Variation Of CO Concentration Research Articles

EFFECT OF METAL CONCENTRATION ON PHYSICOCHEMICAL PROPERTIES OF COBALT/REDUCED GRAPHENE OXIDE THROUGH ONE-POT GREENER CHEMICAL-THERMAL REDUCTION USING ULTRASONIC ACTIVATION

A combination of ultrasonically supported one-step chemical thermal reductions for synthesizing cobalt/reduced graphene oxide (Co/RGO) has been successfully carried out. This study aims to investigate the variation of Co concentration to GO (1, 5, and 10% w/w) on its physicochemical properties. GO precursor was prepared by the Tour method with an oxidizing agent:graphite weight ratio of 3.5. According to the findings of the investigation, in XRD spectra, the reduction treatment succeeded in shifting the diffraction peaks from 10° of GO to ~24° of Co/RGO. In FTIR spectra, the intensity of absorption peaks of O-H and C=O vibrations decreased after reduction. In SAA isotherm, Co-5/RGO material has the largest specific surface area of 109.753 m2 /g with a pore volume of 0.158 cc/g and a pore diameter of 3.469 nm. Thus, this ratio (5% w/w) is the most optimal Co concentration that can be loaded to GO material.

Oxidation and pyrolysis of methyl propyl ether

AbstractThe ignition, oxidation, and pyrolysis chemistry of methyl propyl ether (MPE) was probed experimentally at several different conditions, and a comprehensive chemical kinetic model was constructed to help understand the observations, with many of the key parameters computed using quantum chemistry and transition state theory. Experiments were carried out in a shock tube measuring time variation of CO concentrations, in a flow tube measuring product concentrations, and in a rapid compression machine (RCM) measuring ignition delay times. The detailed reaction mechanism was constructed using the Reaction Mechanism Generator software. Sensitivity and flux analyses were used to identify key rate and thermochemical parameters, which were then computed using quantum chemistry to improve the mechanism. Validation of the final model against the 1–20 bar 600–1500 K experimental data is presented with a discussion of the kinetics. The model is in excellent agreement with most of the shock tube and RCM data. Strong non‐monotonic variation in conversion and product distribution is observed in the flow‐tube experiments as the temperature is increased, and unusually strong pressure dependence and significant heat release during the compression stroke is observed in the RCM experiments. These observations are largely explained by a close competition between radical decomposition and addition to at different sites in MPE; this causes small shifts in conditions to lead to big shifts in the dominant reaction pathways. The validated mechanism was used to study the chemistry occurring during ignition in a diesel engine, simulated using Ignition Quality Test (IQT) conditions. At the IQT conditions, where the MPE concentration is higher, bimolecular reactions of peroxy radicals are much more important than in the RCM.

Incorporating land-use regression into machine learning algorithms in estimating the spatial-temporal variation of carbon monoxide in Taiwan

This paper is the first of its kind to use machine learning algorithms in conjunction with a Land-use Regression (LUR) model for predicting the spatiotemporal variation of CO concentrations in Taiwan. We used daily CO concentration from 2000 to 2016 to develop model and data from 2017 to 2018 as external data to verify the model reliability. Location of temples was used as a predictor to account for Asian culturally specific sources. With the ability to capture nonlinear relationship between observations and predictions, three LUR-based machine learning algorithms were used to estimate CO concentrations, including deep neural network (DNN), random forest (RF), and extreme gradient boosting (XGBoost). The results showed that LUR-based machine-learning model (LUR-XGBoost) has the best computation efficiency and improved adjusted R2 from 0.69 to 0.85. Our studies demonstrate the ability of the LUR-based machine learning algorithms to estimate long-term spatiotemporal CO concentration variations in fine resolution.

