# Synthesis and Features of Luminescent Bromo- and Iodohectorite Nanolay Materials
## 3 Results  
### Structural Characterization and Purity  
The XPD patterns of the bromohectorite and iodohectorite (Figure 1) show that both materials have a hexagonal crystal structure similar to nanocrystalline fluorohectorite, indicating that no crystalline impurities were detected within the detection limit of the equipment. The Br-Hec and I-Hec have a d\({}_{001}\) spacing of 14.30 A (equivalent to 6.2\({}^{\circ}\) in 20), indicating two hydrate layers in their interlayers when recorded at room temperature [28]. The spacing falls in the middle of the range of 10-20 A predicted for the basal spacing of smectites [29]. Due to the nanosize of the crystallites, the respective reflections are regularly broad, generating an extensive overlap that does not allow for an accurate determination of their FWHMs. However, the single (001) reflection at 6.2\({}^{\circ}\) (in 20) is suitable for carrying out the Scherrer calculations [25] to determine the diffracting domain size, which indicates the size of approximately 3 nm along the 001 direction for both materials. The XPD patterns of the materials also indicate the formation of a plate-like morphology, because the (001) reflections are wider than the others, which means that the crystallites are larger in the other directions, i.e., the (h00) and (0k0) directions. The XRF spectra of Br-Hec and I-Hec (Figure 2) confirmed the expected chemical composition of the materials. Both spectra show the lines related to the Mg K\({}_{\alpha 1}\), Si K\({}_{\alpha 1}\), and Ca K\({}_{\alpha 2}\) emissions at 1.25, 1.74, and 3.69 keV, respectively [31]. Here the presence of calcium may be associated to its common presence as impurity in the sodium halide precursors used in the synthesis. Therefore, it is expected  
Figure 1: The XPD patterns of the bromohectorite and iodohectorite. The reference patterns for nano- and microcrystalline fluorohectorite were calculated with PowderCell v 2.4 program ([PERSON] and [PERSON], BAM, Berlin, Germany, 2000) using structural data from [30]. that the calcium cations share the interlayer space of the nanoclay materials together with the Na\({}^{+}\) ions. Also, the spectra show the lines of Ag L\({}_{1}\), L\({}_{\alpha 1,2}\), L\({}_{\beta 1}\), L\({}_{\beta 2}\) and L\({}_{\gamma 1}\), from 2.63 to 3.52 keV [31], which are due to the silver excitation source of the equipment. The XRF spectrum of the Br-Hec exhibits the line of Br L\({}_{\alpha 1,2}\) emission at 1.48 keV, confirming the presence of bromine. Similarly, the iodine in the composition of the I-Hec is observed as the emission lines of I L\({}_{\alpha 1}\), L\({}_{\beta 1}\) and L\({}_{\beta 2}\) at 3.94, 4.22 and 4.51 keV, respectively. Moreover, the spectra of both materials indicate the presence of Ti as an impurity witnessed by the weak K\({}_{\beta 1}\) line at 4.9 keV. The FTIR spectra of Br-Hec and I-Hec (Figure 3) show a strong band at 460 cm\({}^{-1}\) related to the symmetric stretching of Mg-O in the octahedral units of hectorite type clay minerals [32]. In addition, both spectra present the Si-O-Si bands of the tetrahedral layers of ordered hectorite at 660, 800, and 1010-1090 cm\({}^{-1}\) related to the bending as well as symmetric and asymmetric stretching modes of Si-O-Si, respectively [32; 33]. None of the synthesized materials show indication of an amorphous silica phase that would be observed as a weak band at 1200 cm\({}^{-1}\)[33]. The weak bands at ca. 1625 and 3300 cm\({}^{-1}\) are assigned to the H-O-H bending and stretching, respectively, indicating low amounts of adsorbed water on the clays and/or water present in the hydration shell of the Na\({}^{+}\) cations in the  
Figure 2: The XRF spectra of bromohectorite (**top**) and iodohectorite (**bottom**). The upper insertions show the presence of Ti impurities in both materials (\(\bullet\): instrumental signal). interlayer space of both clay materials [34]. Moreover, in the FTIR spectra of Br-Hec or I-Hec there are no bands related to the vibration of hydroxyl groups in the octahedral layers of clay minerals.