Effects of Hydrogen Peroxide and Frequency for the Sonochemical

Effects of Hydrogen Peroxide and Frequency

for the Sonochemical Degradation of Aqueous Phenol

Myunghee Lim,Younggyu Son,Mingcan Cui,and Jeehyeong Khim?

Department of Civil,Environmental and Architectural Engineering,Korea University,

5-ga,Anam-dong,Seongbuk-gu,Seoul136-701,Korea

Received November24,2008;accepted January22,2009;published online July21,2009

The effect of hydrogen peroxide and frequency on the degradation of phenol was investigated in this study.The concentrations of phenol and hydrogen peroxide were0.05and0.0018mM,respectively.When a high frequency of sonication(1MHz)was irradiated to a phenol solution,the efficiency of decomposition of phenol was about95%within120min.At a low frequency,the phenol degradation was slower than at a high frequency,while the degradation of the total organic carbon at a low frequency was nearly the same as that at a high frequency.Hydrogen peroxide was formed due to the dissipation of water.Through a comparison,it can be seen that the order of degradation rates of phenol and the formation rate of hydrogen peroxide were not the same.The relationship between the degradation rate of compounds and the formation rate of hydrogen peroxide was not clear.With the addition of hydrogen peroxide in phenol solution,the phenol concentration was almost completely degradable within30min.In the case of total organic carbon(TOC),the concentration was degraded by50%.Therefore,for the decomposition of total organic carbon,the addition of hydrogen peroxide or other catalysts was required.#2009The Japan Society of Applied Physics

DOI:10.1143/JJAP.48.07GH07

1.Introduction

The chemical e?ects of ultrasound can enhance chemical reactivity through the cavitation event.Sonication of aqueous solutions produces the formation,growth and collapse of cavitation bubbles.The collapse of the cavitation bubble creates a localized high temperature(5000K)and pressure(1000atm).1)

The main reaction mechanisms of sonochemical in aqueous solutions are radical reaction(decomposition of water can produce

.H and.OH)and pyrolysis.In the case of volatile and hydrophobic compounds,they are directly volatilized inside the cavitation bubble(the surface of the bubble is hydrophobic)and are decomposed by pyrolysis (due to high temperature and pressure).However,non-volatile and hydrophilic compounds barely di?used into the bubble,and were therefore indirectly degraded by radicals in the bulk solution or interface of bubbles.2,3)

Using ultrasound,many researchers have investigated the degradation of organic compounds(aromatic,aliphatic, explosive and surfactants)in aqueous solution.These studies investigated various factors of sonochemistry;frequency,2–7) pH,9,10)saturating gas,10)additives,10–12)and a combination of advanced oxidation processes.9,13)The e?ect of frequency on the degradation of organic compounds has been studied by many researchers.The presence of optimum frequency for the speci?c compounds that have di?erent properties was revealed.3)However,the results of optimum frequency di?ered from other groups results3,4)because the exper-imental conditions(power,transducer type and size,reactor type)di?ered.Therefore,further research on frequency (dealing with various compounds and under the same conditions)is needed.

Phenol is a hazardous chemical in the priority pollutant list.14)It has been widely detected in waste water and ground water.To enhance the degradation rate of phenol,various attempts have been made for the application of high frequency ultrasound,3)combinations of oxidants/additives (hydrogen peroxide,Fe2t,CuSO4,TiO2,etc.)10–12)and integration with ultraviolet rays.10,13,15)

In this study,the e?ect of frequency on the degradation of phenol in aqueous solution and total organic carbon(TOC) was examined.The range of frequencies is35,110,300kHz and1MHz under the same experimental conditions.The e?ect of the combination of hydrogen peroxide was also examined.

2.Experimental Procedure

2.1Materials

In this study,the following were used:high-purity phenol (Samchun),hydrogen peroxide(34.5%,Junsei),potassium biphthalate(Junsei),potassium iodide(Samchun),sodium hydroxide(Junsei)and ammonium molybdate(Junsei).The initial concentrations of phenol and hydrogen peroxide were 0.05and0.0018mM,respectively.

