Jaromír Jirkovský

Kinetics of photocatalytic degradation of diuron in aqueous colloidal solutions of Q-TiO2 particles

Abstract Kinetics of the photocatalytic degradation of a phenylurea herbicide diuron in aqueous colloidal solutions of Q-TiO 2 nanoparticles was analyzed in detail applying a model of parallel consecutive reactions of the first-order. The found mechanism was compared with the reaction pathways of electrochemically assisted photoprocesses on illuminated TiO 2 layers, polarized by external voltage, in various solvents. While a reductive dechlorination on benzene ring of diuron represented the major pathway in acetonitrile, a consecutive oxidative demethylation on the aliphatic side chain was mainly observed in water.

Inactivation of microorganisms in a flow-through photoreactor with an immobilized TiO2 layer

A laboratory flow-through photoreactor with an immobilized layer of TiO2 (total volume of the liquid 5000 cm 3, photoactive area 60 cm long and 30 cm wide; irradiation source UV lamps Eversun, Osram, light intensity from 0.9 to 6.2×10−9 Einstein cm−2 s −1) was tested for the inactivation of Escherichia coli (strain DH5α) and bacteriophage λNM1149. The kinetics of the deactivation were approximately first order and the initial reaction rate depended on the light intensity. At maximum intensity, the rate constants of the bacteria and viruses inactivation were 2.3×10−4 and 7.2×10−4 s−1, respectively. Bacterial inactivation was also accomplished with solar excitation. © 1999 Society of Chemical Industry

Photocatalytic behavior of nanosized TiO2 immobilized on layered double hydroxides by delamination/restacking process

IntroductionEfficient immobilization of TiO2 nanoparticles on the surface of Mg2Al-LDH nanosheets was performed by delamination/restacking process.Experimental partThe structural and textural properties of as-prepared nanocomposite were deeply analyzed using different solid-state characterization techniques such as: X-ray powder diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopies, chemical analysis, X-ray photoelecton spectroscopy, N2 adsorption–desorption, and electronic microscopy.Results and discussionThe photocatalytic properties of immobilized TiO2 nanoparticles on Mg2Al were investigated using the photodegradation of two model pollutants: Orange II and 4-chlorophenol, and compared with pure colloidal TiO2 solution.ConclusionIt appears that Orange II photodegradation was systematically faster and more efficient than 4-chlorophenol photodegradation regardless of the medium pH. Moreover under slightly basic conditions, even if the TiO2 photocatalytic efficiency decreases, photodegradation performed in presence of easily recovered TiO2/Mg2Al1.5 nanocomposite gives rise to comparable or better results than pure TiO2.

Fe(III) photoinduced and Q-TiO2 photocatalysed degradation of naphthalene: comparison of kinetics and proposal of mechanism

Abstract Degradation of naphthalene was investigated in two systems producing hydroxyl radical: in homogeneous solution of Fe(III) perchlorate and in heterogeneous colloidal solution of Q-TiO2. The Fe(III) photoinduced degradation of naphthalene approximately followed first order kinetics with rate constant strongly dependent on the content of most photoactive Fe(III) species, Fe(OH)2+. In the case of the degradation photocatalysed by Q-TiO2, more complicated kinetics controlled by a charge-transfer surface complex with naphthalene degradation intermediates was observed. The primary degradation intermediates (2-formylcinnamaldehyde, 1,2-naphthoquinone, 1,4-naphthoquinone, 1-naphthol, 2-naphthol) were the same for both systems. The reaction mechanism of the degradation was proposed assuming the attack of hydroxyl radical followed by the addition of dioxygen, resulting in the direct opening of the aromatic ring.

Photodegradation of metamitron (4-amino-6-phenyl-3-methyl-1,2,4-triazin-5(4H)-one) on TiO2

Abstract Photodegradation of metamitron in aqueous solution (i) on a plate photoreactor with immobilized TiO2 layer and (ii) in a tube photoreactor in the presence of quantum sized Q-TiO2 particles was investigated and compared. Both processes, heterogeneous photocatalysis and homogeneous direct photolysis, took part on the overall photodegradation of metamitron. Deaminometamitron (6-phenyl-3-methyl-1,2,4-triazin-5(4H)-one), hydroxymetamitron (4-amino-6-(2′-hydroxyphenyl)-3-methyl-1,2,4-triazin-5(4H)-one) and deaminohydroxymetamitron (6-(2′-hydroxyphenyl)-3-methyl-1,2,4-triazin-5(4H)-one) were identified as main products. A reaction scheme of these phototransformations was proposed.

