Search

This work demonstrates that using sodium silicate as precursor, hierarchical mesoporous silica (HMS) microspheres with ordered mesochannels and large intra-particulate mesopores can be prepared by partitioned cooperative self-assembly process based on a P123 templated system. The influence of various experimental parameters on mesostructures and particle morphology was investigated, including the ethanol, addition combinations, interval times, synthesis temperatures and hydrothermal treatment temperatures. Importantly, the crucial role of ethanol in shaping the particle morphology and hierarchical mesostructures was identified. The resultant micro-sized HMS microspheres reveal clew-like feature: the ‘yarns’ comprise bundles of ordered mesochannels (1st mode mesopores, ca. 10–15 nm in sizes), while the 2nd mode intra-particulate pores (ca. 20–45 nm in sizes) exist between the intertwined ‘yarns’. For example, a representative HMS microsphere prepared under optimized conditions (6-6 h-4Et5@36H140) shows two modes of mesopores, 12.3 nm and 27.7 nm for the 1st and 2nd mode mesopores, respectively. The spherical particle size is around 1.5 μm. Both the regularity of the 1st mode mesostructure templated by the P123 and well-defined 2nd mode mesostructures can be secured when the hydrothermal treatment (HTT) temperature is controlled at 140 °C, while higher HTT temperature at 160 °C disintegrates the 1st mode mesostructures and thus destroy the meso-orderings. In the release performance tests of indomethacin (IMC) in simulated intestinal fluid (SIF), HMS microspheres with high 2nd mode mesoporosity show higher drug release rate than that with low 2nd mode mesoporosity, while two of them both show higher drug release rate than conventional SBA-15 fibers. This work, as we believe, also represents a new strategy to regulate drug releasing performance by simply tuning the hierarchical mesostructures of HMS and can allow flexible design of IMC/meso-silica formulations.

Based on the simplest TEOS/P123/HCl(aq.) templating system, it is demonstrated in this work that different SBA-15 platelets can be controllably prepared via the partitioned cooperative self-assembly (PCSA) process without using any additives or complicated procedures. Experimental results show that the reduced amounts of TEOS added in the 2nd additions in the PCSA process play a determining role in transforming the SBA-15 platelet morphologies from the plane ones to a unique kind of UFO-shaped ones. The obtained SBA-15 platelets, plane or UFO-shaped ones, are composed of plugged mesochannels aligned in a 2D hexagonal symmetry, with neighboring channels connected by large tunnel holes (intrawall pores). Different platelet morphologies and their evolution were found to be dependent on partitioning conditions (2nd TEOS addition and interval time). A competitive process involving the aggregation of SBA-15 primary particles dictates the formation of SBA-15 particles with different morphologies, meanwhile the UFO-shaped SBA-15 platelets (U-SBA-15P) can be deemed as intermediate ones between rod-like particles and plane platelets. Moreover, upon the release of indometacin (IMC) in simulating intestinal fluid, UFO-shaped SBA-15 platelets show faster drug release performance compared with their plane counterparts or conventional SBA-15 fibers. The larger the protruded areas in UFO-shaped platelets, the higher the release rate will be. This work, as we believe, presents a new strategy to regulate drug releasing performance by simply tuning particle morphologies of SBA-15 platelets and can allow rational design of IMC/meso-silica formulations.

In this work, it is demonstrated that hierarchical mesoporous silica monoliths (HMSMs) with trimodal porosities can be facilely prepared using P123 as structure-directing agent and tetraethoxysilane as precursor. In such HMSMs, classic co-continuous macrostructures with interconnected macropores and smooth isotropic skeletons can be obtained in a tunable way, depending on the synthesis variables, including the amounts of P123 and 1,3,5-trimethylbenzene and acid concentrations. Skeletons feature randomly oriented SBA-15-type primary particles with 2D hexagonally ordered mesochannels largely accessible from bimodal macropores. Co-continuous macropore size of a typical HMSM (P1.2) is 19.6 μm, intra-skeleton macropore of 1.9 μm and mesopore size of 9.9 nm. The BET surface area by N2 sorption and total pore volume by Archimedes principle reach 590 m2 g-1 and 3.56 cm3 g-1, respectively. Based on systematic study on the relationship between synthetic compositions and porous structures, the ternary diagram and formation mechanism of these HMSMs were analyzed.

