Papers by Keyword: No₂

Abstract: The sensing characteristics of pristine, Ni-doped, and C-vacancy graphene towards CO and NO₂ gas molecules were studied using density functional theory (DFT). The adsorption energies, electronic properties, charge transfer, and stable geometries were calculated to evaluate the gas-surface interaction mechanisms. Both pristine and vacancy graphene have smaller CO and NO₂ adsorption energies and charge transfer than the Ni-doped graphene, whereas the adsorption energy on Ni-doped vacancy graphene is higher than that of Ni-doped graphene. The results indicate that both CO and NO₂ gas molecules only attach to pristine graphene through weak physical adsorption. Stronger chemisorption occurs when the gas molecules adsorb on the surface of vacancy, Ni-doped, and Ni-doped vacancy graphene. Additionally, the results demonstrated that Ni-doped vacancy graphene has higher sensitivity and selectivity towards the NO₂.

Abstract: Lichen or commonly known as symbiotic organism lies between fungi and algae. It is a non vascular simple organism and it is very sensitive to environmental conditions. The research method used was an exploration. It was then continued with the analysis of the pollutant uptake test by a spectrophotometer. To determine the sampling point, the purposive sampling technique was used. The study was divided into 3 main areas based on the environmental differences, namely urban, suburban and forest. There were about 30 trees sticked by corticolous lichens. The pollutant parameters measured were SO2 (sulfur dioxide) and NO2 (nitrogen dioxide). The air quality data were the secondary data such as NO2 and SO2 ambient air that issued by the Environmental Services (DLH) of Surakarta Government Central Java Indonesia. The range of NO2 ambient content in the research locations, namely in the city of Surakarta and the suburban of Jaten Karanganyar was still below the Ambient Air Quality Standards (ABML) issued by the Government, which ranged from 4.29 - 49.72 μg / Nm3.3. The Quality Standard values for ambient NO2 were 316 and μg / Nm3. At the same time, the ambient SO2 values ranged from 0.153 to 36.74 μg / Nm3, still below the threshold of Ambient Air Quality Standards for SO2 issued by the Government on 632 μg / Nm3. The values for SO2 content in the lichen thalli ranged from 0.17 to 4.05 and it was from 0.773 to 4.03 for the NO2 content. The SO2 and NO2 content values in the lichen thalus found in lichens that grow in urban areas are the highest than in urban and forest suburbs. There is a content of pollutant compounds that are identical between thalus lichen and pollutants in the atmosphere (ambient air) so that lichen thalus is able to absorb pollutant compounds in the atmosphere which can be characterized by the morphological characters of thalli that live in urban, suburban and forests. We will be able to publish your paper in electronic form on our web page http://www.scientific.net if the paper format and the margins are correct. Your manuscript will be reduced by approximately 20% by the publisher. Please keep this in mind when designing your figures and tables, etc.

Abstract: Most of the recent reduced graphene oxide (rGO) based sensors shows gas sensitivity above 50^o to 150°C. The present investigation deals with the gas sensing at 50°C temperature. In the present research work, thick film sensors of rGO were developed on glass substrate by using standard screen-printing technique. The silver paste of rGO was used to make electrodes for contact on thick films for the electrical and gas sensing system. The electrical properties of rGO thick films such as resistivity, activation energy and temperature coefficient were studied. The resistivity of rGO thick films was found to be 84.84 Ω/m. The morphological, elemental and structural properties of rGO thick films were analyzed by SEM, EDS and XRD techniques respectively. The crystallite size of rGO thick films was found as 28.42 nm by using Scherer’s formula. The rGO thick films were prepared and exposed to Ethanol, NH₃, NO₂ and LPG gases to determine sensitivity and selectivity. The sensitivity of NO₂ has been found to be maximum among other exposed gases. The maximum sensitivity of NO₂ gas was 92.55 % at 50 °C found with fast response (~ 11 sec) and recovery (~ 19 sec) time.

Abstract: It is necessary to develop NO₂ gas sensors as NO₂ is a pollutant. While, different from the reducing gases, oxidizing gas NO₂ will put up a complicated sensing process. Density functional theory (DFT) calculations are necessary to be performed to understand NO₂-sensing mechanisms at the atomic level. In this study we introduce NO₂ to SnO₂ (110) surface with oxygen species pre-adsorbed. The results show that NO₂ sensing mechanism of SnO₂ surface strongly depends on the concentration of oxygen in the ambient atmosphere (usually, no effects of temperature and pressure are considered). The direct interactions between NO₂ molecule and SnO₂ sub-reduced surface (with two rows of fold-coordinated bridging oxygens removed) for very low oxygen concentrations show that, NO₂ gas molecules interact directly with Sn instead of reacting with oxygen species, resulting in an increase in resistance of SnO₂. We investigate gas-sensing processes of interaction between NO₂ molecule and SnO₂ surface with pre-adsorbed oxygen species for the case of considerable high oxygen concentrations. Adsorbed molecular oxygen ions compete with adsorbing NO₂ molecules for available surface sites and electrons from the SnO₂. As the availability of oxygen ions on the SnO₂ surface increasing, the interaction between NO₂ and adsorbed oxygen species give rise to a reducing interaction, which brings a decrease in resistance of SnO₂.

