Research On Intercalation Reaction And Exfoliation Behavior Of Layered Inorganic Compounds

Inorganic layered compounds are important functional materials. They have wide application in adsorption, conduction, separation, catalysis and so on. The intercalation and exfoliation technique of layered inorganic compounds have attracted increasing attention due to their particular structure characteristic. Generally, the intercalation reactions take place between guest species and host materials through an ion exchange mechanism, which overcomes the interaction force between the interlayers. Based on the host-guest interaction involving ionic bonding, hydrogen bonding, Van der Waals forces and so on, the intercalated compounds can be obtained. Up to now, a series of inorgano-organic or inorgano-inorganic hybrid materials with supermolecule structure have been synthesized by the intercalation reaction. On the other hand, the intercalation of the guest species into the interlayer will cause in a swelling of the inorganic layered materials. The exfoliation of layered inorganic materials is occurred when the high degree of swelling driven by intercalation of the guest species. Once a layered compound is disintegrated into its elementary layers, the resulting individual layer can be regarded as a new class of nanoscale material, which has been called nanosheet because of its two-dimensional morphology and extremely small thickness around 1 nm. The delaminated single nanosheet has novel properties, such as the surface effect, the volume effect, the quantum effect and the macroscopic quantum tunneling effect. Therefore, a number of nanostructured materials included nanoplate, nanofiber, nanotube, functional film, and so forth can be fabricated with these funcationl nanosheets.This paper mainly consists of two sections, review and experiments. The structure characteristic, class and the intercalation and exfoliation reactions of layered inorganic materials were reviewed, particually for typical birnessite-type manganese oxides with negative host layer and layered double hydroxide (LDHs) with positive host layer. Meanwhile, the application fileds of layered inorganic materials were also discussed in the first section (Charpter 1). The intercalation of aminoundecanoic acid (H₂N (CH₂)₁₀COOH, abbreviated as AUA) species into the interlayers of birnessite-type manganese oxides and LDHs materials and their exfoliation in water were described in the experiments section (Charpter 2, and 3). The conventional intercalation and exfoliation reactions of layered manganese oxides and LDHs are in organic solvent such as organic ammino, formamide and so on with strong causticity yet. Therefore, it is disadvantage in environment and difficult for the further application of the delaminated nanosheets. With emphasis on the insights above mentioned, we successfully carried out a novel exfoliation process of layered compounds via the electrostatic repulsive force between guest species of AUA and inorganic host layers. In this paper, we reaserched the new exfoliation technique of inorganic layered compounds with different electricity and mainly consisted of the following two parts:(1) The Intercalation and Exfoliation Reaction of Inorganic Layered Materials with Negative ChargesNa-type birnessite manganese oxide (Na-BirMO) was firstly synthesized by the hydrothermal technique. H-type manganese oxide (H-BirMO) was obtained by an acid exchange mechanism from Na-BirMO. By controlling the pH value of the solution, AUA (H₂N (CH₂)₁₀COOH) was converted into cationic aminoundecanoic acid (⁺H₃N (CH₂)₁₀COOH). Birnessite manganese oxide intercalated with AUA (BirMO-AUA) was obtained in different concentration of amion acide by an ion-exchange reaction. Then the delamination behavior of BirMO-AUA material in basic solution was studied. The results showed that when the amount of AUA added was 15 fold of the exchangeable capacity for H-BirMO, BirMO-AUA material could be formed through an ion-exchange reaction for 5 days. BirMO-AUA material was soaked in a solution (pH=12) for 1 day. The amino cationic (⁺H₃N (CH₂)₁₀COOH) in the interlayer was transfered into anionic (H₂N (CH₂)₁₀COO^-) in basic solution. Because of the electrostatic repulsive force between guest AUA species and inorganic manganese oxide host layers, BirMO-AUA material was successfully delaminated into their nanosheets in water. The materials obtained by intercalation and exfoliation reactions were confirmed by XRD, TGA-DSC, IR, AFM, and TEM analyses.(2) The Intercalation and Exfoliation Behavior of Inorganic Layered Materials with Positive ChargeNi/Fe layered double hydroxides (Ni/Fe LDHs) with aminoundecanoic acid (AUA) as pillared species (Ni/Fe LDHs-AUA) was prepared in different pH of solution by a co-precipitation method, and its delamination behavior was also studied in an acid solution. The results showed that Ni/Fe LDHs-AUA with H₂N (CH₂)₁₀COO^- as guest species was obtained at pH ca. 10.4 with the molar ratio of AUA to Ni amount of 2.75. The basal spacing of Ni/Fe LDHs-AUA was 1.72 nm. The amino anionic (H₂N (CH₂)₁₀COO^-) in the interlayer was transfered into cationic (⁺H₃N (CH₂)₁₀COOH) in acid solution. Because of the electrostatic repulsive force between guest AUA species and inorganic LDH host layers, Ni/Fe LDHs-AUA material was successfully delaminated into their nanosheets in water by a novel host-guest repulsive interaction process. The materials obtained by intercalation and exfoliation reactions were confirmed by XRD, TGA-DSC, IR, AFM, and TEM analyses.