Preparation Of Organic Titanium Dioxide Pillared Montmorillonite And Application In The Photocatalytic Degradation Of Halogenated Organic Pollutants

Chlorophenols (CPs) and polybrominated diphenyl ethers (PBDEs) are two types of halogenated organic compounds with toxic properties. They are of environmental concern due to their long half life, bioaccumulation, widespread distribution and potential adverse effects in wildlife and sensitive human populations. Many of these substances are persistent and lipophilic. These properties make them easy to bioaccumulate while difficult to be eliminated from the environment via biodegradation method. So a cost-effective technology for water treatment to eliminate these organic pollutants has currently become research focus of environment pollution control.Pillared clay has attracted a lot of attention as it is a new type of porous catalytic nanocomposite in the past few decades. Compared with the raw montmorillonite, the clay modified by organic surfactant possesses higher surface area, more Lewis surface acidity and better porosity. The pillaring reaction not only extends their interlayer spacing, but also transforms them from hydrophilic into hydrophobic. This organic modification can obviously enhance the pollutant adsorption to the montmorillonite from the aqueous environment. Meanwhile, many references showed that titania can be used to pillar the montmorillonite very well. After titanic ions were exchanged into the montmorillonite, the subsequent interface chelation can narrow the forbidden band of the semiconductor, and reduce the electron-hole pair recombination rate. Such coordination enables the composite photocatalysts to utilize solar light effectively and improves their photocatalytic activity.The TiO₂ exhibits excellent photocatalytic mineralization to organic pollutants, and the organic pillared montmorillonites have strong adsorption to them. But both materials have their own disadvantages for wastewater treatment. To obtain mutual and complementary advantages, two new types of composite photocatalysts, organic TiO₂ pillared montmorillonite and TiO₂ immobilized organic pillared montmorillonite, have been investigated in this thesis. Both prepared composite photocatalysts possess high photocatalytic activity to organic pollutants utilizing the UV light as source effectively. The adsorption function of organic pillared montmorillonite as adsorbent can be regenerated in situ after the adsorbed contaminants are completely mineralized via TiO₂ photocatalysis. Moreover, as hydrophobic photocatalyst support, the pillared montmorillonite enables the immobilized TiO₂ to be easily precipitated and reused practically. As a new class of photocatalyst, TiO₂ immobilized organic pillared montmorillonite has extensive potential in water pollution control and environment remediation, especially in the elimination of organic pollutants from waste water.The organic TiO₂ pillared clays were prepared at certain Ti(OC₄H₉)₄: HCl rations by Sol-gel technology after being modified with three different surfactants, such as polyvinyl alcohol(PVA), Cetyltrimethyl ammonium bromide(CTMAB) and Dodecyl benzene sulfonic acid sodium salt(DBS). And the TiO₂ immobilized hydrophobic montmorillonites were also designed and prepared by immobilizing TiO₂ onto hydrophobic montmorillonite, which was synthesized by ion exchange reaction between the montmorillonite layers with cation surfactant, CTMAB. The components and texture of all prepared composite photocatalysts were characterized with X-ray powder diffraction, scanning electron microscope and energy dispersive Spectrometry. The adsorption and photocatalytic performance of these prepared photocatalysts were also investigated, using methyl orange (MO), 2, 4, 6-trichlorophenol (TCP) and Decabromodiphenyl ether (BDE 209) as mode pollutants. Main photocatalytic intermediates were detected and identified by using liquid-liquid extraction, GC-MS and LC-MS-MS. A degradation mechanism was tentatively proposed based on the identification of all by-products generated during the degradation of original compounds. The experimental results indicated that the performance of pillared clays depend on the adding orders of CTMAB and TiO₂ sol during preparation, and the adsorption capacities and photocatalytic activities of pillared clays modified by different surfactants are distinguished. The mode pollutants can be removed by the prepared photocatalysts completely. The removal efficiency trend of mode pollutants showed that the more TiO₂ was pillared or immobilized to hydrophobic clay, the higher removal efficiencies were achieved.