Katalitske sposobnosti razvejanih struktur titanovega dioksida

Butala, Nejc (author), Podgornik, Aleš (mentor), Likozar, Blaž (co-mentor)

Titanov dioksid se v naravi nahaja v treh polimorfnih modifikacijah: kot rutil, anatas in brookit. Najstabilnejša oblika TiO2 je rutil in kristalizira v tetragonalnem kristalnem sistemu. Heterogena fotokataliza z uporabo polprevodniškega TiO2, omogoča alternativno katalitično oksidno tehnologijo preko reakcij, ki potekajo pri sobni temperaturi in normalnem zračnem tlaku. Znanstveniki so ugotovili, da so TiO2 nanodelci pokazali najboljšo fotokatalitsko učinkovitost s hkratnim povečanjem hitrosti razvoja fenola in zmanjšanjem nastanka stranskega produkta hidrokinona. V zadnjih desetletjih so bili nanometrski TiO2 praški uporabljeni za fotokatalizo, zlasti za fotolizo vode in pretvorbo sončne energije. Po drugi strani pa je glavna pomanjkljivost uporabe TiO2, kot fotoaktivnega katalizatorja, njegova energija prepovedanega pasu 3,2 eV, kar omejuje fotokatalitsko aktivnost tega materiala na valovne dolžine pod 385 nm. V sklopu magistrskega dela sem poizkušal dobiti najboljšo fotokatalitično aktivnost katalizatorja TiO2 pri pretvorbi benzena v fenol. Ob tem sem pazil na čim boljšo selektivnost. Najprej sem sintetiziral prahove TiO2, z različno obliko kristalov, po hidrotermalnem postopku. To sem storil tako, da sem izoborjene kristale Ti kompleksa raztopil v različnih volumnih destilirane vode, ter tako pripravil raztopine z različnimi koncentracijami: 1.00 M, 0.50 M, 0.125 M, 0.06 M in 0.03 M. Posamezne raztopine sem zaprl v avtoklave s teflonskimi lončki, ter postavil v ogret sušilnik na 200°C za 50 h. Analitske metode, ki sem jih uporabil v namen določanja oblike in strukture sta bili vrstična elektronska mikroskopija (SEM) in rentgenska praškovna difrakcija (RTG). Pri posnetkih s SEM, sem opazil kako razvejanost kristalov TiO2 pada s padajočo koncentracijo izhodne raztopine Ti kompleksa. V naslednji fazi sem prahove TiO2 uporabil za testiranje fotokatalitične aktivnosti pri pretvorbi benzena v fenol. Za reakcijo sem uporabil destilirano vodo, vodikov peroksid, acetonitril in benzen. Kot vir svetlobe sem uporabil UV luč. Konverzijo in selektivnost sem najprej povečal tako, da sem TiO2 dopiral z bakrom. Za ta postopek sem uporabil bakrov acetat in polivinilpirolidon. Na koncu sem testiral tudi vpliv zlata na konverzijo in selektivnost. Uporabil sem etilen glikol in zlatov klorid. Preizkusil sem tudi katera količina oksidanta je najprimernejša za reakcijo. Ugotovil sem, da čisti TiO2 ni primeren katalizator za fotokatalitično reakcijo benzena v fenol. Boljše rezultate pretvorbe sem dobil, ko sem TiO2 dopiral z bakrom. Tako konverzija kot tudi selektivnost je naraščala z naraščajočo vsebnostjo bakra. Najboljše rezultate sem dobil, ko sem kombiniral baker in zlato. Predvsem selektivnost je po dodatku zlata zelo narasla.

• Language: Slovenian
• Keywords: fotokataliza, TiO2, hidrotermalna sinteza, konverzija, selektivnost
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2020
• PID: 20.500.12556/RUL-117123
• COBISS.SI-ID: 21076227
• Publication date in RUL: 24.06.2020

Secondary language

• Language: English
• Title: Catalytic capabilities of branched titanium dioxide structures

Abstract

In nature titanium dioxide is found in three polymorphic modifications; rutile, anatase and brookite. The most stable form of TiO2 is rutile and crystallizes in a tetragonal crystal system. Semi-conductive material such as TiO2 can be used in heterogeneous photocatalysis. It offer an alternative catalytic oxidation technology because the reactions take place at ambient temperature and pressure. Scientists reported that the TiO2-supported nanoparticles show the best photocatalytic efficiency by simultaneously increasing the rate of phenol development and reduce the formation of hydroquinone by-product. In recent decades, nano-sized TiO2 powders have been used for photocatalysis, in particular for photo-splitting of water and solar energy conversion. However as the size reduces also bandgap energy shifts to higher values reaching energies around 3.2 eV which limits the photocatalytic activity of this material to the UV region i.e. to the wavelengths below 385 nm. In my work, I optimized photocatalytic activity of the TiO2 catalyst in the conversion of benzene to phenol. At the same time, I was trying to sustain selectivity as high as possible. I first synthesized TiO2, from Ti-complex in concentrations of 1.00 M, 0.50 M, 0.125 M, 0.06 M and 0.03 M. The solutions were hydrothermally treated in teflon lined autoclave for 50 h at 200°C. To determine the shape and the crystal structure of the synthesized material I used scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). In particular with SEM I was able to specify how the specific surface area of TiO2 crystals decreases with decreasing concentration. In the following phase, I used TiO2 powders of different morphology to test the photocatalytic activity for the conversion of benzene to phenol. In the reaction I used distilled water, hydrogen peroxide, acetonitrile and benzene and a UV light as a light source. To increase conversion and selectivity I doped TiO2 with copper. For this I used copper acetate and polyvinylpyrrolidone. Finally, I also tested the effect of gold on conversion and selectivity. I used ethylene glycol and gold chloride. I also found the amount of oxidant optimal for the reaction. I have concluded that TiO2 alone is not suitable as a catalyst for the photocatalytic reaction of benzene to phenol. However, by doping it with copper the results are much better. Both conversion and selectivity increased with increasing copper content. The best results were obtained with the combination of copper and gold whereas selectivity increased greatly after the addition of gold.

• Keywords: photocatalysis, TiO2, hydrothermal synthesis, conversion, selectivity