# Ni/Zn Layered Double Hydroxide (LDH) Micro/Nanosystems and Their Azorubine Adsorption Performance
## 4 Results and Discussion  
### Characterization of Adsorbent  
The description of the XRD pattern and FTIR spectrum of the as-synthesized Ni/Zn based nanohybrid which will be used as adsorbent in this investigation are presented in Figure 1. Figure 1a shows the formation of bi-nanostructures based on nickel hydrate hydroxide (\(\alpha\)-Ni(OH)\({}_{2}\) 0.75 H\({}_{2}\)O) and zinc carbonate hydroxide (Zn\({}_{5}\)(CO\({}_{3}\))\({}_{2}\) (OH)\({}_{6}\)) which are assigned to rhombohedral [JCPDS no. 038-0715] and monoclinic [JCPDS no. 19-1458] structure, respectively, with 54% crystallinity order. Figure 1: Adsorbent based on Ni/Zn LDH bi-nanostructure nanohybrid synthesized via hydrothermal process at 6h/180 \({}^{\circ}\)C: XRD diffractogram (**a**) and FTIR spectrum (**b**). Table 1 summarizes the bi-phase nanohybrid structural characteristics depending to their diffractogram. The FTIR spectrum of this nanoadsorben as shown in Figure 1b is typical of a hydrotalcite-like material showing a broad and intense band at 3336 cm-1 hatcan be attributed to hydroxyl (OH\({}^{-}\)) stretching vibrations from structural hydroxyl groups and interlayer water molecules [36]. In addition, bands at 1362 cm-1 (\(\
u_{3}\)), 1043 cm-1 (\(\
u_{1}\)) and 745 cm-1 (\(\
u_{2}\)) [37] show the presence of carbonate anion (CO\({}_{3}\)-2) in the interlayer [38]. However, the bands at 953 and 836 cm-1 are associated withimetal-oxygen (M-O) and metal-hydroxyl (M-OH) groups in the lattice of LDHs. More precisely, below 642 cm-1, the recorded bands are attributed to 8 Ni/Zn-OH or \(\
u\) Ni/Zn-O as reported in many studies [39; 40; 41]. Moreover, the sharp band at 836 cm-1 is associated with in-plane quadrant bending [39; 40; 41]. These results clearly prove the XRD identification reported above. The morphological and textural properties of this Ni/Zn based LDH nanohybrid illustrate that it possesses precisely special membranous morphology with non-homogeneous mesopores in an agglomerated way as shown in Figure 2a. The specific surface area (SSA--S\({}_{\text{BET}}\)) of this bi-phase nanohybrid was estimated from the adsorbed-desorbed nitrogen quantity in relation to its pressure at liquid boiling point and under normal atmospheric pressure. Figure 2b shows the obtained information of adsorption and desorption isotherms of nitrogen at 77 K and their pores size and volume distribution according to the BET and BJH model, respectively. The isotherm shows an hysteresis IV-type with S\({}_{\text{BET}}\) of about 110.38 m\({}^{2}\) g-1. However, the pores distribution illustrated inset this figure indicates the collection of multiporous nanohybrid with average pore size essentially centered at 2, 3, 24 and 32 nm, which demonstratethe mesoporous texture nanohybrid (pores between 2 and 50 nm) [42]. This distribution confirms, again, the dishomogeneous porous morphology observed in almost micro/nanospheric membranous architecture via FESEM microscopy as shown above. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Phase** & **a (Å)** & **b (Å)** & **c (Å)** \\ \hline ZnS(CO\({}_{3}\))\({}_{2}\) (OH)\({}_{6}\) & 13.83 & 6.19 & 5.386 \\ Ref. [JCPDS no.19 1458] & 13.58 & 6.28 & 5.41 \\ \(\alpha\)-Ni(OH)\({}_{2}\).075H\({}_{2}\)O & 3.06 & - & 24 \\ Ref. [JCPDS no.038-0715] & 3.08 & - & 23.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Structural characteristics of Ni/Zn based bi-phase nanohybrid. Figure 2: FESEM micrographs (**a**) and their N\({}_{2}\) adsorption-desorption isotherms (inset pore distribution) (**b**) of adsorbent based of Ni/Zn bi-phase nanohybrid. To better understand the composition of the used nanohybrid based adsorbent as well as the existing functional groups that act on the adsorption mechanism, XPS analysis was performed. Figure 3 shows the deconvolution of main asymmetric peaks (Ni2p, Zn2p, C1s, and O1s) of high-resolution core-level XPS spectra, using L/G fitting method consistent with the literature data [36; 43].