56 research outputs found
A study of photodegradation of arylazo pyridone dyes
U ovom radu prouÄavana je fotokatalitiÄka degradacija arilazo piridonskih boja, 5-(4-
supstituisani fenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona, koriÅ”Äenjem simulirane
sunÄeve svetlosti. Kao katalizatori koriÅ”Äeni 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 naÄina. Prvi naÄin sinteze obuhvata reakcije
diazotovanja supstituisanih anilina i kuplovanja dobijene diazonijum soli sa 6-hidroksi-
4-metil-3-cijano-2-piridonom. Drugim naÄinom 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
koriÅ”Äenjem Hammett-ove jednaÄine (princip linearnih korelacija slobodnih energija -
LFER princip). Dobijeni rezultati su pokazali da elektron-akceptori prisutni na fenilom
jezgru utiÄu na poveÄanje Ļ,Ļ-konjugacije u hidrazo tautomeru, dok elektron-donori utiÄu na
poveÄanje Ļ,Ļ-konjugacije u azo tautomeru. Pokazano je da je elektronsko ponaÅ”anje
atoma azota azo i hidrazo grupe razliÄito kod boja sa elektron-donorskim i elektronakceptorskim
supstituentima. TakoÄe, dobijeni rezultati su pokazali da je udeo hidrazo
komponente i konstanta kiselosti najmanji kod nesupstituisanih boja, dok sa
poveÄanjem elektron-donorskih i elektron-akceptorskih svojstava supstituenata u diazo
komponenti boja ove vrednosti rastu.
U drugom delu rada prouÄavana je fotokatalitiÄka degradacija arilazo piridonskih boja
koriÅ”Äenjem komercijalnog katalizatora TiO2, Aeroxide P25. Ispitivan je uticaj sledeÄih
reakcionih parametara na brzinu fotodegradacije 5-(4-sulfofenilazo)-6-hidroksi-4-metil-
3-cijano-2-piridona: koliÄina katalizatora, poÄetna 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 uspeŔno demineralizovati ispitivanim
fotokatalitiÄkim procesom. U ovom delu rada prouÄavan je i uticaj elektronskih
svojstava suspstituenata na fenilnom jezgru supstituisanih boja na brzine
fotodegradacije. Brzine fotodegradacije su korelisane sa Hammett-ovim konstantama
supstituenata. NajveÄe brzine degradacije su dobijene kod boja sa elektronakceptorskim
supstituentima, dok su najmanje brzine degradacije dobijene kod boja sa
elektron-donorskim supstituentima.
U treÄem delu rada prouÄavana je fotodegradacija arilazo boje, 5-(4-sulfofenilazo)-6-
hidroksi-4-metil-3-cijano-2-piridona koriÅ”Äenjem poroznih TiO2 filmova. TiO2 filmovi
su sintetisani na nosaÄu od nerÄajuÄeg Äelika metodom sprej pirolize. Pripremljene su
dve grupe filmova: prva grupa polazeÄi od koloidnog TiO2 rastvora dobijenog
hidrotermalnim postupkom i druga grupa polazeÄi od suspenzije TiO2, Aeroxide P25.
Dobijeni filmovi su žareni na razliÄitim temperaturama, a potom okarakterisani
primenom sledeÄih metoda: (1) rendgenostrukturna analiza (XRD), (2) Hgporozimetrija
i N2-fizisorpcija, (3) skenirajuÄa 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, morfoloŔka i teksturalna svojstva filmova zavise u velikoj meri
od temperature žarenja. Rezultati fotokatalitiÄkih testova su pokazali da se fotoaktivnost
filmova smanjuje sa poveÄanjem temperature žarenja, usled promena u njihovim
svojstvima. PoreÄenjem fotoaktivnosti filmova razliÄitih debljina zakljuÄeno je da su
usled difuzionih ograniÄenja 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 izvrÅ”eno i poreÄenje fotoaktivnosti Aeroxide P25 TiO2
praha, i filma dobijenog iz suspenzije TiO2, Aeroxide P25. Dobijeni rezultati su
pokazali da je fotoaktivnost filmova znaÄajno manja u odnosu na fotoaktivnost
ogovarajuÄih prahova ne samo usled difuzionih ograniÄenja u sloju filma, veÄ
najverovatnije i usled prisustva metala iz nosaÄa.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 Ļ,Ļ-conjugation in hydrazo tautomer,
while electron-donating substituents increase Ļ,Ļ-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 Ļp 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 Ļp 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 Ā°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 FEāSEM and laser diffraction particle size analyzer, respectively. The textural properties were determined from NĀ¬2Ā¬ adsorption/desorption experiments, while the optical properties were studied using UVāVis 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 koriÅ”Äenjem 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
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