A study of photodegradation of arylazo pyridone dyes

U ovom radu proučavana je fotokatalitička degradacija arilazo piridonskih boja, 5-(4-supstituisani fenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona, korišćenjem simuliranesunčeve svetlosti. Kao katalizatori korišćeni su komercijalni TiO2 (Aeroxide P25) i TiO2filmovi.U prvom delu rada opisana je sinteza i karakterizacija arilazo piridonskih boja.Arilazo boje su sintetisane na dva načina. Prvi način sinteze obuhvata reakcijediazotovanja supstituisanih anilina i kuplovanja dobijene diazonijum soli sa 6-hidroksi-4-metil-3-cijano-2-piridonom. Drugim načinom arilazo piridonske boje su dobijenekuplovanjem diazonijum soli sa ketoestrom uz ciklizaciju nastalog proizvoda etil 3-okso-2-(supstitisanifenildiazenil)butanoata sa cijanoacetamidom. Da bi se ispitao uticajelektronskih efekata supstituenata na apsorpcione spektre sintetisanih boja, azo-hidrazotautomeriju i konstante kiselosti, sintetisano je jedanaest boja koje su se razlikovale poprirodi supstituenta na fenilnom jezgru diazo komponente. Ovi uticaji su kvantifikovanikorišćenjem Hammett-ove jednačine (princip linearnih korelacija slobodnih energija -LFER princip). Dobijeni rezultati su pokazali da elektron-akceptori prisutni na fenilomjezgru utiču na povećanje π,π-konjugacije u hidrazo tautomeru, dok elektron-donori utiču napovećanje π,π-konjugacije u azo tautomeru. Pokazano je da je elektronsko ponašanjeatoma azota azo i hidrazo grupe različito kod boja sa elektron-donorskim i elektronakceptorskimsupstituentima. Takođe, dobijeni rezultati su pokazali da je udeo hidrazokomponente i konstanta kiselosti najmanji kod nesupstituisanih boja, dok sapovećanjem elektron-donorskih i elektron-akceptorskih svojstava supstituenata u diazokomponenti boja ove vrednosti rastu.U drugom delu rada proučavana je fotokatalitička degradacija arilazo piridonskih bojakorišćenjem komercijalnog katalizatora TiO2, Aeroxide P25. Ispitivan je uticaj sledećihreakcionih parametara na brzinu fotodegradacije 5-(4-sulfofenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona: količina katalizatora, početna koncentracija boje, temperatura, pH,koncentracija H2O2, prisustvo etanola. Pokazano je da reakcije fotodegradacije sledekinetiku pseudo prvog reda, prema Langmuir-Hinselwood-ovom modelu. RezultatiTOC analize su pokazali da se boja može uspešno demineralizovati ispitivanimfotokatalitičkim procesom. U ovom delu rada proučavan je i uticaj elektronskihsvojstava suspstituenata na fenilnom jezgru supstituisanih boja na brzinefotodegradacije. Brzine fotodegradacije su korelisane sa Hammett-ovim konstantamasupstituenata. Najveće brzine degradacije su dobijene kod boja sa elektronakceptorskimsupstituentima, dok su najmanje brzine degradacije dobijene kod boja saelektron-donorskim supstituentima.U trećem delu rada proučavana je fotodegradacija arilazo boje, 5-(4-sulfofenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona korišćenjem poroznih TiO2 filmova. TiO2 filmovisu sintetisani na nosaču od nerđajućeg čelika metodom sprej pirolize. Pripremljene sudve grupe filmova: prva grupa polazeći od koloidnog TiO2 rastvora dobijenoghidrotermalnim postupkom i druga grupa polazeći od suspenzije TiO2, Aeroxide P25.Dobijeni filmovi su žareni na različitim temperaturama, a potom okarakterisaniprimenom sledećih metoda: (1) rendgenostrukturna analiza (XRD), (2) Hgporozimetrijai N2-fizisorpcija, (3) skenirajuća elektronska mikroskopija (SEM), (4)foto-elektronska spektroskopija X-zracima (XPS), (5) difuziono-refleksionaspektroskopija ultravioletne i vidljive oblasti (DR UV/Vis). Dobijeni rezultati supokazali da strukturna, morfološka i teksturalna svojstva filmova zavise u velikoj meriod temperature žarenja. Rezultati fotokatalitičkih testova su pokazali da se fotoaktivnostfilmova smanjuje sa povećanjem temperature žarenja, usled promena u njihovimsvojstvima. Poređenjem fotoaktivnosti filmova različitih debljina zaključeno je da suusled difuzionih ograničenja boje i/ili slabijeg prodiranja svetlosti, donji delovi filmamanje aktivni nego gornji. Pokazano je da difuzija boje i svetlosti zavisi od teksturalnihsvojstava filmova. U radu je izvršeno i poređenje fotoaktivnosti Aeroxide P25 TiO2praha, i filma dobijenog iz suspenzije TiO2, Aeroxide P25. Dobijeni rezultati supokazali da je fotoaktivnost filmova značajno manja u odnosu na fotoaktivnostogovarajućih prahova ne