Síntese, caracterização e aplicação do nanocompósito CDots_EuBDC como sonda raciométrica luminescente de temperatura e Cr(VI)

Abstract

Luminescent materials have been showing promising characteristics in several scientific and technological, such as optical thermometer and chemical sensors. Nevertheless, traditional sensors with a single emission channel may present some disadvantages, such as photodegradation of the material, the influence of the microenvironment and others that may compromise the reliability of the response. In this context, the development dual-emission luminescent materials has emerged as an excellent strategy for the design of new and advanced ratiometric luminescent devices applied in various areas, including chemical and temperature sensors. Thus, for the first time, an ultrasound-assisted synthesis has been prepared and mediated by the passive agent polyvinylpyrrolidone (PVP), a dual-emission nanocomposite based on Carbon Dots (CDots) from chitosan and Metal-Organic Frameworks (MOF) based on europium nitrate and disodium benzene-1,4-dicarboxylate (CDots/EuBDC), to be applied as a ratiometric temperature sensor and Cr(VI). The synthesized Cdots presented an average size of 7.2 ± 2.2 nm and emission in the blue region with maximum centered at 440 nm (λexc= 350 nm). The incorporation of these nanoparticles in situ to obtain the CDots/EuBDC did not change the crystalline structure of EuBDC as indicated in the DRX patterns. Furthermore, the CDots/EuBDC and EuBDC exhibited similar degrees of crystallinity (~ 50%). The incorporation of CDots in the formation of the CDots/EuBDC was confirmed by the images of MET and porosimetry, the last technique indicated a significant decrease in volume and pore diameter of 42.1% and 24.3%, respectively. The thermogravimetric analysis of the materials showed an increase in thermal stability for the CDots/EuBDC. The photophysical properties of the nanohybrid revealed the presence of a dual-emission, with a 420 nm centered broadband associated to the CDots and emission lines relative to the transitions 5D0→7FJ (J = 1, 2, 3 and 4) of the Eu(III) ion. The CDots/EuBDC system was explored as a ratiometric luminescent sensor of Cr(VI) and temperature. Thermometry results showed that the emission of CDots (ICDots) decreased with increasing temperature, while that of the europium (IEu;5D0→7F2) remained constant (reference signal). The ratio of the intensities (ICDots/IEu) to temperature revealed that the CDots/EuBDC had one linear range in the intervals of 303-393 K, with maximum relative thermal sensitivity of 1.16% K-1 in 333 K. In addition, the nanohybrid was incorporated in a cyanoacrylate membrane (M_CDots/EuBDC) and exploited for Cr(VI) detection in an aqueous system in a simple and easy and practical way. The preliminary tests in Britton-Robinson buffer solution at 1 mM pH 9 showed a linear range of 0.03 to 0.15 mgL-1 corresponding to the equation [(ICdots/IEu)0/(ICdots/IEu)] = 1.627 (± 0.074) CCr(VI) + 1.133 (± 0.007) with r2 = 0.9916. Finally, the CDots/EuBDC is a good candidate for both optical thermometry and Cr(VI) detection.