Hydrogen Production From Water Under UV Radiation with Carbon Dioxide Mediation

A simple method of hydrogen production through the decomposition of water subjected to UV radiation is presented. Water contained dissolved sodium hydroxide and the solution was saturated with carbon dioxide gas. During saturation, the pH value dropped from about 11.5 to 7-8. The produced bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing recombination of hydroxyl and hydrogen radicals, and giving priority to the formation of hydrogen gas.In the presented method, the production of hydrogen is combined with the utilization of carbon dioxide.

Effect of Steam on the Homogeneous Conversion of Tar Contained from the Co-Pyrolysis of Biomass and Plastics

The co-pyrolysis tar formed from microcrystalline cellulose (MCC) and polyethylene (PE) was used to study their further conversion path under the effect of steam. This paper addressed the yield and transformation of tar with different steam/feedstock mass ratios (S/F= 0.8, 1.6) in a two-stage fixed-bed when the two stages furnace temperature was set at 600℃ and 800℃, separately. Compared with pyrolysis, steam promoted tar cracking effectively, the tar yield decreased at least 1/3. However, with the addition of steam, the cracking effect of tar is not further improved. The tar yield depended more on the PE content in the mixture, which was enhanced with PE increment. Besides, the H/C atom ratio was related to the conversion path of tar. Steam was beneficial to the cracking of compounds, but the generated hydrogen radicals affected the direction of the subsequent reaction. The steam mainly promotes the cracking of long-chain hydrocarbons, accompanied by cyclization and aromatization when the steam was limited. Nevertheless, these reactions were hindered when the steam was excessive due to the apparent effect of hydrogenation. In this process, the short-chain hydrocarbons come to recombine instead of cyclization and aromatization.

Electronic structure and reactivity of tirapazamine as a radiosensitizer

Tirapazamine (TP) has been shown to enhance the cytotoxic effects of ionizing radiation in hypoxic cells, thus making it a candidate for a radiosensitizer. This selective behavior is often directly linked to the abundance of O2. In this paper, we study the electronic properties of TP in vacuum, micro-hydrated from one up to three molecules of water and embedded in a continuum of water. We discuss electron affinities, charge distribution, and bond dissociation energies of TP, and find that these properties do not change significantly upon hydration. In agreement with its large electron affinity, and bond breaking triggered by electron attachment requires energies higher than 2.5 eV, ruling out the direct formation of bioactive TP radicals. Our results suggest, therefore, that the selective behavior of TP cannot be explained by a one-electron reduction from a neighboring O2 molecule. Alternatively, we propose that TP’s hypoxic selectivity could be a consequence of O2 scavenging hydrogen radicals.

Model simulations of chemical effects of sprites in relation with observed HO₂ enhancements over sprite-producing thunderstorms

Recently, measurements by the Superconducting Submillimeter-Wave Limb Emission Sounder (SMILES) satellite instrument have been presented which indicate an increase in mesospheric HO2 above sprite-producing thunderstorms. The aim of this paper is to compare these observations to model simulations of chemical sprite effects. A plasma chemistry model in combination with a vertical transport module was used to simulate the impact of a streamer discharge in the altitude range 70–80 km, corresponding to one of the observed sprite events. Additionally, a horizontal transport and dispersion model was used to simulate advection and expansion of the sprite air masses. The model simulations predict a production of hydrogen radicals mainly due to reactions of proton hydrates formed after the electrical discharge. The net effect is a conversion of water molecules into H+OH. This leads to increasing HO2 concentrations a few hours after the electric breakdown. Due to the modelled long-lasting increase in HO2 after a sprite discharge, an accumulation of HO2 produced by several sprites appears possible. However, the number of sprites needed to explain the observed HO2 enhancements is unrealistically large. At least for the lower measurement tangent heights, the production mechanism of HO2 predicted by the model might contribute to the observed enhancements.

Estimation of the Generation Rate of H· Radicals in a Megasonic Field Using an Electrochemical Technique

Radical formation and detection in aqueous solutions under acoustic irradiation are important during wet cleaning processes in semiconductor industries. Oxidizing radicals such as hydroxyl and hydroperoxyl radicals have been widely studied and characterized using fluorescence and chemiluminescence methods. Hydrogen radicals, which are strongly reducing in nature, have not received much attention. In this study, the rate of hydrogen radical generation in a megasonic field (0.93 MHz) was measured using an electrochemical technique. Specifically, the method is based on the reduction of cupric ions to cuprous chloride complex by the hydrogen radicals in the presence of an excess of chloride ions. This is followed by chronoamperometric determination of the oxidation of cuprous chloride complex back to cupric ions. Hydrogen radical generation rate was measured at different megasonic power densities.

