of CO and enhance the reducibility of methanation catalysts. Additionally, the special interaction between Co species and Ni species is likely favorable for the dissociation of adsorbed CO on the surface of catalyst, and this may also contribute to the high activity of 5Co-Ni/SiC catalyst for CO methanation reaction. For 5Cu-Ni/SiC catalyst and 5Zn-Ni/SiC catalyst, Cu and Zn species could cover partial nickel particles and decrease the chemisorption amount of CO. These could be responsible for the low methanation activity. In addition, a 150h stability test under 2 MPa and <TEX>$300^{\circ}C$</TEX> showed that 5Co-Ni/SiC catalyst was very stable for CO methanation reaction.

A comprehensive study on Pt/Al2O3 granular catalyst used for sulfuric acid decomposition step in sulfur–iodine thermochemical cycle: Changes in catalyst structure, morphology and metal-support interaction

In continuation with our last communication on granular Fe2O3 catalysts (Banerjee et al., Applied Catalysis B: Environmental 127 (2012) 36–46), we report here a thorough investigations on Pt/Al2O3 catalyst in granular form of 4–6mm diameter for sulfuric acid decomposition reaction in absence of any carrier or diluents gas in a dual tube quartz catalytic reactor, which served as an integrated boiler, preheater and catalytic decomposer. SO2 yield were evaluated as a function of reaction variables e.g. time, temperature and sulfuric acid flux for Pt/Al2O3 catalyst and compared with earlier results obtained with Fe2O3 based catalysts. The SO2 yield increased as a function of temperature while it decreased with an increase in sulfuric acid flux. A decrease in SO2 yield from 80% to 73% was observed for Pt/Al2O3 catalyst during a 100h run at 800°C and at an acid flux of 0.63mlmin−1 (WHSV of ∼3.4g acid g−1h−1). To determine the cause of this deactivation, both the fresh and spent catalysts were characterized for structure and morphology by ICP-AES, N2-adsorption desorption isotherm, pulsed chemisorption of H2, XRD, FTIR, SEM, TEM and HR-TEM. The support alumina underwent major physicochemical changes on prolonged use under the harsh reaction conditions at elevated temperatures viz. reduction in porosity and surface area, sulfation, and partial phase transformation. On the other hand, the active metal Pt, which exhibited a small and narrow particle size distribution and good dispersion in the fresh catalyst, suffered thermal sintering on long term use to form large agglomerates with a non-uniform size distribution and poor dispersion. An attempt was made to understand the existence of any metal-support interaction by recording the TG-DTG-evolved gas analysis of the spent catalyst and comparing it with the thermal properties of bulk aluminum sulfate. The thermal investigations revealed that a synergistic effect existed between the Pt-particles and the sulfated alumina support.

Trace-moisture generator designed for performance tests of trace-moisture analyzers

The National Metrology Institute of Japan (NMIJ) developed a trace-moisture generator, named the “simplified trace-moisture generator (STMG),” which was designed particularly for effectively testing the performance of trace-moisture analyzers. The STMG produces trace moisture in nitrogen gas from approximately 10nmol/mol (ppb) to 10μmol/mol (ppm) in amount fraction (mole fraction) of water, using diffusion-tube and two-stage dilution methods. In contrast to the magnetic suspension balance/diffusion-tube humidity generator (MSB/DTG) developed at NMIJ in 2007, the STMG does not require an MSB to measure the evaporation rate of water from the diffusion cell (hence, the name “simplified”). Instead, a moisture analyzer based on cavity ring-down spectroscopy (CRDS) calibrated in a manner traceable to the International System of Units (SI) measures the amount fraction of water in the generated gas. By introducing a sonic nozzle placed at the outlet of the generation chamber, the pressure stability in the chamber is maintained even after the rapid change in the flow rate of the diluent nitrogen gas. This enabled smooth moisture-concentration switching within 1min for 90 % response to the step change between 11nmol/mol and 8.8μmol/mol. The controllability and short-term stability of the moisture content in the generated gas were demonstrated successfully. The long-term stability of moisture generation was evaluated by estimating evaporation rate from the flow rate of nitrogen and the amount fraction of water measured by the CRDS trace-moisture analyzer. It was confirmed that the STMG can generate trace moisture in nitrogen with good stability and repeatability for five consecutive months.

Study of SiO2 coat preparation and its anti-coking behaviour

A SiO2 coat was prepared on an HP40 steel surface via atmospheric-pressure chemical vapour deposition (APCVD). The composition and surface appearance of the coat were then investigated with the aid of energy dispersive spectrometry and scanning electron microscopy, and its anti-coking ability was analysed by virtue of anti-coking mechanism and an anti-coking test. A 5 μm-thick SiO2 coat was prepared through APCVD at 800°C, with tetraethyl orthosilicate as the source material and air as the carrier and diluent gas. The prepared SiO2 coat can effectively prevent catalyst coking (with an anti-coking rate above 70%) under pyrolysis conditions and can improve the anti-coking ability of HP40 steel.