Photocatalytic degradation of diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea] on the layer of TiO2 particles in the batch mode plate film reactor

The photocatalytic degradation of diuron in aqueous solution on TiO 2 layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0.8-8.0x10 -5 mol/dm 3 ) and on the light intensity (0.8-2.7x10 -9 einstein/cm 2 .s) but independence on the flow rate (2.5-3.6 dm 3 /min) were found. A reaction scheme was proposed following the main identified primary (3-(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methyl-urea) and secondary (3-(3,4-dichlorophenyl)-1-formylurea and 3,4-dichloro-phenylurea) products.

Effect of dissolved ozone or ferric ions on photodegradation of thiacloprid in presence of different TiO2 catalysts.

Combining TiO(2) photocatalysis with inorganic oxidants (such as O(3) and H(2)O(2)) or transition metal ions (Fe(3+), Cu(2+) and Ag(+)) often leads to a synergic effect. Electron transfer between TiO(2) and the oxidant is usually involved. Accordingly, the degree of synergy could be influenced by TiO(2) surface area. With this in mind, the disappearance of thiacloprid, a neonicotinoid insecticide, was studied applying various photochemical AOPs and different TiO(2) photocatalysts. In photocatalytic ozonation experiments, synergic effect of three different TiO(2) photocatalysts was quantified. Higher surface area resulted in a more pronounced synergic effect but an increasing amount of TiO(2) did not influence the degree of the synergy. This supports the theory that the synergy is a consequence of adsorption of ozone on the TiO(2) surface. No synergy was observed in photocatalytic degradation of thiacloprid in the presence of dissolved iron(III) species performed under varied experimental conditions (concentration, age of iron(III) solution, different TiO(2) films, usage of TiO(2) slurries). This goes against the literature for different organic compounds (i.e., monuron). It indicates different roles of iron(III) in the photodegradation of different organic molecules. Moreover, TiO(2) surface area did not affect photodegradation efficiency in iron(III)-based experiments which could confirm absence of electron transfer between TiO(2) photocatalyst and iron(III).

Photoelectrochemical properties of sol-gel and particulate TiO2 layers

Polarization curves on irradiated TiO2 layers were measured in various electrolytes, namely sodium hydroxide, sulphuric acid, oxalic acid and potassium oxalate. Photocurrents measured in 0.1M NaOH are very small and decrease with increasing number of Degussa P25 TiO2 layers. Photocurrents for sol-gel TiO2 layers in 0.1M NaOH are about five times higher than for P25 TiO2 layers and increasing with number of layers. The same holds for Na2SO4, but in H2SO4 the difference between P25 and sol-gel diminishes, however the sol-gel layers still show the higher currents. In solutions of oxidizable substrates the trend is inversed: P25 layers show higher currents, with a steep increase with concentration of solute. The shape of the polarization curves was interpreted in terms of response time to irradiation and photocurrent depletion. Degradation experiments demonstrated that the effect (and advantage) of biasing the electrode depends on adsorption properties of substance and surface area of electrode material.

Notes on heterogeneous photocatalysis with the model azo dye acid orange 7 on TiO2

Photocatalytic activities of a series of well available commercial TiO2 powders in both suspended and immobilized forms were determined by kinetic measurements of the degradation of acid orange 7 as model compound. Although the powders showed lower photoactivity in the immobilized than suspended form, the differences among particular materials considerably varied. The porosity of the photocatalysts and related adsorption/desorption phenomena strongly influence the photocatalytic degradations occurring in aqueous suspension. The adsorption of the azo dye has a significant effect on observed concentration changes during irradiation and must be taken in account in the evaluation of degradation rates in suspensions. No direct correlation between photocatalyst material properties and photoactivity was found. The paper brings a convincing discussion that, with only minor exceptions, it is not possible to form any general conclusions on the performance of a standard type photocatalyst, even if a model reactant is used.

Degradation of supramolecular complexes photoinduced by iron(III): The influence of the host on the reactivity of the guest

Fe(III)-photoinduced degradation of two different supramolecular host-guest complexes, naphthalene with alpha-cyclodextrin and 4-chloroaniline with p-sulfonic-calix[4]arene; was studied in aqueous solution. The stoichiometries, equilibrium constants and conformations of these complexes were characterized. In both cases, the degradation of the guest could not be accounted for by simple competition kinetics of OH radical attack on the guest and host molecules, respectively. This observation was explained by the occurrence of subsequent radical reactions of transients resulting from an OH attack onto the host molecule, which are assumed to be able to induce additional degradation reactions of the guest. An inhibiting influence of the calix[4]arene host on the abundance of oligomeric degradation intermediates of 4-chloroaniline was observed.