Universiẗat, Diss., 2002--Kiel.

Die vorliegende Arbeit entstand im Zeitraum von 05/2014 bis 03/2017 in Kooperation mit Umicore AG & Co. KG und ist thematisch direkt mit dem BMWi-Projekt „NeoKarII“ mit der Suche nach neuartigen, oxidischen Elektrodenmaterialien für Polymerelektrolytbrennstoffzellen (PEM-FC) verknüpft. In dieser Arbeit wurden verschiedene oxidische Materialien über Sol-Gel- und Imprägnationsverfahren hergestellt und deren Eignung für eine Brennstoffzellenanwendung geprüft. Neben umfassenden röntgenographischen Untersuchungen zu den Stoffsystemen IrO2-TiO2, IrO2-SnO2 und Cr2O3-TiO2 sind in dieser Arbeit auch zusammensetzungsabhängige Änderungen der elektrischen Leitfähigkeit gezeigt. Zu diesem Zweck wurde ein neuer Leitfähigkeitsversuchsstand mit einer 2-Punkt-Durchgangswiderstandsmessmethode entwickelt und in Betrieb genommen. Der halbautomatische Versuchsstand ermöglicht eine temperatur- und druckprogrammierte Vermessung pulverförmiger Werkstoffe. / This thesis was developed between 05/2014 and 03/2017 together with Umicore AG & Co. KG and is related to the BMWi project 'NeoKarII' with the search for novel, oxidic electrode materials for polymer electrolyte fuel cells (PEM-FC). In this work, various oxidic materials were prepared by sol-gel and impregnation processes and their suitability for a fuel cell application was tested. In addition to comprehensive X-ray diffraction examinations of the materials systems IrO2-TiO2, IrO2-SnO2 and Cr2O3-TiO2, the composition dependence of electrical conductivity is also shown. For this purpose, a new measurement setup with a 2-point resistance measurement method was developed and brought into services. The semi-automatic setup allows a temperature- and pressure-programmed measurement of powdered materials.

Study of structural and particularly dynamical properties of the interface of water with graphite and rutile surfaces points towards anomalous behavior of water molecules close to solid matter. Evaluation of statistical properties like translational and rotational diffusivity, residence times and autocorrelation functions of orientation vectors indicates that the translation and rotation of water molecules can be not only hindered, but also facilitated, according to the particular local density, interactions and and geometrical structure of the surface. The newly developed methods for the measurement of statistical rotational properties near to liquid-solid boundary overcomes the difficulties that are closely related to the measurement of dynamical properties in strongly inhomogeneous environment in a way, that can be applied to other model systems of this type.

Hydrogen-related defects in single-crystal ZnO and rutile TiO2 are investigated by means of infrared absorption, Raman scattering, photoluminescence and photoconductivity. Four different defect centers in ZnO are considered: bond-centered hydrogen (HBC ), hydrogen bound within the oxygen vacancy (HO), hydrogen molecules, and a defect, which gives rise to a local vibrational mode at 3326 cm−1 . The measurements identify HBC as a shallow donor with an ionization energy of 53 meV. The internal 1s → 2p transition of HBC is detected at 330 cm−1 in the Raman scattering and photoconductivity spectra. The decay of an exciton bound to HBC results in the photoluminescence line at 3360.1 ± 0.2 meV. The local vibrational mode of the O–H bond for bond-centered hydrogen has a frequency of 3611 cm−1 (H-I) and an effective charge of 0.28±0.03e. It is found that bond-centered hydrogen is unstable against annealing at 190 °C due to diffusion and trapping by other defects. The dominant sink is the hydrogen molecule. It is demonstrated that the well-known I4 photoluminescence line at 3362.8 meV is due to the recombination of excitons bound to the HO donor. The ionization energy of the HO donor is determined to be 47 meV. The 1s → 2pz (2pxy) electronic transition of HO is detected at 265 cm−1 in photoconductivity spectra. The formation of HO occurs via trapping of HBC at vacancies left by out-diffusing oxygen. It is shown that sub-band gap illumination leads to an intensity reduction of the O–H local vibrational mode at 3326 cm−1 and the appearance of a previously unreported infrared absorption line at 3358 cm−1. The signals are identified as stretch modes of an O–H bond associated with the same defect in different charge states. The measurements indicate that this defect has a deep level in the band gap of ZnO at roughly Ec − 1.7 eV. Additionally, results on the thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented. Interstitial hydrogen in rutile TiO2 is studied by infrared absorption. It is shown that the defect is a shallow donor with an ionization energy of 10 meV. The absorption lines at about 3290 cm−1 consists of local vibrational modes due to the neutral and the positive charge states of the donor with relative intensities depending on the measurement conditions. In the neutral charge state, the defect reveals two modes at 3288.3 and 3292 cm−1 (10 K), whereas the positive charge state has a vibrational mode at 3287.4 cm−1. An unknown hydrogen complex was found to contribute to the 3288 cm−1 feature.

