Crystalline/Amorphous Blend Identification from Cobalt Adsorption by Layered Double Hydroxides

Abstract

In this study, the adsorption behavior of CaAl-Cl layered double hydroxide (CaAl-Cl-LDH) with a controlled pH value (pH = 6) on Co(II) ions ([Co] = 8 mM) is investigated. The comprehensively accepted mechanism of cobalt adsorption on LDH is considered to be co-precipitation, and the final adsorbed products are normally crystalline Co-LDH. One unanticipated finding is that crystalline/amorphous blends are found in the X-ray diffraction (XRD) pattern of Co-adsorbed LDH. To shed light on the adsorption products and the mechanisms in the adsorption process of Co(II) in an aqueous solution by CaAl-Cl-LDH, a series of testing methods including Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), High-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP) are applied to clarify the interaction between cobalt and CaAl-Cl-LDH. According to the comprehensive analysis, the formation of the crystalline/amorphous blends corresponds to two adsorption mechanisms. The crystalline phases are identified as Co6Al2CO3(OH)16·4H2O, which is attributed to the co-precipitation process occurring in the interaction between Co(II) and CaAl-Cl-LDH. The formation of the amorphous phases is due to surface complexation on amorphous Al(OH)3 hydrolyzed from CaAl-Cl-LDH.

Functionalized layered double hydroxide applied to heavy metal ions absorption: A review

“…The focus of XPS and FT-IR are the analysis of the valence state of metal elements and the functional groups composed of C, O, and H. Morphology is mainly characterized by SEM and TEM. For example, as shown in Figure 4 (previous research study of our team) [55], when CaAl-LDH adsorbs Co 2+ , Co 2+ replaces Ca 2+ in the crystal lattice. Due to the difference in ionic radius Co 2+ and Ca 2+ , the crystal structure (Figure 4a, f, and g), chemical bond (Figure 4b and c), and morphology ( Figure 4e, d, and h) have changed.…”

“…The mechanisms of LDH removing heavy metal ions mainly include isomorphic substitution, complexation, and electrostatic interaction [55,56]. The process of electrons interacting with donors and electron acceptors to form complexes is complexation, which is the most important absorption mechanism for functionalized LDH.…”

Layered Double Hydroxides Precursor as Chloride Inhibitor: Synthesis, Characterization, Assessment of Chloride Adsorption Performance

“…The correlation coefficients R 2 of the Freundlich and Langmuir model are 0.907 and 0.989, respectively. Langmuir adsorption isotherm is known as the formation process of a monolayer metal ions on the outer surface of the adsorbent, and Freundlich adsorption isotherm is usually applied to describe the adsorption characteristics of the heterogeneous surface [25]. Therefore, the chloride ions were adsorbed first on the LDH precursors edges, surface region, and then the interlayer space via diffusion [26,27].…”

Effects of Physiochemical Properties of Nano-Clays on the Removal of Heavy Metals from Acid Mine Drainage

“…The sharpest diffraction peak for the (003), (006), and (009) planes proves that it had the best crystallinity and are essentially maintained after adsorption. The peak at 11.73 2 for all samples of hydrotalcite was attributed to the reflections from (003) of crystallographic planes [20].This peak is also described as a characteristic of divalent cations occupying the interlayer sites, see figure 2 for more description of the peak [21]. Figure 2 shows the change in intensity of the peak at 11.73 2θ .…”