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 simulirane sunčeve svetlosti. Kao katalizatori korišćeni su komercijalni TiO2 (Aeroxide P25) i TiO2 filmovi. U prvom delu rada opisana je sinteza i karakterizacija arilazo piridonskih boja. Arilazo boje su sintetisane na dva načina. Prvi način sinteze obuhvata reakcije diazotovanja supstituisanih anilina i kuplovanja dobijene diazonijum soli sa 6-hidroksi- 4-metil-3-cijano-2-piridonom. Drugim načinom arilazo piridonske boje su dobijene kuplovanjem diazonijum soli sa ketoestrom uz ciklizaciju nastalog proizvoda etil 3- okso-2-(supstitisanifenildiazenil)butanoata sa cijanoacetamidom. Da bi se ispitao uticaj elektronskih efekata supstituenata na apsorpcione spektre sintetisanih boja, azo-hidrazo tautomeriju i konstante kiselosti, sintetisano je jedanaest boja koje su se razlikovale po prirodi supstituenta na fenilnom jezgru diazo komponente. Ovi uticaji su kvantifikovani korišćenjem Hammett-ove jednačine (princip linearnih korelacija slobodnih energija - LFER princip). Dobijeni rezultati su pokazali da elektron-akceptori prisutni na fenilom jezgru utiču na povećanje π,π-konjugacije u hidrazo tautomeru, dok elektron-donori utiču na povećanje π,π-konjugacije u azo tautomeru. Pokazano je da je elektronsko ponašanje atoma azota azo i hidrazo grupe različito kod boja sa elektron-donorskim i elektronakceptorskim supstituentima. Takođe, dobijeni rezultati su pokazali da je udeo hidrazo komponente i konstanta kiselosti najmanji kod nesupstituisanih boja, dok sa povećanjem elektron-donorskih i elektron-akceptorskih svojstava supstituenata u diazo komponenti boja ove vrednosti rastu. U drugom delu rada proučavana je fotokatalitička degradacija arilazo piridonskih boja korišćenjem komercijalnog katalizatora TiO2, Aeroxide P25. Ispitivan je uticaj sledećih reakcionih 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 slede kinetiku pseudo prvog reda, prema Langmuir-Hinselwood-ovom modelu. Rezultati TOC analize su pokazali da se boja može uspešno demineralizovati ispitivanim fotokatalitičkim procesom. U ovom delu rada proučavan je i uticaj elektronskih svojstava suspstituenata na fenilnom jezgru supstituisanih boja na brzine fotodegradacije. Brzine fotodegradacije su korelisane sa Hammett-ovim konstantama supstituenata. Najveće brzine degradacije su dobijene kod boja sa elektronakceptorskim supstituentima, dok su najmanje brzine degradacije dobijene kod boja sa elektron-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 filmovi su sintetisani na nosaču od nerđajućeg čelika metodom sprej pirolize. Pripremljene su dve grupe filmova: prva grupa polazeći od koloidnog TiO2 rastvora dobijenog hidrotermalnim postupkom i druga grupa polazeći od suspenzije TiO2, Aeroxide P25. Dobijeni filmovi su žareni na različitim temperaturama, a potom okarakterisani primenom sledećih metoda: (1) rendgenostrukturna analiza (XRD), (2) Hgporozimetrija i N2-fizisorpcija, (3) skenirajuća elektronska mikroskopija (SEM), (4) foto-elektronska spektroskopija X-zracima (XPS), (5) difuziono-refleksiona spektroskopija ultravioletne i vidljive oblasti (DR UV/Vis). Dobijeni rezultati su pokazali da strukturna, morfološka i teksturalna svojstva filmova zavise u velikoj meri od temperature žarenja. Rezultati fotokatalitičkih testova su pokazali da se fotoaktivnost filmova smanjuje sa povećanjem temperature žarenja, usled promena u njihovim svojstvima. Poređenjem fotoaktivnosti filmova različitih debljina zaključeno je da su usled difuzionih ograničenja boje i/ili slabijeg prodiranja svetlosti, donji delovi filma manje aktivni nego gornji. Pokazano je da difuzija boje i svetlosti zavisi od teksturalnih svojstava filmova. U radu je izvršeno i poređenje fotoaktivnosti Aeroxide P25 TiO2 praha, i filma dobijenog iz suspenzije TiO2, Aeroxide P25. Dobijeni rezultati su pokazali da je fotoaktivnost filmova značajno manja u odnosu na fotoaktivnost ogovarajućih prahova ne samo usled difuzionih ograničenja u sloju filma, već najverovatnije 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. The commercial TiO2, Aeroxide P25 and immobilized films were used as photocatalysts. The first part of the dissertation describes synthesis and characterization of arylazo pyridone dyes. The arylazo pyridone dyes having different substituents (from electron-donating to electon-withdrawing) on phenyl ring of diazo component were synthesized by two ways. The first synthesis way includes diazotization-coupling reactions and involves the conversion of 4-sulphoaniline to the diazonium ion intermediate 4-sulphobenzendiazonium ion, followed by the reaction with 3-cyano-6- hydroxy-4-methyl-2-pyridone. In the second way, the dyes were synthesized by coupling diazonium salts with ketoesters followed by condensation with cyanoacetamide. The influence of electronic effects of substituents group in the arylazo component on the absorption spectra, azo/hydrazo tautomerism and acid constants of dyes was investigated and quantified using Hammett equation (principle of linear free energy relationship-LFER). The obtained results showed that electron-withdrawing substituents in the arylazo component increase π,π-conjugation in hydrazo tautomer, while electron-donating substituents increase π,π-conjugation in azo tautomer. In addition, it was observed that the electronic behaviour of the nitrogen atoms of azo and hydrazo group is different between derivates with electron-donating and electron-withdrawing substituents. The results also showed that the quantity of hydrazo component and pKa values increased with increasing electron-donating and electron-withdrawing efects of substituents. In the second part of the dissertation the photocatalytic degradation of synthesized dyes using commercial TiO2 Aeroxide P25 was investigated. The influence of different process parameters (catalyst concentration, initial dye concentration, temperature, pH, H2O2 concentration, ethanol concentration) on photodegradation rate of 5-(4-sulpho phenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone was studied. The reaction kinetics analysis showed that photodegradation exhibits pseudo first-order kinetics according to Langmuir-Hinshelwood model. The results from TOC analysis showed that dye is efficiently mineralized using investigated photocatalytic process. In addition, the effect of substituents in the diazo component of the dyes on their photocatalytic degradation was studied and quantified using Hammett equation. The results indicated that the photodegradation rates were in a good degree dependent on the substituent electronic effects being accelerated by electron-withdrawing groups and retarded by electrondonating groups. 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. Two groups of films were synthesized: first from hydrothermally prepared colloidal TiO2 solution and second group using TiO2 Aeroxide P25 suspension. The prepared films were 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) UVVisible Diffuse Reflectance spectroscopy (DR UV/Vis). The obtained results showed that films annealed at different temperature had different structural, textural and morphological properties. The results from photocatalytic tests showed that photoactivity of the films decreased with increasing anenealing temperature, due to alterations in the films properties. Comparation of photoactivity of films with different thickness 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 limitations depends on textural properties of films. In addition, the photoactivity of TiO2 powder Aeroxide P25 and corresponding film was compared. The difference in photoactivity arises not only from diffusion limitations in films, but also from the presence of different metals in film layer

