当前位置：文档库 › Photocatalytic oxidation of dibenzothiophenes in acetonitrile using TiO2

Photocatalytic oxidation of dibenzothiophenes in acetonitrile using TiO2

Journal of Photochemistry and Photobiology A:Chemistry149(2002)

183–189

Photocatalytic oxidation of dibenzothiophenes in acetonitrile using TiO2: effect of hydrogen peroxide and ultrasound irradiation

Sadao Matsuzawa a,?,Jun Tanaka b,Shinya Sato a,Takashi Ibusuki a

a National Institute of Advanced Industrial Science and Technology(AIST),AIST West,16-1Onogawa,Tsukuba,Ibaraki305-8569,Japan

b Saitama Institute of Technology,1690Fusaiji,Okabe-machi,Osato-gun,Saitama369-0293,Japan

Received6August2001;received in revised form13December2001;accepted17December2001

Abstract

Photocatalytic oxidation of dibenzothiophene(DBT)and4,6-dimethyldibenzothiophene(4,6DMDBT)in acetonitrile using titanium dioxide(TiO2)was studied.Results obtained here can be used as the reference for evaluating reactions in hydrocarbons,which aims at the development of an oxidative desulfurization process for oils.A200W Hg–Xe lamp(>290nm,19mW/cm2)was used as a light source, and the catalytic performances of four commercially available TiO2photocatalysts(PC-1,PC-2,PC-3and P25)were compared.

DBT was more stable than4,6DMDBT under light and in the presence of photocatalyst in acetonitrile.Of the photocatalysts used,P25 showed the highest rate of photooxidation.However with P25,the decrease in initial concentration of DBT or4,6DMDBT was less than 40%after10h of irradiation.To accelerate the reaction,the effect of addition of hydrogen peroxide(H2O2)and/or ultrasound irradiation on the TiO2-containing system was studied.Although the addition of hydrogen peroxide(3%)and/or ultrasound irradiation more than doubled the rate of photooxidation,this ef?ciency was obtainable with H2O2alone.Tentatively identi?ed reaction products from DBT and4,6DMDBT included the5-oxide(sulfoxide)and the5,5-dioxide(sulfone)of each substrate.Oxidation of the methyl group mainly occurred when4,6DMDBT was reacted using only TiO2.This result led to a?nding that the acceleration of oxidation for the methyl group occurs in non-polar hydrocarbons.?2002Elsevier Science B.V.All rights reserved.

Keywords:Photooxidation;Desulfurization;Photocatalyst;TiO2;Dibenzothiophene;4,6-Dimethyldibenzothiophene

1.Introduction

Catalytic hydrodesulfurization is commonly used to de-crease the sulfur content of oil.Desulfurization is generally conducted at high pressure(>50kg/cm3)and high temper-ature(>250?C)by reacting hydrogen gas with sulfur com-pounds in the presence of a catalyst.Hydrogen sul?de(H2S) is mainly produced.Among the various sulfur compounds in oil,dibenzothiophenes(DBTs)are the most resistant to hydrogenation and require the use of a modi?ed catalyst and more severe reaction conditions[1].

Sulfur compounds in petroleum products can cause https://www.wendangku.net/doc/a311191547.html,bustion of heavy oils containing more than0.1% of sulfur compounds emits sulfur dioxide(SO2),which causes asthma in humans.This is a major problem in indus-trial cities of the developing countries.Recently,attention has been focused on decreasing the sulfur content in gas oil for diesel engines.Catalyst ef?ciency in removing NO x and particulate matter(PM)from diesel exhaust is adversely affected by the presence of sulfur compounds in gas oil,?Corresponding author.Tel.:+81-298-61-8262;fax:+81-298-61-8258. E-mail address:s-matsuzawa@aist.go.jp(S.Matsuzawa).and it is important to decrease the sulfur content in gas oil below50ppm(deep desulfurization).However,deep desul-furization requires the use of a modi?ed catalyst and more severe reaction conditions to enable stable DBTs to react with hydrogen,making deep desulfurization an expensive process.

