Search

The ammonia adsorption on the nanostructured carbon thin film was significantly influenced by the choice of deposition temperature and deposition time of thin film synthesis. The thin films were prepared on Si/SiO2 substrates by chemical vapour deposition in Ar/C2H2 gas mixture using iron catalytic nanoparticles. The analysis of the grown layer by the scanning and transmission electron microscopy showed the transition from long multiwalled nanotubes (MWCNTs) to bamboo-like hollow carbon nanofiber structure with the decrease of the deposition temperature from 700 to 600°C. Further, the material was analyzed by energy-dispersive X-ray spectroscopy and Raman spectroscopy confirmed the transition from graphitic sp structure to highly defective structure at lower deposition temperature. The resistance of the prepared layer strongly depends on deposition temperature ( Td ) and deposition time ( td ). High resistance layer, 38.6 k, was formed at Td 600°C and td 10 min, while at Td 700°C and td 60 min, the resistance decreased to 860 ohms. Such behaviour is consistent with MWCNTs being responsible for the formation of the conductive network. Such system was studied using chemiresistor ammonia gas sensor configuration. The sensor resistance increased when exposed to ammonia in all the cases, but their response varied considerably. A decrease in deposition time, from 60 to 10 min, and the deposition temperature, from 700 to 600°C, led to the 10-fold increase in the sensor response. The measurements carried out at room temperature showed the higher sensor response than the measurements carried out at 200°C. This behaviour can be explained by the change in adsorption-desorption equilibrium at different temperatures. Analysis of dependence of the sensor response on the ammonia concentration proved that the underlying resistance change mechanism is chemisorption of ammonia molecules on the carbon network corresponding to the Langmuir isotherm.

Graphite oxide synthesis dynamics were investigated using a sampling technique. The synthesis of graphite oxide was carried out by a modified Hummers’ method. Small samples of the solid phase (30–50 mg) were collected from the reaction mixture and analyzed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, energy dissipative X-ray spectroscopy, and X-ray photoelectron spectroscopy. The strongest oxidation was detected 10 min after the start of the synthesis, i.e., after the addition of KMnO4, when the formation of the graphite oxide phase with intercalated guest molecules begins. The intercalation of graphite started after 30 min of synthesis when the temperature was increased to 35°C. The addition of ice into the reaction mixture leads to the increase in the COOH group concentration, whereas the concentration of C=O groups slightly changes, and the concentration of the C–O and C=O groups remains almost constant. It was found that the degree of oxidation of graphite oxide exhibited complex change, and H2O2 plays a significant role not only in the removal of impurities but also in the increase in the GO oxidation degree that is reflected by a higher concentration of oxygen-containing functional groups. Differential scanning calorimetry and thermogravimetric analysis data confirmed that the additions of ice and H2O2 induce the stronger formation of surface functional groups instead of intercalated guest species.

The ammonia adsorption on the nanostructured carbon thin film was significantly influenced by the choice of deposition temperature and deposition time of thin film synthesis. The thin films were prepared on Si/SiO2 substrates by chemical vapour deposition in Ar/C2H2 gas mixture using iron catalytic nanoparticles. The analysis of the grown layer by the scanning and transmission electron microscopy showed the transition from long multiwalled nanotubes (MWCNTs) to bamboo-like hollow carbon nanofiber structure with the decrease of the deposition temperature from 700 to 600°C. Further, the material was analyzed by energy-dispersive X-ray spectroscopy and Raman spectroscopy confirmed the transition from graphitic sp structure to highly defective structure at lower deposition temperature. The resistance of the prepared layer strongly depends on deposition temperature ( Td ) and deposition time ( td ). High resistance layer, 38.6 k, was formed at Td 600°C and td 10 min, while at Td 700°C and td 60 min, the resistance decreased to 860 ohms. Such behaviour is consistent with MWCNTs being responsible for the formation of the conductive network. Such system was studied using chemiresistor ammonia gas sensor configuration. The sensor resistance increased when exposed to ammonia in all the cases, but their response varied considerably. A decrease in deposition time, from 60 to 10 min, and the deposition temperature, from 700 to 600°C, led to the 10-fold increase in the sensor response. The measurements carried out at room temperature showed the higher sensor response than the measurements carried out at 200°C. This behaviour can be explained by the change in adsorption-desorption equilibrium at different temperatures. Analysis of dependence of the sensor response on the ammonia concentration proved that the underlying resistance change mechanism is chemisorption of ammonia molecules on the carbon network corresponding to the Langmuir isotherm.

