Josef Krýsa

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.

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.

Critical assessment of suitable methods used for determination of antibacterial properties at photocatalytic surfaces.

This work describes the development of methods necessary for antibacterial effect evaluation on irradiated TiO(2) layers. Two methods using bacteria suspensions and the glass adhesion method (based on ISO 27447:2009(E)) were critically assessed and compared. As test bacteria gram negative Escherichia coli and gram positive Enterococcus faecalis were employed. The method using 50 cm(3) of bacteria suspension is convenient for testing layers with strong antibacterial effect (prepared from powder photocatalysts). For the evaluation of the antibacterial effect of sol gel layers, the glass adhesion method based on the ISO is more appropriate than the method with 3 cm(3) of bacteria suspension. The reason is that the later does not allow a distinction between the inhibition effect of TiO(2) and UV light itself. Some improvements of the ISO method were suggested, namely the use of gelatinous pills (CCM) of bacteria, using saline solution instead of nutrient broth for bacteria suspension preparation and the application of selective media for bacteria cultivation. Decreasing the light intensity from 0.6 mW cm(-2) to 0.2 mW cm(-2) (fulfilling the requirements of the ISO) results in almost negligible effect of UV light itself, thus enabling proper testing of the antibacterial properties of TiO(2) thin films.

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.

Transparent Nanotubular TiO2 Photoanodes Grown Directly on FTO Substrates

This work describes the preparation of transparent TiO2 nanotube (TNT) arrays on fluorine-doped tin oxide (FTO) substrates. An optimized electrolyte composition (0.2 mol dm−3 NH4F and 4 mol dm−3 H2O in ethylene glycol) was used for the anodization of Ti films with different thicknesses (from 100 to 1300 nm) sputtered on the FTO glass substrates. For Ti thicknesses 600 nm and higher, anodization resulted in the formation of TNT arrays with an outer nanotube diameter around 180 nm and a wall thickness around 45 nm, while for anodized Ti thicknesses of 100 nm, the produced nanotubes were not well defined. The transmittance in the visible region (λ = 500 nm) varied from 90% for the thinnest TNT array to 65% for the thickest TNT array. For the fabrication of transparent TNT arrays by anodization, the optimal Ti thickness on FTO was around 1000 nm. Such fabricated TNT arrays with a length of 2500 nm exhibit stable photocurrent densities in aqueous electrolytes (~300 µA cm−2 at potential 0.5 V vs. Ag/AgCl). The stability of the photocurrent response and a sufficient transparency (≥65%) enables the use of transparent TNT arrays in photoelectrochemical applications when the illumination from the support/semiconductor interface is a necessary condition and the transmitted light can be used for another purpose (photocathode or photochemical reaction in the electrolyte).

Advanced oxidation processes for water/wastewater treatment

This special issue of Environmental Science and Pollution Research is a compilation of 22 original research papers that were presented as either oral or poster communications during the 5th European Conference on Environmental Applications of Advanced Oxidation Processes (EAAOP-5, http://www. eaaop5.com) held in Prague, the Czech Republic, between 25 and 29 June 2017. This well-established series of events attracts researchers and professionals from all over the world to discuss advances and recent trends in the field of AOPs and environment-related applications. The number of attendees of EAAOP-5 has exceeded 270 participants from 42 countries covering 4 continents. They came from different geographical areas including the EU (Austria, Cyprus, Czech Republic, Belgium, Estonia, France, Germany, Greece, Hungary, Italy, Norway, Poland, Portugal, Romania, Slovak Republic, Slovenia, Spain, the UK), Mediterranean countries (Algeria, Egypt, Israel, Morocco, Turkey), South and North America (Argentina, Brazil, Canada, Chile, Colombia, Mexico, the USA), Asia (China, India, Japan, Republic of Korea, Singapore), and other countries such as the Russian Federation, Switzerland, and South Africa. They produced a valuable amount of information and knowledge, contained in more than 330 contributions (80 oral and 250 poster communications). The number of contributions in EAAOP conference series increases gradually since the first edition in September 2006 (Crete, Greece), which also points out an increasing interest of the scientific community on the advanced oxidation processes. This conference represents a good international opportunity to highlight and improve the recent knowledge and research about the treatment of waters, wastewaters, gaseous pollutants, and soils by AOPs. About 25% of the papers in this issue are devoted to photocatalytic processes, while 20% to Fenton and Fenton-like processes. The remaining part (about 55%) deals with the activated persulfate process, electrochemical oxidation, ozonation, as well as combinations of various AOPs. Theguesteditorswouldliketothankallauthorscontributingto this issue, as well as the many reviewers called upon to offer constructive advice for the improvement of submissions. They extendtheirsincerethankstoSpringerfor theopportunityprovided to compile this special issue andwould like to thank in particular Dr. Philippe Garrigues, Editor-in-Chief of Environmental Science and Pollution Research, and the Editorial Assistants of thejournalfor theirgreatsupportandpatienceateverystageinthe preparation of the issue. There appears to be a long-lasting and constructive relationship between Environmental Science and PollutionResearchand theEAAOPseriesof conferences,which we hopewill continue in the years to come. Josef Krysa would like to thank for the financial support from the Ministry of Education, Youth and Sport of the Czech Republic (project LTACH17007) and from a specific university research grant (MSMT No. 20-SVV/2017).