Rate Constants For Reduction Research Articles

Scanning Electrochemical Microscope Studies of Charge Transfer Kinetics at the Interface of the Perovskite/Hole Transport Layer

Interfacial carrier transfer kinetics is critical to the efficiency and stability of perovskite solar cells. Herein, we measure the regeneration rate constant, absorption cross-section, reduction rate constant, and conductivity of hole transport layered perovskites using scanning electrochemical microscopy (SECM). The SECM feedback revealed that the regeneration rate constant, absorption cross-section, and reduction rate constant of the nickel oxide (NiO) layer perovskite layer are higher than those of the poly (3,4-ethyenedioxythiophene)-poly (styrenesulfonate) layered perovskite. Also, at a specific flux density ( J h v ), the value of the regeneration rate constant (keff) in both blue and red illuminations for the NiO/CH3NH3PbI3 film is significantly higher than in both PEDOT: PSS/CH3NH3PbI3 and FTO/CH3NH3PbI3 films. The difference in keff between layered and nonlayered perovskite conforms to the impact of the hole conducting layer on the charge transfer kinetics. According to the findings, SECM is a powerful approach for screening an appropriate hole transport layer for stable perovskite solar cells.

Heterogenous Preparations of Solution-Processable Cobalt Phthalocyanines for Carbon Dioxide Reduction Electrocatalysis

The development and implementation of technology that can capture and transform carbon dioxide (CO2) is of ongoing interest. To that end, the integration of molecular electrocatalysts into devices is appealing because of the desirable features of molecules, such as the ability to modify active sites. Here, we explore how the identity of the aliphatic group in 1,4,8,11,15,18,22,25-octaalkoxyphthalocyanine cobalt(II) affects the catalytic behavior for heterogeneous CO2 reduction electrocatalysis. The alkyl R-groups correspond to n-butoxy, sec-butoxy, and 2-ethylhexoxy. All of the catalysts are soluble in organic solvents and are readily solution-processed. However, the larger 2-ethylhexoxy group showed solution aggregation behavior at concentrations ≥1 mM, and it was, in general, an inferior catalyst. The other two catalysts show comparable maximum currents, but the octa sec-butoxy-bearing catalyst showed larger CO2 reduction rate constants based on foot-of-the-wave analyses. This behavior is hypothesized to be due to the ability of the sec-butoxy groups to eliminate the ability of the alkoxy oxygen to block Co Sites via ligation. CO2 reduction activity is rationalized based on solid-state structures. Cobalt(II) phthalocyanine and its derivatives are known to be good CO2 reduction catalysts, but the results from this work suggest that straightforward incorporation of bulky groups can improve the processability and per site activity by discouraging aggregation.

Impacts of the invasive Spartina anglica on C-S-Hg cycles and Hg(II) methylating microbial communities revealed by hgcA gene analysis in intertidal sediment of the Han River estuary, Yellow Sea

We investigated the impact of invasive vegetation on mercury cycles, and identified microorganisms directly related to Hg(II) methylation using hgcA gene in vegetated mud flats (VMF) inhabited by native Suaeda japonica (SJ) and invasive Spartina anglica (SA), and unvegetated mud flats (UMF) in Ganghwa intertidal sediments. Sulfate reduction rate (SRR) and rate constants of Hg(II) methylation (Km) and methyl-Hg demethylation (Kd) were consistently greater in VMF than in UMF, specifically 1.5, 2 and 11.7 times higher, respectively, for SA. Both Km and Kd were significantly correlated with SRR and the abundance of sulfate-reducing bacteria. These results indicate that the rhizosphere of invasive SA provides a hotspot for Hg dynamics coupled with sulfate reduction. HgcA gene analysis revealed that Hg(II)-methylators were dominated by Deltaproteobacteria, Chloroflexi and Euryarchaeota, comprising 37.9%, 35.8%, and 6.5% of total hgcA gene sequences, respectively, which implies that coastal sediments harbor diverse Hg(II)-methylating microorganisms that previously underrepresented.

Reduction of transient carnosine radicals depends on β-alanyl amino group charge.

