| Abstract | Najčešće korišteni poluvodič kao fotokatalizator za fotooksidaciju, u heterogenom fotokatalitičkom sustavu za razgradnju onečišćivala u vodi, koristi se titanijev dioksid
TiO2-P25. Razlog njegovog korištenja ogleda se u velikoj moći fotogeneriranja parova elektrona i šupljina, niskoj cijeni, velikoj aktivnosti i slično. Međutim, problem koji ograničava primjenu TiO2 fotokatalizatora je apsorpcija zračenja valnih duljina većih od 400 nm, kao i problem uklanjanja suspenzije fotokatalizatora nakon završenog procesa fotokatalitičke oksidacije i njegova ponovna upotreba. Osim navedenoga, ne postoji jednostavan matematički model, koji opisuje heterogeni fotokatalitički proces, a da posjeduje konstantu brzine razgradnje organske tvari neovisnu o geometriji fotoreaktora. Navedeni model mogao bi se koristiti za uvećanje procesa. Prema navedenom, u ovom radu istražen je heterogeni fotokatalitički proces u cilju pronalaženja rješenja za navedene probleme koji ograničavaju primjenu TiO2 fotokatalizatora. Kao modelno onečišćivalo korištena je salicilna kiselina. Istraživanje je pokazalo da se metodom redukcije srebra uz kitozan može sintetizirati srebrom dopirani fotokatalizator koji pri zračenju valnih duljina > 400 nm pokazuje fotokatalitičku aktivnost (kvis = 0,0037 min^-1), dok pri umjetnom sunčevom zračenju pokazuje 1,4 puta veću aktivnost od nedopiranog suspendiranog TiO2-P25 pri istim uvjetima. Primjenom željezove soli moguće je poboljšati proces fotokatalize i provesti separaciju suspenzije fotokatalizatora koagulacijom (nakon 60 min uklonjeno 89,55 % TiO2-P25), ako se željezova sol dodaje samo u svrhu koagulacije tada je separacija izraženija (nakon 60 min uklonjeno 95,05 % TiO2-P25). Kitozan kao koagulanta također pokazuje zadovoljavajuće rezultate uklanjanja suspenzije TiO2-P25 (nakon 60 min uklonjeno > 95 % TiO2-P25). Istraživanje je pokazalo kada je separacija TiO2-P25 fotokatalizatora temeljena na koagulaciji, bilo željezovom soli ili kitozanom, nije moguće upotrijebiti istaloženi fotokatalizator u novom fotokatalitičkom ciklusu. Međutim, istraživanje je pokazalo da se imobilizacijom fotokatalizatora može riješiti problem ponovne upotrebe fotokatalizatora u novom ciklusu. Rezultati su pokazali da ne dolazi do pada aktivnosti kada se TiO2 imobilizira na stijenku reaktora i primijeni u više ciklusa zargradnje salicilne kiseline. Istraživanje je provedeno na
6 ciklusa fotokatalize (1 ciklus trajao je 60 min). Konstanta brzine imobiliziranog fotokatalizatora na stijenci reaktora koja uzima u obzir masu fotokatalizatora ima 6,3 puta veću vrijednost od procesa s suspendiranim TiO2- P25. Osim na staklenoj stjenci imobilizacija TiO2 provedena je i na nosaču hidroksiapatita. Iako je aktivnost navedenog imobiliziranog fotokatalizatora pokazala jednaku aktivnost kao i suspendirani TiO2-P25, zbog raspadanja nosača tijekom miješanja, pokazao se kao neučinkovit. Razvijen je matematički model za sustav s imobiliziranim TiO2 na stijenci reaktora. Kinetički model uključuje model emisije zračenja, te konstantu brzine neovisnu o geometriji reaktora koja opisuje razgradnju salicilne kiseline, 2,5-dihidroksibezojeve kiseline, 2,3-dihidroksibenzojeve kiseline i grupu spojeva koju čine katehol, resorcinol, hidrokinon, alifatske kiseline kao i ostali organski spojevi kuji su, kao grupa organski nusprodukti, praćeni metodom ukupnog organskog ugljika. |
| Abstract (english) | Titanium dioxide TiO2-P25 is the most commonly used semiconductor as photocatalyst for photooxidation, in the heterogeneous photocatalytic system for the degradation of pollutants in water. The reason for its use is reflected in the great power of photogeneration of pairs of electrons and cavities, low cost, high activity and similar. However, the problem limiting the application of TiO2 photocatalyst is the absorption of radiation of wavelengths exceeding
400 nm, as well as the problem of removing the photocatalyst suspension after the photocatalytic oxidation process has been completed and its re-use. Apart from the above, there is no simple mathematical model describing a heterogeneous photocatalytic process which also possesses a rate constant of degradation of organic matter independent of the geometry of the photoreactor. The mentioned model could be used for scaling up process. Accordingly, in this paper, a heterogeneous photocatalytic process was investigated in order to find a solution to the stated problems which limit the application of TiO2 photocatalyst. Salicylic acid was used as a model pollutant. The research showed that with the method of reduction of silver with chitosan the silver-doped photocatalyst can be synthesized, which exhibits photocatalytic activity (kvis = 0.0037 min^-1) under the radiation of wavelengths
> 400 nm, while it exhibits 1.4 times higher activity under artificial solar radiation than undoped suspended TiO2-P25 under the same conditions. By using iron salt it is possible to improve the photocatalysis process and to carry out the separation of the photocatalyst suspension by coagulation (after 60 min 89.55% TiO2-P25 is removed), and if the iron salt is added for coagulation purposes only then the separation is more pronounced (after 95 min 95.05% TiO2-P25 is removed). Chitosan as a coagulant also showed satisfactory results of the TiO2-P25 suspension removal (after 60 min is removed> 95% TiO2-P25). The research showed that when the separation of TiO2-P25 photocatalyst is based on coagulation, whether iron salt or chitosan, it is not possible to use a precipitated photocatalyst in a new photocatalytic cycle. However, the research has shown that by photocatalyst immobilization can be solved the problem of reusing photocatalysts in a new cycle. The results showed that no decrease in activity occurs when TiO2 is immobilized on the reactor wall and applied to multiple salicylic acid degradation cycles. The research was conducted on 6 cycles of photocatalysis (1 cycle lasted 60 min). The rate constant of the immobilized photocatalyst on the reactor wall considering the mass of the photocatalyst is 6.3 times higher than the process with suspended TiO2-P25. In addition to the glass wall, TiO2 immobilization was also carried out on a hydroxyapatite carrier. Although the activity of said immobilized photocatalyst showed the same activity as suspended TiO2-P25, due to carrier decomposition during mixing, it proved to be ineffective. A mathematical model for a system with immobilized TiO2 on a reactor wall has been developed. The kinetic model includes a radiation emission model and a rate constant independent of the reactor geometry describing the degradation of salicylic acid, 2,5-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid and a group of compounds consisting of catechol, resorcinol, hydroquinone, aliphatic acids and other organic compounds which are, as a group organic by-products, followed by the total organic carbon method. |
