Síntese e caracterização de silsesquioxanos organofuncionalizados para aplicações tecnológicas

Abstract

In the present work, the silsesquioxane hybrid materials were obtained by two distinct synthesis routes, by the sol-gel method and organofunctionalized by means of SN2 reaction with the organic ligands 2-aminopyrimidine, 4-vinylpyridine, 4-mercaptopyridine, obtaining respectively 3-n-propyl(2-aminopyrimidine) chloride (Si2am2py), 3-n-propyl(4-vinylpyridine chloride (Si4vinylpy+Cl-) and 3-n-propyl(4-mercaptopyridine chloride (Si4merpy+Cl- ). One of the synthetic routes was carried out in two steps, where first the precursor (xerogel) was prepared by the sol-gel method from the catalysis by fluoride ions and subsequently it was organofunctionalized. The other synthetic route consisted of a single step (direct synthesis), where in the same reaction medium the organofunctionalization and sol-gel synthesis were carried out with acid catalysis (HCl), directly obtaining the final materials (designated with one or two asterisks for the 1:1 and 2:1 2ampy/CPTMS ratios, respectively). In the direct synthesis, Si2am2py*, Si4merpy+Cl-* in the 1:1 ratio and Si2am2py**, in the 2:1 ratio (2ampy/CPTMS) were obtained. The synthesized silsesquioxanes were characterized by FTIR, 13C and 29Si NMR, XRD, and SEM-FEG to confirm their structures. In the materials Si4vinylpy+Cl- and Si4merpy+Cl-, the bond of the –α carbon of the n-propyl group to the nitrogen of the pyrimidinium ring was verified, which conferred a positive charge to the materials with the chloride ion as counterion. For the materials Si2am2py, Si2am2py* and Si2am2py**, the bond of the –α carbon of the group n-propyl occurs in the amine group linked to the pyrimidine ring. The two synthesis routes provided the materials Si2am2py, Si2am2py* and Si2am2py** with different exchange capacities: 0.30 mmol g-1, 0.60 mmol g-1 and 2.09 mmol g-1, respectively. These results indicate that the direct synthesis route presented a better organofunctionalization due to the greater amount of chloride ions in the structure. Due to its hydrophobicity and greater exchange capacity, Si2am2py* was applied for the adsorption of Cu2+ and Cr3+ ions. The results showed the feasibility of using Si2am2py* as an adsorbent material. The adsorption isotherms of Cu2+ and Cr3+ ions followed the Freundlich and Sips models, indicating heterogeneous and multilayer adsorption. Si2am2py* was able to adsorb 1.21 mmol g-1 of Cu2+ and 0.27 mmol g- 1 of Cr3+. Si2am2py** was water-soluble, therefore its capacity as a stabilizer of gold nanoparticles (AuNPSi2am2py) was studied, obtaining spherical AuNPs with sizes of ~12 nm. This material was also used as an adhesion agent on the surface of the oxidized glassy carbon electrode (ECV-OX). By incorporating graphene oxide into this material (AuNPSi2am2py- GO), it was applied as an electrochemical sensor for nitrite detection. The ECV- OX/AuNPSi2am2py-GO sensor demonstrated a detection limit of 3.7 M with a linear detection range of 0.25-5.00 mM. The detection performance of the electrode was also investigated using tap, bottled and lake water spiked with different nitrite concentrations with an excellent recovery of 93% to 102.4%, demonstrating potential material for monitoring water quality.