Comparative study on different reactivation approaches of composite photocatalysts used in water treatment

Zbog potencijalnog negativnog utjecaja na okoliš i ljudsko zdravlje nekoliko je farmaceutika, među kojima i diklofenak (DCF), uključeno na tzv. „watch“ listu u sklopu Okvirne direktive o vodama 2013/39/EU. Iz tih razloga javlja se potreba za istraživanjem učinkovitih ali i ekološki prihvatljivih metoda obrade u svrhu uklanjanja farmaceutika i ostalih prioritetnih tvari iz voda pri čemu napredni oksidacijski procesi pokazuju veliki potencijal. Cilj ovoga rada bio je utvrditi aktivnost TiO2–SnS2 fotokatalizatora, imobiliziranog na staklene pločice, pod djelovanjem simuliranog Sunčevog zračenja za uklanjanje diklofenaka u ponovljenim ciklusima. Reaktivacija korištenog fotokatalizatora TiO2-SnS2 u formi tankog filma između ciklusa provedena je upotrebom ozona u vodenom mediju i termičkom obradom. Naposljetku određeni su KPK i BPK5 pokazatelji kvalitete vode. Provedbom eksperimenta utvrđeno je da smanjenje uklanjanja DCF-a nakon termičke reaktivacije u odnosu na prvi ciklus nije znatno izraženo, dok uklanjanje TOC-a pokazuje nešto veći pad nakon reaktivacije pri najnižoj temperaturi. Temperatura od 200 °C pokazala se nedovoljno visokom za uklanjanje adsorbirane organske tvari te je aktivnost skoro istovjetna fotokatalizatoru koji nije reaktiviran. Kemijska reaktivacija nije imala znatan utjecaj na adsorpciju DCF-a u slijednom ciklusu, ali se znatnije odrazila na uklanjanje organske tvari, pri čemu su najviše pogodovali blagi uvjeti reaktivacije. Agresivniji uvjeti kemijske reaktivacije znatno su se nepovoljno odrazili na konverziju DCF-a. Povećanjem broja ciklusa biorazgradivost se smanjuje, što ukazuje na smanjenje fotokatalitičke aktivnosti.Diclofenac is one of the most frequently detected pharmaceuticals in the environment. Because of the potential negative impact on the environment and human health 3 pharmaceuticals, including diclofenac (DCF) are included on “watch” list under the Water Framework Directive 2013/39/EU. For these reasons there is a need to explore effective and environmentally acceptable method of treatment for removal of pharmaceuticals and other priority substances from water with an advanced oxidation processes show great potential. The aim of this study was to determine the activity of TiO2–SnS2 photocatalyst, immobilized on glass plates, under the effect of simulated solar radiation for the removal of diclofenac in repeated cycles. Reactivation of the used photocatalyst TiO2–SnS2 in a form of thin film between cycles was performed using ozone in an aqueous medium and thermal treatment. Finally, the COD and BOD water quality indicators were defined. The implementation of the experiment it was found that the reduction removal DCF upon reactivation heat from the first cycle is not essential, and the removal of TOC indicates a greater drop after reactivation at the lowest temperature. A temperature of 200 °C has proved to be sufficiently high to remove adsorbed organic matter this activity is almost identical to the photocatalyst which is not reactivated. Chemical reactivation did not have a significant impact on the adsorption of DCF in the sequence cycle, but has significantly affected the removal of organic matter, which was conducted in mild experimental conditions of reactivation. Aggressive chemical conditions of reactivation had a significant adverse effect on the conversion of DCF. By increasing the number of cycles, biodegradability decreases, which indicates a loss of photocatalytic activity