Inorganic-organic hybrid materials through post-synthesis modification: Impact of the treatment with azides on the mesopore structure.

Miriam Keppeler,Jürgen Holzbock,Nicola Hüsing,Johanna Akbarzadeh,Herwig Peterlik

doi:10.3762/bjnano.2.52

Miriam Keppeler, Jürgen Holzbock + Show 3 more

Open Access

https://doi.org/10.3762/bjnano.2.52

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Abstract

Hybrid, hierarchically organized, monolithic silica gels, comprising periodically arranged mesopores and a cellular macroscopic network, have been prepared through a co-condensation reaction of tetrakis(2-hydroxyethyl)orthosilicate with chloromethyl-trimethoxysilane or 3-(chloropropyl)-triethoxysilane. Subsequent conversion of the chloro groups into azido groups, by nucleophilic substitution with NaN3 in N,N-dimethylformamide, was conducted upon preservation of the monolithic structure. However, treatment with NaN3 had a strong influence on the structure in the mesoporous regime, with changes such as an increase of mesopore diameter, pore volume and lattice constants, as well as a concomitant decrease of the pore wall thickness, as confirmed by small angle X-ray scattering, transmission electron microscopy, and nitrogen sorption analysis. Similar effects were observed for unmodified silica gels by simple ageing in azide-containing media, whether a relatively small or a sterically demanding counter ion (Na+ or (H3C)4N+) was used. The structural modification did not seem to depend greatly on whether an organic aprotic solvent (N,N-dimethylformamide, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone) or a protic solvent that can form hydrogen bonds, such as water, was used.

Highlights

Inorganic–organic hybrid materials with tailored porosity on several length scales are of interest for a variety of applications, such as separation, adsorption, catalysis, energy storage, etc., due to the benefits arising from each pore size regime, e.g., rapid mass transport through macropores combined with selectivity provided by meso- or micropores
For ordered mesoporous materials, whose syntheses are based on block copolymers such ethylene oxide (EO)x–propylene oxide (PO)y–ethylene oxide (EO)x, this can be achieved by variation of the length of the EO or PO blocks, by increasing the synthesis temperature or by the addition of inorganic salts [6,9,13]
Pure silica gels were kept for 3 d at 60 °C in solutions of NaN3 in different solvents ranging from N,Ndimethylformamide (DMF), 1,1,3,3-tetramethylurea (TMU), 1,3-dimethyl-2-imidazolidinone (DMI) to H2O

Summary

Introduction

Inorganic–organic hybrid materials with tailored porosity on several length scales are of interest for a variety of applications, such as separation, adsorption, catalysis, energy storage, etc., due to the benefits arising from each pore size regime, e.g., rapid mass transport through macropores combined with selectivity provided by meso- or micropores. Nucleophilic substitution of chloroalkyl-modified silica monoliths to azide-containing monoliths (SiO2–(CH2)1,3–Cl → SiO2–(CH2)1,3–N3) was conducted in a saturated solution of NaN3 in DMF on monolithic silica gels that had been treated with trimethylchlorosilane (Figure 1).

Results

Conclusion