Fotokatalitikus mineralizáció és hidrogén fejlődés mechanizmusa UV-látható fénnyel gerjesztett fotokatalizátorokon = Mechanism of photocatalytic mineralization and hydrogen production on UV-visible excited photocatalysts

A projekt három éve alatt 14 cikket publikáltunk a témához kapcsolódó eredményekből, mely cikkek összimpaktja 52,696. 16 hazai és 20 nemzetközi konferencia előadással és poszterrel is igyekeztünk szélesebb körben megismertetni a fontosabb megfigyeléseinket és következtetéseinket. A projekt során nagy UV aktivitású lánghidrolitikus és szol-gél szintézisű titán-dioxid minták előállítását valósítottuk meg. A prekurzor gőz beviteli sebességének optimalizálásal poliéderes morfológiájú, viszonylag nagy részecskeméretű (50 nm) és főleg anatáz fázisú katalizátort sikerült készítenünk. Hasonlóan nagy UV aktivitású minta volt előállítható a szol-géles szintézisű alapanyagból az általunk fejlesztett gyors kalcinálási módszerrel. A rosszul adszorbeálódó szerves vegyületek esetében a fenti két módszer a legalkalmasabb nagy UV aktivitású minták előállítására. Nemesfém nanorészecskék méretkontrollált leválasztásával nagy aktivitású Au/TiO2 és Pt/TiO2 minták állíthatók elő. Az arany esetében az 5-6 nm, míg platina esetében 3,0-3,5 nm-es részecskeátmérő bizonyult a leghatékonyabbnak oxálsav jelenlétében a hidrogén előállítására. Látható fényt hasznosító, vassal, jóddal és nitrogénnel dópolt fotokatalizátorokat is sikerült előállítanunk. Fenol esetében a nagyobb fajlagos felület, kisebb részecskeméret (D = 6.5-9.0 nm) volt a kedvező. Ugyanakkor fenol oxidációjára és baktériumok pusztítására is kiválóan alkalmas a nagyobb részecskeméretű rutil fotokatalizátor VIS megvilágítás mellett. | During the three years of the project 14 articles were published, the total impact number of these publications is 52.696. The results were also shown with oral and poster presentations in 16 conferences in Hungary and in 20 international conferences too. High UV activity photocatalysts were developed by flame hydrolysis and novel sol-gel methods. Anatase nanoparticles with relatively large particle size (50 nm) were produced by controlling the precursor feeding rate in the flame. Similarly active photocatalysts were synthesized from sol-gel synthesized amorphous materials applying our new rapid heating and short exposure calcination technique. The ill-adsorbing organic compounds can be the most efficiently decomposed under UV irradiation on photocatalysts prepared in these two synthesis methods. Highly efficient UV active TiO2/Au and TiO2/Pt catalysts can be prepared by the controlled deposition of noble metal nanoparticles. The optimal particle diameter is 5-6 nm for gold and 3.0-3.5 nm for platinum nanoparticles when oxalic acid is used as sacrificial agent for hydrogen production. Visible light can be efficiently harvested by our new nitrogen, iodine and iron doped photocatalysts. In the case of phenol, higher specific surface area and smaller particle diameter (6.5-9 nm) is the most beneficial under VIS irradiation. However, phenol can be also degraded and bacteria killed under VIS irradiation very efficiently when larger rutile particles are applied

Photocatalytic H2 Evolution Using Different Commercial TiO2 Catalysts Deposited with Finely Size-Tailored Au Nanoparticles: Critical Dependence on Au Particle Size

One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO2 photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO2 surface by photo- or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO2 composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H2 production activities of the samples were studied in aqueous TiO2 suspensions irradiated with near-UV light in the absence of dissolved O2, with oxalic acid or methanol as the sacrificial agent. The H2 evolution rates proved to be strongly dependent on Au particle size: the highest H2 production rate was achieved when the Au particles measured ~6 nm

UV-induced photooxidation of phenyl urea pesticides toxicology aspects

Phenylurea herbicides, like diuron, monuron, linuron, are photosynthesis inhibitors killing the entire plant by this effect. These pesticides and their intermediates formed due to their UV induced transformation could be toxic and carcinogenic to animals and humans. Thus, the investigation of the UV induced transformation of these phenyl urea pesticides from toxicology aspects is suitable. In this work, the ecotoxicology effect of the multicomponent solutions formed during the UV photolysis (254 nm) was investigated by Daphtoxkit F™ Magna and Algaltoxkit F™. The genotoxicology effect of the multicomponent solutions was investigated using the Ames tests

