Investigation Of Anion-exchangeable Hybrid Mesoscopic Materials

It is well known that studies on materials, especially oninorganic materials, with anion-exchange capacity are rarelymade. The most commonly used anion exchangers areanion-exchange resins, which is organically based. Layereddouble hydroxides are one class of inorganic materials withanion-exchange property. As for mesoporous materials, whichhave larger open framework than conventional zeolites, thereare only a few reported examples on anion-exchange property.So far, there is no silica-based mesoporous material withanion-exchange capacity reported in literature to ourknowledge. On the other hand, the development of hybridmesoporous organosilicas has been greatly made. Becauseinorganic-organic hybrid mesoporous materials are easilyintroduced various functional groups, they attract muchattention in these years. Recently, a new kinds of ordered silica-based inorganic-organichybrid mesoscopic materials were reported, which are metalcation-mediated bridged and therefore designed as MBH. MBH — Ⅰ —Jilin University Ph. D. Thesiscontains metal ions (Cd2+, Zn2+ and Ni2+) as an integral part of theirbackbone, which have strong coulombic interaction with anionicsurfactant and are coordinated by functional ligands of3-aminopropyltriethoxysilane (aptes, H2NCH2CH2CH2Si(OEt)3). Thesiloxanes (aptes) connect with one another by condensation to form thewhole framework. Thus, metal ions, organic functional ligands, andsilica are uniformly distributed in the framework of MBH. In thisinvestigation, we find a remarkable anion-exchange capacity of MBH,which results from the presence of metal ions in the framework. Due tothe soft alkyl chains in the framework, MBH is prone to change itsstructure to accommodate anions with various sizes. Therefore bothsmall anions and large anions could be easily exchanged.Correspondingly, reversible phase transitions take place along withanion exchange process in MBH. Notably, its anion-exchange capacity(3.9mmol·g-1) is higher than that of some well- knownanion-exchangers (such as anion-exchange resins, and LDH). This isthe first example of silica-based inorganic-organic hybrid mesoscopicmaterial with high anion-exchange capacity. However, to fulfill the need of an anion-exchanger that can beused in practical application, the stability of MBH has to beeffectively improved. In the previous reports, the metal ions andsiloxanes in the framework of MBH connect to each other via weakcoordinate interactions. We proposed that the anion-exchangeproperty of MBH results from the presence of metal ions in theframework. Especially, the siloxane (aptes) used in this case is anunidentate ligand, which almost has the weakest coordinated abilityamong all kinds of ligands. This means that the metal ions in the — Ⅱ —Abstractframework of MBH are easy to leach during repeated ion-exchangeprocedures and the anion-exchange capability will graduallydecrease. In this work, a new siloxane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (H2NCH2CH2HNCH2CH2CH2Si(OMe)3,aeaptms), is used to prepared stable MBH instead of aptes and theobtained product is designated MBH-S. Because the two aminegroups in aeaptms can chelate the metal ion in the framework, themetal ions in MBH-S are so resistant to leaching that theanion-exchange capacity of MBH-S are almost unchanged even afterrepeated anion-exchange process. Moreover, MBH-S has awell-defined two-dimensional hexagonal mesostructure rather thanin the case of MBH, where only a poorly ordered two-dimensionalhexagonal phase could be obtained. Particularly, MBH-S shows aremarkable higher anion-exchange capacity (5.4mmol·g-1) andhydrothermal stability than MBH. Some functional anion moleculescan be easily exchanged into MBH-S. For example, luminescentmolecule tri(8-hyd...