Effect of (Ag, Co) co-doping on the structural and antibacterial efficiency of CuO nanoparticles: A rapid microwave assisted method

Abstract In the last decade, a great interest in doped metal oxide nanoparticles (NPs) has been fascinated, particularly, as alternative antibacterial agents due to the spread of multidrug resistant infections. A lot of methods are available for the synthesis of NPs, but the microwave assisted method is facile, rapid, and improving various properties of the synthesized material. To date, little work has been reported to investigate the effectiveness of co-doped CuO NPs synthesized by using microwave energy, against the multidrug resistant pathogens. The aim of present study, therefore, was to synthesize, pure and (Ag, Co) co-doped CuO NPs (Cu1-x-y AgxCoy O) (where x = 0.02 M and y = 0.02, 0.04, 0.06, and 0.08 M, respectively) by rapid microwave assisted method. The prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transforming infrared (FTIR) spectroscopy, and UV–vis (UV–vis) absorption spectroscopy. XRD patterns proved the existence of pure monoclinic crystalline structure of synthesized NPs. Interestingly, the morphology was found to change considerably from nanorods to grain-like then to nanospheres with the variation of Co concentration. The optical band gap was found to be 1.42 eV for pure CuO and increases up to 1.58 eV with increasing cobalt content. The effect of (Ag, Co) co-doping on the antibacterial efficiency of the CuO NPs has been tested against four bacteria, namely, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa.

Tuning of opto-electrical properties of hematite thin films using Co2+ doping

Hematite thin films have attracted widespread interest in recent years because of their advanced electronic and optical properties. Optical and electronic properties of hematite thin films can be enhanced/tuned using doping or additive-based strategies. An application oriented sol–gel method is used for the synthesis of cobalt (Co) doped hematite sol with variation in Co concentration in the range of 0–10 wt%. Hematite phase is observed in undoped thin films annealed at 300 °C under 500 Oe magnetic field for 60 min. Strengthening of hematite phase is observed with increase in Co concentration up to a value of 8 wt%. Bond angle with +ive tilt (i.e. ~ 19.74°) was observed in refined structural parameters for thin films prepared with Co concentration in the range of 0–8 wt%. Higher Co concentration, i.e. 10 wt%, results in decrease in crystallinity of the films along with smaller +ive tilt in bond angle (i.e. ~ 8.82°). High transmission (~ 88%) is observed for thin film prepared using dopant concentration of 8 wt% in the visible and infrared regions. The energy band gap varies from 2.42 to 2.25 eV with variation in Co concentration from 0 to 10 wt%. Relatively smaller band gap values are correlated with defect induced states in the band gap. Spectroscopic ellipsometry is used for calculation of refractive index and high values are indication of high density of thin films. Relatively higher value of dielectric constant (~ 183, log f = 5.0) along with lower value of tangent loss is observed at Co concentration of 8 wt%. Higher grain boundary resistance (1.88 × 105 Ω) was observed at 8 wt% Co concentration. Variation in d.c. conductivity with dopant concentration is studied in detail using Jonscher’s power law. The value of frequency exponent (n) lies in the range of 0.88–0.98 (< 1) with variation in dopant concentration signifying that motion of charge carriers involves translational motion along with sudden hopping process. It is important to mention here that combined tuning of optical and electrical properties are observed in the present study with no change in phase pure hematite crystallographic structure.

Synergistic effect in structural and supercapacitor performance of well dispersed CoFe2O4/Co3O4 nano-hetrostructures

Herein, we report a facile homogeneous urea – assisted hydrothermal approach for the design of CoFe2O4/Co3O4 nano hetrostructure. A variation in Co concentration leads to smartly designed composite material namely CFC-11 and CFC-12 where CFC-12 appreciates the benefits of both CoFe2O4 and Co3O4 nanoparticles. The physico – chemical properties of as developed materials were investigated by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron microscopy (XPS) and Raman spectroscopy. The specific surface area and pore size distribution was determined by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halendo (BJH) respectively. Magnetic measurements via. vibrating sample magnetometer (VSM) demonstrate that saturation magnetization decreases with the incorporation of Co3O4 antiferromagnetic nanoparticles. To explore the utility of as designed nano-hetrostructures as supercapacitor electrodes, we employed cyclic voltammetry (CV) and electrochemical impedence spectroscopy (EIS) measurements. A high specific capacitance of 761.1 F g−1 at 10 mV s−1, admirable cyclic durability of 92.2% and a low resistance value obtained from impedence measurements was observed for CFC-12. The favorable performance demonstrates the synergistic effect of CoFe2O4 and Co3O4 nanoparticles and thus promise an excellent material for energy storage devices.

