Volume 91, Nº 3 (2017)
- Ano: 2017
- Artigos: 33
- URL: https://journals.rcsi.science/0036-0244/issue/view/10322
Article
Local equations of state in nonequilibrium heterogeneous physicochemical systems
Resumo
Equations describing local thermal and caloric equations of state in heterogeneous systems at any degree of their states’ deviation from equilibrium are derived. The state of a system is described by equations of the transfer of mixture components; these generalize the equations of classical non-equilibrium thermodynamics for strongly nonequilibrium processes. The contributions from reactions and external fields are taken into account. The equations are derived using the lattice gas model with discrete molecular distributions in space (on a scale comparable to molecular dimensions) and continuous molecular distributions (at short distances inside cells) during their translational and vibrational motions. For simplicity, it is assumed that distinctions between the sizes of mixture components are small. Contributions from potential functions of intermolecular interaction (of the Lennard-Jones type) to some coordination spheres are considered. The theory provides a unified description of the dynamics of distributions of concentrations and pair functions of mixture components in three aggregate states, and at their interfaces. Universal expressions for the local components of the pressure tensor and internal energy inside multicomponent bulk phases and at their interfaces are obtained. Local components of the pressure tensor and the internal energy are universally expressed through local unary and pair distribution functions (DFs) in any nonequilibrium state. The time evolution of the unary and pair DFs themselves is determined from the derived system of equations of mass, momentum, and energy transfer that ensure the transition of the system from a strongly nonequilibrium state to both the local equilibrium state described within traditional nonequilibrium thermodynamics and the complete thermodynamic equilibrium state postulated by classical thermodynamics.
Chemical Thermodynamics and Thermochemistry
Phase diagrams of low-density polyethylene–alkylbenzene systems
Resumo
Complete phase diagrams for mixtures of low-density polyethylene with p- and m-xylene are plotted by optical means in developing the concept of which partially crystalline polymers are microstructured liquids. It is shown that in contrast to the ones presented in the literature, both diagrams contain the solubility boundary curve of the low-molecular weight component in the polymer, above which the polyethylene has the structure of a single-phase gel (crosslinks formed by crystallites and amorphous regions saturated with xylene). At the figurative point on the diagrams, a situation is observed in which the dissolution of all the liquid contained in the initial two-phase system in the polymer is accompanied by its simultaneous complete amorphization. The parameters of the figurative point allow us to estimate the thermodynamic affinity of different alkylbenzenes toward polyethylene.
Heat capacities and thermodynamic functions of new nanosized ferro-chromo-manganites LaM0.5IIFeCrMnO6.5 (MII–Mg, Ca, Sr, Ba)
Resumo
The heat capacities of nanosized ferro-chromo-manganites LaM0.5IIFeCrMnO6.5 (MII–Mg, Ca, Sr, Ba) are measured via dynamic calorimetry in the temperature range of 298.15–673 K using an IT-S-400 instrument. It is established that the C°p~f(T) function of LaM0.5IIFeCrMnO6.5 (MII–Mg, Ca, Sr, Ba) has λ-type effects, due probably to phase transitions of the second order. Considering the temperatures of the phase transitions, equations of the heat capacity of ferro-chromo-manganites LaM0.5IIFeCrMnO6.5 (MII–Mg, Ca, Sr, Ba) as a function of temperature are derived on the basis of experimental data. Thermodynamic functions Н°(Т)–Н°(298.15), S°(Т), and Фхх(Т) are calculated in the temperature range of 298.15–675 K.
Chemical Kinetics and Catalysis
Kinetics of metal exchange in Cd(II) octa(4-bromophenyl)porphyrinate with d-metal salts in organic solvents
Resumo
The reaction of metal exchange between Cd(II) octa(4-bromophenyl)porphyrinate with СuCl2 and ZnCl2 in DMFA and DMSO is studied by means of spectrophotometry. The kinetic parameters of the metal exchange reaction are calculated, a stoichiometric reaction mechanism is proposed. The effect the natures of the solvent, salt solvate, and the chemical modification of tetrapyrrole macrocycle have on the kinetic parameters of the metal exchange reaction are revealed.