To save energy and reduce costs,an alternative desulfu-rization process needs to be developed.For this purpose, some oxidative desulfurization processes which include oxidation of DBTs with oxidants followed by the removal of products have been investigated[2].As one of the pro-cesses,photochemical reaction with sunlight as an energy source is also promising.Although DBT is stable against direct photolysis[3,4],slow photooxidation occurs in nat-ural and simulated marine environments[3–6].Patel et al.

[5]observed formation of compounds with sulfoxide moi-eties from DBT and its C1-,C2-,and C3-alkyl homologs. Later,Payne and Phillips[4]and Berthou and Vignier[6] reported that DBT sulfoxide and DBT sulfone are formed by photolysis of DBT.Although Mill et al.[3]detected?ve products by HPLC,attempts to characterize these products by GC–MS were unsuccessful.Andersson and cowork-ers[7–9]later reported details about the photochemical

184S.Matsuzawa et al./Journal of Photochemistry and Photobiology A:Chemistry149(2002)183–189

degradation and degradation products from DBTs.Ac-cording to Berthou and Vignier[6]and Andersson[7], alkylated DBTs are more stable than DBT on the surface of water.

Several research groups have recently demonstrated photooxidative desulfurization of oil.Hirai et al.[10–16] achieved deep desulfurization of gas oils by photooxidizing DBTs.They developed several processes,including pho-tooxidation in solution followed by liquid–liquid extraction of the oxidation products.Meille et al.[17]and Shiraishi et al.[18,19]used photoinduced charge-transfer reactions (oxidation)for desulfurization.Although the desulfuriza-tion rate for gas oil with these methods was over50%, irradiation time was generally long(>5h).Using a photo-catalyst may reduce the time for the treatment.However for photocatalytic oxidation,only one report by Abdel-Wahab and Gaber[20]was present for DBT and no report was found for4,6-dimethyldibenzothiophene(4,6DMDBT). Abdel-Wahab and Gaber[20]used anatase-type TiO2 produced by Aldrich and obtained information about the conversion rate and products in acetonitrile.

Here,we report results on photooxidation of DBT and 4,6DMDBT in acetonitrile using another commercially available titanium dioxide(TiO2)including well-known P25.The effect of addition of hydrogen peroxide(H2O2) and/or ultrasound irradiation on the TiO2-containing sys-tem is also reported.We chose acetonitrile as the sol-vent for the reaction since this solvent is relatively stable and gives results usable for comparison.Furthermore, addition of H2O2and ultrasound irradiation was exam-ined in order to increase the rate of oxidation reaction. The results obtained here can be used as the reference for evaluating reactions in hydrocarbons,which aims at the development of the photooxidative desulfurization process.

2.Experimental section

2.1.Chemicals

DBT and4,6DMDBT were purchased from Aldrich (Wisconsin,USA)and ACROS(Belgium),respectively. HPLC-grade acetonitrile(Aldrich)was used as a solvent for the reaction.DBT5,5-dioxide(sulfone)(Aldrich)was used for identi?cation of oxidation products.

Four kinds of TiO2powder were used as photocatalysts: P25(Aerosil,Japan)and PC-1,PC-2and PC-3(Ishihara Sangyo,Japan).The authors altered the names of the latter three products.The characteristics of the TiO2photocata-lysts are given in Table1.Except for PC-3(rutile-type),the main crystalline type of TiO2is anatase.For PC-1and PC-2, high ef?ciencies for photodecomposition of volatile gases such as acetaldehyde and ammonia have been reported[21]. H2O2solution(30%,Wako Pure Chemicals Industries)was used as an oxidation agent.Table1

Characteristics of titanium dioxide(TiO2)used in this study Photocatalyst Particle

size(nm)

Speci?c surface

area(m2/g)