Theoretical study of substituent effects on structural properties of arylazo pyridone dyes

Quantum chemical calculations performed by the density functional theory (DFT) were used to determine the structural parameters of arylazo pyridone dyes. The influence of electronic effects of substituent in diazo moiety of dyes on their structure properties was studied and quantified using Hammett equation. The correlation between dye bond length and Hammett substituent constants σp gave us possibility to locate the most sensitive bond to substituent effects

Hydrogen production from glycerol photo-reforming over Pt/N-doped titanate photocatalysts

Conversion of sunlight energy via photocatalytic water splitting and photo-reforming of renewable biomass organic derivates has been increasingly utilized for hydrogen production. Photocatalytic processes have been used due to their sustainability, environmental-safety, and effectiveness. Pt/Ndoped titanate photocatalysts were synthetized via alkaline hydrothermal treatment, followed by Na+/NH4+ion exchange, impregnation and gaseous reduction. The activities of the photocatalysts were tested for hydrogen production via photocatalytic reforming of glycerol under simulated solar irradiation. The improved hydrogen production from photo-reforming of glycerol was attributed to the anatase active phase and surface area which enhanced the adsorption of glycerol onto the surface of catalysts; metallic Pt suppress the electron/hole recombination by trapping the photo-generated electrons; reduced band gap by incorporation of N into lattice of TiO2

Nickel doped titanate catalysts for photocatalytic hydrogen generation

This study will focus on investigation of photocatalytic hydrogen production activity over low cost Ni modified titanates, as alternatives for highly cost and low-abundance noble metal based catalysts. The catalysts with different nickel loading were synthesized by deposition of predetermined amount of nickel on hydrothermally prepared titanate support, followed by hydrogen temperature programmed reduction (TPR). The final catalysts were characterized using various methods, such as N2 physisorption, XRD, TPR. The study showed that adequate selection of synthesis parameters results in catalyst with improved textural, morphological and structural properties. The investigation on the effect of the nickel content on the photocatalytic hydrogen production allowed us to define the optimal metal content in the synthesized catalysts

Theoretical study of substituent effects on structural properties of arylazo pyridone dyes

