Res Chem Intermed(2012)38:2191–2204
DOI10.1007/s11164-012-0536-7
Kinetic model for formation of DMPO-OH in water
under ultrasonic irradiation using EPR spin trapping method
Masaki Kubo•Kazuhiro Sekiguchi•
Naomi Shibasaki-Kitakawa•Toshikuni Yonemoto
Received:22November2011/Accepted:14March2012/Published online:31March2012
ÓSpringer Science+Business Media B.V.2012
Abstract The rate of the formation of the2-hydroxy-5,5-dimethyl-1-pyrrolidiny-loxy(DMPO-OH)radical in water during ultrasonic irradiation was evaluated both experimentally and theoretically.The hydroxyl radical(OH radical)was indirectly detected using5,5-dimethyl-1-pyrroline N-oxide(DMPO)as the spin trapping com-pound,and the generated DMPO-OH by the reaction between the OH radical and DMPO
was measured by an electron paramagnetic resonance.The rate of change in the concentration of the DMPO-OH decread with time,suggesting that not only the formation reaction of DMPO-OH but also the degradation reaction would take place by ultrasonic irradiation.The formation rate of the DMPO-OH was higher with ultrasonic power intensity and lower with reaction temperature.Bad on the exper-imental results,a kinetic model for the formation of the DMPO-OH was propod by considering the formation reaction,the ultrasonic degradation,and spontaneous degradation of DMPO-OH.The model well described the effect of the ultrasonic power intensity and the reaction temperature on the formation rate of DMPO-OH.The rate of the formation of the DMPO-OH was evaluated with the aid of the kinetic model. Keywords Ultrasonic irradiationÁHydroxyl radicalÁElectron paramagnetic resonanceÁSpin trapping methodÁKinetic model
Introduction
Advanced oxidation process(AOP)is one of the water treatment technologies to eliminate hazardous organic compounds with powerful oxidizing species[1–3].The hydroxyl radical(OH radical)is the most powerful oxidant and enhances the M.Kubo(&)ÁK.SekiguchiÁN.Shibasaki-KitakawaÁT.Yonemoto
Department of Chemical Engineering,Tohoku University,Aoba-yama6-6-07,
自我鉴定300字
Sendai,Miyagi980-8579,Japan
e-mail:kubo@hoku.ac.jp
2192M.Kubo et al. degradation of hazardous organic compounds,such as chlorinated organic compounds[3],phenol[4,5]and phenolic compounds[6],and dyes[7,8].
Ultrasonic irradiation is propod as one of the techniques to generate the OH radical.The ultrasonic irradiation to water results in the formation and collap of microscale bubbles[9,10].The local high temperature caud by the collapd bubbles forces the decomposition of water to generate the OH radical[11].The generation of the OH radical is an important factor for the rate of degradation of organic compounds.
The generation rate of the OH radical may depend not only on operational conditions,such as ultrasonic power intensity,reaction temperature,and dissolved gas concentration,but also on the configuration of the ultrasonic irradiation system, such as type of ultrasonic irradiation system,the shape of the probe and reaction vesl,and so on[12].It is desired to evaluate the rate of the generation of the OH radical quantitatively for the design of the reactor and the determination of reaction conditions.However,the lifetime of the OH radical is too short to directly measure its concent
ration[13].
A spin trapping technique in conjunction with electron paramagnetic resonance (EPR)has been widely ud for the indirect detection of short-lived radicals[14].A spin trapping compound is ud to convert a short-lived radical into a relatively longer-lived radical ,a spin adduct,easily detected by EPR.Makino et al.[15,16]measured the concentration of the spin adduct of5,5-dimethyl-1-pyrroline N-oxide(DMPO),2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxy(DMPO-OH),under ultrasonic irradiation with a frequency of50kHz to evaluate the amount of the OH radical.Nam et al.[17]reported that the concentration of DMPO-OH under ultrasonic irradiation with a frequency of20kHz incread early in the stage and then approached the plateau value.They concluded that the degradation of the DMPO-OH also took place during the ultrasonic irradiation.Their result suggested that the existing amount of DMPO-OH estimated from the measured concentration was not equal to the integrated amount of DMPO-OH formed.
In order to accurately evaluate the generation rate of the OH radical,it is necessary to elucidate the mechanism of formation and degradation of the DMPO-OH. Yanagida et al.[18]ud the high frequency ultrasound of1,000kHz and obrved that the decay of the concentration of the DMPO-OH.They propod that‘‘the unknown scavenger’’was generated to decrea the concentration of th
e DMPO-OH. Nakamura et al.[19]also ud the high frequency ultrasound of1,650kHz and investigated kinetics of formation and decay of DMPO-OH.They concluded that DMPO-OH formation was saturated even though the OH radical was generated continuously and the concentration of DMPO-OH decread after stopping ultrasonic irradiation.The kinetic model is a uful tool for the evaluation of each reaction rate.The model including both the formation and degradation reactions is expected to provide a rigorous estimation of the rate of DMPO-OH formation.
We focud on the formation of DMPO-OH by low frequency ultrasound,which was effective for the degradation of the organic compounds in water[20].The time cour of the concentration of DMPO-OH during ultrasonic irradiation was measured by an EPR spin trapping method.The effect of the ultrasonic power intensity and the reaction temperature on the behavior of the formation of
DMPO-OH was investigated.The kinetic model for the formation of DMPO-OH was propod,including both the formation and degradation reactions of DMPO-OH,and then the formation rate of DMPO-OH was estimated.
