| Various pollutants enter into environment accompany with the development of human civilization. The pollutant category has been enlarging in recent years, from traditional pollutants like dyes, herbicide and raw industry chemical material etc. to emerging pollutants like pharmaceuticals and personal care products, endocrine disruptor chemicals and flame retardant. The existing form of these pollutants becomes more and more complicated in order to satisfy the specific needs. Once enters into environment, The existing form also becomes various rather than the simple free form, including adsorption on the dissolved organic matter and humic acid aggregate, and also can enter into some micelles and vesicles. These couled be defined as broad host-guest like interactions. Therefore, it is worthwhile to study the pollutants degradation in the presence of "host", which is more close to the practicle condition. There are only a few reports about the degradation of host-guest complex. The effect of cyclodextrin on the UV photolysis and TiO2 photocatalysis of pollutants was investigated in this work, and a novelβ-cyclodextrin (β-CD) grafted titanium dioxide (TiO2/β-CD) heterosupramolecular catalyst was synthesized as well as its photoreactivity was investigated. The specific work and results were shown below.The overview of the research on the effect of cyclodextrin on the UV photolysis of pharmaceuticals and personal care products, endocrine disruptor chemicals and pesticides, the use of cyclodextrin on the remediation of contaminated soils and the use of cyclodextrin based functional materials in pollutants treatment was summaried.The influence ofβ-cyclodextrin (β-CD) on the photochemistry and photophysical properties of 2,2-Bis(4-hydroxyphenyl)propane (bisphenol A, BPA) and Bis-(4-hydroxyphenyl)methane (bisphenol F, BPF) was investigated in this work. The photolysis of BPA and BPF was accelerated in the presence ofβ-CD and the enhancement efficiency increased with the increasing ofβ-CD. The enhancement efficiency for BPA is much higher than that for BPF. Both BPA and BPF form a 1:1 complex withβ-CD, and the equilibrium constant for BPA is 4.3 times larger than that for BPF. Laser flash photolysis results showed the primary process is the biphotonic photoionization reaction. The biphotonic photoionization efficiency for BPA and BPF increased in the presence ofβ-CD, which was probably resulted from the prolonged fluorescence lifetime. The enhancement ofβ-CD on BPA and BPF photolysis is due to the increased biphotonic photoionization efficiency.The effect ofβ-CD on the UV photolysis of acetaminophen was carried out in Chapter 3.β-CD showed retardation effect on the degradation of acetaminophen, which is different from that of BPA and BPF. Laser flash photolysis results showed the primary process is the photoionization reaction. GC-MS analysis showed the primary process probably includes the photo-Fries rearrangement as well as the photoionization process. The rearrangement was inhindered because of the steric hinerance effect ofβ-CD, andβ-CD could also shield acetaminophen from the attack of hydroxyl radical. Therefore, the overall degradation of acetaminophen was retarded in the presence ofβ-CD.The effect ofβ-cyclodextrin on the photocatalytic degradation of phenolic compounds in TiO2 suspension was also investigated in this study.β-CD showed selectively effect on the photocatalytic degradation. Typically, the degradation of the guest which has a high inclusion constant withβ-CD was accelerated, otherwise, the degradation is retarded. The pollutants could have both direct degradation and indirect degradation (through the cavity of cyclodextrin) in TiO2 suspension in the presence ofβ-CD. The indirect degradation can make complementarity on the lose of direct degradation for the guest which has a high inclusion constant withβ-CD. Indirect degradation was not supposed to occur for the pollutants which have a small inclusion constant withβ-CD, which caused the inhibition of guest degradation. Quantum calculation and GC-MS analysis allowed to propose reasonable mechanism for the photocatalytic degradation of pollutants in TiO2 suspension.In this work, cyclodextrin modified TiO2 (TiO2/β-CD) heterosupramolecular catalyst was synthesized by physical adsorption and photo induced self-assembly method. The photocatalysis performance of TiO2/β-CD on the degradation of dye pollutants (OrangeⅡand rhodamine B) and corlorless organic pollutants (bisphenol A, bisphenol E and bisphenol F) was carried out in detail. The TiO2/β-CD hybrid material synthesized by adsorption method only showed enhancement on the degradation of dye pollutants, while the TiO2/β-CD hybrid material synthesized by photo induced assembly method promoted the degradation of both dye pollutants and corlorless organic pollutants. The visible reactivity of TiO2/β-CD was correlated with the semiconductor’s surface area. The ability in forming host-guest complex played a key role in the guest degradation over TiO2/β-CD. Superoxide radicals were shown to be the main reactive species that caused the degradation of pollutants under visible irradiation. The reaction betweenβ-CD and Superoxide radicals was negligible, which makes TiO2/β-CD an effective and stable catalyst. |
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