Main crystalline

type

P252150Anatase

PC-17300Anatase

PC-27250Anatase

PC-3–30Rutile

2.2.Apparatus

Sample solutions were photoirradiated in a glass reactor consisting of two parts:a vessel with a volume of200ml and a quartz cap with an inlet tube for introducing air and an outlet tube for releasing air and gaseous products.A mag-netic stirrer(Pasolina TR-100)under the reactor was used to stir the solution except when ultrasound irradiation was applied to accelerate photooxidation.For ultrasound irradia-tion,a soni?er(Bransonic12,45kHz,50W)with a constant volume of water was used instead of the magnetic stirrer. Keeping a constant water depth was necessary to produce the same strength of ultrasound for each experiment.Arti-?cial air(O2:21%,N2:78%)was introduced from a gas cylinder at a?ow rate of10ml/min through a needle valve to dissolve O2in the acetonitrile solution.A200W Hg–Xe lamp(Sanei Denki Seisaku-sho,19mW/cm2)was used as the light source for photoirradiation.Light from this lamp was directed into the glass reactor through a glass?ber cable and the quartz cap.A?lter was placed before the quartz cap to remove shorter wavelengths of light(<290nm).During photoirradiation,the glass reactor was wrapped with alu-minum foil to shield against other laboratory light sources.

2.3.Photoirradiation and analysis

Photooxidation experiments were carried out as follows. An acetonitrile solution of DBT or4,6DMDBT(100ml, 5×10?4M)was placed in a glass vessel and0.2g of TiO2 was added to the solution.The solution was photoirradiated for0–10h with continuous bubbling of air and magnetic stirring(or ultrasound irradiation).After1,2,4,6,8and 10h of photoirradiation,samples(2ml)were collected from the glass vessel and analyzed to determine substrate con-centration and reaction products.Prior to analysis,samples were centrifuged to remove?ne TiO2particles.An HPLC apparatus equipped with a UV–Vis photodiode array de-tector(Shimadzu SPD-M10A)and a?uorescence detector (JASCO FP-929A)was mainly used for analysis.Substrate and reaction products were separated on an Inertsil ODS-2 column(GL Sciences,4.6mm i.d.×250mm)using ace-tonitrile/water(76/24)eluent.Capillary gas chromatographs with a sulfur-selective detector(Sievers Model355)and an EI-MS detector(Hewlett-Packard HP5971)were also used to identify reaction products.An HP-5MS column(0.32mm i.d.×30m,0.25?m?lm thickness,Hewlett-Packard)and

S.Matsuzawa et al./Journal of Photochemistry and Photobiology A:Chemistry 149(2002)183–189185

HP-50column (0.25mm i.d.×30m,0.25?m ?lm thick-ness,Hewlett-Packard)were used.The temperature of the injection port of the gas chromatograph was kept rela-tively low (200?C)since DBT oxides decompose at 250?C [5].Absorption spectra of the products observed with the SPD-M10A HPLC detector were also used for identi?ca-tion.Thermal analysis (TGA and DTA)and infrared spectral analysis of the TiO 2powders were respectively carried out with a Shimadzu DTG-50thermal analyzer and a Nicolet Magna 560FT-IR spectrometer equipped with a diamond ATR accessory (DuraScope,SensIR Technologies).

The rate constants for the apparent consumption of DBT (or 4,6DMDBT)were obtained from the relation:

?ln C t

C 0 =k p t (1)

where C 0and C t are the concentrations of substrate at time zero and time t (s),and k p the ?rst-order rate constant (s ?1).Half-lives (t 1/2(s))were calculated using Eq.(2),which was derived from Eq.(1)by replacing C t with C 0/2t 1/2=

0.693k p

(2)

