Studies On The Assembly And Inclusion Properties Of Carboxymethyl-β-cyclodextrin Intercalated Layered Double Hydroxides

Based on the conception of intercalation chemistry,with layered double hydroxides(LDHs) chosen as host material and carboxymethyl-β-cyclodextrinas(CMCD) as guest species,CMCD intercalated LDHs powder and film materials have been successfully synthesized by the use of ion-exchange and in situ crystallization techniques,respectively.The chiral adsorption of 1-phenyl-1,2-ethanediol (PED) by CMCD-LDH has been studied in detail.The enantioselective adsorption mechanism for the CMCD-LDH has been systematically investigated.We also investigate the inclusion of dodecylbenzene(DDB) by CMCD-LDH as well as the double-confinement effect on the included guest.The CMCD-LDH powder sample was obtained by the method of ion exchange.Characterization using XRD,FT-IR,ICP and TG-DTA techniques confirm the supramolecular structure of CMCD-LDH,and the corresponding structural model are presented.CMCD molecule is accommodated as monolayer arrangement with its cavity axis perpendicular to the LDH host layer and carboxymethyl groups on the narrow side of the cyclodextrin cavity attaching to the LDH surface.Both electrostatic attraction and hydrogen bonding are involved in the host-guest interactions.Moreover,the enantioselective adsorption of racemic PED by CMCD-LDH has been investigated by chiral HPLC.The adsorption isotherms of enantioselective as well as non-enantioselective adsorption of PED by CMCD-LDH have been investigated,and it was found that the Langmuir-Frendlich and Frendlich model can be respectively used to describe the two different adsorptions satisfactorily. Furthermore,the intraparticle diffusion model is successfully validated in this work.The film of carboxymethyl-β-cyclodextrin-intercalated Zn-Al layered double hydroxide(CMCD-LDH) has been prepared by in situ crystallization on a porous anodic alumina/aluminum(PAO/Al) substrate. The structure of the CMCD-LDH film was investigated by XRD,FT-IR, SEM and EDX.CMCD adopt a monolayer arrangement with its cavity axis perpendicular to the LDH layer and the ab-face of LDH microcrystals is predominantly perpendicular with respect to the substrate. This film can be used to enantioselectively separate racemic PED.The adsorption isotherms of enantioselective as well as non-enantioselective adsorption of PED by CMCD-LDH film have been investigated,and it was found that the Langmuir-Frendlich and Frendlich model can be respectively used to describe the two different adsorptions satisfactorily. Furthermore,the plane sheet diffusion model is successfully validated in this work.As the structured CMCD-LDH film is conveniently used and exhibits high enantioselective adsorption ratio compared with the powder material,it can be expected that this film could be feasibly applied in the field of industrial chiral adsorption and separation.A novel nanocage derived from CMCD-LDH has been demonstrated in this work,whose gates can be controlled by the process of swelling/drying the CMCD-LDH.Dodecylbenzene(DDB) as the guest molecule has been incorporated into the nanocage,through two different routes:the intercalation-inclusion method andthe inclusion-intercalation method.For the convenience of using this nanocage as absorbent and storage vessel for neutral guest,films of the resulting composite materials (CMCD-LDH) were fabricated by the method of solvent evaporation on glass substrates.The structure,chemical composition,morphology and physicochemical properties of the materials were characterized by XRD, TG-MS,elemental analysis,SEM,fluorescence spectroscopy and time-resolved fluorescence decay measurements.Moreover,the combined confinement effect of both the LDHs layers and cyclodextrin cavity on the optical properties of encaged guest has been investigated. Compared with the confinement effect produced from cyclodextrin only, this double-confinement imposes stronger confinements on the mobilities of the guest molecule,which causes the blue shift in fluorescence spectrum and prolongs the decay time of the guest.Consequently,the elucidation of the enantioselective adsorption mechanism as well as the illustration of the inclusion process and the host-guest interaction of CMCD-LDH,affords a convincing and useful theoretical foundation for the application of CMCD-LDH as chiral adsorbents,synergistic agents and storage vessels.