Removes toxic dyes from textile effluents
Scientists from the University of Calcutta have found that zinc oxide (ZnO), a common semiconductor, safely disposes of two harmful dyes -- methylene blue (MB) and eosin Y (EY) -- present in effluents of textile industry (see: United Colours of Industry , Down To Earth, February 28, 2005). "On being exposed to ultraviolet (UV) radiation, the semiconductor triggers a set of chemical reactions in the presence of air and water rendering the dyes colourless as well as harmless," says Binay K Dutta, the lead researcher. The semiconductor acts as a catalyst.
"The other methods merely transfer dyes from the liquid to the solid phase causing pollution and requiring further treatment," says Sampa Chakrabarti, co-author of the study. EY is a skin and eye irritant and also a gene-toxin. MB is a blood toxicant. The study is published in the Journal of Hazardous Materials (Vol 112, No 3).
In an experiment, the scientists used 0.4g of ZnO particles in 400 ml of dye solution through which air was bubbled. It was then exposed to the light from four UV lamps for 2 hours at 30C. Except a lower airflow for MB, all other experimental conditions were same for both dyes. They found 58 per cent of MB and 39 per cent of EY were destroyed because of the strong oxidising agents produced by exposure to UV light. In separate experiments, the team found an increase in ZnO used and the airflow rate enhanced the degradation of MB to a maximum of 76 per cent and EY to 63 per cent.
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