Progress on Diamane and Diamanoid Thin Film Pressureless Synthesis

Nanometer-thick and crystalline sp3-bonded carbon sheets are promising new wide band-gap semiconducting materials for electronics, photonics, and medical devices. Diamane was prepared from the exposure of bi-layer graphene to hydrogen radicals produced by the hot-filament process at low pressure and temperature. A sharp sp3-bonded carbon stretching mode was observed in ultraviolet Raman spectra at around 1344–1367 cm−1 while no sp2-bonded carbon peak was simultaneously detected. By replacing bi-layer graphene with few-layer graphene, diamanoid/graphene hybrids were formed from the partial conversion of few-layer graphene, due to the prevalent Bernal stacking sequence. Raman spectroscopy, electron diffraction, and Density Functional Theory calculations show that partial conversion generates twisted bi-layer graphene located at the interface between the upper diamanoid domain and the non-converted graphenic domain underneath. Carbon-hydrogen bonding in the basal plane of hydrogenated few-layer graphene, where carbon is bonded to a single hydrogen over an area of 150 μm2, was directly evidenced by Fourier transform infrared microscopy and the actual full hydrogenation of diamane was supported by first-principle calculations. Those results open the door to large-scale production of diamane, diamanoids, and diamanoid/graphene hybrids.

The response of mesospheric H₂O and CO to solar irradiance variability in models and observations

Water vapor (H2O) is the source of reactive hydrogen radicals in the middle atmosphere, whereas carbon monoxide (CO), being formed by CO2 photolysis, is suitable as a dynamical tracer. In the mesosphere, both H2O and CO are sensitive to solar irradiance (SI) variability because of their destruction/production by solar radiation. This enables us to analyze the solar signal in both models and observed data. Here, we evaluate the mesospheric H2O and CO response to solar irradiance variability using the Chemistry-Climate Model Initiative (CCMI-1) simulations and satellite observations. We analyzed the results of four CCMI models (CMAM, EMAC-L90MA, SOCOLv3, and CESM1-WACCM 3.5) operated in CCMI reference simulation REF-C1SD in specified dynamics mode, covering the period from 1984–2017. Multiple linear regression analyses show a pronounced and statistically robust response of H2O and CO to solar irradiance variability and to the annual and semiannual cycles. For periods with available satellite data, we compared the simulated solar signal against satellite observations, namely the GOZCARDS composite for 1992–2017 for H2O and Aura/MLS measurements for 2005–2017 for CO. The model results generally agree with observations and reproduce an expected negative and positive correlation for H2O and CO, respectively, with solar irradiance. However, the magnitude of the response and patterns of the solar signal varies among the considered models, indicating differences in the applied chemical reaction and dynamical schemes, including the representation of photolyzes. We suggest that there is no dominating thermospheric influence of solar irradiance in CO, as reported in previous studies, because the response to solar variability is comparable with observations in both low-top and high-top models. We stress the importance of this work for improving our understanding of the current ability and limitations of state-of-the-art models to simulate a solar signal in the chemistry and dynamics of the middle atmosphere.

Model simulations of chemical effects of sprites in relation with satellite observations

Recently, measurements by the Superconducting Submillimeter-Wave Limb Emission Sounder (SMILES) satellite instrument have been presented which indicate an increase of mesospheric HO2 above sprite producing thunderstorms. These are the first direct observations of chemical sprite effects, and provide an opportunity to test our understanding of the chemical processes in sprites. In the present paper, results of numerical model simulations are presented. A plasma chemistry model in combination with a vertical transport module was used to simulate the impact of a streamer discharge in the altitude range 70–80 km, corresponding to one of the observed sprite events. Additionally, a horizontal transport and dispersion model was used to simulate advection and expansion of the sprite volumes. The model simulations predict a production of hydrogen radicals mainly due to reactions of proton hydrates formed after the electrical discharge. The net effect is a conversion of water molecules into H + OH. This leads to increasing HO2 concentrations a few hours after the electric breakdown. According to the model simulations, the HO2 enhancements above sprite producing thunderstorms observed by the SMILES instrument can not solely be attributed to the detected one sprite event for each thunderstorm. The main reason is that the estimated amount of HO2 released by a sprite is much smaller than the observed increase. Furthermore, the advection and dispersion simulations of the observed sprites reveal that in most cases only little overlap of the expanded sprite volumes and the field of view of the SMILES measurements is expected.