Generación de Quimiosensores del Nanocomposito Celulosa Bacteriana/Puntos Cuánticos como Indicador de Contaminación por Metales Pesados en Muestras Acuosas

Abstract

In the last decade, contamination by heavy metals in aqueous media has become a global problem that has increased with the confluence of natural sources and, mainly, anthropogenic activities (industrial activities, mining activities, use of pesticides, among others). This condition has generated an increase in the concentration of heavy metals in water effluents, generating therefore a risk for the health of any living system. Metal ions have the capacity to bioaccumulate and biomagnifies in the organism, causing the alteration of numerous biochemical and physiological processes in animals and plants, triggering various pathologies. Currently, the identification and removal of heavy metals from water sources is a costly and slow process and, in most cases, it is not carried out adequately due to the complicated instrumental techniques used and their detection limits. In Colombia, for example, the monitoring of these metals in water for human consumption is not required according to Chapter V and VI of Resolution 2115 of 2007, therefore, there is no control of this type of contaminants in the country's water sources. Currently, the identification and quantification of heavy metals is carried out using medium/high complexity and high-cost equipment and procedures (techniques such as atomic absorption and mass spectrometry). This situation is unfavorable in view of the regional, national, and global need for rapid identification and quantification of this type of ions. So that the contamination of the effluent can be evidenced in an efficient manner. Nowadays, several methods have emerged that can carry out the identification and quantification of these ions in a fast and selective way. Within this set of methods, the use of various nanomaterials stands out, which, due to their luminescent properties, have become chemosensors of interest in this field. Within this type of nanomaterials, quantum dots (QDs) respond to the presence of certain heavy metals by modifying their luminescence depending on the concentration of the metal. Additionally, the use of these nanomaterials in conjunction with a nanocellulose (NC) support enhances their properties, making them a promising material for the in-situ identification of heavy metals in water effluents. Considering the current interest in rapid detection techniques for heavy metals, in the present work, the production of CdTe and CdTe/ZnS QDs was carried out by colloidal aqueous synthesis, which fulfill their function as sensitizing agents allowing the generation of the chemosensor based on their coupling with bacterial nanocellulose (NCB), evaluating different charge ratios in the nanocomposite. For the nano paper or chemosensor, it was evidenced that the optimal NCB loading per unit area was 2.21 mg NCB/cm2, this ratio allowed obtaining a homogeneous and appropriate nano paper for the adsorption of QDs. Additionally, the chemosensor and its constituent elements were structurally and morphologically characterized by UV-vis, IR, XRD, fluorescence, SEM and TEM techniques that allowed identifying the particle size of the QDs (~ 2.4 nm), having a core with a face-centered cubic crystalline structure (CCC) and organic ligands evidenced by IR showing their characteristic signals. Finally, the chemosensor was shown to be sensitive to heavy metals such as chromium, silver, copper, mercury, and lead, finding that mercury is the most influential metal in the variation of the fluorescence of the QDs generating an almost total quenching of the fluorescence of the chemosensor at concentrations above 1 µM.