Síntese e caracterização de novos materiais híbridos orgânicos- inorgânicos visando diferenciadas aplicações

Abstract

This work reports the preparation, characterization and application of new silsesquioxanes hybrid materials obtained from the sol-gel synthesis method, which consisted of hydrolysis and polycondensation reactions of the silica-based precursors and SN2 reaction of the precursors with 4-(aminomethyl)pyridine and imidazole groups, obtaining Si4ampy+Cl- and SiImi+Cl-, respectively. Silsesquioxanes with nitrogen groups were characterized by techniques such as NMR, XRD, MEV, UV-VIS, FTIR and BET to confirm the structures presented in this thesis, as well as the materials functionalization. In the case of Si4ampy+Cl- two reaction sites were observed with carbon-α of the n-propyl group bonding with the amino group and the pyridinium ring, having as proposal two arrangements of the carbonic chain. The Si4ampy+Cl- was applied in the construction of electrodes modified with NiTsPc using the LbL technique for the thin films manufacture. The electrode in the configuration (Si4ampy+Cl-/NiTsPc)11 was applied for nitrite electrochemical sensor, with r = 0.999 in the range of 0.113 mmol L-1 to 0.860 mmol L-1, LD and LQ of 0.026 mmol L-1 and 0.127 mmol L-1, respectively and standard deviation values of approximately 3%, according to recommendations of ANVISA and Inmetro. Another use of Si4ampy+Cl- was the stabilization of silver nanoparticles for the thin films production. The presence of Ag-NPs/Si4ampy+Cl- was confirmed by UV-VIS technique by the plasmon band at 426 nm which presented a distribution with approximate size between 12 and 131 nm, verified by DLS and MEV, presenting good stability (= +43.4 mV). The Ag-NPs/Si4ampy+Cl- showed promising in the modification of the ITO electrode with NiTsPc, showing linear growth of the LbL film and redox processes related to the oxidation of the metal center and to the oxidation of the phthalocyanine ring observed by cyclic voltammetry, exhibiting the performance of the modified electrode (Ag-NPs/Si4ampy+Cl-/NiTsPc)7 to electrocatalyse chemical species. In general, the modified electrodes (Si4ampy+Cl-/NiTsPc)11 and (Ag-NPs/Si4ampy+Cl-/NiTsPc)7 obtained an improvement in the anodic current response and reduction of the oxidation potential compared to the unmodified electrode (ITO) in the presence of nitrite. The SiImi+Cl- was used to adsorb Cu2+, Cd2+ and Ni2+ ions and presented ion exchange capacity of 2.944 mmol g-1, which was considered excellent according to the literature for the proposed application. The adsorption results showed the viability of using SiImi+Cl- as an efficient adsorbent material, exhibiting a higher affinity for the Cu2+ ions at pH 4. Applying the Langmuir and Freundlich models to the adsorption isotherms, it was verified that both the pH as the nature of the ion are factors that influenced the adjustment of the isotherms to the proposed models.