samo usled difuzionih ograničenja u sloju filma, većnajverovatnije i usled prisustva metala iz nosača.In this dissertation photocatalytic degradation of 5-(4-substituted phenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone using simulated sun light was investigated. Thecommercial TiO2, Aeroxide P25 and immobilized films were used as photocatalysts.The first part of the dissertation describes synthesis and characterization ofarylazo pyridone dyes. The arylazo pyridone dyes having different substituents (fromelectron-donating to electon-withdrawing) on phenyl ring of diazo component weresynthesized by two ways. The first synthesis way includes diazotization-couplingreactions and involves the conversion of 4-sulphoaniline to the diazonium ionintermediate 4-sulphobenzendiazonium ion, followed by the reaction with 3-cyano-6-hydroxy-4-methyl-2-pyridone. In the second way, the dyes were synthesized bycoupling diazonium salts with ketoesters followed by condensation withcyanoacetamide. The influence of electronic effects of substituents group in the arylazocomponent on the absorption spectra, azo/hydrazo tautomerism and acid constants ofdyes was investigated and quantified using Hammett equation (principle of linear freeenergy relationship-LFER). The obtained results showed that electron-withdrawingsubstituents in the arylazo component increase π,π-conjugation in hydrazo tautomer,while electron-donating substituents increase π,π-conjugation in azo tautomer. In addition, itwas observed that the electronic behaviour of the nitrogen atoms of azo and hydrazo groupis different between derivates with electron-donating and electron-withdrawing substituents.The results also showed that the quantity of hydrazo component and pKa values increasedwith increasing electron-donating and electron-withdrawing efects of substituents.In the second part of the dissertation the photocatalytic degradation of synthesizeddyes using commercial TiO2 Aeroxide P25 was investigated. The influence of differentprocess parameters (catalyst concentration, initial dye concentration, temperature, pH,H2O2 concentration, ethanol concentration) on photodegradation rate of 5-(4-sulphophenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone was studied. The reaction kineticsanalysis showed that photodegradation exhibits pseudo first-order kinetics according toLangmuir-Hinshelwood model. The results from TOC analysis showed that dye isefficiently mineralized using investigated photocatalytic process. In addition, the effectof substituents in the diazo component of the dyes on their photocatalytic degradationwas studied and quantified using Hammett equation. The results indicated that thephotodegradation rates were in a good degree dependent on the substituent electroniceffects being accelerated by electron-withdrawing groups and retarded by electrondonatinggroups.The third part of the dissertation describes the photocatalytic degradation of 5-(4-sulphophenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone using porous TiO2 films.TiO2 films were prepared on stainless steel substrate by spray pyrolysis technique. Twogroups of films were synthesized: first from hydrothermally prepared colloidal TiO2solution and second group using TiO2 Aeroxide P25 suspension. The prepared filmswere annealed at different temperatures and characterized using following methods: (1)X-ray diffraction analysis (XRD) (2) Hg-porosimetry and N2-physisorption (3)Scanning electron microscopy (SEM) (4) Photo-electron spectroscopy (XPS) (5) UVVisibleDiffuse Reflectance spectroscopy (DR UV/Vis). The obtained results showedthat films annealed at different temperature had different structural, textural andmorphological properties. The results from photocatalytic tests showed thatphotoactivity of the films decreased with increasing anenealing temperature, due toalterations in the films properties. Comparation of photoactivity of films with differentthickness showed that, due to limitations imposed by light transport and dye diffusion,the inner parts of films are less active than outer parts. These difusion limitationsdepends on textural properties of films. In addition, the photoactivity of TiO2 powderAeroxide P25 and corresponding film was compared. The difference in photoactivityarises not only from diffusion limitations in films, but also from the presence ofdifferent metals in film layer