Modification of structure and photoactivity of titanium(IV) oxide nanotubes by doping and applying of photosensitive components

Ekološki izvori energije i ekonomične metode prečišćavanja vode i vazduha velika supotreba današnjeg tehnološki razvijenog sveta. Fotoaktivni materijali mogu da obezbede ekološkualternativu fosilnim gorivima kada je u pitanju proizvodnja energije i omoguće saniranje nastalihpromena u životnoj sredini. Naime, fotoaktivni materijali apsorbuju svetlost i tada dolazi dopobuđivanja elektrona, koji su odgovorni za prenos električne struje ili učestvuju u procesurazgradnje zagađujućih materija. Postoji veliki broj fotoaktivnih materijala, među kojima se izdvajaTiO2, kojeg odlikuje hemijska inertnost, otpornost na fotoindukovanu i hemijsku koroziju inetoksičnost. Na fotoaktivnost TiO2 utiču mnogi faktori, kao što su morfologija, kristalna struktura istepen rekombinacije nosilaca naelektrisanja.Cilj ove doktorske disertacije je poboljšanje fotokatalitičke i fotoelektrične aktivnosti TiO2nanocevi. U tu svrhu, TiO2 nanocevi su sintetisane metodom elektrohemijske anodizacije pločicetitana. Ispitivan je uticaj procesnih parametara anodizacije na morfologiju i fotokatalitičku aktivnostnanocevi TiO2 u procesu razgradnje boje. Utvrđeno je da sa porastom napona anodizacije rastuvisina i prečnik nanocevi, što utiče na pomeraj apsorpcione granice ka vidljivom delu spektra i napoboljšanje fotokatalitičke aktivnosti. Određen je uticaj temperature žarenja na kristalnu strukturu,morfologiju i fotokatalitičku aktivnost TiO2 nanocevi. Žarenjem nanocevi na 450 °C dobijena jekristalna modifikacija anatasa sa veoma malim sadržajem faze rutila. Sa daljim porastomtemperature žarenja (600 i 650 °C) uočeno je prisustvo obe faze, anatasa i rutila, u različitimodnosima, a do kompletne transformacije anatasa u rutil došlo je na 700 °C. Pored promenekristalne strukture, uočen je uticaj temperature žarenja na morfologiju nanocevi. Sa povišenjemtemperature žarenja, visina nanocevi se smanjivala, kao i poroznost nanocevi, da bi na 700 °C došlodo kolapsa nanocevne morfologije. Sagledan je uticaj kristalne strukture i morfologije TiO2nanocevi na fotokatalitičku razgradnju boje metil-oranž. Zaključeno je da istovremeno prisustvoanatasa i rutila obezbeđuje bolju fotokatalitičku aktivnost u odnosu na čist anatas i čist rutil.Kako bi se ispitao uticaj dopiranja TiO2 azotom na fotokatalitičku aktivnost, nanocevi TiO2su žarene u atmosferi amonijaka, na temperaturi od 450 °C, pri različitim dužinama žarenja.Ispitivan je uticaj vremena žarenja na količinu i vrstu dopiranja. Uočeno je da žarenje u atmosferiamonijaka, pri različitim vremenima, nije uticalo na morfologiju nanocevi. Hemijska analizapovršine TiO2 nanocevi rendgenskom fotoelektronskom spektroskopijom pokazala je da sa dužimvremenom žarenja opada ukupan sadržaj azota u nanocevima. Osim toga, dužina žarenja uamonijaku je uticala i na prirodu inkorporiranja azota u TiO2. Pri kraćem vremenu žarenja zapaženje veći sadržaj intersticijskog azota, a manji sadržaj supstitucijskog azota. S dužim vremenomžarenja u amonijaku, sadržaj intersticijskog azota opada, dok sadržaj supstitucijskog raste.Apsorpcioni spektri su pokazali da uzorak sa najvećom količinom azota i najvećim sadržajemintersticijskog azota pokazuje najveći pomeraj granice apsorpcije ka većim talasnim dužinama. Istoje uočeno i za fotokatalitičku efikasnost. Najveću fotokatalitičku razgradnju boje postigao je uzorakžaren u amonijaku pri najkraćem vremenu.Dalje istraživanje je išlo u smeru proširenja saznanja o pojedinačnim i kombinovanimuticajima dopiranja azotom i deponovanja kvatnih tačaka neorganskog senzivatora nafotokatalitičku aktivnost TiO2 nanocevi. Zapaženo je da deponovanje kvantnih tačaka CdS nijeuticalo na morfologiju nanocevi, ali je na pojedinim mestima došlo do aglomeracije CdSnanočestica, što je dovelo do zatvaranja otvora nanocevi. Utvrđeno je da je fotokatalitičkaefikasnost azotom dopiranih nanocevi poboljšana nakon deponovanja CdS nanočestica. Najvećufotokatlitiču efikasnost pokazao je uzorak sa najvećim sadržajem ukupnog azota i intersticijskogazota u kombinaciji sa deponovanim CdS nanočesticama...Environmental friendly power sources and cost-effective methods for water and airpurification, are a necessity in modern technologically developed world. Photoactive