Molecular modelling of proton transfer in aminopropylfunctionalized anatase and cristobalite surfaces

V. M. SÁNCHEZ; A CALVO; P C ANGELOMÉ; G.J.A.A. SOLER-ILIA; F. J. WILLIAMS; D. A. SCHERLIS PEREL

Santa Barbara

Workshop; Grand Challenges of Electron Chemistry & Catalysis at Interfaces Summer Workshop; 2008

PIRE-ECCI y ICMR

The field of mesoporous materials is nowadays expanding. Mesoporous hybrid thin films (MHTFs)present a great interest for their potential in domains such as optics, electronics, chemical sensing,catalysis, separation, and so forth.The introduction of organic or metallo-organic functions on the surface of mesopores is a stepforward toward the creation of complex chemical systems with tuned reactivity. The possibility ofaccommodating molecular functions with a well-defined location in space opens the path for newconcepts in catalysis, separation, nanobiomaterials, and so forth. Several organic functions havebeen introduced in both silica or nonsilica matrices. In particular, amino groups are interestingbecause of the possibility of creating pH-responsive charged surfaces with perm-selective properties,biomolecule binding, or creation of enzyme-like surface sites for advanced catalysis.Relevant data have been obtained in modified mesoporous powders by X-ray photoelectronspectroscopy (XPS) or MAS-NMR. The acid-base behavior of surface amino functions found in selfassembledmonolayers (SAMs) has been studied by spectroscopic or titration methods. Thisbehavoir is a crucial issue for the future applications of these materials in several fields, such assensing and protein immobilization.In our work we study the structure behavior of amine functionalized MHTFs by means of Densityfunctional theory (DFT) calculations. Our simulations were performed in vacuum and in presence oftwo water monolayers, to examine the surface equilibrium amino/ammonium under differentenvironments. These calculations describe the variation of the ratio R = [-NH3+]/ [-NH2] with pH andwith the nature of M, and complement the XPS results allowing for a complete picture of the surfacebehavior.