Values obtained in seconds were converted to hours.3.Results and discussion

3.1.Effect of the presence of photocatalyst (TiO 2)on photooxidation of DBT and 4,6DMDBT in acetonitrile The effect of the presence of TiO 2on the photooxida-tion of DBT and 4,6DMDBT in acetonitrile was

assessed

Fig.1.Photooxidation of DBT and 4,6DMDBT in acetonitrile under various conditions:(–?–)without photocatalyst;(–?–)with photocatalyst (TiO 2:P25);(– –)with photocatalyst and ultrasound irradiation;(–?–)with H 2O 2and photocatalyst;(–?–)with H 2O 2,photocatalyst and ultrasound irradiation;(–?–)with H 2O 2alone.

from plots of ?ln(C t /C 0)vs.t obtained with and without photocatalyst (TiO 2:P25)(Fig.1).In the absence of pho-tocatalyst (white square and a solid line),DBT (Fig.1,left panel)did not react at all even after 10h of photoirradiation.We con?rmed that the decrease in DBT concentration was quite small up to 50h.However,when TiO 2was present in the solution (black triangle and a solid line),photooxidation of DBT occurred more rapidly.After 10h of irradiation,?ln(C t /C 0)was 0.356,which means C t /C 0was about 0.7.Thus,after 10h of irradiation,the decrease in DBT con-centration was about 30%.4,6DMDBT (Fig.1,right panel)was somewhat more reactive than DBT.The concentration decreased slightly in the absence of photocatalyst (white square and a solid line).A value of 0.94was obtained for C t /C 0after 10h of photoirradiation,which indicates that the concentration decreased by 6%.When TiO 2was present (black triangle and a solid line),4,6DMDBT reacted more rapidly,as in the DBT case.After 10h of photoirradiation,?ln(C t /C 0)was 0.462,which means that the 4,6DMDBT concentration decreased by about 37%.The rate con-stants (k p )and half-lives (t 1/2)for reactions of DBT and 4,6DMDBT with and without photocatalyst (TiO 2:P25)are listed in Table 2.With photocatalysis,4,6DMDBT had slightly larger k p and slightly shorter t 1/2values than did DBT.In case of DBTs,the oxidation of sulfur occurs by the electrophilic addition reaction of oxygen atoms [2].There-fore the higher is the electron density of a sulfur atom in a sulfur-containing compound,the higher is the reactivity of oxidation.Higher reactivity for 4,6DMDBT may be at-tributed to higher electron density of a sulfur atom donated by two methyl groups.

Also listed in Table 2are the rate constants and half-lives obtained for photooxidation of 4,6DMDBT with three other

186S.Matsuzawa et al./Journal of Photochemistry and Photobiology A:Chemistry 149(2002)183–189

Table 2

Rate constants and half-lives for photooxidation of DBT and 4,6DMDBT in acetonitrile Substrate Photocatalyst Rate constant (s ?1)Half-life (h)DBT None –a

–a DBT

P259.74×10?619.84,6DMDBT None 1.83×10?61054,6DMDBT P251.21×10?515.94,6DMDBT PC-1

7.31×10?72634,6DMDBT PC-1(calcinated)2.67×10?672.14,6DMDBT PC-21.38×10?61394,6DMDBT

PC-3

3.18×10?6

60.5

These values could not be calculated since the concentration of substrate did not change.

TiO 2photocatalysts (PC-1,PC-2and PC-3).In these cases,the concentration of 4,6DMDBT decreased very slowly compared with the P25case and the rate constants were on the order of 10?6or 10?7.The activity of anatase-type TiO 2(PC-1and PC-2)was lower than the activity of rutile-type TiO 2(PC-3),contrary to prediction.Thermal analysis and ATR infrared spectral measurements revealed that PC-1and PC-2contained more adsorbed water than P25and PC-3.In thermal analysis,PC-1and PC-2showed a strong en-dothermic peak in the DTA curve in the range 70–80?C and a decrease in TG %above 80?C.The difference in water content is more clearly indicated in the re?ective infrared absorption spectra measured using ATR for the four kinds of TiO 2(Fig.2).The absorbance in the 3100–3600cm ?1range,where the O–H stretch of water molecules appears is weak for P25and PC-3,whereas a broad band with

