The combination of an oxidation and a reduction in a cascade allows performing transformations in a very economic and efficient fashion. The challenge is how to combine an oxidation with a reduction in one pot, either by running the two reactions simultaneously or in a stepwise fashion without isolation of intermediates. The broader availability of various redox enzymes nowadays has triggered the recent investigation of various oxidation–reduction cascades.
Knowing the thermodynamic stability of transition metal oxide nanoparticles is important for understanding and controlling their role in a variety of industrial and environmental systems. Using calorimetrie data on surface energies for cobalt, iron, manganese, and nickel oxide systems, we show that surface energy strongly influences their redox equilibria and phase stability. Spinels (M₃O₄) commonly have lower surface energies than metals (M), rocksalt oxides (MO), and trivalent oxides (M₂O₃) of the same metal; thus, the contraction of the stability field of the divalent oxide and expansion of the spinel field appear to be general phenomena. Using tabulated thermodynamic data for bulk phases to calculate redox phase equilibria at the nanoscale can lead to errors of several orders of magnitude in oxygen fugacity and of 100 to 200 kelvin in temperature.
This study involves elucidating the destruction mechanisms of four tetracyclines via reactions with OH and solvated electrons ( ). The first step is to evaluate the bimolecular rate constants for the reaction of OH and . Transient absorption spectra for the intermediates formed by the reaction of OH were also measured over the time period of 1–250 μs to assist in selecting the appropriate wavelength for the absolute bimolecular reaction rate constants. For these four compounds, tetracycline, chlortetracycline, oxytetracycline, and doxycycline, the absolute rate constants with OH were (6.3 ± 0.1) × 10 , (5.2 ± 0.2) × 10 , (5.6 ± 0.1) × 10 , and (7.6 ± 0.1) × 10 M s , and for were (2.2 ± 0.1) × 10 , (1.3 ± 0.2) × 10 , (2.3 ± 0.1) × 10 , and (2.5 ± 0.1) × 10 M s , respectively. The efficiencies for OH reaction with the four tetracyclines ranged from 32% to 60%. The efficiencies for reaction were 15–29% except for chlortetracycline which was significantly higher (97%) than the other tetracyclines in spite of the similar reaction rate constants for in all cases. To evaluate the use of advanced oxidation/reduction processes for the destruction of tetracyclines it is necessary to have reaction rates, reaction efficiencies and destruction mechanisms. This paper is the first step in eventually realizing the formulation of a detailed kinetic destruction model for these four tetracycline antibiotics.
The work presented here evaluated the impact of reduction-oxidation-reduction (ROR) pre-treatment on 5 and 10% Ni-SiO as an efficient and inexpensive manner of enhancing catalysts for the carbon dioxide reforming of methane. Samples were reduced, oxidised and subsequently re-reduced, with the Ni deposit characteristics being analysed at each step. It was demonstrated that ROR treatment decreased the average Ni deposit size and altered the interaction between the Ni and SiO , which significantly enhanced catalytic performance. ROR pre-treatment resulted in an increase in CH conversion, most significantly for the 10% Ni-SiO samples (from 57% to 69% at 800 °C) with comparable carbon formation between the reduced and ROR pre-treated samples. During 600 °C stability tests the 10% reduced samples deactivated, due to carbon build-up, after 3–4 h reaction time. In contrast, at 600 °C the ROR sample maintained stable conversion after 6 h over a 12 h time frame. Additionally, for all samples ROR pre-treatment resulted in a more stoichiometric H /CO ratio. The reduction in both Ni deposit size and crystallinity increased conversion and selectivity. This derived from a greater active metal surface area for conversion as well as a decrease in the prevalence of methane decomposition and the reverse water gas shift reaction by influencing the desorption of CO and lowering the occurrence of bulk NiO. Ultimately, ROR pre-treatment provides a simple and inexpensive means of improving dry reforming catalysts.
