Persulfate Ions Research Articles

Graphene‐Assisted Room‐Temperature Synthesis of 2D Nanostructured Hybrid Electrode Materials: Dramatic Acceleration of the Formation Rate of 2D Metal Oxide Nanoplates Induced by Reduced Graphene Oxide Nanosheets

A new prompt room temperature synthetic route to 2D nanostructured metal oxide-graphene-hybrid electrode materials can be developed by the application of colloidal reduced graphene oxide (RGO) nanosheets as an efficient reaction accelerator for the synthesis of δ-MnO2 2D nanoplates. Whereas the synthesis of the 2D nanostructured δ-MnO2 at room temperature requires treating divalent manganese compounds with persulfate ions for at least 24 h, the addition of RGO nanosheet causes a dramatic shortening of synthesis time to 1 h, underscoring its effectiveness for the promotion of the formation of 2D nanostructured metal oxide. To the best of our knowledge, this is the first example of the accelerated synthesis of 2D nanostructured hybrid material induced by the RGO nanosheets. The observed acceleration of nanoplate formation upon the addition of RGO nanosheets is attributable to the enhancement of the oxidizing power of persulfate ions, the increase of the solubility of precursor MnCO3, and the promoted crystal growth of δ-MnO2 2D nanoplates. The resulting hybridization between RGO nanosheets and δ-MnO2 nanoplates is quite powerful not only in increasing the surface area of manganese oxide nanoplate but also in enhancing its electrochemical activity. Of prime importance is that the present δ-MnO2 -RGO nanocomposites show much superior electrode performance over most of 2D nanostructured manganate systems including a similar porous assembly of RGO and layered MnO2 nanosheets. This result underscores that the present RGO-assisted solution-based synthesis can provide a prompt and scalable method to produce nanostructured hybrid electrode materials.

Atom-economical in situ synthesis of BaSO4 as imaging contrast agents within poly(N-isopropylacrylamide) microgels using one-step droplet microfluidics

A novel in situ synthesis of BaSO4 as an X-ray imaging contrast agent within poly(N-isopropylacrylamide) (PNIPAM) microgels has been accomplished by one-step droplet microfluidics with interlinking reactions. A one-step droplet microfluidics device with wavy channels is employed to produce monodispersed PNIPAM microgels (∼40 μm) via free radical polymerization by the initiation of the ammonium persulfate (APS) and N,N,N′,N′-tetramethylethylenediamine (TEMED) complex. The resulting PNIPAM microgels are subsequently dripped into a collecting bath containing an aqueous BaCl2 solution. For the in situ synthesis of BaSO4, Ba2+ ions would diffuse into the PNIPAM microgels and further react with SO42− ions originated from the decomposed by-product of the APS–TEMED complex during the initiation, yielding almost 100% atom efficiency of persulfate ions. The morphologies and the composition of the PNIPAM microgels containing in situ synthesized BaSO4 (BaSO4–PNIPAM microgels) are characterized by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM–EDX) and X-ray diffraction (XRD). These results show that 14 nm BaSO4 crystallites have been in situ synthesized in the PNIPAM microgels. The resulting BaSO4–PNIPAM microgels are also visible under X-ray radiation by an in vitro fluoroscopic evaluation. This droplet microfluidics based method provides a green and atom-economical reaction approach to synthesize functionalized microgels with a uniform distribution of BaSO4 nano-crystallites. Moreover, the radiopaque BaSO4–PNIPAM microgels also possess great potential in the fields of endovascular embolization, diagnostic imaging, and visible implantation materials.

A novel approach for determining total titanium from titanium dioxide nanoparticles suspended in water and biosolids by digestion with ammonium persulfate

Titanium dioxide (i.e. TiO 2) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO 2 nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO 2 as Ti 4+ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO 2 nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti 4+ from 6 μg mL −1 aqueous suspensions prepared from 10 μg mL −1 suspension of different forms of TiO 2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL −1, and the limit of quantification (LOQ) was 0.20 ng mL −1. Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO 2 of 1.8 and 1.6 ng mL −1 for the wastewater samples, respectively, and 317.4 ng mg −1 dry weights for the biosolids. The reactions between persulfate ions and TiO 2 were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.