Reduction of transient carnosine (β-alanyl-L-histidine) radicals by L-tryptophan, N-acetyl tryptophan, and the Trp-Gly peptide in neutral and basic aqueous solutions was studied using the technique of time-resolved chemically induced dynamic nuclear polarization (TR CIDNP). Carnosine radicals were generated in the photoinduced reaction with triplet excited 3,3',4,4'-tetracarboxy benzophenone. In this reaction, carnosine radicals with their radical center at the histidine residue are formed. Modeling of CIDNP kinetic data allowed for the determination of pH-dependent rate constants of the reduction reaction. It was shown that the protonation state of the amino group of the non-reacting β-alanine residue of the carnosine radical affects the rate constant of the reduction reaction. The results were compared to those obtained previously for the reduction of histidine and N-acetyl histidine free radicals and to newly obtained results for the reduction of radicals derived from Gly-His, a homologue of carnosine. Clear differences were demonstrated.

Kaolin-Supported Silver Nanoparticles as an Effective Catalyst for the Removal of Methylene Blue Dye from Aqueous Solutions.

Water contamination by organic dyes has become a reason for severe environmental pollution and has been threatening the aquatic ecosystem. In this study, kaolin-supported silver nanoparticle (Ag-NP) composites were synthesized by a facile two-step adsorption-reduction method through the reduction of silver ions adsorbed onto locally available, inexpensive, and easily pretreated kaolin surfaces by using sodium borohydride (NaBH4) for the catalytic degradation of methylene blue (MB) dye in aqueous solution. The morphology, structure, surface area, and interaction of the synthesized materials were investigated by scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopy, respectively. Characterization results showed the successful growth of Ag-NPs on the kaolin surface. To understand the catalytic degradation performance of the catalyst, batch experiments were carried out using MB dye as a model dye. The catalytic reduction tests confirmed the importance of Ag-NPs and the high catalytic activities of the synthesized Ag-NPs/kaolin composite toward MB dye reduction. The degradation results indicated that the increased Ag-NP content on the kaolin surface through repeating cycles could effectively enhance the removal of MB dye from an aqueous solution. The kinetic analysis of the MB dye degradation of the catalyst has fitted the pseudo-first-order kinetic model. More than 97% removal efficiency was still present after five reuse cycles, demonstrating exceptional stability and reusability of the composite. In conclusion, the Ag-NPs supported kaolin (Ag-NPs/kaolin) composite was found to be a promising catalyst for the excellent catalytic activity to reduce a model dye MB from the aqueous solution in the presence of NaBH4 with catalytic efficiency higher than 97% and a reduction rate constant, k red, higher than 0.86 min-1.

Development of a Coal Combustion Model Compliant with the CHEMKIN Format for Use in Co-Firing Analysis with Hydrogen and Low-Carbon Fuels

We developed a simplified coal combustion model that is used in combination with detailed gas reaction models. This model aimed to develop co-firing systems for decarbonized fuels such as coal and hydrogen. The reaction mechanism was described in the CHEMKIN format. We aimed to develop a coal combustion model that is easy to handle even for experts in gas combustion. Based on the experimental results, we modified the following reaction models. (1) Determining the rate constant of NOx reduction by char in the presence of oxygen. (2) Determining the gasification reaction rate constants, especially the rate constant of the steam gasification reaction, from staged combustion experiments. (3) Adoption of a chemical structural model of char based on elemental analysis results. Char was composed of carbon; C, nitrogen; N, and hydrocarbons; CnHm. As a result of the improvement, we achieved the NOx prediction error halved. Improving the calculation accuracy of the coal burnout was most important for improving the accuracy of the gas reactions. If there was an error in the calculated coal burnout due to an error in the gasification reaction, and so forth, the amount of C, H, O, and N species in the coal released into the gas phase would change. These changed the burning conditions, for example, stoichiometric ratio, in the gas phase. As a result, the concentration of radicals such as H, O, and OH changed, causing a decrease in NOx prediction accuracy. We obtained outline of the combustion performances when decarbonized fuel such as hydrogen and coal were co-combusted.

Electrocatalytic reduction of nitrate ions in neutral medium at coinage metal-modified platinum electrodes.

