[Show abstract][Hide abstract] ABSTRACT: Silica-titania materials with improved catalytic performances were elaborated as mesoporous microparticles by combining sol-gel and spray-drying processes with the self-assembly properties of α-chitin nanorods acting as bio-templates. Three different synthesis’ approaches are discussed, leading to materials with varied textural and chemical characteristics studied by SEM, N2 volumetry, TEM, XPS and DR-UV techniques. The use of water or ethanol as initial solvent for the chitin nanorods’ suspensions, as well as the mixing conditions of the precursors show to have a significant impact on the final properties. Materials of specific surface areas of up to 590 m2.g-1 and porous volumes of up to 0.84 mL.g-1, with low surface Si/Ti ratio could be disclosed. Properties were further investigated by employing the silica-titania materials as heterogeneous catalysts for the sulfoxidation of bulky model compounds. The location of Ti active sites at the pore surface has been maximized and allows for improved productivity.
[Show abstract][Hide abstract] ABSTRACT: The Density Functional Theory based method with periodic boundary conditions and addition of a pair wised empirical correction for the London dispersion energy (DFT-D) was used to study the NMR quadrupolar interaction (coupling constant CQ and asymmetry parameter ηQ) of 14N nuclei in a homologous series of tetra-n-alkylammonium halides (CxH2x+1)4N+X- (x =1 - 4), (X = Br, I). These 14N quadrupolar properties are particularly challenging for the DFT-D computations because of their very high sensitivity to tiny geometrical changes, being negligible for other spectral property calculations as for example NMR 14N chemical shift. In addition, the polarization effect of the halide anions in the considered crystal mesophases combines with interactions of van der Waals type between cations and anions. Comparing experimental and theoretical results, the performance of PBE-D functional is preferred than that of B3LYP-D. The results demonstrated a good transferability of the empirical parameters in the London dispersion formula for crystals with two or more carbons per alkyl group in the cations, whereas the empirical corrections in the tetramethylammonium halides appeared inappropriate for the quadrupolar interaction calculation. This is attributed to the enhanced cation-anion attraction, which causes a strong polarization at the nitrogen site. Our results demonstrated that the 14N CQ and ηQ are predominantly affected by the molecular structures of the cations, adapted to the symmetry of the anion arrangements. The long-range polarization effect of the surrounding anions at the target nitrogen site becomes more important for cells with lower spatial symmetry.
The Journal of Physical Chemistry A 04/2014; 118(19). DOI:10.1021/jp502858n · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Local order in as-synthesised zeolites templated by tetraalkylammonium cations is proven from solid-state (14)N NMR and related quadrupolar parameters, opening new perspectives in the study of porous materials.
[Show abstract][Hide abstract] ABSTRACT: Uniaxially anisotropic chitin-silica nanocomposite solids have been obtained thanks to the electric field-induced macroscopic alignment of liquid-crystalline reactive co-suspensions. We demonstrate how chitin nanorods (260 nm long, 23 nm thick) can be aligned upon the application of an a.c. electric field, and within water-ethanol suspensions containing reactive siloxane oligomers (Dh ~ 3 nm). The alignment at the millimeter length scale is monitored by in situ SAXS and polarized light optical microscopy. The composition and state (isotropic, chiral nematic) of the co-suspensions are proven to be determining factors. For nematic phases, the alignment is preserved when the electric field is switched off. Further solvent evaporation induces sol-gel transition, and uniaxially anisotropic chitin-silica nanocomposites are formed after complete drying of the aligned nematic suspensions. Here, the collective response of colloidal mesophases to external electric fields and the subsequent formation of ordered nanocomposite solids would represent a new opportunity for materials design.
[Show abstract][Hide abstract] ABSTRACT: In this tutorial review we intend to give an overview of the potential of NMR spectroscopy, and in particular solid-state NMR, in characterising micelle-templated mesoporous materials. Different topics are covered including the study of formation mechanisms, the characterisation of structures, textures, surfaces and interfaces, functionalisation, dynamic properties and structure-reactivity correlations. Some selected examples illustrate the variety of information provided by this spectroscopy. Particular attention is paid to recent technological and/or methodological developments.
