Efficiency Of OH Research Articles

Theoretical simulation of ion transport in main-chain poly(arylene piperidinium) anion exchange membranes with crown ether groups

ABSTRACT Experimental studies have confirmed that introduction of the proper content of dibenzo-18-crown-6-ether (DE) into main-chain poly(arylene piperidinium) anion exchange membranes (AEMs) improved the efficiency of OH− transport. In this study, models of the AEMs (PDTP-x) were constructed with varying molar contents of DE groups (x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25). Molecular dynamics simulations were employed to investigate the microscopic effects of the DE groups on OH− transport. The analysis examined the impact of the volume of the overlapping hydration shells around piperidinium groups and the continuities and uniformities of the ion transport channels. Furthermore, the stabilities of the hydrogen bonds between water molecules explained the effect of x on OH− transport. The results showed that the total overlap volume initially increased and then decreased as x increased. When the content of DE groups was appropriate, the hydration shells of the cations exhibited considerable overlap, which facilitated the formation of continuous and uniform ion transport channels. Additionally, the stabilities of the water hydrogen bonds initially decreased and then increased as x increased. The stabilities of the hydrogen bonds were lowest when the DE content was optimal, which facilitated the transport of OH−.

Construction of Ni2P@NiCo-BLDH nanocomposite with hierarchical porous structure on nickel foam as advanced oxygen evolution electrocatalyst

The fabrication of two-dimensional layered double hydroxides (LDHs) materials still faces great challenges, particularly in achieving precise modulation of lamellar metals and interlayer anions for electrocatalytic oxygen evolution reaction (OER). Herein, a hierarchical porous nanocomposite assembled by foam nickel (NF) supported borate anions incorporated bimetallic NiCo hydrotalcite (NiCo-BLDH) on the surface of nickel phosphide sheets (NF/Ni2P @ NiCo-BLDH) is prepared through the NF in-situ phosphating and electrodeposition approach as an electrocatalyst for achieving superior OER catalysis. In this design, introducing multi-phase and incorporated borate anions into LDHs can regulate their structure and properties, creating unique active sites and enhancing the adsorption efficiency of OH- to effectively improve the OER activity. Remarkably, the NF/Ni2P @ NiCo-BLDH electrode shows a low overpotential of 293 mV at 100 mA cm−2 for OER and a Tafel slope of 108.3 mV dec−1 in a 1.0 M KOH medium, surpassing most previously reported NiCo-based catalysts. Nevertheless, the NF/Ni2P electrode exhibits a lower overpotential for the hydrogen evolution reaction (HER) in a 1.0 M KOH medium compared to the NF/Ni2P @ NiCo-BLDH electrode. This work not only advances the catalytic activity of the NiCo-LDH-based materials in OER but also provides a new idea for large-scale electrocatalytic water splitting applications.

Na+ migration facilitated separation of hydrogen and hydroxide for efficient hardness removal via an integrated electrochemical precipitation approach

In this study, efficient H+–OH– separation was achieved employing Na+ migration in anode chamber in a cation exchange membrane assembled electrochemical system for enhanced hardness removal. It was found that the OH– current efficiency could reach 91.3%, when hydraulic residence time (HRT) of anode chamber and the electrode distance were 1 min and 1 cm, respectively. Then, most of the retained OH– would be transported to a separated crystallizer to react with the feed water to perform hardness removal. Besides, Na+ balance could be maintained using accumulated Na+ in the crystallizer to backfill the anode circulator, so as to strengthen the current efficiency of OH– of the cathode chamber throughout the process. Specifically, at a current density and an inflow rate of 10 mA/cm2 and of 20 mL/min, hardness removal efficiency and the energy consumption reached 92.1% and 2.26 kWh/kg CaCO3, respectively. Moreover, it was found that large specific surface area of the carbon felt adopted for precipitation and crystallization could be recycled up to 15 repeated cycles (about 180 h) in terms of the pure water permeance. Finally, aragonite was characterized to be dominant at the reaction, whereas magnesium calcite could also be observed at the end of the reaction process (12 h). In conclusion, Na+ migration as well as carbon felt dependent precipitation impelled integrated electrochemical system would increase hardness removal efficiency sustainably.