Materials and methods
Ultrasonic irradiation experiment
繁忙反义词
DMPO and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL)were obtained from Sigma-Aldrich Chemical,St.Louis,MO,USA,and were ud without further purification.The general expression of the reaction between DMPO and free radicals (R )is shown in Fig.1.DMPO reacts with short-lived free radicals (R )to convert into longer-lived spin adducts.The shape of EPR signal of spin adduct is associated with the structure of the free radical,so that the free radical can be identified by the EPR spectrum.
The schematic illustration of the apparatus ud for the ultrasonic irradiation is shown in Fig.2.A horn-type ultrasonic homogenizer (Sonifier 250;Branson Ultrasonics,Danbury,CT,USA)operating at a constant frequency of 20kHz was ud.The diameter and surface area of the probe was 1.3cm and 1.19cm 2,
Fig.2Experimental apparatus
八年级上册英语第六单元单词
EPR spin trapping method 2193
2194M.Kubo et al. respectively.Three sizes of reaction vesls made of stainless steel(SUS304)were ud;vesl1was32mm inner diameter(i.d.)and75mm height,vesl2was40mm i.d.and82.5mm height,vesl3was50mm i.d.and93mm height.The solution volumes were25,50,and100cm3for vesls1,2,and3,respectively.The vesls were placed in a temperature-controlled water bath who temperature was regulated using a water circulator(CTE-82A;,Yamato Science,Tokyo,Japan).To avoid the degradation of DMPO by light,the reaction system was covered by a blackout curtain.
A10mol/m3DMPO aqueous solution was poured into the reaction vesl.The DMPO concentration was high enough to achieve the excess amount of DMPO compared to the amount of generated the OH radical,according to the results of Makino et al.[16]and Num et al.[17].The ultrasonic horn was then immerd in the solution.The reaction was started by irradiating the ultrasound to the solution. The ultrasonic power intensity was defined as the input power of the ultrasound per volume of the solution and regulated in the range of0.25–3W/cm3.The temperature of the reaction solution was reg
ulated in the range of293–313K by balancing the heat generation due to the ultrasonic irradiation and the heat emission to the water bath.All the experiments were conducted under air atmosphere. EPR measurements
During the ultrasonic irradiation,small amounts of the solution were taken with capillary tube at specified time intervals.The EPR spectrum was measured at room temperature using an EPR spectrometer(e-scan;Bruker BioSpin,Rheinstetten, Germany)with microwave of3.6mW(9.8GHz),modulation frequency of86kHz, modulation amplitude of0.306mT,afield t of3,498G with a scan range of60G, and number of scans of64.The concentration of the spin-adduct was determined from the EPR spectrum.TEMPOL was ud as the standard.
In order to elucidate the spontaneous degradation of the formed spin adducts,the time cour of the concentration of the spin-adduct after stopping the ultrasonic irradiation was measured at293K.
Measurement of the concentration of DMPO
The concentration of DMPO was measured during the ultrasonic irradiation to verify whether the ultrasonic degradation of DMPO took place or not.The solution was taken for specific time intervals and was diluted appropriately with water.The absorbance of the DMPO in the solution was measured
at227nm using a spectrophotometer(U-2010;Hitachi,Tokyo,Japan).
船怎么画Results and discussion
Ultrasonic irradiation of the DMPO aqueous solution
红龙鱼价格Figure3shows the EPR spectra.Abscissa is the magneticfield.The relative value of the magneticfield is important,since the absolute value of the magneticfield is depends
on the tup of the each EPR equipment.Figure 3a shows the spectrum of the aqueous solution of 5910-3mol/m 3TEMPOL,the standard material for the quantification of radical concentration.Figure 3b,c show the spectra of the DMPO aqueous solution before and after the ultrasonic irradiation at 3W/cm 3for 60min,respectively.Before the ultrasonic irradiation,only a signal of the noi of the measurement system was obrved in Fig.3b.After the ultrasonic irradiation,a quartet signal with the intensity ratio of 1:2:2:1,the characteristic spectrum of DMPO-OH,was appeared as shown in Fig.3c.Therefore,only the OH radical was considered to evolve.
During the ultrasonic irradiation,water is directly decompod to generate hydrogen and the OH radical as
H 2O !H ÁþÁOH ð1Þ
The experiment was conducted in the air atmosphere,so that there existed dissolved oxygen in the aqueous solution.The hydrogen radical rapidly reacts with the oxygen molecule to form a hydroperoxy radical as [21]
H ÁþO 2!HO 2Á
ð2Þ
甘肃人社厅官网首页The hydroperoxy radical disappears by the bimolecular reaction as
呼啦圈瘦身2HO 2Á!H 2O 2þO 2ð3ÞThe reactions (2)and (3)were very fast so that the hydrogen radical and hydro-peroxy radical disappeared before reacting with DMPO.Therefore,the OH radical was considered to be alone detected.-5 10
40
月球温度5 10
4(a) TEMPOL (5x10-3 mol/m 3)-5 10
40
5 10
4(b) DMPO solution without irradiation -5 1040
5 10
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Magnetic field [G]
(c) DMPO solution after irradiation (3W/dm 3, 60min)
Fig.3ESR spectra of DMPO solution and DMPO-OH.a 5mol/dm 3TEMPOL solution,the standard for the quantification of radical concentration,b DMPO solution without ultrasonic irradiation,c DMPO solution after ultrasonic irradiation at 3W/cm 3for 60min
EPR spin trapping method 2195