Chemical Society Reviews 11/2012; 42(9). DOI:10.1039/c2cs35368g · 30.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mesoporous silica–titania materials of tunable composition and texture, which present a high catalytic activity in the mild oxidation of sulfur compounds, have been obtained by combining the spray-drying process with the colloidal self-assembly of a-chitin nanorods (biopolymer acting as a template) and organo-metallic oligomers. The quest for synthetic routes leading to mesoporous silica materials bearing titania has been launched since the discovery that Ti containing zeolites such as TS-1 and b-Ti were efficient catalysts for the oxidation of a variety of organic compounds. 1 Due to their limited accessibility for large molecules, strategies for the design of mesoporous silica–titania materials have been developed, such as the direct synthesis of ordered mesoporous materials (e.g. Ti-MCM-41, Ti-MCM-48), 2 the grafting of Ti species onto meso-porous silicas 3 and both hydrolytic 4 and non-hydrolytic 5 sol–gel synthesis routes, which permitted to widen the application spectrum considerably. These materials show promising results for the mild oxidation of bulky molecules. 6 Yet, their synthesis relies on tedious procedures (use of a glove box, dry solvents, etc.), often requires expensive template materials such as CTAB, and in some cases low final Ti loadings are obtained. Bio-inspired templating techniques using biopolymers are valuable strategies that open up the way for alternative syntheses 7 and thus responding directly to the needs of Green Chemistry. 8 The ambition behind this is the transcription of the natural textural traits within the newly formed material. 9 A novel and general route for the formation of biopolymer– oxide nano-composites from sol–gel chemistry and colloidal self-assembly involving a-chitin nano-rods has recently been proposed. 10 The mesoporous silica obtained from these nano-composites showed a high modularity in the textural proper-ties. 11 Using chitin as a template provides the additional benefit of being purified from renewable resources, i.e. industrial wastes from shrimp fisheries. Recently, sol–gel chemistry has been combined with spray-drying processes to form new alumino-silicate catalysts. 12 Spray-drying is indeed an interesting process adapted to large-scale production in a continuous regime. Moreover, spray-drying allows the quenching of metastable states by fast solvent evaporation and solidification, whilst offering oppor-tunities to fine-tune the mesoporosity and chemical composi-tion of the resulting solid. 12,13 Herein, we describe for the first time the synthesis of mesoporous silica–titania materials using a-chitin-nanorods as a natural template, by exploiting the self-assembly proper-ties of these nanoparticles 14 associated with sol–gel chemis-try. 10,11 We demonstrate that textural properties (surface area, pore volume) of the synthesized materials can easily be tuned by varying the volume fraction of chitin particles added during the synthesis. Additionally, Si/Ti molar ratios can be adjusted. These materials have proven to be efficient catalysts for the oxidation of sulphur-containing compounds using hydrogen peroxide as a mild oxidation agent. The catalytic output of the performed reactions can perfectly be controlled by tuning the textural properties of the silica–titania material. The silica–titania catalysts are prepared by mixing first an ethanolic suspension of siloxane oligomers (B3 nm) with variable amounts of the titanium monomer precursor Ti(O i Pr) 2 (acac) 2 (Scheme 1).z The results presented here cor-respond to Si/Ti molar ratios from 19 to 70. An aqueous suspension of chitin nanorods (L = 260 AE 80 nm Â D = 23 AE 3 nm) is subsequently introduced, and the resulting sol is exchanged with ethanol. Chitin-oxide microparticles are then formed by spray-drying the ethanolic solution with a variable chitin volume fraction, f CHI . And the final mesoporous samples are obtained by calcination. Dense particles with micrometer diameters (2.2 to 2.8 mm on average, see S2.3, ESIw) are obtained. Their surface roughness increases with the chitin content (Fig. 1a and c), in agreement with former results for chitin–silica nano-composites. 10 The electron-clear struc-tures observed in TEM reveal the presence of elongated pores Scheme 1 Synthesis of silica–titania nano-composites.