Ionization‐engineered two‐dimensional confined channels in GO membranes for highly efficient OH− separation

AbstractOH− sieving membranes provide a valuable means for treating alkaline effluents but their development presents several challenges. In this study, the concept of ionization engineering is applied to two‐dimensional (2D) laminated membranes to facilitate OH− separation. This concept is demonstrated through the stacking of the self‐designed sulfonated graphene oxide (SGO) nanosheets to fabricate 2D membranes. The SGO membranes enhance synergistically the OH− dialysis coefficients and separation factors when treating simulated NaOH/Na2WO4 alkaline wastewater, compared with the performance of 2D GO membranes and commonly adopted polymeric cation exchange membranes. Furthermore, the separation factor achieved by the SGO membranes is considerably higher than that of most of the existing alkali recovery membranes. Results of molecular dynamics simulations indicate that the high efficiency of OH− separation in the 2D SGO confined channels is attributable to dehydration effects and intensified electrostatic repulsion. Overall, this research provides an alternative strategy for achieving rapid OH− sieving through the ionization of 2D confined channels.

Highly efficient heterogeneous electro-Fenton degradation of organic pollutants using a FeNi-OH/NF cathode

The electro-Fenton (EF) technology provided a promising way to degrade organic pollutants by in-situ producing H2O2 and decomposing it into hydroxyl radicals (OH). However, the degradation rate is restricted by the two-electron oxygen reduction reaction (ORR) rate of H2O2 generation and the production efficiency of OH, and the efficient EF cathode is important. Herein, we designed an efficient heterogeneous EF system with a Fe-doped β-Ni(OH)2 nanosheets/nickel foam (FeNi-OH/NF) cathode for phenol removal in water. FeNi-OH enhanced the electrochemically active area for H2O2 production and produced OH for pollutant degradation. The FeNi-OH/NF cathode demonstrates excellent heterogeneous EF catalytic activity with a degradation efficiency of phenol (99.4%) and total organic carbon (67.4%) in 2 h. The experiments and density functional theory (DFT) calculations further confirmed that the Fe-doped β-Ni(OH)2 on the nickel foam enhanced H2O2 adsorption and accelerated Fe3+/Fe2+ circulation, promoting the reaction of H2O2 with Fe2+ to produce OH for phenol degradation. This study provides a novel and efficient heterogeneous EF cathode for accelerating pollutant degradation securely and quickly.

Development and Characterization of Grain Husks Derived Lignocellulose Filler Containing Polypropylene Composites

Oat and spelt husks (OH and SH, respectively) lignocellulosic biomass derived fillers have been compared with commercial wood flour (WF) in respects to their morphology, chemical composition, bulk density, aspect ratio, and thermal stability. OH and SH have been obtained by both mechanical milling and steam explosion auto‐hydrolysis treatment at various processing conditions. Reinforcement efficiency of OH and SH derived lignocellulosic biomass fillers on the flexural properties of maleic acid‐grafted polypropylene (PPgMA) compatibilized polypropylene (PP) composites is compared with that of WF. The compatibilized PP composites have been manufactured by melt compounding. Flexural test specimens of the compatibilized PP composites have been manufactured by injection molding. It has been demonstrated that both the husks derived lignocellulose fillers can be used to improve flexural modulus and maximal flexural strength of PP, although its modifying effect is somewhat smaller in comparison to WF reinforcement, most probably due to higher cellulose content of the latter. Husks derived lignocellulose filler‐reinforced PP composites, however, demonstrate increased flexibility in comparison to WF‐filled systems. POLYM. ENG. SCI., 59:2467–2473, 2019. © 2019 Society of Plastics Engineers

