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In this study, free-radical polymerisation inside MCM-41 mesopores was examined to expose a construction route for a temperature-responsive switchable polymer–silica nanohybrid material with well-defined porosity. Herein, we introduced a vinyl monomer (N-isopropyl acrylamide), a cross-linker, and an AIBN initiator into the palladium nanoparticle incorporated MCM-41 pore channels using the wet-impregnation method followed by in situ radical polymerisation. The structural properties of the synthesised PNIPAM–PdNP–MCM-41 catalyst were analysed by various sophisticated analytical techniques. The temperature switchable nanohybrid catalyst was used to reduce carbonyl compounds to their corresponding alcohols. The catalyst showed high catalytic efficiency and robustness in an aqueous medium at 25 °C. Moreover, the system's polymer layer remarkably boosted catalytic selectivity and activity for carbonyl compound reduction as compared to other controlled catalysts. The suggested switchable system can be employed as a temperature-controllable heterogeneous catalyst and highlights a substitute technique to counter the methodical insufficiency in switchable supported molecular catalytic system production.

International audience; Highly monodispersed silica nanoparticles (SiNPs) were synthesised using a fluorinated surfactant, HOCH2CH(CF3)CO2H, and its efficiency was compared with efficiencies of five other surfactants. The size of the SiNPs (∼50–200 nm) was controlled by controlling the surfactant amount. The short alkyl-chain fluoro surfactant was found to be more efficient at producing monodispersed SiNPs than its long alkyl-chain fluoro or non-fluorinated surfactant counterparts.

Stimuli-responsive organic-inorganic mesoporous silica hybrid materials have attracted significant attention because of their tuning properties that enable a wide range of applications. The characteristic properties of nanohybrids can be further manipulated by various external stimuli, such as pH, temperature, light, magnetic and electrical fields, redox, and enzymes. The tuning of the properties leads to the alternating nature of the hybrids and exhibition of on-off behaviour under different stimulations. Stimuli-responsive mesoporous silica hybrid materials find applications in diverse fields, such as catalysis, drug delivery, gene delivery, sensing, and imaging. In this review, we discuss the synthetic techniques, physicochemical properties, and behaviour of various responsive materials, along with the potential applications of mesoporous silica hybrids in a wide range of fields. In addition, the scope and future development of stimuli-responsive mesoporous silica hybrids are examined in detail.

The design of switchable hybrid systems to control the catalytic activity using stimuli-responsive polymers have a great significance in the precise manipulation of the oxidation reactions. Herein, we proposed a novel and facile approach for the synthesis of a dual-responsive silica nanohybrid catalyst by combining the temperature-responsive poly N-isopropylacrylamide (PNIPAM) and pH-responsive poly 4-vinylpyridine (P(4-VP)) with MCM-41 as integrated support via free radical polymerization. The prepared switchable material was decorated with silver nanoparticles (AgNPs) through the co-reduction approach. The X-ray photoelectron spectroscopy (XPS) data confirmed the existence of AgNPs in the zero oxidation state while the dynamic light scattering (DLS) measurements revealed that the material exists in maximum swelling confirmation at low temperature (

Herein, we develop an efficient and novel catalytic system, i.e. silver nanoparticles (AgNPs) incorporated mesoporous silica SBA‒15/copolymer hybrid material, for selective oxidation of different alcohols to aldehydes or ketones under ‘mild’ conditions. The copolymer of N,-N-dimethylaminoethyl methacrylate and 2-hydroxyethyl acrylate (p(DMAEMA-co-HEA)) was used to graft the surface-modified SBA‒15 (MS) using free radical polymerization method. Then AgNPs were decorated on the polymer grafted SBA‒15. The dual (thermal and pH) responsive behaviors of the AgNPs/p(DMAEMA-co-HEA)/MS catalyst were investigated using the dynamic light scattering technique. The lower critical solution temperature (LCST) of the copolymer was found to be approximately 30–35 °C. The catalytic activity of AgNPs/p(DMAEMA-co-HEA)/MS was investigated for the selective oxidation of different alcohols to aldehydes or ketones. The conversion of catalytic products and selectivity were calculated using gas chromatographic techniques, whereas the molecular structure of products was determined using 1H and 13C nuclear magnetic resonance spectroscopy. The catalyst showed improved catalytic activity toward the oxidation of alcohols to aldehydes in aqueous medium below LCST and pKa value (7–7.5) of the copolymer. The selectivity toward the corresponding aldehyde was found to be significantly high (99%). The main advantages of the hybrid catalyst as compared to existing catalysts include outstanding alcohol conversion (up to 99%), short reaction time (1 h), small necessary amount of catalyst (6 mg), and performing the catalytic conversion at room temperature using water as a solvent, which are highly beneficial for organic conversion under mild reaction conditions.

