Temperature Carbon Monoxide Research Articles

The emission of CO from tropical rainforest soils

Abstract. Soil carbon monoxide (CO) fluxes represent a net balance between biological soil CO uptake and abiotic soil and (senescent) plant CO production. Studies largely from temperate and boreal forests indicate that soils serve as a net sink for CO, but uncertainty remains about the role of tropical rainforest soils to date. Here we report the first direct measurements of soil CO fluxes in a tropical rainforest and compare them with estimates of net ecosystem CO fluxes derived from accumulation of CO at night under stable atmospheric conditions. Furthermore, we used laboratory experiments to demonstrate the importance of temperature on net soil CO fluxes. Net soil surface CO fluxes ranged from −0.19 to 3.36 nmol m−2 s−1, averaging ∼1 nmol CO m−2 s−1. Fluxes varied with season and topographic location, with the highest fluxes measured in the dry season in a seasonally inundated valley. Ecosystem CO fluxes estimated from nocturnal canopy air profiles, which showed CO mixing ratios that consistently decreased with height, ranged between 0.3 and 2.0 nmol CO m−2 s−1. A canopy layer budget method, using the nocturnal increase in CO, estimated similar flux magnitudes (1.1 to 2.3 nmol CO m−2 s−1). In the wet season, a greater valley ecosystem CO production was observed in comparison to measured soil valley CO fluxes, suggesting a contribution of the valley stream to overall CO emissions. Laboratory incubations demonstrated a clear increase in CO production with temperature that was also observed in field fluxes, though high correlations between soil temperature and moisture limit our ability to interpret the field relationship. At a common temperature (25 °C), expected plateau and valley senescent-leaf CO production was small (0.012 and 0.002 nmol CO m−2 s−1) in comparison to expected soil material CO emissions (∼ 0.9 nmol CO m−2 s−1). Based on our field and laboratory observations, we expect that tropical rainforest ecosystems are a net source of CO, with thermal-degradation-induced soil emissions likely being the main contributor to ecosystem CO emissions. Extrapolating our first observation-based tropical rainforest soil emission estimate of ∼ 1 nmol m−2 s−1, global tropical rainforest soil emissions of ∼ 16.0 Tg CO yr−1 are estimated. Nevertheless, total ecosystem CO emissions might be higher, since valley streams and inundated areas might represent local CO emission hot spots. To further improve tropical forest ecosystem CO emission estimates, more in situ tropical forest soil and ecosystem CO flux measurements are essential.

Effect of tin content on TiO2-supported platinum-tin bimetallic catalysts for low temperature CO oxidation reaction

Removal of carbon monoxide (CO) is a significant issue in fuel processing for the production of hydrogen. Bimetallic platinum-tin catalysts are well-known as efficient catalysts for oxidation process due to their synergistic bi-functional mechanism, their ability to dissociate molecular oxygen at low temperature, and their capacity to adsorb both atomic oxygen and CO. In this study, we synthesized titanium dioxide supported platinum-tin bimetallic catalysts for low temperature CO oxidation process with different amount of tin. Titanium dioxide provided oxygen to active sites due to its abundant oxygen vacancies and prevented metal sintering of active platinum nanoparticles. We confirmed that our titanium dioxide supported platinum-tin bimetallic catalysts showed excellent performance for low temperature CO oxidation. Moreover, the amount of tin on titanium dioxide affected the adsorption behaviors of CO and O2, resulting in the difference in catalytic activity of Pt based catalysts.

Influence the performances of hopcalite catalysts by the addition of gold nanoparticle for low temperature CO oxidation

The catalytic conversion of carbon monoxide (CO) into carbon dioxide (CO 2 ) at a low temperature is very important procedure for all living beings present in the environment. The present study represents that the addition of gold (Au) nano-particles, by the deposition-precipitation method into the hopcalite (CuMnOx) catalyst has been improving their performances for CO oxidation. The CuMnOx catalyst loading by 0.75 wt% Au was representing that the best catalytic activity for CO oxidation than the other catalysts loading by 0.25, 0.5 and 1 wt% Au. The small amount of Au doping (0.75 wt%) in CuMnOx catalyst improves their performances for CO oxidation at an ambient conditions. The gold nano-particles will be introducing the new active sites into the CuMnOx catalyst surfaces and decreases the deactivation of catalyst. The lattice oxygen movement was a major important factor which can influences the performances of hopcalite catalyst for CO oxidation. The calcinations strategies (reactive calcinations and traditional calcinations) of the precursor have huge impacts on the performances of resulting catalysts. The reusability of Au promoted CuMnOx catalyst was also measured and found that this catalyst does not have any major changes in its catalytic performances still after the reuses.

