| With the increasingly serious environmental pollution, environmental protection consciousness of people were gradually increased and extracted from natural plant pigment as a dye trend of the times,which got the favour of more and more people of all ages. Natural pigment on the fiber with lower affinity, lower percentage on dyeing and dyeing wastewater has high chroma, also need to treat wastewater. Photodegradation of dyes in the environment was an important approach to decomposition and transformation.This paper through studying the stability and ultraviolet degradation performance of different structure of natural pigment, discussed the stability of the natural pigments, light degradation and its impact on the environment, was conducive to better development and utilization of natural pigment.Spectrophotometric method was made to explore the natural pigment of several different structures of the acid-base stability, temperature stability, light stability and metals ion stability. Studies have shown that: red rice red pigment was stable at a p H of between 2 to 4, with poor heat resistance, and its dyeing temperature should not exceed 70℃; pigment in light conditions was severely degraded and its stability was influenced by Fe3+, Fe2+. Sorghum pigment stable value was between 3-5 in the p H, with good heat resistance and light stability and Mg2+, Al3+, Zn2+ had a hypochromic effect on Sorghum pigment; Chestnut shell pigment in the range of p H=2-9 were relatively stable, with good heat resistance and excellent light stability, which can be dyed under high temperature conditions and Al3+, Fe3+, Fe2+ had an effect on it. Lac red pigment stable value was between 3-5 in the p H, with good thermal stability and light stability and Fe3+, Fe2+ had obvious influence on it.Water-soluble curcumin relatively stabled at p H between 2 to 7, with a certain heat resistance and poor light resistance and Fe3+, Fe2+ had greater impact on the shade.The photodegradation kinetics of different natural pigment were explored. The experimental results showed that under the condition of red rice red pigment in the p H = 3.6,photodegradation process was consistent with the secondary dynamic model and its dynamic equation was 1/Ct=0.0065t+0.01334, the rate constant k = 0.0065 L·mg-1·h-1; the photodegradation process of Lac red pigment was consistent with first order kinetics model under the condition of p H = 3.6 and its dynamic equation was ln(C0/Ct)=0.0548t-0.052,the rate constant k=0.0548h-1; the photodegradation process of Sodium copper chlorophyll was consistent with the secondary order kinetics model under the condition of neutral and its dynamic equation was 1/Ct =0.00393 t +0.07602,rate constant k =0.00393 L·mg-1·h-1; the photodegradation process of Gardenia yellow pigment was consistent with the secondary dynamic model under the condition of p H = 7 and the dynamic equation was 1/Ct =0.026 t +0.0057,the rate constant k = 0.026 L·mg-1·h-1; the photodegradation process of Beet red pigment accorded with zero order kinetics model under the condition of p H = 3.6, the dynamic equation was Ct =-4.45167 t+41.80368,the rate constant k =4.45167mg·L-1·h-1; the photodegradation of Water-soluble curcumin was in line with the level 2 dynamic model under the condition of the p H = 3.6, dynamic equation was 1/Ct =0.00452t+0.00172,the rate constant k=0.00452 L·mg-1·h-1.Further studies on the factors affecting photodegradation of natural pigment were explored. It was concluded that the relationship between the structure of natural pigment and its degrading properties,and pigment solution p H, light time and pigment mass concentration, dosage of photocatalytic and other factors on the efficiency of the natural pigments photodegradation. Research had shown that UV light degradation of natural pigment was feasible, with good decolorizing effect. |
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