Quantum chemical calculations performed by the density functional theory (DFT) were used to determine the structural parameters of arylazo pyridone dyes. The influence of electronic effects of substituent in diazo moiety of dyes on their structure properties was studied and quantified using Hammett equation. The correlation between dye bond length and Hammett substituent constants σp gave us possibility to locate the most sensitive bond to substituent effects

Photocatalytic activity of peg-modified catalysts

This work is focused on the influence of polyethylene glycol (PEG) on structural, textural and photocatalytic properties of titanium dioxide (TiO2) catalyst. Catalysts were synthesized by sol-gel method using PEG with different molecular weight (600 and 10000) as pore generating agent. The results showed that PEG enhances not only porous structure but also change anatase to rutile ratio. The photocatalytic activity of the synthesized catalyst was measured by decomposition of phenol. The order of catalyst photoactivity was: TiO2/P600>TiO2/P10000>TiO2.The difference in catalyst photoactivity is attributed to their surface area and anatase fraction, rather then pore size

Enhanced natural sunlight- and artificial UV-driven photocatalytic activity of mechanically activated ZnO/SnO2 composite

Over the past four decades there is an increasing interest to develop highly efficient semiconductor photocatalysts for degradation of organic and biological pollutants in water under light irradiation. The semiconductor band gap determines which wavelength of light will be absorbed; precisely, semiconductors with a wide band gap (> 3 eV) can absorb only UV light, while those with a narrow band gap (< 3 eV) can be activated by visible light. In this study we examined structural, morphological, textural and optical properties of ZnO/SnO2 composite as potential photocatalyst. Mechanical activation of commercial ZnO and SnO2 powders has been used to produce a composite with high density of surface defects. To investigate the influence of thermal treatment on the physical properties, and consequently on photoactivity, the composite has been traditionally annealed at 400 and 700 °C. The phase purity, crystal structure and average crystallite size of pristine metal oxides and the composites were investigated by X-ray diffraction and Raman spectroscopy. The particles morphology and size distributions were studied by FE–SEM and laser diffraction particle size analyzer, respectively. The textural properties were determined from N¬2¬ adsorption/desorption experiments, while the optical properties were studied using UV–Vis diffuse reflectance and photoluminescence spectroscopy. Photocatalytic activity of pristine ZnO and ZnO/SnO2 composites were examined via de-colorization of methylene blue under: (1) direct natural sunlight, and (2) artificial UV irradiation. In both cases enhanced photocatalytic activity of ZnO/SnO2 has been found. Enhanced photocatalytic activity can be attributed to the surface defects and to created ZnO/SnO2 heterojunctions which reduced electron-hole recombination time

Photocatalytic activity of peg-modified catalysts

This work is focused on the influence of polyethylene glycol (PEG) onstructural, textural and photocatalytic properties of titanium dioxide (TiO2)catalyst. Catalysts were synthesized by sol-gel method using PEG withdifferent molecular weight (600 and 10000) as pore generating agent. Theresults showed that PEG enhances not only porous structure but also changeanatase to rutile ratio. The photocatalytic activity of the synthesized catalystwas measured by decomposition of phenol. The order of catalystphotoactivity was: TiO2/P600>TiO2/P10000>TiO2.The difference in catalystphotoactivity is attributed to their surface area and anatase fraction, ratherthen pore size

Sinteza 5-(supstituisanih fenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona iz etil-3-okso-2-(supstituisanih fenilazo)butanoata

A new procedure for the synthesis of known azo pyridone dyes is presented. A series of 5-(substituted arylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridones were prepared from ethyl 3-oxo-2-(substituted phenylazo)butanoates and cyanoacetamide in acetone using potassium hydroxide as a catalyst by simple refluxing the reaction mixture. The structure of these dyes was confirmed by FT-IR, NMR and UV-Vis spectroscopy.Novi postupak za sintezu poznatih azo-piridonskih boja je opisan u radu. Serija 5-(supstituisanih fenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona je pripremljena iz etil-3-okso-2-(supstituisanih fenilazo)butanoata i cijanoacetamida u acetonu korišćenjem kalijum-hidroksida kao katalizatora uz zagrevanje

Morphology and fractal dimension of tio2 thin films

The influence of annealing temperature on the morphology and surface fractal dimension of titanium dioxide (TiO2) films prepared via the spray deposition process was investigated. Thin films with various morphologies were obtained at different temperatures and characterized by X-ray diffraction and atomic force microscopy (AFM). It was found that the crystalline structure of TiO2 films depends strongly on annealing temperature. At higher temperatures, the partial phase transformation of anatase-to-rutile was observed. The morphology and surface fractal dimensions were evaluated by image analysis methods based on AFM micrographs. The results indicate that the value of surface roughness (the standard deviation of the height values within the given area of AFM image) of TiO(2)films increases with increasing annealing temperature. Fractal analysis revealed that the value of the fractal dimension of the samples decreases slowly from 2.23 to 2.15 following the annealing process