Hydrogen-related defects in single-crystal ZnO and rutile TiO2 are investigated by means of infrared absorption, Raman scattering, photoluminescence and photoconductivity. Four different defect centers in ZnO are considered: bond-centered hydrogen (HBC ), hydrogen bound within the oxygen vacancy (HO), hydrogen molecules, and a defect, which gives rise to a local vibrational mode at 3326 cm−1 . The measurements identify HBC as a shallow donor with an ionization energy of 53 meV. The internal 1s → 2p transition of HBC is detected at 330 cm−1 in the Raman scattering and photoconductivity spectra. The decay of an exciton bound to HBC results in the photoluminescence line at 3360.1 ± 0.2 meV. The local vibrational mode of the O–H bond for bond-centered hydrogen has a frequency of 3611 cm−1 (H-I) and an effective charge of 0.28±0.03e. It is found that bond-centered hydrogen is unstable against annealing at 190 °C due to diffusion and trapping by other defects. The dominant sink is the hydrogen molecule. It is demonstrated that the well-known I4 photoluminescence line at 3362.8 meV is due to the recombination of excitons bound to the HO donor. The ionization energy of the HO donor is determined to be 47 meV. The 1s → 2pz (2pxy) electronic transition of HO is detected at 265 cm−1 in photoconductivity spectra. The formation of HO occurs via trapping of HBC at vacancies left by out-diffusing oxygen. It is shown that sub-band gap illumination leads to an intensity reduction of the O–H local vibrational mode at 3326 cm−1 and the appearance of a previously unreported infrared absorption line at 3358 cm−1. The signals are identified as stretch modes of an O–H bond associated with the same defect in different charge states. The measurements indicate that this defect has a deep level in the band gap of ZnO at roughly Ec − 1.7 eV. Additionally, results on the thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented. Interstitial hydrogen in rutile TiO2 is studied by infrared absorption. It is shown that the defect is a shallow donor with an ionization energy of 10 meV. The absorption lines at about 3290 cm−1 consists of local vibrational modes due to the neutral and the positive charge states of the donor with relative intensities depending on the measurement conditions. In the neutral charge state, the defect reveals two modes at 3288.3 and 3292 cm−1 (10 K), whereas the positive charge state has a vibrational mode at 3287.4 cm−1. An unknown hydrogen complex was found to contribute to the 3288 cm−1 feature.

<p>Kao &scaron;to je poznato, RS-2-(4-hlor-o-toliloksi)propionska kiselina (MCPP),&nbsp;(4-hlor-2-metilfenoksi)sirćetna kiselina (MCPA) i 3,6-dihlorpiridin-2-karboksilna kiselina &nbsp;(klopiralid) su herbicidi sa veoma &scaron;irokim spektrom dejstva, a pored toga su rastvorljivi u&nbsp;vodi, te&scaron;ko biorazgradljivi i prema literaturnim podacima su, nažalost, veoma često prisutni&nbsp;herbicidi u pijaćoj vodi. Proces heterogene fotokatalize uz primenu TiO₂i UV zračenja se&nbsp;pokazao kao veoma pogodan način za njihovo uklanjanje iz vode. Međutim, zbog velikog&nbsp;energetskog procepa od 3,2 eV (anataze-oblik), odnosno, 3,0 eV (rutil-oblik), veoma mali&nbsp;udeo bliskih UV zraka iz sunčeve svetlosti (oko 3&minus;4%) biva iskori&scaron;ćen u toku&nbsp;fotokatalitičkog procesa, &scaron;to ukazuje na to da je TiO_2&nbsp;praktično neaktivan u prisustvu&nbsp;sunčeve svetlosti. Na osnovu literaturnih podataka je zapaženo da postoji mogućnost&nbsp;fotorazgradnje pojedinih supstrata u prisustvu