Nitrate is a water-soluble toxic pollutant that needs to be excluded from the environment. For this purpose, several electrochemical studies have been conducted but most of them focused on the nitrate reduction reaction (NRR) in alkaline and acidic media while insignificant research is available in neutral media with Pt electrode. In this work, we explored the effect of three coinage metals (Cu, Ag, and Au) on Pt electrode for the electrochemical reduction of nitrate in neutral solution. Among the three electrodes, Pt-Cu exhibited the best catalytic activity toward NRR, whereas Pt-Au electrode did not show any reactivity. An activity order of Pt-Cu > Pt-Ag > Pt-Au was observed pertaining to NRR. The Pt-Ag electrode produces nitrite ions by reducing nitrate ions ([Formula: see text]. Meanwhile, at Pt-Cu electrode, nitrate reduction yields ammonia via both direct ([Formula: see text] and indirect ([Formula: see text] reaction pathways depending on the potential. The cathodic transfer coefficients were estimated to be ca. 0.40 and ca. 0.52, while the standard rate constants for nitrate reduction were calculated as ca. 2.544 × 10-2cm.s-1 and ca. 1.453 × 10-2cm.s-1 for Pt-Cu and Pt-Ag electrodes, respectively. Importantly, Pt-Cu and Pt-Ag electrodes execute NRR in the neutral medium between their respective Hydrogen-Evolution Reaction (HER) and Open-Circuit Potential (OCP), implying that on these electrodes, HER and NRR do not compete and the latter is a corrosion-free process.

Electrochemical Screening of Au/Pt Catalysts for the Thermocatalytic Synthesis of Hydrogen Peroxide Based on Their Oxygen Reduction and Hydrogen Oxidation Activities Probed via Voltammetric Scanning Electrochemical Microscopy

Electrochemical analysis provides a convenient way to screen active materials for thermocatalytic processes involving implicit electrochemical redox mechanisms. Here, we show how a combinatorial method based on scanning electrochemical microscopy (SECM) rapidly screens multiple catalysts for hydrogen peroxide direct synthesis reaction by independently analyzing their hydrogen oxidation and oxygen reduction reactivities on the same chip. We present a reproducible and quantifiable procedure to fabricate catalyst spot array samples using photolithography and microdispensing. This procedure enables the exploration of up to 10 catalysts with three replicates each on one chip, allowing us to study 30 compositions to identify reactive trends in a vast compositional space. SECM imaging with linear sweep voltammetry improved the accuracy and efficiency of data collection. Kinetic parameters of both half-reactions for each catalyst were extracted from experimental data with the help of established analytical theory and finite element analysis simulation. A library of AuxPty catalysts with a range of Au/Pt ratios from 1200:1 to 120:12 were examined. For the synthesized AuxPty catalysts, the rate constants of oxygen reduction and hydrogen reduction increase as Pt content increases and then level off beyond Au120Pt7. Therefore, to achieve the highest activity while keeping the cost low, Au120Pt7 would be a promising composition to further investigate. We believe this SECM-based technique will expedite the catalyst design and discovery process for classes of thermochemical reactions involving underlying heterolytic electrochemical mechanisms, thus assisting in the synthesis and utilization of sustainable fuels and commodity chemicals.

One‐step synthesis of silver nanoparticles exposed on the chitosan‐covered polyamide 6 electrospinning nanofibers

AbstractA one‐step method was developed for synthesizing Ag nanoparticles exposed on the chitosan‐covered polyamide 6 (CS‐Ag@PA6) nanofibers by the in‐situ reduction of silver nitrate during the electrospinning process. The bioderived CS was employed as a stabilizer and chelating carrier of Ag0/Ag+ through its functional groups. CS was also used as a tractive agent to promote the surface migration of Ag atoms owing to its polyelectrolytic properties and immiscibility with PA6. Formic acid was used as the co‐solvent for PA6 and CS and the reducing agent for Ag+. It was verified that the Ag nanoparticles (AgNPs) with 31.7% Ag0 were embedded inside the pure PA6 nanofibers. However, the incorporation of CS achieved the AgNPs with an improved reduction efficiency (i.e., 67.5% of Ag0). In particular, the CS nanolayers were covered on the PA6 nanofiber skeleton, where the AgNPs migrated on the surface of the CS nanolayers. This surface migration of CS and AgNPS endowed a significantly enhanced catalytic activity to the reduction of 4‐nitrophenol, where the reduction rate constant (k) and turnover frequency (TOF) were an order of magnitude higher than that of the CS‐free nanofibers.

