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Plastoviti dvojni hidroksidi (LDH, angl. layered double hydroxides) so raznoliki materiali z značilno plastovito strukturo. Zaradi delne zamenjave dvovalentnih kovinskih kationov s trivalentnimi so sestavljeni iz pozitivno nabitih plasti hidroksida, med plasti pa se za izenačitev naboja interkalirajo anioni. Tovrstna struktura tem materialom omogoča izmenjavo interkaliranih anionov, kar uporabljamo za določene aplikacije. Nekateri LDH so tudi polprevodniki, kar jim daje fotokatalitske lastnosti. S toplotno obdelavo iz LDH dobimo mešane kovinske okside. Namen mojega diplomskega dela je bila sinteza cink-aluminijevih LDH z interkaliranimi kloridnimi ioni, ter cink-aluminijevih LDH z interkaliranimi karbonatnimi ioni. Sintezo smo izvedli z metodo soobarjanja pri konstantnem pH. Iz pripravljenih LDH smo s peptizacijo pripravili sol, iz katerega smo s tehniko potapljanja pripravili tanke plasti, ki smo jih nato toplotno obdelali. Strukturo pripravljenih LDH v praškasti obliki in tankih plasti smo preverili z metodo rentgenske praškovne difrakcije. Določili smo sorpcijske in fotokatalitske lastnosti tankih plasti, ki smo jih termično obdelali pri 600 °C. V raztopino barvila Plasmocorinth B znane začetne koncentracije smo potopili pripravljene plasti in z UV-Vis spektrofotometrijo spremljali časovno odvisnost zniževanja koncentracije barvila. Potek absorpcije smo določali v temi, fotokatalitsko učinkovitost pa med izpostavitvijo opisanega sistema UV ali vidni svetlobi. Izkazalo se je, da so toplotno obdelane tanke plasti Zn-Al LDH z interkaliranimi karbonatnimi ioni učinkovit sorbent in deloma tudi fotokatalizator. Toplotno obdelane plasti Zn-Al LDH z interkaliranimi kloridnimi ioni so slab sorbent, a zelo učinkovit fotokatalizator. Layered double hydroxides (LDH) are diverse materials with a characteristic layered structure. As a result of the partial exchange of divalent cations with trivalent ones, they consist of positively charged hydroxide layers, while anions are intercalated between the layers to neutralize the charge. This structure gives these materials the ability to exchange intercalated anions, which can be used for certain applications. Some LDHs are also semiconductors, which leads to their photocatalytic properties. We can produce mixed metal oxides by calcination of LDHs. The aim of my diploma work was to synthesize zinc-aluminium LDH with intercalated chloride ions, and zinc-aluminium LDH with intercalated carbonate ions. The synthesis was carried out by the coprecipitation method at constant pH. Sols were prepared from the synthesized LDHs by peptization, from which thin films were prepared by dip-coating technique. The thin films were then thermally treated. The structure of the prepared LDHs was determined by X-ray diffraction. The sorption and photocatalytic properties of the thin films, thermally treated at 600°C, were determined. The prepared thin films were immersed in a solution of Plasmocorinth B dye of known concentration. Then the change of dye concentration with increasing time was monitored using UV-Vis spectrophotometry. Sorption process was performed in the dark, while the determination of photocatalytic properties was performed by irradiating the described system with UV or visible light. It was found that calcined thin films of Zn-Al LDH, intercalated with carbonate ions, are an effective sorbent and a partially effective photocatalyst. Thermally treated thin films of Zn-Al LDH with intercalated chloride ions are an ineffective sorbent, but a very effective photocatalyst.

V okviru magistrskega dela sem pripravila tanke plasti natrijevega niobata s sintezo v raztopini. Poleg prekurzorske raztopine v organskem topilu, ki je služila kot referenca, sem pripravila tudi vodno raztopino prekurzorja natrijevega niobata. Pripravila sem tudi prekurzorski raztopini z dodatkom 1 množinskega % Mn kot dopanta. Raziskala sem vpliv izbire prekurzorjev in pogojev toplotne obdelave na fazno sestavo, mikrostrukturo in funkcijski odziv tankih plasti. Alkoksidno prekurzorsko raztopino sem pripravila iz natrijevega acetata, niobijevega(V) etoksida ter dietanolamina, pri čemer sem kot topilo uporabila 2-metoksietanol. Plasti sem pripravila s petimi ponovitvami nanosa raztopine na podlago platiniziranega silicija z metodo vrtenja podlage, sušenja in pirolize, ter končnim segrevanjem pri 650 °C. Plasti so kristalizirale v perovskitni fazi. Debelina plasti je bila okrog 150 nm, velikost zrn na površini pa okrog 300 nm pri hitrosti segrevanja ≤ 12,5 K/s. Hitrost segrevanja je nekoliko vplivala na povprečno velikost zrn in njihovo velikostno porazdelitev. S piezoelektričnim modulom mikroskopa na atomsko silo smo potrdili, da plasti izkazujejo lokalni piezoelektrični in feroelektrični odziv. Vodno prekurzorsko raztopino sem pripravila iz natrijevega nitrata in amonijevega niobijevega oksalata hidrata ter ji dodala polivinil alkohol v 1 masnem odstotku za boljše omakanje podlage. Segrevanje plasti po petih nanosih raztopine na podlago je ne glede na hitrost segrevanja vodilo do kristalizacije faze Na2Nb4O11. Plasti so kristalizirale v perovskitni fazi samo, če smo jih pripravili tako, da smo jih segrevali po vsakem nanosu raztopine na podlago, torej v celoti petkrat pri 600 °C. Debelina plasti je bila okrog 100–140 nm, velikost zrn na površini plasti pa okrog 350 nm. Vzorci so izkazali šibek piezo- in feroelektrični odziv, ki se je nekoliko izboljšal z dodatkom mangana. In the master thesis, sodium niobate thin films were prepared by chemical solution deposition. The precursor solution, which served as a reference, was synthesized in an organic solvent. In addition, the sodium niobate precursor was also synthesized in an aqueous solution. To both solutions, 1 mol% of manganese was added as a dopant and the influence of the choice of precursor and heat treatment conditions on the phase composition, microstructure and functional response of the sodium niobate thin film was investigated. The reference precursor solution was prepared from sodium acetate, niobium(V) ethoxide and diethanolamine in 2-methoxyethanol as solvent. The films were prepared by repeating the deposition of the solution on a platinized silicon substrate five times by spin-coating, drying and pyrolysis with the final heating at 650 °C. The films crystallized in the perovskite phase. The film thickness was about 150 nm and the surface grain size was about 300 nm at the heating rate ≤ 12.5 K/s. The heating rate slightly affected the average grain size and size distribution. Using a piezoelectric module of the atomic force microscope, we confirmed that the films showed local piezoelectric and ferroelectric responses. The aqueous precursor solution was prepared from sodium nitrate and ammonium niobium oxalate hydrate with the addition of 1 wt% polyvinyl alcohol to improve substrate wetting. Final annealing of the films after applying the solution five times resulted in crystallization of the Na2Nb4O11 phase, regardless of the heating rate. The films crystallized in the perovskite phase only when they were annealed after each deposition of the solution onto the substrate, followed by drying and pyrolysis steps, i.e., a total of five times at 600 °C. The thickness of the films was about 100–140 nm, and the surface grain size was about 350 nm. The samples exhibited weak piezoelectric and ferroelectric behaviour, which was slightly improved by the addition of manganese.

