Synthesis of b‐Oriented TS‐1 Films on Chitosan‐Modified α‐Al₂O₃ Substrates

Abstract

Zeolite films have attracted much attention from the scientific community because of their potential applications as selective membranes, chemical sensors, and microelectronic devices. [1][2][3] The performance of permeable films can be greatly improved by controlling the crystal orientation on the substrate surface. [4,5] Thus far, significant progress in directing the crystal orientation on the substrate surface has been made for LTA and UTD-1, especially for MFI-type zeolite films.[6]Wang and Yan reported a highly b-oriented pure silica MFI film on porous stainless steel synthesized by in situ crystallization. [7] They could manipulate the crystal orientation by using an in situ hydrothermal reaction method, and control over the orientation on the substrate surface was achieved by simply changing the composition of the synthesis solution. By using the seeded growth method, Tsapatsis and co-workers successfully created b-oriented siliceous zeolite ZSM-5 membranes with molecular recognition ability on porous alumina substrates. [8,9] Highly selective and permeable membranes were obtained based on a good understanding of both crystal growth and interaction between crystal grains and the substrate surface.[5] The separation factor of para-to ortho-xylene isomers could be up to several hundred while keeping the permeance of para-xylene high. Based on induction by surface matrices, Yoon and co-workers could pack silicalite-1 crystals of a uniform size over a glass surface in a desired orientation.[10]Compared with Al-ZSM-5 and silicalite-1, TS-1 zeolite possesses a variety of special features. In addition to the molecular sieving effect, TS-1 films catalyze oxidative reactions as well, including selective oxidation of alcohols, [11] epoxidation of alkenes, [12] hydroxylation of aromatics, [13] oxyfunctionalization of n-hexane to hexanols and hexanones, [14,15] and photocatalytic oxidation. [16] Obviously, the availability of highly oriented TS-1 films, especially along the b-axis, will trigger their application in innovative materials, microreactors, and even microelectronic devices. [17][18][19] TS-1 zeolite has the same tetrahedral framework as Al-ZSM-5 and silicalite-1 MFI zeolites. However, the introduction of Ti atoms into the framework requires a substantially longer hydrothermal reaction time. Several research groups have synthesized TS-1 monoliths, [20,21] films, [6,22,23] and membranes. [16,24] However, all the TS-1 films and membranes reported are randomly oriented, except in the work of Lee et al. who used poly(ethylene oxide) (PEO) as a template to direct the oriented growth of TS-1 films on glass.[6] To date, we have found no published work on the synthesis of b-oriented TS-1 films on porous substrates. Here, we report a new synthesis strategy for manufacturing b-oriented TS-1 films on porous a-Al 2 O 3 substrates. Chitosan will serve as the structure-directing matrix to induce the orientation of the crystal grains with the b-axes perpendicular to the substrate surface. Finally, the performance of the s...

Selective Defect‐Patching of Zeolite Membranes Using Chemical Liquid Deposition at Organic/Aqueous Interfaces

“…[1][2][3] With the development of synthesis strategies and post-thermal treatments, zeolite membranes have been successfully utilized in separation, [4] catalytic reaction, [5] and optoelectronic devices. [6] A defectfree zeolite membrane can principally distinguish components in gaseous and liquid mixtures due to its molecular sieving effect and the mutual interactions between the molecules and the zeolitic pores.…”

Cubes of Zeolite A with an Amorphous Core

“…Chitosan, containing abundant amino and hydroxy groups, was used as the orientation-directing matrix for the synthesis of boriented TS-1 films. [10] Glutaraldehyde-crosslinked chitosan (GA-CS) hydrogels were recently used to control zeolite crystallization, and thus zeolite A and Y nanocrystals were synthesized. [11] It is noted that chitosan is only soluble in an acidic aqueous solution, and the resulting chitosan solution turns into a polymer hydrogel when an alkaline solution penetrates through the gel.…”

Zeolite Thin Films and Membranes: From Fundamental to Applications

“…Recently, it was reported that continuous b -oriented MFI zeolite fi lms can be synthesized by microwaveassisted in situ crystallization and that a certain nuclei concentration at the aging stage is necessary [ 45 ]. b -Oriented TS-1 fi lms could be grown on chitosan-modifi ed α-Al 2 O 3 substrates [ 46 ].…”