2.2Experimental apparatus

The sonochemical reaction was carried out in a300mL pyrex bottle(the reactor total volume,500mL).The pyrex bottle reactor was submerged into an acryl reactor(Fig.1). The reaction temperature was maintained at16–18 C by a cooling water system.The35and110kHz frequencies were emitted from the Frexonic(Mirae Ultrasonics Tech.)which consisted of nine piezoelectric transducers(PZT;Tamura). The300kHz and1MHz were individually irradiated by the MX-300and Megasonic(Mirae Ultrasonics Tech.) with three PZT(Tamura).The size of the transducer is 20?20?7cm3(length?width?height)and is the same for di?erent frequencies.For each frequency,the same input power240W(0.8W/mL)was https://www.360docs.net/doc/ae11259001.html,ing the calori-metric method the energy output was modi?ed.

2.3Analysis

The total sonication time was2h.Every15min,1mL of liquid was individually analyzed for the phenol and TOC concentrations.All experiments were conducted more than three times and samples were analyzed immediately after collection.The phenol and TOC concentrations were measured by the direct photometric method(5530D, standard methods for the examination of water and waste-water20th edition,APHA)and a TOC analyzer(GE SEIVERS5310C laboratory analyzer).The hydrogen per-

?E-mail address:hyeong@korea.ac.kr

Japanese Journal of Applied Physics48(2009)07GH07REGULAR PAPER

oxide produced by the sonication of water was detected by the iodometric method.5)The iodide ion(Ià)reacts with H2O2to form the triiodide ion(I3à)that is absorbed at 352nm.

3.Results and Discussion

The concentration change of phenol is shown in Fig.2(a).A more rapid degradation of phenol occurred during sonolysis at1MHz than that at35,110,and300kHz.At a higher frequency,the power of the cavitation e?ect decreased. Therefore,the cavitation event occurring at a low frequency is more violent and e?cient on the inside of the cavitation bubble.However,at a high frequency the acoustic period is shorter and the size of the cavitation bubble decreases. Consequently,most of the formed radicals have su?cient time to recombine at a low frequency.Also,at low frequency,hydroxyl radical can be scavenged by reaction with the hydroperoxyl radical[eq.(1)]and recombine other radicals to form H2O,O[eqs.(2)and(3)].7)

HOátáOOH!H2OtO2e1T

HOátáH!H2Oe2T

2HOá!H2O2tOe3TIn most cases,there is an optimum frequency at which the rate of chemical production and the duration of cavity collapse provide the best conditions for the destruction of the target chemical.7,8)

As a result,a high frequency creates higher degradation

rates for non-volatile compounds(e.g.,phenols)than a low frequency.Previous researchers have shown that the degradation rate of non-volatile compounds(chlorobenzene, phenol,1,4-dioxane)at a higher frequency is faster than at a lower frequency.2,3,5,11)However,there was no agreement on the optimum frequency for the degradation of pollutants. While there was agreement with previous research2,11)on the tendency of the frequency e?ect,the experimental con-ditions(size of transducer,input power,power density)in di?erent frequencies were not the same as those in previous studies.2–4,11)A comparison of the results at di?erent frequencies is only valid when the conditions of the experiments are the same.2)Therefore,the frequency e?ect was investigated under the same experimental conditions. In this study,the same experimental conditions(power,size of transducer)were applied at di?erent frequencies.

The kinetic constants of phenol are shown in Table I.In the case of1MHz,kinetic constants of0.0243minà1were almost20times higher than other frequencies(35,110, and300kHz).At300kHz,the kinetic constant was slightly higher than at35and110kHz.Between the kinetic constants of35and110kHz,there was almost no change.

