Chemical Reduction Rate Research Articles

Structural and optical properties of polymer blend nanocomposites based on PVP/PVA incorporated AgNO3

In this study, polymer nanocomposite based on polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and silver nitrate (AgNO3) has been prepared through chemical reduction rate and casting method for varying concentrations of AgNO3. The PVP/PVA blend consisted of 0.6 wt% PVP and 0.4 wt% PVA. Following that, polymer nanocomposites were prepared by incorporating different concentrations of AgNO3 (0, 10, 20, 30, 40, and 50 wt%) into the polymer blend. The effects of different concentrations of AgNO3 on the structural and optical properties of the PVP/PVA blend were investigated using x-ray diffraction (XRD) and UV–vis absorption spectroscopy. The XRD analysis demonstrated that increasing the concentration of AgNO3 results in a decrease in the degree of crystallinity from 53.73 in the PVP/PVA blend to 15.77 in the PVP/PVA nanocomposite containing 50 wt% AgNO3. UV–vis absorbance spectra were examined to determine optical properties such as the absorption coefficient, absorption edge, optical band gap, and tails of localized states. The results revealed that the increase in AgNO3 concentrations caused a reduction in the absorption edge and optical band gap, alongside an increase in Urbach energy.

Biosynthesis of silver nanocatalyst and its application for the efficient hydrogenation of nitroarenes

The utilization of plant extracts for the synthesis of silver nanoparticles (Ag-NPs) has attracted attention from all over the world due to its unique physicochemical characteristics and significance in the field of environment. Here, Nepal pepper fruit extract was successfully employed to synthesize Ag-NPs. As obtained, Nepal pepper-mediated Ag-NPs were employed for the catalytic conversion of nitroarenes including 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 2-nitroaniline (2-NA), and 2,4,6-trinitrophenol (2,4,6-TNP), into their corresponding amino derivatives using sodium borohydride (NaBH4). The Ag-NPs were analyzed using UV–visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-rays (EDX), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), X-rays Diffraction (XRD), and Zeta potential. TEM micrographs revealed the prepared Ag-NPs were predominantly spherical, with an average diameter of 13.9 nm. DLS and zeta potential studies showed stable small-size Ag-NPs of an average size of 6.8 nm. Ag-NPs elucidate outstanding reduction efficiency against 4-NP, 2-NP, 2-NA, and 2,4,6-TNP with rate constants of 1.71 × 10−3 s−1, 2.32 × 10−3 s−1, 2.88 × 10−3 s−1, and 1.54 × 10−3 s−1, respectively. Additionally, stability and reusability of Ag-NPs revealed stability for up to 15 days and excellent recyclability with small activity loss. This study constittutes an environmentally friendly approach for the synthesis of Ag-NP nanoparticles and their applications in improved organic chemical reduction rates and transformations.

Reduction of bromate and chlorate contaminants in water using aqueous phase corona discharge

This work demonstrates the ability of aqueous phase corona discharge to chemically reduce bromate and chlorate ions, common disinfection byproducts, to bromide and chloride ions, respectively. A high voltage pulse was applied to a needle electrode, submerged in the target solution, to generate highly reactive oxidative and reductive species in a temperature-controlled reactor. Optimal water matrix conditions were sought through changing the solution pH, temperature, and dissolved oxygen concentration. Additionally, several oxidative species scavengers were investigated, including methanol, ethanol, sucrose, and D-sorbitol. Chemical reduction rates were improved at low pH (3.5). The presence of dissolved oxygen significantly reduced the chemical reduction rate, and thus high solution temperature (50 °C) also achieved better chemical reduction. All oxidative species scavengers improved the chemical reduction rate; however, methanol and ethanol were superior as these compounds generate hydrogen bubbles in the presence of plasma, which deoxygenates the solution further improving the chemical reduction rate. The application of this technology to 30 μM bromate and chlorate solutions, under optimal water matrix conditions and with the addition of 72 g/L-COD methanol, achieved greater than 95% removal of the target compounds within 60 min. Increasing the initial concentration of the target compounds to 300 μM required 90 and 150 min to achieve similar chemical reductions for bromate and chlorate, respectively.