Radiolysis of acetic acid aqueous solutions—Effect of pH and persulfate addition

The degradation of acetic acid in aqueous solution by ionizing radiation was studied. The radiolysis of acetic acid solution induces the almost complete degradation and mineralization of this compound. The high yield of acetic acid mineralization is explained by the degradation of oxalic acid by solvated electron. The degradation of acetic acid depends on the pH of the solution. The best degradation is observed at pH 4.5 due to the higher rate constant of reaction of acetate with hydroxyl radicals and the competitive reactions of inorganic carbon which occur at higher pH. The influence of persulfate ion (S 2O 8 2−) addition that forms the sulfate radical (SO 4 −) during irradiation in solution was examined. The persulfate addition induces an almost constant degradation of acetic acid whatever the initial pH of the solution. The decrease of pH during the persulfate radiolysis partly explains the high degradation observed. But the additional radicals formed by the persulfate introduction also improve the degradation.

Parametric optimization of individual and hybridized AOPs of Fe 2+/H 2O 2 and UV/S 2O 82− for rapid dye destruction in aqueous media

The aim of the study was to assess and optimize the UV/S 2O 8 2− (activated persulfate ion), Fe 2+/H 2O 2 (Fenton), UV/Fe 2+/H 2O 2 (photo-Fenton), and their hybridized processes for discoloration, degradation and mineralization of an azo dye, Direct Red 16, as a model pollutant, in aqueous media. A special air bubbling photo-reactor, with a perfect photon utilizing of an only 6 W, UV-C light source, was employed and a promising hybridized homogeneous AOP, as: UV/S 2O 8 2−/Fe 2+/H 2O 2, under initial natural pH of 6.0, was introduced. This process exhibits a rapid discoloration (100% in 30 min), as well as aromatic rings degradation (more than 86% in 40 min) and mineralization (more than 50% in 60 min) of DR16 with 30 mg/L initial concentration at 25 °C. The optimum parameters of initial pH, initial reagents dosage and temperature were reported for each process. The ferrous ion catalyst concentration was much less than its standard limit. Different processes kinetic relationships were introduced in a power law model and as a function of dye concentration and temperature. Moreover, synergism impact of UV light on the catalytic center of Fenton process was proved based on a kinetic analysis.

Room Temperature Synthesis Routes to the 2D Nanoplates and 1D Nanowires/Nanorods of Manganese Oxides with Highly Stable Pseudocapacitance Behaviors

The 2D nanoplates of δ-MnO2 and the 1D nanowires/nanorods of α-MnO2 can be synthesized at room temperature via one-pot oxidation reaction of commercially available divalent manganese compounds. Treating the MnO or MnCO3 precursor with persulfate ions for 1–2 days yields layered δ-MnO2 2D nanoplates, whereas the same oxidation reaction for the MnSO4 precursor produces γ-MnO2-structured 3D urchins. As the reaction time is extended for ∼14–21 days, not only δ-MnO2 nanoplates but also γ-MnO2 urchins are changed to well-separated 1D nanostructured α-MnO2 materials with controllable diameters. According to N2 adsorption–desorption isotherm measurements and Mn K-edge X-ray absorption spectroscopy, all the obtained manganate nanostructures show expanded surface areas of ∼50–120 m2 g–1 and the mixed oxidation state of Mn3+/Mn4+, respectively. All the present nanostructured manganese oxides exhibit pseudocapacitance behaviors with large specific capacitance and excellent capacitance retention, highlighting their promising functionality as a supercapacitor electrode. Among the materials under investigation, the δ-MnO2 2D nanoplates show the largest specific capacitance (∼180–210 F g–1). The present finding clearly demonstrates that the room-temperature oxidation reaction of the MnO or MnCO3 precursor can provide a facile soft-chemical route to 2D δ-MnO2 nanoplates and 1D α-MnO2 nanowires/nanorods with highly stable pseudocapacitance behaviors.

