Professor Volodymyr Zaitsev

Professor, D.Sc., PhD, Corr. Member Acad. of Sci. of Ukraine

Albina Mikhraliieva

Synthesis and characterization of hybrid silica-based nanostructures with immobilized carbogenic materials having enriched π-electron system and their analytical applications

https://doi.org/10.17771/PUCRio.acad.51021

Tese de Doutorado
Thesis presented to the Programa de Pós-graduação em Química of PUC-Rio in partial fullfilment of the requirements for the degree of Doutor em Química.
Rio de Janeiro Maio 2020

Advisor: Prof. Volodymyr Zaitsev

Abstract

The objective of the present research was devoted to the preparation of new silica-based hybrid materials having covalently immobilized carbon-containing molecular and nanoscale systems with delocalized π-electrons that can be used as adsorbents and electrodes for preconcentration and determination of aromatic compounds. For this purpose, methodologies for covalent immobilization of anthracene (Ant), graphene oxide quantum dotes (GOQDs) and carbon nanodots (CDs) on silica surface (SiO2) have been developed. These compounds have a conjugated system of π-electrons and thus can form molecular complexes with aromatic compounds. The nanocomposite with immobilized GOQDs was prepared by covalent immobilization of nanoscale GO fragments. Three sets of SiO2-Ant were obtained using reaction surface assembling reactions by alkylation and condensation of silica with immobilized primary amines. These materials can have different arrangements of anthracene ligands on silica surface and so π-donor properties. Silica gel nanocomposites with immobilized CDs were prepared by two different approaches. For the first one, the CDs were obtained from the molecular precursor and then immobilized on silica. For the second method, CDs were prepared “in situ” directly in silica gel pores. The second method is facile and robust and also allows better control of the particle size and composition. The effects of silica gel modification, pore size, synthesis time, hydrolytic stability, carbon nanoparticle size and quantum yield of the fluorescence were studied. It was demonstrated that the carbonization of aminosilica gel with embedded citric acid resulted in the formation of unbound CDs and immobilized CDs. Due to firm attachment to the surface CDs can be easily separated from low-molecular impurities and CDs by simple rinsing of the nanocomposite with water. As prepared CDs demonstrate excitation-independent photoluminescence at 445 nm with QY up to 80% that makes them attractive for bioanalytical application. The composition of the surface layer of the adsorbents was determined from elemental and thermogravimetric analysis, X-ray photoelectron, solid nuclear magnetic resonance, Raman, FTIR, and fluorescent spectroscopy. The textural properties of the adsorbents were determined as well as ligand immobilization kinetics, the degree of surface transformation and hydrolytic stability of the grafted groups, the effect of silica porosity on ligand conversion degree. The adsorption properties of the materials were studied in dynamic and static SPE modes for the model compounds: methylene blue, and anthracene in various aqueous-organic and organic mobile phases, in the presence of interfering components. It was demonstrated that studied materials have a higher affinity towards aromatic compounds than commercial C18 SPE cartridges in organic mobile phases that allow one-step separation of PAHs in the matrix with high concentration of fatty acids. Also, silica-immobilized GOQDs was used for electrochemical analysis of selected antibiotics and hormones. The electrode demonstrated electrocatalytic activity towards estriol (EST), diethylstilbestrol, sulfamethoxazole, and trimethoprim that made it possible to determine these analytes with up to 0.009 μmol L-1 (EST).

Keywords: Carbon nanomaterials; Nanoreactor confinement; Immobilization; SPE.

full text https://www.maxwell.vrac.puc-rio.br/colecao.php?strSecao=resultado&nrSeq=51021@1

Laboratório de adsorventes para análise química, proteção de ambiente e biomedicina (LAQAPAB)
Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio)
tel: +55 21 980551969,
e-mail: vnzaitsev@puc-rio.br,
http://zaitsev.usuarios.rdc.puc-rio.br

ORCID