Numerical simulation of CO distribution discharged by flame-proof vehicle in underground tunnel of coal mine

CO discharged by mine flame-proof vehicles can result in wrong signals to the early-warning system of spontaneous combustion often occurred in coal mines as CO is one of the index gases when forecasting and early warning coal spontaneous combustion in underground mine. Traditional method is to install sensors in the air intake system to monitor the CO concentration. In the present paper, a number of CO distribution simulations are performed using commercial FLUENT software. When a mine flame-proof vehicle running at a speed of 7 m s−1 in an underground tunnel while the inlet velocity of roadway is 3 m s−1, dynamic distribution of CO concentration discharged by mine flame-proof vehicle within t = 1–5 s is obtained, and variation of CO concentration on static monitoring points is obtained at the same time while simulating. The simulation results indicate that: the region of CO concentration greater than 0.0024% was in the scope from vehicle tailgate to the back which is irregular shapes, and it reduces to less than 0.0024% in short time, about 1 s. In front of the vehicle CO concentration is always a fixed value or even lower than 0.0019%. For comparative analysis, 4 monitoring points are arranged to monitor the CO concentration in actual underground roadway. And the actual measured data verified the correctness of numerical simulation data.

Inclusion of surface heterogeneity in bridging PEM fuel cell electrode contamination kinetics and transport via a competitive Langmuir-Freundlich isotherm

This paper reports the development of mathematical model that bridges PEMFC transport phenomena with surface reaction kinetics in rough and heterogeneous electrodes, in which specifically the anode is modeled under carbon monoxide contamination. The mathematical bridging is done by converting surface concentration of reactants and contaminant into surface coverage of relevant adsorbates using the Langmuir-Freundlich isotherm to statistically include heterogeneity in binding site energetics. Thermodynamically optimized kinetic rate and equilibrium constants are calculated using coverage-dependent activation energies and provided as input to the HOR, ORR, and a kinetic-based limiting current model developed to solve for the distribution of activation overpotential. A novel model for a closed-form calculation of activation overpotential is proposed to allow numerical investigation via a galvanostatic approach. The kinetic reaction models are highly coupled with three-dimensional transport equations and solved iteratively under single-phase and steady-state conditions. Comparison is done with respect to two sets of available literature data in order to test the kinetic model validity under variation of CO concentrations and cell operating temperatures, in which good agreement is found. The results confirm that a Langmuir-Freundlich isotherm could be a more suitable isotherm compared to the extensively used Langmuir-specific isotherm for rough heterogeneous surfaces physically found in PEMFC catalysts. Results from the model show that rate of HOR is higher under the ribs of the cell since most of the active sites under channel are blocked with CO, with the effect exacerbated at lower temperatures.

Optical and magnetic properties of Co-doped CuO flower/plates/particles-like nanostructures.

In this study, pure and Co-doped CuO nanostructures (0.5, 1.0, 1.5, and 2.0 at wt% of Co) were synthesized by microwave combustion method. The prepared samples were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). Powder X-ray diffraction patterns refined by the Rietveld method indicated the formation of single-phase monoclinic structure. The surface morphology and elemental analysis of Co-doped CuO nanostructures were studied by using HR-SEM and EDX. Interestingly, the morphology was found to change considerably from nanoflowers to nanoplates then to nanoparticles with the variation of Co concentration. The optical band gap calculated using DRS was found to be 2.1 eV for pure CuO and increases up to 3.4 eV with increasing cobalt content. Photoluminescence measurements also confirm these results. The magnetic measurements indicated that the obtained nanostructures were ferromagnetic at room temperature with an optimum value of saturation magnetization at 1.0 wt.% of Co-doped CuO, i.e., 970 micro emu/g.