Efficient Fe(III)/Fe(II) cycling triggered by MoO2 in Fenton reaction for the degradation of dye molecules and the reduction of Cr(VI)

There is a relatively low efficiency of Fe(III)/Fe(II) conversion cycle and H2O2 decomposition (<30%) in conventional Fenton process, which further results in a low production efficiency of OH and seriously restricts the application of Fenton. Herein, we report that the commercial MoO2 can be used as the cocatalyst in Fenton process to dramatically accelerate the oxidation of Lissamine rhodamine B (L-RhB), where the efficiency of Fe(III)/Fe(II) cycling is greatly enhanced in the Fenton reaction meanwhile. And the L-RhB solution could be degraded nearly 100% in 1 min in the MoO2 cocatalytic Fenton system under the optimal reaction condition, which is apparently better than that of the conventional Fenton system (∼50%). Different from the conventional Fenton reaction where the OH plays an important role in the oxidation process, it shows that 1O2 contributes most in the MoO2 cocatalytic Fenton reaction. However, it is found that the exposed Mo4+ active sites on the surface of MoO2 powders can greatly promote the rate-limiting step of Fe3+/Fe2+ cycle conversion, thus minimizing the dosage of H2O2 (0.400 mmol/L) and Fe2+ (0.105 mmol/L). Interestingly, the MoO2 cocatalytic Fenton system also exhibits a good ability for reducing Cr(VI) ions, where the reduction ability for Cr(VI) reaches almost 100% within 2 h. In short, this work shows a new discovery for MoO2 cocatalytic advanced oxidation processes (AOPs), which devotes a lot to the practical water remediation application.

Effects of pulse width on He plasma jets in contact with water evaluated by OH(A–X) emission and OHaq production

Nanosecond pulsed helium plasma jets impinging on water produce hydroxyl radicals both in gas- and liquid-phase. In this study, the effects of pulse width on a repetitively pulsed plasma jet in contact with water are evaluated via OH(A–X) emission and OHaq production in water for various pulse widths ranging from 200 to 5000 ns. The maximal energy efficiency of OH(A–X) emission is obtained for pulse widths of 600–800 ns whereas the maximal efficiency of OHaq production is at 200 ns. Temporally-resolved emission spectroscopy shows that more than 40% of OH(A–X) emission is produced during the first 200 ns of the voltage pulse regardless of the pulse width. An equivalent circuit model of the plasma jet impinging on water is compiled to understand the charge transfer process, which is important for OHaq production via charge exchange reactions.

Role of exposed facets and surface OH groups in the Fenton-like reactivity of lepidocrocite catalyst

Heterogeneous Fe-based Fenton-like reaction is an efficient technology in wastewater treatment. However, few studies reveal the effects of exposed facets and surface OH groups of iron oxides on its reactivity. In this study, two lepidocrocite samples with lath- and rod-like morphologies were synthesized and applied to the adsorption and degradation of Orange G (OG). The OG molecule could be adsorbed vertically on the lath-like sample by the interaction with the μ−OH groups of the (010) facet. The molecule could also be adsorbed laterally on the rod-like sample by the interactions with the μ−OH and μ3−OH groups of the (010) and (001) facets. When the data were normalized to the unit surface area, the adsorption capacity of OG, the production efficiency of OH, the degradation rate in dark, and the total degradation rates under visible light irradiation in the lath-like system were 9.625-, 3.34-, 2.75-, and 1.98-fold higher than those in the rod-like system, respectively.