materials canprovide an environmentally friendly alternative to fossil fuels in power production and enable theremediation of changes in the environment. Namely, photoactive materials absorb light, whichexcites electrons that are responsible for generating electricity or participate in the process ofdecomposition of pollutants. There are a large number of photoactive materials, among which TiO2has attracted particular attention, due to its chemical inertness, resistance to photo and chemicalcorrosion and non-toxicity. The photoactivity of TiO2 depends on many factors, such asmorphology, crystal structure and the degree of recombination of charge carriers.The aim of this doctoral dissertation is to improve the photocatalytic and photoelectricactivity of TiO2 nanotubes. For this purpose, TiO2 nanotubes were synthesized by theelectrochemical anodization of a titanium plate. The influence of the anodization process parameterson the morphology and photocatalytic activity of TiO2 nanotubes for color degradation wasinvestigated. It was found that an increased anodization voltage leads to increased heights anddiameters of nanotubes, causing the shift of the absorption limit towards the visible part of thespectrum and the improvement of the photocatalytic activity. The influence of the annealingtemperature on the crystal structure, morphology and the photocatalytic activity of TiO2 nanotubeswas determined. The anatase crystalline modification with a very low rutile phase content wasobtained by annealing nanotubes at 450 °C. When the annealing temperature was further increased(600 and 650 °C), the presence of both phases, anatase and rutile, was observed in different ratios,and the complete transformation of anatase to rutile occurred at 700 °C. Besides the change in thecrystal structure, the influence of the annealing temperature on the morphology of the nanotubeswas observed as well. As the annealing temperature increased, the height and porosity of nanotubesdecreased, so that the nanotube morphology collapsed at 700 °C. The influence of the crystalstructure and morphology of TiO2 nanotubes on the photocatalytic degradation of methyl-orangewas observed. It was concluded that the simultaneous presence of anatase and rutile provides betterphotocatalytic activity than pure anatase and pure rutile.In order to investigate the effect of nitrogen doping of TiO2 on photocatalytic activity, TiO2nanotubes were annealed in an ammonia atmosphere, at a temperature of 450 °C, for differentannealing times. The influence of the annealing time on the amount and type of doping wasinvestigated. It was observed that annealing in an ammonia atmosphere, for different periods, didnot affect the morphology of nanotubes. A chemical analysis of the surface of TiO2 nanotubes by Xray photoelectron spectroscopy showed that the total nitrogen content in nanotubes decreased withlonger annealing times. In addition, the annealing duration in ammonia also influenced the nature ofnitrogen incorporation into TiO2. With a shorter annealing time, a higher content of interstitialnitrogen and a lower amount of substitution nitrogen were observed. With a longer annealing timein ammonia, the amount of interstitial nitrogen decreased, while the substitution nitrogen increased.The absorption spectra showed that the sample with the highest amount of nitrogen and the highestcontent of interstitial nitrogen showed the largest shift towards higher wavelengths. The sameapplies to the photocatalytic efficiency. The greatest photocatalytic degradation of the dye wasachieved in the sample annealed in ammonia for the shortest time.Further research was directed towards expanding the knowledge of individual and combinedeffects of nitrogen doping and deposition of the quantum dots of inorganic sensors on thephotocatalytic activity of TiO2 nanotubes. It was observed that the deposition of CdS quantum dotsdid not affect the morphology of nanotubes, but in some places agglomeration of CdS nanoparticlesoccurred, due to which nanotube openings closed. The photocatalytic efficiency of nitrogen-dopednanotubes was improved after CdS nanoparticle deposition. The sample with the highest amount oftotal nitrogen and interstitial nitrogen in combination with deposited CdS nanoparticles exhibitedthe highest photocatalytic efficiency..