Doped rutile TiO2 mechanism for changing photocatalytic activity

Cilja doktorske disertacije sta bila razvoj fotokatalitsko aktivnega TiO2 v rutilni kristalni modifikaciji na vidni svetlobi in razvoj UV absorberja rutilnega TiO2, ki je fotokatalitsko neaktiven. S tem namenom smo v okviru doktorske disertacije poiskali dopanta, ki sta ustrezno modificirala kristalno strukturo TiO2. Proučili smo vpliv kovinskih in nekovinskih dopantov na fotokatalitsko delovanje TiO2, za kar smo uporabili rutilno kristalno modifikacijo TiO2 in hidrotermalno metodo. Pred tem smo z uporabo hidrotermalne metode proučili različne pogoje za nastanek monokristaliničnih rutilnih TiO2 delcev. Za proučevanje kovinskih dopantov smo uporabili ione Fe, Mn in Cu. Ugotovili smo, da uporabljeni kovinski dopanti inhibirajo fotokatalitsko delovanje TiO2, vendar se v učinkovitosti inhibicije razlikujejo. Dopant, ki najučinkoviteje inhibira fotokatalitsko aktivnost TiO2, je Mn. Pri inkorporaciji kovinskih dopantov v kristalno rešetko TiO2 smo znižali energijsko vrzel in premaknili absorpcijski rob dopiranih vzorcev v vidni del svetlobnega spektra. Pri proučevanju vpliva nekovinskih dopantov na povišanje fotokatalitske aktivnosti rutilnega TiO2 smo proučili ione dopantov N in S. Pri nekovinskih dopantih ne velja splošno pravilo o povišanju fotokatalitske aktivnosti. Rezultati kažejo, da ioni dopanta S znižajo fotokatalitsko aktivnost TiO2, medtem ko ioni N učinkovito zvišajo fotokatalitsko aktivnost v UV in vidnem delu svetlobnega spektra. Ugotovili smo, da z dopiranjem rutilnega TiO2 z N lahko izdelamo fotokatalizator, ki deluje na vidni svetlobi. Pri inkorporaciji nekovinskih dopantov ne pride do znižanja energijske vrzeli, kot tudi ne do večjega premika absorpcijskega roba v vidni del svetlobnega spektra. Dopant N se intersticijsko vgradi v kristalno rešetko. Rutilna kristalna modifikacija je bila na področju razvoja fotokatalizatorja na vidni svetlobi do sedaj v ozadju, saj ni izkazovala dobrih fotokatalitskih lastnosti. Z našimi preliminarnimi raziskavami pa smo ugotovili, da rutilna kristalna modifikacija izkazuje višjo fotokatalitsko aktivnost kot anatasna. Z razvojem rutilnega vidnega fotokatalizatorja smo rutilni kristalni modifikaciji pripisali velik pomen na področju fotokatalize. Hkrati pa smo tudi razjasnili vpliv uporabe kovinskih in nekovinskih dopantov na fotokatalitsko aktivnost rutilnega TiO2 ob uporabi hidrotermalne sinteze. Naši izsledki imajo pomemben doprinos k razvoju znanosti na tem področju.The aim of the present work was to develop a photocatalytically active rutile TiO2 under visible light conditions. Furthermore, the aim was also to develop a UV absorber based on rutile TiO2 that would have no observable photocatalytic activity. To achieve the aims of the present work, we focused our examination on finding appropriate dopants that enable the modification of rutile crystal structure and thus influence its photocatalytic activity. We investigated incorporation of both metal and nonmetal dopants and their respective influence on the photocatalytic activity of rutile TiO2. The doping of rutile TiO2 was carried out using the hydrothermal method. The hydrothermal method was also used to study various synthesis parameters and their influence on the formation of monocrystalline particles. Metals dopants used in the present study were ions of Fe, Mn and Cu. We have determined that the used metal ions inhibit the photocatalytic activity of TiO2 and that the level of inhibition varies on the type of metal dopant. The most effective metal dopant to inhibit the photocatalytic activity is Mn. We have also found out that when metal ions are incorporated into the crystal lattice, the TiO2 bandgap is lowered and the absorption edge is shifted into the visible light range. To enhance the photocatalytic activity of TiO2, we used nonmetal dopants, N and S. We have found that there is no general rule on how the nonmetal dopants influence the photocatalytic activity of TiO2, since our results show that S dopant lowers, while N dopant effectively enhances the photocatalytic activity in both UV and visible light spectra, respectively. By incorporating N dopant into the TiO2 crystal lattice, we were able to produce a photocatalyst that is active in visible light spectra. We determined that nonmetal dopants do not lower the TiO2 bandgap and also do not shift the TiO2 absorption edge at the visible light wavelength position. We conclude that N ions are interstitially incorporated into the TiO2 crystal lattice. Based on the literature overview, it was clearly observed, that the rutile TiO2 modification was not regarded as a potentially suitable visible light photocatalyst, since the observed activities were mostly lower than with anatase. Our findings, however, have shown that by using appropriate dopants, rutile TiO2 can be transformed into a superior photocatalyst than anatase. Therefore, the rutile TiO2 can be a potentially very important material that enables visible light photocatalytic activity. In our work we have also clarified the influence of both metal and nonmetal dopants on the TiO2 photocatalytic activity of materials prepared by using the hydrothermal method. Our findings are therefore a major contribution in the field of heterogenous photocatalysis