TiO_2&nbsp;primenom vidljive svetlosti. Na&nbsp;primeru MCPP je ispitana aktivnost TiO_2&nbsp;Degussa P25 kao fotokatalizatora u prisustvu&nbsp;vidljive svetlosti. Na osnovu refleksionih spektara je utvrđeno da MCPP adsorbovan na&nbsp;TiO_2&nbsp;Degussa P25 apsorbuje vidljivi deo spektra (&lambda; &ge;400 nm). Nastali prelazni kompleks&nbsp;je potvrđen FTIR merenjima. Efikasnost TiO2Degussa P25 primenom vidljive svetlosti je&nbsp;upoređena sa sunčevim i UV zračenjem, kao i direktnom fotolizom u prisustvu pomenutih&nbsp;izvora zračenja. Brzina fotokatalitičke razgradnje MCPP primenom vidljive svetlosti iznosi&nbsp;0,86 &mu;mol dm^&minus;3min^&minus;1, &scaron;to je oko 4 puta brže u poređenju sa direktnom fotolizom. Nadalje&nbsp;je ustanovljena optimalna masena koncentracija katalizatora od oko 8 mg cm^&minus;3, koja je&nbsp;znatno vi&scaron;a u poređenju sa primenom UV zračenja. Razlog je najverovatnije različit&nbsp;mehanizam fotorazgradnje koji se odvija primenom vidljivog i UV zračenja. Naime,&nbsp;prisustvo 2-metil-2-propanola (poznatog hvatača&nbsp;^&bull;OH-radikala) praktično ne utiče na&nbsp;brzinu fotokatalitičke razgradnje MCPP p rimenom vidljive svetlosti, &scaron;to ukazuje da se&nbsp;mehanizam razgradnje MCPP primenom &nbsp;vidljive svetlosti ne odvija posredstvom&nbsp;^&bull;OH-radikala, za razliku od onog uz primenu UV zračenja.</p><p>S obzirom da se katalizator TiO_2&nbsp;Degussa P25 uz primenu vidljive svetlosti nije&nbsp;<br />pokazao kao naročito efikasan kada je u pitanju razgradnja sva tri herbicida i imajući u&nbsp;vidu da se u poslednje vreme iz razloga praktične primene sve vi&scaron;e pribegava procesu dopovanja TiO_2&nbsp;različitim tipovima metala (alkalnih, zemnoalkalnih, prelaznih i dr.) i nemetala (halogenida, halkogenida i dr.), u okviru ove doktorske disertacije je ispitana aktivnost N-TiO₂(sintetisanih mokrim i suvim putem) i TiO_2&nbsp;(rutil) dopovanog sa različitim količinama Fe³⁺-jona (0,13&minus;1,48 at.%) pri razgradnji herbicida MCPP i MCPA primenom vidljive svetlosti. Pored toga je ispitana efikasnost TiO_2&nbsp;(anataze) takođe dopovanog sa različitim količinama Fe³⁺-jona (0,71&minus;1,80 at.%) na primeru MCPP.&nbsp;</p><p>Poredeći N-TiO_2&nbsp;(sintetisan mokrim putem) i N-TiO_2&nbsp;(sintetisani suvim putem), primećeno&nbsp;je da je u drugom slučaju efikasnost katalizatora veća oko 2 puta. Isto tako je zapažena u&nbsp;slučaju MCPP ne&scaron;to veća fotokatalitička aktivnost N-TiO_2&nbsp;(sintetisani suvim putem) u&nbsp;poređenju sa TiO_2&nbsp;(anataze). Kada je u pitanju MCPA aktivnost sva tri katalizatora je&nbsp;veoma slična. Pored toga je zapažena veća efikasnost N-TiO_2&nbsp;(sintetisan mokrim putem) u&nbsp;poređenju sa TiO_2&nbsp;Degussa P25 (oko 1,5 puta) i oko 5 puta u odnosu na direktnu fotolizu,&nbsp;dok su N-TiO_2&nbsp;(sintetisani suvim putem) oko 3 puta efikasniji u poređenju sa TiO_2&nbsp;Degussa P25 i oko 10 puta u &nbsp;poređenju sa direktnom fotolizom. Brzina solarne razgradnje&nbsp;je preko 100 puta manja nego primenom vidljivog i UV zračenja, &scaron;to je posledica različitih&nbsp;intenziteta pomenutih izvora ozračivanja i različitih uslova pri kojima je vr&scaron;ena razgradnja. &nbsp;Ustanovljena je optimalna masena koncentracija N-TiO_2&nbsp;(sintetisan mokrim putem) od&nbsp;4 mg cm^&minus;3.</p><p>Prilikom razgradnje MCPP i MCPA je nađeno da je brzina veća kada se kao&nbsp;katalizator &nbsp;koristi TiO_2&nbsp;(rutil) u poređenju sa Fe-TiO_2&nbsp;i da sa povećanjem količine Fe³⁺-jona fotokatalitička aktivnost uglavnom opada. Kada je kao fotokatalizator kori&scaron;ćen TiO_{2 &nbsp;}<br />(anataze) dopovan različitim količinama Fe³⁺-jona (od 0,71 do 1,80 at.