Chemical Communications 09/2012; 48(48):10648-10650. DOI:10.1039/C2CC35127G · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Silica microspheres encapsulating ibuprofen in separated domains at the nanometre scale are formed by spray-drying and sol-gel processes. A detailed (1)H and (13)C NMR study of these microspheres shows that ibuprofen molecules are mobile and are interacting through hydrogen bonds with other ibuprofen molecules. (1)H magnetisation exchange NMR experiments were employed to characterize the size of the ibuprofen domains at the nanometre scale. These domains are solely formed by ibuprofen, and their diameters are estimated to be ∼40 nm in agreement with TEM observations. The nature and formation of these particular texture and drug dispersion are discussed.
[Show abstract][Hide abstract] ABSTRACT: Isotherms are measured for nitrogen, n-hexane, triethylamine, and water vapor adsorption on silicas of different origins, the surface layers of which contain functional groups of the ≡Si(CH2)2P(O)(OH)2 composition, namely, ethylene- and phenylene-bridged polysilsesquioxane xerogels produced by the sol-gel method, silica microspheres synthesized from tetraethoxysilane in the presence of [CH3(CH2)17N(CH3)3]Br as a template by spray-drying method, and SBA-15 mesoporous silica produced based on tetraethoxysilane using Pluronic 123 as a template. It is shown that all of the samples possess high specific surface areas, while the types of adsorption isotherms and the accessibility of active acidic sites for adsorption interactions with electron-donor molecules depend on the structures of pores and surface layers, which are governed by the methods of synthesis and postsynthesis sample treatment.
[Show abstract][Hide abstract] ABSTRACT: The developed methods using tetraethoxysilane and trifunctional silanes were applied to obtain Fe3O4 magnetic particles that contain amino groups with compositions of ≡Si(CH2)3NH2, ≡Si(CH2)3NH(CH2)2NH2, and [≡Si(CH2)3]2NH. The XRD data show that the nuclei of nanoparticles in the obtained materials preserve the structure of the primary carrier, namely, that of Fe3O4 magnetite. The thermograms show a high thermal stability of the applied surface layers, i.e., their destruction was found to start at temperature above 250°C. The DRIFT spectra indicate the formation of the silica bond framework in the surface layers of nanoparticles and also the existence of hydrogen bonds between amino groups and silanol groups with the participation of water molecules aided. All of the obtained materials exhibit magnetic properties and offer promising application in medicine.
[Show abstract][Hide abstract] ABSTRACT: The sorption properties towards dysprosium(III) ions of three samples of mesoporous silicas functionalized with phosphonic
groups ≡ Si(CH2)2P(O)(OH)2 were studied. It was found that for the sample synthesized by spray-drying using OTAB as a template both sorption and desorption
rate of Dy3+ ions is high, due to the defined porosity of the sorbent. Sorption of Dy3+ ions by bridged silsesquioxane xerogels with disordered structure is significantly hindered by diffusion processes, due to
the chaotic packing of globules. Using a model for the chemical reactions, the composition of dysprosium(III) complexes with
surface phosphonic groups were determined, and their formation constants were calculated. It was shown that xerogels with
higher surface concentration of ligand groups (L), can form complexes DyL3 and DyL4
−. Meanwhile, the sample synthesized by spray-drying method forms only DyL2
+ and DyL3 complexes. For this sample, complexes DyL3 are more stable than for xerogels. So, mesoporous silica derived by spray-drying method, with defined spatial porosity and
relatively low surface concentration complexation groups, is characterized by the best sorption properties towards dysprosium(III)
(adsorption and desorption kinetics, the value of the static sorption capacity).
Journal of Porous Materials 01/2012; DOI:10.1007/s10934-011-9508-3 · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied new mesoporous materials with original properties and obtained from self-assembled chitin–silica nano-composites. Our novel synthesis allows the controlled colloidal assembly of α-chitinnanorods (bundles of elongated chitin monocrystals) and siloxane oligomers. Calcination of nano-composites results in mesoporous silica materials. Their pore volume fraction POR (0–0.52) is strongly correlated to the initial chitin content. Using N2 sorption and TEM data, we identify and characterize primary and secondary textural units related to the imprints of chitin monocrystals (2.5 nm wide) and nanorods (20–30 nm wide) respectively. Primary textural units are preserved over a wide POR range (linear relationship between pore volume and specific surface area). The coating of monocrystals by siloxane oligomers leads to a siloxane network of fractal nature as deduced from complementary SAXS data. Beyond a critical value POR′ estimated near 0.2, the coating is partial, and the porosity becomes more open and connected. At larger scales, the arrangements of secondary textural units result in complex textures and long-range ordering, showing similarities with textural features found in natural materials. We discuss the competition between entropy-driven transitions typical of anisotropic particles and kinetic arrest due to colloidal gelation and inorganic condensation. Finally, a schematic model for texture formation is given.
