Renoxification is the process of recycling NO3- / HNO.sub.3 into NO.sub.x under illumination and is mostly ascribed to the photolysis of nitrate. TiO.sub.2, a typical mineral dust component, is able ...to play a photocatalytic role in the renoxification process due to the formation of NO.sub.3 radicals; we define this process as "photocatalytic renoxification". Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere, may participate in the renoxification of nitrate-doped TiO.sub.2 particles. In this study, we established a 400 L environmental chamber reaction system capable of controlling 0.8 %-70 % relative humidity at 293 K with the presence of 1 or 9 ppm HCHO and 4 wt % nitrate-doped TiO.sub.2 . The direct photolyses of both nitrate and NO.sub.3 radicals were excluded by adjusting the illumination wavelength so as to explore the effect of HCHO on the "photocatalytic renoxification". It was found that NO.sub.x concentrations can reach up to more than 100 ppb for nitrate-doped TiO.sub.2 particles, while almost no NO.sub.x was generated in the absence of HCHO. Nitrate type, relative humidity and HCHO concentration were found to influence NO.sub.x release. It was suggested that substantial amounts of NO.sub.x were produced via the NO3--NO.sub.3 â«-HNO.sub.3 -NO.sub.x pathway, where TiO.sub.2 worked for converting "NO3-" to "NO.sub.3 â« ", that HCHO participated in the transformation of "NO.sub.3 â« " to "HNO.sub.3 " through hydrogen abstraction, and that "HNO.sub.3 " photolysis answered for mass NOx release. So, HCHO played a significant role in this "photocatalytic renoxification" process. These results were found based on simplified mimics for atmospheric mineral dust under specific experimental conditions, which might deviate from the real situation but illustrated the potential of HCHO to influence nitrate renoxification in the atmosphere. Our proposed reaction mechanism by which HCHO promotes photocatalytic renoxification is helpful for deeply understanding atmospheric photochemical processes and nitrogen cycling and could be considered for better fitting atmospheric model simulations with field observations in some specific scenarios.
Au modified TiOsub.2/Insub.2Osub.3 hollow nanospheres were synthesized by the hydrolysis method using the carbon nanospheres as a sacrificial template. Compared to pure Insub.2Osub.3, pure TiOsub.2, ...and TiOsub.2/Insub.2Osub.3 based sensors, the Au/TiOsub.2/Insub.2Osub.3 nanosphere-based chemiresistive-type sensor exhibited excellent sensing performances to formaldehyde at room temperature under ultraviolet light (UV-LED) activation. The response of the Au/TiOsub.2/Insub.2Osub.3 nanocomposite-based sensor to 1 ppm formaldehyde was about 5.6, which is higher than that of Insub.2Osub.3 (1.6), TiOsub.2 (2.1), and TiOsub.2/Insub.2Osub.3 (3.8). The response time and recovery time of the Au/TiOsub.2/Insub.2Osub.3 nanocomposite sensor were 18 s and 42 s, respectively. The detectable formaldehyde concentration could go down as low as 60 ppb. In situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was used to analyze the chemical reactions on the surface of the sensor activated by UV light. The improvement in the sensing properties of the Au/TiOsub.2/Insub.2Osub.3 nanocomposites could be attributed to the nanoheterojunctions and electronic/chemical sensitization of the Au nanoparticles.
The corresponding formazans were synthesized by the reaction of phenylhydrazones of nitro-substituted benzaldehydes and 4-pyridinecarbaldehyde with arenediazonium salts obtained from p-substituted ...anilines. Formazans were converted into the corresponding 5,6-dihydro-1,2,4,5-tetrazinium triflates by the action of formalin in the presence of CF.sub.3SO.sub.3H. When tetrazinium salts were treated with D-glucose in a weakly alkaline medium (NH.sub.4OH) in the presence of atmospheric oxygen, stable tetrazinyl radicals were formed. Formazans, tetrazinium triflates, and tetrazinyl radicals were isolated in the individual state and characterized by elemental analysis, IR, UV, NMR, or ESR (radicals) spectroscopy.
In this work, the effects of surface area and mesopore size on gas-sensing properties of SnO.sub.2 hollow microfibers assembled by nanocrystals were investigated. When the sintering time was ...increased from 2 to 24 h, the specific surface area (SSA) of SnO.sub.2 microfibers decreased from 103.6 to 59.8 m.sup.2 g.sup.-1, whereas the mesopore diameter gradually increased from 2.8 to 10.9 nm. Interestingly, it was found that their gas-sensing properties to ppb-level formaldehyde were determined by both SSA and mesopore size. The gas response increased firstly and then decreased with decreasing SSA and increasing mesopore size and reached the maximum value when the sintering time was 11 h. When the sintering time was <11 h, mesopore size (<8.5 nm) dominated sensing behavior by controlling gas diffusion rate. Once the sintering time was more than 11 h, the decreased SSA (<70.8 m.sup.2 g.sup.-1) dominated sensing performance by influencing the surface reaction activity. Therefore, the competitive influence of surface area and mesopore size on gas-sensing properties of mesoporous SnO.sub.2 microfibers was revealed. This work could provide a new understanding for microstructural design of the mesoporous gas-sensing metal oxide materials.
Formaldehyde in summer Preunkert, S; Legrand, M; Frey, M. M ...
Atmospheric chemistry and physics,
06/2015, Letnik:
15, Številka:
12
Journal Article
Recenzirano
During the 2011/12 and 2012/13 austral summers, HCHO was investigated for the first time in ambient air, snow, and interstitial air at the Concordia site, located near Dome C on the East Antarctic ...Plateau, by deploying an Aerolaser AL-4021 analyzer. Snow emission fluxes were estimated from vertical gradients of mixing ratios observed at 1 cm and 1 m above the snow surface as well as in interstitial air a few centimeters below the surface and in air just above the snowpack. Typical flux values range between 1 and 2 Ã 10.sup.12 molecules m.sup.-2 s.sup.-1 at night and 3 and 5 Ã 10.sup.12 molecules m.sup.-2 s.sup.-1 at noon. Shading experiments suggest that the photochemical HCHO production in the snowpack at Concordia remains negligible compared to temperature-driven air-snow exchanges. At 1 m above the snow surface, the observed mean mixing ratio of 130 pptv and its diurnal cycle characterized by a slight decrease around noon are quite well reproduced by 1-D simulations that include snow emissions and gas-phase methane oxidation chemistry. Simulations indicate that the gas-phase production from CH.sub.4 oxidation largely contributes (66%) to the observed HCHO mixing ratios. In addition, HCHO snow emissions account for ~ 30% at night and ~ 10% at noon to the observed HCHO levels.
The first example of 16-membered aminomethylphosphines with pyridyl substituents on the phosphorus atom was synthesized as an RSSR isomer by covalent self-assembly in the system 1,3-bis(pyridin2- ...yl)phosphinopropane-formaldehyde-isopropylamine. Keywords: macrocycle, corand, aminomethylphosphine, covalent self-assembly DOI: 10.1134/S1070363218110336
