Search

Due to many advantageous physiochemical properties, titanium dioxide (TiO2) is the most widely used photocatalyst in numerous applications, such as wastewater treatment and air purification, self-cleaning surfaces and energy conversion (H2 generation). However, one of its disadvantages is the high electron-hole recombination rate, and coupling with other semiconductors is one of the strategies to improve it. The objective of this dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by tin modification and to explain the mechanism of increased or hindered photoactivity in correlation with the structural properties of the modified TiO2 photocatalysts. A new low-temperature sol-gel synthesis route was developed to prepare Sn- or SnO2-modified TiO2 photocatalysts. In both cases, organic tin and titanium precursors were used. Tin in the form of Sn cations was used to prepare Sn-modified TiO2. In this case, the precursors went through the sol-gel reaction together to form a Sn-TiO2 sol. In the case of SnO2 modification, the SnO2 sol was prepared separately and additionally mixed with the TiO2 sol to form a TiO2/SnO2 bicomponent semiconductor system. Different molar ratios of tin to titanium were prepared to investigate the correlation between the tin concentration and the photocatalytic properties of the photocatalysts in the form of thin films. The results were used to optimize the synthesis conditions to obtain an improved activity of the modified TiO2 photocatalysts under UV-irradiation. The photocatalytic activity of the thin films was determined by measuring the degradation rate of an azo dye. An increase of up to 40 % in the photocatalytic activity of the dried samples (at 150 °C) was achieved when the TiO2 was modified with the Sn or SnO2 in a concentration range of 0.1 to 1 mol.%. At higher Sn or SnO2 loadings and after calcination of the samples at 500 °C, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. Different characterization techniques (UV-Vis, XRD, nitrogen physisorption, TEM, SEM and XAS) were employed to clarify the mechanism responsible for the enhanced and hindered photocatalytic performance of the Sn- and SnO2-modified TiO2 photocatalysts. The results showed that a nanocrystalline structure is already achieved in the samples by the low-temperature film treatment (drying at 150 °C) and that the photocatalytic efficiency is mainly influenced by the crystalline phase composition: anatase/rutile in the case of Sn-modified and TiO2/SnO2 in the case of SnO2-modified TiO2. The crystal size and specific surface area differ insignificantly between the equally thermally treated samples and partly explain the differences in photoefficiency of the calcined samples compared to the dried samples. The structural study at the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation sites for the anatase to rutile transformation in the Sn-modified TiO2 photocatalysts, while in the SnO2-modified TiO2 samples the nanocrystalline cassiterite SnO2 is bound to the TiO2 nanocrystallites via the Sn-O-Ti bond. In both cases, the advantage of coupling the two semiconductors was achieved by separating the charge carriers and thus prolonging their lifetime for accessibility to participate in the redox reactions. The maximum activity enhancement was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases are obtained for the given physical parameters, such as particle size, shape and specific surface area of the catalyst.

Plastoviti dvojni hidroksidi (angl. layered double hydroxides – LDH) so strukturno podobni alumosilikatom, ki so glavna sestavina glin. Sestavljeni so iz pozitivno nabitih plasti, v katerih se nahajajo kationi vsaj dveh različnih kovin. Pozitivni naboj plasti kompenzirajo anioni, ki se skupaj z vodo nahajajo v sloju med plastmi. LDH je enostavno sintetizirati z veliko različnimi kationi in medplastnimi anioni. Pri njihovi toplotni obdelavi nastanejo mešani oksidi. Lastnosti kot sta velika specifična površina in ionsko izmenjevalna kapaciteta, omogočajo raznoliko uporabo LDH in njihovih mešanih oksidov. Med drugim se uporabljajo kot ionski izmenjevalci, antacidi, adsorbenti v odpadnih vodah, katalizatorji in nosilci katalizatorjev. Namen mojega diplomskega dela je bila sinteza in karakterizacija cink-aluminijevih in cink-kromovih plastovitih dvojnih hidroksidov in njihovih mešanih oksidov. Primerjali smo stopnjo kristaliničnosti ter potek termičnega razpada Zn-Al LDH in Zn-Cr LDH, vpliv hidrotermalne obdelave na kristaliničnost dobljenih produktov ter anionsko