Degradation of 2,4,5-trichlorophenoxyacetic acid by a novel Electro-Fe(II)/Oxone process using iron sheet as the sacrificial anode

A novel electrochemically enhanced advanced oxidation process for the destruction of organic contaminants in aqueous solution is reported in this study. The process involves the use of an iron (Fe) sheet as sacrificial anode and a graphite bar as cathode. In the oxidation process, once an electric current is applied between the anode and the cathode, a predetermined amount of Oxone is added to the reactor. Ferrous ions generated from the sacrificed Fe anode mediate the generation of highly powerful radicals (SO 4 •−) through the decomposition of Oxone. The coupled process of Fe(II)/Oxone and electrochemical treatment (Electro-Fe(II)/Oxone) was evaluated in terms of 2,4,5-Trichlorophenoxyacetic acid degradation in aqueous solution. Various parameters were investigated to optimize the process, including applied current, electrolyte and Oxone concentration. In addition, low solution pH facilitates the system performance due to the dual effects of weak Fenton reagent generation and persulfate ions generation, whereas the system performance was inhibited at basic pH levels through non-radical self-dissociation of Oxone and the formation of ferric hydroxide precipitates. Furthermore, the active radicals involved in the Electro-Fe(II)/Oxone process were also identified. The Electro-Fe(II)/Oxone process demonstrates a very high 2,4,5-T degradation efficiency (over 90% decay within 10 min), which justifies the novel Electro-Fe(II)/Oxone a promising treatment process for herbicide removal in water.

Increasing the catalytic activities of iodine doped titanium dioxide by modifying with tin dioxide for the photodegradation of 2-chlorophenol under visible light irradiation

The photocatalytic degradation of 2-chlorophenol (2-CP) irradiated with visible light over iodine doped TiO 2 (IT) modified with SnO 2 (SIT) nanoparticles has been investigated in this study. The structure and optical properties of the SIT catalysts have been well characterized by X-ray diffraction, the Brunauer–Emmett–Teller method, transmission electron microscopy, UV–visible absorption spectra and X-ray photoelectron spectroscopy. The effects of preparation conditions, such as SnO 2 content and calcination temperature, on the photocatalytic degradation efficiency have been surveyed in detail. The improved photocatalytic activity of SIT is derived from the synergistic effect between the SnO 2 and IT, which promoted the efficiency of migration of the photogenerated carriers at the interface of the catalysts and thereby enhanced the efficiency of photon harvesting in the visible region. The action of scavengers (fluoride ion, iodide ion, tert-butyl alcohol, and persulfate ion), as well as N 2 purging on the photodegradation rate reveal that the valence band hole is mainly responsible for the effective photocatalytic removal of 2-CP and the corresponding TOC reduction.

Polymerization kinetics of acrylonitrile by oxidation: Reduction system using potassium persulfate/ascorbic acid in an aqueous medium

AbstractThe kinetics of acrylonitrile polymerization initiated by free radicals formed in situ in a potassium persulfate/ascorbic acid redox system was investigated in an aqueous sulfuric acid medium in the temperature range of 40–70°C. The rate of polymerization and the rate of the disappearance of potassium persulfate were measured. A kinetic scheme involving the production of initiating radicals from the oxidation of ascorbic acid by potassium persulfate ions and termination exclusively by the interaction of chain radicals with persulfate ions is proposed. The effects of some water‐miscible organic solvents on the rate of polymerization were investigated. The temperature dependence of the rate was studied. A possible mechanism consistent with the experimental data is proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Electron beam irradiation of aqueous solution of persulfate ions

The radiolysis of persulfate (S 2O 8 2−) aqueous solution was studied for the enhancement of electron beam process applied to water treatment. It was shown that the persulfate ion reacts with aqueous electron and produces additional radical species in aqueous solution. The oxidative radical species formed (sulfate radical SO 4 − ) is a very strong oxidant able to react with various recalcitrant pollutants. A model of the evolution of persulfate concentration in solution was performed. It was shown that the presence of persulfate induces a decrease of pH and also an increase of dissolved oxygen concentration in solution during irradiation. Moreover the interest of persulfate addition for the improvement of an organic compound degradation by radiolysis was shown.