Graphite oxide synthesis dynamics were investigated using a sampling technique. The synthesis of graphite oxide was carried out by a modified Hummers’ method. Small samples of the solid phase (30–50 mg) were collected from the reaction mixture and analyzed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, energy dissipative X-ray spectroscopy, and X-ray photoelectron spectroscopy. The strongest oxidation was detected 10 min after the start of the synthesis, i.e., after the addition of KMnO4, when the formation of the graphite oxide phase with intercalated guest molecules begins. The intercalation of graphite started after 30 min of synthesis when the temperature was increased to 35°C. The addition of ice into the reaction mixture leads to the increase in the COOH group concentration, whereas the concentration of C=O groups slightly changes, and the concentration of the C–O and C=O groups remains almost constant. It was found that the degree of oxidation of graphite oxide exhibited complex change, and H2O2 plays a significant role not only in the removal of impurities but also in the increase in the GO oxidation degree that is reflected by a higher concentration of oxygen-containing functional groups. Differential scanning calorimetry and thermogravimetric analysis data confirmed that the additions of ice and H2O2 induce the stronger formation of surface functional groups instead of intercalated guest species.

Graphite oxide has been investigated as a possible room-temperature chemiresistive sensor of ammonia in a gas phase. Graphite oxide was synthesized from high purity graphite using the modified Hummers method. The graphite oxide sample was investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetry and differential scanning calorimetry. Sensing properties were tested in a wide range of ammonia concentrations in air (10–1000 ppm) and under different relative humidity levels (3%–65%). It was concluded that the graphite oxide–based sensor possessed a good response to NH3 in dry synthetic air (R/R0 ranged from 2.5% to 7.4% for concentrations of 100–500 ppm and 3% relative humidity) with negligible cross-sensitivity towards H2 and CH4. It was determined that the sensor recovery rate was improved with ammonia concentration growth. Increasing the ambient relative humidity led to an increase of the sensor response. The highest response of 22.2% for 100 ppm of ammonia was achieved at a 65% relative humidity level., Byl zkoumán oxid grafitu jako možný materiál pro chemiresistivní senzor amoniaku za pokojové teploty. Oxid grafitu byl syntetizován z vysoce čistého grafitu modifikovanou Hummers metodou. Vzorek oxidu grafitu byl analyzován pomocí skenovací elektronové mikroskopie, energiově disperzní rentgenové spektroskopie, rentgenové difrakce, thermogravimetrie a diferenční skenovací kalorimetrie. Senzorické vlastnosti byly testovány v širokém rozmezí koncentrací amoniaku ve vzduchu (10 – 1000 ppm) a za různé relativní vlhkosti (3-65 %). Byl učiněn závěr, že senzor na bázi oxidu grafitu má dobrou odezvu na NH3 v suchém syntetickém vzduchu (R/R0 se pohyboval od 2,5 % do 7,4 % pro koncentrace 100-500 ppm při relativní vlhkosti 3 %) se zanedbatelnou krossensitivitou na H2 a CH4. Bylo zjištěno, že se s růstem koncentrace amoniaku zkracovala doba zotavení senzoru. Zvyšení relativní vlhkosti prostředí vedlo k zvýšení odezvy senzoru. Při relativní vlhkost 65 % bylo dosaženo nejvyšší odezvy 22,2 % pro 100 ppm amoniaku.