Influence of pH on Cr(VI) reduction by organic reducing substances from sugarcane molasses

The remediation of Cr(VI) is one of the hot issues in groundwater pollution remediation. The influences and effects of pH on Cr(VI) reduction by organic reducing substances in sugarcane molasses were studied under the sterilization and unsterilization conditions by means of batch laboratory-scale experiments. The results showed that pH of reaction solution has a great influence on the reduction of Cr(VI) by sugarcane molasses. When pH ≥ 3.0, the final removal efficiency of Cr(VI) on the condition of sterilization and unsterilization at pH values of 8.0, 5.8, 4.0 and 3.0 was 15.441%, 17.945%, 29.205%, 36.258% and 99.236%, and 98.577%, 99.235% and 99.368%, respectively. When pH < 3.0, the final removal efficiency of Cr(VI) on the condition of sterilization and unsterilization at pH values of 2.5 and 2.0 was 99.631% and 99.895%, and 99.631% and 99.895%, respectively. The main mechanism involves chemical reduction and biological reduction. And biological reduction in the process of Cr(VI) reduction by sugarcane molasses is of the first priority when pH ≥ 3.0; when pH < 3.0, the rate of chemical reduction was higher and it was not the basic existing biological reduction. The relationship between pH and pseudo-first-order rate constant (kobs) on both the sterilization and unsterilization conditions was satisfied with Boltzmann model. There is an inflection point at the pH of about 2.6, which also indicated the influence mechanism of pH on the reduction of Cr(VI) by sugarcane molasses.

Reduction kinetics of commercial haematite pellet in a fixed bed at 1123–1273 K

In the present study a model for future use in the modelling of moving bed direct reduction reactors has been developed. The model of a fixed bed reactor for the production of sponge iron from haematite incorporates both heat- and mass-transfer, as well as the chemical reduction rate. The model results were compared to the experimental data obtained from a lab scale reactor in the temperature range 1123–1273 K, as well as to the output from a simple model assuming isothermal conditions. The H2/CO ratio (β) of the reducing gas was in all cases varied from 0.8 to 2.0. Overall the non-isothermal model developed permits a more accurate representation of the experimental data than the isothermal estimates, with a typical discrepancy of only 1.3%.

Initial Reaction Mechanism of Platinum Nanoparticle in Methanol-Water System and the Anomalous Catalytic Effect of Water.

Understanding the detailed reaction mechanism in the early stage of noble metal nanoparticles is very critical for controlling the final crystal's size, morphology, and properties. Here, we report a systematic study on the initial reaction mechanism of Pt nanoparticles in methanol-water system and demonstrate an anomalous catalytic effect of H2O on the reduction of H2PtCl6 to Pt nanoparticles using a combination of UV-vis, X-ray absorption spectroscopy (XAS), liquid chromatography mass spectrometry (LCMS), and first-principles calculation methods. The observations reveal the transformation route [PtCl6](2-) → [PtCl5(CH3O)](2-) → [PtCl4](2-) → [PtCl3(CH3O)](2-) → [PtCl2](2-) and finally to form Pt nanoparticles in a pure CH3OH solution. With 10 vol % water adding in the CH3OH solution, a new and distinct chemical reduction pathway is found in which the precursors change from [PtCl6](2-) to [PtCl5(CH3O)(H2O)](2-) to [PtCl4](2-) to [PtCl3(CH3O)(H2O)](2-) to [PtCl2](2-) and to Pt nanoparticles. Notably, the supernumerary water molecular can significantly accelerate the rate of chemical reduction and greatly shorten the reaction time. This work not only elucidates the initial reaction mechanism of Pt nanoparticles but also highlights the pronounced influence of H2O on the reaction pathway, which will provide useful insights for understanding the formation mechanism of noble metal nanoparticles and open up a high efficient way to synthesize new functional nanomaterial.

The impact of the confinement of reactants on the metal distribution in bimetallic nanoparticles synthesized in reverse micelles.

A kinetic study on the formation of bimetallic nanoparticles in microemulsions was carried out by computer simulation. A comprehensive analysis of the resulting nanostructures was performed regarding the influence of intermicellar exchange on reactivity. The objects of this study were metals having a difference in standard reduction potential of about 0.2–0.3 V. Relatively flexible microemulsions were employed and the concentration of the reactants was kept constant, while the reaction rate of each metal was monitored as a function of time using different reactant proportions. It was demonstrated that the reaction rates depend not only on the chemical reduction rate, but also on the intermicellar exchange rate. Furthermore, intermicellar exchange causes the accumulation of slower precursors inside the micelles, which favors chemical reduction. As a consequence, slower reduction rates strongly correlate with the number of reactants in this confined media. On the contrary, faster reduction rates are limited by the intermicellar exchange rate and not the number of reactants inside the micelles. As a result, different precursor proportions lead to different sequences of metal reduction, and thus the arrangement of the two metals in the nanostructure can be manipulated.

