Role Of Hydrogen Gas Research Articles

Toward a hydrogen-free reductive catalytic fractionation of wheat straw biomass.

The reductive catalytic fractionation (RCF) of lignocellulosic biomass is an attractive method for the conversion of lignin toward valuable low-molecular weight aromatics. A limitation to the upscaling of such technology is represented by the use of pressurized hydrogen gas. Here, the role of hydrogen gas within the RCF of wheat straw biomass is investigated. The use of H2 is shown to enhance lignin depolymerization, by virtue of an improved hydrogenolysis and hydrogenation of lignin fragments, with a yield of phenolic monomers that increased from ~12 wt% of acid-insoluble lignin in the initial biomass under inert atmosphere, up to ~25 wt% under H2 (in methanol, at 250 °C, with Ru/C). The adoption of methanol, ethanol or isopropanol as hydrogen-donor solvents was also investigated in the absence of H2. Ethanol was found to give the highest yield of monophenolics (up to ~20 wt%) owing to a better balance between solvolysis, hydrogenolysis, and hydrogenation of lignin. Nevertheless, a substantial loss of the carbohydrate fraction was observed. The use of a lower temperature (200 °C) in combination with H3PO4 resulted in an improved recovery of cellulose in the pulp and in the solubilization of hemicellulose and lignin, with the formation of monosaccharides (~14 wt% of polysaccharides in the initial biomass) and phenolic monomers (up to 18 wt%, in the absence of H2). Overall, a tradeoff exists between the removal of H2 from the process and the production of low-MW phenolics during RCF.

Achievements and Challenges of Graphene Chemical Vapor Deposition Growth

AbstractGraphene, since the first successful exfoliation of graphite, has continuously attracted attention due to its remarkable properties and applications. Recently, the research focus on graphene synthesis has been directed to the controllable synthesis of large‐area and high‐quality graphene. In the last decade, there has been great progress in the chemical vapor deposition (CVD) growth of graphene. Theoretical investigations have led to an enhanced understanding of puzzles on hydrocarbon species stability, key reaction pathways, the role of hydrogen gas, the morphology of graphene islands, and the alignment of graphene on substrates. Experimentally, high‐quality graphene is epitaxially grown on both insulating and metal substrates. Progress has also been reported on low‐temperature graphene growth and on controlling the thickness and stacking of graphene layers. In this review, the authors summarize the previous theoretical and experimental studies on graphene CVD growth and discuss the future challenges on the growth of graphene i) on insulating substrates, ii) at low temperature, iii) with controllable thickness, and iv) with selected stacking twist angles. The authors assert that the key to the continuous advancement of graphene growth is the synergy of experimental and theoretical investigations.

Protective effects of hydrogen gas in a rat model of branch retinal vein occlusion via decreasing VEGF-\u03b1 expression

BackgroundOxidative stress (OS) is an essential factor in the pathogenesis of branch retinal vein occlusion (BRVO). Studies have demonstrated the role of hydrogen gas in the regulation of OS. This study was designed to evaluate the efficacy of hydrogen gas on the BRVO rat model.MethodsTwenty-four BRVO rats were randomly divided into two groups: the hydrogen gas (H) group (42% H2, 21% O2, 37% N2) and the model (M) group (21% O2, 79% N2). Rats in the H group inhaled hydrogen gas for 8 h every day up to 30 d post-occlusion. Twelve age-matched healthy rats served as the control (C) group. Retinal function and morphology were detected at 1, 7, 14 and 30 d post-occlusion. Furthermore, the expression of vascular endothelial growth factor (VEGF-α) was detected by immunofluorescent staining.ResultsFull-field electroretinography (ffERG) revealed that the amplitude of the b-wave (dark-adaptation 3.0 response), the amplitude of the OPs2 wave and the light-adapted flicker response in the H group were all higher than those in the M group at 7 d post-occlusion (all p < 0.05). The reopen time of occlusive retinal vessels in the H group was 2.235 ± 1.128 d, which was shorter than that in the M group (4.234 ± 2.236 d, p < 0.05). The rats in the H group had a thinner IPL + GCL + NFL and an increased total retina compared with those in the M group at 3 d post-occlusion (p < 0.05), while the rats in the H group had a thicker INL, IPL + GCL + NFL and total retina compared with those at 7, 14 and 30 d post-occlusion (p < 0.05). Moreover, the flow velocity of ear vein blood was increased in the H group compared with that in the M group (p < 0.05). The expression of VEGF-α in the H group was dramatically decreased compared with that in the M group at 1, 7 and 14 d post-occlusion (p < 0.05), while the expression kept in similar level at 30 d post-occlusion (p > 0.05).ConclusionsOur findings demonstrate that inhalation of hydrogen gas could alleviate retinal oedema, shorten reopen time and improve retinal function, and the potential mechanism might be related to a decrease in VEGF-α expression.

