Tuning the acid content of propylsulfonic acid-functionalized mesoporous benzene-silica by microwave-assisted synthesis

resumo

Propylsulfonic-acid functionalized mesoporous phenylene-silicas have potential use in catalysis and applications demanding protonic conduction such as fuel cells. Their synthesis by conventional co-condensation is time consuming and with poor control of the incorporation of sulfonic acid. Here we report a fast, microwave-assisted synthetic route to prepare these materials with controlled acid load and structural order. It is found that the microwave energy strongly improves the kinetics of the various steps of the process, including the self-assembly of precursors (stirring), consolidation of the framework (hydrothermal treatment), surfactant extraction and the oxidation of the thiol to the sulfonic acid group. The concentration of incorporated acid groups increases linearly with the self-assembly time under microwave radiation, enabling the largest improvement of all synthetic steps. However, the mesopore order decreases significantly for microwave-assisted self-assemblies in excess of 6 h, and for microwave assisted hydrothermal treatments longer than 3 h. The multivariate analysis of kinetic data is presented and used to derive kinetic parameters enabling the prediction of the acid load and the structural order of the materials as a function of the synthesis time under microwave radiation. For similar acid contents, full microwave synthesis is completed within 12 h, whereas nearly 84 h are needed with conventional heating sources. The protonic conductivity increases linearly with increasing acid load regardless of the used combination of synthetic steps, including MW or not. This is seen as a confirmation that the distribution of the acid groups in the pore surface is not affected by MW. (C) 2016 Elsevier Inc. All rights reserved.

palavras-chave

MOLECULAR-SCALE PERIODICITY; CATALYTIC-ACTIVITY; HYBRID MATERIAL; ORGANIC GROUPS; ORGANOSILICA; WALLS; CONDUCTIVITY; MEMBRANES; MCM-41; WATER

categoria

Chemistry; Science & Technology - Other Topics; Materials Science

autores

Domingues, EM; Bion, N; Figueiredo, FM; Ferreira, P

Grupos

G2 - Materiais Fotónicos, Eletrónicos e Magnéticos
G3 - Materiais Eletroquímicos, Interfaces e Revestimentos

Projectos

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

Acid-functionalised hybrid membranes for intermediate temperature proton exchange membrane fuel cells (HyPEM) (PTDC/CTM-CER/109843/2009)

Design of acid-functionalised periodic mesoporous organosilica catalysts for reactions with/in water (PTDC/QUI-QUI/113678/2009)

agradecimentos

This work was developed in the scope of the project CICECO-Aveiro Institute of Materials POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by National Funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. The financial support from FCT/FEDER/QREN-COMPETE, projects PTDC/CTM-CER/109843/2009 (FCOMP-01-0124-FEDER-014605) and PTDC/QUI-QUI/113678/2009 (FCOMP-01-0124-FEDER-015644). The authors acknowledge the bilateral action CNRS/FCT for funding. ED, FMF and PF are indebted to FCT for the PhD fellowship (SFRH/BD/48043/2008) and IF grants (IF/01174/2013 and IF/00327/2013, respectively).