Development and evaluation of novel molecularly imprinted thin-films for phenol and application of direct spectroscopic detection for petrogenic contaminants adsorbed to molecularly imprinted films

Gryshchenko, Andriy O. (2014) Development and evaluation of novel molecularly imprinted thin-films for phenol and application of direct spectroscopic detection for petrogenic contaminants adsorbed to molecularly imprinted films. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Phenol and alkylphenols are priority water pollutants from oil extraction, pyrolysis, and industry. The adsorption of phenols is required for the separations in analytical chemistry and industry. Molecularly imprinted polymers (MIPs) are novel adsorbents with the template shaped binding sites. A MIP has to be prepared in film format to be combined with an analytical technique to accomplish rapid and direct detection of phenols and other water pollutants. Films from MIP particles and monolithic films, having 20 and 100 μm thicknesses and bound to a glass slide, were fabricated by UV-initiated radical polymerization between two inert surfaces. The morphology, thickness, and porosity of MIP films were studied by scanning electron microscopy and gravimetric analysis. Porosity was rendered using alcohol-water mixtures as a solvent and, in some instances, polyethyleneglycol and polyvinylacetate as solvent modifiers. Many MIPs for phenol were synthesized through non-covalent imprinting by hydrogen bonding and hydrophobic interactions. The MIP components included functional monomer (itaconic acid, 4-vinylpyridine, and styrene) and solvent, cross-linker (ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, divinylbenzene, pentaerythritol triacrylate—PETA), and template (phenol, xylene). The binding and imprinting properties of the MIPs were assessed based on adsorption capacities and cross-binding towards other phenolics and polycyclic aromatic hydrocarbons (PAHs). A MIP with increased styrene content and xylene along with a copolymer of divinylbenzene and PETA, both acting by hydrophobic interactions, can be recommended for practical applications. The higher content of styrene and/or more hydrophobic monomers such as divinylbenzene increased the binding capacity. The hydrophilicity of PETA rendered water compatibility to the films. The modest imprinting effect is attributed to a tight polymer network formed with PETA as well as xylene as a hydrophobic template. Alcohol-water mixtures promoted the imprinting by hydrophobic interactions and, concurrently, lead to homogeneous, porous, and rigid morphology of the films. Surface enhanced Raman spectroscopy with silver nanoparticles, and fluorimetry, were unsuccessfully attempted for the direct detection of phenol on MIP films because of the low sensitivity and MIP background issues. The direct fluorimetric detection of light PAHs, as another group of pollutants from oil, was showen to be sensitive and selective, when front-face illumination geometry, 100 μm thick films, and synchronous scanning were used.

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