Samočistilne, protizarositvene in aseptične tanke plasti, ki temeljijo na fotokatalitski aktivnosti in superhidrofilnosti titanovega dioksida, so v komercialni uporabi dostopne že več desetletij. Titanov dioksid je široko dostopen in poceni polprevodniški naravni mineral, pri aplikaciji samočistilnih tankih plasti v fotokatalitske namene pa ima dve glavni pomanjkljivosti, ki zmanjšujeta njegovo učinkovitost: (1.) relativno širok prepovedani pas (3,2 eV za anataz) povzroča absorpcijo pri nizkih valovnih dolžinah - v UV delu, ki predstavlja manj kot 5% sončeve svetlobe in (2.) hitra rekombinacija fotoinduciranih parov elektron-vrzel, ki nastanejo po ločitvi naboja pod vplivom fotonov. Eden izmed postopkov izboljšave teh pomanjkljivosti je dopiranje različnih elementov v TiO2 strukturo, med drugimi tudi dopiranje z vanadijem. V okviru magistrskega dela je bila s pomočjo sol-gel postopka pripravljena koloidna raztopina TiO2-SiO2 z različnimi vsebnostmi dopiranega vanadija. S potapljanjem (dip-coating tehnika) različnih podlag so bili pripravljeni vzorci različnih debelin tanke plasti. S pomočjo različnih spektroskopskih (UV-Vis spektroskopija, IR spektroskopija, Ramanska spektroskopija) in drugih tehnik (vrstična elektronska mikroskopija, rentgenska praškovna difrakcija, merjenje kontaktnega kota) so bile določene strukturne, optične in fotokatalitske značilnosti. V poglavju 4. Rezultati in razprava so podane ključne ugotovitve magistrskega dela. Med drugim je bilo ugotovljeno, da so bili kljub nizki temperaturi priprave vsi vzorci transparentni in fotoaktivni. Rentgenska praškovna difrakcija, Ramanska in IR spektroskopija dokazujejo, da obstaja velika verjetnost vgrajevanja vanadija v strukturo TiO2-SiO2. Optične značilnosti vzorcev so pokazale, da vanadij bistveno ne vpliva na prepustnost, odbojnost in motnost. Optične lastnosti so napovedovale dobro fotokatalitsko aktivnost, a vseh predvidenih fotokatalitskih eksperimentov ni bilo mogoče izvesti zaradi ukrepov Vlade RS za zajezitev bolezni COVID-19 (marec–junij 2020). Self-cleaning, anti-fogging and aseptic thin films based on photocatalytic and superhydrophilic properties of TiO2, have been used for commercial purposes worldwide for decades. TiO2 is a commercially available natural material with semiconducting characteristics, with two main disadvantages referring to self-cleaning thin films applications: (1.) wide bandgap (3,2 eV for anatase) with absorption in UV spectral region, representing less than 5% of sunlight and (2.) fast recombination of pairs electron-hole, produced by photon interaction. Doping with elements is one of methods which improves these disadvantages, and vanadium may be suitable dopant. In this work, TiO2-SiO2 thin films with different amounts of vanadium dopant were prepared by sol-gel synthesis and dip-coated on different substrates. We used different techniques for structural, optical and photocatalytic characterisation (UV-Vis, IR and Raman spectroscopy, SEM, XRD, Contact angle measurements …). Despite low temperature preparation TiO2-SiO2 thin films all were transparent and showed excellent photocatalytic properties. XRD, Raman and IR spectroscopy showed possible incorporation of vanadium into TiO2-SiO2 structure. UV-Vis spectroscopy results showed that transparency, spectral reflectance and haze do not change significantly with adding vanadium dopant. It brought no specific improvements in optical, structural or photochemical characteristics. However, optical properties promised good photocatalytic results. Due to Coronavirus pandemic (March–June 2020) we could not perform all scheduled photocatalytic experiments.

