RESUMEN
A silica zeolite (RWZ-1) with a very high framework density (FD) was synthesized from highly crystalline natural layered silicate magadiite, bridging the gap between the two research areas of zeolites and dense silica polymorphs. Magadiite was topotactically converted into a 3D framework through two-step heat treatment. The resulting structure had a 1D micropore system of channel-like cavities with an FD of 22.1 Si atoms/1000â Å3 . This value is higher than those of all other silica zeolites reported so far, approaching those of silica polymorphs (tridymite (22.6) and α-quartz (26.5)). RWZ-1 is a slight negative thermal expansion material with thermal properties approaching those of dense silica polymorphs. It contributes to the creation of a new field on microporous high-density silica/silicates. Synergistic interactions are expected between the micropores with molecular sieving properties and the dense layer-like building units with different topologies which provide thermal and mechanical stabilities.
RESUMEN
Acid treatment of crystalline silicates is a facile method of creating pores for the preparation of crystalline silica-based microporous materials, but its success depends on the acid treatment conditions and both the composition and crystallinity of the starting silicates. Here, europium silicate Eu-AV-9 containing Na+, K+, and Eu3+ ions was treated with acetic acid for 1 d or 14 d to synthesize microporous silicate with high Eu loading by the selective leaching of K+ and Na+ from the silicate. The acid-treated Eu-AV-9 had both crystallinity and microporosity capable of adsorbing CO2, while the adsorption of Ar was very low. In addition, the values of both micropore volume and BET area of acid-treated samples increased when the time of acid treatment was increased. This result was attributed to the formation of structural defects caused by eliminating Eu in Eu-AV-9 over time of acid treatment.
RESUMEN
The interlayer condensation of layered silicates is a unique method for synthesizing zeolites and is effective for the introduction of metal species into platy zeolite frameworks. Layered silicate RUB-15 is a useful starting material because metal ions can be introduced between the layers and zeolite frameworks (all-silica SOD-type zeolite; silica sodalite) can be formed through interlayer condensation. In this study, Cu ions were intercalated into layered silicate RUB-15, and metal Cu nanoparticles were formed in the nanovoids of silica sodalite by a simple heat treatment in an inert atmosphere. Both interlayer condensation and the reduction of Cu2+ ions were confirmed by in situ XRD analysis performed during the heat treatment. The residual interlayer tetramethylammonium ions played two roles: the control of stacking sequence in the interlayer condensation and the reduction of Cu2+ ions. The formed Cu nanoparticles were stable in air atmosphere because of their confinement in the nanovoids of the sodalite frameworks.
RESUMEN
We report silicate nanoscrolls composed of only SiO4 tetrahedra with crystalline walls for the first time in this study. The procedure consists of the intercalation of layered octosilicate with dioctadecyldimethylammonium bromide ((C18)2DMABr) and the subsequent solvothermal treatment of the intercalated material in heptane. The walls of the obtained nanoscrolls are crystalline, which originates from layer crystallinity in the pristine silicate. The direction of rolling up is fixed at the a- or b-axis of the silicate based on the electron diffraction patterns of the nanoscrolls. Desorption of (C18)2DMABr, which is present in addition to (C18)2DMA cations, from the interlayer during solvothermal treatment is likely related to the nanoscrolling process. Although the yield of nanoscrolls is low, these findings will lead to the re-estimation of many layered silicates intercalated with long-chain alkylammonium compounds as precursors for silicate nanoscrolls with crystalline walls.
RESUMEN
Silica sodalite was obtained using topotactic conversion of layered silicate RUB-15 through stepwise processes that consisted of the control of stacking sequence of the layers, interlayer condensation by refluxing, and elimination of intercalated guest species. The interlayer condensation of RUB-15, in which acetic acid was pre-intercalated between the layers to control the stacking sequence, afforded a sodalite framework containing organic guest species by refluxing in N-methylformamide (NMF). The pre-intercalated acetic acid molecules were largely replaced with NMF. This formation process of silica sodalite containing large amounts of intercalated organic guest species is in clear contrast to the previously reported process that used direct calcination of an intercalation compound of layered RUB-15 accommodating acetic acid between the layers. Calcination of the condensed product provided sodalite with fewer defects than the directly calcined product, thus indicating the advantage of the stepwise process. The method reported here is useful for the preparation of pure silica sodalite with relatively low defects and plate-like morphology.
RESUMEN
A single-crystalline macroporous layered silicate was obtained for the first time. Firstly, UTL-type zeolite with macropores was prepared hydrothermally under the presence of acetylene black as a macropore template and the subsequent calcination to remove the template. Double four-membered ring (d4r) units in the UTL framework were selectively dissolved to yield a layered silicate with macropores. Intercalation of tetrabutylammonium ions into the macroporous layered silicate is accelerated if compared with that into the same silicate without macropores, indicating the effectiveness of macropores due to easy diffusion. The layered silicate with macropores was converted into PCR-type zeolite with macropores, a hierarchically micro- and macroporous material, through interlayer condensation.