The influence of persulfate addition for the degradation of micropollutants by ionizing radiation

Nowadays the removal of organic micropollutants is one of the major challenges of water and wastewater treatment plants. The objective of this study was to investigate the influence of persulfate addition on micropollutants degradation by ionizing radiation. In this system, the radicals SO 4 −/OH can be present simultaneously due to persulfate reaction with solvated electrons. Ibuprofen (IB), progesterone (Pg) and benzotriazole (BT) have been selected for this study. The degradation of micropollutants was followed at various radiation doses and under the influence of persulfate (S 2O 8 2−) addition at a fixed dose (30 Gy), in deionized and tap water. In deionized water the addition of 500 μM persulfate improved the degradation of BT, IB and Pg by 17%, 36% and 24% respectively and the removal of micropollutants was increased when the concentration of persulfate ions increased. No influence of the presence of persulfate ions was observed in tap water. Contrary to tap water experiments, the persulfate (500 μM) increases the elimination of BT slightly in the presence of bicarbonate ions. In the case of IB and Pg the influence of persulfate addition is significant even in the presence of bicarbonate ions which indicate that the bicarbonate ions do not completely inhibit the influence of persulfate addition in tap water. Even if the bicarbonate ions have an inhibitory effect on the irradiation system, it was suggested that the inhibition could be explained by the presence of nitrate ions, which would prevent the formation of sulfate radicals.

Influence of persulfate ions on the removal of phenol in aqueous solution using electron beam irradiation

The removal of phenol (Co = 100 μM) during electron beam irradiation was studied in pure water and in the presence of HCO 3 − and Br − ions. It was found that the introduction of S 2O 8 2− ions (1 mM), by generating SO 4 − radicals increases the radiation yield of phenol removal. 90% removal of phenol was obtained with radiation doses 600 and 1200 Gy with and without S 2O 8 2− ions respectively. This system induced smaller oxygen consumption with smaller concentration of catechol and hydroquinone found in the solution. HCO 3 − and Br − have an inhibiting effect in the presence as in the absence of S 2O 8 2−. In most cases, the introduction of S 2O 8 2− ions in water radiolysis system can advantageously increase the yield of organic compounds removal by oxidation.

O60 Use of blue light and laser in the treatment of Alzheimer's dementia and Parkinson's disease

Electrochemical non-enzyme sensors based on metal and metal oxide nanocomposites are still a new challenge and a huge potential area. In this work, a ternary flower-like Cu2O-Cu-Au (CCAu) was designed and constructed as electrochemical material for glucose detection. In which, under the combined action of hydroxide ions and persulfate ions, several micrometer-long radial Cu(OH)2 branches were grown on the surface of the Cu sphere precursor. And then Au nanoparticles decorated Cu2O-Cu ternary nanocomposites formed by heat treatment and surface loading. As active materials for the electrochemical non-enzymatic glucose detection, the CCAu modified electrode showed a sensitivity of 1.082 mAmM−1cm−2 and a detection limit of 1.71 uM. The good performance of CCAu/GCE can be attributed to the compound and synergistic effect of Cu and Cu2O builds a mixed valence Cu0/Cu+, the special surface area and triple active substances with many active centers, and the dendritic structure which is conducive for the penetration of electrolyte. In addition, the CCAu electrode showed a performance comparable to that of a commercial analyzer in testing the blood glucose concentration in human serum, indicating that it has a great potential in the practical electrochemical sensors.

