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. Multifunkcionalninanomaterijali koriste sprege između više svojih svojstava kako bi obavljali kompleksnefunkcije. U ovoj doktorskoj disertaciji sintetisane su nanočestice magnezijum-ortotitanata, kao inanočestice magnezijum-ortotitanata dopiranog jonima retkih zemalja i jonima prelaznih metalasa multifunkcionalnim svojstvima. Navedeni prahovi predstavljaju odličan izbor za brojneprimene. Korišćena je Pećini metoda sinteze koja se pokazala kao efikasna metoda za dobijanjenanočestica magnezijum-ortotitanata sa tačno određenom strukturom i morfologijom, svojstvimakoji su od presudnog značaja za unapređenje funkcionalnih karakteristika ovih prahova. U ovojdoktorskoj disertaciji istražena su strukturna, morfološka, luminescentna i fotokatalitičkasvojstva ovih nanomaterijala.U okviru ove doktorske disertacije korišćena je metoda Pećinijevog polimerizovanogkompleksnog rastvora za pripremu nanočestica Mg2TiO4, nedopiranog i dopiranog jonima retkihzemalja (Eu3+ i Sm3+). Ispitivan je uticaj procesnih parametara na strukturu i svojstva navedenihprahova, 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 veličinakristalita od svega nekoliko nanometara. Morfološke karakteristike sintetisanih uzorakaispitivane su transmisionom elektronskom mikroskopijom (TEM) i skenirajućom elektronskommikroskopijom (SEM). Utvrđeno je da su nanočestice aglomerisane i imaju nepravilan zaobljenoblik. Optička svojstva ispitana su fotoluminescentnom spektroskopijom i snimljeni su emisionispektri svih sintetisanih uzoraka. Potvrđeno je da intenzitet emisije kod uzoraka dopiranihjonima retkih zemalja raste sa povećanjem temperature žarenja. Kod uzoraka magnezijumortotitanatadopiranog jonima retkih zemalja uočeni su svi karakteristični f↔f prelazi, koji potičuod aktivnih centara Eu3+ (5D0 → 7FJ) i Sm3+ (4G5/2 →6HJ). Proračunati su i analizirani JuddOfelt-oviparametri za uzorak Mg2TiO4:Eu3+ koji karakterišu lokalnu strukturu i veze u okolinijona retke zemlje. Takođe je potvrđeno da najbolja luminescentna svojstva pokazuju nanočesticepripremljene na 600°C/1h. Takođe, metodom Pećinijevog polimerizovanog kompleksa na temperaturi od 600°C/1hsintetisan 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 sukarakteristični d↔d2Eg →4A2g elektronski prelazi kod uzorka dopiranog jonima prelaznogmetala (Mn4+) koji su odgovorni za intenzivnu crvenu emisiju čestica. Primenom modelarazmene naelektrisanja dobijene su vrednosti parametara kristalnog polja Mn4+ u trigonalnomkristalnom polju Mg2TiO4. Jasno se može uočiti slaganje između proračunatih vrednostienergetskih nivoa i eksperimentalnih vrednosti eksitacionog i emisionog spektra.Ispitivana su fotokatalitička svojstva čistog Mg2TiO4 i površinski modifikovanog Mg2TiO4primenom bidentatnih benzenovih derivata, 5-amino salicilne kiseline i katehola. Na taj načinformiran je kompleks prenosa naelektrisanja usled čega dolazi do pomeranja apsorpcije premavidljivom spektralnom regionu. Fenomenom fizičke adsorpcije gasova na spoljnu i unutrašnjupovršinu nanopraha magnezijum-ortotitanata pomoću BET metode utvrđena je specifičnapovršina i mezoporoznost ovog praha. Degradacija organske boje (kristal ljubičasta) korišćena jeu cilju ispitivanja fotokatalitičkih svojstava čistog i površinski modifikovanog Mg2TiO4nanopraha pod osvetljenjem u različitim spektralnim regionima. Ekscitacijom pomoću UVsvetlosti indukovana su po prvi put fotokatalitička svojstva ovih prahova. Takođe, ekscitacijompomoću vidljive svetlosti ukazalo je na to da površinski modifikovani nanoprah magnezijumortotitanataima bolje fotokatalitičke performanse zbog sniženja energije zabranjene zone negošto je to u slučaju kod čistog magnezijum-ortotitanata. Dobijeni eksperimentalni rezultatiupoređeni su sa najviše proučavanim fotokatalitičkim materijalom TiO2 (komercijalno DegussaP25).

