Napredne oksidacijske tehnologije (engl. Advanced Oxidation Technologies, AOTs), predstavljaju atraktivnu alternativu tradicionalnim metodama za rješavanje problematike otpadnih voda opterećenih različitim postojanim organskim onečišćivalima. U ovoj disertaciji pozornost je usmjerena iznalaženju optimalnih uvjeta pripreme kitozan/TiO2 filmova koja pokazuju fotokatalitička svojstva pri sunčevom zračenju. Učinkovitost pripravljenog fotokatalizatora pratila se na modelnoj otopini površinske aktivne tvari anionskog tipa: natrijevog dodecilbenzensulfonata (SDBS). Posebni naglasak disertacije je stavljen na održivost, posebno očuvanja energije, ali i sirovinskih izvora, jer su za izradu fotokatalitičkih filmova korišteni otpadni materijali kao što su biootpad kitozan, otpadni tonerski prah te kao nosači fotokatalitičkih filmova upotrebljene su otpadne tiskarske ploče. Povezivanje kitozana s fotokatalizatorom TiO2 ima višestruku korist. Novo pripremljeni fotokatalitički filmovi pokazuju sinergijski efekt koji se očituje kroz njegova adsorpcijsko-fotokatalitička svojstva, pri čemu se dodatno povećava kapacitet adsorpcije kroz interakciju naboja između molekule onečišćivača i kitozana. Unutar istraživanja opisan je način izrade senzibiliziranih fotokatalitičkih filmova i provedena njihova karakterizacija. Različita kationska i anionska bojila, pigmenti te otpadni tonerski prah ispitani su unutar ovog znanstvenog–istraživačkog rada kao mogući senzibilizatori osnovne matrice filmova na bazi kitozan/TiO2. Novo pripravljeni fotokatalitički filmovi imobilizirani su na prstenaste i pločaste nosače od stakla, nehrđajućeg čelika (18/8) i otpadne tiskarske ploče. Razgradnja SDBS praćena je na temelju analitičkih metoda i to: ultraljubičastom i vidljivom spektrofotometrijom (UV/Vid), tekućinskom kromatografijom s masenim detektorom (LC/MS-MS) i analizatorom organskog ugljika (TOC). Eksperimenti su provedeni u kotlastom šaržnom reaktoru (CBR) uz korištenje umjetnog izvora zračenja: UV-C, (niskotlačna živina elektrolučna svjetiljka) te cijevnom solarnom reaktoru s potpunom recirkulacijom (CBSR) uz korištenje umjetnog izvora zračenja: ksenon elektrolučna svjetiljka (>290 nm, 1500 W) i uz upotrebu prirodnog sunčevog zračenja (>290 nm). Unutar rada provedena je detaljna kinetička studija te provedeno matematičko modeliranje koje je uspješno validirano u različito postavljenim uvjetima provedenih pokusa.
|Abstract (english)|| |
Optimal conditions development for preparation of immobilized visible light sensitized chitosan/TiO2 films, with the aim of increasing the potential utilization of solar energy and their applications in the treatment of waste water have been widely studied in the frame of this work. Surfactants as an integral part of many commercial products and technological processes, are one of the most widespread group of substances that are plaguing today's environment. Anionic surfactants represents almost 65% of the world's total surfacants compsumtions. The presence of these compounds in water is a problem with the two main aspects of water management: water source protection and re-use of most municipal and industrial wastewater, therefore the selection of acceptable solutions to reduce the burden of waste water poses a major significance for the conservation of aquatic ecosystems, and the principles of sustainable development. Implementation of heterogene photocatalysis as an advanced oxidation process and photocatalyst modification, with the purpose of improving the photocatalytic activity under visible light (solar radiation >290 nm), represents an attractive alternative to conventional biological, physical and chemical methods of the treatment of wastewaters. Semiconductor photocatalysis showed a great potential as sustainable treatment technology according to the "zero" waste scheme in the wastewater treatment facilities. When the surface of a semiconductor catalyst is illuminated by photons (hν) having energy equal to or greater than the energy of their forbidden zone Eg (hν≥Eg) creates electron-hole pairs (e/h+). The separation of electric charge is key, because holes caused valent bands to act as strong oxidants, while the free electrons in the conduction band act as reducing agents. Simultaneously, electron-hole pairs still participating in redox reactions with molecules adsorbed to the surface of the catalyst, such as water, hydroxyl ions, or organic compounds of oxygen. The result of these reactions is the formation of highly reactive radicals (∙OH, O2∙-) that quickly and indiscriminately react with most organic compounds by degrading them to simple non-toxic molecule that is CO2 and H2O, improving in this way the ecological characteristics of wastewater . Within this study TiO2 is due to its characteristics almost ideal photocatalyst selected as a photocatalyst. Sensitization of its surface using different dyes and pigments is undoubtedly one of the possibilities for a shift of absorption of ultraviolet (UV) to the visible (Vis) part of the electromagnetic spectrum. For this purpose, different cationic and anionic dyes, and also pigments, were applied as sensitizers for chitosan –TiO2 films. The use of biopolymer chitosan as a carrier/auxiliary substances in heterogeneous photocatalysis shows multifunctional effect of TiO2 in heterogeneous photocatalytic technology improving adsorption - photocatalytic processes . The mechanism of adsorption - photocatalytic process suggests that the installation of chitosan on the surface of TiO2 leads to the formation of synergistic effect by increasing the adsorption capacity through the charge interaction. The main objective of the research is focused on the possibilities for reuse of waste off-set printing plate as the solid support and sensitization of the surface of TiO2/waste printer toner powder, with the purpose of monitoring the new guidelines of sustainability and conservation of energy and raw material sources. The research methodology consists of : (i) dyes and pigments sensitised photocatalytic films (chitosan -TiO2); (ii) waste printer toner powder sensitised photocatalytic films (chitosan-TiO2) (iii) finding the optimal composition of the dye sensetised photocatalytic films ; (iv) application of developed films for photocatalytic treatment of selected model solution SDBS; (v) optimal working conditions in laboratory reactor with UV-C irradiation (vi) the implementation of photocatalysis in boat flow reactor under natural solar irradiation (vii) In order to estimate the reaction rate constant for SDBS degradation over irradiated photocatalytic films and to evaluate the effects of photon absorption under different irradiation conditions a detailed kinetic model was developed.
