Jasmina Dostanić

Spectroscopic and quantum chemical investigations of substituent effects on the azo-hydrazone tautomerism and acid–base properties of arylazo pyridone dyes

A series of 5-(4-substituted arylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone dyes was synthesized and the structure of the dyes was confirmed by UV-Vis, FT-IR, (1)H NMR and (13)C NMR spectroscopic techniques. The azo-hydrazone tautomeric equilibrium was found to depend on the substituents as well as on the acidity and basicity of the media. Ionization constant, pKa, of the dyes was determined by UV-Vis spectroscopy and correlated with the Hammett substituent constants, σp and σI. The interpretation of the effect of different substituent in phenyl ring of arylazo pyridone dyes on their spectroscopic and structural properties was based on quantum chemical calculations performed by the density functional theory (DFT/M06-2X) method. The DFT calculations confirmed the existence of two forms in water solution: hydrazone form in acidic and neutral media and anionic form in basic media. The different contribution of azo and hydrazone canonical forms of anionic form is observed for dyes with electron-donating and dyes with electron-withdrawing groups. The dependence of absorption spectra and determined pKa values to the substituent type seems to be mostly due to azo/hydrazone canonical structure ratio in their anionic form.

Influence of process parameters on the photodegradation of synthesized azo pyridone dye in TiO2 water suspension under simulated sunlight

Photocatalytic degradation of synthesized azo pyridone dye (5-(4-sulpho phenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone), in aqueous solutions by simulated sunlight in the presence of commercial TiO2, Aeroxide P25, was studied. The reaction kinetics analysis showed that photodegradation exhibits pseudo first-order kinetics according to Langmuir-Hinshelwood model. The effects of various process parameters on the photocatalytic degradation were investigated. The optimal catalyst content and pH were determined. A decrease in the reaction rate was observed upon the increase of the initial dye concentration. Degradation of the dye was enhanced by hydrogen peroxide, but it was inhibited by ethanol. The influence of temperature was studied, and the energy of activation was determined. According to total organic carbon (TOC) analysis, 54% of TOC remained when 100% of the dye was decolorized. Although the intermediates were not determined in this study, the TOC results clearly indicate their presence during the reaction. In addition, photocatalytic degradation of simulated dyehouse effluents, containing tested azo pyridone dye and associated auxiliary chemicals was investigated.

Photocatalytic degradation of azo pyridone dye: Optimization using response surface methodology

Abstract Response surface methodology (RSM) and central composite design have been applied to describe and optimize photocatalytic degradation of azo pyridone dye using TiO2, H2O2, and simulated sun light. The mutual interactions between three independent variables, viz. H2O2 concentration, irradiation time, and TiO2 content were obtained. The results revealed that the most influential variables under selected reaction conditions were irradiation time and TiO2 content. The optimized conditions for the photocatalytic degradation of azo pyridone dye were as follows: H2O2 concentration: 130.5 mg/L, irradiation time: 54.8 min, and TiO2 content: 2.48 g/L. Under these conditions, the maximum decolorization efficiency of 96.43% was achieved. This experimental value was in good agreement with the predicted one, which proved the validity of the model. Operation cost analysis indicated that irradiation time had the major influence on total process cost. The RSM based on the central composite design was shown to be ...

Quantitative structure-activity relationship analysis of substituted arylazo pyridone dyes in photocatalytic system: Experimental and theoretical study

A series of arylazo pyridone dyes was synthesized by changing the type of the substituent group in the diazo moiety, ranging from strong electron-donating to strong electron-withdrawing groups. The structural and electronic properties of the investigated dyes was calculated at the M062X/6-31+G(d,p) level of theory. The observed good linear correlations between atomic charges and Hammett σp constants provided a basis to discuss the transmission of electronic substituent effects through a dye framework. The reactivity of synthesized dyes was tested through their decolorization efficiency in TiO2 photocatalytic system (Degussa P-25). Quantitative structure-activity relationship analysis revealed a strong correlation between reactivity of investigated dyes and Hammett substituent constants. The reaction was facilitated by electron-withdrawing groups, and retarded by electron-donating ones. Quantum mechanical calculations was used in order to describe the mechanism of the photocatalytic oxidation reactions of investigated dyes and interpret their reactivities within the framework of the Density Functional Theory (DFT). According to DFT based reactivity descriptors, i.e. Fukui functions and local softness, the active site moves from azo nitrogen atom linked to benzene ring to pyridone carbon atom linked to azo bond, going from dyes with electron-donating groups to dyes with electron-withdrawing groups.

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

Mechanical milling of commercial ZnO and SnO2 was used to produce a ZnO/SnO2 composite with a high density of surface defects; in particular, zinc interstitials (Zni) and oxygen vacancies (VO). To determine the impact of surface defects on photocatalytic activity, the relative concentration ratio of bulk defects to surface defects was modified by annealing at 400 and 700 °C. The possible application of the ZnO/SnO2 composite as a natural sunlight and UV-light driven photocatalyst was revealed via de-colorization of methylene blue. In both cases the ZnO/SnO2 composite exhibited enhanced photocatalytic activity as compared to the pristine ZnO. In order to investigate the origin of the enhancement, the pristine metal oxides and composites were characterized using a variety of techniques, including X-ray diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), laser diffraction particle size analysis, Brunauer–Emmett–Teller, UV-Vis diffuse reflectance and photoluminescence spectroscopy. High-resolution transmission electron microscopy (HRTEM) and elemental mapping analyses were used to reveal the presence of SnO2 nanocrystallites on the surface of larger ZnO particles. The enhanced photocatalytic activity of the composite can be attributed to the synergetic effect of the surface defects and the ZnO/SnO2 heterojunction particles, which facilitated charge separation, thereby hindering the recombination of photogenerated carriers. This study draws attention to mechanical activation as an inexpensive and environmentally friendly technique for the large-scale production of the composite with an enhanced photocatalytic activity under illumination of either UV or sunlight.

Modification of dense TiO2 particles using polyethylene glycol template: Synthesis, characterization, and photocatalytic activity

In this study, an effort has been made to prepare TiO2 materials by sol–gel technique using polyethylene glycol (PEG) as pore directing agent. Different PEG amounts were used during samples preparation in order to investigate the change in intrinsic material properties. The photocatalytic activity of prepared catalysts was estimated by measuring the decomposition of arylazo pyridone dye. The optimum template amount was determined, resulting in catalyst with enhanced textural properties, optimal anatase/rutile ratio and hence improved photocatalytic properties. Specific surface area and anatase/rutile ratio were found to be the main contributing factors to the catalyst activity. A synergistic effect between anatase and rutile TiO2 has been observed, since the presence of relatively inactive rutile phase enhanced the photoactivity of mixed TiO2.