On the use of 1,3-diphenylisobenzofuran (DPBF). Reactions with carbon and oxygen centered radicals in model and natural systems

1,3-diphenylisobenzofuran (DPBF) is a fluorescent molecule which possesses a highly specific reactivity towards singlet oxygen (¹O₂) forming an endoperoxide which decomposes to give 1,2-dibenzoylbenzene. This reaction between DPBF and ¹O₂ can be followed by measuring the decrease in fluorescence intensity of DPBF. In order to check the specificity of DPBF toward free radicals a series of experiments was carried out in Triton-X micelles and in natural systems (rat liver microsomes), in which DPBF was reacted with hydroxy (HO^•), alkyloxy (RO^•), alkylperoxy (ROO^•), and C-centered radicals (2-cyanoisopropyl radical). In all cases, the DPBF is rapidly transformed to 1,2-dibenzoylbenzene in the case of O-centered radicals and to the corresponding adduct in the case of 2-cyanoisopropyl radical. The experiments in the model systems were also carried out from the chemical point of view and the reaction products were isolated and identified. From the results obtained, it should be stressed that DPBF must be used with caution in complex biological systems for the detection of ¹O₂, as it also reacts with different radical species.     

Type I Photosensitized Oxidation of Methionine†

Methionine (Met) is an essential sulfur‐containing amino acid, sensitive to oxidation. The oxidation of Met can occur by numerous pathways, including enzymatic modifications and oxidative stress, being able to cause relevant alterations in protein functionality. Under UV radiation, Met may be oxidized by direct absorption (below 250 nm) or by photosensitized reactions. Herein, kinetics of the reaction and identification of products during photosensitized oxidation were analyzed to elucidate the mechanism for the degradation of Met under UV‐A irradiation using pterins, pterin (Ptr) and 6‐methylpterin (Mep), as sensitizers. The process begins with an electron transfer from Met to the triplet‐excited state of the photosensitizer (Ptr or Mep), to yield the corresponding pair of radicals, Met radical cation (Met^?+) and the radical anion of the sensitizer (Sens^??). In air‐equilibrated solutions, Met^?+ incorporates one or two atoms of oxygen to yield methionine sulfoxide (MetO) and methionine sulfone (MetO₂), whereas Sens^?? reacts with O₂ to recover the photosensitizer and generate superoxide anion (O₂^??). In anaerobic conditions, further free‐radical reactions lead to the formation of the corresponding dihydropterin derivatives (H₂Ptr or H₂Mep).     

Kinetics of the reaction between 1,3-diphenylisobenzofuran and nitrogen dioxide studied by steady-state fluorescence

1,3-Diphenylisobenzofuran (DPBF) is a fluorescent molecule which is believed to react highly specifically toward reactive oxygen species such as singlet oxygen (¹O₂), hydroxy (HO^·), alkyloxy (RO^·), and alkylperoxy (ROO^·) radicals. In all cases the reaction product is 1,2-dibenzoylbenzene. In order to prove that DPBF gives the same product in contact with reactive nitrogen species, its reaction with nitrogen dioxide radical has been studied in 2,2,4-trimethylpentane using the steady-state fluorescence method and mass spectrometry. The progress of the studied reaction was measured by observation of changes in fluorescence intensity of DPBF after addition of nitrogen dioxide (NO₂). The rate constants of DPBF fluorescence decay affected by NO₂ have been determined. Experiments were conducted over the temperature range of 13–37 °C and for NO₂ concentrations from 0.02 to 0.14 mmol dm^?3. It has been found that the reaction between 1,3-diphenylisobenzofuran and nitrogen dioxide proceeds in two steps. The first step is a very rapid reaction whose rate could not be measured under established experimental conditions. The second step is slower. The reaction product was identified by registration of mass spectra. The probable reaction mechanism is proposed.     

