Zeolite optimization (FAU, BEA and MFI) for pesticide removal from aquatic environments

Abstract

This doctoral dissertation examines the removal of pesticides from aquatic environments on FAU, BEA and MFI zeolites, using adsorption, as a simple and effective method for surface and waste water purification. Different cationic surfactants, metal ions and heteropoly-anions were used for zeolite functionalization. By optimizing zeolite surface, new materials were obtained: Y (FAU) zeolites functionalized with cationic surfactants (benzalkonium chloride, cetylpyridinium chloride and tetrapropylammonium chloride), Y, β (BEA) and ZSM-5 (MFI) zeolites modified with iron ions and ZSM-5 zeolites modified with potassium tungstophosphate. The adsorption properties of optimized FAU, BEA, and MFI zeolites for adsorption of following pollutants: nicosulfuron herbicide, acetamiprid insecticide and polyphenol (tannic acid). The catalytic properties of i) iron-modified zeolites were tested in heterogeneous Fenton system for pesticides oxidation and ii) zeolites and potassium tungstophosphate composites in ethene production. Finally, the influence of the obtained materials on the cytotoxicity of selected pesticides was investigated. In the first part of the thesis, in addition to acetamiprid adsorption study, the influence of consecutive adsorption of polyphenol on the toxicity of adsorbed acetamiprid was examined. It has been shown that tannic acid is not crucial for toxicity modulation, but that the presence of zeolite has the largest impact on the viability of cells exposed to pesticide. The results showed the significant capacity of these materials as adsorbents in wastewater treatment for the removal of tannic acid, as well as other similar polyphenolic compounds. In the second part of the thesis, the effectiveness of physical and chemical methods for the removal of acetamiprid, as well as the impact of those methods on cytotoxicity, was discussed. Fe-modified zeolites prepared by the ion exchange process of three different zeolites (MFI, BEA and FAU) were tested as adsorbents and catalysts in the Fenton system. The type of zeolite network was found to be crucial for specific applications in the removal of acetamiprid. Fe-ZSM-5 zeolites predominantly induce catalyzed decomposition, Fe-Y zeolites adsorption, while both adsorption and catalytic degradation of acetamiprid were detected in the presence of Fe-β zeolites. It was concluded that the combination of physical and chemical treatments for water remediation represents a method for reducing the toxic effects of pesticides in the environment if the adsorbents are based on zeolites with modified iron as an non-framework cation. In the third part, a bifunctional composite was prepared and tested as efficient adsorbent for nicosulfuron and a catalyst in green reactions for ethene production as an important precursor in the chemical industry. New composite materials were composed of potassium tungstophosphate and ZSM-5 zeolite, and the samples were obtained by different methods of sample preparation (potassium tungstophosphate was synthesized in situ on zeolite while varying the order of addition of precursors to optimize the experimental procedure) and post-synthesis treatments. Experiments have shown that the binding of potassium tungstоphosphate to ZSM-5 zeolites of different Si/Al ratios affects the formation of active centers for catalytic and adsorption applications. Brønsted active sites are present in zeolites and contribute to the activity together with Lewis centers formed by the introduction of potassium ions, which leads to improved stability and activity of the synthesized materials in the ethanol dehydration reaction. It was shown that the aluminum content in the zeolite in combination with the two-stage in situ preparation of potassium tungstоphosphate as an active phase is crucial for the formation of isolated active sites for both catalytic and adsorption applications. The results of the thesis unequivocally indicate that the improvement of the adsorption and catalytic properties of zeolite can be carried out through the optimization of experimental parameters used for zeolite optimization, and the newly synthesized and optimized materials have the potential to be used in real systems for environmental protection, and as promising adsorbents and catalysts in wastewater treatment.