| Abstract | Keliranjem titanijeva n-butoksida, Ti(OnBu)4, s etil-acetoacetatom, C6H10O3 u različitim molarnim omjerima pripravljena je serija solova. Solovi su potom izloženi utjecaju atmosferske vlage kako bi se sporom hidrolizom transformirali u gelove. Gelovi su termički obrađeni pri različitim temperaturama s ciljem dobivanja čistog nanokristaličnog anatasa. Uzorci solova, gelova te toplinski obrađeni uzorci potom su istraživani metodama 1H, 13C i HSQC NMR, FTIR spektroskopije, UV-Vis i DRS spektroskopije, XRD analize, DTA/TGA, FE-SEM, HR-TEM i N2 adsorpcijsko/desorpcijskim izotermama kako bi se proučio utjecaj dodanog EAA na novonastale vrste i njihove kvantitativne odnose, strukturu i svojstva gelova i toplinski obrađenih uzoraka te tijek same kristalizacije. Utvrđeno je da nastaju tri kelatne vrste i to
bis-kelirani monomer, Ti(OnBu)2(EAA)2, bis-kelirani dimer, (Ti(OnBu)3EAA)2 i monokelirani dimer, Ti2(OnBu)7EAA. Porastom udjela kelirajućeg agensa mijenja se dominantna molekula kompleksa, od monokeliranog i bis-keliranog dimera do bis-keliranog monomera. Zapaženo je i da dolazi do reakcije transesterifikacije, što utječe na sastav spojeva. Također je utvrđeno da su modificirani alkoksidi djelomično hidrolizirani te sadrže različite količine butoksi i etil-acetoacetatnih grupa vezanih na titanij. Rendgenskom difrakcijskom analizom uzoraka gela uočeno je postojanje uređenosti na nivou mezostrukture popraćeno karakterističnim širokim maksimumom pri nižim kutovima 2θ, što je nadalje potvrđeno
HR-TEM mikroskopijom. Nastala mezostruktura izgrađena je od anorganskoorganskih nanoklastera različite veličine i sastava. Utvrđen je tijek procesa do kojih dolazi termičkom obradom gelova. Toplinskom obradom uzoraka gela pri temperaturi od 350 °C u trajanju 2 h dobiven je čist nanokristaličan anatas. Relativno mala specifična površina anatasa posljedica je smanjenja volumena mezopora zbog prisutnosti zaostale organske faze u porama. Fotokatalitička učinkovitost pripravljenog anatasa je ispitana pri razgradnji organskog bojila metilensko plavilo. Zapaženo je da svi uzorci imaju vrlo dobra fotokatalitička svojstva.
Na temelju dobivenih rezultata raspravljeno je o učinku modifikacije titanijeva n-butoksida s etil acetoacetatom na pojavu molekulskih vrsta u solu, strukturu gelova i toplinski obrađenih uzoraka te tijek kristalizacije i svojstva anatasa. Čist, nanokristaličan, fotokatalitički aktivan anatas pripravljen je jednostavnim i ekonomičnim postupkom. |
| Abstract (english) | Series of sols have been prepared by chelation of titanium n-butoxide, Ti(OnBu)4, with ethyl acetoacetate, C6H10O3, in various ratios. Sols were subsequently transformed to gels by slow hydrolysis after exposition to air moisture. The gels were thermally treated at various temperatures in order to obtain pure nanocrystalline anatase. Sols, gels and thermally treated samples were investigated by means of 1H, 13C i HSQC NMR, FTIR, UV-Vis spectroscopy, DRS, XRD, DTA/TGA, FE-SEM, HR-TEM, N2 adsorption/desorption isotherms in order to provide insight in compounds obtained, their quantitative relationships, structure and properties of gels and thermally treated samples as well as crystallization path. Three compounds, bis-chelated monomer, Ti(OnBu)2(EAA)2, bis-chelated dimer, (Ti(OnBu)3EAA)2 and monochelated dimer, Ti2(OnBu)7EAA have been established. As the molar ratio
EAA/Ti(OnBu)4 increases, the dominant complex molecule changes from the monochelated and bis-chelated dimer to bis-chelated monomer. Additionally, the transesterification reaction, influencing the chemical composition of the compounds has been noted. It was also determined that modified alkoxides are partially hydrolyzed having different amounts of butoxide and ethyl acetoacetate groups attached to titanium. XRD pattern of gels exhibited broad, low-angle reflection, which indicates the existence of some degree of ordering on the mesostructure scale. HR-TEM of the gels also revealed the presence of mesostructure. Observed mesostructure was found to consist of inorganic-organic nanoclusters, exhibiting some polydispersity in the size and variations in composition. Thermal evolution processes path of gels have been established. After thermal treatment of the gels at 350 °C for 2 h, pure nanocrystalline anatase was obtained. Relatively low specific surface area of anatase was ascribed to the reduction of mesopores volume due to blockage with carbonaceous material. The photocatalytic efficiency of the prepared nanocrystalline anatase has been tested on the degradation of synthetic organic dye methylene blue. It has been noted that all samples possess very good photocatalytic properties. From the results obtained, the effect of modification of titanium n-butoxide with ethyl acetoacetate on molecular species in sol,
on gel structure and crystallization behavior and properties of anatase crystallized thereof was discussed. Pure, nanocrystalline, photocatalytically active anatase has been prepared through simple and affordable procedure. |