For the case of TOC,the concentration is shown Fig.2(b). The concentrations of TOC were nearly the same for sonication times.There is no di?erence with frequencies. Previous research has shown the same tendency.Inoue et al.16)investigated the sonication of bisphenol A,where after10h,the15.4%of TOC is only degradable.Therefore, the addition of catalysts(FeSO4,H2O2,etc.)was needed for the TOC degradation.

Hydrogen peroxide was produced from the dissipation of water[eqs.(4)and(5)].2)The concentration of H2O2was measured for30min of sonication time(Fig.3).

2HOá!H2O2e4T

2HOOá!H2O2tO2e5T

Time (min)

0306090120 P

(

)

0.0

0.2

0.4

0.6

0.8

1.0

(a)

Time (min)

0306090120 T

(

)

0.0

0.2

0.4

0.6

0.8

1.0

(b)

Fig.2.Effect of ultrasonic frequency on phenol and TOC degrada-tion:(a)phenol;(b)TOC.

Table I.Kinetic constants for phenol with different frequencies.

Frequency

(kHz)

(minà1)

350.00140.835

110

0.00150.961

3000.00190.959

1,0000.02430.894 Fig.1.(Color online)Schematic of sonochemical reactor.

The amounts of H 2O 2were in the order of 1MHz >110kHz >300kHz >35kHz.The degradation rate of phenol was in the order of 1MHz >300kHz >110kHz >35kHz,which did not concur with the order of formation of H 2O 2.The relationship between the degradation rate of contaminants and the formation rate of hydrogen peroxide was not clear in previous research.5)Therefore,a number of studies were needed that dealt with the relationship of sonochemical dosimetry and degradation of pollutants.

Many researchers have investigated the frequency e?ect on sonochemical reaction,especially of non-volatile com-pounds.3,5–8,11)However,these investigations only measured the concentration of compounds 5,6,8,11)and intermediates.In this study,we measured phenol and TOC concentration.At 1MHz,phenol was nearly 97%degraded within 2h.However,the TOC concentration was almost the same after 2h sonication.This means that some organic intermediates were produced and they could not be degraded into inorganic compounds.The hydrogen peroxide was therefore placed in the phenol solution.Among the four frequencies of 35,110,300kHz,and 1MHz,the e?ects of the three frequencies of 35,110,and 300kHz on the degradation of phenol solution were almost the same.Therefore,the e?ect of hydrogen peroxide was only examined at the two frequencies of 35kHz and 1MHz.

With the individual addition of hydrogen peroxide two times in the phenol solution (initial,15min),the concen-tration of phenol decreased above 90%within 30min [Fig.4(a)].In the case where only ultrasound was applied to the phenol solution,the phenol degradation reached more than 95%within 2h [1MHz,Fig.2(a)].However,when hydrogen peroxide was added to the phenol solution,phenol was almost degraded within 30min.Therefore,the addition of hydrogen peroxide can enhance the degradation of phenol.These results agreed with those obtained in previous studies.6,7)At a high frequency (1MHz),the degradation rate was slightly higher than at a low frequency (35kHz).However,the di?erence of phenol degradation at the two frequencies when hydrogen peroxide and sonication were combined was lower than only sonication.

In the case of TOC,the concentration decreased with the addition of H 2O 2.When H 2O 2was directly added to the phenol solution,the TOC concentration directly decreased

[Fig.4(b)].Within 30min,50%of the TOC was degraded.Previous researchers 6,7,14)have used other additives such as hydrogen peroxide and Fe 2SO 4in phenol solutions.The addition of additives can enhance the degradation of phenols concentration.Therefore,the addition of H 2O 2,or another catalyst such as Fe 2SO 4and a combination of advanced oxidation processes (AOPs)are required for the degradation of TOC.

Figure 5shows the results for the case where hydrogen peroxide concentration was directly degraded immediately after the hydrogen peroxide was put into the phenol solution.These results were the same for 35and 1,000kHz.4.