Oxidation reactions of 1,3-diphenylpropane-1,3-dione

The free radical scavenging properties and possible antioxidant activity of 1,3-diphenylpropane-1,3-dione (1) are reported. Pulse radiolysis technique was employed to study the one-electron oxidation of 1 with various radicals viz. CCl₃O₂ ^•, N₃ ^• and^•OH in homogeneous aqueous solution. All these radicals reacted with 1 under ambient conditions at almost diffusion controlled rates producing transient species with an absorption maximum around 420 nm that decayed at first order rates. The transient absorption peak was shifted in the case of CCl₃OO^• radical reaction with 1 due to change in the polarity of the medium. Formation of a stable product with a broad absorption band starting from 400 nm and cut off at 230 nm was observed in the oxidation of 1 with^•OH and^•N₃ radicals. In a biological system also, 1 showed significant inhibitory activity against Fe²⁺-mediatedlipidperoxidation. Based on these observations, a suitable mechanism for the oxidation of 1 has been proposed.     

Facile ion-exchange synthesis of Gd-doped K2Ta2O6 photocatalysts with enhanced visible light activity

One of the well-known ways of increasing the visible light absorption capability of semiconducting materials is cation doping. This study aims to use Gd doping to tailor the bandgap energy of K₂Ta₂O₆ (KTO) for photocatalytic degradation of organic pollutants under visible light irradiation. Accordingly, the parent KTO and Gd-doped KTO with different Gd concentrations (K_2-3xGd_xTa₂O₆; x = 0.025, 0.05, 0.075 and 0.1 mol%) were synthesized by hydrothermal and facile ion-exchange methods, respectively. The powder XRD, FT-IR, SEM-EDS, TEM-SAED, N₂ adsorption-desorption, XPS, UV–Vis DRS, PL and ESR techniques were used to investigate the effect of Gd dopant concentration on the structural and photocatalytic properties of KTO. The photocatalytic activity of these samples was investigated for the photocatalytic degradation of methylene blue (MB) dye in an aqueous solution at room temperature under visible light irradiation. The experimental results show that all Gd-doped KTO samples exhibit enhanced photocatalytic activity compared with parent KTO toward MB degradation. In particular, Gd-KTO obtained by doping of 0.075 mol% shows the highest photocatalytic activity among the Gd-doped samples and the degradation efficiency of MB was 79% after 180 min of visible light irradiation, which is approximately 1.5 times as high as that by parent KTO (53%). In addition, trapping experiments and electron spin resonance (ESR) analysis demonstrated that the hydroxyl radicals (^?OH) have played a crucial role in the photocatalytic degradation of MB. The reusability and stability of Gd doped-KTO with a Gd content of 0.075 mol% against MB degradation were examined for five cycles. Based on the present study results, a visible light induced photocatalytic mechanism has been proposed for Gd0075-KTO sample.     

Binary α-Fe2O3–Co3O4 nanostructures for advanced oxidation process: Role of synergy for enhanced catalysis

Iron and its binary oxides are meticulously exploited for environmental remediations. However, only limited studies have been carried out on the degradation of industrial organics by advanced oxidation process. In this study, iron oxide, cobalt oxide, and iron–cobalt binary oxides were synthesized by a modified hydrothermal method as heterogeneous Fenton-like catalysts for the removal of methylene blue (MB) from wastewaters. The oxide nanostructures were characterized by different analytical techniques. Studying the effects of various parameters such as catalyst dose, MB concentration, and H₂O₂ concentration, the reaction conditions were optimized to enhance the removal of MB dye. The results revealed that α-Fe₂O₃–Co₃O₄ shows much higher activity than both Co₃O₄ and α-Fe₂O₃ for the degradation of MB at room temperature and beyond. The binary α-Fe₂O₃–Co₃O₄ shows degradation efficiency of 96.4% at 65 °C within 60 min. Furthermore, the binary α-Fe₂O₃–Co₃O₄ catalyst retains its activity for up to four successive cycles. A probable mechanism is also proposed, involving the generation of ‧OH radical as well as Fe²⁺/Fe³⁺ or Co²⁺/Co³⁺ redox couple of the binary α-Fe₂O₃–Co₃O₄ catalyst.     

