title: Characterization of the hydrophobicity of mesoporous silicas and clays with silica pillars by water adsorption and DRIFT.
abstract: The hydrophobic-hydrophilic properties of a solid are related to the material chemistry and, often, these properties are relevant to the applications of a particular material. Contrarily to what happens with other properties, such as specific surface areas or pore volumes, the methodologies to ascertain on the hydrophilicity of a porous material are not well defined. In this work, we discuss and relate the information on the hydrophobicity degree obtained from water adsorption isotherms and from diffuse reflectance infrared Fourier transform (DRIFT), in a set of porous materials. The studied materials were mainly mesoporous solids, namely of MCM-41 and SBA-15 types, two xerogels and also different porous clays heterostructures. Both techniques were informative on the hydrophobic-hydrophilic properties of the studied samples, but the correlation between the information obtained by each technique was not straightforward. Water adsorption isotherms are much more sensitive to the differences of the studied materials than the DRIFT spectra. For silica-based mesoporous materials with similar surface chemistry, the water adsorption process and hence, the hydrophobic-hydrophilic properties, is mainly dependent on the pore diameters. However, water adsorption is much more sensitive to changes in the nature of the adsorbent surface than to changes in the pore diameter.
authors.affiliation: Departamento de Química e Bioquímica da Faculdade de Ciências de Lisboa, Centro de Química e Bioquímica, Edifício C8, Campo Grande, Lisboa, Portugal. jpsilva@fc.ul.pt
authors.forename: João
authors.initials: J
authors.lastname: Pires
authors.forename: Moisés
authors.initials: M
authors.lastname: Pinto
authors.forename: Juncal
authors.initials: J
authors.lastname: Estella
authors.forename: Jesús C
authors.initials: JC
authors.lastname: Echeverría
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D057927:Hydrophobic and Hydrophilic Interactions; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation / Q000379:methods; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; C509968:MCM-41; C509969:SBA-15; D014867:Water; D012822:Silicon Dioxide; D000077215:Clay