This study explores the potential use of sulfate radical-based advanced oxidation technologies (SR-AOTs) for the degradation of the naturally occurring hepatotoxin, microcystin-LR (MC-LR). The generation of sulfate radicals was achieved by activation of the oxidants persulfate (PS) and peroxymonosulfate (PMS) through electrophilic transition metal cations (Ag+ and Co2+, respectively), radiation (UV 300  − has similar redox potential to hydroxyl radical (HO ), to the best of our knowledge, SR-AOTs have not been tested for the degradation of cyanotoxins. In this study, PMS was activated very efficiently with Co2+ at neutral pH and increasing catalyst concentration resulted in dramatic increase of the initial rates of degradation that reached a plateau for CCo(II) ≥ 1 mg. Based on the optimum pH conditions for each system, the efficiency order is Co2+/PMS > Fe2+/H2O2 ≫ Ag+/PS, which we believe is associated with the energy of the lower unoccupied molecular orbital of the oxidants. When UV (300  Since, the UV lamps used in the study emit light at a range of wavelengths (300

Degradation of microcystin-LR using sulfate radicals generated through photolysis, thermolysis and e− transfer mechanisms

Atmospheric aerosol particles play pivotal roles in climate and air quality. Just as chemically reduced gases experience oxidation in the atmosphere, it is now apparent that solid and liquid atmospheric particulates are also subject to similar oxidative processes. The most reactive atmospheric gas-phase radicals, in particular the hydroxyl radical, readily promote such chemistry through surficial interactions. This Review looks at progress made in this field, discussing the radical-initiated heterogeneous oxidation of organic and inorganic constituents of atmospheric aerosols. We focus on the kinetics and reaction mechanisms of such processes as well as how they can affect the physico-chemical properties of particles, such as their composition, size, density and hygroscopicity. Potential impacts on the atmosphere include the release of chemically reactive gases such as halogens, aldehydes and organic acids, reactive loss of particle-borne molecular tracer and toxic species, and enhanced hygroscopic properties of aerosols that may improve their ability to form cloud droplets.

Heterogeneous oxidation of atmospheric aerosol particles by gas-phase radicals

Ultrasound (US) was shown to activate persulfate (PS) providing an alternative activation method to base or heat as an in situ chemical oxidation (ISCO) method. The kinetics and mechanism of ultrasonic activation of PS were examined in aqueous solution using an in situ electron paramagnetic resonance (EPR) spin trapping technique and radical trapping with probe compounds. Using the spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), hydroxyl radical (•OH) and sulfate radical anion (SO4•–) were measured from ultrasonic activation of persulfate (US-PS). The yield of •OH was up to 1 order of magnitude greater than that of SO4•–. The comparatively high •OH yield was attributed to the hydrolysis of SO4•– in the warm interfacial region of cavitation bubbles formed from US. Using steady-state approximations, the dissociation rate of PS in cavitating bubble systems was determined to be 3 orders of magnitude greater than control experiments without sonication at ambient temperature. From calculations of the interf...

Kinetics and Mechanism of Ultrasonic Activation of Persulfate: An in Situ EPR Spin Trapping Study.

Electrochemical preparation of peroxodisulfuric acid using boron doped diamond thin film electrodes

A Chemical Aqueous Phase Radical Mechanism (CAPRAM) for modelling tropospheric multiphase chemistry is described. CAPRAM contains (1) a detailed treatment of the oxidation of organic compounds with one and two carbon atoms, (2) an explicit description of S(IV)-oxidation by radicals and iron(III), as well as by peroxides and ozone, (3) the reactions of OH, NO 3 ,C l 2 , Br 2 ,a nd CO 3 radicals, as well as reactions of the transition metal ions (TMI) iron, manganese and copper. A modelling study using a simple box model was performed for three different tropospheric conditions (marine, rural and urban) using CAPRAM coupled to the RADM2-mechanism (Stockwell et al., 1990) for liquid and gas phase chemistry, respectively. In the main calculations the droplets are assumed as monodispersed with a radius of 1m and a liquid water content of 0.3 g m 3 .I n the coupled mechanism the phase transfer of 34 substances is treated by the resistance model of Schwartz (1989). Results are presented for the concentration levels of the radicals in both phases under variation of cloud duration and droplet radius. The effects of the multiphase processes are shown in the loss fluxes of the radicals OH, NO 3 and HO2 into the cloud droplets. From calculations under urban conditions considering gas phase chemistry only the OH maximum concentration level is found to be 5:5 10 6 cm 3 . In the presence of the aqueous phase (r D 1 m, LWC D 0: 3g m 3 ) the phase transfer constitutes the most important sink (58%) reducing the OH level to 1:0 10 6 cm 3 . The significance of the phase transfer during night time is more important for the NO3 radical (90%). Its concentration level in the gas phase (1:9 10 9 cm 3 ) is reduced to 1:4 10 6 cm 3 with liquid water present. In the case of the HO2 radical the phase transfer from the gas phase is nearly the only sink (99.8%). The concentration levels calculated in the absence and presence of the liquid phase again differ by three orders of magnitude, 6 10 8 cm 3 and 4:9 10 5 cm 3 , respectively. Effects of smaller duration of cloud occurrence and of droplet size variation are assessed. Furthermore, in the present study a detailed description of a radical oxidation chain for sulfur is presented. The most important reaction chain is the oxidation of (hydrogen) sulphite by OH and the subsequent conversion of SO 3 to SO 5 followed by the interaction with TMI (notably Fe 2C )a nd chloride to produce sulphate. After 36 h of simulation ((H2O2U0 D 1 ppb; (SO2U0 D 10 ppb) the direct oxidation pathway from sulfur(IV) by H2O2 and ozone contributes only to 8% (2:9 10 10 M s 1 ) of the total loss flux of S(IV) (3 :7 10 9 Ms 1 ).