In this paper a graphite oxide is investigated as a possible sensing layer of room temperature ammonia chemiresistive gas sensor. The sensing properties were tested in a wide range of ammonia concentrations in air (10-1000 ppm) and under different humidity levels (3-65 %). It was concluded that the graphite oxide based sensor possessed high response to NH3 in synthetic air (R/R0 ranged from 2.5 to 7.4 % for concentrations of 100-500 ppm and 3 % relative humidity) with negligible cross-sensitivity towards H2 and CH4. It was determined that the sensor recovery rate was improved with ammonia concentration growth. Increasing of ambient relative humidity led to increase of sensor response. The highest response of 22.2 % for 100 ppm of ammonia was achieved at 65 % relative humidity level., V článku je oxid grafitu jako možná citlivá vrstva chemorezistivního senzoru na amoniak pracujícího při pokojové teplotě. Snímací vlastnosti byly testovány v širokém rozmezí koncentrací amoniaku ve vzduchu (10-1000 ppm) a při různé vlhkosti (3-65 %). Byl učiněn závěr, že senzor s oxidem grafitu vykazoval vysoké odezvu na NH3 v syntetickém vzduchu R/R0 v rozmezí 2,5 až 7,4 % pro koncentrace 100-500 ppm a 3 % relativní vlhkosti) se zanedbatelnou krossenzitivitou vůči H2 a CH4. Bylo zjištěno, že rychlost zotavení senzoru se zlepšovala s rostoucí koncentrace amoniaku. Zvýšení relativní vlhkosti prostředí vedlo ke zvýšení odezvy senzoru. Na úrovni relativní vlhkosti 65 % bylo dosaženo nejvyšší odezvy 22,2 % pro 100 ppm amoniaku.

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 um were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures., Vertikálně uspořádané vícestěnné uhlíkové nanotrubice (VA-MWCNTs) se středním průměrem pod 80 nm a tloušťce VA-MWCNT vrstvy asi 16 um byly vyrobeny v mikrovlnném plazmovém výboji a testovány na vybrané funkční vlastnosti. IR absorpce důležitá pro stavbu bolometrů byla studována pomocí Fourierovy infračervené spektroskopie. Základní elektrochemická charakterizace byla provedena pomocí cyklické voltametrie. Srovnáme-li získané výsledky se standardními nebo MWCNT modifikovanými tištěnými elektrodami, připravené VA-MWCNT elektrody ukazují vysoký potenciál pro konstrukci elektrochemických senzorů. Rezistivní CNT senzor plynu ukázal dobrou citlivost na amoniak při pokojové teplotě. Emisni vlastnosti rovněž potvrdili, že CNTs jsou vhodné pro aplikaci ve snímačích tlaku, kdy je měřena změna emisního proudu ve struktuře diody během ohýbání membrány. Výhody růstu CNTs v mikrovlnném plazmovém výboji, jako jsou rychlost a všestrannost procesu, mohou být plně využity pro integraci povrchově vázaných, přímo rostlých, CNTs do různých snímacích struktur.

The patent describes a sleeved filter for the cleaning of dusty gas consisting of a body, filtering sleeves, gas ducts, sleeve agitation mechanism, and trapped dust outlet. A frame is suspended within the filter body with the capability of motion relative to the body, which frame consists of upper and lower rigidly interconnected plates, between which the sleeves are fastened in a tense state., Edited trans. of Patent (USSR) 332 840 p1-2, 21 Mar 72, by Michael L. Seidel.

The effect of fractional structure of the granulated nanofiber carbon filler on the electrical properties of epoxy resin composites has been investigated in this article. The conductivity and permittivity of composite materials has been measured in the frequency range of 100 Hz – 1 MHz. It was shown that the grain-size distribution of the applied filler effects the electrical properties of epoxy resin / carbon nanofiber composites.