A tough and highly active catalyst carrier tailored by nanoparticles-encapsulation poly(ionic liquid) hydrogel: Synthesis and catalytic applications

The design and fabrication of functional hydrogel materials for catalysis environmental pollutants has gained immense interest. However, fabricating a hydrogel with both excellent mechanical and catalytic properties remains a challenge. Herein, we successfully achieved polyacrylamide/dimethylaminoethyl methacrylate bromododecane p(AM/DMLB) hydrogel with poly(ionic liquids) microspheres as toughened point and catalytic sites. Under the dual effect of ionic crosslinking network and hydrophobic association network, p(AM/DMLB)/PILs-MPs hydrogels exhibit excellent mechanical properties, such as the tensile strength (1.38 MPa), elongation (2000%), and toughness (1.15 MJ∙m−3). Simultaneously, the hydrogel could act as a template for loading of Pd nanoparticles without the addition of other additives and crosslinking agents. The metal-loaded composite hydrogels exhibits excellent catalytic property in the reduction of 4-nitrophenol (4-NP) reaction, and reduction rate constants (Kapp) was 0.226 min−1. The strategy offers a novel economically feasible route to catalytic use in the sewage-disposal industry.

On the Kinetic Mechanisms of the Reduction and Oxidation Reactions of Iron Oxide/Iron Pellets for a Hydrogen Storage Process

This work aims at investigating the kinetic mechanisms of the reduction/oxidation (redox) reactions of iron oxide/iron pellets under different operating conditions. The reaction principle is the basis of a thermochemical hydrogen storage system. To simulate the charging phase, a single pellet consisting of iron oxide (90% Fe2O3, 10% stabilising cement) is reduced with different hydrogen (H2) concentrations at temperatures between 600 and 800 °C. The discharge phase is initiated by the oxidation of the previously reduced pellet by water vapour (H2O) at different concentrations in the same temperature range. In both reactions, nitrogen (N2) is used as a carrier gas. The redox reactions have been experimentally measured in a thermogravimetric analyser (TGA) at a flow rate of 250 mL/min. An extensive literature review has been conducted on the existing reactions’ kinetic mechanisms along with their applicability to describe the obtained results. It turned out that the measured kinetic results can be excellently described with the so-called shrinking core model. Using the geometrical contracting sphere reaction mechanism model, the concentration- and temperature-dependent reduction and oxidation rates can be reproduced with a maximum deviation of less than 5%. In contrast to the reduction process, the temperature has a smaller effect on the oxidation reaction kinetics, which is attributed to 71% less activation energy (Ea,Re=56.9 kJ/mol versus Ea,Ox=16.0 kJ/mol). The concentration of the reacting gas showed, however, an opposite trend: namely, to have an almost twofold impact on the oxidation reaction rate constant compared to the reduction rate constant.

The characteristics of molasses-based reductive removal of Cr(VI) from groundwater by Bacillus sp.

This study was implemented to compare between the effect of molasses on chemical reduction and bioreduction of Cr(VI) in groundwater and further investigate its potential in enhancing bioreduction of Cr(VI) by indigenous strains from a Cr(VI)-contaminated site. High concentration of molasses (5.7 g/L) showed strong potential for chemical reduction of Cr(VI) at neutral pH under abiotic condition. Low concentration of molasses (1 g/L), which had limited chemical reduction potential for Cr(VI), could significantly enhance Cr(VI) bioreduction and was demonstrated stronger than sucrose which is the main stream product for molasses production. The strongest strain isolated from the site soils belonged to Bacillus sp. which was not reported for Cr(VI) reduction based on molasses as the sole carbon source. The Cr(VI) reduction behavior of the strain using molasses was further investigated. The reaction rate constant decreased with the increase of initial Cr(VI) concentration due to the toxic effect of Cr(VI). The greatest Cr(VI) bioreduction performance was observed at pH of 7.0, while the reduction rate was distinctly inhibited under acidic or alkaline conditions. The peak reduction rate constant was obtained at the temperature of 35 °C. Decrease of the rate constant was observed with the increasing concentration of SO42-, showing competitive inhibition of reduction by ions with a structure similar to CrO4-. The results of this study provide some useful information to support application of molasses in remediation of Cr(VI)-contaminated groundwater.