Mesoporous silica SBA-15 was modified with Schiff bases of 2-hydroxybenzaldehyde (2-HB) or 4-hydroxybenzaldehyde (4-HB), after silanization with (3-aminopropyl)triethoxysilane (3-APTES). The obtained heterogeneous Schiff bases (2-HB-SBA-15 and 4-HB-SBA-15) were analysed using sophisticated characterization techniques to disclose their successful formation and physico-chemical properties. Whether chelation plays any key role in the selective adsorption of metal ions was evaluated using aqueous mixtures containing Mn(II), Co(II), Ni(II), Cu(II), Cr(III), Zn(II), Pb(II) and Cd(II) ions in the pH range 2−6. Both materials exhibited different affinity towards metal ions from the same mixture under various pH conditions. 2-HB-SBA-15 exhibited 100 % selectivity towards Pb(II) ion at pH 2 while the selectivity turned to Cu(II) at higher pH. 4-HB-SBA-15, however, showed an affinity towards Cr(III) and Pb(II) at pH 2 while a distributed selectivity was observed with major portion to Cr(III), Pb(II) and Cu(II) at higher pH conditions. The observed affinity towards a particular metal ion was enhanced when considering the Cr(III), Pb(II) and Cu(II) ions in single and double concentrations in the mixture at pH 5. When analyzing the structure of both organic molecules, 2-HB-SBA-15 has a chelation possibility but 4-HB-SBA-15 has less. The difference in molar adsorption selectivities of the two organically modified mesoporous materials, 2-HB-SBA-15 and 4-HB-SBA-15 clearly indicates the effect of chelation in ligand over selective adsorption of metal ions from aqueous mixtures at identical adsorption conditions.

A pH-responsive poly(methacrylic acid) (PMAA) functionalized SBA-15 nanohybrid has been synthesized via free radical polymerization method. Furthermore, silver nanoparticles (Ag NPs) were impregnated to the polymerized SBA-15-PMAA by using co-reduction approach. The resultant AgNPs-SBA-15-PMAA catalyst was used for the reduction of various dyes using NaBH4 as the reducing agent. Compared to all other synthesized catalysts in this work as well as with the existing catalyst in the literatures, our synthesized AgNPs-SBA-15-PMAA catalyst showed significantly higher activity for the reduction of dyes due to the synergistic effect of Ag NPs and pH responsive PMAA. The effects of reaction parameters such as pH, amount of nanoparticles, and NaBH4 concentrations were also studied in detail to obtain the optimized condition for the reaction. The overall catalytic performance showed that the reduction reaction is more efficient under low pH. In addition, the catalyst could be re-used without obvious losses of catalytic activity at least more than five cycles.

Functionalised mesoporous silica SBA-15 was designed to exhibit dual responsive behaviour by grafting poly [2- (N, N-dimethylamino) ethyl methacrylate] (PDMAEMA) via free radical polymerisation. For this, the SBA-15 was modified by 3-(trimethoxy silyl) propyl methacrylate (TMSPM) for allowing methacrylate functionality on the mesoporous surface for free radicle polymerisation (m-SBA-15). Temperature and pH responsive PDMAEMA were grafted on the well-ordered rod-like m-SBA-15. Monometallic palladium (Pd) nanoparticles (NPs) were then incorporated in the pre-synthesised m-SBA-15/PDMAEMA. The morphology and structure of resulting materials were characterised by powder X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, and nitrogen adsorption-desorption isotherms. The dual stimuli-responsive behaviour of the hybrid material was monitored by dynamic light scattering measurement. Synthesised materials were tested for their dual stimuli (pH and temperature)-responsive catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It was observed that the catalytic activity of the Pd/m-SBA-15/PDMAEMA catalyst was significantly higher at a given pH and temperature than any of SBA-15 only without using PDMAEMA and Pd NPs, m-SBA-15 grafted with PDMAEMA without Pd NPs, or Pd NPs incorporated m-SBA-15 without grafting PDMAEMA.

MCM-41 was functionalized with thermoresponsive poly (N-isopropyl acrylamide) (p-NIPAM) by free radical polymerization. The surface of the p-NIPAM-coated on MCM-41 (MCM-41/p-NIPAM) nanocatalyst was decorated with bimetallic Ag–Pd nanoparticles for catalytic applications. The nanocatalyst was characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption/desorption analysis, thermograviametric analysis (TGA), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray (EDX) spectroscopy, x-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS). The thermoresponsive behavior of the synthesized nanocatalyst was analyzed by UV–vis spectroscopy (UV–vis) and DLS analysis. The distribution of bimetallic nanoparticles and their compositions on the polymer-coated mesoporous silica surface were investigated by EDX mapping analysis. The specific surface area was characterized by nitrogen adsorption/desorption analysis. The nanocatalyst was tested for the catalytic reduction of benzaldehyde by UV–vis analysis. Interestingly, the bimetallic nanoparticle-supported MCM-41/p-NIPAM nanocatalyst showed higher activity compared to the other counterparts. In addition, the nanocatalyst showed thermoresponsive behavior at different temperatures and could be recycled for consecutive five cycles with minimal loss in activity. This study is expected to open promising probability for the use of the above material for a range of catalytic applications.