Photocatalytic Degradation Of Phthalic Acid Esters In Water By TiO₂/Pumices

Phthalic acid esters (PAEs) was one the most common plasticizers, which been applied in plastics field widely. It attracted wide attention in recent years since its harmfulness to environment, special to the water. At present, it is still difficult to eliminate PAEs in water treatment technology. An effective new method to eliminate PAEs was in dire need. Titanium dioxide (TiO2) photocatalysis was one of the most potential methods to treat the recalcitrant pollutants in micro-polluted water. So it's great meaningful to treatment the PAEs by TiO2 photocatalysis. The dipping method of catalyst, degradation rules of three phthalic acid esters (DMP, DEP, DBP), influential factors and degradation mechanism were investigated in this paper.The results showed that the catalyst of power dipping method were more durable. Degradation rate reached 93.5% after 5 h with the TiO2/pumices dosage 30.0g/L, initial concentration of DMP was 20.0 mg/L. Degradation rate still reached 86.4% in despite after the catalyst used three times.The rates of photocatalytic degradation on DMP, DEP and DBP followed first-order kinetics, and the half-life sequence was:DEP>DMP>DBP. Different initial concentration of DMP also fitted first-order kinetics with prolonged half-life and increased concertration. Effect of pH value on DMP degradation was investigated in the range from 2.0 to 11.0, when pH< 6.5, the rate was found increased with the pH value, and when pH> 6.5, the rate unchanged basically.Inorganic salts and humic acid (HA) inhibited the effect of DMP degradation. The results showed that there is no significant differences of the inhibited effects between different cations, while significant differences between different anions. The sequence of four anions inhibition capability for DMP:HCO3-> NO3-> SO42-> Cl-.HA restrained the degradation significantly, and enhanced with the HA concentration increased. It's also found that the degradation rate of DMP in secondary effluent was much slower than in the distilled water.The intermediate products of DMP, DEP and DBP were analyzed by LC/MS, and the pathway was discussed in this paper. The break of carbon chains in DMP, DEP started from benzene ring, while DBP started from side chain.