Organic–Inorganic Hybrid Pigments Based on Bentonite: Strategies to Stabilize the Quinoidal Base Form of Anthocyanin

Abstract

Anthocyanins are one of the natural pigments that humanity has employed the most and can substitute synthetic food dyes, which are considered toxic. They are responsible for most purple, blue, and red pigment nuances in tubers, fruits, and flowers. However, they have some limitations in light, pH, oxygen, and temperature conditions. Combining biomolecules and inorganic materials such as clay minerals can help to reverse these limitations. The present work aims to produce materials obtained using cetyltrimethylammonium bromide in bentonite clay for incorporation and photostabilization of anthocyanin dye. Characterizations showed that the organic molecules were intercalated between the clay mineral layers, and the dye was successfully incorporated at a different pH. Visible light-driven photostability tests were performed with 200 h of irradiation, confirming that the organic–inorganic matrices were efficient enough to stabilize the quinoidal base form of anthocyanin. The pigment prepared at pH 10 was three-fold more stable than pH 4, showing that the increase in the synthesis pH promotes more stable colors, probably due to the stronger intermolecular interaction obtained under these conditions. Therefore, organobentonite hybrids allow to stabilize the fragile color coming from the quinoidal base form of anthocyanin dyes.

Bimetallic Organic Gel for Effective Methyl Orange Dye Adsorption

“…Generally, in the process of MOG synthesis, the important factors affecting gel formation include the following: reactant ratio, reaction temperature, solvent type, reaction time, pH, surfactants, and inhibitors [ 30 , 31 ]. In this work, six reactant ratios (1:8, 1:5, 1:4, 1:2, 1:1, and 3:2) were investigated using single-factor experiments, and the results are described in Figure S1 .…”

“…Langmuir, Freundlich, and Temkin models were used to describe the adsorption experimental data. The equilibrium models can be explained as follows [ 29 , 31 ]: where C e (mg/L) is the equilibrium concentration; B (kJ/mol) is the adsorption heat factor; q m (mg/g) is the maximum amount adsorbed; K l (L/mg), K f ((mg/g)/(mg/L) 1/n ), and K t (L/g) are Langmuir, Freundlich, and Temkin adsorption constants, respectively; and n is a measure of adsorption intensity.…”

Adsorption of Methylene Blue Dye by Cetyltrimethylammonium Bromide Intercalated Polyaniline-Functionalized Montmorillonite Clay Nanocomposite: Kinetics, Isotherms, and Mechanism Study

“…Compared to Mt, the relative composition of aliphatic/aromatic The textural characteristics of the prepared adsorbents were analyzed through N 2 adsorption-desorption isotherm tests (Figure 2b). All the isotherms showed a type II isotherm with a distinctive type H3 hysteresis loop, suggesting the presence of a small macroporous component [12,17]. The pore size data width of the adsorbents is summarized in Table 2.…”

“…The adsorption isotherms can be described as the process of mass transfer rate between the solid adsorbent and the adsorbate at constant temperature. Adsorption isotherms including Langmuir, Freundlich and Temkin were used to investigate the experimental data for adsorption using the following formulas [16][17][18]: Langmuir formula :…”