Kinetics of oxidation of quinol and ascorbic acid with the phen substituted semiquinone ligand, (5,6-dioxolene-1,10-phenanthroline-O,O), bound to the Ru II(bipy) 2 moiety

In 10% (v/v) CH 3CN–H 2O media, the parent complex [Ru(bpy) 2(sqphen)] + ( I +) coexists with its conjugate acid [Ru(bpy) 2(sqphenH)] 2+ (H I 2+): H I 2 + ⇌ H + + I +; (deprotonation constant, K a ox = 0.01; (bpy = 2,2 ′-bipyridine; sqphen = 5,6-dioxolene-1,10-phenanthroline-O,O). Electrochemical reduction, and also chemical reductions with quinol and ascorbic acid, produced the corresponding catechol complex [Ru(bpy) 2(catphen)] ( I R ), which also in solution coexists with its conjugate acid, [Ru(bpy) 2(catphenH)] + ( H I R + ) (deprotonation constant, K a red = 0.002). Progressive increase in [ascorbic acid] led to rate saturation, indicating adduct formation (formation constant, Q = 990 ± 80 M −1). Added H +, and also redox-innocent Lewis acid Zn 2+, increased E 1/2 but decreased the chemical reduction rates. Only an insignificant solvent isotope effect ( k H 2 O / k D 2 O ) was noted. An increased percentage of CH 3CN in the solvent also retards the rate. [Ru(bpy) 2(sqphen)] + ( I +) reacts at a much slower rate than [Ru(bpy) 2sq] + (sq = the unsubstituted semiquinone). Phen in the substituted ligand sqphen is known to become a much weaker base (sqphen < phen); O,O-coordination to the Ru II(bpy) center further lowers the basicity of sqphen. Catphen (O,O) in I R, produced on reduction of I +, is a stronger base than the O,O-coordinated sqphen in I +.

Influence of temperature and pH on the nonenzymatic reduction of triphenyltetrazolium chloride.

The effects of temperature and pH on the nonenzymatic (chemical) reduction of triphenyltetrazolium chloride (TTC) to triphenyl formazan (TF) in cheese whey and municipal solid waste compost samples were studied. Ten different incubation temperatures and 13 pH levels were tested. The study showed that the TTC could be reduced nonenzymatically at high temperatures and/or under alkaline pH conditions. The nonenzymatic TTC reduction was observed at pH values greater than 9.5 and 11.0 for the cheese whey and compost, respectively. The TTC chemical reduction rate followed the same trend in both media. The TF content increased with increasing the pH value, reaching its maximum at a pH of 12, then decreased and was not detected at a pH of 13. The TTC was also reduced nonenzymatically at temperatures higher than 70 and 85 degrees C for cheese whey and compost, respectively. Evaporation did not seem to have any significant effect on the TTC chemical reduction since less than 3% of water content was lost at a temperature of 100 degrees C. It was noticed that the TF yield in cheese whey samples was higher than that in compost samples. This was due to the higher moisture content of cheese whey and the presence of copper in the compost samples, which reacted chemically with the TF causing reduction in the red color. For a given incubation period, the effect of pH on the TTC chemical reduction was more significant than the effect of incubation temperature (at a 2 h incubation period, 57.5% and 17.9% of the TTC were chemically reduced at a pH of 12 compared to 10.9% and 7.7% at an incubation temperature of 100 degrees C, for cheese whey and compost, respectively). Among the six metals tested (Ca, Cu, K, Na, Ni, and Zn) only Cu affected the color intensity of the TF. The activation energy of the TTC chemical reduction was 168,808 and 239,102 J/mol in cheese whey and municipal solid compost, respectively. For dehydrogenase activity measurement, the pH of the samples and the incubation temperature should not be higher than 9 and 60 degrees C in order to ensure that the TTC reduction is caused only by the biochemical reaction. Measuring the color intensity of TF in waste samples that contain copper could give misleading results as a result of the formation of formazan copper complex, which reduces the red color.