Black phosphorus@Au NPs decorated on a porous spherical montmorillonite as a self-sedimentary catalyst for cost-effective and efficient catalysis

Black phosphorus (BP) has exhibited its potential application as the cocatalyst substrate for catalytic reduction of organic pollutants due to its excellent electron transfer ability. However, the application was limited by the reuse process due to its light mass with abundant recovery devices involved. In this work, a micro-sized spherical montmorillonite (SMt) with the self-sedimentary property was used to support BP@Au NPs. The strong adsorption ability of porous SMt could increase the concentration of 4-nitrophenol near the catalytic active sites, thus, accelerating the catalytic process. The optimized apparent reduction rate constant of 6.1 min−1 and the turnover frequency of 648 h−1 were obtained, which was one of the most efficient catalytic system. More importantly, the fabricated SMt supported heterogeneous catalyst could be facile recycled without any devices involved. The morphology and catalytic performance were almost unaltered after recycling 20 times. Our straightforward strategy to solve the issue of the reuse process through a self-sedimentary substrate facilitates the practical application of these catalysts in the reduction of organic pollutants.

Regulation of nitrite reductase and lipid binding properties of cytoglobin by surface and distal histidine mutations

Cytoglobin is a hemoprotein widely expressed in fibroblasts and related cell lineages with yet undefined physiological function. Cytoglobin, as other heme proteins, can reduce nitrite to nitric oxide (NO) providing a route to generate NO in vivo in low oxygen conditions. In addition, cytoglobin can also bind lipids such as oleic acid and cardiolipin with high affinity. These two processes are potentially relevant to cytoglobin function. Little is known about how specific amino acids contribute to nitrite reduction and lipid binding. Here we investigate the role of the distal histidine His81 (E7) and several surface residues on the regulation of nitrite reduction and lipid binding. We observe that the replacement of His81 (E7) greatly increases heme reactivity towards nitrite, with nitrite reduction rate constants of up to 1100 M−1s−1 for the His81Ala mutant. His81 (E7) mutation causes a small decrease in lipid binding affinity, however experiments on the presence of imidazole indicate that His81 (E7) does not compete with the lipid for the binding site. Mutations of the surface residues Arg84 and Lys116 largely impair lipid binding. Our results suggest that dissociation of His81 (E7) from the heme mediates the formation of a hydrophobic cavity in the proximal heme side that can accommodate the lipid, with important contributions of the hydrophobic patch around residues Thr91, Val105, and Leu108, whereas the positive charges from Arg84 and Lys116 stabilize the carboxyl group of the fatty acid. Gain and loss-of-function mutations described here can serve as tools to study in vivo the physiological role of these putative cytoglobin functions.

Light Stimulates Copper-Limited Growth of an Oceanic Diatom by Increasing Cellular Copper(II) Reduction─A Rate-Determining Step in Copper Uptake.

Uptake of Cu by Thalassiosira oceanica requires that Cu(II) is reduced to Cu(I) prior to transport across the cell membrane. The reduction step is mediated biochemically by cellular reductases active with a broad range of Cu chemical species. Here, we report on the cellular Cu(II) reduction and Cu(I) uptake of a diatom under saturating and subsaturating irradiance. An increase in growth irradiance, from 50 to 400 μmol photons m-2 s-1, increased the rate of extracellular Cu(II) reduction and steady-state Cu uptake. Under these conditions, Cu-limited cells acquired Cu more efficiently and maintained faster rates of growth than Cu-limited cells in low light. Pseudo-first-order reaction rate constants were about 70-fold faster for Cu(I) uptake than for Cu(II) reduction so that reduction was the rate-determining step in Cu acquisition. Accordingly, steady-state Cu uptake rates predicted from the reduction rate constants agreed well with measured rates of Cu uptake obtained from cultures growing at low nanomolar Cu concentrations. Transcript abundance of putative Cu(II) reductases followed a similar pattern to cupric reductase activity, increasing in Cu-limited cells and with increasing growth irradiance. The results are significant in showing Cu(II) reduction as the rate-determining step in Cu uptake: they suggest that biologically mediated Cu(II) reduction may be an important part of the Cu cycle in surface waters of the open sea.

