Combined photooxidation/photoreduction using TiO2 photocatalysts to treat organic/inorganic metal-laden wastewaters

摘要

Titanium dioxide (TiO(sub 2)) colloids prepared from titanium chloride (TiCl(sub 4)) were used as photocatalysts in the experiments. Cysteine was selected as the model derivative for the surface modification of the TiO(sub 2) nanoparticles. Testing of TiO(sub 2) photocatalysts conducted in the absence of organic compounds demonstrated that adsorption of lead ions occurred in the system with either untreated (virgin) or treated (modified using cysteine) TiO(sub 2) photocatalysts. Adsorption rates of the metal ions in the systems that used treated TiO(sub 2) photocatalysts were about three times faster than those where untreated TiO(sub 2) photocatalysts were used. Lead ion concentrations in the irradiated solutions decreased as the UV irradiation time increased; greater metal removals were achieved at longer irradiation times. The rate of decreasing lead ion concentrations in the system that used treated TiO(sub 2) photocatalysts was about two to three times faster than that in the system using untreated TiO(sub 2) photocatalysts. Experiments were also performed in which organic compounds (naphthalene or phenol) and heavy metals (Pb(sup 2+)) were simultaneously treated with TiO(sub 2) photocatalysts. The presence of lead ions did not interfere with the photo-degradation of the selected organic compounds from solution. The presence of phenol compound appeared not to affect the photoreduction of lead ions, while addition of naphthalene compound resulted in a lag-time effect on the photoreduction of lead ions from solution. All of the experimental results showed that the cysteine-modified TiO(sub 2) resulted in faster and more effective removal than that for the untreated TiO(sub 2) system. This technique has resulted in the simultaneous photocatalytic removal/recovery of organic and inorganic compounds in the system.