Kinetics and mechanism of the catalytic reaction between alcohols and dimethyl carbonate
Resumo
The mechanism of the reaction between alcohols and dimethyl carbonate, catalyzed by dicobalt octacarbonyl Co2(CO)8, is studied by means of mathematical modeling. Kinetic models for possible schemes of chemical transformations are constructed at different initial concentrations of the catalyst. Based on a comparative analysis of activation energies of possible stages of chemical transformations, possible reaction pathways are determined and an appropriate mechanism is selected.
Catalytic conversion of aliphatic alcohols on carbon nanomaterials: The roles of structure and surface functional groups
Resumo
Carbon nanomaterials with the structure of graphene and different compositions of the surface groups are used as catalysts for the conversion of С2–С4 aliphatic alcohols. The conversions of ethanol, propanol- 1, propanol-2, butanol-1, butanol-2, and tert-butanol on carbon nanotubes, nanoflakes, and nanoflakes doped with nitrogen are investigated. Oxidized and nonoxidized multiwalled carbon nanotubes, nanoflakes, and nanoflakes doped with nitrogen are synthesized. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning and transmission electronic microscopies, Brunauer–Emmett–Teller method, derivatographic analyses, and the pulsed microcatalytic method are used to characterize comprehensively the prepared catalysts. It was established that all of the investigated carbon nanomaterials (with the exception of nondoped carbon nanoflakes) are bifunctional catalysts for the conversion of aliphatic alcohols, and promote dehydration reactions with the formation of olefins and dehydrogenation reactions with the formation of aldehydes or ketones. Nanoflakes doped with nitrogen are inert with respect to secondary alcohols and tert-butanol. The role of oxygen-containing and nitrogen-containing surface groups, and of the geometrical structure of the carbon matrix of graphene nanocarbon materials in the catalytic conversion of aliphatic alcohols, is revealed. Characteristics of the conversion of aliphatic alcohols that are associated with their structure are identified.
Kinetics of the hydrogenation of 2-chloro-4-nitroaniline over skeletal nickel and supported palladium catalysts in an aqueous solution of 2-propanol
Resumo
The kinetics of the liquid-phase hydrogenation of 2-chloro-4-nitroaniline in an aqueous solution of 2-propanol over skeletal nickel and supported palladium catalysts is studied. The selectivity of the reaction with respect to 2-chloro-1,4-phenylenediamine is determined. It is found that samples of supported palladium catalysts differ with respect to the amount of the active component and the nature of the support. Some of their structural characteristics are provided.
Catalyst for the oxidation of sulfur-containing compounds based on a polyamide membrane modified with cobalt phthalocyanine
Resumo
The catalytic activity of phthalocyanine metal complex immobilized on the surface of a porous polyamide membrane is studied in the oxidation reaction of n-propyl mercaptan. Since noncatalytic oxidation is possible in the presence of oxygen, the kinetics of n-propyl mercaptan oxidation is analyzed as its aqueous alkaline solution passes through unmodified membranes. Characteristics of the catalyst’s performance are selected to evaluate the efficiency of the catalytic process. It is shown that the modified membranes with pore diameters of 1 and 2 μm are the most effective catalysts.
Effect of hydrostatic pressure, temperature, and solvent on the rate of the Diels–Alder reaction between 9,10-anthracenedimethanol and maleic anhydride
Resumo
The rate of the reaction between 9,10-anthracenedimethanol and maleic anhydride in 1,4-dioxane, acetonitrile, trichloromethane, and toluene is studied at 25, 35, 45°C in the pressure range of 1–1772 bar. The rate constants, enthalpies, entropies and activation volumes are determined. It is shown that the rate of reaction with 9,10-anthracenedimethanol is approximately one order of magnitude higher than with 9-anthracenemethanol.
Catalytic properties of Fe/SiO2–Al2O3 systems, obtained via sol–gel method
Resumo
The high efficacy of iron-containing catalysts based on SiO2–Al2O3 systems obtained via sol–gel method in the oxidative destruction of carmoisine azo dye in aqueous solutions is demonstrated. It is found that the stability of the catalysts with respect to the leaching of iron ions into a solution during catalysis grows along with the aluminum content in the composition of aluminosilicate supports. It is concluded that the synthesized catalysts are promising materials for purifying wastewaters contaminated with organic dyes.