Controlling surface chemistry of CO reactions on Fe surface by S blocking: A first-principles and microkinetic studies

A combination of plane waves first principles approach and microkinetics are employed to study the energetic and kinetics of Fe (110) surface with adsorbates such as carbon monoxide (CO), sulfur (S) and their co-adsorption (CO+S), aiming to investigate the effect of S as an inhibiting agent in the adsorption and dissociation of CO. The structural properties as well as the adsorption energetics of these systems are calculated and analyzed. The presence of sulfur adsorbate on the iron surface is found to reduce the adsorption energy of CO on Fe (110) surface hence lowering its the sticking probability in the surrounding of the adsorbate. Results from our microkinetic model provide insights into how factors such as temperature and partial pressure can be tuned to control the reaction of CO on Fe surface. The calculated kinetic results show that CO adsorbs on the iron surface in molecular state up to 440 K, beyond this threshold temperature CO starts to dissociate into C and O atoms. The introduction of sulfur adsorbate on iron surface increases the threshold of CO dissociation temperature to 480 K emphasizing its impact on the reactivity of carbon monoxide on Fe (110) surface due to the sulfur blocking effect. Finally, we demonstrate that the range of sulfur blocking effect on controlling surface chemistry of CO reactions on Fe surface to be long ranged with respect to the simulation model adopted in this work.

The short-term associations of chronic obstructive pulmonary disease hospitalizations with meteorological factors and air pollutants in Southwest China: a time-series study

Chronic obstructive pulmonary disease (COPD) is the fourth major cause of mortality and morbidity worldwide and is projected to be the third by 2030. However, there is little evidence available on the associations of COPD hospitalizations with meteorological factors and air pollutants in developing countries/regions of Asia. In particular, no study has been done in western areas of China considering the nonlinear and lagged effects simultaneously. This study aims to evaluate the nonlinear and lagged associations of COPD hospitalizations with meteorological factors and air pollutants using time-series analysis. The modified associations by sex and age were also investigated. The distributed lag nonlinear model was used to establish the association of daily COPD hospitalizations of all 441 public hospitals in Chengdu, China from Jan/2015–Dec/2017 with the ambient meteorological factors and air pollutants. Model parameters were optimized based on quasi Akaike Information Criterion and model diagnostics was conducted by inspecting the deviance residuals. Subgroup analysis by sex and age was also performed. Temperature, relative humidity, wind and Carbon Monoxide (CO) have statistically significant and consistent associations with COPD hospitalizations. The cumulative relative risk (RR) was lowest at a temperature of 19℃ (relative humidity of 67%). Both extremely high and low temperature (and relative humidity) increase the cumulative RR. An increase of wind speed above 4 mph (an increase of CO above 1.44 mg/m3) significantly decreases (increases) the cumulative RR. Female populations were more sensitive to low temperature and high CO level; elderly (74+) populations are more sensitive to high relative humidity; younger populations (< = 74) are more susceptible to CO higher than 1.44 mg/m3. Therefore, people with COPD should avoid exposure to adverse environmental conditions of extreme temperatures and relative humidity, low wind speed and high CO level, especially for female and elderly patients who were more sensitive to extreme temperatures and relative humidity.

To optimized various parameters of Hopcalite catalysts in the synthetic processes for low temperature CO oxidation

Carbon monoxide (CO) is very poisonous gasses present in the atmosphere and lower temperature complete oxidation of CO is very important processes for all life support. The automobile vehicles exhaust is one of the major sources of CO produced into the environment. The application of catalytic converter in automobile vehicles reduces the toxic gasses emission. There are lots of catalysts used in the catalytic converter for CO oxidation purposes among these catalysts the Hopcalite (CuMnOx) is one of the oldest and best-known catalysts for low temperature CO oxidation. The hopcalite catalyst is prepared by the co-precipitation method and preparation parameters like magnetic shaker shaking speed, shaking time, shaking temperature and pH has an influence on the activity of resultant catalysts. The activity of catalyst was measured in reactive calcinations (RC) conditions at the presence of (1.5% CO) and air. The reaction temperature was increased from room temperature to higher temperature at which the total oxidation of CO was achieved. The characterizations of catalysts are done by several techniques like XRD, FTIR, BET and SEM-EDX. These results are interpreted in terms of structure the active catalyst. The reusability of CuMnOx catalyst was also tested and also found that this catalyst does not show any high level of significant change in its catalytic performances even after reuses.