In this work, hierarchically mesoporous silica (HMS) microspheres with ordered mesochannels and ultra-large intra-particulate pores are for the first time prepared via a ternary nonionic surfactant templating system (TEOS/P123/HCl(aq.)). Several crucial experimental parameters pertaining to the employed partitioned cooperative self-assembly process and their roles in shaping the mesostructures and morphology were investigated. It was found that relatively low synthesis temperatures, optimal at 36 °C, lead to much improved meso-ordering in the 1st mode mesostructures, while partitioned addition combinations of silica precursor ( e.g. , 6/4 combination) at such temperatures show to play an important role in inducing spherical particle morphology. By simply increasing the hydrothermal treatment (HTT) temperature up to 140 °C, enhanced porosity together with ultra-large intra-particulate pores can be obtained without compromising meso-orderings, depending mainly on the HTT induced mesostructural transformation process. Higher HTT temperature causes the fragmentation in the 1st mode mesostructures and disappearance of meso-orderings. The resultant micro-sized HMS spheres reveal certain clew-like features: the ‘yarns’ comprise bundles of ordered mesochannels (1st mode mesopores, ca. 8–12 nm), while the 2nd mode intra-particulate pores ( ca. 33–128 nm in sizes) exist between the intertwined ‘yarns’. Such HMS microspheres with tunable porous structures might find some interesting applications in chromatographic separations and controlled delivery, etc.

In this work, a facile and controllable multi-templating approach based on a solo nonionic surfactant P123 and peroxotitanic acid (PTA) was reported for the preparation of bimodal meso-mesoporous titania (BMM-TiO 2 ) with high surface area (150–243 m 2 g −1 ), high pore volume (0.3–0.6 cm 3 g −1 ), large mesopore sizes spanning from 8 to 16 nm (BJH pore size), and high & tunable crystallinity (Anatase or Anatase + Rutile). The BMM-TiO 2 was shown to be a homogeneous ‘mixture’ of two series of wormhole mesostructures with two modes of mesopore sizes that depend on both the contents of P123 and synthetic conditions. The formation of BMM structures was proposed to arise from both the formation of differentiated micellar structures of P123 (dual soft-templating) and their subsequent different mesostructural shrinkages driven by prolonged drying process ( i.e. , 100 °C for 12 h) in the presence of PTA. The low-temperature crystallization behaviours of PTA, unusual hard-templating effect of P123 and its carbon derivatives (3rd fold templating), large mesopores relative to the surrounding TiO 2 crystals are all believed to be responsible for the high thermal stability of the obtained BMM-TiO 2 . To our knowledge, it is for the first time reported that P123 plays such multiple templating roles (three folds in this work) in the preparation of meso-TiO 2 , not to mention that P123 was also confirmed to be a prerequisite for the formation bi-crystalline BMM-TiO 2 . In the photodegradation test of Rhodamine B in water by UV irradiation, other than the high surface area and synergistic effect between anatase and rutile phases, the BMM structures were also found to be advantageous to enhance the photocatalytic properties of mesoporous TiO 2 .

This work reports a simple two-step synthesis method for the preparation of SBA-15 microspheres using poly (vinyl alcohol) (PVA) as a solo additive based on classic P123 templating system. Both spherical particle morphology and long-range 2D-hexagonally ordered mesostructures can be achieved. It is demonstrated that the particle sizes and mesopore sizes of SBA-15 microspheres can be facilely tuned by varying synthesis parameters, including standstill temperatures, hydrothermal treatment temperatures, etc. It is proposed that the addition of PVA in combination with the standstill step at low temperatures (1st step) suppress the rapid growth and aggregation behavior of silicate/P123 primary particles and favor their aggregation into spherical SBA-15 particles, while the meso-ordering and particle uniformity are improved by stirring step at relatively high temperatures (2nd step). This two-step synthesis method based on the PVA-assisted TEOS/P123/HCl(aq.) templating system thus represents a novel and simple pathway to preparing SBA-15 microspheres. Instead of HCl, other mineral acids, including sulfuric acid and nitric acid, can also be used to prepare SBA-15 microspheres. Via sulfuric acid catalyzed system, the carbonization of P123 also enables more direct preparation of mesoporous carbon microspheres.

With bi-continuous cubic mesostructures of Ia3d symmetry and interpenetrating cylindrical pore system, KIT-6 type mesoporous silica has attracted a great deal of interest for its application in various areas. Unfortunately, so far the reports on the tuning of mesostructures or other physical properties are rather limited due to the restrictions on synthetic conditions. In this work, one previously reported partitioned cooperative self-assembly (PCSA) process was applied for the synthesis of KIT-6s with good meso-orderings, allowing facile manipulation over mesostructures, e.g. the mesopore size, pore wall thickness and particle sizes. By simply partitioning the addition of tetraethoxysilane (TEOS), the mesopore sizes of KIT-6s can be varied between around 8 and 10 nm (KJS). For a given addition combination (1st part of 7.0 g and 2nd part of 3.0 g in total 10.0 g TEOS), the meso-orderings show some improvement with the increase in the interval time from 1 to 5 h. In combination with hydrothermal treatment at high temperatures (e.g. 140 °C), the PCSA process, though not yielding larger mesopore sizes, favors the formation of KIT-6 with higher meso-orderings than that of conventional method derived KIT-6. Moreover, the particle sizes of KIT-6s can be significantly reduced from sub-millimeter to several microns via the PCSA process. The PCSA process thus represents a simple but effective way to manipulate the mesostructures and particle sizes of KIT-6s.