Photochemical decomposition of perfluorodecanoic acid in aqueous solution with VUV light irradiation

The photochemical decomposition of perfluorodecanoic acid (PFDeA) in water in the presence of persulfate ion (S 2O 8 2−) and sulfur ion (S 2−) was investigated under vacuum ultraviolet (VUV) light irradiation. PFDeA was decomposed under VUV light irradiation. With the addition of S 2O 8 2− or S 2−, the photo-decomposition and defluorination of PFDeA were enhanced significantly. Sulfate radical anion (SO 4 − ) generated from photolysis of S 2O 8 2− initiated PFDeA oxidation. While the S 2− ion, acting as a OH scavenger, enhanced the role of reduction pathway induced by aqueous electrons (e aq −). The shorter-chain perfluorocarboxylic acids (PFCAs), formed in a stepwise manner from longer-chain PFCAs, were identified as products by HPLC/MS.

Visible Light-Induced Degradation of Phenol over Iodine-Doped Titanium Dioxide Modified with Platinum: Role of Platinum and the Reaction Mechanism

The role of platinum deposited on iodine-doped titanium dioxide (Pt/I-TiO2) catalyst during photodegradation of phenol under irradiation with visible light was investigated. The results of this study demonstrate that the Pt/I-TiO2 photocatalyst enhanced the phototransformation of phenol, with a negligible increase upon photomineralization. The results of the phototransformation of para substiuted phenols (p-methylphenol, phenol, p-chlorophenol, and p-nitrophenol) show that the phenol−TiO2 interaction, influenced by the Hammett constants, has the principal role in photodegradation. Furthermore, the action of scavengers (iodide ion, tert-butyl alcohol, fluoride ion, and persulfate ion), as well as N2 purge on the photodegradation of phenol prove that the phototransformation of phenol occurs on the surface of the photocatalyst and is initiated mostly by a valence band hole (hvb+), and the degradation process is limited by the keto−enol tautomeric equilibrium between hydroquinone and quinone. On the basis of ...

Effects of synthesis temperature and precursor composition on the crystal structure, morphology, and electrode activity of 1D nanostructured manganese oxides

1D nanostructured manganese oxides are prepared by oxidation reaction of precursor LiMn 2− x Cr x O 4 microcrystals under hydrothermal condition. The crystal structure and morphology of the obtained manganese oxides are strongly dependent on the reaction condition and the chemical composition of the precursors. The α-MnO 2 nanowires are prepared by reaction at 120 °C, and their aspect ratios decrease with the Cr content in the precursor. Treating precursors with persulfate ions at 160–180 °C yields the β-MnO 2 nanorods for the precursors LiMn 2− x Cr x O 4 with lower Cr content and the α-MnO 2 nanowires for the precursors with higher Cr content. The structure dependence of the products on the Cr content in the precursors is related to the high octahedral site stabilization energy of Cr 3+ ions and/or to the increase of Mn valence state upon Cr substitution. The increase of Cr content in the precursors degrades the electrode performance for the manganates prepared at 160 °C but improves electrode activity for those prepared at 180 °C. This observation can be explained by the structural variation and chromium substitution of the hydrothermally treated manganates. We conclude that the use of spinel LiMn 2− x Cr x O 4 as precursors provides an effective way to synthesize 1D nanostructured manganate with tailored crystal structure and morphology.

Origin of Improved Electrochemical Activity of β-MnO2 Nanorods: Effect of the Mn Valence in the Precursor on the Crystal Structure and Electrode Activity of Manganates