Fig.2.Re?ective infrared absorption spectra of TiO 2used in this study.

stronger absorption appears below 3400cm ?1for PC-1and PC-2.This difference in infrared absorption may be related to the method used to synthesize the TiO 2(wet or dry method).Although detailed information is not available,PC-1and PC-2are synthesized in solution and P25and PC-3are synthesized at high temperature.We examined the effect of heat treatment (350?C,15h)on the activity of PC-1and found that such treatment resulted in the increase in the rate of photooxidation (see results for PC-1(calcinated)in Table 2).This means that the activity of TiO 2is partly con-trolled by water content.Active sites on TiO 2surface may be covered with water molecules or water–acetonitrile clus-ters [22,23].As apparent from Table 2,reaction rate after heat treatment is still low compared with that of P25.We therefore suppose that other factors (e.g.the surface area and the purity of the TiO 2crystallite)affect the activity.More detailed studies are needed to explain the difference in photooxidation activity for TiO 2.

As described above with the most effective photocatalyst (P25),the decrease in concentration of DBT and 4,6DMDBT after 10h of photoirradiation was only about 30and 37%,respectively.Practical applications of photocatalytic oxida-tion require improvement in reaction ef?ciency.Thus,we studied the effect of addition of H 2O 2and ultrasound irra-diation on the P25-containing system.

3.2.Effect of addition of hydrogen peroxide (H 2O 2)to the TiO 2-containing system

We studied the effect of adding H 2O 2to the TiO 2(P25)-containing system for the photooxidation of DBT and

S.Matsuzawa et al./Journal of Photochemistry and Photobiology A:Chemistry149(2002)183–189187 4,6DMDBT.The?ln(C t/C0)vs.t relationships obtained

with photocatalyst(TiO2:P25)and H2O2are also shown

in Fig.1with black circles and solid lines.Since the rate

of reaction decreased when more than3%of H2O2was

added,the concentration of H2O2was kept at3%(10vol.%

of a commercial30%H2O2solution in a sample solution).

We think that the decrease in the rate of reaction is caused

by an increase in the water content in the acetonitrile so-

lution.We previously con?rmed that the solubility of oxy-

gen in acetonitrile solution decreases with increasing water

content[24].A decrease in oxygen content results in a low

rate of reaction.The relations,in Fig.1,for P25–H2O2sys-

tems show that the rates of reaction for DBT(left panel)and

4,6DMDBT(right panel)increase with the addition of H2O2.

When H2O2was added,the value of?ln(C t/C0)became

larger than0.5(40%reacted)after6h of photoirradiation

for DBT and after2h of photoirradiation for4,6DMDBT.

However,as can be seen from Fig.1,the rates of reactions

obtained when both P25and H2O2were used are slower

than when H2O2was used alone(black square and a solid

line).Depression of the reaction may occur when the two

reaction accelerators are combined.Nakano[25]obtained a

similar result in case of the study on decolorization of water.

He reported that depression of the activity for TiO2occurred

when H2O2was added to anatase-type TiO2.Poisoning of

anatase TiO2surface by H2O2[26]may cause such an ad-

verse effect.The rate constants and half-lives obtained for

the P25–H2O2systems are listed in Table3.

When H2O2is added,OH radicals may not be ef?ciently

formed from H2O2in the solution since UV absorption by

H2O2at wavelengths above290nm is very weak.The high

ef?ciency with H2O2alone(Fig.1)may be due to direct

oxidation.We con?rmed that DBT in3%H2O2–acetonitrile

solution gives0.54for?ln(C t/C0)(42%reacted)under stir-

ring for8h without light.Therefore,the increase in the

rate of reaction for the P25–H2O2system may be attributed

to direct oxidation by H2O2.In this case,the ef?ciency

for direct oxidation by H2O2is depressed by the presence

of TiO2.

