Sepiocite, Sepiolite-Like Nanoclay Derived from Hydrotalcite-Like Layered Double Hydroxide

Abstract

Sepiocite, a synthetic sepiolite-like nanoclay, was derived from hydrotalcite-like Mg2Al(CO3)0.5-layered double hydroxide (LDH) under phase transformation at 270 +/- 3 degrees C. The crystal structure of sepiocite is conceptually very similar to that of sepiolite derived from montmorillonite clay because sepiocite is formed through the alternation of the blocks and tunnels along the crystallographic c-axis, with a partial dehydroxylation of the octahedral Mg-(OH)-Al configuration into tetrahedral ones. Three important findings regarding sepiocite were arrived at: (i) its high specific surface area of 128.25 m2/g with an average particle size of 200 nm, which is approimately equal to 3.5 times larger than the specific surface area of the pristine LDH (34.21 m2/g); (ii) its non-swelling property; and (iii) its strongly reduced anion-exchange capacity.

Hydrotalcite–Niclosamide Nanohybrid as Oral Formulation towards SARS-CoV-2 Viral Infections

“…On the other hand, the characteristic -OH and the -CO 3 2− bands were fairly reduced after the calcination process, which was evidenced by TGA (thermogravimetric analysis) and DTA (differential thermal analysis), as shown in Figure S3. Interestingly, the carbonate peak at ~1360 cm -1 corresponding to HT was split in two (Figure 2c) indicating their structural transformation to DHT, as previously reported by our group [52]. One thing to note here was that the specific bands for -OH and -NH were reduced in the NIC-DHT sample after hybridization, indicating the successful loading of NIC on DHT.…”

Development of Mesopore Structure of Mixed Metal Oxide through Albumin-Templated Coprecipitation and Reconstruction of Layered Double Hydroxide

“…Upon calcination, a broad peak at around 74.3 ppm appeared, indicating the formation of 4-coordinate Al 3+ environment (Figure 4b). It is known that the Al 3+ in the octahedral (O h ) site of LDH partially migrates to tetrahedral site (T d ) to interstratify MgO domains [22,23,27,35]. It is noticeable that the peak area ratio T d /O h of 0.145 (Table 1) in AO-1 was lower than the previously reported values ranging 0.59-1.32 [27,35], indicating that local disorder around Al 3+ was less severe than usual.…”

“…Second, the specific surface area increases, and porous structure can be obtained. The metal oxide domains produced during thermal treatment can be connected by the trivalent metals migrated to tetrahedral site [23,24], resulting in intra-particle mesopores [25][26][27]. It is generally known that LDHs prepared by conventional coprecipitation method tend to have specific surface area (S BET ) around 20-60 m 2 /g [28][29][30], while the corresponding LDO had S BET higher than 100 m 2 /g [27,30].…”

Effect of Tetrahedrally Coordinated Al on the Surface Acidity of Mg-Al Binary Mixed Oxides

“…As previously reported [ 25 ], MgAl-CO 3 -LDH underwent dehydration, dehydroxylation, and decarbonization upon heat treatment resulting in the evolution of mixed metal oxide. During the course, most of the Mg 2+ cations maintained their coordination site in the octahedral center; on the other hand, the Al 3+ cations underwent partial preservation of octahedral coordination and partial migration to the tetrahedral site [ 15 ]. In this way, the major building block of MO would be MgO rather than Al 2 O 3 .…”

“…As the LDH is composed of a mixed metal hydroxide layer with a positive charge (M 2+ 1−x M 3+ x (OH) 2 x+ ) and charge-compensating anions, thermal treatment evaporates the structural hydroxide and anion species to leave only metal oxide crystallites which are interconnected to each other [ 14 ]. In addition to the global structural changes, local crystal deformation of the metal hydroxide layers gives rise to coordination disorder around a metal center; this phenomenon is mediated by the partial migration of the trivalent ion—usually Al 3+ in the MgAl-CO 3 -LDH—from an octahedral site (Oh) to a tetrahedral site (Td), acting as a bridging component between metal oxide crystallites [ 15 ].…”