1D nanorods/nanowires of manganese oxides with different crystal structures and morphologies were prepared and characterized to understand the influence of the Mn valence in the solid-state precursor on the electrochemical activity of these nanomaterials and to elucidate the mechanism responsible for the excellent activity of β-MnO2 nanorods as well. According to powder X-ray diffraction analyses, treating manganese oxide precursors that have an oxidation state of ≤+3 with persulfate ions under hydrothermal conditions yields manganese oxides with the β-MnO2 structure. In contrast, the use of a LiMn2O4 precursor with a higher Mn valence leads to the formation of the α-MnO2-structured manganese oxide. Electron microscopic studies clearly show a 1D nanorod-type morphology for the β-MnO2 material, whereas a 1D nanowire-type morphology with a higher aspect ratio is observed for the α-MnO2 material. The diameter of the β-MnO2 nanorods decreases as the Mn valence in the precursors becomes smaller. According to electrochemical measurements, the formation of nanorods dramatically improves the electrode performance of the β-MnO2 phase. This compares with a relatively weak performance enhancement for the α- and δ-MnO2 phases upon the nanowire formation. The optimum electrode property results from the smaller β-MnO2 nanorods prepared with the MnO precursor. 7Li magic angle spinning nuclear magnetic resonance spectroscopy clearly demonstrates that Li+ ions in the lithiated β-MnO2 phase are adsorbed mainly on the sample surface. On the basis of this finding, we attribute the improved electrode performance of the β-MnO2 nanorods to their expanded surface area.

Degradation of acetic acid with sulfate radical generated by persulfate ions photolysis

The photolysis of S 2 O 8 2 - was studied for the removal of acetic acid in aqueous solution and compared with the H 2O 2/UV system. The SO 4 - radicals generated from the UV irradiation of S 2 O 8 2 - ions yield a greater mineralization of acetic acid than the OH radicals. Acetic acid is oxidized by SO 4 - radicals without significant formation of intermediate by-products. Increasing system pH results in the formation of OH radicals from SO 4 - radicals. Maximum acetic acid degradation occurred at pH 5. The results suggest that above this pH, competitive reactions with the carbon mineralized inhibit the reaction of the solute with SO 4 - and also OH radicals. Scavenging effects of two naturally occurring ions were tested; in contrast to HCO 3 - ions, the presence of Cl − ions enhances the efficiency of the S 2 O 8 2 - /UV process towards the acetate removal. It is attributed to the formation of the Cl radical and its great reactivity towards acetate.

Persulfate: A self-activated cathodic electron acceptor for microbial fuel cells

Abstract Potassium persulfate aqueous solution without pH adjustment is used as the cathodic electron acceptor in a two-chamber microbial fuel cell (MFC) in the present study. The performance of the MFC with K 2 S 2 O 8 solution is evaluated and compared with that of K 3 Fe(CN) 6 solution. The results show that the maximum power density of the K 3 Fe(CN) 6 used MFC doubled that with K 2 S 2 O 8 solution when fresh aqueous solution is used. However, a significant increase in electrical power generation is observed in the case of the MFC with K 2 S 2 O 8 solution after 2-day operation under an external resistance of 1000 Ω. This improvement can be attributed mainly to the increased cathode performance as a result of the hydrolysis of the persulfate ion in aqueous solution. It is demonstrated that persulfate can be used as an effective cathodic electron acceptor due to its unique capability of self pH adjustment.

Mechanism of the Photocatalytic Degradation of C.I. Reactive Black 5 at pH 12.0 Using SrTiO3/CeO2 as the Catalyst

The photocatalytic degradation mechanism of an azo dye, C.I. Reactive Black 5 (RB5), has been investigated in an aqueous suspension of SrTiO3/CeO2 composite under 250 W UV irradiation at pH 12.0. The process was studied by monitoring the change in RB5 concentration and the intermediate products employing UV-visible spectrophotometry, ion chromatography (IC), and gas chromatography/ mass spectrometry (GC/MS) techniques and depletion in total organic carbon (TOC) content as a function of irradiation time. The adsorption peaks at wavelengths of 600, 312, and 254 nm were identified as the chromophore structure, and the naphthalene and benzene components of RB5, respectively. Little influence of iodide ion, tert-butyl alcohol, fluoride ion, or persulfate ion as h(vb)+, *OH, or e(cb)- scavengers on the decolorization proved that the decolorization of RB5 primarily proceeded by photolysis and/or O2*- in the bulk solution. After the decolorization, the process could shift progressively from the bulk solution to the surface of the catalysts and cleavage of the naphthalene and benzene rings was mainly attributed to the h(vb)+ pathway and *OH(ads) reactions, which was further verified by the effect of scavengers.