High-pressure low-temperature ignition behavior of syngas mixtures

Ignition properties of simulated syngas mixtures were systematically investigated at high-pressure low-temperature conditions relevant to gas turbine combustor operation using the University of Michigan Rapid Compression Facility. Pressure time history measurements and high-speed imaging of the ignition process in this facility were used to determine auto-ignition delay times and observe and characterize ignition behaviors. The simulated syngas mixtures were composed of H2 and CO with a molar ratio of 0.7, for equivalence ratios (φ) of 0.1 and 0.5, near air dilution (i.e. molar O2 to inert gas ratio of 1:3.76), with N2 as the primary diluent gas. The pressures and temperatures after compression ranged from 3–15atm and 870–1150K respectively. The comprehensive results of the present work combined with those from previous shocktube studies in the literature clearly illustrate the existence of both homogeneous and inhomogeneous auto-ignition behaviors at these conditions. Analysis of patterns in the ignition behaviors revealed a dependence on temperature, pressure, and equivalence ratio with distinct thermodynamic regions in which the ignition behavior is consistent and repeatable. Predicted locations of the strong ignition limit made using a criterion which compares laminar flame speed to a thermal gradient driven front propagation speed have excellent agreement with the experimental findings for each φ and an assumed gradient of 5K/mm. Experimental validation of this unique and powerful criterion means that it can be used for a priori prediction of the strong ignition limit using basic computational simulations. The validity of this criterion is fundamentally important, quantitatively describing the roles of chemical kinetics, thermo-physical properties, and device dependent thermal characteristics in determining auto-ignition behavior. Additionally, a comparison of the measured auto-ignition delay times to predictions made using zero-dimensional homogeneous reactor modeling revealed that agreement was dependent on φ, with excellent agreement for φ=0.1 and large discrepancies for φ=0.5. These results indicate that while inhomogeneous ignition phenomena are not entirely avoidable by reducing equivalence ratio, the subsequent effects on the accuracy of typical auto-ignition delay time predictions may be reduced or eliminated.

The effects of addition of La2O3 on the microstructure and mechanical properties of carbon/carbon composites

For the purpose of comparison, C/C composites were prepared with and without lanthanum oxide (La2O3) by thermal gradient chemical vapour infiltration (TCVI). Natural gas was used as the carbon source, and N2 was selected as the diluent gas and protected gas in the experiments. The effects of percentage composition of La2O3 on the microstructure and mechanical properties were investigated. The microstructure was investigated via polarized light microscope (PLM) and scanning electron microscope (SEM). The mechanical properties were studied via three-point flexural testing. The results indicate that the addition of La2O3 has a considerable effect on pyrocarbon texture, with the matrix of the pure C/C composite being composed of ISO and smooth laminar (SL) pyrocarbon, whereas the matrix of composites with La2O3 was mainly dominated by SL pyrocarbon. The differences are the refinement of pyrocarbon texture and increase of the extinction angle with the increasing content of La2O3. Moreover, it was observed that the ultimate flexural strength of C/C composites with La2O3 was significantly improved, from which it can be deduced that La2O3 improves the interface roughness and interface bonding strength between carbon fibres and the pyrocarbon matrix by interfacial chemical reaction.

Flammability limits of binary mixtures of dimethyl ether with five diluent gases

Flammability limits of binary mixtures of dimethyl ether with five kinds of diluent gases were measured by ASHRAE method at room temperature. The five diluent gases are nitrogen, carbon dioxide, chlorodifluoromethane (HCFC-22), 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). The experimental results were correlated with the extended Le Chatelier's formula. It was found that the experimental results were well reproduced by the formula. In addition, flammability limits of binary mixtures of dimethyl ether with nitrogen and carbon dioxide were compared with the estimated values based on the adiabatic flame temperature method. The experimental results were found to be in satisfactory agreement with the estimated values.

Effect of diluent gas on ethylene epoxidation activity over various Ag-based catalysts on selective oxide supports

The influence of different diluent gases (He, Ar, N2, CH4, and CH4 balanced with He) on the epoxidation of ethylene was comparatively studied over three different catalysts, including a commercial 14.86wt.% Ag/α-Al2O3, a bimetallic 1.41wt.% Cu–17.16wt.% Ag/SrTiO3, and a 0.32wt.% Sn-promoted on 1.39wt.% Cu–17.16wt.% Ag/SrTiO3 catalyst. The best diluent gas for ethylene epoxidation was CH4 balanced with He over all catalysts. CH4 enhanced C2H4 conversion while He provided both high EO selectivity and yield. Thus, the 35% CH4 balanced with 53% He diluent gas provided the highest synergistic effect toward the ethylene epoxidation reaction, while also leading to the lowest level of coke formation.

