Comparison Of Phytotoxicity Of Organic Dyes With Different Structures And Their Photocatalytic Oxidative Removal

In order to investigate the toxic effect of organic dyes with different structures and their photocatalytic degradation products,four cationic dyes and eleven anionic dyes were selected as the model dyes.The germination tests of radish（Raphanus sativus）and cucumber（Cucumis sativus）seeds were respectively carried out using aqueous solutions containing different concentration of dyes as culture media.The root length,fresh weight and dry weight of the germinated seeds were determined and the corresponding inhibition rate and half inhibition concentration(IC₅₀)of the dyes used in the seed germination tests to evaluate and compare their phytotoxicity.The nano-Ti O₂loaded polyester fabric was then used in the photocatalytic degradation treatment of cationic and anionic dyes with different structures.UV-Vis and TOC measurements and GC-MS method were applied to identify the degradation products during the photocatalytic treatment.The germination tests of two kinds of seeds was also conducted using the photocatalytic treated aqueous solutions containing different dyes.Several parameters mentioned above were measured and calculated to indicate the reduction effect on phytotoxicity of the dyes in the solution.The results showed that increasing dye concentration led to a gradual reduction in the root length,fresh weight and dry weight of the germinated seeds.Cationic dyes showed much higher IC₅₀values than anionic dyes in the germination tests of radish and cucumber seeds.This mean that cationic and anionic dyes exhibited phytotoxicity for two kinds of seeds.Cationic dyes had a significant toxic effect on germinated seeds than anionic dyes at the same conditions.This is mainly because of the number of quaternary ammonium in their structures.Increasing the number of quaternary ammonium enhanced their toxicity.Specially,different dyes showed higher IC₅₀values for radish than cucumber at the same conditions.This indicated that radish had a better sensibility to dyes present in water than cucumber during the germination tests.More importantly,the photocatalytic degradation of the cationic and anionic dyes in the solution could be performed in the presence of nano-Ti O₂loaded polyester fabric.In case of cationic dyes,increasing photocatalytic degradation duration significantly reduced their toxicity.When degradation time was 12h,The root length,fresh weight and dry weight of the germinated seeds using degraded dye aqueous solution as culture medium were almost same as those in the control test（distilled water as culture medium）.In case of anionic dyes,short degradation time increased the toxicity of dye solution.The toxicity of dye solution could be gradually limited,until almost completely removed by increasing degradation time.This was because dyes were gradually decomposed and mineralized into the inorganic matters in water.