Preparation of novel hybrid nanomaterials based on LaFeO3 and phosphotungstic acid as a highly efficient magnetic photocatalyst for the degradation of methylene blue dye solution

Novel magnetic hybrid nanomaterials 1 (LaFeO₃.Fe₃O₄@SiO₂-NH₂/PW₁₂) were synthesized by supporting phosphotungstic acid (H₃PW₁₂O₄₀; PW₁₂) on LaFeO₃.Fe₃O₄ nanomaterials through sono-assisted method. The synthesized nanomaterials were fully characterized by using FT-IR, XRD, UV–vis, BET-BJH, VSM, SEM, and TEM analyses. FT-IR, XRD, and UV–vis confirmed successful synthesis of nanomaterials. The SEM and TEM images revealed spherical morphology with core-shell structure for hybrid nanomaterials 1 . VSM results confirmed the magnetic property of hybrid nanomaterials 1 and suggested it as easily recyclable photocatalyst for removal of organic dyes from aqueous solution. The photocatalytic activity of hybrid nanomaterials 1 has been studied over the degradation of methylene blue (MB) and methyl orange (MO) solution under UV–vis light irradiation. Importantly the hybrid nanomaterials 1 showed outstanding degradation efficiency for MB solution in comparison with bare LaFeO₃.Fe₃O₄ and PW₁₂. The photocatalytic activity was enhanced mainly due to the high efficiency in separation of electron–hole pairs induced by the remarkable synergistic effects of LaFeO₃.Fe₃O₄ and PW₁₂ semiconductors. After the photocatalytic reaction, the nanocomposite can be easily separated from the reaction solution and reused several times without loss of its photocatalytic activity. Trapping experiments indicated that hole (h_VB⁺) and ^•OH radicals were the main reactive species for dye degradation in the present photocatalytic system. On the basis of the experimental results and estimated band gaps, the mechanism for the enhanced photocatalytic activity was proposed.     

Construction of oxygen defective ZnO/ZnFe2O4 yolk-shell composite with photothermal effect for tetracycline degradation: Performance and mechanism insight

Oxygen vacancy induced photothermal effect is of great significant but lack of adequate attentions for environmental remediation. In this paper, green recyclable ZnO/ZnFe₂O₄ with oxygen vacancy was prepared by a solvothermal-calcination method. The UV-vis light capture ability of ZnO/ZnFe₂O₄ microspheres is improved with the multiple light reflections due to the yolk-shell structure, and the oxygen vacancy expands the absorption range of photocatalyst and enhances photothermal conversion. The optimized photocatalyst can heat the solution from room temperature to 70 °C within 60 min of visible light illumination, and the light to heat conversion efficiency is achieved by 61.3%. Compared with the degradation efficiency at 20 °C, photothermal catalysis achieves a stable degradation in 80 min, and the degradation efficiency is increased by 41.5%. This can be attributed to the fact that light induced thermal energy accelerates the migration of electrons and holes, and promotes the diffusion of free radicals by heating active centers in situ. The active species contributing to the degradation, in order of importance, are the superoxide radical, hydroxyl radical, hole and electron. The light-to-thermal assisted photocatalysis with ZnO/ZnFe₂O₄ provides a new sight for the pollution control in the future practical applications.     

Enhanced photodegradation of methylene blue with alkaline and transition‐metal ferrite nanophotocatalysts under direct sun light irradiation

It is highly desired to synthesize low‐cost photocatalysts for the degradation of colored dyes to safeguard our environment for the future generations. Here, we report an extremely efficient and low‐cost synthesis of alkaline earth and transition‐metal ferrite photocatalysts (MgFe₂O₄, CaFe₂O₄, BaFe₁₂O₁₉, CuFe₂O₄, and ZnFe₂O₄) from their chloride salts and their applications for the degradation of methylene blue (MB) dye under UV–visible and direct sunlight irradiation. The as‐prepared photocatalysts displayed enhanced photoactivities under both conditions of irradiation. After calcination at 600°C, the photocatalytic degradation increased significantly, and 96 and 85% MB was removed with ZnFe₂O₄ under UV–visible and direct sunlight irradiation, respectively. Moreover, large amounts of hydroxyl free radicals were produced under both irradiation conditions, which participated in the degradation of MB. The enhanced photodegradation activities of these photocatalysts are attributed to their extended visible light absorption and low bandgaps. This work will provide a feasible route to the synthesis of efficient and low‐cost photocatalysts to utilize sunlight for environmental remediation.     