%), razgradnja&nbsp;<br />MCPP je u svim slučajevima znatno sporija u odnosu na TiO_2&nbsp;(anataze).</p><p>S obzirom da su prema literaturnim podacima kinetika i mehanizam fotokatalitičke&nbsp;<br />razgradnje klopiralida nepoznati, ispitana je njegova stabilnost pri različitim&nbsp;eksperimentalnim uslovima. Tokom ispitivanja uticaja pH kako u prisustvu, tako i u&nbsp;odsustvu dnevne svetlosti u intervalu pH od 1,0&minus;9,0, nađeno je da ni u jednom slučaju ne&nbsp;dolazi do razgradnje supstrata u periodu od sedam meseci koliko je proces praćen. Takođe&nbsp;je ispitana kinetika fotokatalitičke razgradnje klopiralida primenom UV i vidljivog&nbsp;zračenja u prisustvu TiO_2&nbsp;Degussa P25, kao i direktna fotoliza primenom oba izvora&nbsp;zračenja. Nađeno je da je brzina fotokatalitičke razgradnje primenom UV zračenja veća&nbsp;oko 5 puta u odnosu na direktnu fotolizu. Za praćenje toka fotokatalitičke razgradnje&nbsp;klopiralida je izabrana pH-vrednost od 3,2. Nadalje je zapaženo da se u ispitivanom opsegu početnih koncentracija supstrata (0,5&ndash;3,0 mmol dm^&minus;3) kinetika fotokatalitičke razgradnje klopiralida može opisati pseudo-prvim redom. Pri ispitivanju uticaja masene koncentracije katalizatora (0,5&ndash;8 mg cm^&minus;3) na brzinu razgradnje klopiralida, ustanovljena je optimalna masena koncentracija primenjenog fotokatalizatora od oko 4 mg cm^&minus;3. Izračunata ukupna &nbsp;prividna energija aktivacije iznosi 7,74 kJ mol^&minus;1. Pored toga, prisustvo kiseonika ubrzava reakciju 2 puta, dok dodatak elektron-akceptora kao &scaron;to su (NH₄)₂S₂O₈, H₂O_2&nbsp;i KBrO_3&nbsp;pokazuje značajan i različit efekat na kinetiku fotokatalitičke razgradnje klopiralida. Pri ispitivanju uticaja etanola, kao hvatača slobodnih radikala, nađeno je da se heterogena fotokataliza odvija uglavnom preko ^&bull;OH-radikala.</p><p>Na osnovu LC&ndash;MS/MS (ESI+) merenja ustanovljeno je prisustvo nekoliko&nbsp;intermedijera: 3,6-dihlor-piridin-2-ol, 3,6-dihlor hidroksipiridin-2-karboksilna kiselina i&nbsp;3,3&#39;,6,6&#39;-tetrahlor-2,4&#39;-bipiridin-2&#39;-karboksilna kiselina. Na osnovu identifikovanih&nbsp;intermedijera, kao i kinetičkih rezultata, predložen je mogućput mehanizma fotokatalitičke&nbsp;razgradnje klopiralida.</p><p>Prilikom ispitivanja uticaja strukture molekula na brzinu razgradnje, konstatovano&nbsp;<br />je da u slučaju klopiralida praktično ne dolazi do fotokatalitičke razgradnje u prisustvu&nbsp;TiO_2&nbsp;(anataze) i N-TiO_2&nbsp;(sintetisani suvim putem) uz primenu vidljive svetlosti, kao i u&nbsp;slučaju TiO_2&nbsp;Degussa P25. Pored toga, primenom TiO_2&nbsp;(rutil) i Fe-TiO_2&nbsp;kao&nbsp;fotokatalizatora, sa povećanjem količine Fe³⁺-jona od 0,13 do 1,27 at.% raste brzina&nbsp;razgradnje klopiralida, ukazujući da strukturne osobine supstrata utiču na brzinu njihove&nbsp;razgradnje.</p> / <p>It is well known that RS-2-(4-chloro-o-tolyloxy)propionic acid (MCPP), (4-chloro-2- methyl-phenoxy)acetic acid (MCPA) and 3,6-dichloropyridine-2-carboxylic &nbsp;acid&nbsp;(clopyralid) are herbicides of wide activity spectrum. They are soluble in water, hardly&nbsp;biodegradable and, unfortunately, often present in drinking water.</p><p>Heterogeneous photocatalysis by application of TiO_2&nbsp;and UV radiation proved to&nbsp;be very suitable for their removal from water. However, due toits large energy gap, i.e.