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    Inclusion of alkali carboxylate salts at the two-dimensional space of layered alkali titanate via carboxylic acids intercalation
    (2020-11-01)
    Maluangnont, Tosapol
    ;
    Sooknoi, Tawan
    The formation of organic salts trapped at the two-dimensional (2D) space of layered solids is typically not well-defined, lacks stoichiometric relation, and depends on the chain length of the organic moieties. In contrast to this conventional salt intercalation, we report herein the inclusion of alkali carboxylates by intercalation of carboxylic acids to lepidocrocite-type alkali titanate microcrystals. The intercalated organic content of 15.9–37.0 ​wt% is high for a solid with low specific surface area (3 ​m<sup>2</sup>/g). A small interlayer expansion (~0.7 ​Å) was observed with decanoic, palmitic, and sebacic acids which form the trapped carboxylate salts. Meanwhile, acetic acid produced a typical protonic titanate as with mineral acids. The inclusion of carboxylate anion and the accompanying carboxylic acid spectator was proven by their characteristics IR vibrations. Using K<inf>0.8</inf>M<inf>y</inf>Ti<inf>2-y</inf>O<inf>4</inf> (M ​= ​Zn, Ni, Co, Fe, Mg, Li), we showed that the host-guest, acid-base interaction influenced the thermal decomposition of the intercalated species. A correlation was observed between the partial charge at the O atom (normalized by the intercalate content) vs the decomposition temperature of the trapped species. The formation of sodium carboxylates similarly occurred with sodium titanate nanotubes.
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    Surface and interlayer base-characters in lepidocrocite titanate: The adsorption and intercalation of fatty acid
    (2016-06-01)
    Maluangnont, Tosapol
    ;
    Arsa, Pornanan
    ;
    Limsakul, Kanokporn
    ;
    Juntarachairot, Songsit
    ;
    Sangsan, Saithong
    While layered double hydroxides (LDHs) with positively-charged sheets are well known as basic materials, layered metal oxides having negatively-charged sheets are not generally recognized so. In this article, the surface and interlayer base-characters of O<sup>2-</sup> sites in layered metal oxides have been demonstrated, taking lepidocrocite titanate K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> as an example. The low basicity (0.04 mmol CO<inf>2</inf>/g) and low desorption temperature (50-300 °C) shown by CO<inf>2</inf>- TPD suggests that O<sup>2-</sup> sites at the external surfaces is weakly basic, while those at the interlayer space are mostly inaccessible to CO<inf>2</inf>. The liquid-phase adsorption study, however, revealed the uptake as much as 37% by mass of the bulky palmitic acid (C<inf>16</inf> acid). The accompanying expansion of the interlayer space by ~0.1 nm was detected by PXRD and TEM. In an opposite manner to the external surfaces, the interlayer O<sup>2-</sup> sites can deprotonate palmitic acid, forming the salt (i.e., potassium palmitate) occluded between the sheets. Two types of basic sites are proposed based on ultrafast <sup>1</sup>H MAS NMR and FTIR results. The interlayer basic sites in lepidocrocite titanate leads to an application of this material as a selective and stable two-dimensional (2D) basic catalyst, as demonstrated by the ketonization of palmitic acid into palmitone (C<inf>31</inf> ketone). Tuning of the catalytic activity by varying the type of metal (Zn, Mg, and Li) substituting at Ti<sup>IV</sup> sites was also illustrated.