Photocatalytic oxidation of pollutants in wastewater using visible light and TiO 2 based photocatalysts

Vse večji in naprednejši razvoj industrije ter kmetijstva vzporedno z rastjo populacije povzroča ogromno škodo okolju z izpustom škodljivih kemikalij in ostalih organskih onesnaževal. Večina teh polutantov je toksičnih, mutagenih in karcinogenih, ki so zelo obstojni ter se zlahka bioakumulirajo. V to kategorijo sodijo tudi motilci endokrinega sistema (bisfenol A) z močnim vplivom na fiziološke procese v človeškem organizmu in zaskrbljujoča nova onesnaževala (farmacevtske učinkovine) z znanimi ali domnevnimi učinki na okolje ter zdravje človeka. V odgovor ekološki zaskrbljenosti zaradi obsežnega onesnaževanja pitne vode, rek, jezer in morja, se je v zadnjih desetletjih med znanstveniki povečalo zanimanje za razvoj novih tehnologij na področju čiščenja odpadnih voda. Velik potencial pri učinkovitem odstranjevanju organskih onesnaževal iz vodnih sistemov so pokazali napredni oksidacijski procesi, ki s prilagajanjem postopkov oksidacije dosežejo neselektivno razgradnjo organskih snovi do CO2 in vode. Med temi procesi velja metoda heterogene fotokatalize z uporabo fotokatalizatorjev na osnovi TiO2 za najbolj raziskano, obetavno, enostavno in okolju prijazno. Namen magistrske naloge je bil z metodo mokre impregnacije pripraviti fotokatalizatorje na osnovi TiO2 nanodelcev, ki bodo uspešno razgradili organska onesnaževala v šaržnem reaktorju ob obsevanju z vidno svetlobo. Ker je čisti TiO2 aktiven samo v ultravijoličnem spektru svetlobe, smo na njegovo površino dopirali plazmonski žlahtni kovini (Au, Pt) in njune zlitine. S karakterističnimi metodami smo sintetiziranim katalizatorjem določili njihove optične, strukturne in površinske lastnosti ter preverili učinkovitost pri tvorjenju reaktivnih kisikovih zvrsti (HO• s kumarinom ter O2•- in e- z ABTS•+). Fotokatalitsko aktivnost pri razgradnji bisfenola A pod svetlobo v vidnem delu spektra smo ugotovili s tekočinsko kromatografijo visoke ločljivosti in z merjenjem celotnega organskega ogljika pred in po fotokatalizi določili stopnjo mineralizacije onesnaževal. Sintetizirani fotokatalizatorji so se med seboj razlikovali v optičnih in površinskih lastnostih, po učinkovitosti tvorbe reakcijskih kisikovih zvrsti ter razgradnje bisfenola A. Ugotovili smo tudi, da nanos Au, Pt in njunih zlitin na površino nosilca TiO2 ne vpliva na njegovo morfologijo. Pri razgradnji bisfenola A je bil najbolj učinkovit fotokatalizator z nanosom zlitine 0,25 % Au + 0,75 % Pt (80,7 %), sledil mu je katalizator z nanosom zlitne 0,5 % Au + 0,5 % Pt (74,5 %), še sprejemljivo razgradnjo pa je dosegel katalizator z nanosom 1 % Pt (70,9 %). Ker je katalizator z dopirano zlitino 0,5 % Au + 0,5 % Pt teoretično izkazoval potencialno veliko katalitsko aktivnost, smo ga uporabili še za preverjanje učinkovitosti razgradnje farmacevtskih učinkovin, kot so aspirin, kofein in paracetamol. Izbrani katalizator je bil najbolj uspešen pri razgradnji aspirina (97 %), naslednji je bil kofein (79 %), paracetamola pa se je razgradilo nekoliko majn (62 %). Zbrani podatki so potrdili fotokatalitski potencial katalizatorjev z dopiranimi zlitinami Au in Pt, kjer ima Pt prevladujoč ali enak deleže od Au pri razgradnji bisfenola A in farmacevtskih učinkovin (aspirin, kofein in paracetamol).Growing and developing industry and agriculture, combined with population growth, is causing significant environmental damage through the release of harmful chemicals and other organic pollutants. Most of them are toxic, mutagenic and carcinogenic and have high resistance and bioaccumulation. This category also includes substances that disrupt the endocrine system (bisfenol A) and severely affect processes in the human organism, as well as emerging compounds (pharmaceutical agents) with known and suspected effects on the environment and human health. To respond to environmental problems caused by severe pollution of drinking water, rivers, lakes, and oceans, scientists have shown increased interest in developing new technologies for wastewater treatment. Greater potential for effective removal of organic pollutants from aquatic ecosystems has been achieved through advanced oxidation processes that enable non-selective degradation of organics to CO2 and water by adjusting oxidation processes. Among these processes, heterogeneous photocatalysis using TiO2-based photocatalysts is considered the most researched, promising, simple and environmentally friendly. The aim of this master thesis was to prepare TiO2 nanoparticle-based photocatalysts by wet impregnation, which can successfully degrade organic pollutants with visible light in a batch reactor. Since TiO2 is active only in the ultraviolet spectral region, plasmonic noble metals (Au, Pt) and their alloys were doped onto its surface. We specified the optical, structural and surface properties of the catalysts synthesised by characteristic methods and checked their efficiency in the formation of reactive oxigen species (HO - with coumarin, O2-- and e- with ABTS-+). The photocatalytic activity in the decomposition of bisfenol A under visible light was determined by high-resolution liquid surface chromatography, and the degree of contaminant mineralization was determined by measurements of total organic carbon before and after photocatalysis. The synthesised photocatalysts differed in their optical and surface properties, reactive oxygen species formation efficiency, and bisfenol A degradation. We also found that the use of Au, Pt and their alloys on the TiO2 support did not affect its morphology. For the degradation of BPA, the photocatalyst with alloy 0.25% Au + 0.75% Pt (80.7%) was the most efficient, followed by a catalyst with alloy 0.5% Au + 0.5% Pt (74.5%), although degradation was also possible with a catalyst with 1% Pt (70.9%). Since the catalyst with 0.5% Au + 0.5% Pt theoretically has potentially high catalytic activity, we additionally used it to test the decomposition efficiency of pharmaceutical agents such as aspirin, caffeine, and acetaminophen. The selected catalyst was most successful in decomposing aspirin (97%), followed by caffeine (79%) and a slightly lower decomposition of paracetamol (62%). The data collected confirm the catalytic potential of doped Au and Pt alloys, with Pt playing a dominant role in the decomposition of bisfenol A and pharmaceutical agents (aspirin, caffeine, paracetamol), or just ahead of Au