CuFe2O4@GO nanocomposite as an effective and recoverable catalyst of peroxymonosulfate activation for degradation of aqueous dye pollutants

Recently, heterogeneous activation of peroxymonosulfate (PMS) to oxidatively degrade organic pollutants has been a hotspot. In the present work, copper ferrite-graphite oxide hybrid (CuFe₂O₄@GO) was prepared and used as catalyst to activate PMS for degradation of methylene blue (MB) in aqueous solution. A high degradation efficiency (93.3%) was achieved at the experimental conditions of 20 mg/L MB, 200 mg/L CuFe₂O₄@GO, 0.8 mmol/L PMS, and 25 °C temperature. Moreover, CuFe₂O₄@GO showed an excellent reusability and stability. The effects of various operational parameters including pollutant type, solution pH, catalyst dosage, PMS dosage, pollutant concentration, temperature, natural organic matter (NOM), and inorganic anions on the catalytic degradation process were comprehensively investigated and elucidated. The further mechanistic study revealed the Cu(II)/Cu(I) redox couple on CuFe₂O₄@GO played the dominant role in PMS activation, where both hydroxyl and sulfate radicals were generated and proceeded the degradation of pollutants. In general, CuFe₂O₄@GO is a promising heterocatalyst for PMS-based advanced oxidation processes (AOPs) in wastewater treatment.     

过硫酸盐激活协同可见光催化降解四环素的机理和降解路径

为了提升微污染水体中抗生素的降解效率,利用过硫酸钠(PDS)激活协同手性介孔TiO₂可见光催化(PDS/vis-TiO₂)对四环素(TC)进行降解。详细对比研究了以手性TiO₂作为催化剂的PDS激活(PDS/TiO₂)、可见光催化(vis-TiO₂)和PDS/vis-TiO₂三种体系中,降解污染物的活性物种和污染物降解路径等的差异。结果表明,不对称的螺旋堆积结构在手性介孔TiO₂中引入了丰富的Ti³⁺,不仅提升了其可见光响应,同时能够激活PDS生成自由基。PDS/vis-TiO₂体系中光生空穴h⁺和·OH等多种自由基可以同时参与TC的降解,5 h内其对TC去除率可达到95%以上,远超PDS/TiO₂体系(TC去除率为48.9%)和vis-TiO₂体系(TC去除率为71.1%)。PDS加入到光催化体系中,会受到光生电子的激活而产生自由基,从而消耗光生电子,提升光生空穴和电子的分离率,达到协同增强污染物的降解能力。另外PDS激活后产生自由基也会大大增加体系对TC的降解性能。密度泛函理论计算和中间产物分析结果表明,TC在PDS/vis-TiO₂体系中的降解路径包含了光生空穴h⁺攻击TC的降解路径,同时也包括自由基攻击TC的降解路径。     

过硫酸盐激活协同可见光催化降解四环素的机理和降解路径

为了提升微污染水体中抗生素的降解效率,利用过硫酸钠（PDS）激活协同手性介孔TiO₂可见光催化（PDS/vis-TiO₂）对四环素（TC）进行降解。详细对比研究了以手性TiO₂作为催化剂的PDS激活（PDS/TiO₂）、可见光催化（vis-TiO₂）和PDS/vis-TiO₂三种体系中,降解污染物的活性物种和污染物降解路径等的差异。结果表明,不对称的螺旋堆积结构在手性介孔TiO₂中引入了丰富的Ti³⁺,不仅提升了其可见光响应,同时能够激活PDS生成自由基。PDS/vis-TiO₂体系中光生空穴h⁺和·OH等多种自由基可以同时参与TC的降解,5 h内其对TC去除率可达到95%以上,远超PDS/TiO₂体系（TC去除率为48.9%）和vis-TiO₂体系（TC去除率为71.1%）。PDS加入到光催化体系中,会受到光生电子的激活而产生自由基,从而消耗光生电子,提升光生空穴和电子的分离率,达到协同增强污染物的降解能力。另外PDS激活后产生自由基也会大大增加体系对TC的降解性能。密度泛函理论计算和中间产物分析结果表明,TC在PDS/vis-TiO₂体系中的降解路径包含了光生空穴h+攻击TC的降解路径,同时也包括自由基攻击TC的降解路径。     