Sketching functional, ubiquitous ZnO nano-sensors on paper

We report the fabrication of functional nanoelectronic sensors on regular copy paper by simply sketching electrode lines and painting the resistively sensing nanostructured film using synthesized zinc oxide (ZnO) nanoparticle (NP) inks. A repeatable three orders of magnitude increase in conductance is demonstrated when the sensors are exposed to 30 s long 1220 μW cm−2 ultra-violet (UV) irradiation pulses in the dark with a 6 s and 3 s rise and recovery times, respectively. Moreover, a 200% increase in current is also observed at room temperature, when these sensors are exposed to successive pulses of pure CO. The sensors exhibit a fast response to variations in concentration of CO as small as a 1% volume change. The sensitivity to CO concentration can be significantly improved by using UV irradiation. This work shows that sketching of metal oxide nanostructures with controlled nanoscale properties on paper can be employed for fabrication of accurate and reliable sensors that can find applications in ubiquitous environmental sensing, electronic paper, wearable electronics, and sensor networks.

Kinetic analysis of co formation under oxy-combustion conditions

The paper reports the results of numerical computations concerning the formation of CO in the kinetic flame during natural gas oxy-combustion. The effect of temperature, reagent residence time and the composition of an atmosphere containing CO2 with 21 and 29 vol % O2 on the variation of CO concentration in the flame was examined. The oxy-combustion process was conducted with a 25 % excess oxygen. The analysis of reactions in flames at temperatures of 1500 K and 1800 K was performed within the Chemked II program using the combustion mechanism proposed by Mendiara & Glarborg, which includes 779 reactions. The computation results have confirmed that the rate of the key reactions responsible for the production of CO in the flame depends on the flame temperature and the oxy-combustion temperature. The peak CO concentrations are higher for the oxidizing mixture containing 29 vol % O2. After attaining a maximum, the CO flame concentration drops faster for an atmosphere richer in oxygen. The longer the time of reagent residence in the flame region, the lower the CO concentration. In different atmospheres and at different combustion temperatures, an identical CO level can be achieved in wet combustion gas. Irrespective of the temperature and atmosphere of oxy-combustion, most CO is produced as a result of the reaction OH + CO HCO2. The reduction of oxygen in the oxidizing atmosphere at flame temperatures of 1500 and 1800 K lowers the CO production in the dominant reactions responsible for CO formation. The contribution of individual reactions in the CO production for the identical atmospheres is different with varying temperature. In the case of the reaction HCO + O2 HO2 +CO, the temperature increase reduces the CO production. A reverse dependence of CO production on temperature characterizes the reaction H2 + CO + M CH2O + M. In addition, change in temperature changes the order in which the dominant reactions occur. Within the residence time equal to 100 ms, two periods of intensified CO production and consumption can be identified. The peak concentrations of H, OH and O radicals in the flame attain a maximum within the same time; as time goes by, the highest concentration is achieved by OH radicals. The presence of considerable levels of CO2 in the combustion substrates has an inhibiting effect on the natural gas oxidation process.

Analysis of long-term variation in CO concentration and emission source contribution based on a tagged transport model

Analysis of long-term variation in CO concentration and emission source contribution based on a tagged transport model

Air pollution forecasting in Ankara, Turkey using air pollution index and its relation to assimilative capacity of the atmosphere

Spatial and temporal variations in concentrations of CO, NO, NO(2), SO(2), and PM(10), measured between 1999 and 2000, at traffic-impacted and residential stations in Ankara were investigated. Air quality in residential areas was found to be influenced by traffic activities in the city. Pollutant ratios were proven to be reliable tracers to differentiate between different sources. Air pollution index (API) of the whole city was calculated to evaluate the level of air quality in Ankara. Multiple linear regression model was developed for forecasting API in Ankara. The correlation coefficients were found to be 0.79 and 0.63 for different time periods. The assimilative capacity of Ankara atmosphere was calculated in terms of ventilation coefficient (VC). The relation between API and VC was investigated and found that the air quality in Ankara was determined by meteorology rather than emissions.