Conclusions

The e?ect of frequency and hydrogen peroxide on phenol solution was investigated.The following results were found:1)A high frequency can create a faster degradation rate of phenol than that of a low frequency.This is because the acoustic period of high frequency is shorter than that of low frequency,where most of the formed radicals escape from the aqueous solution.Therefore,the kinetic constant of phenol solution at 1MHz was higher than at low frequencies (35,110,and 300kHz).This result of frequency e?ect agreed with previous results.

2)In the case of TOC concentration,there is no di?erence in the sonication times (2h).Although the phenol

Frequency

35 kHz

110 kHz

300 kHz

1 MHz

H 2O 2 c o n c . (m M )

0.000

0.0020.0040.0060.0080.010

0.012Fig.3.Hydrogen peroxide formation in water with different frequen-cies.

Time (min)

P h e n o l c o n c . (C /C 0)

(a)

Time (min)

T O C (C /C 0

)

0.0

0.2

0.4

0.6

0.8

1.0

(b)

Fig.4.Effect of hydrogen peroxide on phenol and TOC degrada-tion:(a)phenol;(b)TOC.

concentration decreased 90%within 120min at 1MHz,some type of catalyst was needed to degrade the TOC.3)The tendencies di?ered between the degradation rate of phenol and the formation rate of hydrogen peroxide.Further research of this relationship is needed.

4)The addition of hydrogen peroxide in phenol solution can enhance the degradation of phenol and TOC concentration.Within 30min,the phenol concentration was decreased completely and TOC concentration was decreased almost 50%.Therefore,to degrade the TOC,a number of additives needed to be included.

Acknowledgement

This subject is supported by Ministry of Environment,Republic of Korea as ‘‘The Eco-technopia 21project’’(No.061-081-042).

1)M.Lim,Y.Son,J.Yang,and J.Khim:Jpn.J.Appl.Phys.47(2008)

4123.

2)P.Kruus,R. C.Burk,M.H.Entezari,and R.Otson:Ultrason.

Sonochem.4(1997)229.

3) C.Pe

′trier and A.Francony:Ultrason.Sonochem.4(1997)295.4)H.Hung and M.R.Ho?mann:J.Phys.Chem.A 103(1999)2734.5)M.A.Beckett and I.Hua:J.Phys.Chem.A 105(2001)3796.

6)J.Liang,S.Komarov,N.Hayashi,and E.Kasai:Ultrason.Sonochem.

14(2007)201.

7)Y.Jiang,C.Petrier,and T.D.waite:Ultrason.Sonochem.13(2006)

415.

8)R.Kidak and N.H.Ince:J.Hazardous Mater.137(2006)1453.

9)J.Lin,C.Chang,and J.Wu:Water Sci.Technol.33(1996)No.6,75.10) C.Wu,X.Liu,D.We,J.Fan,and L.Wang:Water Res.35(2001)

3927.

11)M.H.Entezari,C.Pe

′trier,and P.Devidal:Ultrason.Sonochem.10(2003)103.

12)M.Kubo,K.Matsuoka,A.Takahashi,N.Shibasaki-Kitakawa,and T.

Yonemoto:Ultrason.Sonochem.12(2005)263.

13)R.A.Torres,J.I.Nieto,https://www.360docs.net/doc/ae11259001.html,bet,C.Pe

′trier,and C.Pulgarin:Appl.Catal.B 80(2008)168.

14)USEPA,National Recommended Water Quality Criteria (2006).

15) E.Na?rechoux,S.Chanoux, C.Pe

′trier,and J.Suptil:Ultrason.Sonochem.7(2000)255.

16)M.Inoue,Y.Masuda,F.Okada,A.Sakurai,I.Takahashi,and M.

Sakakibara:Water Res.42(2008)1379.

Time (min)

H 2O 2 c o n c . (m M )

Fig.5.Change of hydrogen peroxide concentration with sonication

time.