1. Materials with controlled porosity

2. IUPAC definition of porous materials:
Microporous: < 2 nm
Mesoporous : nm
Macroporous: > 50 nm
Molecular dimension
Shape-selectivity
Molecular sieves

3. porosity is controlled by the crystalline structure
microporous
ZEOLITES
porosity is controlled by the crystalline structure
crystalline aluminosilicates used as catalysts for oil refining, petrolchemistry (e. g. catalytic cracking), and organic synthesis in the production of fine chemicals
MFI
MOR

4. mesoporous SOL-GEL SYNTHESIS
Synthetic approach: use of surfactant in the synthesis batch to form large pores
MESOPORES
AMORPHOUS SILICA WALLS
C. T. Kresge et al., Nature, 1992, 359,

5. This procedure is an example of nanotechnology, because structures of nanometric size are obtained
surfactant molecules self-assembly spontaneously
porosity is controlled by synthesis conditions, e.g. the length of the chain and the possible presence of swelling aromatics

6. M41S* * Mobil materials Temperature: 20-150 °C
Surfactant: cationic (R’3RN+), neutral (EO20–PO70–EO20, RNH2), anionic (ROSO3-)
R = CnH2n+1, n = 8-22
pH: acidic (HCl), basic (NaOH),  7
Surfactant removal: CALCINATION ( °C) EXTRACTION ( < 100 °C)
M41S*
* Mobil materials

7. The symmetry of the mesophase may affect the particles morphology

8. High-resolution microscopy reveals the ordered array of uniform pores

9. The mesophase symmetry may be revealed by X-ray diffraction at low angle
cubic
hexagonal
lamellar
ill-defined

10. The mesoporosity may be revealed by N2 adsorption isotherm
classification of hysteresis loops proposed by De Boer
Adsorption isotherm of nitrogen on MCM-41 with 4.0 nm pores at 77 K

11. Not only silicas…
► other sol-gel oxides (Al2O3, TiO2,…)
► replica materials by casting

12. Catalytic and sensing behavior not dealt with in the present talk.
Ordered mesoporous silicas used as:
catalyst
sensors
hosts for immobilized molecules (enzymes)
hosts for mobile molecules (drug release)
Catalytic and sensing behavior not dealt with in the present talk.

13. Two topics
► formation of active species at the inner surface of pores: functionalization with organic moieties
► deposition of active species on the inner surface of pores: immobilization of enzymes

14. In silica-based materials the surface may be covered by
Silanols (Si-OH)
Si-O-Si bridges
Physisorbed water
► The amount and distribution of these species affect the hydrophobic/hydrophilic properties of the surface
► Si-OH species are reactive functionalities for the incorporation of catalytic active species
D. Brunel, A. Cauvel, F. Di Renzo, F. Fajula, B. Fubini, B. Onida and E. Garrone,
New J. Chem., 24 (2000) 807.

15. Introduction of active species

16. Frequently used alkylsilanes for anchoring molecules
Frequently used alkylsilanes for anchoring molecules. These functional groups can also be used as active catalytic sites by themselves.

17. Organic BASES anchored to MCM-41 surface
Post-synthesis grafting
Brunel et al. Catalysis Today 2629 (2002) 1–14

18. Catalytic cycle during Knoevenagel condensation using MCM-41-grafted primary amine
M. Laspéras, T. Llorett, L. Chaves, I. Rodriguez,
A. Cauvel, D. Brunel, Stud. Surf. Sci. Catal. 108 (1997) 75.

19. co-condensation route to surface tailoring:
R-Si(OR)3
(RO)4Si + R
remove
template
H2O+
surfactant

20. Organic ACID anchored to MESOPOROUS SILICA surface
X = -SO3H, -COOH
MOLECULAR SPECIES WHICH MAY BE INVESTIGATED BY VIBRATIONAL SPECTROSCOPY (VIBRATIONAL MODES!)

21. Infrared spectroscopy
Dosage of ammonia: study of the acidity and accessibility of –COOH species
7COOH-SBA-15 outgasssed at 473 K
- C=O stretching mode peak decreases
two band appears at 1550 cm-1 and
1407 cm-1, due respectively to
the asymmetric (νas) and symmetric
(νs) stretching vibration of the
carboxylate group –COO-
Sonia Fiorilli et al., submitted, 2004

22. NH3 strips the proton from carboxylate anion –COO- and
Infrared spectroscopy
Dosages of ammonia: study of the acidity and accessibility of –COOH species
difference spectra with respect to background.
- a broad absorsorption due to NH4+ deformation vibration at around 1456 cm-1
NH3 strips the proton from
–COOH to give
carboxylate anion –COO- and
ammonium ion (NH4+)
Sonia Fiorilli et al., submitted, 2004

23. ► formation of active species at the inner surface of pores: functionalization with organic moieties
► deposition of active species on the inner surface of pores: immobilization of enzymes

24. Horseradish peroxidase
S. Inagaki and coworkers, Chem. Mater. 2000, 12,
Toyota Central R&D Laboratories
Horseradish peroxidase

25. 1,2-diaminobenzene oxidation, TBHP as oxidant

26. ► the loading efficiency shows clear correlation with the porosity of silica support;
► when the average mesopores size just matches the molecular diameters of the enzyme, immobilized HRP exhibits the peak activity in an organic solvent and the best stability;
► enzyme immobilization with FSM-16 or MCM-41 having a suitable mesopore size would be useful for and
applicable to industrial processes and other applications,
especially certain environmentally useful enzymatic reactions such as the decomposition of lignin or dioxins.

27. A. Corma, Chemical Review, 1997, Vol. 97, No. 6
A. Taguchi, F. Schüth, Microporous and Mesoporous Materials, 77 (2005), available on web

28. The end