izmenjavalno kapaciteto in fotokatalitsko aktivnost produktov, toplotno obdelanih pri različnih temperaturah. Cink-aluminijeve in cink-kromove plastovite dvojne hidrokside sem sintetizirala z metodo soobarjanja pri konstantnem pH. Raztopini prekurzorskih kationov (Zn2+, Al3+ oz. Zn2+, Cr3+) sem pripravila tako, da je bil delež trivalentnega kationa (x) enak 0,25. S tem sem upoštevala pogoj za pripravo enofaznih LDH (0,2≤x≤0,33). Pri obeh sintezah sem kot bazo uporabila raztopino NH3 (c = 2,0 M). Polovica sintetiziranih LDH je bila hidrotermalno obdelana pri 100 °C. Prav tako sem pri delu pripravljenih produktov izvedla zamenjavo kloridnih ionov s karbonatnimi. Vsak dobljen vzorec je bil nato še toplotno obdelan pri 300 °C, 400 °C, 500 °C in 600 °C. Na koncu sem vzorce karakterizirala z rentgensko praškovno difrakcijo (XRD), termogravimetrijo (TG) in Uv-Vis spektrometrijo. S slednjo sem preko razgradje azo barvila Plasmocorinth B merila adsorpcijsko sposobnost in fotokatalitsko aktivnost vzorcev. Pri svojem delu sem uspešno sintetizirala Zn-Al in Zn-Cr LDH. Zamenjava kloridnih ionov s karbonatnimi je potekla, kar smo dokazali z XRD in TG analizo. Ugotovila sem, da se kristaliničnost produkta zmanjša ob zamenjavi Al3+ ionov s Cr3+ ioni, medtem ko se ob zamenjavi Cl- ionov s CO32- ioni kristaliničnost poveča pri Zn-Al LDH in zmanjša pri Zn-Cr LDH. Na potek termičnega razpada precej bolj vpliva zamenjava kloridnih ionov s karbonatnimi med plastmi, kot pa zamenjava aluminijevih kationov s kromovimi v plasteh. Izkaže se, da so Zn-Cr LDH boljši adsorbenti od Zn-Al LDH in da so dobri fotokatalizatorji hidrotermalno obdelani vzorci s kloridnimi ioni, toplotno obdelani pri 600 °C. Layered double hydroxides (LDHs) are structurally similar to aluminosilicates, which are the main constituents of clays. They consist of positively charged layers containing cations of at least two different metals. The positive charge of the layer is compensated by anions, which are located in the interlayer together with water molecules. LDHs are easily synthesized with many different cations and interlayer anions and during thermal treatment form mixed oxides. Properties such as a large specific surface area and high capacity for ion exchange allow for a diverse use of LDHs and their mixed oxides, such as ion exchangers, antacids, wastewater adsorbents, catalysts and catalyst supports. The purpose of this diploma work was the synthesis and characterization of zinc-aluminium and zinc-chromium layered double hydroxides and their mixed oxides. Crystallinity and the course of thermal decomposition of Zn-Al LDHs and Zn-Cr LDHs, the influence of hydrothermal treatment on the crystallinity of the obtained products, the anion exchange capacity and photocatalytic activity of products heat treated at different temperatures, were examined. Zinc-aluminium and zinc-chromium layered double hydroxides were synthesized by the coprecipitation method at a constant pH level. The solution of precursor cations (Zn2+, Al3+ or Zn2+, Cr3+) was prepared so that the mole fraction of the trivalent cation (x) was equal to 0,25 so the condition for the preparation of pure LDHs (0,2≤x≤0,33) was fulfilled. In both syntheses a NH3 solution (c = 2.0 M) was used as the base. Half of the synthesized LDHs were hydrothermally treated at 100 °C. For half of the products, the chloride ions were replaced with carbonate ions. Each sample was then further heat treated at 300 °C, 400 °C, 500 °C and 600 °C. The samples were characterised by X-ray powder diffraction (XRD), thermogravimetry (TG) and UV-Vis spectrometry. The latter was used to measure the adsorption capacity and photocatalytic activity of the samples through the degradation of the azo dye Plasmocorinth B. Results show that Zn-Al and Zn-Cr LDHs were successfully synthesised. The replacement of chloride ions with carbonate ones was successful, which was proven by XRD and TG analysis. The crystallinity of the product was found to decrease upon replacement of Al3+ ions with Cr3+ ions, while replacing Cl- ions with CO32- ions increased the crystallization degree of Zn-Al LDHs, the opposite was observed for Zn-Cr LDHs. The replacement of chloride ions with carbonate ones between the layers has a much greater effect on the curve of thermal decomposition than a replacement of aluminium cations with chromium ones in the layers. It turns out that Zn-Cr LDHs are better adsorbents than Zn-Al LDHs and that good photocatalysts are both hydrothermally treated samples with chloride ions, heat treated at 600 °C.