Aqueous oxidation of dimethyl phthalate in a Fe(VI)-TiO 2-UV reaction system

The application of a combined ferrate–photocatalysis process for the aqueous degradation of dimethyl phthalate (DMP) has been studied. The behaviour of the Fe(VI)-TiO 2-UV process at pH 9 in the presence and absence of dissolved oxygen (DO) has been compared and significant differences have been found. In comparative tests under N 2 and O 2 bubbling, the chemical reduction rate of ferrate as conduction band electron acceptor was similar, but the resulting degradation of DMP was substantially lower in the presence of oxygen. It is speculated that the presence of oxygen leads to the formation of Fe–O–(organic) complex species that adsorb to, and deactivate, the surface of the photocatalyst. The presence of surface-adsorbed complex species was indicated by FTIR spectroscopy and a reduced TiO 2 adsorption capacity for DMP. In the presence of typical environmental levels of DO (∼9 mg L −1), the Fe(VI)-TiO 2-UV process achieved a modest degree of DMP degradation (40% in 120 min).

Kinetics of oxidation of ascorbic acid and 1,4-dihydroxybenzene by semiquinone radical bound to ruthenium(ii)

In 40% (v/v) MeOH–H2O media, containing [H+] (0.001–0.038 mol dm−3), the semiquinone (sq) radical, bound to Ru(II) in [Ru(bpy)2(sq)]+1, oxidises ascorbic acid (H2A) to dehydroascorbic acid (A), and 1,4-dihydroxybenzene (H2Q) to p-benzoquinone (Q); 1 is itself reduced to [Ru(bpy)2(Hcat)]+2H. The reactions are centred at sq not Ru(II). The sq/cat couple in 1 is reversible and its E1/2 increases with increasing [H+]; rate of chemical reduction of 1 to 2H increases in parallel. Rate increases also with increasing mole percent of D2O in the solvent suggesting a preliminary protonation equilibrium producing 1H, in which a H+ binds to the π-electron cloud of Ru(II)-bound sq. Under the experimental conditions, the kinetically significant species are 1H, H2Q, H2A and HA−. The kinetic activity of HA− ion is only ≈200 times more than that of H2A. This testifies against a purely outer-sphere mechanism and suggests significant electronic interaction between the redox partners. Increased percentage of MeOH in the solvent decreases λmax for the LMCT band; reaction rate for ascorbic acid decreases in parallel.

The role of (auto)catalysis in the mechanism of an anaerobic azo reduction

Azo dyes are non-specifically reduced under anaerobic conditions, but the slow rates at which many dyes react may present a serious problem for the application of anaerobic technology as a first stage in the complete biodegradation of these compounds. Therefore, it is significant to explore the mechanism of anaerobic azo reduction, especially with respect to its kinetics. With that purpose, decolouration of the monoazo dye C.I. Acid Orange 7 (AO7) was studied in batch experiments. Experiments indicated that chemical reduction by sulphide is partially responsible for the anaerobic conversions of AO7. Mathematical evaluation of the experimental results pointed out that autocatalysis played an important role in the chemical reduction of AO7. Further tests made clear that 1-amino-2-naphthol was the dye's constituent aromatic amines that accelerated the reduction process, possibly by mediating the transfer of reducing equivalents. The impact of redox mediation by quinones was further evaluated by testingthe catalysing effects of anthraquinone-2,6-disulphonic acid (AQDS) and of autoclaved sludge. AQDS appeared to be an extremely powerful catalyst, capable of increasing the first-order chemical reduction rate constants by a factor 10 to 100. Also autoclaved sludge, possibly because of mediation by sludge organic matter, accomplished accelerated azo reduction rates. Azo reduction in living sulphidogenic anaerobic sludge environments is 3 times more rapid than the chemically catalysed reaction with sulphide. The exact role of the biological activity remains to be clarified.

Electrochemical and spectroelectrochemical studies on cobalt myoglobin

The cobalt protoporphyrin-IX reconstituted myoglobin (Co-Mb) was prepared and its electrochemical and spectroelectrochemical properties were studied in comparison with native myoglobin. Unlike native myoglobin, a slow electron transfer reaction for Co(III)-Mb/Co(II)-Mb was detected by cyclic voltammogram and spectroelectrochemical methods. The chemical reduction rate of Co(III)-Mb with dithionite was also slow compared with that of native myoglobin. Direct electron transfer between Co-Mb and an In 2O 3 electrode was observed, with spectroscopic verification of different redox states of Co-Mb using an optically transparent thin layer electrode (OTTLE) cell. The reversible electrochemical redox reaction of Co(III)-Mb/Co(II)-Mb was observed using azure A, 3-amino-7-dimethylaminophenazathionium chloride, as an electron transfer mediator for the first time. The Nernst plot was obtained for Co-Mb with E 0′ of −100 mV versus Ag ∣ AgCl (sat. KCl) and n=1 at 25°C.