[Show abstract][Hide abstract] ABSTRACT: We explored the sensitivity of the (14)N quadrupolar interaction toward the characterization of surfactant-oxide interfaces. For the first time, experimental (14)N NMR spectra are recorded, modeled, and compared for three different mesostructured silica (hexagonal p6mm, cubic Ia3d, and lamellar) templated by hexadecyltrimethylammonium cations (CTA(+)). Broad distributions in quadrupolar coupling constant C(Q) are obtained showing differences between phases. In parallel, quantum chemical calculations using the Born-Oppenheimer molecular dynamics in combination with DFT have been successfully undertaken in a time scale of 25-32 ps to better understand the experimental results. From the two simulated models (CTA(+) alone vs CTA(+) in interaction with a D4R(-) silicate oligomer), we evidenced the relative effect of fast conformational variations and of intermolecular interactions on the time-averaged quadrupolar parameters. (14)N relaxation and (13)C CSA NMR data are also briefly presented and discussed. Our approach opens new directions for studying a wide range of mesostructured materials.
The Journal of Physical Chemistry C 09/2011; 115(39-39):19293-19302. DOI:10.1021/jp206567q · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Materials based on ureidopyrimidinone (UPY) dimers and Adenine (A) / Thymine (T) derivatives were synthesized and characterized by advanced solid state NMR (Nuclear Magnetic Resonance) techniques. Silylated UPY molecules were used as model compounds, leading to structured organic-inorganic materials after hydrolysis and condensation processes (sol-gel reactions). High resolution 1H solid state NMR has been extensively used for the in-depth description of the H-bond networks, including very fast MAS (Magic Angle Spinning) experiments at very high field and DQ (double quantum) recoupling experiments. The chemical nature of the organic-inorganic interface has been illuminated by such techniques. In, particular, it has been demonstrated that H-bond networks were preserved during sol-gel reactions and were comparable to those observed in the UPY crystalline precursors.
[Show abstract][Hide abstract] ABSTRACT: A new family of chitin-silica nanocomposites has been synthesized by using a versatile colloid-based combination of self-assembly and sol-gel chemistry (see picture). Various textures and morphologies can be obtained by adjusting the evaporation-based processes or by applying external fields. After calcination, textures and birefringence are preserved in the resulting mesoporous silicas.
[Show abstract][Hide abstract] ABSTRACT: The characterization of the organization of matter at different length scales is one of the main features in the field of mesostructured materials. Here, SAXS, solid-state multinuclear (29Si, 1H) MAS NMR spectra and one-dimensional 1H spin diffusion MAS NMR experiments have been used to characterize the structure and the copolymer−siloxane interfaces of monolithic hybrid organic−inorganic membranes. The membranes were prepared by cohydrolysis of organically modified alkoxysilanes (methyltriethoxysilane (MTES) and dimethyldimethoxysilane (DMDES)) with tetraethylorthosilicate (TEOS) and using a triblock copolymer PEO-PPO-PEO as templating agent. After careful drying, a cubic Im3m̅ mesostructure is obtained. Variations in the composition of the hybrid membrane have been found to affect the adsorption of water at the copolymer−siloxane interface as well as the spatial distribution of propylene oxide (PO), ethylene oxide (EO), and siloxane domains in the final mesostructures. In that sense, the modulation of the polarity of the interfaces by simply adjusting the nature and quantity of organically modified alkoxides seems to be a promising way for the control of the final mesostructures
The Journal of Physical Chemistry C 06/2010; 114(27):11730-11740. DOI:10.1021/jp101652a · 4.77 Impact Factor