Multifunkcionalne nanočestice magnezijum-ortotitanata dopiranog jonima retkih zemalja i prelaznih medalja

Abstract

Multifunkcionalni materijali se dizajniraju na taj način da mogu da ispune ciljane funkcije, prilagode se specifikacijama proizvoda i multifunkcionalnim primenama. Multifunkcionalni nanomaterijali koriste sprege između više svojih svojstava kako bi obavljali kompleksne funkcije. U ovoj doktorskoj disertaciji sintetisane su nanočestice magnezijum-ortotitanata, kao i nanočestice magnezijum-ortotitanata dopiranog jonima retkih zemalja i jonima prelaznih metala sa multifunkcionalnim svojstvima. Navedeni prahovi predstavljaju odličan izbor za brojne primene. Korišćena je Pećini metoda sinteze koja se pokazala kao efikasna metoda za dobijanje nanočestica magnezijum-ortotitanata sa tačno određenom strukturom i morfologijom, svojstvima koji su od presudnog značaja za unapređenje funkcionalnih karakteristika ovih prahova. U ovoj doktorskoj disertaciji istražena su strukturna, morfološka, luminescentna i fotokatalitička svojstva ovih nanomaterijala. U okviru ove doktorske disertacije korišćena je metoda Pećinijevog polimerizovanog kompleksnog rastvora za pripremu nanočestica Mg2TiO4, nedopiranog i dopiranog jonima retkih zemalja (Eu3+ i Sm3+). Ispitivan je uticaj procesnih parametara na strukturu i svojstva navedenih prahova, a u cilju optimizacije sinteze uzorci su žareni u temperaturnom opsegu od 400 – 650°C. Rendgeno-strukturnom analizom utvrđena je kubna struktura inveznog spinela i veličina kristalita od svega nekoliko nanometara. Morfološke karakteristike sintetisanih uzoraka ispitivane su transmisionom elektronskom mikroskopijom (TEM) i skenirajućom elektronskom mikroskopijom (SEM). Utvrđeno je da su nanočestice aglomerisane i imaju nepravilan zaobljen oblik. Optička svojstva ispitana su fotoluminescentnom spektroskopijom i snimljeni su emisioni spektri svih sintetisanih uzoraka. Potvrđeno je da intenzitet emisije kod uzoraka dopiranih jonima retkih zemalja raste sa povećanjem temperature žarenja. Kod uzoraka magnezijumortotitanata dopiranog jonima retkih zemalja uočeni su svi karakteristični f↔f prelazi, koji potiču od aktivnih centara Eu3+ ( 5D0 → 7 FJ) i Sm3+ ( 4G5/2 → 6HJ). Proračunati su i analizirani JuddOfelt-ovi parametri za uzorak Mg2TiO4:Eu3+ koji karakterišu lokalnu strukturu i veze u okolini jona retke zemlje. Takođe je potvrđeno da najbolja luminescentna svojstva pokazuju nanočestice pripremljene na 600°C/1h. Takođe, metodom Pećinijevog polimerizovanog kompleksa na temperaturi od 600°C/1h sintetisan je Mg2TiO4:Mn4+ i dobijene su čestice veličine od oko 10 nm. Izvršene su strukturne, morfološke, spektroskopske analize, kao i analiza kristalnog polja ovog materijala. Uočeni su karakteristični d↔d 2 Eg → 4A2g elektronski prelazi kod uzorka dopiranog jonima prelaznog metala (Mn4+) koji su odgovorni za intenzivnu crvenu emisiju čestica. Primenom modela razmene naelektrisanja dobijene su vrednosti parametara kristalnog polja Mn4+ u trigonalnom kristalnom polju Mg2TiO4. Jasno se može uočiti slaganje između proračunatih vrednosti energetskih nivoa i eksperimentalnih vrednosti eksitacionog i emisionog spektra. Ispitivana su fotokatalitička svojstva čistog Mg2TiO4 i površinski modifikovanog Mg2TiO4 primenom bidentatnih benzenovih derivata, 5-amino salicilne kiseline i katehola. Na taj način formiran je kompleks prenosa naelektrisanja usled čega dolazi do pomeranja apsorpcije prema vidljivom spektralnom regionu. Fenomenom fizičke adsorpcije gasova na spoljnu i unutrašnju površinu nanopraha magnezijum-ortotitanata pomoću BET metode utvrđena je specifična površina i mezoporoznost ovog praha. Degradacija organske boje (kristal ljubičasta) korišćena je u cilju ispitivanja fotokatalitičkih svojstava čistog i površinski modifikovanog Mg2TiO4 nanopraha pod osvetljenjem u različitim spektralnim regionima. Ekscitacijom pomoću UV svetlosti indukovana su po prvi put fotokatalitička svojstva ovih prahova. Takođe, ekscitacijom pomoću vidljive svetlosti ukazalo je na to da površinski modifikovani nanoprah magnezijumortotitanata ima bolje fotokatalitičke performanse zbog sniženja energije zabranjene zone nego što je to u slučaju kod čistog magnezijum-ortotitanata. Dobijeni eksperimentalni rezultati upoređeni su sa najviše proučavanim fotokatalitičkim materijalom TiO2 (komercijalno Degussa P25).