Table3

Rate constants and half-lives for photooxidation of DBT and4,6DMDBT

in acetonitrile with the addition of hydrogen peroxide and/or ultrasound

irradiation

Substrate Additive a Rate constant

(s?1)Half-life (h)

DBT P25–H2O23.1×10?5 5.6

DBT H2O24.4×10?5 4.3

DBT P25–UI2.9×10?5 6.7

P25–H2O2–UI5.3×10?5 3.6

4,6DMDBT P25–H2O25.7×10?5 3.3

4,6DMDBT H2O21.0×10?4 2.2

4,6DMDBT P25–UI4.1×10?5 4.1

P25–H2O2–UI9.7×10?5 2.0

a Abbreviations:P25,TiO2:P25;H2O2,hydrogen peroxide;UI,ul-trasound irradiation.3.3.Effect of ultrasound irradiation on the

TiO2-containing system

We also investigated the effect of ultrasound irradiation on the photooxidation of DBT and4,6DMDBT for the TiO2-containing system.In Fig.1,results for the system containing only TiO2(P25)are plotted with white triangles and a dotted line and those for the system containing both TiO2(P25)and H2O2are plotted with white circles and a dotted line.For both systems,the rates of photooxidation of DBT and4,6DMDBT increased with ultrasound irradia-tion.Rate constants and half-lives are listed in Table3.For both DBT and4,6DMDBT with ultrasound irradiation,the rate constant for the P25system increased by a factor of3 and that for the P25–H2O2system increased by a factor of https://www.wendangku.net/doc/a311191547.html,ing4,6DMDBT as the substrate,we con?rmed that no reaction occurred with ultrasound irradiation alone,i.e. in the absence of TiO2or light.In other words,the oxida-tion reaction is controlled not by ultrasound irradiation,but rather by a photocatalytic effect.Ultrasound does however accelerate the photocatalytic reaction.

For the effect of ultrasound irradiation,we expected the prevention of agglomeration for TiO2?ne particles and the increase in the surface area usable for photooxidation.How-ever,Kado et al.[27]recently reported,for their work on photocatalytic oxidation of aliphatic alcohols,that the parti-cle size of the TiO2powder decreases for the initial period (<1min)and then increases(the surface area decreases)by ultrasound irradiation.Therefore the cause of acceleration was not attributed to an increase in the surface area.Kado et al.[27,28]suggested that ultrasound activate the surface of TiO2and this phenomenon and enhancement of mass transfer accelerate the reactivity.We think that oxidation of DBTs were similarly accelerated by these effects.In addi-tion,Kado et al.[27]reported that reaction condition such as ultrasound power,stirring speed,amount of TiO2,concen-tration of substrate and pretreatment of TiO2powder affect the oxidation reaction.

As described above,photooxidation in the TiO2and TiO2–H2O2systems can be accelerated with ultrasound irradiation.However,the ef?ciencies achieved are still low or similar compared with that obtained with H2O2alone (see Fig.1and Table3).

3.4.Products formed by photocatalytic oxidation

of DBT and4,6DMDBT

Fig.3shows structures of tentatively identi?ed reaction products of DBT and4,6DMDBT.For DBT,the main prod-ucts identi?ed by GC–MS and UV absorption spectroscopy were DBT5-oxide(DBT sulfoxide)and DBT5,5-dioxide (DBT sulfone)regardless of whether the oxidizing agent was TiO2or H2O2.The formation of these products is consis-tent with the results obtained by Abdel-Wahab and Gaber [20].The mass spectrum of DBT5-oxide contains fragment ion peaks at m/z200,184,171,152and139,and that of

188S.Matsuzawa et al./Journal of Photochemistry and Photobiology A:Chemistry 149(2002)

183–189

Fig.3.Reaction products of DBT and 4,6DMDBT.

