Thioether‐bridged Mesoporous Organosilicas: Mesophase Transformations Induced by the Bridged Organosilane Precursor

Abstract

The achievement of structural control over thioether‐bridged mesoporous organosilicas is reported. The mesoporous materials have been synthesized by co‐condensation of bis[3‐(triethoxysilyl)propyl]tetrasulfide (TESPTS) and tetramethoxysilane (TMOS) in acetic acid/sodium acetate buffer solution (HAc–NaAc, pH 4.4), using the nonionic surfactant P123 as a template. The mesostructure of the material is mainly controlled by the molar ratio of TESPTS/TMOS in the initial gel mixture. A mesophase transformation, progressing from a highly ordered 2D hexagonal structure via a vesiclelike structure to a mesostructured cellular foam, can be clearly observed when the molar ratio of TESPTS/TMOS is increased in increments. Solid‐state NMR results show that TESPTS is not completely hydrolyzed and condensed at the applied buffer conditions. At low concentrations, the unhydrolyzed TESPTS can penetrate into the core of the surfactant micelles and change the packing parameter of the P123 surfactant. Above a certain concentration, the TESPTS can form a microemulsion with P123 surfactant molecules. Therefore, the vesiclelike structure or cellular foam structure can be synthesized by simply controlling the molar ratio of TESPTS/TMOS. This approach provides a novel method for the facile synthesis of organic–inorganic hybrid materials with a controllable mesostructure under mild synthetic conditions.

Periodic Mesoporous Organosilica Materials: Self‐Assembly of Carbamothioic Acid‐Bridged Organosilane Precursors

“…Triblock copolymer poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) block copolymer ((EO) 20 (PO) 70 (EO) 20 ; Pluronic 123 (P123); MW = 5800) was purchased from Sigma-Aldrich (USA). The silica sources tetraethyl orthosilicate (TEOS), (3-isocyanatopropyl)triethoxysilane (IPTES), (3-mercaptopropyl)triethoxysilane (MPTES), and other reagents were procured from the Nanjing Chemical Reagent Company (China).…”

“…Only Olkhovyk and Jaroniec [19] have reported the successful incorporation of an isocyanurate (ICS) ring with three trimethoxysilyl groups through flexible propyl chains into the silica framework, and when samples were synthesized with a higher percentage of ICS (50 %), a wormhole-like structure was still observed in the TEM image. Li et al [20] introduced a thioether-bridged group to the mesoporous organosilica, Abstract: A new series of carbamothioic acid-containing periodic mesoporous organosilica (PMO) materials has been synthesized by a direct cocondensation method, in which an organosilica precursor N,S-bis [3-(triethoxysilyl)propyl]-carbamothioic acid (MI) is treated with tetraethyl orthosilicate (TEOS), and the nonionic surfactant Pluronic 123 (P123) is used as a template under acidic conditions in the presence of inorganic additives. Moreover, the synthesis of the PMO material consisting of the MI precursor without TEOS has been realized.…”

Swelling‐Agent‐Free Synthesis of Siliceous and Functional Mesocellular Foam‐Like Mesophases by Using a Carboxy‐Terminated Triblock Copolymer

“…[48] The structure of SH-MCF is quite different from that of the thiol-functionalized material prepared by applying the P123/TMB microemulsion in formamide. [32] On the other hand, the hysteresis loops for CA-MCF and I-MCF also close at the same relative pressure but they are not typical H1-type or H2-type. These characteristics may be associated with a more open MCF-like pore structure in these materials.…”

“…One of the reasons may be associated to possible destabilization of the P123/TMB microemulsion by the organosilanes in the synthesis mixture. Therefore, except for limited cases (e.g., thiol-functionalized and thioether-bridged MCF materials), [31,32] post-synthesis grafting instead of cocondensation is often chosen to prepare functional MCF materials. [26][27][28] Very recently, preparation of MCF materials without using swelling agents has been reported.…”

Functionalized periodic mesoporous organosilicas: Hierarchical and chiral materials

“…Compared with the commonly used strongly acidic or basic synthesis media, a mildly acidic buffer medium is beneficial for the incorporation of acid-or basesensitive organic groups into mesoporous materials; however, it has been rarely used for the synthesis of mesoporous organosilicas. Under weakly acidic conditions (acetic acid/ sodium acetate buffer solution, HOAc-NaOAc, pH = 4.4), thioether-bridged mesoporous organosilicas with multimodal porous structure were synthesized by co-condensation of tetramethoxysilane (TMOS) and bis[3-(triethoxysilyl) propyl]tetrasulfide (TESPTS) using the block copolymer P123 as template [21]. We found that the structure transformation from a highly ordered 2-D hexagonal structure to a vesicle-like structure and then to a mesostructured cellular foam can be fulfilled by simply tuning the molar ratio of TESPTS/TMOS as shown in Figure 2.…”