Photocatalysis is a well-known process for the last few decades it is predominantly used for water and air purification, but also for self-cleaning and antibacterial surfaces. The photocatalytic process is one of the advanced oxidation processes, where semiconductors are mainly used as photocatalysts. The most known and used semiconductor is nanosized titania, which can non-selectively decompose organic matters. One of the side effects of nano TiO2 under UV irradiation is photoinduced hydrophilicity, which furthermore improves the self-cleaning effect. The main drawback of TiO2 is that for its activation UV light is needed, which represents only 5 percent of the solar spectrum. Consequently, actinic irradiance power is low and the response of photocatalyst is limited. Novel approaches are being introduced to improve TiO2 response to visible light such as doping, coupling, modification of surface morphology and others. The thesis consists of five principal chapters. The first chapter is focused on a short literature review and explanation of some basic terms and principles that are related to this thesis. The aim of the research was to prepare transparent photocatalytically active thin films on glass and thermosensitive substrates. Four thermosensitive substrates were used: polyvinyl chloride (PVC) foil, polymethyl methacrylate (PMMA) sheet and polyester (PES) fabric coated with a polyvinyl and acrylic coating, with (D1) or without (D2) an additional polyvinylidene fluoride topcoat. The synthesis of films was modified with the introduction of zirconium aiming at improving the photocatalytic activity of the TiO2 films, and the final films had a SiO2 phase present for increased mechanical robustness. The third chapter is dedicated to the experimental part of the thesis. The detailed process of synthesis is described. The sol-gel process was used to prepare initial Ti-Zr sols, colloidal aqueous solutions with TiO2 and ZrO2 nanoparticles derived from titanium and zirconium alkoxides. The four different Ti-Zr sols were prepared with 0, 5, 10 and 20 molar % of Zr according to Ti. The depositing solution was prepared by mixing Ti-Zr sol, SiO2 sol binder, 1-propanol and 2-propoxyethanol, and then thin films were deposited by dip-coating technique. After the deposition, samples did not require high-temperature calcination since the photocatalytic anatase phase was present already after drying the deposited layers. Coated glass slides were put into a furnace at 150 °C, while samples on thermosensitive substrates were just treated by a heat gun. Samples in powder and thin film form were characterized by UV-Vis, FTIR-ATR and laser beam deflection spectroscopy, X-ray diffraction, scanning electron microscopy and thermal analysis. One of the main aspects of the photocatalyst is its activity. Photocatalytic activity of the thin films was determined, either quantitatively by the formation of fluorescent hydroxyterephthalic acid, one of the first degradation products of terephthalic acid deposit, or qualitatively by a visual-based method where degradation of resazurin ink was observed. Two additional methods were used on glass samples, electron paramagnetic resonance, and degradation of methyl stearate by observing the change in water contact angle under UVA irradiation. Mechanical stability of films on various substrates is an essential factor, describing how successful was immobilization of the photocatalytic materials on the substrate. It was determined by the pencil hardness test, i.e., Wolff-Wilborn method. In the fourth chapter, titled “Results and Discussion,” the most important part of the thesis is placed. Materials characterization and associated discussion of the results are divided into three major parts: i) powder samples characterization ii) characterization of thin films on a glass substrate, and iii) characterization of films on thermosensitive substrates. In the conclusions, the main findings of the Ph.D. research work are summarized. One of our initial hypotheses was disapproved, thin films were not more active with a higher content of zirconium. However, they were more durable. All the obtained films were transparent and photoactive, despite the low-temperature synthesis procedure. Besides commonly used glass substrate, immobilization on thermosensitive substrates was also successful. Fotokataliza je postala v zadnjih nekaj desetletjih zelo razširjena uporablja se predvsem za čiščenje vode in zraka, za samočistilne ter protibakterijske površine. Fotokatalitski proces spada med napredne oksidacijske procese in kot fotokatalizatorji so največkrat uporabljeni polprevodniki. Najbolj znan in najpogosteje uporabljen polprevodnik je (nano) titanov dioksid, ki lahko neselektivno razgradi organske snovi ob UV sevanju. Pri obsevanju TiO2 z UV svetlobo se pojavi tudi fotovzbujena hidrofilnost, ki še dodatno izboljša samočistilni učinek. Ena od glavnih pomanjkljivosti TiO2 je, da se za njegovo fotoaktivacijo uporablja UV svetloba, ki predstavlja le pet odstotkov sončnega spektra. Za boljši odziv TiO2 na vidno svetlobo se razvijajo novi postopki, na primer dopiranje, kombiniranje z drugimi polprevodniki, modifikacija morfologije površine itd. Doktorsko delo ima pet glavnih poglavij. Prvo poglavje je osredotočeno na krajši pregled obstoječe literature in razlago nekaterih osnovnih pojmov. V drugem poglavju je predstavljen namen doktorskega dela. Pripravila sem transparentne fotoaktivne tanke plasti na steklu in temperaturno občutljivih podlagah. Izbrala sem štiri različne občutljive podlage: polivinil kloridna (PVC) folija, polimetil metakrilat (PMMA) plošča in poliesterska (PES) tkanina, prevlečena s slojem polivinila in akrila z (D1) ali brez (D2) dodatne poliviniliden fluoridne (PVDF) prevleke. Postopek priprave filmov smo obogatili z vpeljavo cirkonija, tako naj bi izboljšali aktivnost samih TiO2 filmov, končni raztopini je bil dodan tudi SiO2, ki je izboljšal mehanske lastnosti filmov. Tretje poglavje je posvečeno eksperimentalnemu delu. V poglavju je opisan podroben proces sinteze tankih plasti. Sol-gel postopek sem uporabila za pripravo začetnih Ti-Zr solov izhajajoč iz titanovega in cirkonijevega alkoksida. Pripravila sem štiri različne Ti-Zr sole z 0, 5, 10 in 20 množinskimi % cirkonija glede na titan. Raztopine za nanašanje so vsebovale Ti-Zr sol, SiO2 vezivo, 1-propanol in 2-propoksietanol tanke plasti pa so bile nanešene s tehniko potapljanja. Tanke filme po nanosu ni bilo potrebno termično obdelati na visoki temperaturi, ker je fotoaktivna anatazna faza že prisotna po sušenju vzorcev. Tako so bili vzorci na steklu toplotno obdelani v peči pri 150 ° C, vzorce na termično neobstojnih podlagah pa sem utrdila zgolj s toplotno pištolo. Praškaste vzorce in tanke plasti smo karakterizirali z naslednjimi metodami: UV-Vis, FTIR-ATR spektroskopijo in spektroskopijo z odklonom laserskega žarka, rentgensko praškovno difrakcijo, presevno elektronsko mikroskopijo in termično analizo. Najpomembnejša lastnost fotokatalizatorja je fotoaktivnost, ta je bila določena na tankih plasteh z dvema različnima metodama kvantitativno z merjenjem koncentracije hidroksiteraftalne kisline po razgradnji teraftalne kisline in kvalitativno, z opazovanjem razgradnje barvila resazurin. Z dvema dodatnima metodama smo izmerili fotoaktivnost tankih plasti na stekleni podlagi, z elektronsko paramagnetno resonanco in z merjenjem kontaktnega kota po razgradnji metil stearata pri UV obsevanju. Zelo pomembna lastnost tankih plati je mehanska odpornost in z merjenjem le te lahko ocenimo, če je bila imobilizacija na podlago uspešna. Mehansko stabilnost filmov smo določili z Wolff-Wilborn-ovo metodo. V četrtem poglavju je opisana karakterizacija materialov s spremljajočo razpravo o rezultatih, ki je razdeljena na tri glavne dele: i) karakterizacija praškastih vzorcev ii) karakterizacija tankih plasti na stekleni podlagi in iii) karakterizacija tankih plasti na termično neobstojnih podlagah. V zaključku so povzete glavne ugotovitve. Ena od naših začetnih hipotez ni bila potrjena, saj tanke plasti z višjo vsebnostjo cirkonija niso bile aktivnejše, izkazovali pa so večjo mehansko odpornost. Vsi vzorci so bili, kljub nizki temperaturi pripravi, transparentni in fotoaktivni. Imobilizacija fotokatalizatorjev je bila uspešna na steklu kot tudi na termično neobstojnih podlagah.

