•Porous stannosilicate beads have been prepared using porous anion-exchange resin as hard template.•Sn species in the beads can be highly accessible via the continuous large-mesopore system.•Thanks to their bead format, the catalysts could be extremely straightforward separated from the reaction media.Porous anion-exchange resin was introduced as hard template to hydrothermally synthesize tin-containing mesoporous silica beads (Sn-MesoSB) with the diameter in the range of 0.3–0.9 mm. The characterization results showed the existence of continuous large-mesopore channels and tetrahedral tin species in the bead samples. Sn-MesoSB proved to exhibit high catalytic performances in the Baeyer-Villiger oxidation of adamantanone by using H2O2 as green oxidant, mainly attributed to the enhancement of the access to the catalytic tin sites through the continuous large-mesopore channels. Under the optimized experimental conditions, the conversion of adamantanone approached ca.100% in dioxane for 3 h at 90 °C. Notably, the bead format of such material could be remained during the catalysis procedure, which favors to the straightforward separation from the reaction system without any means of filtration or centrifugation. Working as a liquid-phase heterogeneous catalyst, this is pretty appealing to potential industrial applications. The catalyst was robust and can be reused up to 5 times without significant loss of activity and selectivity, pointing out that the tin species incorporated in the framework possessed high stability. Moreover, the bead material exhibits activity and selectivity in the Baeyer-Villiger oxidations with a broad range of substrates.Mesoporous stannosilicate beads are highly active for Baeyer-Villiger oxidations with H2O2 and can be easily separated from the reaction solution.Download high-res image (150KB)Download full-size image

An optical simulation is adopted to examine the effects of the pore channels with different sizes and architectures on the ability of light absorption in photocatalysts. The simulation results are utilized to guide the synthesis of a novel porous graphitic carbon nitride (g-C3N4) material in bead form, using millimeter-scale porous SiO2 beads as a template. The obtained g-C3N4 beads possess a unique porous architecture with 3D interconnected and continuous meso/macropore channels at 30–90 nm in size, which is identical to the simulation result. Compared with pristine g-C3N4, the prepared material exhibits significantly enhanced visible light-induced catalytic performances for H2 evolution (8 times), photoreduction of nitrobenzene (3 times) and degradations of rhodamine B (4 times), methyl orange (2 times) and phenol (3 times). The unique pores and skeleton structures not only promote light penetration inside the material and light absorption at the edge of pore channels, but also improve mass transfer and inhibit the recombination of photogenerated electrons and holes. Moreover, this optical simulation approach could be adopted to guide the synthesis of other porous photocatalysts, and to verify their light absorption and infiltration properties in photocatalysis.

Mesoporous silica spheres with hierarchical hollow/nano structure (MSSH-H/N) have been successfully prepared by a template-guided approach, in which cetyltrimethyl ammonium bromide (CTAB) and polystyrene (PS) emulsion was used as the template of mesopores and hollow core, respectively. A consecutive template mechanism and the formation of the hierarchical hollow/nano structure were proposed on basis of the combined characterizations including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction patterns (XRD) and nitrogen sorption analysis, which showed that the hierarchical structure is composed of mesoporous hollow SiO2 spheres and discrete mesoporous SiO2 nanoparticles coating on the shell. Ibuprofen (IBU) was chosen as a drug model in delivery and release experiments, and these MSSH-H/N samples exhibited higher drug loading capacity, desired low initial IBU release rate and typical two-phase drug release behavior compared with conventional single-structure (single-shelled) hollow mesoporous silica spheres due to their unique hierarchical hollow/nano structure.

•Fabrication of core–shell nanoreactor with multiple ultrasmall nano-Fe2O3 cores and mesoporous SiO2 shell.•Thermally stable, movable and fully accessible nano-Fe2O3 particles.•A stable Fenton-like catalyst immune to iron leaching in the presence of hydrogen peroxide.A new and facile method has been developed in this study for the fabrication of multicore–shell type nanoreactor. On the basis of the characterization results from X-ray diffraction, scanning and transmission electron microscopy, Raman and X-ray photoelectron spectroscopy, and N2 adsorption/desorption analysis, it has been proved that ultrasmall iron oxide particles (∼10 nm) were firstly encapsulated in the matrix of polystyrene spheres via a microemulsion-polymerization-assisted approach, and then were introduced as movable cores inside mesoporous SiO2 shell. The size of iron oxide particles retained almost unchanged even during the calcination procedure in air, indicating high thermal stability, due to the protection of polystyrene matrix. The obtained nanoreactor was applied as an effective heterogeneous catalyst for total oxidation of methylene blue with aqueous hydrogen peroxide and the ultrasmall iron oxide particles within the hollow interior proved to be active sites for such reaction. Mesoporous SiO2 shell not only protects the nanometer-sized iron oxide particles against leaching from the nanoreactor into reaction solution, but also enriches the reactant molecules around multiple ultrasmall iron oxide cores and thus enhances the catalytic activity and reaction rate. Importantly, the nanoreactor can be easily recovered by external magnetic field and reused in successive catalytic cycles without significant loss of activity.Magnetic core–shell nanoreactor with multiple cores of ultrasmall Fe2O3 nanoparticles (∼10 nm) and mesoporous SiO2 shell was fabricated, in which the nano-Fe2O3 cores are thermally stable, movable and fully accessible. The nanoreactor not only showed excellent activity in Fenton-like reaction towards total degradation of methylene blue, but also can be straightforward recovered by external magnetic field and reused in successive catalytic cycles without loss of activity.

