Novel polyoxometalate (POM)-grafting mesoporous hybrid silicas, XW11/MHS (X = P, Si) and TBAPW11Si2/MHS, have been prepared respectively by co-condensation and post-synthesis routes based on the employment of Keggin-type monovacant XW11 or a Si-substituted compound TBAPW11Si2 as POM precursors. Upon characterization of the samples by FT-IR, XRD, ICP-AES, TEM and N2 adsorption–desorption measurement, it was found that Keggin units were retained perfectly in ordered hexagonal mesopore channels with SBA-15 architecture and immobilized by covalent linkages on the mesopore wall. These materials, especially the co-condensed samples, exhibited stable and reversible photochromic properties under UV irradiation although no special organic component was supplied additionally as an electron donor. An investigation of the photochromism revealed that the photochromic response depended on the centre atom of the POM species (i.e., the redox potential of the POM), the content of the POM and the synthetic route of the sample, while the bleaching process was correlated not only to the redox potential but also to the pore size of the sample. The photochromic mechanism was also studied in detail by cyclic voltammetry, ESR, FT-IR and XPS techniques. It was found that the remaining P123 template acted as a reducing agent and was oxidized during the photochromic process accompanied by the reduction of the POM to heteropolyblue. Thus, a close contact between the POM and the remaining P123 chain in the sample is necessary. Low close-contact degree results in poor photochromic behavior of the post-synthesized sample and impregnated samples.

Thermosensitive nanocomposites based on mesoporous SBA-15 silica and poly(N-isopropylacrylamide) (PNIPAAm) have been synthesized via in situ polymerization of monomers deposited on the pore walls. The introduction of monomers and polymerization were examined by Fourier-transform infrared spectroscopy (FT-IR). The structures and properties of the composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption−desorption, thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). It was demonstrated that the polymerization initiated by free radicals occurred within the channels of SBA-15, and the polymer layer fixed by the penetration of polymer chains into the complementary pores was formed on the pore walls. The distribution and uniformity of the polymer coating along the channel walls depend on the content of polymer in the composite, which can be controlled by altering the monomer/SBA-15 mass ratio in the synthesis. Higher polymer content gives rise to mesopores plugged partly but does not alter the ordered hexagonal mesostructure of the material. Moreover, the thermosensitive property of PNIPAAm is retained in the naonocomposites, which have a lower critical solution temperature (LCST) close to that of pure PNIPAAm.

Novel polyoxometalate (POM)-functionalized mesoporous hybrid silicas, SiW11/MHS, have been synthesized by a co-condensation route and employment of Keggin-type monovacant SiW11 as POM precursor in the presence of block copolymer EO20PO70EO20 (P123) under acidic conditions. This synthesis allows a bulky inorganic metal–oxygen cluster to be grafted directly on the surface of ordered mesoporous silica with SBA-15 architecture. The as-obtained SiW11/MHS samples were characterized by FT-IR, UV-vis/DRS, 29Si CP MAS NMR, XRD, TEM, N2 adsorption–desorption measurement and elemental analysis. These materials possess not only hexagonal mesoscopic order and homogeneous pore sizes, but also intact Keggin units immobilized in channels by covalent linkages with the mesopore walls. This covalent bond results from the reaction of TEOS with SiW11, in which Si species are inserted into the vacancy of lacunary SiW11 to form Si–O–W bonds and an intermediate SiW11Si2, by which the POM is bound onto the framework of mesoporous silica. Investigation of the synthesis conditions indicates that the quality of the product depends on the initial SiW11 concentration, the aging temperature of the sample and the prehydrolysis time of TEOS. A higher SiW11 concentration can enhance the loading of SiW11 to a certain extent, but leads to a disordered structure owing to the salting-out effect of POM if the prehydrolysis time is not long enough. Increased aging temperature is favorable for the formation of ordered mesostructures. However, hydrolysis of Si–O–W bonds and consequent removal of SiW11 from the silica framework also occur at such temperatures. Finally, the chemical linkage between the POM and the surface of mesoporous silica is further confirmed by the higher stability of the hybrid materials in water-leaching experiments compared to the impregnated samples, suggesting that the hybrid materials and the strategy for synthesizing these materials are significant for the acquisition of supported POM catalysts of high efficiency and practicability in applications using polar solvents as media.

Novel polyoxometalate (POM)-grafting mesoporous hybrid silicas, XW11/MHS (X = P, Si) and TBAPW11Si2/MHS, have been prepared respectively by co-condensation and post-synthesis routes based on the employment of Keggin-type monovacant XW11 or a Si-substituted compound TBAPW11Si2 as POM precursors. Upon characterization of the samples by FT-IR, XRD, ICP-AES, TEM and N2 adsorption–desorption measurement, it was found that Keggin units were retained perfectly in ordered hexagonal mesopore channels with SBA-15 architecture and immobilized by covalent linkages on the mesopore wall. These materials, especially the co-condensed samples, exhibited stable and reversible photochromic properties under UV irradiation although no special organic component was supplied additionally as an electron donor. An investigation of the photochromism revealed that the photochromic response depended on the centre atom of the POM species (i.e., the redox potential of the POM), the content of the POM and the synthetic route of the sample, while the bleaching process was correlated not only to the redox potential but also to the pore size of the sample. The photochromic mechanism was also studied in detail by cyclic voltammetry, ESR, FT-IR and XPS techniques. It was found that the remaining P123 template acted as a reducing agent and was oxidized during the photochromic process accompanied by the reduction of the POM to heteropolyblue. Thus, a close contact between the POM and the remaining P123 chain in the sample is necessary. Low close-contact degree results in poor photochromic behavior of the post-synthesized sample and impregnated samples.

Novel polyoxometalate (POM)-functionalized mesoporous hybrid silicas, SiW11/MHS, have been synthesized by a co-condensation route and employment of Keggin-type monovacant SiW11 as POM precursor in the presence of block copolymer EO20PO70EO20 (P123) under acidic conditions. This synthesis allows a bulky inorganic metal–oxygen cluster to be grafted directly on the surface of ordered mesoporous silica with SBA-15 architecture. The as-obtained SiW11/MHS samples were characterized by FT-IR, UV-vis/DRS, 29Si CP MAS NMR, XRD, TEM, N2 adsorption–desorption measurement and elemental analysis. These materials possess not only hexagonal mesoscopic order and homogeneous pore sizes, but also intact Keggin units immobilized in channels by covalent linkages with the mesopore walls. This covalent bond results from the reaction of TEOS with SiW11, in which Si species are inserted into the vacancy of lacunary SiW11 to form Si–O–W bonds and an intermediate SiW11Si2, by which the POM is bound onto the framework of mesoporous silica. Investigation of the synthesis conditions indicates that the quality of the product depends on the initial SiW11 concentration, the aging temperature of the sample and the prehydrolysis time of TEOS. A higher SiW11 concentration can enhance the loading of SiW11 to a certain extent, but leads to a disordered structure owing to the salting-out effect of POM if the prehydrolysis time is not long enough. Increased aging temperature is favorable for the formation of ordered mesostructures. However, hydrolysis of Si–O–W bonds and consequent removal of SiW11 from the silica framework also occur at such temperatures. Finally, the chemical linkage between the POM and the surface of mesoporous silica is further confirmed by the higher stability of the hybrid materials in water-leaching experiments compared to the impregnated samples, suggesting that the hybrid materials and the strategy for synthesizing these materials are significant for the acquisition of supported POM catalysts of high efficiency and practicability in applications using polar solvents as media.