V zadnjih desetletjih postaja dostop do čiste vode vse večja težava, ki jo lahko pripišemo eksponentni rasti prebivalstva in industrializaciji, zaradi česar se je pojavila potreba po ponovni uporabi očiščenih vod. V ta namen je bilo razvitih veliko metod za čiščenje odpadnih voda, ki pa so lahko pri odstranjevanju težje odstranljivih organskih onesnažil manj učinkovite ali celo neučinkovite. Enega največjih problemov predstavljajo odpadne vode v tekstilni industriji, saj so se konvencionalne metode čiščenja izkazale kot zelo neučinkovite pri odstranjevanju tekstilnih barvil, zaradi česar odpadne vode ostanejo obarvane. To lahko vodi do sprememb v bioloških ciklih vodnih organizmov, saj obarvanost preprečuje dostop sončne svetlobe in s tem zmožnost poteka fotosinteze v takem deležu, kot le-ta poteka v prosojni vodi. Zaradi tega se je pojavila potreba po razvoju tehnologije, ki bi lahko učinkovito odstranila onesnažila, prisotna v odpadnih vodah. Fotokataliza se je zaradi svoje zmožnosti popolne mineralizacije organskih onesnažil (razgradnja do CO2 in H2O) na tem področju izkazala za zelo obetavno metodo. Proces fotokatalize temelji na osvetljevanju fotokatalizatorja s svetlobo določene valovne dolžine, ki vzbudi elektrone iz valenčnega v prevodni pas, pri čemer v valenčnem pasu nastanejo elektronske vrzeli. Generirani nosilci naboja nato potujejo do površine fotokatalizatorja, kjer preko nastalih močno reaktivnih specij reagirajo z adsorbiranim onesnažilom in posledično katalizirajo njegovo razgradnjo. Pri fotokatalizi se kot fotokatalizator najpogosteje uporablja TiO2. Zaradi širine njegovega prepovedanega pasu med (3,2 eV za anatas) lahko fotokatalitske reakcije potekajo predvsem pri osvetljevanju s svetlobo z valovno dolžino, nižjo od 390 nm (UV območje). Zaradi tega je bilo v zadnjih desetletjih veliko raziskav posvečenih zoževanju prepovedanega pasu TiO2, s čimer bi se povečala njegova fotokatalitska aktivnost pri osvetljevanju z vidno svetlobo. V dokrorskem delu delu sem se ukvarjal s sintezo TiO2, ki bi imel čim višjo fotokatalitsko aktivnost pri osvetljevanju z vidno svetlobo, kar sem dosegel z dopiranjem z nekovinami in kovinami. Vzorci TiO2 so bili pripravljeni s sol-gel sintezo, z uporabo TiCl4 kot prekurzorja (anorganska pot). Stabilnost solov sem dosegel z ustrezno nizko vrednostjo pH, kar sem dosegel z nakisanjem z uporabo različnih kislin (HCl in H2SO4). V vzorce sem dodal še različne dopante, ki so delovali kot vir dopiranega dušika (sečnina, NH4NO3), žvepla (tiosečnina) in platine (H2PtCl6). Pripravljene raztopine sola sem nato z uporabo tehnike potapljanja (dip-coating) nanesel na objektna stekelca in silicijeve rezine, kristalizacijo amorfnega TiO2 pa sem dosegel s termično obdelavo v komorni peči. Prahove sem pripravil s sušenjem raztopine sola do kserogela in nadaljnjo termično obdelavo v komorni peči. Fotokatalitska učinkovitost tankih plasti pri osvetljevanju z UV in vidno svetlobo sem določil z meritvami hitrosti razgradnje organskega barvila Plasmocorinth B, ki se veliko uporablja v tekstilni industriji. Fotokatalitsko aktivnost prahov je bila določena z merjenjem hitrosti oksidacije izopropanola v aceton. Strukturne in morfološke lastnosti tankih plasti in ustreznih prahov so bile določene z uporabo različnih karakterizacijskih metod. Prav tako sem z uporabo različnih tehnik (kromatografija, meritve pH in prevodnosti) določil mehanizem razgradnje Plasmocorinth B. Ugotovil sem, da so strukturne in morfološke lastnosti tankih plasti in prahov odvisne od vrste in količine dodane kisline, dopanta in temperature termične obdelave. Vsi omenjeni parametri imajo velik vpliv na fotokatalitsko aktivnost tankih plasti in prahov. Vzorci, dopirani in ko-dopirani s kovinami in nekovinami imajo veliko višjo aktivnost pri osvetljevanju z UV in vidno svetlobo. Najbolj aktivni so bili vzorci, kodopirani z dušikom in žveplom, modificirani s platino. Access to clean water has become a major problem in the last decades. This is due to the exponential growth of human population and industrialization. Because of this, the need for reuse of treated waste waters has arisen. A lot of methods for waste water treatment have been developed, but they can be inefficient for the degradation of persistent organic pollutants. A major environmental problem are textile industry effluents since conventional treatment methods are not able to remove textile dyes from waste waters. Because of that, waste waters remain colored, which can alter biological cycles of water organisms, by blocking access of sunlight and consequentially blocking photosynthesis. There is therefore a need for the development of a method, which could efficiently degrade pollutants present in textile industry waste waters. Because of its ability to completely oxidize organic pollutants to CO2 and H2O, photocatalysis has emerged as a promising technique for waste water treatment. The term photocatalysis is used to describe a process during which light of a certain wavelength excites an electron from the valence band onto the conductive band of a photocatalyst. The resulting charge carriers (electron and hole) then travel to the surface of the photocatalyst, where they can catalyze the degradation of adsorbed organic pollutants. Because of its advantageous properties, titanium dioxide (TiO2) has been one of the most widely used photocatalysts. One of the main drawbacks of TiO2 is the width of its band gap (3.2 eV for anatase), which means that an electron can only be excited onto the conduction band when illuminated with UV light with a wavelength lower than 390 nm. A lot of studies have focused on narrowing the