Optimal Synthesis of Environment-Friendly Iron Red Pigment from Natural Nanostructured Clay Minerals

Abstract

A series of environment-friendly clay minerals—α-Fe2O3 iron-red hybrid pigments—were prepared by a simple one-step hydrothermal reaction process using natural nanostructured silicate clay minerals as starting materials. The influence of structure, morphology and composition of different clay minerals on the structure, color properties, and stability of the pigments was studied comparatively by systematic structure characterizations with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmittance electron microscope (TEM), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS) and CIE-L*a*b* Colorimetric analyses. The results showed that the clay minerals act as green precipitants during the hydrothermal reaction to induce in-situ transformation of Fe(III) ions into Fe2O3 crystals. Meanwhile, they also act as the “micro-reactor” for forming Fe2O3 crystals and the supporter for inhibiting the aggregation of Fe2O3 nanoparticles. The color properties of iron-red hybrid pigments are closely related to the surface charges, surface silanol groups, and solid acid sites of clay minerals. The clay minerals with higher surface activity are more suitable to prepare iron-red pigments with better performance. The iron-red hybrid pigment derived from illite (ILL) clay showed the best red color performance with the color values of L* = 31.8, a* = 35.2, b* = 27.1, C* = 44.4 and h° = 37.6, and exhibited excellent stability in different chemical environments such as acid, alkaline, and also in high-temperature conditions.

Fabrication of Eco-Friendly Betanin Hybrid Materials Based on Palygorskite and Halloysite

“…EDS analysis is used to reveal the surface chemical compositions of betanin/Pal and betanin/Hal samples ( Figure S1 ), and their atomic percent with different elements is presented in Figure 1 c,d, respectively. The O, Si, Mg, Al, Fe, and Ca elements are derived from Pal and Hal [ 34 , 51 , 52 ]. Furthermore, the presence of C and N demonstrates the successful loading of betanin on Pal and Hal.…”

“…In the case of the high-resolution spectra of Si2p of Pal, the binding energies the surface silanol groups and Si–O bonds increase from 103.15 eV to 103.29 eV, and 102.48 eV to 102.72 eV after incorporation of betanin ( Figure 4 d) [ 34 , 66 , 67 ], and this change suggests that there is an interaction between the betanin molecules and the surface silanol groups and Si-O of Pal. Meanwhile, the Mg1s binding energy of Pal increases from 1304.20 eV to 1304.23 eV with the introduction of betanin ( Figure 4 e), while two peaks of Al2p at 74.95 (Al–OH) and 74.53 eV (Al–O) also shifts to 75.42 eV and 74.61 eV, respectively ( Figure 4 f).…”

“…Clay minerals have high specific surface area, cation exchange capacity and excellent adsorption properties [ 29 , 30 , 31 , 32 ]. In addition, different clay minerals have different morphologies, structures, chemical compositions, and properties [ 33 , 34 , 35 ]. Therefore, the eco-friendly natural clay minerals have become the focus of the relevant researches on the loading of natural pigments in the last few years, and the interaction between clay minerals and natural pigments is explored and guide to improve the properties of natural pigments.…”

A Comparative Study on Color Stability of Anthocyanin Hybrid Pigments Derived from 1D and 2D Clay Minerals

“…The diffraction peaks of dolomite were found at 2θ = 31.04°, 41.22°, 45.01°, and 50.62°. Furthermore, the characteristic peaks of quartz were observed at 2θ = 20.84°, 26.63°, 42.48°, 50.13°, and 59.98° [23,31,32,33]. The typical diffraction peaks of Kal ( 2θ = 12.32° and 24.88°), Mt ( 2θ = 6.32°), Hal ( 2θ = 12.04° and 24.72°) and Sep ( 2θ = 7.39°) were all observed in their XRD patterns [31,34,35,36,37].…”

“…In addition, our groups recently synthesized the reversible allochroic hybrid pigments with excellent stability by incorporation of ACN into palygorskite (Pal) [18]. However, it is well-known that different clay minerals have different morphologies, structures, chemical compositions, and properties depending on the arrangement of tetrahedral and octahedral sheets [19,20,21,22,23]. These factors might be closely related to the formation mechanism and properties of hybrid pigments composed of clay minerals and dyes.…”