Submerged Arc Breakdown of Methylene Blue in Aqueous Solutions

Low voltage, low energy submerged pulsed arcs between a pair of carbon or iron electrodes with a pulse repetition rate of 100?Hz, energies of 2.6?C192?mJ and durations of 20, 50 and 100???s were used to remove methylene blue (MB) contamination from 30?ml aqueous solutions. The MB concentration decreased exponentially with rates of 0.0006?C0.0143?s^?1 during processing with the carbon electrode pair. With the iron electrodes, the MB concentration initially decreased faster (0.030?s^?1) than with the carbon electrodes, but later saturated. However when microparticles produced with the iron electrodes were periodically filtered, the high removal rate was maintained. Under these conditions, the volume of water which can be treated per unit energy expenditure was much higher with the submerged arc than with other plasma processes. A kinetic model based on MB degradation by OH· radicals formed by the discharge was formulated. The higher initial MB removal rate with iron electrodes is explained by additional OH· production from Fenton??s reaction between Fe⁺⁺ and H₂O₂ produced by the discharge. This rate is maintained if the eroded iron particles are filtered, but if eroded iron particles accumulate, degradation slows down and stops, possibly because the iron particles catalytically decompose H₂O₂ and hence stops Fenton??s reaction, and either directly or via increased Fe⁺⁺ dissolved from the particles, scavenge the OH· radicals.     

Degradation of n-butylparaben and 4-tert-octylphenol in H2O2/UV system

The degradation of two endocrine disrupting compounds: n-butylparaben (BP) and 4-tert-octylphenol (OP) in the H₂O₂/UV system was studied. The effect of operating variables: initial hydrogen peroxide concentration, initial substrate concentration, pH of the reaction solution and photon fluency rate of radiation at 254 nm on reaction rate was investigated. The influence of hydroxyl radical scavengers, humic acid and nitrate anion on reaction course was also studied. A very weak scavenging effect during BP degradation was observed indicating reactions different from hydroxyl radical oxidation. The second-order rate constants of BP and OP with OH radicals were estimated to be 4.8×10⁹ and 4.2×10⁹ M^?1 s^?1, respectively. For BP the rate constant equal to 2.0×10¹⁰ M^?1 s^?1was also determined using water radiolysis as a source of hydroxyl radicals.     

One-dimensional porous Ag/AgBr/TiO<Subscript>2</Subscript> nanofibres with enhanced visible light photocatalytic activity

One-dimensional (1D) Ag/AgBr/TiO₂ nanofibres (NFs) have been successfully fabricated by the one-pot electrospinning method. In comparison with bare TiO₂ NFs and Ag/AgBr/PVP (polyvinylpyrrolidone) NFs, the 1D Ag/AgBr/TiO₂ NFs photocatalyst exhibits much higher photocatalytic activity in the degradation of a commonly used dye, methylene blue (MB), under visible light. The photocatalytic removal efficiency of MB over Ag/AgBr/TiO₂ NFs achieves almost 100 % in 20 min. The photocatalytic reaction follows the first-order kinetics and the rate constant (k) for the degradation of MB by Ag/AgBr/TiO₂ NFs is 5.2 times and 6.6 times that of Ag/AgBr/PVP NFs and TiO₂ NFs, respectively. The enhanced photocatalytic activity is ascribed to the stronger visible light absorption, more effective separation of photogenerated electron-hole pairs, and faster charge transfer in the long nanofibrous structure. The Ag/AgBr/TiO₂ NFs maintain a highly stable photocatalytic activity due to its good structural stability and the self-stability system of Ag/AgBr. The mechanisms for photocatalysis associated with Ag/AgBr/TiO₂ NFs are proposed. The degradation of MB in the presence of scavengers reveals that h⁺ and ^?O ₂ ^? significantly contribute to the degradation of MB.     