Design of a five-bar linkage for an automated power window

Recently designed passenger vehicles with heightened features are entering the market every year. One of them is the power window which enables the fast movement of window-panes. Not opening of window-pane in an emergency is responsible for the death of passengers in some cases. Deaths of children, the disabled or older person have been reported due to carbon monoxide(CO) poisoning. Simultaneously, they were allowed to stay inside a static, locked car in the absence of other assisting occupants. Fatal injuries have also been reported repeatedly due to the sinking of the vehicle in a water body. In this paper, the design of an automatic opening mechanism is discussed for a car window during such crises.In this system, the temperature sensor, Carbon-monoxide sensor and water pressure sensor are placed inside a car cabin to monitor the temperature range, CO levels and water pressure continuously. In case of high internal temperatures or raised carbon monoxide in the cabin due to incomplete fuel combustion or excessive heat or vehicle rested under the Sun for long, or if the vehicle is subjected to pressure by flowing or static water, the sensors send signals to the motor controlling power window to slide it down. It also sends a warning message to the registered mobile phone of the vehicle owner.

Carbon monoxide poisoning: a prediction model using meteorological factors and air pollutant

BackgroundWhile the influence of meteorology on carbon monoxide (CO) poisoning has been reported, few data are available on the association between air pollutants and the prediction of CO poisoning. Our objective is to explore meteorological and pollutant patterns associated with CO poisoning and to establish a predictive model.ResultsCO poisoning was found to be significantly associated with meteorological and pollutant patterns: low temperatures, low wind speeds, low air concentrations of sulfur dioxide (SO2) and ozone (O38h), and high daily temperature changes and ambient CO (r absolute value range: 0.079 to 0.232, all P values < 0.01). Based on the above factors, a predictive model was established: “logitPj = aj - 0.193 * temperature - 0.228 * wind speed + 0.221 * 24 h temperature change + 1.25 * CO - 0.0176 * SO2 + 0.0008 *O38h; j = 1, 2, 3, 4; a1 = -4.12, a2 = -2.93, a3 = -1.98, a4 = -0.92.” The proposed prediction model based on combined factors showed better predictive capacity than a model using only meteorological factors as a predictor.ConclusionLow temperatures, wind speed, and SO2 and high daily temperature changes, O38h, and CO are related to CO poisoning. Using both meteorological and pollutant factors as predictors could help facilitate the prevention of CO poisoning.

Highly Sensitive Room Temperature CO Gas Sensor Based on MWCNT-PDDA Composite

In this work, a resistive sensor based on multiwalled carbon nanotube (MWCNT) - poly(diallyldi- methylammonium chloride) solution (PDDA) composite is proposed for highly sensitive carbon monoxide (CO) detection at room temperature. The surface of MWCNTs is functionalized with PDDA, and the functionalization is investigated by Fourier transform infrared and Raman spectroscopy. The MWCNT-PDDA composite is used as a sensing material with deposited interdigitated electrodes (IDE) of silver (Ag) on glass substrates. The resistance of the sensors changes due to charge transfer from CO to the positively charged quaternary ammonium group present on PDDA. The developed sensors are able to detect very low concentrations of CO gas ranging from 1 to 20 ppm with high sensitivity and limit of detection (LOD) of 127 ppb. The interference of other gases and volatile organic compounds is investigated, and the results are presented. The influence of humidity and temperature on the sensors is also explored. The stability and repeatability of the sensors are examined, and the sensors are almost stable for 2 months with excellent reproducibility. The sensors also follow the Langmuir adsorption/desorption model. The sensors have shown excellent potential for rapid CO gas sensing, and it can be used in wearable electronics applications.