Multifunctional materials are designed in order to fulfill the causes of achieving aimed functions,adjusting to the specifications of products and being multifunctionally applied. Multifunctionalmaterials use the relations among various characteristics of their own in order to completecomplex functions. In this thesis nanoparticles of the magnesium-orthotitanate are synthetized, aswell as nanoparticles of magnesium-orthotitanate doped with rare earth and transition metals ionswith multifunctional properties. These materials represent an excellent choice for numerousapplications. The Pechini method of synthesis was used which proved itself as an efficientmethod for emanating nanoparticles of the magnesium-orthotitanate with the precisely fixedstructure and morphology, which are characteristics essential for improving of functionalcharacteristics of these powders. Moreover, in this thesis, structural, morphological, luminescentand photocatalytic characteristics of synthesized materials were researched.Within this doctoral thesis, for the preparation of nanoparticles of Mg2TiO4, undoped and dopedwith the ions of rare earth (Eu3+ i Sm3+), was used the Pechini’s polymerizable complex solutionmethod. There was investigated the effect of the processual parameters on structure andcharacteristics of the mentioned powders, and, in order to optimize the synthesis, the sampleshad been fired at a temperature range of 400 – 650ºC. The application of the X-ray structuralanalysis identified the cubic structure of the inverse spinel and the crystallite size of only a fewnanometers. Morphological characteristics of the synthetized samples were investigated viatransmission electronic microscopy (TEM) and scanning electronic microscopy (SEM). As aresult, it was established that nanoparticles are agglomerated and have an irregular orbicularshape. Optical characteristics were investigated by photoluminescence spectroscopy and therewere recorded emission spectra of all synthesized samples. It was confirmed that the emissionintensity of the samples doped by rare earth ions grows with the increase of the heatingtemperature. As far as samples of the magnesium-orthotitatanate doped with the rare earth ionsshowed all characteristic peaks arising from f↔f transitions, emanating from the active centers ofEu3+ (5D0 → 7FJ) 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 structureand relations within the environment of rare earth ions. In addition to this, it was confirmed thatnanoparticles prepared at 600ºC per hour show optimal luminescent characteristics.The Pechini’s polymerizable complex method, there was also synthetized Mg2TiO4:Mn4+ at600ºC per hour and there were obtained particles of about 10 nm in size. There were performedstructural, morphological and spectroscopic analyses, as well as the analysis of the crystal field.Moreover, there were observed characteristic d↔d2Eg →4A2g electronic transitions on a sampledoped with the transition metal ions (Mn4+) which are responsible for the intensive red particleemission. The application of the charge-transfer model yielded the values of the parameters ofthe crystal field of Mn4+ ions within the trigonal crystal field of Mg2TiO4. The matching betweencalculated values of energy levels and the experimental values of excitation and emission spectracan be noted.Photocatalytic properties of pure Mg2TiO4 and surface modified Mg2TiO4 via application ofbidentate benzene derivatives, a 5-amino salicylic acid and catechol, were researched. In thisway there was formed the charge transfer complex, during which occurs the moving of theabsorption towards the visible spectral area. By the application of the phenomenon of thephysical adsorption of gases on the external and internal surface of the nanopowder ofmagnesium- orthotitanate via BET method there was established specific surface andmesoporosity of this powder. The degradation of the organic colour (crystal violet) was used inorder to examine photocatalytic properties of the surface modified Mg2TiO4 nanopowder underthe luminance in different spectral areas. Using the excitation, via UV luminance there were, forthe first time, induced photocatalytic properties of this povder. Moreover, the excitation via thevisible light pointed out that the surface modified nanopowder of magnesium-orthotitanate hasbetter photocatalytic performances due to the lowering energy within the forbidden areacompared with the pure magnesium-orthotitanate. The obtained experimental results werecompared with the most frequently examined photocatalytic material TiO2 (commercially calledDegussa P25).