Preparation of solid polymer electrolyte composites: investigation of the precipitation process

A model for the chemical reduction of platinum tetramine in perfluorinated Nafion® membranes using sodium borohydride as reducer is proposed. A Nernst-Planck equation is employed for the description of ion transport by diffusion and migration and a reaction term accounts for the in situ chemical reduction. Time-dependent concentrations of the diffusing species within the membrane are obtained numerically by an iterative technique until completion of the precipitation. The model assumes that mass transport is limited by diffusion and migration within the membrane and that the concentrations remain constant at the interfaces during the precipitation. The model shows the effect of (i) the reducer concentration in the solution, (ii) the number of precipitation cycles and (iii) the rate of chemical reduction. To check the validity of the model, metallic platinum concentration profiles across the membrane thickness are obtained by electron microprobe analysis. Values of the diffusion coefficients of the diffusing species within the membrane are obtained from conductivity and permeation measurements.

A Mechanistic Theory for the Relationship between Growth Rate and the Concentration of Nitrate-N or Organic-N in Young Plants derived from Nutrient Interruption Experiments

A simple assumption about nitrate assimilation (incorporating a single parameter to represent the conversion of nitrate into organic-N) has been used to derive mechanistic equations to describe the interrelationships between the concentrations of nitrate-N and organic-N, and dry weight for both the whole plant and its shoot in nutrient interruption experiments. These equations have been combined with a logistic growth model, which was derived from initial assumptions about the way in which plants use stored N under these conditions (Burns, 1994), to quantify effects of nitrate-N and organic-N concentrations on relative growth rate. The models were tested by fitting equations for the predicted relationships to data for young cabbage and lettuce plants, from which estimates of the N assimilation parameter were obtained. The tests showed that predictions of relative growth rate were generally in good agreement with the data over the whole range, as were those for the corresponding relationships between dry weight and either nitrate-N or organic N- concentration, and for the interrelationships between the two forms of N. The most reliable estimates of the N assimilation parameter were obtained from relationships where nitrate-N concentration was the explanatory (independent) variable, because the fits of the corresponding relationships with organic-N were relatively insensitive to large changes in its values. The results showed no evidence of any consistent variation in the size of this N assimilation parameter with the nitrate status of the plant. However, small between-crop differences in its value suggest that shoot nitrate may have been assimilated slightly more efficiently in cabbage than in lettuce.The new model predicts that dry matter production is restricted as soon as the external N supply is withheld (irrespective of the plant nitrate status), producing a slow but consistent decline in relative growth rate which is maintained until nitrate is almost depleted, whereupon it falls rapidly. This implies that the rate of chemical reduction of stored nitrate was not sufficient to maintain an adequate supply of organic-N for the production of new dry matter (even when its concentration in the plants is still high). The results show that nitrate concentrations in excess of 0·1 mmol g-1 are required in plants to avoid serious reductions in growth rate when N is in short supply.

The enzymatic and chemical reduction of extended biliverdins

The substrate specificity of rat liver biliverdin reductase was probed using helical and extended biliverdins. The former were the ZZZ-all-syn biliverdins IX α and IX γ, and the latter were the 5Z-syn, 10Z-syn, 15z-anti; 5Z-anti, 10Z-syn, 15Z-anti; 5Z-syn, 10E-anti, 15Z-syn; 5Z-syn, 10E-anti, 15Z-anti and 5Z-anti, 10E-anti, 15E-anti biliverdins. It was found that the reduction rates of the biliverdins increased with the progressive stretching of their conformations. The most extended biliverdin was reduced at a higher rate than biliverdin IX α. The chemical reduction rates to bilirubins followed a similar pattern. Nuceophilic ad dition of 2-mercaptoethanol to the C10 methine was also favored in the extended biliverdins.

Kinetics of the Chemical and Electrochemical Reduction of Platinum Black Surface Oxides

A comparative study of the reductions of platinum black surface oxides by electrochemical (at constant current) and chemical means (by propane) has been made. From the nature of the rates of the chemical reduction, from potential‐time behavior, and from the two breaks observed in potential vs. logarithm coulombs for reductions at <1.60v oxidation, two types of surface oxides at the platinum black electrode have been observed. The chemical reduction of the platinum black surface oxide, when the electrode is oxidized to a potential in the range of 1.30–1.60 v vs. hydrogen electrode, is zero order with respect to oxide formation and has a rate of or “67 ma/cm2.” The zero order reaction observed suggests that the oxygen is strongly adsorbed. The chemical reduction rate of the surface oxide formed at potentials less than 1.30v, is not constant, and the oxygen is held loosely at the platinum surface.