Objective To measure oxidative reduction potential (ORP) in semen and seminal plasma and to establish their reference levels. Design ORP levels were measured in semen and seminal plasma. Setting Tertiary hospital. Subject(s) Twenty-six controls and 33 infertile men. Intervention(s) None. Main Outcome Measure(s) Static ORP (sORP) and capacitance ORP (cORP) were measured in semen and seminal plasma at time 0 and 120 minutes. Correlation of ORP was assessed between  semen and seminal plasma and  time 0 and 120 minutes. The association with sperm parameters was studied in (a) controls and (b) infertile patients, and a receiver operating characteristic curve was generated to establish the sORP cutoff. Result(s) Semen sORP and cORP levels were associated with seminal plasma levels at time 0 and time 120 minutes. In controls and infertile patients, an inverse relationship of sORP levels was established with concentration and total sperm count in semen as well as seminal plasma at time 0 and 120 minutes. Classification of subjects based on sperm motility showed that subjects with abnormal motility present with poor concentration, total count, morphology, and elevated levels of semen and seminal plasma sORP at time 120 minutes. The sORP cutoff of 1.48 in semen and 2.09 in seminal plasma based on motility was able to distinguish subjects with normal semen quality from those with abnormal semen quality. Conclusion(s) The MiOXSYS System can reliably measure ORP levels in semen and seminal plasma. ORP levels are not affected by semen age, making this new technology easy to employ in a clinical setting.
In the paper the ability of CeO2-x, nanoparticles (nanoceria) to inactivate free radicals formed during water photolysis under UV irradiation is shown. UV irradiation of nanoparticles with sizes less than 10 nm in the aqueous medium promotes Ce4+ -> Ce3+ reduction, and after the cessation of irradiation Ce3+ -> Ce4+ reverse process is observed. The displacement of Ce3+ reversible arrow Ce4+ equilibrium in one direction or another occurs with time delay. Pre-irradiated nanoparticles in hydrosols are more active antioxidants than unirradiated ones. A possible mechanism of the antiradical action of nanoceria in aqueous solutions under UV irradiation was proposed.
The electrochemical behavior of hydrogen peroxide (H2O2) at carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (N-CNTs) was investigated over a wide potential window. At CNTs, H2O2 will be oxidized or reduced at large overpotentials, with a large potential region between these two processes where electrochemical activity is negligible. At N-CNTs, the overpotential for both H2O2 oxidation and reduction is significantly reduced; however, the reduction current from H2O2, especially at low overpotentials, is attributed to increased oxygen reduction rather than the direct reduction of H2O2, due to a fast chemical disproportionation of H2O2 at the N-CNT surface. Additionally, N-CNTs do not display separation between observable oxidation and reduction currents from H2O2. Overall, the analytical sensitivity of N-CNTs to H2O2, either by oxidation or reduction, is considerably higher than CNTs, and obtained at significantly lower overpotentials. N-CNTs display an anodic sensitivity and limit of detection of 830 mA M-1 cm(-2) and 0.5 mu M at 0.05 V, and a cathodic sensitivity and limit of detection of 270 mA M-1 cm(-2) and 10 mu M at -0.25 V (V vs Hg/Hg2SO4). N-CNTs are also a superior platform for the creation of bioelectrodes from the spontaneous adsorption of enzyme, compared to CNTs. Glucose oxidase (GOx) was allowed to adsorb onto N-CNTs, producing a bioelectrode with a sensitivity and limit of detection to glucose of 80 mA M-1 cm(-2) and 7 mu M after only 30 s of adsorption time from a 81.3 mu M GOx solution.
Abstract Objectives To evaluate 1) the relationship between oxidation-reduction potential (ORP) and abnormal sperm quality, 2) changes in ORP and sperm parameters over time, in search of a potential surrogate marker of poor sperm quality that may assist in the diagnosis of oxidative stress- related male infertility. Methods 194 infertile men were included and 28 patients were identified to have repeated semen analyses and ORP measurements. The semen samples obtained were categorized into normal and abnormal sperm parameters based on the World Health Organization (WHO) 5th edition guidelines. Wilcoxon tests were used to compare the results of different groups. Correlations were analyzed by Spearman's rank order and receiver operating characteristic (ROC) analysis was used to estimate optimal ORP cut-offs for identifying abnormalities. Results ORP levels were significantly elevated in semen samples with abnormal sperm parameters. ORP at a cut-off of 1.57 (mV/106 sperm) was able to detect at least one abnormal sperm parameter with a sensitivity 70.4% and specificity 88.1%. ORP at a cut-off of 2.59 (mV/106 sperm) had the highest predictive value in detecting oligozoospermia; 88% sensitivity and 91.2% specificity. The increases in sperm concentration and motility in patients tested for semen analysis at two consecutive time intervals were related to a decline in ORP levels. Conclusion Oxidation-reduction potential is a reliable method in predicting poor sperm quality. Its introduction in male infertility evaluation may help overcome the high technical variability of semen analysis and assist in the diagnosis of oxidative stress-related infertility.