Synthesis and applications of titanium oxide catalysts for lower temperature CO oxidation

Carbon monoxide (CO) is one of the very poisonous gasses and major sources of CO produced into the environment by the automobile vehicles exhaust. There are various types of catalysts have been used in the catalytic converter for CO oxidation. The titanium dioxide (TiO2) is one of the best transitional metal oxides catalysts for lower temperature CO oxidation. A small amount of TiO2 was deposited on the mesoporous Al2O3 using atomic layer deposition and subsequent oxidation at the different temperatures. The lightly reduced support improves the high catalytic activity of the adparticles, a strongly reduced one quenches the CO oxidation. The quenching is due to thermally activated diffusion of Ti3+ interstitials from the bulk to the surface where they deplete the oxygen adsorbed onto the clusters by the formation of TiOx (x ​≃ ​2) structures. The additions of promoters and support in titanium oxide catalysts improved their performances and reduced their stability. The bulk reduction state of TiO2 strongly affects the catalytic activity of supported metal clusters in the chemical reactions between oxygen and other molecules. The certain attention has been paid on the recovery of TiO2 catalysts from reaction systems and their reuse for various times without losses of catalytic activity in CO oxidation. This investigation will shown scientific basis for potential design of Ti-oxide nano-particle catalysts for lower temperature CO oxidation.

Synthesis of Hopcalite catalysts by various methods for improved catalytic conversion of carbon monoxide

The conversion of carbon monoxide (CO) at ambient condition is major procedure for human life protection. The Hopcalite (CuMnOx) is one of the best known catalysts for lower temperature CO conversion. The synthesis of hopcalite catalysts by various methods including Co-precipitation (CP), Sol-gel (SG), Reactive grinding (RG), Impregnation (I) and Pyrolysis (P) highly effects on the performance of final catalysts for CO conversion. In this experimental work various types of hopcalite catalysts prepared by various methods (CP, SG, RG, I, and P) followed by calcination in reactive (CO-air) mixture and traditional calcination conditions. The performance of different hopcalite catalysts for CO conversion reaction was as follows: CuMnCP > CuMnRG > CuMnSG > CuMnP > CuMnI. The Co-precipitation method synthesized hopcalite catalyst followed by reactive calcination conditions represents that the most excellent catalytic performance for complete conversion of CO at 80 °C. The order of synthetic conditions based on the activity of hopcalite catalysts matched with their characterization. Our effort to demonstrates that the simplistic and potential strategy for improvement of catalytic perfromances over hopcalite catalysts, which should be suitable for different chemical reactions. Hopcalite is a lower cost, simply aviliable and recycle catalysts for application in catalytic converter for CO conversion purposes.

Highly anti-sintering and anti-coking ordered mesoporous silica carbide supported nickel catalyst for high temperature CO methanation

The inhibition of sintering and coking of supported nickel catalysts remains a great challenge in high-temperature carbon-monoxide (CO) methanation. Ordered mesoporous silica carbide (OM-SiC) was fabricated via a nanocasting technique as a nickel catalyst support for CO methanation. Compared with either SiC or SBA-15 supported nickel catalysts, the Ni/OM-SiC exhibited the best activity for CO methanation from 240 to 600 °C, originated from the highest dispersion of Ni. Below 800 °C, 1.0 MPa, and a gas hourly space velocity (GHSV) of 15,000 mL g−1 h−1, a superior activity is close to the theoretical values. In addition, the Ni/OM-SiC catalyst shows far superior anti-coking and anti-sintering properties than the other two kinds of catalysts. The improved catalytic performance can be attributed to a unique pore structure that offers a spatial confinement effect for the nickel particles, and the high thermal conductivity that avoids the formation of hot-spots during reaction. These findings are helpful to develop an efficient nickel-based methanation catalyst to produce synthetic natural gas.

Ambient temperature complete oxidation of carbon monoxide using hopcalite catalysts for fire escape mask applications

Carbon monoxide (CO) is one of the most poisonous gases present in the atmosphere. It also called the silent killer of twenty-first century. CO is produced into the environment by incomplete combustion of carbon containing compounds. It causes lots of people die every year including the firefighters. The main aim of this work to find out the literature study of standard respiratory escape masks for ambient temperature CO oxidation purposes. The research under concern is applicable for developing respiratory protection systems for military, mining, and space devices. There are many catalysts which are active for this process under different conditions. Among these catalysts, the hopcalite (CuMnOx) is one of the best-known catalysts for low-temperature CO oxidation. It is a low-cost, easily available, and highly stable catalyst. The hopcalite catalyst is active for a longer time and would be tolerant of moisture and impurities in reacting gases. The catalyst surface and reacting gases forever play a key role in catalytic reactions. Hopcalite is an ideal catalyst for use in next-generation respiratory protection devices. Although there are numerous research papers present on this topic until now no one review are present for demanding this issue. So there is a space in this area; it has been made an attempt to seal this hole by this review.