Efficient oxidation of macro-crude oil in soil using oil-absorbing Fe catalyzing H2O2

This study investigated the oxidizing ability of OH for macro-crude oil in soil using oil-absorbing Fe catalyzing H2O2. Two types of oil-contaminated soil were tested: (i) macro long-chain crude oil-contaminated soil (LO-soil) was dominated by long-chain alkanes, and (ii) macro common crude oil-contaminated soil (CO-soil) was dominated by both short- and long-chain alkanes. LO-soil contained 38% (C30 – C27: 1490 mg/kg) macro-crude oil, and CO-soil contained 38% (C30, C29, C15 and C14: 1473 mg/kg) macro-crude oil. The results showed that the greatest removal of macro-crude oil (LO-soil: 938 mg/kg, CO-soil: 821 mg/kg) was observed by H2O2/oil-absorbing Fe, an increase of twofold compared with by H2O2/non oil-absorbing Fe. In addition, the removal of macro-crude oil by per unit iron species in H2O2/oil-absorbing Fe was as high as 0.25–0.35 mg oil/mg Fe, twice that (0.13–0.17 mg oil/mg Fe) achieved by H2O2/non oil-absorbing Fe. The utilization efficiency of OH is improved by H2O2/oil-absorbing Fe. Further analysis found that the oil-absorbing Fe could bind with hydrophobic humic-like acid and fulvic-like acid, increasing the hydrophobicity of oil-absorbing Fe. Thus, macro-crude oil could be efficiently oxidized in soil by oil-absorbing Fe catalyzing H2O2.

Electrocatalytic cogeneration of reactive oxygen species for synergistic water treatment

This study examines the co-generation effect of hydroxyl radicals (OH) via water oxidation and H2O2 via O2 reduction in electrocatalytic processes with Sb-doped SnO2 (SS) anode and carbon nanotube (CNT) cathode pairs facing each other as a function of applied SS/CNT cell voltage and purging gas (O2 vs. N2). Prior to coupling the electrodes, both electrodes are examined for the generation kinetics and current efficiency of reactive oxygen species as well as the decomposition kinetics and total organic carbon (TOC) removal of phenol, as a function of applied half-potential (ESS or ECNT) and the purging gas. Regardless of the purging gas, a stepwise increase in ESS enhances the OH generation and phenol decomposition, yet inversely decreases the current efficiency of OH (max. ∼30%), owing to competitive O2 evolution. Similar to this, the current efficiency of H2O2 is high at a less negative ECNT, reaching ∼80% with O2 purging. However, phenol decomposition with CNT is trivial, owing to the limited reactivity between H2O2 and phenol. With N2 purging, H2O2 is not produced nor is phenol decomposed. Compared to the sum of the performance of the two half-electrodes, the SS/CNT pair exhibits similar OH generation kinetics regardless of the purging gas, yet significantly enhanced H2O2 generation kinetics. The phenol decomposition and TOC removal with the pair are more than double their sums of the two half-electrodes at all Ecells with O2 purging, whereas such a synergistic effect is found only at high Ecells when N2 is purged. The simultaneous evolution of O2 microbubbles appears to create an in situ oxic environment between the SS and CNT, leading to a synergistic effect through the production of H2O2, even under anoxic and anoxic-like conditions.

Photocatalytic Activity of TiO2 Modified with Hexafluorometallates—Fine Tuning of Redox Properties by Redox-Innocent Anions

A group of selected hexafluorometallates ([AlF6]3–, [TiF6]2–, [ZrF6]2–, and [SiF6]2–) has been adsorbed at the surface of titanium dioxide. Such modification influenced the electronic and chemical properties of TiO2, as well as its photoactivity. The modification with [TiF6]2– inhibited the efficiency of OH• production but enhanced the generation of photocurrent and singlet oxygen. The results of modifications with [ZrF6]2– were the opposite—generation of 1O2 was not observed in this case and photocurrents were lower; however, due to a better OH• production, degradation of herbicides was faster.

What does the global mean OH concentration tell us?