Hydrogen enhances adaptation of rice seedlings to cold stress via the reestablishment of redox homeostasis mediated by miRNA expression

The role of hydrogen gas (H2) in modulating cold tolerance was investigated. A combination of physiological and molecular approaches was used to study the effect of H2 on the alleviation of cold stress. Cold stress stimulated the production of H2 in rice seedlings. The pretreatment with exogenous H2 not only mimicked above physiological response, but also prevented cold-induced growth inhibition. With 0.39 mM H2 pretreatment, rice seedlings exhibited the maximum improving responses, including alleviating the decrease of chlorophyll contents and photosynthetic activity. The lipid peroxidation and the overproduction of reactive oxygen species (ROS) were decreased as well. These results were supported by the changes of total and isozymatic activities of antioxidant enzymes. In comparison with cold stress alone, miR398 transcripts were down-regulated by H2, and expression levels of its targets Cu/Zn-SOD1 (CSD1) and Cu/Zn-SOD2 (CSD2) were increased. By contrast, miR319 transcripts were differentially increased, showing a relatively negative correlation with its target genes PROLIFERATING CELL FACTOR5 (PCF5) and PROLIFERATING CELL FACTOR8 (PCF8). Our results suggested that endogenous H2 might contribute to the enhancement of cold tolerance, at least partially, by the reestablishment of redox homeostasis via miR398 and miR319.

Role of hydrogen gas in regulating of poly (ADP-ribose) polymerase-1 dependent cell death in rat Schwann cells

To investigate the protective effects and underlying molecular mechanisms of hydrogen (H2) on high glucose-induced poly (ADP-ribose) polymerase-1 (PARP-1) dependent cell death (PARthanatos) in primary rat Schwann cells. Cultured primary rat Schwann cells were randomly divided into five groups: blank control group (C group), H2 control group (H2 group), high osmotic control group (M group), high glucose treatment group (HG group), and H2 treatment group (HG+H2 group). The cells in H2 group and HG+H2 group were cultured with saturated hydrogen-rich medium containing 0.6 mmol/L of H2, and those in three control groups were cultured with low sugar DMEM medium containing 5.6 mmol/L of sugar, and the cells in HG and HG+H2 groups were given 44.4 mmol/L of glucose in addition (the medium containing 50 mmol/L of glucose), the cells in C group and H2 group were given the same volume of normal saline, and the cells in M group were given the same volume of mannitol. Cytotoxicity was evaluated using lactate dehydrogenase (LDH) release rate assays after treatment for 48 hours in each group. The contents of peroxynitrite (ONOO(-)) and 8-hydroxy-2-deoxyguanosine (8-OHdG) reflecting oxidative stress injury and DNA damage were detected by enzyme linked immunosorbent assay (ELISA). Poly (ADP-ribose) (PAR) protein expression was analyzed by Western Blot, and immunofluorescence staining was used to determine the nuclear translocation of the apoptosis-inducing factor (AIF). The cytotoxicity in HG and HG+H2 groups was significantly increased as compared with that of C group [LDH release rate: (61.40±2.89)%, (42.80±2.32)% vs. (9.92±0.38)%, both P < 0.01], the levels of ONOO(-) and 8-OHdG were markedly elevated [ONOO(-) (ng/L): 853.58±51.00, 553.11±38.66 vs. 113.56±14.22; 8-OHdG (ng/L): 1?177.37±60.97, 732.06±54.29 vs. 419.67±28.77, all P < 0.01], and the PAR protein expression was up-regulated (A value: 0.603±0.028, 0.441±0.010 vs. 0.324±0.021, both P < 0.01). The cytotoxicity, the levels of ONOO(-) and 8-OHdG, and PAR expression in HG+H2 group were significantly lower than those of the HG group (all P < 0.01). There were no significant differences in above parameters between H2 group as well as M group and C group. It was shown by immunofluorescence that AIF was expressed in the cytoplasm in C group, H2 group and M group, AIF was expressed in the whole cell in HG group, and the expression in the nucleus was particularly increased. A small amount of AIF expression was found in the nucleus of HG+H2 group, which indicated that high glucose could promote the AIF nuclear translocation, and that hydrogen-rich medium could prevent the process of translocation. High glucose levels could enhance DNA damage that enhance PARthanatos in primary rat Schwann cells. However, H2 can not only reduce DNA damage of injured cells, but also inhibit the special death process, reduce the cell toxicity, all of which have protective effects.

