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•Electronic effects of para substituted arylazo pyridone dyes.•Linear relationship between Hammett σp constants and dyes photoreactivity.•The photocatalytic reactions facilitated by ...el.-acceptors and retarded by el.-donors.•Fukui functions to analyze the reactivity on concurrent sites within a molecule.•Hydroxyl radicals sustain attack from two reaction sites, depending on a substituent type.
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.
TiO2 powders with different specific surface area were prepared using reproducible, sol–gel synthetic route and their ability to form hybrids with catechol and 5-amino salicylic acid was compared ...with the commercially available Degussa P25 TiO2 powder. Microstructural characterization involving transmission electron microscopy, X-ray diffraction analysis and nitrogen adsorption–desorption isotherms indicated that TiO2 samples cover reasonably wide size and/or specific surface area range (50–115 m2/g). The surface modification of TiO2 powders with catechol and 5-amino salicylic acid induced significant shift of absorption to the visible spectral region due to charge transfer complex formation. It should be emphasized that tunable optical properties of TiO2 in powder form have never been reported in the literature. The largest red shift of the absorption onset was observed for sample with the largest specific surface area upon surface modification with both ligands. The binding of the modifier molecules to the surface Ti atoms was studied using Fourier transform infrared spectroscopy.
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•Adjustment of optical properties of commercial and mesoporous TiO2 powders.•Charge transfer complex formation between surface Ti atoms and benzene derivatives.•Extent of absorption in visible proportional to the specific surface area of TiO2.•Tunable optical properties are not exclusive for “small” TiO2 particles.
•A good linear correlation between bond length and Hammett σp constants was observed.•Difference in λmax between hydrazone and anionic forms correlates well with σp.•The pKa values showed good ...correlations with σI constants.•N3C5 bond length is the most sensitive to the electronic effects of substituents.
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, 1H NMR and 13C 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.
•Photocatalytic degradation of substituted aryl azo pyridone dyes.•The proposed reaction mechanism of first step of OH-initiated photodegradation.•Pyridone carbon atom as the most preferable reaction ...site.•ΔG negatively correlated to electron-withdrawing properties of substituents.•Enabling possibility to design dye molecules with preferable degradation pathway.
Understanding the degradation behavior of azo dyes in photocatalytic wastewater treatment is of fundamental and practical importance for their application in textile-processing and other coloration industries. In this study, quantum chemistry, as density functional theory, was used to elucidate different degradation pathways of azo pyridone dyes in a hydroxyl radical (HO•)-initiated photocatalytic system. A series of substituted azo pyridone dyes were synthesized by changing the substituent group in the para position of the benzene moiety, ranging from strong electron-donating to strong electron-withdrawing groups. The effect of dye molecular structure on the photocatalytic degradation reaction mechanism was analyzed and quantification of substituent effects on the thermodynamic and kinetics parameters was performed. Potential energy surface analysis revealed the most susceptible reaction site for the HO• attack. The calculated reaction barriers are found to be strongly affected by the nature of substituent group with a good correlation using Hammett σp constants and experimentally determined reaction rates. The stability of pre-reaction complexes and transition state complexes were analyzed applying the distortion-interaction model. The increased stability of the transition state complexes with the distancing from the substituent group has been established.
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The simultaneous photocatalytic degradation of two dyes: methylene blue (MB), a cationic dye, and arylazo pyridone dye (SD), an anionic dye was investigated using sol–gel prepared TiO
2
particles. ...The paper shows the main difference in degradation kinetics between single dye solution and binary dye solutions. The effects of competitive adsorption and the concentration of the dyes on degradation rate were analyzed. The preferential adsorption capacity of TiO
2
toward MB was attributed to electrostatic interactions between the cationic dye and negatively charged TiO
2
surface, while repulsion between the negatively charged surface of the catalyst and SD dye results in its lower adsorption capacity. The TiO
2
surface charge and accordingly adsorption affinity of investigated dyes were found to be the main factors affecting degradation rate of the dyes. In the single dye system, the catalyst showed considerably higher degradation activity toward MB than to SD. In binary dye systems, the presence of SD did not affect the degradation of MB. On the other hand, the degradation efficiency of SD was found to be highly influenced by initial MB concentration and absorption ability of MB. In addition, higher MB concentration induces the production of a higher amount of reaction products, which also determine the SD degradation rate. Three kinetic regimes for the photodegradation of SD in binary mixtures were observed, used as a starting point to elucidate most influencing parameters for SD reaction kinetics.
•New type of catalyst feeder as a catalyst delivery system.•Correlation between iodine value, refractive index and H2 consumption in hydrogenation of sunflower oil using Ni/SiO2 catalysts.•Evaluation ...of kinetic model and reaction rate constants.•Catalyst activity and reaction pathways correlation.