width of the band gap of TiO2, which would increase its photocatalytic activity under visible light illumination. In my research work, I focused on preparing TiO2 with high photocatalytic activity under visible light illumination. This was achieved by non-metal and metal doping. Samples were synthesized using a sol-gel synthesis with titanium tetrachloride as a precursor (inorganic path). During the synthesis, solutions were acidified with two different acids (HCl and H2SO4). To increase the activity of TiO2 under visible light illumination, diferent dopants, acting as a source of doped nitrogen (NH4NO3, urea), sulfur (thiourea) and platinum (H2PtCl6), were added. Afterward, the prepared sols were deposited onto object glasses using dip-coating and thermally treated in a muffle furnace to promote crystallization. Corresponding powders were prepared by drying the prepared sols, followed by thermal treatement in a muffle furnace. Photocatalytic activity of the prepared thin films was tested by observing the degradation rate of Plasmocorinth B textile dye. The photocatalytic activity of powders was determined by observing the rate of isopropanol to acetone oxidation. Thin films and corresponding powders were characterized by various techniques. Moreover, the degradation mechanism of Plasmocorinth B was determined using various techniques (chromatography, pH and conductivity). Results of these characterization techniques have shown that the type and amount of acid and dopant used and also the temperature of thermal treatment have a large effect on the structural, surface and morphological properties and consequentially the photocatalytic activity of thin films and corresponding powders. Results have shown a significant increase in activity in samples, doped and co-doped with metals and non-metals, under UV and visible light illumination. The highest activity was observed in samples, co-doped with nitrogen and sulfur and modified with platinum.

In this paper, we report on the current status of absorber attributes in Liquid Phase Crystallized Silicon (LPC-Si) cells. To this end, an absorber doping series (ND = 2·1016/cm³ to 7·1017/cm³) and an absorber thickness variation (14 and 33 µm) are evaluated. Best cells from the batches for these series showed open circuit voltages up to 640 mV and fill factors above 70%. It is observed that for state-of-the-art cells, thicknesses over 15 µm are not beneficial due to limited diffusion lengths. Lower absorber doping concentrations tend to yield longer intra-grain diffusion lengths (Ldiff) and better passivated grain boundaries, which may be due to lower impurity precipitation. The longer Ldiff leads to higher short circuit current densities which over-compensate a decrease in open circuit voltage and fill factor with regards to efficiency. Both front and rear surfaces are sufficiently passivated and at the current status the bulk lifetime has most potential for improvement.

Piezoelektrične in feroelektrične materiale izkoriščamo v številnih aplikacijah, kjer se pojavi potreba po medsebojni pretvorbi mehanskih v električne signale in obratno, recimo v aktuatorjih, senzorjih, ultrazvočnih pretvornikih in shranjevalcih energije. Zadnjih nekaj desetletji smo na trgu priča prevladi piezoelektričnega materiala $rm{Pb(Zr,Ti)O_3}$. Ta material ima odlične funkcionalne lastnosti, vendar je zaradi vsebnosti svinca okolju in človeku škodljiv. Razvoj novih piezoelektričnih materialov je torej usmerjen k piezoelektričnim materialom brez svinca. Tipični predstavnik takšnih materialov je $rm{(K,Na)NbO_3}$. Cilj zaključnega dela je bil preučiti lokalne piezoelektrične in feroelektrične lastnosti polikristalinične tanke plasti $rm({K_{0.5}Na_{0.5})_{0.99}Sr_{0.01}NbO_3}$. Vse eksperimente sem izvedel z mikroskopom na atomsko silo. Sprva sem določil topografijo površja vzorca, hrapavost vzorca ter lokalni piezoelektrični odziv v vertikalni smeri. Hrapavost vzorca, določena na območju velikosti 2 μm x 2 μm, je bila 3 nm, povprečna vrednost lokalnega piezoelektričnega odziva d$_{33}$ pa 42 pm/V. Nadalje sem izmeril lokalno histerezno zanko faznega premika v odvisnosti od jakosti električnega polja s katerim sem obračal polarizacijo. S tem, ko sem obračal polarizacijo v izbrani točki, sem dokazal, da je vzorec lokalno feroelektričen. Piezoelectric and ferroelectric materials are used in numerous applications, such as actuators, sensors, ultrasonic transducers and energy storage devices, where conversion between mechanical and electrical signals is needed. Over the last few decades, materials based on $rm{Pb(Zr,Ti)O_3}$ dominate the market of piezoelectric devices. That material has excellent functional properties, but it is harmful to the environment and humans due to its high content of lead. The development of new piezoelectric materials is therefore oriented towards environmental-friendly lead-free materials, such as $rm{(K,Na)NbO_3}$-based ones. The aim of this work was to study the local piezoelectric and ferroelectric properties of the polycrystalline $rm({K_{0.5}Na_{0.5})_{0.99}Sr_{0.01}NbO_3}$ thin films. I have done all the experiments by atomic force microscope. At first, I determined the sample topography, surface roughness and local piezoelectric response in vertical direction. The surface roughness was 3 nm (scanned on the area of 2 μm x 2 μm). The average value of the local piezoelectric response d$_{33}$ was 42 pm/V. Further, I measured the local hysteresis loop of phase shift in dependence of electric field whom I reoriented polarization. With reorienting polarization in particular point, I proved that the sample is local ferroelectric.