Abstract: The objective of this study is to develop a mathematical model, which can describe the response of a single-wall carbon nanotube (SWNT) as a resistive NO₂ sensor, based on the acquired experimental data. The obtained non-linear regression attempts to simulate and predict the sensor response taking into account the effect of different variables such as NO₂ concentration and operating temperature. The results show that the developed mathematical equation expresses the sensor response as a function of time, gas concentration, and temperature with an R-squared value ranging between 0.65 and 0.97.

Abstract: In this work, SnO₂ porous nanosolids were obtained from SnO₂ nanopowders by using a solvo-thermal hot-press method. Then, by using the conventional thick-film sensors preparation technology, SnO₂ porous thick-film gas sensor was prepared from it. Meanwhile, polyaniline (PANI) was synthesized by chemical oxidation polymerization. After that, by mechanical method, the SnO₂/PANI composite gas sensors were fabricated. The intrinsic resistances and gas sensing properties of sensors to NO₂, NH₃, H₂ and ethanol vapor were tested. Compared with the SnO₂ porous gas sensors, the optimum operation temperature of SnO₂/PANI hybrid gas sensors decreased dramatically. And SnO₂/PANI hybrid gas sensors showed satisfying selectivity and high sensitivity for NO₂.

Abstract: In this paper, the gas sensors using WO₃ as sensitive electrode, Pt mixed potential as the reference electrode was researched. The structures and preparation methods of the sensors were introduced. Besides, the sensitive materials, the electrode surface and the section morphologies were characterized by means of SEM and EDS. Furthermore, the sensing properties of the as-fabricated sensors were examined under different NO_X concentrations and temperatures (500°C, 550°C and 600°C). The results revealed that the response signal become smaller with the temperature increasing, and stronger with the increasing of the NO₂ concentration.

Abstract: Air pollution causes health problem. The paper simply analyzed the changes of air quality in the Yuxi city urban area from 2006 to 2012. In the Yuxi city urban area between 2006 and 2012, SO₂ levels increased about 43.9 percent; NO₂ levels increased about 13.3 percent; PM10 levels in 2012 decreased about 1.5 percent. By evaluating the air quality in the Yuxi city urban area, the results showed that air quality index was the maximum in 2009, and the quality of the air in Yuxi became worse from 2006 to 2012, air pollution in 2009 was the heaviest between 2006 to 2012. After adopting P.R.C EPA air quality standards (GB3095-2012) in 2013, the first air pollutant in Yuxi is PM₁₀, and then it is SO₂ among SO₂, NO₂ and PM₁₀.Much should beend done to reduce the amount of PM₁₀ and SO₂ released.

Abstract: The Changsha city of Hunan province was selected as study area to monitor the concentrations of PM_2.5 and NO₂ in ambient air automatically. The correlation relationship between PM_2.5 and NO₂ was also analyzed. Results showed that the concentrations of PM_2.5 and NO₂ changed significantly with seasons, and they manifested the same change trend, as winter > autumn > spring > concentration in summer. In a day, the lowest concentration of NO₂ generally appeared in the afternoon. However, the present time of lowest and the peak values of PM_2.5 concentration were uncertain. The highest concentration of NO₂ was in the business district, and the distribution of PM_2.5 concentration did not have an obviously regional. Furthermore, the PM_2.5 and NO₂ concentration changed in positive correlation, and these two were easy to produce pollution overlay. On the whole, the main seasons to control PM_2.5 and NO₂ were winter and autumn.

Abstract: Thin-film diode structure is MgAl/PbPc/Cu if lead phthalocyanine is taken as organic semiconductor gas-sensing material with methods such as vacuum thermal evaporation or magnetron sputtering. Use Keithley 4200 semiconductor instrument and Gas-sensing measurement system to analyze gas-sensing characteristic of Schottky diode device, the sensitive degree of NO₂ with different density can be compared through theoretical analysis of measured current and voltage data. The measurement result shows: when the device is placed in 10ppm NO₂ environment, after 74 minutes, forward current is decreased by 65 times, the corresponding MgAl/PbPc Schottky barrier height rises about 20meV. Reversed current of the device is 4 times larger because the increase of minority carrier electron number in PbPc thin-film is being absorbed by NO₂.