Direct Production of CH(A(2)Delta) Radical from Intense Femtosecond Near-IR Laser Pulses

CH(A(2)Delta) radical formation was observed in bromoform and methanol vapor in argon plasma with near-infrared femtosecond laser pulses (43 fs, 1030 nm, 100 kHz, 250 mu J/pulse). The beam was focused with an achromatic lens, creating very high intensity in the plasma that caused Coulomb explosion (calculated intensity was similar to 1.1 X 10(16) W/cm(2) in the focal point). The emitted fluorescence light was measured with high spectral (1-10 cm(-1)) and temporal resolution (5 ns) with an FT-Vis spectrometer. The step-scan technique allowed the reconstruction of the time-resolved fluorescence spectra from CH(A-X) emission. The emission from atomic lines such as H, Br, C, and O was observed and also from C+ cations and CH and C-2 radicals. This indicates that in a significant portion of these organic molecules, all chemical bonds were deaved in the Coulomb explosion. For both organics, the peak maximum of the CH(A) emission occurred at about 10 ns after excitation by the femtosecond pulse. After the maximum, a rapid emission decay was observed in the case of bromoform (monoexponential decay, t = 10 ns). The fluorescence decay was biexponential when methanol was used as the source for CH(A) generation. It can be assumed that CH(A) generation involved a fast and a slower path with some secondary reactions via the stepwise loss of hydrogen atoms from the CH3 group. The time constants were t(1) = 7.8-8.3 ns and t(2) = 78-82 ns for the fast and slow components, respectively, and very similar values were obtained at 10 and 25 mbar total pressures. However, in the case of bromoform, the C-Br bonds are significantly weaker; therefore, these atoms can be removed even in a single step via multiphoton absorption. The rotational temperature of CH(A) radicals generated from methanol decreased rapidly in the 30-55 ns time period from 2770 +/- 80 to 1530 +/- 50 K. The vibrational temperature increased from 3530 +/- 450 to 9810 +/- 760 K in the 30-80 ns time period and then started to decrease (the average temperatures were T-rot = 910 +/- 20 K and T-vib = 7490 +/- 340 K at 100 ns). This initial increase of T-vib is thought to be the result of electron collision with the CH radicals. The high temperatures of the fragment may indicate the roaming reaction associated with the Coulomb explosion of the parent molecule. We demonstrated that CH(A) radicals can be produced from both organic compounds, and the step-scan technique is ideal for the characterization of their time-resolved spectra using the 100 kHz high repetition rate near-infrared femtosecond laser pulses. The FT/UV-vis step-scan technique can detect neutral species directly with high spectral and time resolution, thus it is a complementary technique to the experiments utilizing ion detection schemes, such as velocity map imaging

Photocatalytic H2 Production Using Pt-TiO2 in the Presence of Oxalic Acid: Influence of the Noble Metal Size and the Carrier Gas Flow Rate

The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO2 photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO2 surface was achieved by in situ chemical reduction (CRIS) or by mixing chemically reduced Pt nanoparticle containing sols to the aqueous suspensions of the photocatalysts (sol-impregnated samples, CRSIM). Fine and low-scale control of the size of resulting Pt nanoparticles was obtained through variation of the trisodium citrate concentration during the syntheses. The reducing reagent was NaBH4. Photocatalytic activity of the samples and the reaction mechanism were examined during UV irradiation (λmax = 365 nm) in the presence of oxalic acid (50 mM) as a sacrificial hole scavenger component. The H2 evolution rates proved to be strongly dependent on the Pt particle size, as well as the irradiation time. A significant change of H2 formation rate during the oxalic acid transformation was observed which is unusual. It is probably regulated both by the decomposition rate of accumulated oxalic acid and the H+/H2 redox potential on the surface of the catalyst. The later potential is influenced by the concentration of the dissolved H2 gas in the reaction mixture

Visible light driven photocatalytic elimination of organic-and microbial pollution by rutile-phase titanium dioxides: new insights on the dynamic relationship between morpho-structural parameters and photocatalytic performance

For the visible light driven photocatalytic performance of rutile the presence of Ti–O–O– entities is more preferable than Ti3+.</p