Role of hydrogen in Sb film deposition and characterization of Sb and GexSby films deposited by cyclic plasma enhanced chemical vapor deposition using metal-organic precursors

To meet increasing demands for chemical vapor deposition methods for high performance phase-change memory, cyclic plasma enhanced chemical vapor deposition of Sb and GexSby phase-change films and characterization of their properties were performed. Two cycle sequences were designed to investigate the role of hydrogen gas as a reduction gas during Sb film deposition. Hydrogen gas was not introduced into the reaction chamber during the purge step in cycle sequence A and was introduced during the purge step for cycle sequence B. The role of hydrogen gas was investigated by comparing the results obtained from these two cycle sequences and was concluded to exert an effect by a combination of precursor decomposition, surface maintenance as a hydrogen termination agent, and surface etching. These roles of hydrogen gas are discussed through consideration of changes in deposition rates, the oxygen concentration on the surface of the Sb film, and observations of film surface morphology. Based on these results, GexSby phase-change films were deposited with an adequate flow rate of hydrogen gas. The Ge and Sb composition of the film was controlled with the designed cycle sequences. A strong oxygen affinity for Ge was observed during the X-ray photoelectron spectroscopy analysis of Sb 3d, Sb 4d, and Ge 3d orbitals. Based on the XPS results, the ratios of Ge to Sb were calculated to be Ge0.32Sb0.68, Ge0.38Sb0.62, Ge0.44Sb0.56, Ge0.51Sb0.49 and Ge0.67Sb0.33 for the G1S7, G1S3, G1S2, G1S1, and G2S1 cycles, respectively. Crystal structures of Sb, Ge, and the GeSb metastable phase were observed with various GexSby film compositions. Sb crystallinity decreased with respect to Ge crystallinity by increasing the Ge fraction. A current–voltage curve was introduced, and an electro-switching phenomenon was clearly generated at a typical voltage, Vth. Vth values increased in conjunction with an increased proportion of Ge. The Sb crystallinity decrease and Vth increase were explained via the bonding characteristics of each element.

Propionic acid accumulation in anaerobic digestion of carbohydrates: an investigation on the role of hydrogen gas

This paper describes the experimental investigation into the accumulation of propionic acid under artificially lowered or elevated hydrogen gas levels. Vacuum operation at 0.13, 0.5, and 0.75 atm on the headspace of the reactors, and a selective permeable Teflon membrane placed in the liquid phase, were used to provide low hydrogen concentrations. In the elevated hydrogen concentration experiments, first, hydrogen gas (20% H2 + 80% N2) was bubbled into a batch CSTR reactor. Second, purer H2 gas (80% H2 + 20% CO2) was overpressurized at 2 atm in vials. Suspended cultures were used in all the experiments. The results have suggested no inhibition or stimulation effect by elevated or lowered hydrogen on the accumulation of propionic acid.

Propionic acid accumulation in anaerobic digestion of carbohydrates: an investigation on the role of hydrogen gas

This paper describes the experimental investigation into the accumulation of propionic acid under artificially lowered or elevated hydrogen gas levels. Vacuum operation at 0.13, 0.5, and 0.75 atm on the headspace of the reactors, and a selective permeable Teflon membrane placed in the liquid phase, were used to provide low hydrogen concentrations. In the elevated hydrogen concentration experiments, first, hydrogen gas (20% H 2 + 80% N 2 ) was bubbled into a batch CSTR reactor. Second, purer H 2 gas (80% H 2 + 20% CO 2 ) was overpressurized at 2 atm in vials. Suspended cultures were used in all the experiments. The results have suggested no inhibition or stimulation effect by elevated or lowered hydrogen on the accumulation of propionic acid.

Mechanistic dissimilarities between environmentally influenced fatigue-crack propagation at near-threshold and higher growth rates in lower strength steels

AbstractThe role of hydrogen gas in influencing fatigue-crack propagation is examined for several classes of lower strength pressure-vessel and piping steels. Based on measurements over a wide range of growth rates from 10−8 to 10−2 mm/cycle, crack-propagation rates are found to be significantly higher in dehumidified gaseous hydrogen compared to moist air in two distinct regimes of crack growth, namely, at the intermediate range of growth typically above ∼10−5 mm/cycle and at the near-threshold region below ∼10−6 mm/cycle approaching lattice dimensions/cycle. Both effects are seen at maximum stress intensities K max far below the sustained-load threshold stress intensity for hydrogen-assisted cracking K 1SCC. Characteristics of environmentally influenced fatigue-crack growth in each regime are shown to be markedly different with regard to fractography and the effect of such variables as load ratio and frequency. It is concluded that the primary mechanisms responsible for the influence of the environment ...