The results, discussion and conclusions:
In this work, different dye and pigments and commercial TiO2 powder were integrated within the matrix of chitosan molecules as a thin layer films. Several different approaches were explored: different method preparation of films, and different ratio of TiO2 (4 g and 10 g) and dye or pigments (0.5 g and 0.1 g) in film, respectively. Photocatalytic films were supported on different materials: glass, stainless steel waste offset printing plates, containing aluminum, shape in plates and rings. The development and a partial characterization of the supported catalyst were described within this study. Characterization of photocatalytic films and samples of starting materials together with pure photocatalytic film (CS/TiO2) were carried out by following methods: morphology of photocatalytic film surfaces was analyzed by scanning electron microscopy (SEM), FT-IR spectroscopy was used to determine functional groups within newly synthesized CS/TiO2-dye film. UV/Vis-DRS spectrophotometry was used to check the absorption of visible light and determine potential changes in band gap; TGA study was applied in order to perform a quantitative analysis of the newly prepared photocatalyst films. Gas sorption analysis instrument ware applied for determing accurate and precise surface area and pore size distribution in newly prepared photocatalitic films and there percusors. The developed films contain the high amount of the TiO2, which structure appeared to be intact. Experiments were performed in a batch laboratory reactor using artificial light sources: UV-C (low-pressure mercury lamp) and solar light (suntest chamber equipped with Xenon lamp). In order to evaluate the possibility of using the natural light source, the additional set of experiments has been performed in the boat flow reactor under direct sunlight. The efficiency of the photocatalytic oxidation of the anionic surfactant sodium dodecylbenzenesulfonate (SDBS) has been evaluated by the means of mineralization based on the analysis of total organic carbon (TOC), whose content has been determined by the TOC analyzer. Concentration of SDBS was determined spectrophotometrically with UV/Vis spectrophotometer and aliphatic acids during the treatment were monitoring by LC/MS-MS using an chromatograph coupled to an triple quadrupole mass spectrometer equipped with an electrospray ionization (ESI) interface. Based on the results it was concluded the following: the method of preparation of the film and the number of coating layers of dye sensitised film (optimum weight catalyst) has been show significant impact on the photocatalytic film properties, while the shape and type of support showed no significant influence on the photocatalytic activity. Further research has shown that the efficiency of applied sensitized photocatalytic film significantly varies depending on the pH of the solution; maximum degradation of SDBS was achieved in neutral medium, while the optimum pH of unsensitized film shifts toward acidic medium. Furthermore, removal extents vary due to different energy levels capable of photoexciting TiO2 particle and photodegrate SDBS in aqueous solution. Removal of SDBS (85.77 %) is the most efficient under illuminations of using Xenon lamp in suntest simulator chamber (1500 W), with the apparent rate constant of 0.0536 min-1 and SDBS half-life of 12.92 min. Similar effect have been observed when a source of natural solar light was employed, whereby removal of SDBS of 80.06 % was achieved. In half life time of 17.86 min (kapp=0.0388 min-1) concentration of SDBS fell to half of its initial value. The lowest activity was observed when UV-C light source was used in CBR with obtained SDBS removal of 25.57 % and apparent rate constant of 0.0099 min-1 corresponding to the half life value of 70 min. These findings are results of exclusion of photolysis from overall experimental results, becouse photolysis becomes a dominant process at degradation of SDBS in CBR using UVC lamp, while this is not the case with CBSR using natural solar irradiation and Xenon lamp. The results of detailed kinetic study showed following: (i) the waste toner pigment appears as a good sensitizer according to determined dye sensitization factor, fDS =1.38 ± 0.07 (ii) photocatalytic oxidation of SDBS on studied film surfaces followed a first-order reaction rate according to experimental data Due to the presence of waste pigment particles as a sensitizer in photocatalytic films, SDBS photocatalytic oxidation is faster under natural and artificial solar irradiation that under the high-intensity monochromatic UV-C irradiation. Photosensitization of TiO2 with selected pigment resulted in significant improvement in the ability to remediate wastewater on a laboratory scale under direct sunlight.