Mesoporous titanosilicate nanoparticles with a size of 40 to 75 nm (Nano-Ti-MCM-41) were hydrothermally synthesized from a titanosilicate (TiSil) solution with cetyltrimethylammonium bromide (CTAB) as the template and with a cationic polymer as the size-controlling agent. The particle size is proposed to be controlled by adjusting the size of TiSil-CTA+ micelles influenced by the charge interaction between negatively charged titanosilicate and polymer cationic ions during the formation of TiSil-CTA+ micelles. The presence of n-hexane and hydrogen peroxide in the preparation process proved to favor a well-ordered mesostructure in these nanoparticles: the mesostructure became disordered without using hexane and hydrogen peroxide although the size of mesoporous titanosilicate particles remained in the nanometer scale. The characterization results showed that Nano-Ti-MCM-41 possesses hierarchical porosity (bimodal mesopores) and an ordered mesoporous structure and that the titanium species are predominately located in tetrahedral framework positions. Nano-Ti-MCM-41 is a highly active catalyst for the epoxidation of cyclohexene with hydrogen peroxide, and displayed higher turnover numbers (TONs) based on the cyclohexene conversions and higher selectivity ratio between cyclohexene epoxide and 1,2-cyclohexanediol compared with traditional Ti-MCM-41 prepared without the cationic polymer. The improved catalytic performances are mainly ascribed to the decrease in the particle size of Ti-MCM-41, resulting in the enhanced accessibility of the reactants to the catalytic Ti species via the shorter channels of Nano-Ti-MCM-41 and in the shorter residence time of cyclohexene epoxide in the mesopores of the nanoparticles. Importantly, the mesoporous titanosilicate nanoparticles are stable catalysts immune to titanium leaching, suggesting their good recyclability potential in the epoxidation with aqueous H2O2.

Mesoporous TiO2/Carbon beads have been prepared via a facile impregnation-carbonization approach, in which a porous anion-exchange resin and K2TiO(C2O4)2 were used as hard carbon and titanium source, respectively. Characterization results reveal that the self-assembled composites have disordered mesostructure, uniform mesopores, large pore volumes, and high surface areas. The mesopore walls are composed of amorphous carbon, well-dispersed and confined anatase or rutile nanoparticles. Some anatase phase of TiO2 was transformed to rutile phase via an increase of carbonization temperature or repeated impregnation of the resin with TiO(C2O4)22− species. X-ray photoelectron spectroscopy, carbon, hydrogen, and nitrogen element analysis, and thermal gravity analysis results indicate the doping of carbon into the TiO2 lattice and strong interaction between carbon and TiO2 nanoparticles. A synergy effect by carbon and TiO2 in the composites has been discussed herein on the degradation of methyl orange under visible light. The dye removal process involves adsorption of the dye from water by the mesopores in the composites, followed by photodegradation on the separated dye-loaded catalysts. Mesopores allow full access of the dye molecules to the surface of TiO2 nanoparticles. Importantly, the bead format of such composite enables their straightforward separation from the reaction mixture in their application as a liquid-phase heterogeneous photodegradation catalyst.

•A new approach is applied to prepare a titanosilicate composite containing mesoporous shell and zeolite-large-crystal core.•Such composite is active in the epoxidation of bulky substrates.•The catalyst could be straightforwardly separated from the reaction system, thanks to the large scale in the particle size.Porous titanosilicate composite with a core/shell structure and tetrahedral Ti species was synthesized by one-step process in fluoride medium, in which a mixture of small organic ammonium salt and cationic polymer was used as template. The composite displayed higher activity than the TS-1 large crystals prepared without cationic polymer in the epoxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide, mainly ascribed to the improved accessibility of reactants to the active sites via the mesopores in the shell. Notably, the composite can be easily separated from the reaction solution thanks to its large crystal format.A novel porous titanosilicate composite composed of a core of TS-1 large crystal and a shell of mesoporous titanosilicate was prepared by one-pot process. The composite proved to be an active catalyst for heterogeneous epoxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide, mainly ascribed to the improved accessibility of reactants to the active sites via the mesopores in the shell. Note that the catalyst can be easily separated from the reaction solution thanks to its large crystal format, which is very attractive for a possible industrial application.