Investigation of the characteristics of Zn-Al layered double hydroxides, intercalated with natural dyes from spices, as a cosmetic pigments

Abstract

Pigments are the main components of cosmetics, which determine both toxicity and consumer color characteristics. Zn-Al layered double hydroxides intercalated with anionic food dyes are promising pigments. The best sources of dyes for intercalation are natural ones. The most promising are spices. Natural dyes from spices are often biologically active substances. The parameters of samples of Zn-Al (Zn:Al=3:1) hydroxides intercalated with natural food dyes, synthesized in the medium of aqueous tinctures of saffron and safflower, were studied. The crystal structure of the samples was studied by X-ray phase analysis; color characteristics were studied by spectroscopy and calculation of parameters in the CIE L*a*b system. The possibility of synthesizing Zn-Al colored layered double hydroxides intercalated with natural dyes in the medium of saffron and safflower tinctures was shown. X-ray phase analysis showed that both pigment samples were layered double hydroxides with the α-Zn(OH)2 structure. For the pigment intercalated with saffron dye, the phenomenon of partial decomposition of Zn-Al LDH to ZnO during synthesis was revealed. The color characteristics of the samples were studied. Zn-Al LDH pigment synthesized in a saffron tincture had a bright yellow color determined by intercalated saffron carotenoids (crocin and crocetin). It was suggested that safflower dye flavonoids were partially hydrolyzed (red ones - cartamine and cartamidine, and yellow - Safflor Yellow A), which led to the formation of a dark orange-brown color of the sample. The prospects of using Zn-Al LDH intercalated with saffron food dyes as a cosmetic pigment were shown