Quantum chemical study of the rearrangement of phenoxyl-hydroxyphenyl radicals
Resumo
The absorption spectra and decomposition kinetics of intermediates formed upon the photolysis of p-iodophenol are studied via flash photolysis. The extinction coefficient of the p-iodophenoxyl radical is calculated. It is found that p-iodophenol acts as an inhibitor of light-independent liquid-phase oxidation reactions.
Kinetic characteristics of the destruction of β,β-annelated porphyrazines in a nitrogen-containing base–dimethylsulfoxide system
Resumo
The state of tetra(1,2,5-thiadiazolo)porphyrazine in a dimethyl sulfoxide medium is investigated. Relatively high stability is observed for the resulting proton-transfer complex, and a chemical structure is proposed for it. It is shown that the nature of the substituent in the porphyrazine macrocycle influences the kinetic parameters of the destruction of tetra(1,2,5-thiadiazolo)porphyrazine, tetra(5-tert-butylpyrazino) porphyrazine, octaethyltetrapyrazinoporphyrazine, and octaphenyltetrapyrazinoporphyrazine in a nitrogen-containing base–dimethylsulfoxide system. The effect the NH acidity of the porphyrazine macrocycle and the nature of the nitrogenous bases have on the reaction rate and activation parameters of the destruction of β,β-annelated porphyrazine proton-transfer complexes is established.
Tetrafluoroethylene telomerization initiated by benzoyl peroxide
Resumo
The radical telomerization of tetrafluoroethylene initiated by benzoyl peroxide (BP) photolysis at λ ≥ 365 nm is studied in acetone, dichloromethane, carbon tetrachloride, and Freon 114B2 at 25°C. The products of synthesis are a mixture of telomers of different molar masses, segregated into soluble and insoluble fractions. To characterize the radicals initiating telomerization, crystalline BP and its solution in ethanol are subjected to low-temperature (77 K) photolysis, with the liquid system serving as a model for BP behavior in solutions of telogens. It is established that radicals are not only initiators but also participate in chain termination reactions, lowering the telomers’ molar mass and thus raising the proportion of the soluble fraction. Telomerization initiated by an initiator compound versus initiation by gamma radiation are compared and discussed.
Simultaneous removal of NOx and SO2 by low-temperature selective catalytic reduction over modified activated carbon catalysts
Resumo
A series of modified porous activated carbon (AC) catalysts prepared by impregnation were investigated for the low-temperature (≤250°C) selective catalytic reduction (SCR) of NOx with NH3 with simultaneous removal of SO2. The effects of various preparation conditions and reaction conditions on NO and SO2 conversions were observed, such as support type, active components, copper loading, calcination temperature and presence of H2O and O2. The modified AC catalysts were characterized by BET, XRD, TG and TPX methods. The activity test results showed that the optimal catalyst is 15% Cu/WCSAC which can provide 52% NO conversion and 68% SO2 conversion simultaneously at 175°C with a space velocity of 30000 h‒1, and the optimal calcination temperature was 500°C. The presence of H2O could inhibit NO conversion and promote the SO2 conversion. The effect of O2 (0–5%) was evaluated, and the NO and SO2 conversions were best when the concentration of O2 was 3%. Research demonstrated that Cu/WCSAC catalyst was a kind of potential catalysts due to the amorphous phase, high specific areas and high active ability.
One-pot sequential synthesis of magnetically separable Fe3O4/AgCl photocatalysts with enhanced activity and stability
Resumo
Magnetically separable Fe3O4/AgCl photocatalysts were prepared by a one-pot sequential method. A series of techniques proved the hybrid structure of Fe3O4/AgCl composites. Fe3O4/AgCl composites had a much higher photocatalytic activity toward Rhodamine B (RhB) degradation than pure AgCl under the simulated solar light irradiation. The existence of metal Ag resulted in high photocatalytic activity of Fe3O4/AgCl, which was related with the amount of metallic Ag. The scavenging experiments showed that the degradation reaction most probably was initiated by the photoinduced single-electron transfer, and the generation of superoxide anion (O2-·) played a significant role. The composite photocatalysts could be recycled by applying an external magnetic field, and the reused composites maintained their original photocatalytic activity. Fe3O4/AgCl composites were highly efficient, magnetically separable, and recoverable. This proves their potential applications in the photodegradation of organic pollutants.