Unique multi-hierarchical Z-scheme heterojunction of branching SnIn4S8 nanosheets on ZnIn2S4 nanopetals for boosted photocatalytic performance

Multinary metal sulfides are receiving more and more attention in the field of photocatalysis due to their excellent photoelectronic properties, but they usually suffer from the low photogenerated carrier separation efficiency and poor photostability. In this work, a dual multinary metal sulfides composite system is developed to address these issues. A unique multi-hierarchical Z-scheme heterojunction is successfully constructed by in-situ growth of branched SnIn4S8 nanosheets on nanopetals of flower-like ZnIn2S4. The prepared optimal composite photocatalyst displays significantly enhanced visible-light photocatalytic activity with H2 evolution rate of 2.988 mmol g−1h−1, Cr(VI) reduction rate constant of 0.094 min−1 and dye degradation rate constant of 0.152 min−1, which are 4.5, 9.4 and 19 times of bare SnIn4S8, and 2.9, 4.3 and 3.5 times of bare ZnIn2S4, respectively. The improved photocatalytic performance is primarily attributed to the abundant porous channels of the novel hierarchical flower-shaped architecture and the formation of the direct Z-scheme heterojunction, guaranteeing the richer active sites, better light harvesting, stronger redox capability, and more efficient charge transfer. This work demonstrates the promising applications of the SnIn4S8/ZnIn2S4 hybrid in energy and environmental photocatalysis fields, and should be instructive for the design and modification of multinary sulfide photocatalysts.

Diketone-mediated photochemical reduction of selenite to elemental selenium: Role of carbon-centered radicals and complexation

The reduction of highly toxic selenite (Se(IV)) to insoluble elemental selenium (Se(0)) is an effective strategy to alleviate the toxicity and to recover valuable Se from contaminated waters. Acetylacetone (AcAc) and diacetyl (BD) were found to be able to photoreduce Se(IV) into selenium nanoparticles. However, the kinetics and molecular mechanisms of the diketone-mediated Se(IV) reduction are still open to discussion. Herein, the photo-reduction of Se(IV) was studied with the two diketones and sulfite as reductants, as well as TiO2 as a photocatalyst. The results demonstrate that the two diketones were more effective and robust than sulfite. The reduction rate constants of Se(IV) in the UV/diketone systems were 5.1–6.5 times higher than those of UV/sulfite in a wide pH range (1.0–8.0) and without the need for deoxygenation. Compared with UV/TiO2 reduction, no complicated separation processes were needed after reduction with UV/diketones. After 1 h of irradiation, the recovery rates of Se(0) were 82% and 75% in UV/AcAc and UV/BD, respectively. Interestingly, the reactions that occurred in the UV/AcAc and UV/BD systems were unexpectedly different. On the base of reactive species scavenging experiments and quantum chemical calculations, acetyl radical (CH3C•(O)) and its hydrated product (CH3C•(OH)2) were found to play dominant roles in the UV/BD system, whereas the role of photo-induced complexation between hydrated AcAc and Se(IV) might not be neglected in the UV/AcAc system. Such a difference provides us with some room for choice and adjustment in the further application of UV/diketones for the treatment of Se(IV)-laden wastewater or for the reduction of some other similar metalloids.