V podjetju, ki razvija in proizvaja avtomobilske žaromete, se s tankimi plastmi srečujejo na dnevni ravni. Izdelave žarometov si namreč brez njihove neposredne uporabe ni moč zamisliti. Uporabljajo se v drugi fazi izdelave žarometov, tako imenovani fazi oslojevanja oziroma metalizacije, pri kateri se z namenom dosega primerne svetlobne odbojnosti žarometa nanesejo na obdelovanec s postopkom naparevanja ali naprševanja. Pri nanosu tankih plasti na obdelovanec pa se večkrat zazna problem slabe adhezije, katere vzrok je največkrat slaba plazemska aktivacija oziroma slaba priprava površine obdelovanca za nanos tanke plasti. Za lažje razumevanje nanašanja tankih plasti v postopku izdelave žarometov v uvodnem delu diplomskega dela na splošno predstavim postopke nanašanja tankih plasti in natančneje opišem postopek naparevanja in naprševanja. Ker plazma za omenjena postopka predstavlja osnovo, podrobneje opišem tudi njeno vlogo pri tem. V osrednjem delu diplomskega dela se osredotočim na postopek izdelave žarometov, pri čemer izpostavim nanašanje tankih plasti s postopkom naparevanja, ki ga podjetje, pri katerem sem zaposlen, za ta namen najpogosteje izvaja. Predstavim tudi testiranja, ki se izvajajo pri nanašanju tankih plasti, obstoječe standarde, meritve kakovosti obdelovancev in pojav napak pri nanašanju tankih plasti. V zaključnem delu diplomskega dela se osredotočim na problem slabega nanosa tankih plasti, kjer poskušam optimizirati strojne parametre plazemske aktivacije, ki je ključnega pomena za kakovosten in dober nanos tankih plasti na obdelovanec. The company which develops and manufactures automotive headlamps deals with coating of thin layers on a daily basis. Manufacturing headlights without this technology is hard to imagine. Coating is used in the second stage of manufacturing headlamps called vaporization or metallization which is a process where a metallic layer is deposited on a workpiece by vapor deposition or sputtering with the aim to reach an appropriate light reflectivity of the headlamp. When applying thin layers onto the workpiece, the problem of deficient adhesion can occur. This comes from poor plasma activation process or bad preparation of the workpiece surface before applying thin layers. For ease of understanding of the thin layer deposition in the headlamps manufacturing process, the introduction describes different processes of thin layer deposition, with detail description of vapor deposition and sputtering. Since plasma is the basis of this process its main role is also described. In the central part of the diploma I focused on the manufacturing process of headlamps, with emphasis on the most commonly performed vapor deposition process used by the company where I work. This part also explains that when applying thin layers on workpieces different requirements, standards and quality measurements must be met, or errors may occur. In the conclusion I focused on the problem of low coating quality. With experimentation, I tried to optimize parameters of plasma activation process, which is crucial for the good coating quality of thin layers on the workpieces.

TiO2 - SiO2 composites were synthesized by low-temperature sol-gel impregnation method, using four different titania sources (P-25 from Degussa, PC500 from Millennium, CCA 100 AS and CCA 100 BS from Cinkarna, later denoted as AS and BS, respectively) and deposited on aluminium and glass carriers. Ordered and disordered mesoporous silicas were impregnated with ce{TiO2} in powder or suspension form in the Ti : Si molar ratio 1 : 1. Structure, size, band gap, chemical composition and specific surface area of nanoparticles were determined by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DR-UV-vis), Fourier transform infrared spectroscopy (FT-IR) and ce{N2} physisorption. Additionally, quantity of surface hydroxyl groups, surface acidity and mechanical stability of the coatings were determined by temperature programmed Fourier transform infrared spectroscopy (TPD-IR) and Wolff-Wilborn method, respectively. The photocatalytic activity of TiO2 and TiO2 - SiO2 composites was evaluated in the photodegradation of toluene and formaldehyde, as model VOCs, under UVA light irradiation in lab-made photoreactor system with two different regimes batch and plug-flow mode. These two VOCs are being considered as examples of two of the six major classes of indoor air contaminants. Adsorption properties of the samples with toluene, have shown that the addition of mesoporous silica was beneficial. The increase of the adsorption of the bare AS TiO2 (9.5 %) was higher in the case of ordered silica, SBA-15 (2.8 times for AS/SBA15 to 26.8 %) than disordered SiO2 KIL-2 (2.4 times for AS/KIL2 to 22.7 %) although it was significant in both types of mesoporous silica supports (over 20 %). Adsorption was found to be dependent mostly on the quantity of surface Si-OH groups. Regarding the photocatalytic activities towards toluene degradation, the results with pure TiO2 showed the fastest kinetics in case of sample AS followed by PC500 and P25. The observed behaviour was ascribed to smaller particle size, and consequently higher specific surface area. Grafting titania onto silica showed the importance of structural parameters. Most importantly, if the pore structure of bare TiO2 collapsed, this resulted in decreased activity. On the other hand, retainment of the pore structure improved the distribution of nanoparticles, crystallinity and optical properties, which resulted in improved photocatalytic activity. In the degradation of formaldehyde, it was found that adsorption and degradation abilities of the materials were much more dependent on the structural properties of the samples, i.e., the pore structure. This was explained as a consequence of the different degradation mechanisms of both pollutants. Toluene degradation is governed by the oxidation through photogenerated holes - direct oxidation, whereas in the degradation of formaldehyde, the major oxidative species are OH radicals. In addition, the same as in toluene oxidation, the activity was dependent mainly on the number of crystal defects and the band gap values, that is the oxidation and reduction potentials of the catalysts. The degradation efficiency was increased from 88 % in pure AS TiO2 to 97 % when this titania was grafted onto colloidal silica (7C). An important highlight of the thesis is synthesis of a novel photocatalyst, labelled AS7C, which comprises an acidic colloidal suspension AS as TiO2 source and colloidal silica, using a low-temperature sol-gel impregnation method. This sample used all the above mentioned properties that improve photocatalytic activity towards both pollutants. Mechanical stability of the samples was also