Namen magistrskega dela je bil sintetizirati bizmut molibdenove nanodelce z različnimi metodami ter oceniti fotokatalitsko učinkovitost enega izmed produktov pri razbarvanju RhB ob prisotnosti vidne svetlobe. Prvi sklop eksperimentalnega dela je zajemal sintezo bizmut molibdenovih nanodelcev z različnimi kristalnimi strukturami . Pri tem smo uporabljali mehanokemijsko, hidrotermalno, sonokemijsko in metodo nizko temperaturne taline soli (LTMS). Pripravljeni produkti so bili karakterizirani z rentgensko praškovno difrakcijo (RTG), presevnim elektronskim mikroskopom (TEM) in termogravimetrično analizo (TGA). Fotokatalitsko aktivnost bizmut molibdenovega kristala smo ocenili z izvedbo fotokatalitske degradacije rodamina B pri sobni temperaturi pod vplivom VIS sevanja. Rezultati so pokazali, da smo uspeli sintetizirali vse tri fazne modifikacije bizmutovih molibdatov. Z mehanokemijsko sintezo smo sintetizirali alfa in gama bizmut molibdenove nanodelce, hidrotermalna sinteza je pripomogla k nastanku gama in beta modificiranih bizmutovih molibdatov ter s sonokemijsko sintezo smo ustvarili beta bizmut molibdenov oksid. Z uporabo UV-VIS spektrofotometra smo Bi2Mo3O12 nanodelcem ocenili fotokatalitske sposobnosti degradacije rodamina B (RhB) v raztopini pri sobni temperaturi pod vplivom VIS sevanja. Ugotovljeno je bilo, da je absorpcijski rob Bi2Mo3O12 ocenjen pri 435 nm, kar ustreza vrednosti prepovedanega pasu Eg = 2,78 eV. V prisotnosti obeh ključnih dejavnikov tako svetlobe kot fotokatalizatorja (Bi2Mo3O12) smo po 120 minutah obsevanja z vidno svetlobo dosegli skoraj 100 % razgradnjo RhB. The purpose of the master's thesis was to synthesize bismuth molybdenum nanoparticles using various methods and to evaluate the photocatalytic efficiency of one of the products in RhB discoloration in the presence of visible light. The first set of experimental work involved the synthesis of bismuth molybdenum nanoparticles with different crystal structures. Mechanochemical, hydrothermal, sonochemical and low temperature salt melt (LTMS) methods were used. The prepared products were characterized by X-ray powder diffraction (RTG), transmission electron microscope (TEM) and thermogravimetric analysis (TGA). The photocatalytic activity of bismuth molybdenum crystal was evaluated by performing photocatalytic degradation of rhodamine B at room temperature under the visible light irradiation. The results showed that we were able to synthesize all three phase modifications of bismuth molybdates. Alpha and gamma bismuth molybdenum nanoparticles were synthesized by mechanochemical synthesis, hydrothermal synthesis helped to produce gamma and beta modified bismuth molybdates and sonochemical synthesis created beta bismuth molybdenum oxide. Using the UV-VIS spectrophotometer, Bi2Mo3O12 nanoparticles were evaluated for photocatalytic degradation of rhodamine B (RhB) in solution at room temperature under the VIS radiation. The absorption edge of Bi2Mo3O12 was found to be estimated at 435 nm, which corresponds to the bandgap value Eg = 2.78 eV. In the presence of both key factors, light and photocatalyst (Bi2Mo3O12), we achieved almost 100% degradation of RhB after 120 minutes of visible light irradiation.

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.

The objective of this dissertation was to examine how copper modification can improve the photocatalytic activity of TiO2-SiO2 and to explain the correlation between Cu concentration and chemical state of Cu cations in the TiO2-SiO2 matrix, as well as the photocatalytic activity under the UV/solar irradiation. The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low temperature sol-gel method based on organic copper, silicon and titanium precursors with varied Cu concentrations (from 0.05 to 3 mol%). The sol-gels were dried at 150 °C to obtain the photocatalysts in the powder form. To test thermal stability, additional set of photocatalysts was obtained by calcinating dried samples in air at 500 °C for 1 h. The photocatalytic activity was determined by a fluorescence-based method of terephthalic acid decomposition. Up to three times increase in photocatalytic activity of air-dried samples is obtained when TiO2-SiO2 matrix is modified with Cu in a narrow concentration range from 0.05 to 0.1 mol%. At higher Cu loadings the photocatalytic activity of Cu-modified photocatalyst is smaller than in the unmodified reference TiO2-SiO2 photocatalyst. Calcined samples showed significantly reduced photocatalytic activity compared to air-dried samples. XRD analysis