Nickel Nanocatalyst Ex-Solution from Ceria-Nickel Oxide Solid Solution for Low Temperature CO Oxidation.

In this work, in situ growth of Ni nanocatalysts to attach onto the ceria (CeO2) surface through direct Ni ex-solution from the NiO-CeO2 solid solution in a reducing atmosphere at high temperatures with an aim to improve the catalytic activity, and stability for low temperature carbon monoxide (CO) oxidation reaction have been reported. The NiO-CeO2 solid solutions were prepared by solution combustion method, and the results of XRD and RAMAN showed that doping of Ni increases the oxygen vacancies due to charge compensation. Ni is clearly visible in XRD and TEM of Ni ex-solved sample (R-UCe5Ni10) after reduction of NiO-CeO2 (UCe5Ni10) sample by 5% H2/Ar reduction at 1000 °C. TEM analysis revealed a size of 9.2 nm of Ni nanoparticle that is ex-solved on the surface CeO2. This ex-solved sample showed very high catalytic activity (T50 ~ 110 °C), and stability (100 h) for CO oxidation reaction as compared to prepared solid solution samples. This is due to the highly active metallic nano-phase which is ex-solved on the surface of CeO2 and strongly adherent to the support. The apparent activation energy Ni ex-solved sample is found out to be 48.4 kJ mol-1. Thus, the above Ni ex-solved sample shows a practical applicability for the CO reaction.

Low operating temperature CO sensor prepared using SnO2 nanoparticles

A low operating temperature CO (carbon monoxide) sensor was fabricated from a nanometer-scale SnO2 (tin oxide) powder. The SnO2 nanoparticles in a size range 10–20 nm were synthesized as a function of surfactant (tri-n-octylamine, TOA) addition (0–1.5 mol%) via a simple thermal decomposition method. The resulting SnO2 nanoparticles were first screen-printed onto an electrode patterned substrate to be a thick film. Subsequently, the composite film was heat-treated to be a device for sensing CO gas. The thermal decomposed powders were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), and surface area measurements (BET). The CO-sensing performance of all the sensors was investigated. The experimental results showed that the TOA addition significantly decreased the particle size of the resulting SnO2 nanoparticle. However, the structure of the powder coating was crucial to their sensing performance. After heat-treatment, the smaller particle tended to cause the formation of agglomeration, resulting in the decline of surface area and reducing the reaction site during sensing. However, the paths for the sensed gas entering between the agglomerated structure may influence the sensing performance. As a CO sensing material, the SnO2 nanoparticle (~12 nm in diameter) prepared with 1.25 mol% TOA addition exhibited most stable electrical performance. The SnO2 coating with TOA addition >0.75 mol% exhibited sensor response at a relatively low temperature of <50°C.

Room-temperature highly sensitive CO gas sensor based on Ag-loaded zinc oxide/molybdenum disulfide ternary nanocomposite and its sensing properties

A new ternary nanocomposite of Ag-loaded zinc oxide (Ag-ZnO)/molybdenum disulfide (MoS2) was successfully prepared via layer-by-layer (LbL) self-assembly method for carbon monoxide (CO) sensing application. The microstructure and micromorphology of Ag-ZnO/MoS2 nanocomposite were fully characterized by various analytical techniques. The gas-sensing properties of the Ag-ZnO/MoS2 nanocomposite film were investigated upon exposure to different CO concentrations at room temperature, and compared with the pure ZnO, ZnO/MoS2 and Pt-ZnO/MoS2 sensors. The experimental results indicated that the Ag-ZnO/MoS2 nanocomposite sensor has excellent response, swift response/recovery characteristics, as well as acceptable repeatability and selectivity, which outstripped that of pure ZnO, ZnO/MoS2 and Pt-ZnO/MoS2 film sensors. The underlying sensing mechanism of Ag-ZnO/MoS2 nanocomposite film was attributed to catalytic activity of Ag and synergistic effect of ZnO and MoS2. This work demonstrated the Ag-ZnO/MoS2 is an excellent candidate for constructing room temperature CO gas sensor.