Numerical study and correlation development on laminar burning velocities of n-butanol, iso-octane and their blends: Focusing on diluent and blend ratio effects

Bio-n-butanol as a potential alternative bio-fuel is accepted more and more attention presently in the fields of both scientific research and commercial market; however, n-butanol is impossible to substitute conventional fuels completely in the short and medium term. Therefore, understanding the premixed flame’s characteristics of iso-octane/n-butanol mixture fuels is no doubt an important way to make better use of n-butanol as a fuel applied in conventional SI (spark-ignition) engines. On the other hand, the engines always operate with EGR (exhaust gas recirculation), so the premixed flame characteristics of fuels (pure fuels or iso-octane/n-butanol mixture fuels) are needed to be investigated under EGR operations. Driven by these facts, we performed a numerical study, which is validated by experimental data, on the laminar burning velocity of n-butanol, iso-octane and their blends. Based on this, correlations including the influences of diluent and fuel component blend ratio, respectively, are developed and their fitting parameters are resolved carefully through a wide range of dataset. From results, our correlations are sufficient in accuracy to describe the effects mentioned above. Within each effect, for deeper understanding the appearance influence on the laminar burning velocity, the deep mechanism of chemical kinetic effect is revealed and discussed. In particular, as diluent effect as concerned, each single diluent gas component, such as CO2, H2O, and N2, is analyzed separately, the combined diluent effect can then be solved by grouping contributions brought by each species. In addition, our correlations were compared to those in literature widely. Concerning the mixture fuels, a correction factor is introduced by present study, such that the accuracies of mixing rules are improved at fuel-rich equivalence ratios.

Flameless combustion role in the mitigation of NOXemission: a review

SUMMARY Nitrogen oxide formation is one source of pollution emission in fossil fuel combustion. Numerous technologies, such as flameless combustion, have been introduced to prevent such formation. This paper presents a panorama of flameless combustion and its principles. The influence of this technology on air preheats and gas diluents is discussed, as well as the effect of the firing mode on thermal NOX. The benefits of flameless combustion, including its energy conservation capability and capability to reduce pollutant emissions such as NOX emission to overcome environmental dilemmas in combustion, are discussed in this paper. Copyright © 2014 John Wiley & Sons, Ltd.

Separation Method for Oxygen Mass Transport Coefficient in Gas and Ionomer Phases in PEMFC GDE

A novel method to determine the oxygen mass transport coefficient and its separation into gas and ionomer contributions was developed and validated. The method is based on the use of a limiting current density distribution mathematical model and different diluent gases with varying molecular weights. A linear relationship between the inverse overall mass transport coefficient and the diluent molecular weight was revealed. Because the use of different gas diluents with different molecular weights only affects the mass transport coefficient in the gas phase, an extrapolation to a zero diluent weight gives the O2 mass transport coefficient in the ionomer phase. The gas phase mass transport coefficient is then calculated using the additive relation between the overall mass transport coefficient and its components. The O2 mass transport coefficient in the electrolyte phase was found to be equal to 0.01284 m s−1, while in an N2 diluent, the coefficient is 0.02727 m s−1. Effects of selected operating conditions (temperature, O2 concentration) and membrane/electrode assembly materials (cathode Pt loading and gas diffusion layer) on the O2 mass transport coefficient were studied and discussed.

Improvement of multilayer graphene synthesis on copper substrate by microwave plasma process using helium at low temperatures

A pretreatment method for copper foil substrates for graphene synthesis with microwave plasma has been developed using a helium and hydrogen gas mixture. Contaminants on the surface of the substrate, particularly copper oxides, were effectively removed by this method, which was confirmed by X-ray photoelectron spectroscopy (XPS). Graphene was grown by microwave-plasma-assisted chemical vapor deposition (MWCVD) subsequent to the pretreatment of the substrate in the same apparatus. Using the hydrogen and helium gas mixtures as the diluent gas for methane, the contamination in the deposited graphene by undesirable impurities from the ambient in the reaction apparatus, particularly silicon etched from the quartz window by microwave plasma, was successfully suppressed. The multilayer graphene films synthesized at low temperatures on the pretreated copper foil substrates exhibited higher crystallinity, as shown in transmission electron microscopy (TEM) images and Raman scattering spectra, than those on the untreated substrates.