Regioselective toluene nitration catalyzed with layered HNbMoO6
Resumo
HNbMoO6 layered oxide was obtained by the ion-exchange from LiNbMoO6 prepared by solid state reaction (SSR). The micro-structure, textural characteristics and acidity of the as-prepared catalyst were characterized by powder X-ray diffraction (XRD), laser Raman spectroscopy (LRS) and ammonia temperature- programmed desorption (NH3-TPD). Catalytic performance was evaluated in the regioselective nitration of toluene with a novel nitration system containing acetic anhydride and CCl4. The optimal nitration conditions comprise the application of 95 wt % HNO3, HNO3-to-toluene molar ratio of 2.5, catalyst pretreatment temperature of 503 K, reaction temperature of 313 K, and reaction time of 2.5 h. The toluene conversion rate and para-selectivity were also attributable to the strong acidity and the appropriate interlayer distance of the studied catalyst.
Physical Chemistry of Solutions
Structure of concentrated aqueous solutions of scandium chloride
Resumo
It is shown via X-ray diffraction that aqueous solutions of scandium chloride form ionic associates in a wide range of concentrations. It is established that the Sc3+ ion coordination number increases upon dilution to 8.2 at an unchanged Sc3+–OH2 distance of 0.215 nm. The second coordination sphere of the cation forms at an average distance of 0.420 nm. The number of solvent molecules in the sphere logically increases during dilution. It is concluded that the anion does not form its own sphere in highly concentrated solutions. This coordination sphere begins to form only in solutions with moderate concentrations at a distance of 0.315 nm, and it contains six water molecules in diluted solutions.
Measuring the enthalpies of interaction between glycine, L-cysteine, glycylglycine, and sodium dodecyl sulfate in aqueous solutions
Resumo
Calorimetric measurements of enthalpies of solution ΔsolHm for glycine, L-cysteine, and glycylglycine in aqueous solutions of sodium dodecyl sulfate (SDS) with concentrations of up to 0.05 mol kg–1 are made. Standard enthalpy of solution ΔsolH0 and enthalpy of transfer ΔtrH0 of the dipeptide from water into mixed solvent are calculated. The calculated enthalpy coefficients of paired interactions of amino acids and dipeptide with SDS prove to be positive. Hydrophobic interactions between the biomolecules and SDS are found to have a major impact on the enthalpies of interaction in the three-component systems under study, within the indicated range of concentrations.
Optical and electrical properties of inverted emulsions based on sodium bis(2-ethylhexyl) sulfosuccinate containing cadmium sulfide particles
Resumo
The optical and electrical properties of inverted emulsions based on sodium bis(2-ethylhexyl) sulfosuccinate (AOT) containing nanoparticles of cadmium sulfide are studied. The particle size of the synthesized samples is determined from UV spectroscopy data. The state of solubilized water in invert emulsions is found to change in the presence of cadmium sulfide due to the formation of aqua complexes. The shape of AOT micelles and the structures formed by drying the invert AOT emulsions are shown to be affected by the degree of hydration and the solubilization of CdS particles.
Liquid–liquid phase equilibrium of methanol + ethylbenzene + isooctane + ethanol system at 303 K
Resumo
The phase equilibrium data for methanol + ethanol + isooctane systems were obtained at 303.15 K. Data for methanol + ethylbenzene + isooctane system were taken from literature. The effect of ethanol addition on the system equilibrium was investigated at the same temperature. The distribution curves for ternary and quaternary system was analyzed. The experimental results for ternary systems were correlated with UNIQUAC and NRTL equations. For the ternary systems studied here, the NRTL equation is more accurate than the UNIQUAC. The equilibrium data for the three ternary systems were used to determine interactions parameters for the UNIQUAC equation. For the quaternary system, the experimental data can be fitted more accurately to UNIQUAC equation than by the UNIFAC method.
Structure of Matter and Quantum Chemistry
Visible and near-IR spectroscopy of endohedral Gd@C82(C2v) and Ho@C82(C2v) metallofullerenes and their monoanions
Resumo
Solutions of endohedral Gd@C82(C2v) and Ho@C82(C2v) metallofullerenes are studied by means of visible and near-IR spectroscopy upon their conversion from neutral to the anionic form via a redox reaction with the electron donor potassium perchlorotriphenylmethide K(18-crown-6)[C(C6Cl5)3]. The concentrations of the studied solutions of endohedral Gd@C82(C2v) and Ho@C82(C2v) metallofullerenes in o-dichlorobenzene were determined from the spectroscopic data, and their molar extinction coefficients are calculated.