Total gaseous mercury concentrations at the Cape Point GAW station and their seasonality

Total gaseous mercury (TGM) has been measured at the WMO Global Atmosphere Watch (GAW) station at Cape Point, South Africa, since September 1995, representing the only long term TGM measurement in the Southern Hemisphere (SH) so far. Annual medians suggest a small but significant decrease of TGM concentrations from 1.29 ng m−3 in 1996 to 1.19 ng m−3 in 2004. Background TGM concentrations at Cape Point varied seasonally, with a summer maximum and a winter minimum. Comparison with the seasonal variation of CO concentrations in both hemispheres calls into question the influence of mercury sink by the Hg0 + OH reaction. If confirmed at other sites in the SH, the observed TGM seasonal variation may pose an important constraint on the global models of atmospheric mercury.

Spatial variation of CO concentrations within an office building and outdoor influences

This paper presents the results of a monitoring study to assess the spatial variation of CO concentrations within the Westminster City Council building, an office building close to two busy roads in Central London. In general, CO concentrations and correlations with outdoor CO were found to decrease both horizontally and vertically throughout the building away from the busy roads, while the time delay between outdoor and indoor peaks generally increased. This indicates that, within a building, the protection afforded by the building shell to outdoor pollution may be increased away from busy roads. Additionally, the local meteorological conditions were observed to influence significantly the CO concentrations. In particular, south-easterly winds resulted in the highest indoor and outdoor levels, although the highest I/O ratios were for north-westerly winds.

Mineral chemistry of sphalerite and galena from Pb-Zn mineralization hosted by the Transvaal Supergroup in Griqualand West, South Africa

The relative and absolute abundance of minor and trace elements in ore-forming sphalerite and galena can yield important constraints regarding the metallogenesis of carbonate-hosted Pb-Zn deposits. This contribution presents an extensive set of mineral chemical data for sphalerite and galena from two deposits and several subeconomic occurrences of Pb-Zn mineralization in the Transvaal Supergroup on the Ghaap Plateau in Griqualand West. Significant differences are recognised between different localities and different styles of mineralization, but results obtained compare rather well with literature data of Phanerozoic Mississippi Valley-type deposits. Fe and Cd constitute the two most important minor constituents in sphalerite from the Ghaap Plateau. Average concentrations vary between 0.54 weight % and 3.21 weight % for Fe and 0.13 weight % and 0.67 weight % for Cd. A first order correlation exists between average Fe/Mn ratios in sphalerite and host rock lithologies, while variations in concentrations of Co (7 to 177ppm), Ni (9 to 21ppm), Ga (2 to 99ppm) can only tentatively be attributed to differences in mineralization style, host rock, and metal source. Compared to sphalerite, trace element contents, in galena are very low with only Cd and Ag occurring in concentrations that consistently exceed 10ppm. Concentrations of more than 1000ppm Ag are reported for structurally-controlled Pd-rich subeconomic breccia runs close to the Griquatown fault zone.

Development of FBR measurement of char reactivity to carbon dioxide at elevated temperatures

Gasification kinetics of char is thought as a key factor in designing and operating gasifiers. The widely used present technique, TGA method, is limited in temperature and heating rate ranges. A fluidized bed reactor (FBR) method is described which is suitable for measuring char reactivity at elevated temperatures up to 1873 K by using CO 2 as the gasifying agent. It is capable of carbonizing coal samples under various conditions including rapid heating as well as slow heating, and in-situ measuring char gasification rate directly after carbonization. Char reactivity is evaluated from the time variation of CO concentration in the exit gas. The heterogeneous global model, incorporated with the two-phase model, is used to describe the reaction of chars. On the basis of the model, the film mass transfer resistance and the bubble-emulsion mass transfer resistance are calculated and their influence on the measured results is assessed. Proper selection of operating parameters for assuring reasonable measurement is discussed. Data processing methods have been developed to give fundamental, quantitative measurements of char reactivity, allowing direct comparison of reactivity between chars.