Multifunctional materials are designed in order to fulfill the causes of achieving aimed functions, adjusting to the specifications of products and being multifunctionally applied. Multifunctional materials use the relations among various characteristics of their own in order to complete complex functions. In this thesis nanoparticles of the magnesium-orthotitanate are synthetized, as well as nanoparticles of magnesium-orthotitanate doped with rare earth and transition metals ions with multifunctional properties. These materials represent an excellent choice for numerous applications. The Pechini method of synthesis was used which proved itself as an efficient method for emanating nanoparticles of the magnesium-orthotitanate with the precisely fixed structure and morphology, which are characteristics essential for improving of functional characteristics of these powders. Moreover, in this thesis, structural, morphological, luminescent and photocatalytic characteristics of synthesized materials were researched. Within this doctoral thesis, for the preparation of nanoparticles of Mg2TiO4, undoped and doped with the ions of rare earth (Eu3+ i Sm3+), was used the Pechini’s polymerizable complex solution method. There was investigated the effect of the processual parameters on structure and characteristics of the mentioned powders, and, in order to optimize the synthesis, the samples had been fired at a temperature range of 400 – 650ºC. The application of the X-ray structural analysis identified the cubic structure of the inverse spinel and the crystallite size of only a few nanometers. Morphological characteristics of the synthetized samples were investigated via transmission electronic microscopy (TEM) and scanning electronic microscopy (SEM). As a result, it was established that nanoparticles are agglomerated and have an irregular orbicular shape. Optical characteristics were investigated by photoluminescence spectroscopy and there were recorded emission spectra of all synthesized samples. It was confirmed that the emission intensity of the samples doped by rare earth ions grows with the increase of the heating temperature. As far as samples of the magnesium-orthotitatanate doped with the rare earth ions showed all characteristic peaks arising from f↔f transitions, emanating from the active centers of Eu3+ ( 5D0 → 7 FJ) and Sm3+ ( 4G5/2 → 6HJ) ions. Moreover, there have been calculated and analysed Judd–Ofelt’s parameters for the sample of Mg2TiO4:Eu3+ which mark the local structure and relations within the environment of rare earth ions. In addition to this, it was confirmed that nanoparticles prepared at 600ºC per hour show optimal luminescent characteristics. The Pechini’s polymerizable complex method, there was also synthetized Mg2TiO4:Mn4+ at 600ºC per hour and there were obtained particles of about 10 nm in size. There were performed structural, morphological and spectroscopic analyses, as well as the analysis of the crystal field. Moreover, there were observed characteristic d↔d 2 Eg → 4A2g electronic transitions on a sample doped with the transition metal ions (Mn4+) which are responsible for the intensive red particle emission. The application of the charge-transfer model yielded the values of the parameters of the crystal field of Mn4+ ions within the trigonal crystal field of Mg2TiO4. The matching between calculated values of energy levels and the experimental values of excitation and emission spectra can be noted. Photocatalytic properties of pure Mg2TiO4 and surface modified Mg2TiO4 via application of bidentate benzene derivatives, a 5-amino salicylic acid and catechol, were researched. In this way there was formed the charge transfer complex, during which occurs the moving of the absorption towards the visible spectral area. By the application of the phenomenon of the physical adsorption of gases on the external and internal surface of the nanopowder of magnesium- orthotitanate via BET method there was established specific surface and mesoporosity of this powder. The degradation of the organic colour (crystal violet) was used in order to examine photocatalytic properties of the surface modified Mg2TiO4 nanopowder under the luminance in different spectral areas. Using the excitation, via UV luminance there were, for the first time, induced photocatalytic properties of this povder. Moreover, the excitation via the visible light pointed out that the surface modified nanopowder of magnesium-orthotitanate has better photocatalytic performances due to the lowering energy within the forbidden area compared with the pure magnesium-orthotitanate. The obtained experimental results were compared with the most frequently examined photocatalytic material TiO2 (commercially called Degussa P25).