High-energy ionising radiation initiated decomposition of acetovanillone

Hydroxyl radical, hydrated electron and hydrogen atom intermediates of water radiolysis react with acetovanillone with rate coefficients of (1.05±0.1)×10¹⁰, (3.5±0.5)×10⁹ and (1.7±0.2)×10¹⁰mol^?1 dm³ s^?1. Hydroxyl radical and hydrogen atom attach to the ring forming cyclohexadienyl type radicals. The hydroxyl–cyclohexadienyl radical formed in hydroxyl radical reaction in dissolved oxygen free solution partly transforms to phenoxyl radical. In the presence of O₂ phenoxyl radical formation and ring destruction are observed. Hydrated electron in O₂ free solution attaches to the carbonyl oxygen and undergoes protonation yielding benzyl type radical. In air saturated 0.5 mmol dm^?3 solution using 15 kGy dose most part of acetovanillone is degraded, for complete mineralisation five times higher dose is required. The experiments clearly show that acetovanillone can be efficiently removed from water by applying irradiation technology.     

ESR study of free radicals formed upon UV irradiation of nitropentafluoroacetone in various solvents

The formation of CF₃C(O)CF₂N(O^.)O₂CF₂C(O)CF₃ free radicals upon the UV irradiation of nitropentafluoroacetone (1) in toluene and mesitylene is established by ESR. The most likely cause of their formation is the one-electron oxidation of the solvents by photoexcited1 followed by decay of the radical anion formed from1 with the expulsion of an NO₂ anion and attachment of the radical to a molecule of original1. The irradiation of 1 in triethylsilane results in the elimination of a fluoride ion and fixation of a CF₃COCFN(O^–)O' radical. UV irradiation of ketone1 in pentane results in the abstraction of a hydrogen atom from the solvent and the formation of a CF₃COCF₂N(OH)O ' radical.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 512–514, March, 1993.     

Reduction mechanisms of different oxidizing agents at diamond surfaces

“Electroless” oxidation, at room temperature, of boron-doped diamond (BDD) films with oxidizing agents as Ce⁴⁺, MnO₄^?, H₂O₂ or S₂O₈^2? is an efficient way to transform hydrogen terminations (C-H) into oxygen ones (C-O). To investigate the oxidation mechanism of diamond surfaces through these open current potential (OCP) processes, we study in the present work the reduction mechanisms of the different oxidizing agents at BDD surfaces. Current-voltage measurements were performed using a rotating disk electrode of diamond immersed in a solution containing one of the species. Two different mechanisms were evidenced: an electrochemical for Ce⁴⁺ and MnO₄^? and a chemical one based on the production of radicals under light exposure for H₂O₂ and S₂O₈^2?.     

Current trends in the use of zero-valent iron (Fe0) for degradation of pharmaceuticals present in different water matrices

Zero-valent iron (Fe⁰) has recently been proposed as a potential candidate for the degradation of pharmaceuticals, because Fe⁰ can release dissolved iron species, activate molecular oxygen, and react with oxidant species. Additionally, due to its small particle size and large surface area, this catalyst can provide better degradation results, compared to traditional processes. This work focuses on the elimination of pharmaceuticals present in different water matrices, considering the potential harm that these substances can cause in the environment. The mechanisms of pharmaceutical removal using Fe⁰ particles include reduction, adsorption, precipitation, and oxidation processes. Most studies have focused on oxidation processes in the presence of Fe⁰ and radicals derived from oxidants such as hydrogen peroxide (H₂O₂), ozone (O₃), peroxysulfate (SO₅²⁻), peroxodisulfate (S₂O₈²⁻), and oxygen (O₂). Most of the results have shown that high percentages of pharmaceuticals can be removed, degraded, and mineralized. The mechanisms of oxidation and the parameters that influence the degradation of pharmaceuticals, as well as the possible degradation pathways, are discussed here. This review provides information on trends of different processes that use Fe⁰, considering aspects such as particle size, type of matrix, the pharmaceuticals studied, and the results obtained that can improve understanding of new advances in the field of advanced oxidation processes (AOPs) for the degradation and elimination of pharmaceuticals.