The effect of commuting microenvironment on commuter exposures to vehicular emission in Hong Kong

Vehicular exhaust emission has gradually become the major air pollution source in modern cities and traffic related exposure is found to contribute significantly to total human exposure level. A comprehensive survey was conducted from November 1995 to July 1996 in Hong Kong to assess the effect of traffic-induced air pollution inside different commuting microenvironments on commuter exposure. Microenvironmental monitoring is performed for six major public commuting modes (bus, light bus, MTR, railway, tram, ferry), plus private car and roadside pavement. Traffic-related pollutants, CO, NO x , THC and O 3 were selected as the target pollutants. The results indicate that commuter exposure is highly influenced by the choice of commuting microenvironment. In general, the exposure level in decreasing order of measured pollutant level for respective commuting microenvironments are: private car, the group consisting light bus, bus, tram and pavement, MTR and train, and finally ferry. In private car, the CO level is several times higher than that in the other microenvironments with a trip averaged of 10.1 ppm and a maximum of 24.9 ppm. Factors such as the body position of the vehicle, intake point of the ventilation system, fuel used, ventilation, transport mode, road and driving conditions were used in the analysis. Inter-microenvironment, intra-microenvironment and temporal variation of CO concentrations were used as the major indicator. The low body position and low intake point of the ventilation system of the private car are believed to be the cause of higher intake of exhaust of other vehicles and thus result in high pollution level in this microenvironment. Compared with other metropolis around the world and the Hong Kong Air Quality Objectives (HKAQO), exposure levels of commuter to traffic-related air pollution in Hong Kong are relatively low for most pollutants measured. Only several cases of exceedence of HKAQO by NO 2 were recorded. The strong prevailing wind plus the channeling effect created by the harbor, the fuel used, the relative abundance of new cars and the successful implementation of the vehicle emission control program are factors that compensate the effect of the emission source strength and thus lead to low exposure levels.

Instrumental neutron activation analysis of ferromanganese oxide encrustations of Indian Ocean by the k0 NAA method

Three ferromanganese crusts from different locations of the Indian Ocean were analysed by neutron activation analysis using thek0 method (k0 NAA method) for studying the distribution of some trace elements along with Fe and Mn. Another crust from the Lau basin of the Pacific Ocean was investigated for comparison of the influence of different oceanic conditions on the trace element distributions in ferromanganese crusts. Variation in Co concentration along with the Mn/Fe ratio were discussed in terms of the hydrogenous/hydrothermal nature of the crusts. The normalised REE content was used to identify possible anomalies. The observed Ce anomaly is discussed in the light of the depositional environment. The precision and accuracy of the method were confirmed by measuring the elemental concentrations in a USGS nodule standard NOD A-1.

Carbon monoxide and methane distribution and consumption in the photic zone of the Sargasso Sea

Spatial and temporal distributions of carbon monoxide and methane along with microbial oxidations of these substances were examined on three cruises to the highly oligotrophic southeastern Sargasso Sea between June 1986 and May 1987. Dissolved CO profiles were similar to those reported by previous researchers, with the highest concentrations in the near-surface waters (0–20 m). CO concentrations ranged from 5.8 nM in the photic zone to 0.1 nM in the aphotic zone. CO concentrations decreased steadily throughout the rest of the water column. CH 4 concentrations were more uniform in their distribution and typically decreased only slightly in the top 500 m of the water column. The microbial oxidation rates of both CO and CH 4 were extremely slow when compared with more productive waters. Turnover times for CO ranged from 25 to 2922 h while those for CH 4 ranged from 5 to > 100 years. These low oxidation rates may explain why no discernible diurnal variation in CO concentration was observed and why CH 4, which is usually more conservative than CO, and CO distributions were similar during the June 1986 cruise. Ratios of CH 4/CO oxidation indicate that the ammonium oxidizing bacteria could be responsible for much of the CO and CH 4 oxidation in these waters. Due to the long turnover times for CO and CH 4, the oxidation of these trace gases by bacteria is unlikely to represent a significant link within the carbon cycle in these highly oligotrophic waters.