Individual and combined degradation of N-heterocyclic compounds under sulfate radical-based advanced oxidation processes

Although the inhibitory effect of purines and phenols on the degradation of N-heterocyclic compounds under UV/peroxymonosulfate (PMS) has been reported, the understanding of contaminants' underlying mechanisms and kinetics is still very limited. In this study, five omnipresent nitrogenous bases (adenine, guanine, cytosine, thymine, and uracil) in the aquatic environment were used to study the inhibitory effect of N-heterocyclic compounds under UV/PMS by quantum chemical calculations. We found that HO• and SO4•− initiate base degradation with second-order rate constants of (0.11 – 15.6) × 109 M−1 s−1 and (7.25 – 13.5) × 109 M−1 s−1, respectively, and the primary products contain hydroxyl derivatives (HO-P), intermediate radicals (P(-H)•) and cationic radicals (P•+, only for purines). Because of the lower oxidation potentials of HO-P than their parent compounds (P), we first proposed a self-inhibition pathway in which HO-P can revert P(-H)• and P•+ back to P through H atom abstraction and single electron transfer reactions, respectively. A more significant self-inhibition was found in the degradation of uracil than that of adenine under UV/PMS because the former has a higher yield of hydroxylated derivatives. The main hydroxylated product (6-HO-U) of uracil repairs the uracil radical (U(-4H)•) at the reaction rate constants of 1.01 × 109 M−1 s−1. The combined degradation of bases showed that the reduction rate constants of purine cationic radicals have a linear relationship with the oxidation potentials of reductants. In the adenine-uracil mixture system, adenine inhibits uracil degradation by repairing U(-4H)• (2.33 × 105 M−1 s−1). This work revealed the mechanisms and kinetics of self-inhibition and joint-degradation of N-heterocyclic compounds, which is of great significance for understanding the collective removal of contaminants in the real water environment.

Modeling the Reduction Kinetics of Munition Compounds by Humic Acids.

Dissolved organic matter (DOM) comprises a sizeable portion of the redox-active constituents in the environment and is an important reductant for the abiotic transformation of nitroaromatic compounds and munition constituents (NACs/MCs). Building a predictive kinetic model for these reactions would require the energies associated with both the reduction of the NACs/MCs and the oxidation of the DOM. The heterogeneous and unknown structure of DOM, however, has prohibited reliable determination of its oxidation energies. To overcome this limitation, humic acids (HAs) were used as model DOM, and their redox moieties were modeled as a collection of quinones of different redox potentials. The reduction and oxidation energies of the NACs/MCs and hydroquinones, respectively, via hydrogen atom transfer (HAT) reactions were then calculated quantum chemically. HAT energies have been used successfully in a linear free energy relationship (LFER) to predict second-order rate constants for NAC reduction by hydroquinones. Furthermore, a linear relationship between the HAT energies and the reduction potentials of quinones was established, which allows estimation of hydroquinone reactivity (i.e., rate constants) from HA redox titration data. A training set of three HAs and two NACs/MCs was used to generate a mean HA redox profile that successfully predicted reduction kinetics in multiple HA/MC systems.

Rich oxygen vacancies facilitated visible light-driven removal of phenol and Cr(VI) over Bi2WO6 decorated by sorghum straw carbon

Surface features of photocatalyst perform a significant action in influencing photocatalytic properties by affecting the separation of photoactivated carriers. Surface modification is considered as a robust approach to facilitate the separation of photoactivated carriers. In this presentation, sorghum straw carbon (SSC) treated in NH3 atmosphere was employed to surface modification of Bi2WO6 photocatalyst prepared by a hydrothermal method. The composition, optical absorption and photogenerated carrier separation of the photocatalysts were investigated through various characterization methods. Compared with the pure Bi2WO6, N-containing sorghum straw carbon (N-SSC)/Bi2WO6 composite photocatalysts have higher surface hydroxyl, oxygen defects and photogenerated e-/h+ pairs separation ability. When the mass ratio of N-SSC/Bi2WO6 is 1.5%, the sample manifests excellent visible light activity. The photocatalytic decontamination rate constant of phenol on the 1.5% N-SSC/Bi2WO6 is 8-fold of that on the single Bi2WO6. The photocatalytic reduction efficiency for Cr (VI) on the 1.5% sample is 37.8% after 120 min under visible light photocatalysis, and the photocatalytic reduction rate constant of Cr (VI) over the 1.5% sample is 1.8-fold of that on the neat Bi2WO6. The active species were analyzed, and then the photocatalytic mechanism was interpreted.