Europium luminescent films for metal sensors in aqueous solution

B.C. BARJA; M. BERNARDI; F. IGLESIAS; S. BARI; P.F. ARAMENDÍA

Cubatao, San Pablo, Brasil

Congreso; IX ELAFOT (Encuentro Latinoamericano de Fotoquímica y Fotobiología); 2008

Europium luminescent films for metal sensors in aqueous solution Beatriz C. Barja, M. Bernardi, F. Iglesias, S. Bari and P. F. Aramendía INQUIMAE and Depto. Química Inorgánica, Analítica y Química Física. Facultad de Ciencias Exactas y Naturales. UBA. Pabellón 2. Ciudad Universitaria. C1428EHA Buenos Aires. Argentina Europium compounds are widely used to develop materials capable of detecting different analytes in solution. Europium ions display a well-defined luminescence characterized by narrow and highly structured emission bands with lifetimes in the millisecond timescale. Transition metal ions are known to be efficient quenchers of the emission of lanthanide complexes. Cu (II) ions act much more efficiently than any other fourth period transition metal cations. In this work, we make use of the sol gel chemistry of silicon alcoxides to develop Eu(III) luminescent materials capable of sensing transition metals in aqueous solution. The strategy bases on the synthesis of a silanised organic-inorganic precursor (SL)* containing a suitable ligand capable to efficiently coordinate the Eu(III) ion. This precursor is hydrolyzed and condensed with TEOS (tetraethoxysilane), ethanol and water in different ratios in the presence of an Eu(III) salt, thus obtaining a gel and a monolith. *SL To enhance the porosity of the matrix to permit the entrance and exit of the quenching metals from and to the solution, a surfactant was included during the synthesis, which was later extracted with the proper solvent. Two types of sensor devices were developed: 1. Particulate films and 2.Transparent films obtained by the sol-gel technique. The Stern Volmer constants for Cu(II) quenching for particulate films were KSV= 105 M-1 (where  surfactant was included) permitting a detection limit of 0.05 ppm of Cu(II) for a 10 % quenching**. 2. Starting with the same SL precursor in a molar ratio Si: EtOH: H2O: HCl = 1: 22: 5: 5.10-5  (with a SL: TEOS = 0.066), transparent films were deposited on glass slides by the sol gel technique. Simultaneously, a surfactant (CTAB) was added to compare the performance of both systems. Europium nitrate was added during the synthesis of the gel with a SL/Eu(III) molar ratio of 3. When these films were put in contact with Cu(II), an immediate response to the metal was observed. The Stern Volmer plots show a non linear response to increased concentrations of Cu(II), giving evidence of a static and heterogeneous deactivation process. ** Barja, B.C and P. F. Aramendía, Photochem. Photobiol. Sci., in Press.