Catalytic Properties of Cryogelated Noble Metal Aerogels

Abstract The catalytic properties of cryogelated noble metal aerogel monoliths out of aqueous colloids are investigated using the oxidation of carbon monoxide (CO) as a model reaction, in order to evaluate their potential for catalytic applications. Aerogels built of self-supporting platinum (Pt) and palladium (Pd) nanocrystals (NCs) have a directly accessible catalyst surface and show catalytic performance similar to state of the art catalysts while being support-free and therefore ultralight materials. In addition, these materials provide properties like room temperature CO conversion and spontaneous catalytic reactions. However, full material aerogel catalysts come with the side effect of limited thermal stability, which will have to be overcome in future.

High catalytic activity of Pt–Pd containing USY zeolite catalyst for low temperature CO oxidation from industrial off gases

Small amounts (0.15wt%) of platinum and palladium were incorporated in porous, high surface area, ultra–stable H–USY–Zeolite by ion exchange method, and their catalytic activity was studied for carbon monoxide (CO) oxidation reaction, under various conditions of industrial importance. The catalyst was characterized by p–XRD, chemical analysis, SEM, TEM, evaluated for catalytic activity using a steady state, fixed bed catalytic reactor. The catalysts show high CO oxidation activity and it was possible to convert 0.044 mmols of CO per gram of catalyst at 120 °C, at a space velocity of 60 000 h−1 and with 100 ppm CO concentration in feed gas. The high catalytic activity of this noble metal catalyst also appears to be a factor of porous structure of zeolite facilitating mass transfer; high surface area as well as highly dispersed catalyst sites of palladium and platinum on zeolite structure. Introduction of acidic sites in zeolites probably makes them more resistant towards SO2, while their surface area and pore characteristics make this catalyst efficient even under high space velocity conditions, thus suggesting the potential of larger pore size zeolites over conventional porous materials for industrial applications.

Correlation of carbon monoxide sensing and catalytic activity of pure and cation doped lanthanum iron oxide nano-crystals

For nano-crystalline cobalt (Co) and cobalt/lead (Pb) co-doped lanthanum ferrite (LaFeO3) ceramics, we have investigated the carbon monoxide (CO) sensing characteristics. The catalytic activities toward CO oxidation were investigated for LaFeO3 and LaFe0.8Co0.2O3 powders. At an operating temperature as low as 175°C, Co doped LaFeO3 sensors exhibit excellent low concentration (<100ppm) CO gas sensing characteristics. Also, La0.8Pb0.2Fe0.8Co0.2O3 (LPFC) ceramics selectively senses CO at 150°C. For LaFe0.8Co0.2O3, 0.056mmol of CO conversion per gram of catalyst was measured at 200°C. On the other hand, for LaFeO3 ceramics, CO conversions per gram of catalyst were recorded to be 0.004mmol. The superior low temperature CO sensing characteristics of nano-crystalline LaFe0.8Co0.2O3 ceramics correlates well with its excellent catalytic activity toward CO oxidation. For perovskite LaFe0.8Co0.2O3 sensors it was demonstrated that lower metal-oxygen binding energy, favorable d-orbital electron configuration of Co cation, and nature of surface composition are the three dominant factors control its superior catalytic activity and the CO sensing characteristics.

Room temperature CO sensor fabricated from Pt-loaded SnO2 porous nanosolid

Highly sensitive room temperature carbon monoxide (CO) gas sensor was prepared by Pt-loaded SnO2 porous nanosolid (SnO2:Pt PNS). The effects of preparation conditions on sensor response were studied and the highest response to 100ppm CO at room temperature reached a value of 64.5, which is actually high compared with previous reports. In addition, SnO2:Pt PNS sensor showed a good CO selectivity against H2. Hall effect measurement was conducted to analyze the sensing mechanism, which reveals that SnO2 PNS is highly depleted after Pt-loading and the high response of our sensors depends on the change of both electron concentration and mobility upon exposing to CO gas. The sensor response is also favored by the highly porous, interconnected small-grain structure of SnO2 PNS.