showed that all Cu-modified TiO2-SiO2 nanocomposites with different Cu concentrations have the same crystalline structure as unmodified TiO2-SiO2 nanocomposites (air-dried or calcined). The addition of Cu does not change the relative ratio between the anatase and brookite phase or unit cell parameters of the two TiO2 crystalline structures. TEM analysis showed that the addition of Cu does not change the morphology of TiO2-SiO2 catalyst dried at 150 °C. The Cu K-edge XANES and EXAFS analysis were used to determine valence state and local structure of Cu cations in Cu-modified TiO2-SiO2 photocatalyst. The results elucidate the mechanism responsible for the improved or hindered photocatalytic activity. In the air-dried samples with low Cu content, which exhibit largest activity, Cu-O-Ti connections are formed, suggesting that the activity enhancement is due to Cu(II) cations attachment on the surface of the photocatalytically active TiO2 nanoparticles, so Cu(II) cations may act as free electron traps, reducing the intensity of recombination between electrons and holes at the TiO2 photocatalyst’s surface. At higher Cu loadings no additional Cu-O-Ti connections are formed, instead only Cu-O-Cu connections are established, indicating the formation of amorphous or nanocrystalline Cu(II) oxide, which hinders the photocatalytic activity of TiO2. Calcination of Cu-modified TiO2-SiO2 photocatalysts at 500 °C induces significant structural changes: Cu-O-Ti connections are lost, Cu partially incorporates into the SiO2 matrix and amorphous copper oxides, which again reduce the photocatalytic activity of the material, are formed. Cilj disertacije je raziskati, kako modifikacije z bakrom lahko izboljšajo fotokatalitsko aktivnost nanokompozita TiO2-SiO2, in pojasniti korelacije med koncentracijo, kemijskim stanjem Cu kationov v matrici TiO2-SiO2 ter fotokatalitsko aktivnostjo nanokompozita ob prisotnosti UV/sončnega sevanja. Nanokompozitni fotokatalizator TiO2-SiO2 modificiran z bakrom smo pripravili z nizkotemperaturno sol-gel metodo, zuporabo organskih bakrovih, silicijevih in titanovih prekurzorjev. Dodali smo različne koncentracije Cu (med 0.05 in 3 mol%). Sol-gele smo posušili na zraku pri 150 °C, da smo dobili fotokatalizator v obliki praška. Termično stabilnost fotokatalizatorjev smo preverili s kalcinacijo suhih vzorcev na zraku pri 500 °C za 1 h. Fotokatalitsko aktivnost katalizatorjev smo določili z metodo meritev fluorescence ob fotokatalitski razgradnji terftalatskih kislin. Fotokatalitska aktivnostvzorcev sušenih pri 150 °C se poveča do trikrat, ko je TiO2-SiO2 matrica modificirana z bakrom v ozkem razponu koncentracij med 0,05 in 0,1 mol%. Pri višjih koncentracijah bakra je bila aktivnost modificiranih vzorcev nižja od aktivnosti TiO2-SiO2 fotokatalizatorja brez bakra. Po kalcinaciji pri 500 °C se fotokatalitska aktivnost vzorcev bistveno zmanjša v primerjavi z vzorci sušenimi pri 150 °C. XRD analiza je pokazala, da imajo nanokompoziti TiO2-SiO2 modificirani z različnimi koncentracijami bakra enako kristalno strukturo kot nemodificiran TiO2-SiO2 nanokompozit (sušen na zraku ali kalciniran). Dodatek bakra ni spremenil relativnega razmerja med anatasom in brukitom in ni spremenil parametrov kristalne mreže obeh kristalnih strukturTiO2. TEM analiza pokaže, da modifikacija z bakrom ne spremeni morfologije TiO2-SiO2 nanokompozita. Za določanje valenčnega stanja in lokalne structure bakrovih kationov v modificiranih katalizatorjih smo uporabili metodi rentgenske absorpcijske spektroskopije XANES in EXAFS na bakrovem absorbcijskem robu K. Rezultati so razkrili dva mehanizma, ki vodita do izboljšav ali poslabšanj katalitske aktivnosti. V vzorcih, z nizko vsebnostjo bakra, sušenih pri 150 °C, ki so pokazali najvišjo aktivnost, so prisotne vezi Cu-O-Ti, kar nakazuje, da je povečana fotokatalitska aktivnost posledica Cu(II) kationskih povezav na površini fotokatalitsko aktivnih TiO2 nanodelcev. Cu(II) kationi tako delujejo kot proste elektronske pasti, kar zmanjšajo intenziteto rekombinacij med elektroni in vrzelmina površini TiO2 fotokatalizatorja. Pri višjih koncentracijah bakra nismo opazili dodatnih Cu-O-Ti vezi, prisotne so bile zgolj vezi Cu-O-Cu, kar nakazuje na nastanek amorfnih ali nanokristalnih Cu(II) oksidov, ki zmanjšajo fotokatalitsko aktivnost TiO2. Kalcinacija modificiranih katalizatorjev pri 500 °C povzroči znatne strukturne spremembe: Cu-O-Ti povezave izginejo, baker se delno veže v SiO2 matrico in oblikujejo se amorfni bakrovi oksidi, kar zmanjša fotokatalitsko aktivnost materiala.