DBT 5,5-dioxide contains those at m /z 216,187,168,160,139and 115.When the system contained H 2O 2alone,we also detected smaller amounts of two co-products that eluted from the HPLC column more slowly than the two main products.In addition,the results showed that ultrasound ir-radiation accelerated the oxidation of DBT 5-oxide to DBT 5,5-dioxide in the P25–H 2O 2system.Speci?cally,a larger amount of DBT 5,5-dioxide was formed under ultrasound irradiation than when magnetic stirring was employed.This is the effect of activation of TiO 2surface and enhancement of mass transfer by ultrasound irradiation [27].

In contrast,4,6DMDBT yielded a different main prod-uct depending on the oxidation agent (TiO 2or H 2O 2).When the system contained only P25,a compound that shows fragment ion peaks at m /z 226,197,165and 152was mainly formed.This compound was assumed to be 6-methyldibenzothiophene-4-carbaldehyde,which is formed by oxidation of the methyl group.In addition,mi-nor amounts of other products were detected by HPLC and GC–https://www.wendangku.net/doc/a311191547.html,pounds with parent mass fragment (M +)at 228,244and 279were formed when magnetic stir-ring was employed,while compounds with M +at 228,230and 244were detected in the case of ultrasound https://www.wendangku.net/doc/a311191547.html,rger amounts of M +228and M +224were formed under ultrasound irradiation.The molecules with M +228and M +244are probably 4,6DMDBT 5-oxide and 4,6DMDBT 5,5-dioxide,respectively.The UV ab-sorption spectra for these compounds resembled those of DBT 5-oxide and DBT 5,5-dioxide and were red-shifted about 6nm compared with spectra of oxygenated DBTs.

The structures of the molecules with M +230and M +279are not clear at present.We recently found that oxidation of the methyl group,which occurs as a main reaction in the presence of only P25,is accelerated by more than 10times in non-polar hydrocarbons [29].The rate constant of 1.0×10?4s ?1was obtained in a 2:1:2mixture of n -heptane,2,2,4-trimethylpentane (isooctane)and methylcyclohexane.Details will be published later.

When H 2O 2was added to the solution of 4,6DMDBT,no M +226product was formed.The M +228product was mainly formed in the absence of TiO 2.Adding TiO 2to the H 2O 2system increased the amount of M +244product obtained.For the TiO 2–H 2O 2system,more M +244prod-uct was obtained under ultrasound irradiation than when magnetic stirring was employed.Thus ultrasound irradiation increases the rate of photooxidation.4.Conclusion

We studied the photocatalytic oxidations of DBT and 4,6DMDBT in acetonitrile using TiO 2.We found that DBT is more stable than 4,6DMDBT and that the rate of photoox-idation differs depending on the kind of TiO 2.Although P25showed the highest photooxidation rate,the conversion of DBTs (less than 40%after 10h of photoirradiation)is inad-equate for application (e.g.desulfurization of oils).Adding hydrogen peroxide (3%)to the TiO 2(P25)-containing sys-tem or irradiating the system with ultrasound accelerated the photooxidation.However,these methods were not much

S.Matsuzawa et al./Journal of Photochemistry and Photobiology A:Chemistry149(2002)183–189189

superior to the photooxidation using H2O2alone in the solution.Products from DBT and4,6DMDBT were ten-tatively identi?ed.It seems that oxidation of the methyl group mainly occurred when only TiO2was used and that addition of oxygen to the sulfur atom in the ring occurred when H2O2was used.

In this paper,we did not describe how oil components affect the photooxidation of DBT and4,6DMDBT.Hirai et al.[10]previously reported that photosensitized oxidation is depressed in the presence of naphthalene.In contrast,we recently found that non-polar hydrocarbons accelerate the oxidation of methyl group-substituted DBTs[29].Further studies on avoiding negative effects and increasing the ef?-ciency of the photocatalytic oxidation are in progress in our laboratory and will be reported in the future. References

[1]S.Nagamatsu,J.Yoshida,Petrotech(Tokyo)23(2000)110–115.