&nbsp;3.2 &nbsp;eV (anatase-form) and 3.0 eV (rutile-form), a very small fraction of sunlight in the near&nbsp;UV range (about 3&ndash;4%) is used during photocatalytic process, which is an indication of&nbsp;TiO_2&nbsp;inactivity in the presence of this light source. Some literature data report on the&nbsp;possibility of photodegradation of certain substrates by visible light in the presence of&nbsp;TiO₂. MCPP served as substrate for testing TiO_2&nbsp;Degussa P25 &nbsp;photocatalytic activity in the&nbsp;presence of visible light. On the basis of reflection spectra it was established that MCPP&nbsp;adsorbed on TiO_2&nbsp;Degussa P25 was absorbing visible spectrum radiation (&lambda; &ge;400 nm).&nbsp;The existence of thus formed &nbsp;charge-transfer complex was confirmed with FTIR analysis.&nbsp;The efficiency of &nbsp;TiO_2&nbsp;Degussa P25 with application of visible light was compared to&nbsp;sunlight and UV radiation, as well to directphotolysis in the presence of these light&nbsp;sources. The rate of MCPP photocatalytic degradation by means of visible light is&nbsp;0.86 &mu;mol dm^{&minus;3&nbsp;}min^&minus;1, which is about 4 times faster than direct photolysis. In addition, the&nbsp;optimal &nbsp;catalyst concentration of about 8 mg cm^&minus;3, much higher than using UV radiation,&nbsp;<br />was established. The reason is, probably, a different mechanism of &nbsp;hotodegradation &nbsp;in the&nbsp;presence of visible and UV irradiation. Namely, the presence of 2-methyl-2-propanol&nbsp;(well-known&nbsp;^&bull;OH radical scavenger) has practicallyno effect on the rate of &nbsp;MCPP&nbsp;photocatalytic degradation using visible light, which points that this degradation&nbsp;mechanism does not involve&nbsp;^&bull;OH radicals, in contrast to that established &nbsp;for UV radiation.</p><p>Since the catalyst TiO_2&nbsp;Degussa P25 with application of visible light was not very&nbsp;<br />efficient in degradation of all three herbicidesand in view that nowadays is very &nbsp;popular&nbsp;doping process of TiO₂ with different types of metals (alkali, alkaline-earth, transition, etc.)&nbsp;and non-metals (halogen, chalcogen, etc.), in the scope of this Ph.D. &nbsp;thesis activities of N-TiO_2&nbsp;(synthesized by wet and dry procedure) and TiO_2&nbsp;(rutile) doped with various amounts&nbsp;of Fe^3+&nbsp;(0.13&ndash;1.48 at.%) in degradation processes of &nbsp;herbicides MCPP and MCPA using&nbsp;visible light were studied. In addition, the efficiency of TiO_2&nbsp;(anatase) doped with various&nbsp;amounts of Fe^3+&nbsp;(0.71&ndash;1.80 at.%) was also tested for MCPP degradation. When comparing&nbsp;N-TiO_2&nbsp;(synthesized by wet procedure) and N-TiO₂ (dry procedure), it was observed that&nbsp;in the latter case the catalyst efficiency was about two times higher. In this case for MCPP&nbsp;was also observed somewhat higher photocatalytic activity of N-TiO₂ (synthesized by dry&nbsp;procedure) in comparison with TiO₂. When activities of all three catalysts towards MCPA&nbsp;are compared, the results are very alike. In addition, higher efficiency of N-TiO_{2 &nbsp;}(wet&nbsp;procedure) comparing to TiO_2&nbsp;Degussa P25 (about 1.5 times) and about 5 times in&nbsp;comparison to direct photolysis were recorded, while N-TiO₂ (dry procedure) was about 3&nbsp;times more efficient than TiO_2&nbsp;Degussa P25 and about 10 times in comparison with direct&nbsp;photolysis. The rate of solar degradation is about 100 times lower than by application of&nbsp;UV and visible radiation, as a consequence of various intensities of the mentioned light&nbsp;sources and different conditions of photodegradation. An optimal concentration of N-TiO₂&nbsp;(wet procedure) of 4 mg cm^&minus;3<br />&nbsp;was established.