tested. The tests showed that binder, in the form of colloidal SiO2 (in size of 25 nm) in combination with colloidal titania of appropriate size - 6 nm, produced the highest mechanical stability of the coatings, which also showed excellent photocatalytic activity. Stability of the coatings, using AS as titania source, was greatly improved. The Wolff-Wilborn test on AS coating showed no mechanical resistance, while with the optimal (in terms of photocatalytic performance) addition of 7C SiO2 binder stability was excellent (F, which is in the middle of 6B-6H hardness scale). This sample (AS7C) was also tested for release of aerosols, during operation of the reactor, which could be harmful for human health at longer exposure times. It was found that aerosols are formed, probably as a consequence of detachment of nanoparticles in the first period of photodegradation test. However, their formation in consecutive tests was greatly reduced. Last but not least, a pilot plug-flow reactor was constructed to test the photocatalyst's efficiency in one-pass degradation of toluene. Sample AS7C was able to degrade toluene at conditions applied (v= 400 mL/min, m(catalyst) = 1049 mg, C(0) = 1 ppmv), which means that the out-flow from reactor was clean of the pollutant and any possible intermediates, comprising only of humid air and CO2. Deactivation of the catalyst was found at higher air flow and higher initial concentration of the pollutant. However, the concentrations of pollutants in living conditions are few orders of magnitude lower, hence this is a promising result. Sintetizirani so bili TiO2 − SiO2 kompoziti po nizko-temperaturnem sol-gel postopku impregniranja, z uporabo štirih komercialno dostopnih virov TiO2 (P-25 iz Degusse, PC500 iz Millenniuma ter CCA 100 AS in CCA 100 BS iz Cinkarne, kasneje označena kot AS in BS) ter njihova imobilizacija na aluminij in steklene nosilce. Urejeni in neurejeni mezoporozni SiO2 so bili impregnirani s TiO2 v obliki prahu ali v obliki suspenzije v Ti : Si molskem razmerju 1: 1. Določeni so bili struktura, velikost delcev, energijska vrzel kompozitov, njihova kemična sestava in specifična površina s praškovno rentgensko difrakcijo (XRD), vrstičnim elektronskim mikroskopom (SEM) in transmisijsko elektronsko mikroskopijo (TEM), UV-vis difuzno reflektanco (DR-UVvis), infrardečo spektroskopijo s Fourierjevo transformacijo (FT-IR) in N2 fizisorpcijo. Poleg tega je bila določena količina hidroksilnih skupin na površini, kislost na površini ter mehanske stabilnosti prevlek, določene z uporabo temperaturno programirane infrardeče spektroskopije s Fourierjevo transformacijo (TPD-IR) in Wolff-Wilborn testom trdnosti. Fotokatalitska aktivnost TiO2 in TiO2 − SiO2 kompozitov je bila ocenjena za fotorazgradnjo toluena in formaldehida kot modelnih VOC-ov pod UVA osvetlitvijo v laboratorijsko narejenem fotoreaktorskem sistemu v okviru dveh različnih režimov krožnem in pretočnem. Ta dva VOC-a sta predstavnika dveh od šestih glavnih skupin onesnaževal notranjih prostorov. Absorpcijske lastnosti vzorcev, glede toluena kot onesnaževala, so pokazale, da je dodajanje mezoporoznega SiO2 koristno. Adsorpcija čistega TiO2 vira iz Cinkarne Celje (AS) (9.5 %) se je bolj povišala v primeru dodatka urejenega vira SiO2 – SBA-15 (2,8-krat za AS/SBA15 na 26.8 %) kot neurejenega vira SiO2 – KIL-2 (2,4-krat za AS/KIL2 na 22.7 %). Po drugi strani pa je bilo ugotovljeno, da je adsorpcija odvisna predvsem od količine Si−OH skupin na površini. Še več, impregnacija TiO2 z mezoporozno siliko adsorpcije ne izboljša vedno. Glede fotokatalitskih aktivnosti za razgradnjo toluena, so rezultati z uporabo ˇ cistega TiO2 pokazali najhitrejšo kinetiko v vzorcu AS, ki sta mu sledila PC500 in P25. Opaženo vedenje sem pripisal manjši velikosti delcev in s tem višji specifični površini. Vgradnja TiO2 v/na SiO2 je izpostavila pomen strukturnih parametrov. Kot najpomembnejša se je izkazala porušitev strukture por čistega TiO2, namreč to je povzročilo zmanjšano aktivnost. Po drugi strani pa je ohranitev strukture por pri impregnaciji izboljšala porazdelitev nanodelcev, kristaliničnost in optične lastnosti materiala, kar je povzročilo izboljšano fotokatalitsko aktivnost. Pri razgradnji formaldehida je bilo ugotovljeno, da so adsorpcijske in aktivnostne lastnosti materialov veliko bolj odvisne od strukturnih lastnosti vzorcev, to je strukture por. To si razlagamo kot posledico različnih mehanizmov razgradnje obeh onesnaževal. Razpad toluena poteka z oksidacijo preko fotovzbujenih lukenj - direktno oksidacijo, medtem ko so pri degradaciji formaldehida glavni oksidanti OH radikali. Poleg tega je enako kot pri oksidaciji toluena aktivnost odvisna predvsem od števila napak v kristalni strukturi in velikosti energijske vrzeli, torej redoks potenciala katalizatorjev. Sintetiziral sem nov fotokatalizator, označen z AS7C, ki izhaja iz kisle koloidne suspenzije AS kot vira TiO2 in koloidnega SiO2 kot veziva, z uporabo preproste, nizkotemperaturne sol-gel metode impregnacije. Ta vzorec izkorišča prednosti vseh zgoraj navedenih lastnosti, ki izboljšujejo fotokatalitsko aktivnost pri obeh onesnaževalih. Preizkusil sem tudi mehansko stabilnost vzorcev. Testi so pokazali, da je vezivo v obliki koloidnega SiO2, (velikost SiO2 delcev 25 nm), v kombinaciji s koloidno suspenzijo delcev titanovega dioksida primerne velikosti - 6 nm poveˇ calo mehansko obstojnost premazov. Prav tako so te plasti pokazale odlično fotokatalitsko aktivnost. WolffWilborn-ov test plasti iz čistega AS TiO2 ni pokazal nobene mehanske odpornosti, medtem ko sem z optimalno količino (v smislu fotokatalitske aktivnosti) dodanega 7C SiO2 veziva uspel dobiti plasti, ki so pokazale odlično trdnost (F, kar je na sredini 6b–6H trdnostne lestvice). Vzorec AS7C je bil testiran tudi za nastajanje aerosolov, med delovanjem reaktorja, ki so lahko pri daljših ˇ casih izpostavitve škodljivi za zdravje ljudi. Ugotovil sem, da aerosoli nastajajo, verjetno zaradi odstranjevanja nanodelcev iz plasti v prvem obdobju delovanja reaktorja. Tvorba aerosolov v sledečih testih pa je bila močno zmanjšana, kar kaže na dolgoročno ustreznost uporabe materiala za čiščenje zraka. Nenazadnje je bil izdelan pilotni pretočni reaktor za testiranje učinkovitosti fotokatalizatorja pri razgradnji enkratnega prehoda toluena. Vzorec AS7C je bil sposoben razgraditi začetno koncentracijo toluena, 1 ppmv (pretok zraka = 400 mL/min, m(katalizator) = 1049 mg), kar pomeni, da je bil zrak pri izhodu iz reaktorja čist ter brez vemsnih produktov. Pri višjih pretokih zraka in višji začetni koncentraciji onesnaževala sem zaznal deaktivacijo katalizatorja. Kljub temu pa so koncentracije VOC-ev v bivalnih prostorih nekaj redov velikosti nižje, zato je to obetajoč rezultat.