[2]S.Otsuki,T.Nonaka,W.Qian, A.Ishihara,T.Kabe,Sekiyu

Gakkaishi44(2001)18–24.

[3]https://www.wendangku.net/doc/a311191547.html,l,W.R.Mabey,https://www.wendangku.net/doc/a311191547.html,n,A.Baraze,Chemosphere10(1981)

1281–1290.

[4]J.R.Payne,C.R.Phillips,Environ.Sci.Technol.19(1985)569–579.

[5]J.R.Patel,E.B.Overton,https://www.wendangku.net/doc/a311191547.html,seter,Chemosphere8(1979)557–

561.

[6]F.Berthou,V.Vignier,Int.J.Environ.Anal.Chem.27(1986)81–96.

[7]J.T.Andersson,Chemosphere27(1993)2097–2102.

[8]S.Bobinger,F.Traulsen,J.T.Andersson,https://www.wendangku.net/doc/a311191547.html,p.

21(2000)253–264.

[9]F.Traulsen,J.T.Andersson,M.G.Ehrhardt,Anal.Chim.Acta392

(1999)19–28.[10]T.Hirai,K.Ogawa,I.Komasawa,Ind.Eng.Chem.Res.35(1996)

586–589.

[11]T.Hirai,Y.Shiraishi,K.Ogawa,I.Komasawa,Ind.Eng.Chem.

Res.36(1997)530–533.

[12]Y.Shiraishi,T.Hirai,I.Komasawa,J.Chem.Eng.Jpn.32(1999)

158–161.

[13]Y.Shiraishi,T.Hirai,I.Komasawa,Solvent Extr.Res.Dev.Jpn.6

(1999)137–143.

[14]Y.Shiraishi,T.Hirai,I.Komasawa,Ind.Eng.Chem.Res.37(1998)

203–211.

[15]Y.Shiraishi,H.Hara,T.Hirai,I.Komasawa,Ind.Eng.Chem.Res.

38(1999)1589–1595.

[16]Y.Shiraishi,T.Hirai,I.Komasawa,Ind.Eng.Chem.Res.38(1999)

3300–3309.

[17]V.Meille,E.Schulz,M.Vrinat,M.Lemaire,https://www.wendangku.net/doc/a311191547.html,mun.(1998)

305–306.

[18]Y.Shiraishi,Y.Taki,T.Hirai,I.Komasawa,https://www.wendangku.net/doc/a311191547.html,mun.(1998)

2601–2602.

[19]Y.Shiraishi,Y.Taki,T.Hirai,I.Komasawa,Ind.Eng.Chem.Res.

38(1999)3310–3318.

[20]A.-M.A.Abdel-Wahab,A.E.-A.M.Gaber,J.Photochem.Photobiol.

A114(1998)213–218.

[21]Data in Catalogues,Ishihara Sangyo,Japan.

[22]N.N.Lichtin,M.Avudaithai,Environ.Sci.Technol.30(1996)2014–

2020.

[23]A.Wakisaka,Y.Shimizu,N.Nishi,K.Tokumaru,S.J.Sakuragi,J.

Chem.Soc.,Faraday Trans.88(1992)1129–1135.

[24]L.Moeini-Nombel,S.Matsuzawa,J.Photochem.Photobiol.A119

(1998)15–23.

[25]H.Nakano,Proceedings of the35th Annual Meeting of the Japan

Society on Water Environment,2001,p.544.

[26]A.P.Rivera,K.Tanaka,T.Hisanaga,Appl.Catal.B3(1993)37–44.

[27]Y.Kado,M.Atobe,T.Nonaka,Ultrason.Sonochem.8(2001)69–74.

[28]Y.Kado,M.Atobe,T.Nonaka,Denki Kagaku66(1998)760–762.

[29]S.Matsuzawa,S.Sato,K.Takeuchi,T.Ibusuki,J.Chem.Soc.,

https://www.wendangku.net/doc/a311191547.html,mun.,submitted for publication.