Adsorpcija pesticida na zeolitima, polianilinu i njihovim kompozitima

Abstract

Katalitička svojstva Fe-modifikovanih zeolita zavise od formiranja dimernih i oligomernih vrsta gvožđa, kao i čestica gvožđe-oksida. U ovoj doktorskoj disertaciji je sinteza Femodifikovanih ZSM-5 zeolita izvedena metodom jonske izmene iz razblaženih rastvora različitih soli (Fe(III)citrata, Fe(II)oksalata i Fe(III)nitrata). Pokazano je da aktivnost Femodifikovanih zeolita kao katalizatora zavisi od soli gvožđa u čijem prisustvu se vrši izmena, što ukazuje da je moguće, iz razblaženih rastvora, dobiti različite vrste gvožđa kao centre na zeolitima, dok se izolovani, dispergovani joni, koji su presudni za adsorpciju i katalizu, u velikom prinosu dobijaju samo izmenom iz rastvora Fe(II)oksalata. Oksidacija metilen-plavog u prisustvu vodonik-peroksida kao tipična katalitička test reakcija je pokazala da polazni HZSM-5 ima slabija katalitička svojstva nego Femodifikovani ZSM-5 zeoliti. Najveću aktivnost je pokazao uzorak izmenjen u rastvoru Fe(III)citrata što predstavlja potvrdu da su mononuklearni, izolovani centri gvožđa, čak i pri niskim koncentracijama, od presudnog značaja za aktivnost katalizatora. S obzirom da su se sintetisani Fe-modifikovani zeoliti pokazali kao aktivni katalizatori, ispitana je adsorpcija isparljivih organskih jedinjenja, koja predstavljaju česte zagađivače u životnoj sredini. Ispitivano je da li se na hidratisanim Fe-modifikovanim zeolitima adsorbuju isparljiva organska jedinjenja (n-heksan, benzen, metil-benzen i etil-benzen). Utvrđeno je, na osnovu eksperimenata temperaturski-programirane desorpcije, da se nepolarni molekuli ispitivanih organskih jedinjenja vezuju na hidratisanim zeolitima na specifičnim, jakim adsorpcionim centrima. Do vezivanja najverovatnije dolazi tako što organski molekuli zamenjuju vodu prethodno adsorbovanu na istim centrima, što predstavlja indikaciju da ovi materijali mogu da se koriste za akumulaciju/adsorpciju isparljivih organskih jedinjenja iz vodenih rastvora. Korišćenjem analize masenih spektara je pokazano da se n-heksan i benzen molekulski adsorbuju i desorbuju, dok se u slučaju desorpcije metil-benzena i etil-benzena javljaju novi maseni fragmenti koji potvrđuju da je desorpcija metil-benzena i etil-benzena praćena njihovim razlaganjem na aktivnim centrima hidratisanih zeolita. Analizom ukupnog sadržaja ugljenika potvrđeno da su svi sintetisani FeZSM-5 zeoliti aktivni i kao katalizatori u reakcijama oksidacije metil-benzena i etil-benzena u prisustvu vodonikperoksida. U nastavku teze je razvijen postupak za sintezu novih kompozita polaznog HZSM-5 i modifikovanog FeZSM-5 zeolita sa nanostrukturnim i granularnim polianilinima, kao potencijalnih adsorbenata/katalizatora. Ovi kompoziti su sintetisani oksidativnom polimerizacijom anilina u vodi (bez dodate kiseline) i u vodenom rastvoru sumporne kiseline u prisustvu zeolita, korišćenjem amonijum peroksidisulfata (APS) kao oksidacionog sredstva i različitih početnih masenih odnosa anilin/zeolit. Materijali su okarakterisani velikim brojem fizičko-hemijskih tehnika (HPLC, ULj-Vid, FTIC, ramanska, IKP-OES i EPR spektroskopija, TGA, elementarna analiza, XRD, SEM, TEM, analiza fizisorpcije azota, Hg-porozimetrija i merenje električne provodljivosti)...

The catalytic properties of Fe-exchanged zeolites are influenced by the formation of dimeric and oligomeric iron species and oxide particles. In this thesis, the preparation of FeZSM-5 zeolite by ion-exchange method was carried out using dilute solutions of various salts (Fe(III)citrate, Fe(II)oxalate and Fe(III)nitrate). It has been demonstrated that the activity of the Fe-exchanged zeolite catalyst depends on the iron salt used for ionexchange, indicating that various types of iron can be obtained as active centers in zeolites. However, the isolated, dispersed ions, which are essential for adsorption and catalysis, can be, with high yield, obtained only by ion-exchange in the presence of Fe(II)oxalate. Oxidation of the Methylene Blue dye with hydrogen peroxide is a typical catalytic reaction and this test showed that the starting HZSM-5 expresses lower activity in comparison with Fe-exchanged ZSM-5 zeolites. The highest activity was found for the sample prepared in the presence of Fe(III) citrate which is confirmation that, even at low concentrations, the mononuclear isolated iron centers are crucial for the catalyst activity. Since the Feexchanged zeolites have proved as active catalysts, the adsorption of volatile organic compounds, which are common contaminants in the environment, was tested. We examined whether the volatile organic compounds (n-hexane, benzene, methylbenzene, and ethyl benzene) adsorb on hydrated Fe-exchanged zeolites. It was determined, by means of temperature - programmed desorption coupled with mass spectrometry, that tested, non-polar organic molecules do adsorb on specific, strong adsorption centers in hydrated zeolites. The binding occurred when organic molecules replaced water previously adsorbed at the same centers. This finding suggests that these materials can be used for accumulation/adsorption of volatile organic compounds from aqueous solutions. The analysis of mass spectra has revealed that n-hexane and benzene are both adsorbed and desorbed in molecular form, while new mass fragments were recorded during methylbenzene and ethyl-benzene desorption which implied their decomposition at active sites in hydrated zeolites. The analysis of the total carbon content confirmed that all ionexchanged FeZSM-5 zeolites were active catalysts in oxidation reactions of methylbenzene and ethyl-benzene in the presence of hydrogen peroxide. Subsequently, a method for the synthesis of new composite adsorbent/catalyst materials was developed. Composites, comprising the starting HZSM-5 or ion-exchanged FeZSM-5 zeolite and nanostructured or granular polyanilines, were synthesized by the oxidative polymerization of aniline in water (without added acid) and in an aqueous solution of sulfuric acid in the presence of zeolite, using ammonium peroxydisulfate (APS) as an oxidizing agent. Various initial mass ratios aniline/zeolite were used. These materials were characterized by a large number of experimental techniques (HPLC, UV/Vis, FTIC, Raman, ICP - OES and EPR spectroscopies, TGA, elemental analysis, XRD, SEM, TEM, nitrogen physisorption, Hg-porosimetry and electrical conductivity measurements)...