V delu opisujemo študij kristalizacije in razvoja mikrostrukture tankih plasti na osnovi trdne raztopine 0,85 K0.5Na0.5NbO3 – 0,15 SrTiO3 (KNN-STO), pripravljenih s sintezo iz raztopin, na platiniziranih silicijevih podlagah. Raztopino KNN-STO smo pripravili iz kalijevega acetata KO2C2H3, natrijevega acetata NaO2C2H3, niobijevega etoksida Nb(OEt)5, titanovega propoksida Ti(OC2H4CH3)4 in stroncijevega nitrata Sr(NO3)2. Kot topilo smo uporabili 2-metoksietanol CH3OCH2CH2OH. Plasti smo segrevali po dvostopenjskem in štiristopenjskem postopku segrevanja, kar pomeni, da smo jih po stopnji pirolize segrevali do končne temperature po vsakem drugem, oziroma po vsakem nanosu raztopine s koncentracijo cM = 0,4 M na podlago. Plasti, pripravljene iz raztopin različnih koncentracij (0,1 M, 0,2 M, 0,4 M), smo segrevali do končne temperature po vsakem nanosu raztopine na podlago. Rentgenski difraktogrami plasti kažejo, da vse plasti, ki smo jih segrevali po opisanih postopkih do temperatur med 500 °C in 700 °C, kristalizirajo v perovskitni fazi s psevdo-kubično osnovno celico brez izrazite kristalografske usmerjenosti. Mikrostruktura plasti je odvisna od pogojev priprave. Plasti, pripravljene iz raztopine KNN-STO s koncentracijo 0,4 M z dvostopenjskim segrevanjem, imajo enakomerno mikrostrukturo z enakoosnimi zrni, velikimi ~20 nm, medtem ko je mikrostruktura plasti, pripravljenih s štiristopenjskim segrevanjem, heterogena z zrni velikosti od ~20 nm do ~100 nm. Mikrostruktura plasti, ki smo jih pripravili iz raztopin KNN-STO z različnimi koncentracijami in segrevali po vsakem nanosu, je heterogena, z zrni velikosti od ~50 nm do ~150 nm. Pogoji priprave tankih plasti KNN-STO vplivajo tudi na njihove dielektrične lastnosti. Plasti, pripravljene z dvostopenjskim segrevanjem, imajo večjo vrednost dielektrične konstante kot plasti, pripravljene s štiristopenjskim segrevanjem. Vrednost dielektričnosti se povečuje z naraščajočo temperaturo in časom segrevanja. Plast KNN-STO, pripravljena z dvostopenjskim segrevanjem pri temperaturi T=700 °C in času t=15 min ima največjo dielektričnost in nizke dielektrične izgube, in sicer 700 in 0,04 pri sobni temperaturi in pri frekvenci 100 kHz. Izmerili smo temperaturno in frekvenčno odvisnost dielektričnosti in dielektričnih izgub omenjenega vzorca in ugotovili, da kaže značilen relaksorski odziv, podobno kot volumenska keramika z enako kemijsko sestavo. The work describes the study of crystallization and evolution of microstructure of the 0,85 K0.5Na0.5NbO3 – 0,15 SrTiO3 solid solution based thin films, prepared by Chemical Solution Deposition, on platinized silicon substrates. The solution was synthesized from potassium acetate KO2C2H3, sodium acetate NaO2C2H3, niobium-pentaethoxide Nb(OEt)5, titanium-n-propoxide Ti(OC2H4CH3)4, strontium nitrate Sr(NO3)2, and the solvent 2-methoxyethanol CH3OCH2CH2OH. The films, deposited from the solution with the 0˙4 M concentration by spin-coating, were heated at different temperatures and times by the two-step and four-step rapid thermal annealing. Furthermore, we prepared the films from the solutions with different concentrations, namely 0,1 M, 0,2 M, and 0,4 M, and annealing after each deposition . According to X-ray diffraction analysis, the films crystallized in perovskite phase with a pseudo-cubic unit cell upon heating to temperatures between 500 °C and 700 °C. We observed no preferential orientation of the perovskite phase. The films, prepared by the two-step annealing have got granular and homogeneous microstructures with the grain size of ~20 nm, while the microstructures of the films, prepared by the four-step annealing, are quite heterogeneous with equiaxed grains ranging from ~20 nm to ~100 nm. The films, prepared from the solutions with different concentrations and annealing after each deposition, have got heterogeneous microstructures with the grain size from ~50 nm to ~150 nm. The dielectric permittivity of the KNN-STO films depends on the heating profile. The films, processed by the two-step annealing have got higher values of dielectric permittivity than the films prepared by the four-step annealing. In both cases, the permittivity increases with longer annealing time and higher annealing temperature. The highest dielectric permittivity was obtained for the films, prepared by the two-step annealing at 700 °C for 15 min, namely 700 at room temperature and 100 kHz. The temperature and frequency dependent dielectric measurements revealed the relaxor-like behaviour of the KNN-STO film, similar as the bulk ceramic with the same chemical composition.

Volframske tanke plasti imajo zaradi odličnih mehanskih in kemičnih lastnosti široko uporabo v imdustriji. Eden od načinov priprave volframskih tankih plasti je magnetronsko nanašanje.....