Rovil Nafeev

Nickel hydroxides are widely used as electrochemically active substances in alkaline batteries and hybrid supercapacitors; they can be used for electrocatalysis, in electrochemical sensors, and as pigments. Knowledge of the formation mechanism of nickel hydroxides is necessary for developing and optimizing targeted synthesis methods. The thermal effects of processes in the formation of nickel hydroxide from nitrate were studied by the calorimetry method. The mechanism of precipitate formation was investigated by the method of simultaneous potentiometric (with a glass universal electrode) and conductometric titration. The nickel content in the samples obtained at the determined NaOH/Ni2+ ratios was investigated by the chemical method of trilonometry after preliminary dissolution. Calorimetric investigations showed that the reaction of nickel nitrate with NaOH was exothermic with ΔНreaction=‒28328.5 J/mol. The exothermic nature of the NaOH dilution process was revealed with ΔНdilution =‒2454 J/mol. According to the results of potentiometric titration, the formation of a basic salt of the NiOHNO3 type was not detected. Analysis of the results of conductometric titration revealed a two-stage chemical mechanism for the formation of nickel hydroxide from nitrate. At the first stage, which had a high rate, due to the liquid-phase reaction of the nickel cation with the hydroxyl anion, a primary precipitate of the composition Ni(OH)1.87(NO3)0.13 was formed. In the second stage, as a result of a slow topochemical reaction of the primary precipitate with hydroxyl anions, nitrate ions were displaced from the precipitate to form nickel hydroxide. These data are confirmed by the analysis of precipitate obtained at NaOH/Ni2+ ratios of 1.87 and 2.2: the Ni content was 52.95 % and 55.63 %, corresponding to the formulas Ni(OH)1.87(NO3)0.13∙0.68H2O and Ni(OH)2∙0.71H2O. This clearly indicated that the primary precipitate was nitrate-doped α-Ni(OH)2 and the final precipitate corresponded to the α-modification of nickel hydroxide

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