Sunflower oil hydrogenation process was studied on silica supported nickel catalysts. Three texturally different silica gel materials were used as supports for synthesis of Ni/SiO2 catalyst precursors. After precursors’ reduction and paraffin oil impregnation, obtained catalysts were used in sunflower oil hydrogenation reaction. For catalytic test, a new type of catalyst feeder was constructed and presented. The hydrogenation activity of catalysts was monitored through the decrease of refractive index and hydrogen consumption. A correlation between iodine value, refractive index and hydrogen consumption was established. The reaction rate constants were obtained from fatty acid composition of partially hydrogenated oil and further studied for the investigation of possible reaction pathways. Kinetics and mechanisms were evaluated and tested with the aim to reduce the number of reactions participating in the reaction scheme. A set of ordinary differential equations, corresponding to the investigated model, was solved numerically by Gear's algorithm. It was shown that a number of significant reactions in a model depend on the activity of catalysts. More active catalyst results in more reaction pathways and more side chemical reactions.
Polymer supported catalysts with Co(II) and Cr(VI) ions were prepared and characterized by means of FTIR, diffuse reflectance UV–vis, nitrogen physisorption, mercury porosimetry and SEM–EDX ...measurements. The catalytic activity and selectivity of the polymer supported catalysts were tested in aerobic liquid-phase partial oxidation of cyclohexane in a polytetrafluoroethylene lined reactor. The influence of reaction time and temperature, main products addition, mass of the catalyst and different metals loading was investigated. Product yield and cyclohexyl hydroperoxide formation in the catalytic system were used as critical parameters which could be optimized by changing the cobalt content on the polymer and the catalyst mass used in the catalytic runs. By increasing cobalt content, a higher activity and corresponding lower selectivity towards cyclohexanone were obtained. This study indicates that the selectivity towards cyclohexanone and cyclohexanol is mainly defined by the yield and type of the catalyst with minor influence of temperature and main products addition.
In addition catalysts were used for deperoxidation of cyclohexyl hydroperoxide in mild conditions. Nearly the same selectivity towards cyclohexanone and cyclohexanol is achieved using the cobalt containing catalyst, while a higher selectivity towards cyclohexanone is achieved using the chromium containing catalysts.
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•PEG-modified catalysts were synthesized by sol–gel method.•Improved structural, textural and photocatalytic properties of modified samples.•Crucial catalyst properties were surface ...area and crystalline phase composition.•The order of pollutant reactivity: phenol>Reactive Black 5>arylazo pyridone dye.•Synergistic effect was observed for the most active catalysts.
This study aims to gain insights in structure–activity relationship of TiO2 photocatalysts. For this purpose photocatalysts were synthesized via classical sol–gel method using titanium isopropoxide as a precursor and polyethylene glycols (PEGs) of different molecular mass (Mn=200, 600, 2000, 10,000) as a template agents. Incorporating PEG into TiO2 network enhanced not only catalyst porous structure, but also increased the fraction of anatase phase. The use of low-molecular-weight PEGs resulted in catalysts with increased anatase content and enlarged specific surface area. The catalyst photoactivity was estimated through degradation of organic pollutants: Reactive Black 5, arylazo pyridone dye and phenol. The results revealed that the photoactivity was following the same order independently of target pollutant: TiO2/P600>TiO2/P200>TiO2/P2000>TiO2/P10000>TiO2. BET surface area and anatase fraction, rather than pore diameter or pore volume, were found to be predominant catalyst property determining the activity for particular reaction system. The existence of synergistic effect between anatase and rutile phases was confirmed for the most active catalysts TiO2/P200 and TiO2/P600. These catalysts showed similar activity in dye degradation, while TiO2/P200 displayed significantly lower activity in phenol degradation, which was attributed to its lower sorption capacity and lower UV light utilization. The difference in the reactivity between investigated pollutants was discussed in relationship with their size, structure and sorption ability.
The aim of this study was to obtain enhanced textural properties of macroporous crosslinked copolymer poly(glycidyl methacrylate-
co
-ethylene glycol dimethacrylate) by synthesizing nanocomposites ...with acid-modified bentonite. Nanocomposites were obtained by introducing various amounts of acid-modified bentonite (B
A
) into the reaction system. All samples were characterized by attenuated total reflectance infrared spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), mercury intrusion porosimetry, and low temperature physisorption of nitrogen. The FTIR and TEM analysis confirmed incorporation of B
A
into the copolymer structure and the successful formation of nanocomposites. TEM images confirmed formation of nanocomposites having both intercalated and exfoliated acid-modified bentonite in copolymer matrix. A significant increase of specific surface area, pore volume, and porosity of the nanocomposites in comparison to the copolymer were obtained. The difference between textural properties of nanocomposites with different amounts of incorporated acid-modified bentonite was less prominent.
Investigation was conducted in order to elucidate the possibility of using perlite as support for preparation of nickel based precursor catalyst, potentially applicable in vegetable oil hydrogenation ...process. On three differently prepared expanded perlite, nickel catalyst precursors with identical Ni/SiO
2
= 1.1 and Ni/Mg = 10/1 ratios were synthesized by precipitation-deposition method. Different techniques, SEM micrography, He-pycnometry, calcimetry, Hg-porosimetry, N
2
-physisorption, H
2
-chemisorption and temperature programmed reduction, were used for characterization of obtained samples. Determining the precursor texture, morphology and reducibility shows a successfully deposited nickel phase on perlite support with promising properties for vegetable oil hydrogenation. Chosen precursor was reduced and passivated in paraffin oil and the obtained catalyst showed significant catalytic activity in the test of sunflower oil hydrogenation.
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