Study On The Synergistic Effect Of Photocatalytic Degradation Of Dyes In TiO₂/AC Composite System

Dyes are common contaminants in water,and even can be identified by the naked eye. Dye production in C hina ranks first in the world. However, to produce 1 ton of dye, it is about 10% 20% of the dye is released into water, if dyes wastewater is poured into rivers randomly without treated, the wastewater will not only pollute the environment, but also threaten human health. Because of dye wastewater ’s complex composition, high chroma and poor biodegradability, therefore, biological methods for dye wastewater’s toxic and refractory organics and color out of little effect. However, titanium dioxide（TiO₂） photocatalytic oxidation technology can destroy many structural stability of the dye, and activated carbon（AC） has been proved the effective removal the dyes by adsorption. Together with TiO₂ and AC, it can show the dual function of adsorption and photocatalysis.In this thesis, the synergistic effect between TiO₂ and AC was evaluated in the removal of Orange IV（azo dye） of the TiO₂/AC and TiO₂/AC-PPG composite system. The main research contents are as follows:（1） This paper studied suitable reaction conditions of Orange IV photocatalyzed and absorbed by the suspended nano- TiO₂ and powdered activated carbon. The study found that: when the concentration of TiO₂ was 1.0 g/L, there was the best reaction rate for the degradation of the dye by TiO₂ photocatalysis; when pH was closer to the isoelectric point of TiO₂, the photocatalytic reaction rate was lower; The AC adsorption equilibrium of orange IV dye was reached in four hours. It is not dependent on solution p H.（2） Photocatalytic degradation of Orange IV and Methyl Orange in contact with a suspended mixture of TiO₂ and AC, significant synergy effect appeared in TiO₂/ AC composite system. The mixtures of 1 g/L TiO₂ and 0.1 g/L AC have good synergistic effect. Photocatalytic activity and photocatalytic reaction rate of TiO₂ enhanced greatly to co-existing AC, a synergy effect was observed with an increase of the first order rate constant by a factor of 2.5, also the photocatalytic degradation of Methyl Orange a synergy effect was observed with an increase of the first order rate constant by a factor of 2.9.（3） By measuring the TOC values of TiO₂ photocatalysis, AC adsorption, TiO₂ / AC composite system degradation for Orange IV, the results show that within 4 h TiO₂ / AC composite system removed the TOC value for orange IV greater than the sum of a single AC adsorption and neat TiO₂ photocatalytic oxidation Orange IV, It was certainly attributed to the synergy effect between TiO₂ and AC in the process of photocatalytic degradation of dyes. It is also found that the chroma of dye was removed, and the value of TOC was still greater than zero, dye was not mineralized to CO2 and H2 O directly. The intermediate products were existed in photocatalytic reaction.（4） The buoyant composite photocatalysts were prepared by thermally immobilizing TiO₂ nanaparticles and powdered AC onto polypropylene granules, the performance of the various prepared buoyant composite photocatalysts was evaluated for their efficiency in the removal of Orange IV from aqueous. The experimental results showed that there was a synergistic effect of AC and TiO₂ in the composite photocatalysts, and a TiO₂/AC mass ratio of 10:1 appeared to achieve best orange IV removal performance than other ratios, up to 1.26.（5） The buoyant composite photocatalysts can solve the problem of separation of TiO₂, and more easily recycled and used again. The composite photocatalyst is still good for the degradation of dye after using 4 times, the catalysts were regenerated by the approach of illumination and hydrogen peroxide, and the photocatalytic performance of restored catalysts can almost closer to the initial state.