CAPRAM2.3: A chemical aqueous phase radical mechanism for tropospheric chemistry

In the pulse radiolysis of concentrated sulfuric acid solutions, the absorption spectrum and the molar absorption coefficient (1600 dm3 mol–1 cm–1) of the sulfate radical are unchanged up to 10 mol dm–3 H2SO4, suggesting that the sulfate radical exists in the dissociated form (SO–4). Two formation processes for the sulfate radical have been directly demonstrated in sulfuric acid and hydrogensulfate solutions: a fast one completed in the duration of the electron pulse, and a slow one occurring over a microsecond time range. For sulfate solutions only the fast formation process is observed. In sulfuric acid solutions the slow formation process is OH + HSO–4→ H2O + SO–4(4.7 × 105 dm3 mol–1 s–1) and OH + H2SO4→ HSO4+ H2O → SO–4+ H3O+(1.4 × 107 dm3 mol–1 s–1), and the fast formation process is the direct action of radiation on sulfuric acid with a G value of (2.7 ± 0.4)× 10–2 molecule eV–1. The yields of (OH + SO–4) and H can be quantified as: G(OH + SO–4)= 2.9fw+ 2.7fs and G(H)= 3.7fw+ 2.7fs. The yields of SO–4 have also been evaluated and the decay kinetics and reactions of the sulfate radical studied.

Pulse radiolysis study of concentrated sulfuric acid solutions. Formation mechanism, yield and reactivity of sulfate radicals

The formation of nitrous acid has been studied in the 60Co-γ radiolysis of concentrated nitric acid solutions. The yields of nitrous acid are proportional to the electron fraction of nitric acid, on the basis of which, an additional reaction path, NO–3 [graphic omitted]→ O(3P)+ NO–2 with a primary yield of 0.16 µmol J–1, has been verified for the direct action of radiation on nitric acid.

γ-Radiolysis study of concentrated nitric acid solutions

In the pulse radiolysis of concentrated phosphoric acid solutions, in the direct action on radiation on phosphoric acid gives rise to the phosphate radical. The yields of the phosphate radical and the hydroxyl radical are proportional, respectively, to the electron fractions of phosphoric acid and water, and can be quantified as G(˙OH + H2PO˙4)= 0.30fw+ 0.33fsµmol J–1. The forward and reverse rate constants of the equilibrium ˙OH + H3PO4⇄ H2O + H2PO˙4 were evaluated as 4.2 × 104 and 2.5 × 103 dm3 mol–1 s–1 respectively, from which E0(H2PO˙4, H+/H3PO4)= 2.65 V was derived. The decay kinetics and the reactions of the phosphate radical have also been studied.

Pulse radiolysis study of concentrated phosphoric acid solutions

Pulse and γ-radiolysis of concentrated perchloric acid solutions has been investigated. Since perchlorate ion is unreactive to the water decomposition products such as eeq–, H and OH, solute decomposition occurs only through the direct effect of radiation. From pulse radiolysis experiments using scavengers, G(ClO4˙)= 0.083 ± 0.01 and G(ClO3˙)= 0.052 ± 0.01 µmol J–1 have been determined. In highly concentrated solutions, two components with transient absorption at 350 and 440 nm are observed. The shorter-wavelength component is attributed to ClO3˙. G(ClO3˙) calculated using Iµ= 470 m2 mol–1 at the peak is 0.052 µmol J–1, which is consistent with the value determined from scavenger experiments. The longer-wavelength component is detected in perchloric acid solutions with concentration > 10 mol dm–3. This species is tentatively assigned to HClO4+, formed in the direct decomposition of HClO4 molecule. From γ-radiolysis G(ClO3–)= 0.10 ± 0.01 µmol J–1 was determined, and O(3P) is formed together with ClO3–. With G(ClO4˙)= 0.083, G(ClO3˙)= 0.052 and G(ClO3–)= 0.10 µmol J–1 and the reaction scheme proposed in this work, the yields of the final products reported previously can be explained.

Pulse and γ-radiolysis of concentrated perchloric acid solutions

The Primary yields of water radiolysis have been evaluated as a function of nitric acid or nitrate concentration in the 60Co γ-radiolysis of nitric acid and 0.4 mol dm–3 sulfuric acid with nitric acid or sodium nitrate solutions containing CeIV and CeIII, in the presence and absence of Tl+. The radiolytic decomposition of water is significantly enhanced in these systems, from gw(–H2O)= 0.60 µmol J–1 for 0.4 mol dm–3 sulfuric acid–sodium nitrate solutions to gw(–H2O)= 0.76 µmol J–1 for nitric acid solutions at high solute concentrations.

Pei-Yun Jiang

Papers

Pulse radiolysis study of concentrated sulfuric acid solutions. Formation mechanism, yield and reactivity of sulfate radicals

γ-Radiolysis study of concentrated nitric acid solutions

Pulse radiolysis study of concentrated phosphoric acid solutions

Pulse and γ-radiolysis of concentrated perchloric acid solutions

Primary yields of water radiolysis in concentrated nitric acid solutions