Composition and structure of Pt chloride complexes in hydrothermal solutions, according to X-ray absorption spectroscopy
Resumo
The local atomic environment of Pt in chloride solutions is studied at 25 and 300–350°C via X-ray absorption spectroscopy. A comparison of the Pt L3-edge XANES spectra for aqueous chloride solutions and reference compounds (K2PtCl4 and K2PtCl6) shows that platinum is in oxidation state +2 at all temperatures, and the complex composition remains unchanged in the experimental range of temperatures (25–350°С) and solution compositions (m(Cltot) > 0.4 mol kg−1 of H2O). Based on EXAFS spectral analysis, the composition of the complex being dominant in chloride solutions is found to be PtCl42- with interatomic Pt–Cl distances of 2.31 ± 0.01 Å, regardless of the temperature. It is concluded that the local environments of Pt and Pd in hydrothermal solutions are similar, and the main form of transfer for these metals is a square-planar complex with four Cl ligands and identical interatomic distances.
Physical Chemistry of Nanoclusters and Nanomaterials
Formation of a new adduct based on fullerene tris-malonate samarium salt С60–[C60(=C(COO)2)3]Sm2
Resumo
Gram quantities of a new adduct based on light fullerene tris-malonate samarium salt С60 [C60(=C(COO)2)3]Sm2 are obtained via the reaction of ion exchange. The obtained adduct is studied by means of electron and infrared spectroscopy, X-ray and elemental analysis, electron microscopy, and thermogravimetry. The polythermal solubility of [C60(=C(COO)2)3]Sm2 in water is determined in ampoules via saturation within 20–70°C. The composition of crystalline hydrate [C60(=C(COO)2)3]Sm2 · 36Н2О, which exists in equilibrium with the saturated solution, is estimated.
Formation of grafted surface layers on silicon dioxide particles and their investigation by means of thermoprogrammed oxidation
Resumo
Silica nanoparticles are obtained according to the Stober–Fink–Bohn method, and their surfaces are chemically modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane. It is estimated that sols of porous silica nanoparticles (average sizes, 50–200 nm) form during primary chemical process; the average size of the particles can be increased to 400–500 nm by consecutive growth. Oxythermography (thermoprogrammed oxidation) measurements reveal a stepped dependence between the content of organic substance of nanoparticles and the duration of chemical modification reaction exists. It is concluded that this could be due to the formation of dense shell (or shells) as a result of sols aging between the cycles of growth; such shells impose diffusive restrictions when molecules penetrate into the pores of the internal volume of the particles.
On the possibility of controlling the hydrophilic/hydrophobic characteristics of toroid Mo138 nanocluster polyoxometalates
Resumo
The possibility of changing the hydrophilic (polar) surfaces of toroid nanocluster polyoxomolibdates to hydrophobic (nonpolar) surfaces via the modification of Mo138 nanoclusters by surfactant molecules (dodecylpyridinium chloride) as a result of the interaction between these compounds in solutions is demonstrated. Benzene and methanol are used as molecular probes (indicators of the condition of nanocluster surfaces). Comparative characteristics of the equilibrium sorption of benzene and methanol vapors on the initial and modified surfaces of the solid polyoxometalate, and data on the sorption of organic molecules on the surfaces of Rhodamine B-modified nanoclusters of the toroid (Mo138) and keplerate (Mo132) types are obtained.
Sorption interactions between ethylene glycol and carbon nanotubes
Resumo
The adsorption of ethylene glycol by carbon nanoparticles is studied. Carbon nanoparticles with the highest affinity to ethylene glycol are identified, and an adsorption isotherm is constructed. Based on quantum chemical calculations of the energies of interaction between the sorbate and nanotubes with (4,4) and (6,6) chirality, a change in mechanism is revealed upon the monomolecular adsorption of ethylene glycol on carbon nanotubes, and the adsorption isotherm is thus interpreted.