Abstract. The global mean OH concentration ([OH]GM) has been used as an indicator of the atmospheric oxidizing efficiency and its changes over time. It is also used for evaluating the performance of atmospheric chemistry models by comparing with other models or with observationally-based reference [OH]GM levels. We contend that the treatment of this quantity in the recent literature renders it problematic for either of these purposes. Several different methods have historically been used to compute [OH]GM: weighting by atmospheric mass or volume, or by the reaction with CH4 or CH3CCl3. In addition, these have been applied over different domains to represent the troposphere. While it is clear that this can lead to inconsistent [OH]GM values, to date there has been no careful assessment of the differences expected when [OH]GM is computed using various weightings and domains. Here these differences are considered using four different 3D OH distributions, along with the weightings mentioned above applied over various atmospheric domains. We find that the [OH]GM values computed based on a given distribution but using different domains for the troposphere can result in differences of 10% or more, while different weightings can lead to differences of up to 30%, comparable to the uncertainty which is commonly stated for [OH]GM or its trend. Thus, at present comparing [OH]GM values from different studies does not provide clearly interpretable information about whether the OH amounts are actually similar or not, except in the few cases where the same weighting and domain have been used in both studies. We define the atmospheric oxidizing efficiency of OH with respect to a given gas as the inverse of the lifetime of that gas, and show that this is directly proportional to the [OH]GM value weighted by the reaction with that gas, where the proportionality constant depends on the temperature distribution and the domain. We find that the airmass-weighted and volume-weighted [OH]GM values, in contrast, are generally poor indicators of the global atmospheric oxidizing efficiency with respect to gases such as CH4 and CH3CCl3 with a strong temperature dependence in their reaction with OH. We recommend that future studies provide both the airmass-weighted and the CH4-reaction-weighted [OH]GM values, over the domain from the surface to a climatological tropopause. The combination of these values helps to reduce the chance of coincidental agreement between very different OH distributions. Serious evaluations of modeled OH concentrations would best be done with airmass-weighted [OH]GM broken down into atmospheric sub-compartments, especially focusing on the tropics, where the atmospheric oxidizing efficiency is the greatest for most gases.

Gamma-radiolysis of poly(A) in aqueous solution: efficiency of strand break formation by primary water radicals.

gamma-Radiation-induced single-strand break formation (ssb) in polyadenylic acid (poly(A] has been determined in Ar and N2O-saturated aqueous solution in the presence of different concentrations of t-butanol. Strand breaks were monitored by a low-angle laser light-scattering technique. The efficiencies for strand breakage caused by solvated electrons, hydrogen atoms and OH radicals have been found to be 0.25, 0.20 and 7.8 per cent, respectively. The efficiency of OH radicals depends only slightly on pH (pH 5.0, 7.5 and 9.0) and is independent of the presence of salt (0.01 mol dm-3 NaC1O4) and of the irradiation temperature (20 degrees C and 70 degrees C). The efficiency of OH for ssb formation obtained in this work with poly(A) is much smaller than that of poly(dA). This is explained by the different molecular conformations of the sugar moiety of poly(A) (3'-endo) and poly(dA) (2'-endo). With increasing t-butanol concentration more strand breaks are formed than expected from simple homogeneous competition kinetics of poly(A) and t-butanol for OH radicals. This result is considered to be due to nonhomogeneous reaction kinetics in the above-mentioned competition. The rate constants for the reaction of OH and H with poly(A) have been determined.

OH fluorescence in comets - Fluorescence efficiency of the ultraviolet bands

The present investigation is concerned with the calculation of the fluorescence efficiency of OH over a wide range of heliocentric radial velocities. Three vibrational states in each of the two lowest electronic states are included in these calculations, producing a total of nine vibrational bands in the ultraviolet. The attempt is made to reproduce observed, ultraviolet, cometary spectra of OH by utilizing the Swings fluorescence mechanism. The inclusion of four rotational states within each of the three vibrational states and a detailed solar atlas make it possible to match observations very well, although there remain some discrepancies. This ability to reproduce observations provides confidence that the more general results obtained for the fluorescence efficiency as a function of heliocentric radial velocity can be used in interpreting both previous and future observations of OH in comets.