Abstract:

Taking the photodegradation of synthetic indigo as a model, the degradation of indigo in dimethyl sulfoxide solvent was studied by UV-Vis spectroscopy, and the effects of mass concentration, illumination time and illumination methods on the degradation of indigo were investigated. The process and products of photodegradation of indigo extract(IE) were further studied. The results showed that the higher the concentration of indigo solution, the faster the degradation rate under natural light conditions was achieved. With the extension of time, the degradation rate of indigo solution was first fast and then slow. The degradation was most obvious in the first 5 days. After 17 days, more than 90% of indigo had been degraded, and the degradation was stopped until the 24^th day. The absorbance value at the maximum absorption changed exponentially with time. The effect of ultraviolet light with higher energy on the degradation of indigo solution was stronger than that of sunlight and white flashlight. HPLC analysis showed that the proportion of isatin produced by the degradation of synthetic indigo standard and indigo extract were 56.78% and 85.50%, respectively, which proved that the main product of the degradation of synthetic and natural indigo was isatin.

Key words: indigo, degradation, illumination, isatin, UV-Vis spectroscopy