# Synthesis and Features of Luminescent Bromo- and Iodohectorite Nanolay Materials
## 3 Results
### Porosity, Packing, and Thermal Stability  
The porosity and packing properties of Br-Hec and I-Hec were evaluated through nitrogen sorption isotherms, recorded in triplicate at 77 K for both materials (Figure 5). Both materials display adsorption isotherms with the shape typical of type V, according to the IUPAC classification [38], which is characteristic of mesoporous materials. Since Br-Hec and I-Hec behave as mesoporous materials, the hysteresis loop of their sorption isotherms can be correlated with their texture. The sorption isotherms of both clay materials show the H\({}_{3}\) hysteresis loop, according to the IUPAC classification [38]. Such a type of hysteresis loop points out that these mesoporous materials have slit-shaped pores, which indicates that there are no limitations for adsorption at high p/p\({}_{0}\). This is a typical feature of non-rigid aggregates of plate-like particles [38]. This plate-like structure was also evident in the XPD patterns (discussed above), and is confirmed with the respective N\({}_{2}\) sorption isotherms. The physisorption phenomena were analysed using two data reduction methods, in order to calculate the surface area and the pore volume of each material (Figure 5). The surface areas were calculated using the BET method [26], considering the model of a multilayer coverage. The Br-Hec has a surface area of 385 m\({}^{2}\) g\({}^{-1}\), while the I-Hec gives the area of 363 m\({}^{2}\) g\({}^{-1}\), which are higher than those described in the literature for synthetic hectorites (5 to 300 m\({}^{2}\) g\({}^{-1}\)) [39], but similar to those reported for Laponite(r) (between 279 and 375 m\({}^{2}\) g\({}^{-1}\)) [39; 40]. The volume of the mesopores was calculated using the method described by [PERSON] et al. [27], indicating the value of 0.48 and 0.50 cm\({}^{3}\) g\({}^{-1}\) for the Br-Hec and I-Hec, respectively. The pore volumes of the materials did not change from the adsorption to the desorption curve. Thus, these materials have the reversible adsorption process expected for mesoporous materials and needed for catalysts. The TGA-DSC curves of Br-Hec and I-Hec (Figure 6) show that the mineral structure is stable up to 800 \({}^{\circ}\)C. The materials show the three main events expected for hectorite type of clay minerals. The first asymmetric endothermic signal is related to the loss of adsorbed water molecules [35; 41]. This is observed in the DSC curves as a single event at 89 \({}^{\circ}\)C for the Br-Hec and at 114 \({}^{\circ}\)C for the I-Hec. The temperature ranges related to these occurrences are better observed in the first derivatives of the  
Figure 5: The nitrogen sorption isotherms of bromohectorite and iodohectorite. TGA curves (Figure 1), which indicate that these first events are accompanied with mass losses of 3% (30-135 \({}^{\circ}\)C) and 1.8% (30-191 \({}^{\circ}\)C) for Br-Hec and I-Hec, respectively. The second event represents the loss of the coordinated water from the interlayer space of the smectites (in the inner hydration shell of Na\({}^{+}\)) and locked water inside possible voids in the clays' structure [(35; 41)]. Although the TGA and DSC curves do not show this event clearly, it can be well identified from the first derivatives (Figure 1). This loss of coordinated water involves a mass loss of 7.2% and 6.5% for Br-Hec and I-Hec, respectively. The total water losses were 10.2% and 8.3% for Br-Hec and I-Hec, respectively, which is consistent with the higher surface area observed for Br-Hec. The strong exothermic signal in the DSC curves shows the collapse of the mineral structure (Figure 6). This was observed at 828 and 813 \({}^{\circ}\)C for the Br-Hec and I-Hec, respectively, showing a mass loss of ca. 2.5% for both materials. The total mass losses (from 30 to 1000 \({}^{\circ}\)C) were 12.7% and 10.8% for the bromo and iodo-hectorites, respectively.