Pre-oxidation is effective in enhancing sludge dewaterability. Different types and doses of oxidants are used to improve sludge dewaterability in pre-oxidation. Rapid evaluation of the sludge dewaterability is vital for optimizing the type and dose of oxidants in pre-oxidation. It normally takes more time to evaluate sludge dewaterability by measuring typical indicators such as specific resistance to filtration (SRF), content of bound water, and composition of EPS. This study presented a rapid parameter, oxidation-reduction potential (ORP), to correlate it with the dewaterability of pre-oxidized sludge samples. An index of ΔORP (ΔORP = ORP –ORP ) showed positive correlations with SRF ( = 0.89, < 0.05), content of total organic carbon in soluble and loosely-bound EPS ( = 0.86 and 0.84, < 0.05), zeta potential ( = 0.86, < 0.05), and content of Fe(III) in the sludge cake ( = 0.92, < 0.01). However, the ΔORP index showed negative correlations with tryptophan-like proteins, tyrosine-like proteins, microbial byproduct-like materials in tightly-bound EPS ( = −0.85, −0.90 and −0.90, < 0.05), and sludge particle sizes ( < 0.01). A multiple linear regression model was developed to further reflect the linear correlation between the ΔORP values and the key factors reflecting sludge dewaterability. An optimal dose of oxone (0.4 mmol/g VS) for sludge pre-oxidation with the ΔORP value of 387 mV combined with Fe(III) coagulation conditioning system were verified by the results of dewatering experiments using a laboratory-scale diaphragm filter press. This study demonstrated the feasibility of using ΔORP as a potential rapid evaluation tool for sludge dewaterability.
A convenient method based on photocatalytic reduction was used to prepare graphene-supported Pd, Fe, and bimetallic Pd-Fe nanoparticle (NP) catalysts under mild conditions. The obtained catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Their potential application to the electrocatalytic degradation of chlorinated phenols (CPs) was investigated by cyclic voltammetry (CV) and chronoamperometry. The graphene-supported bimetallic Pd-Fe NP catalyst (Pd Fe /graphene) exhibited the optimal surface performance and contained highly abundant and widespread Pd-Fe NPs of approximately 6.75 ± 0.05 nm in size. It exhibited higher electrocatalytic activity for dechlorination of CPs attributed to its higher hydrogen adsorption peak current of 0.117 mA than that of the Pd/graphene catalyst, with a 1% weight ratio of Pd (Pd /graphene catalyst), and the Fe/graphene catalyst, with a 1% weight ratio of Fe (Fe /graphene catalyst). The highest reductive peak current (0.038 mA) was obtained at −0.347 V when using the Pd Fe /graphene catalyst, indicating that the Pd Fe /graphene catalyst has the highest electrocatalytic activity for accelerating the two-electron reduction of O to H O . In addition, the electrocatalytic activity was enhanced when feeding with O and at pH 12.8. The electrochemical reductive reaction of O is typically a diffusion-controlled electrochemical process. The calculated values of representing the mass transfer rate were in the order Pd Fe /graphene (0.379) > Pd /graphene (0.178) > Fe /graphene (0.175). The reduction peak currents for four CPs decreased in the order 3-chlorophenol (0.0214 mA) > 2,4,5-trichlorophenol (0.0190 mA) > 2,4-dichlorophenol (0.0188 mA) > 4-chlorophenol (0.0178 mA), indicating that the Pd Fe /graphene electrode would show the most powerful indirect electro-oxidation for 3-CP degradation in comparison with the other CPs. Therefore, the Pd Fe /graphene catalyst exhibits a higher electrocatalytic activity than the Pd /graphene catalyst and Fe /graphene catalyst for the reductive dechlorination and indirect electrochemical oxidation of CPs.