Physical Chemistry of Surface Phenomena
Sensory properties of oxide films with high concentrations of conduction electrons
Resumo
The dependence of a sensor’s response to hydrogen on the temperature and hydrogen pressure in an indium oxide nanostructured film is measured. A theory of sensor’s response to reducing gases in nanostructured semiconducting oxides with high concentrations of electrons in the conduction band is developed (using the example of In2O3). It is shown that the capture of conduction electrons by adsorbed oxygen redistributes the electrons in nanoparticles and reduces the surface electron density and the conductivity of a system; the conductivity is proportional to the electron density in nanoparticle contacts, i.e., to the surface electron density. It is found that atomic oxygen ions react with reducing gases (H2, CO) during adsorption of the latter: electrons are released and enter the volumes of nanoparticles; the conductivity of the system grows, creating the sensory effect. Using a model developed earlier to describe the distribution of conduction electrons in a semiconductor nanoparticle, a kinetic scheme corresponding to the above scenario is built and corresponding equations are solved. As a result, a theoretical dependence of a sensor’s sensitivity to temperature is found that describes the experimental data well.
Thermodynamic characteristics of the adsorption of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from methanol and water–methanol solutions onto hypercrosslinked polystyrene
Resumo
The thermodynamic characteristics of the adsorption of several 1,3,4-oxadiazoles and 1,2,4,5- tetrazines from methanol and water-methanol solutions onto neutral hypercrosslinked polystyrene with a degree of crosslinking of 150% are determined via high performance liquid chromatography. It is shown how the obtained characteristics depend on the molecular structure of adsorbed substances and the composition of the liquid phase in which adsorption occurs.
Physical Chemistry of Separation Processes. Chromatography
Monolithic columns with organic sorbent based on poly-1-vinylimidazole for high performance liquid chromatography
Resumo
Monolithic chromatographic columns for HPLC with sorbent based on 1-vinylimidazole are prepared. It is shown that changing the 1-vinylimidazole content in the initial solution allows us to change the polarity of columns. An example of aromatic hydrocarbons separation is presented.
A generalized theory of chromatography and multistep liquid extraction
Resumo
A generalized theory of chromatography and multistep liquid extraction is developed. The principles of highly efficient processes for fine preparative separation of binary mixture components on a fixed sorbent layer are discussed.
Photochemistry and Magnetochemistry
Mechanism of the emergence of the photo-EMF upon silicon liquid crystal–single crystal contact
Resumo
The effect light has on a silicon liquid crystal–single crystal contact at different temperatures of the surface doping of silicon, and when BaTiO3 nanoparticles are added to the composition of a liquid crystal, is studied. The mechanism of the emergence of the photo-EMF in the liquid crystal–silicon structure is explained.
Effect of electrolyte components on the magnetic and magnetoresistive characteristics of Fe-containing plasma electrolytic oxide coatings on titanium
Resumo
The effect replacing Na3PO4 with Na2HPO4 in aqueous phosphate–borate–tungstate electrolyte that additionally contains Fe2(C2O4)3 on the magnetic and magnetoresistive characteristics of oxide coating/ titanium composites formed by means of plasma electrolytic oxidation (PEO) is investigated. It is established that PEO coatings with ferromagnetic characteristics form on titanium in an electrolyte containing Na3PO4 (pH ~ 11) upon adding iron(III) oxalate, while replacing Na3PO4 with Na2HPO4 and the respective drop in the pH of the base electrolyte down to 9.8 results in the formation of coatings with different magnetic characteristics. The correlation between changes in the values of the charge carriers’ activation energy and the magnetic susceptibility is demonstrated for the latter. An increase in the electric resistance of coatings in a magnetic field is observed, and the type of the magnetic resistance temperature dependence is established.
Photochemical oxidation of persistent cyanide-related compounds
Resumo
Kinetic regularities of the photolysis of thiocyanate solutions using of mono- and polychromatic UV radiation sources with different spectral ranges are studied. Comparative experiments aimed at investigating the role of photochemical action during the oxidation of thiocyanates with persulfates and additional catalytic activation with iron(III) ions are performed. The rate of conversion and the initial rate of thiocyanate oxidation are found to change in the order UV < UV/S2O82− < S2O82−/Fe3+ < UV/S2O82−/Fe3+. A synergistic effect is detected when using the combined catalytic method for the destruction of thiocyanates by the UV/S2O82−/Fe3+ oxidation system. This effect is due to the formation of reactive oxygen species, as a result of both the decomposition of persulfate and the reduction of inactive Fe3+ intermediates into Fe3+.