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tetra- and octa-CDDs and their CDFs at 254 nm were in
the range of 2.3±88 min in n-hexane solution,showing
the higher rate constant of 2,3,7,8-TCDF .2:7 Â
10À2 minÀ1; Muto and Takizawa,1991). Dulln et al.
.1986) photolized 2,3,7,8-TCDD in water/acetonitrile
.9:1) solution,and reported that its conversion rates
were 62% at 313 nm for 24 h and 49% at sunlight for
26.3 h. On the other hand,Muto et al. .1991) presented
that for the heterogeneous photolysis of PCDDs in
suspension solution of ¯y ash with water and/or water/
acetonitrile .2:3) at 254 nm,the pseudo-®rst order rate
constants of all PCDD congeners were in the order of
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0.75±1:7 Â 10À3 minÀ1
.
For the TiO2 thin ®lm photocataysis of PCDD/DFs
formed with 2,4,5-TCP by the batch-recycle system, the
photodegradation rate constants of total PCDDs,and
PCDFs and PCDD/DFs and their half-lives were in the
order of 4.8±6:1 Â 10À3 minÀ1 and of 1.9±2.4 h,as-
suming the pseudo ®rst-order reactions for low levels of
PCDD/DFs. Compared to the liquid-phase photolyses
of PCDD/DF isomers mentioned above,these rate
constants were about one order of magnitude small,but
the same order as those in the heterogeneous photolysis
of PCDDs .Muto et al.,1991),in spite of UV irradiation
of more than 300 nm. It was found that the milder
photocatalytic degradation system using TiO2 catalyst
was useful for the PCDD/DF reduction.
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