Dependence of molecule diffusion with pore surface features in mesoporous functionalised thin films assessed by electrochemical tools

EUGENIO OTAL; PAULA C. ANGELOMÉ; GALO J. A. A. SOLER-ILLIA; SARA A. BILMES

Conferencia; European Materials Research Society Spring Meeting; 2005

Mesoporous functionalised thin films are highly interesting for applications ranging from sensors to tailored sorbents to bioactive nanocomposites. A fundamental issue is the accessibility and transport of molecules (analytes, reaction products, biomolecules…) within the pore system, and the role of the pore surface modification in the controlled behaviour of the cavity. Electrochemical methods afford the possibility to evaluate pore accessibility and exposed area to electroactive probes. Mesoporous thin MO2 films (M=Si, Ti, Zr, Si/Ti…) with organic functions (phenyl, polyol, alkyl…) are deposited on conducting substrates (Pt, ITO) by dip-coating, using block copolymer templates. Organic functions are added by post-grafting (using silane or phosphate anchoring groups) after template removal, leading to modified mesoporous electrodes. Film features (eg. exposed substrate area) and properties can be readily evaluated by using electrochemical techniques coupled with spectroscopy. The diffusion of electrochemical probes with different size and polarity (eg. H+, ferrocyanide, ferrocene derivatives, viologen…) was evaluated by cyclic voltammetry. Diffusion values for redox probes in modified MO2 are drastically affected by changing the function size or polarity. All the studied systems present ip = v1/2. While relatively small modifiers (phenyl, glycerol) partially block the pore system, the use of longer chains or bilayers (dodecylphosphate) completely hinders probe diffusion.