</p><p>During degradation of MCPP and MCPA it was observed that the rate is higher if&nbsp;TiO₂(rutile) was applied comparing to Fe-TiO_2&nbsp;and with increasing amount of Fe^3+&nbsp;photocatalytic activity mostly decreases. When TiO₂ (anatase) doped with various amounts&nbsp;of Fe^3+&nbsp;(0.71 to 1.80 at.%) was applied for MCPP degradation, the process was much&nbsp;slower than with undoped catalyst.</p><p>Since we have not found relevant literature data on kinetics and mechanism of&nbsp;photocatalytic degradation of clopyralid, its stability in different experimental conditions&nbsp;was tested. In investigating of influences of pH (1.0&ndash;9.0) both in presence and in absence&nbsp;of daylight, in no cases decomposition was observed during seven months experiments.&nbsp;Also, the kinetics of photocatalytic degradation of clopyralid using UV and visible&nbsp;irradiation in the presence of TiO_2&nbsp;Degussa P25 and in direct photolysis by application of&nbsp;both irradiation sources was studied. It was found that the &nbsp;rate of photocatalytic&nbsp;decomposition using UV radiation was 5 times higher comparing to direct photolysis. For&nbsp;clopyralid photocatalytic monitoring a pH value of &nbsp;3.2 was chosen. In addition, in the investigated concentration range (0.5&ndash;3.0 mmol &nbsp;dm^&minus;3) the photocatalytic degradation kinetics of clopyralid in the first stage of the reaction follows approximately a pseudo-first kinetic order. In investigation of influence of catalyst concentration (0.5&ndash;8 mg cm^&minus;3) on the rate of clopyralid degradation the highest reaction rate was observed at 4 mg cm^{&minus;3&nbsp;}of catalyst concentration The apparent activation energy of the reaction being 7.74 kJ mol^&minus;1. The absence of molecular oxygen resulted in a significant decrease (about 2 times) in the rate of clopyralid photodegradation. The effect of the presence of (NH₄)₂S₂O₈, H₂O_2&nbsp;and KBrO₃, acting as electron acceptors along with molecular oxygen affects clopyralid photocatalytic degradation considerably and indifferent ways. By studying the effect of ethanol as a hydroxyl radical scavenger it was shown that the heterogeneous catalysis takes place mainly via ^&bull;OH radicals.</p><p>LC&minus;MS/MS (ESI+) monitoring of the process showed that several pyridine-containing intermediates are formed: 3,6-dichloropyridin-2-ol, 3,6-dichloro&nbsp;hydroxypyridine-2-carboxylic acid and 3,3&#39;,6,6&#39;-tetrachloro-2,4&#39;-bipyridine-2-carboxylic&nbsp;acid. Based on the identified intermediates and overall kinetic results, a probable&nbsp;photocatalytic degradation mechanism was proposed.&nbsp;</p><p>Finally, in the case of clopyralid it was established that practically no degradation&nbsp;<br />occurs in the presence of TiO_2&nbsp;(anatase) and N-TiO₂ (dry procedure) with visible light &nbsp;and&nbsp;also with TiO_2&nbsp;Degussa P25. Besides of that, by using TiO_2&nbsp;(rutile) and Fe-TiO_2&nbsp;as&nbsp;photocatalysts it was noted that increasing the concentration of Fe^3+&nbsp;from 0.13 to 1.27 at.%&nbsp;comes to increasing photodegradation rate of clopyralid. Results indicate that differences&nbsp;in molecular structure of chosen compound, influence obtained photocatalytic activity to a&nbsp;great extent.</p>

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