Studies on functionalized mesoporous materials: part 2. Characterization of sulphonated inorganic–organic composite materials based on mesoporous MCM-41

Abstract

The sulphonation of organic–inorganic composite materials was performed both by the sulphuric and chlorosulphonic acids. Applying IR spectroscopy, low temperature nitrogen adsorption/desorption (isotherms BET), thermogravimetric measurements and technique of competitive adsorption of toluene and water it was shown that the degree of residual organic modifier grafting, hydrophobicity, surface and volume properties (pore size distribution, pore volume) strongly depends on the nature, amount of sulphonation agent. Strong acidic media could results in partial destruction of organic modifier layer of composite material. Treatment of silylized materials in 20-fold excess of sulfuric acid results in formation of hydrophilic phase. The competitive adsorption of toluene and water data demonstrates the increase in quantity of the adsorbed water from 30 mg/g for MCM-41 to 110–280 mg/g for sulphonated materials. This results in reduction of the Hydrophobicity Index from 5.00 for MCM-41 to 0.3–0.9 for mesoporous material sulphonated by sulfuric and chlorosulphonic acids, respectively. Mild conditions of sulphonation in trichloromethane or acetic anhydride at temperature 275 K increase the hydrophilicity of composites and results in significant increasing of the surface area and pore volume in comparison with the material silylated by chlorodimethylphenylsilane. The TG/DTA data demonstrates high hydrophilicity of sulphonated mesoporous composites based on MCM-41 and high affinity to water molecules with 50–58 % weight loss at 25–100 °C.