Sinteza, karakterizacija i primena funkcionalizovanih ugljeničnih nanocevi

Abstract

U ovoj doktorskoj disertaciji opisana je kovalentna funkcionalizacija višeslojnih ugljeničnih nanocevi (multi-walled carbon nanotubes, MWCNT) pomoću amina. Funkcionalizacija je izvršena hemijskom modifikacijom karboksilnih grupa koje su uvedene na površinu nanocevi metodom oksidacije u smeši koncentrovanih kiselina. MWCNT su funkcionalizovane etilendiaminom (EDA), 1,6-heksandiaminom (HDA), dietilentriaminom (DETA), trietilentetraaminom (TETA) i 1,4-fenilendiaminom (PDA) pomoću O-(7- azabenzotriazol-1-il)-N,N,N',N'-tetrametiluronium heksafluorofosfata (N-HATU) i N,Ndiizopropiletilamina (DIEA). Kuplujući agens N-HATU omogućuje veću brzinu reakcije funkcionalizacije u odnosu na postojeće metode sinteze amida. Dobijeni uzorci su karakterisani različitim tehnikama, kao što su: FTIR, XRD, elementarna analiza, TGA, SEM, TEM, STM, UV-vis spektroskopija i ciklična voltametrija. MWCNT funkcionalizovane sa PDA i EDA poseduju najbolja disperzibilna i elektrohemijska svojstva. Funkcionalizovane MWCNT, u koncentracijama od 1 do 50 μg/ml, nisu citotoksične za fibroblastnu, L929 ćelijsku liniju. Međutim, koncentracije MWCNT veće od 10 μg/ml smanjuju rast ćelija i u tom smislu ovaj nalaz je u pozitivnoj korelaciji sa stepenom njihove internalizacije od strane L929 ćelija. U okviru ove disertacije prikazano je uklanjanje kadmijuma iz vodenih rastvora pomoću netretiranih višeslojnih ugljeničnih nanocevi (n-MWCNT), oksidovanih (o- MWCNT) i etilendiaminom funkcionalizovanih (e-MWCNT). U šaržnim uslovima ispitan je uticaj pH vrednosti rastvora, kontaktnog vremena, početne koncentracije metala i temperature na sorpciju Cd2+ jona na n-MWCNT, o-MWCNT i e-MWCNT. Adsorpcija Cd2+ jona na o- MWCNT i e-MWCNT izrazito zavisi od pH vrednosti rastvora. Vremenski zavisna adsorpcija Cd2+ jona na n-MWCNT, o-MWCNT i e-MWCNT opisana je pomoću kinetičkog modela pseudo drugog reda. Model Langmuirove izoterme najbolje fituje dobijene eksperimentalne ravnotežne podatke. Maksimalni kapacitet od 25,7 mg/g, na 45 °C, dobijen je za e-MWCNT. Termodinamički parametri su takođe, izračunati za adsorpciju Cd2+ jona na n-MWCNT, o- MWCNT i e-MWCNT i rezultati pokazuju da je proces adsorpcije spontan i endoterman. Kovalentna amino-funkcionalizacija MWCNT prikazana je kao pogodan metod za poboljšanje mogućnosti daljeg procesiranja MWCNT. Upotrebom funkcionalizovanih nanocevi dobijeni su homogeni i transparentni kompoziti, na bazi MWCNT i poli(metil metakrilata) (PMMA). Kovalentna veza, koja se formira između amino-funkcionalizovanih MWCNT i PMMA, poboljšava disperziju MWCNT u polimeru kao i električna i mehanička svojstva kompozita...

Since their discovery in 1991 by Iijima, carbon nanotubes (CNTs) have attracted great interest in most areas of science and engineering due to their unique physical and chemical properties, which enable them to be applied for a wide range of applications. However, the application of CNTs has been largely hampered by their poor dispersion into solvents or polymers due to the strong intermolecular van der Waals interactions among the nanotubes, which can lead to the formation of aggregates. A common technique to improve dispersion and realize such a great capability of CNTs is through chemical functionalization, which enables chemical covalent or non-covalent bonding between the CNTs and material of interest. The covalent side-wall modifications of nanotubes, in general, include: (i) amidation or esterification of carboxylated CNTs, (ii) side-wall covalent attachment of functional groups directly to the pristine CNTs. Among them, amino-functionalized CNTs have been investigated because amino group has a high reactivity, and can react with many chemicals, such as polymers, and biological components. Amino-functionalization was also employed and studied in this work. Modified CNTs were examined toward different applications described below. Surface functionalization of multi-walled carbon nanotubes (MWCNTs), with amino groups via chemical modification of carboxyl groups introduced on the nanotube surface, using O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (NHATU) and N,N-diisopropylethylamine (DIEA) was reported. The N-HATU coupling agent provides faster reaction rate and the reaction occurs at lower temperature compared to amidation and acylation-amidation chemistry. The amines, ethylenediamine (EDA), 1,6- hexanediamine (HDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and 1,4- phenylenediamine (PDA) were used. The resulting materials were characterized with different techniques such as FTIR, XRD, elemental analysis, TGA, SEM, TEM, STM, UV-vis spectroscopy and cyclic voltammetry. MWCNTs functionalized with PDA and EDA posses the best dispersibility and electron transfer properties in comparison to the others amines. Functionalized MWCNTs, at the concentrations between 1 and 50 μg/ml, were not cytotoxic for the fibroblast L929 cell line. However, the concentrations of MWCNTs higher of 10 μg/ml reduced cell growth and this effect correlated positively with the degree of their uptake by L929 cells. In batch tests, the influences of solution pH, contact time, initial metal ion concentration and temperature on the sorption of Cd2+ ions onto raw MWCNTs (raw- MWCNT), oxidized MWCNTs (o-MWCNT) and EDA-functionalized MWCNTs (e- MWCNT) were studied. The adsorption of Cd2+ ions by o-MWCNT and e-MWCNT was strongly pH-dependent. The time dependent Cd2+ sorption onto raw-MWCNT, o-MWCNT and e-MWCNT can be described by a pseudo-second-order kinetic model. The Langmuir isotherm model agrees well with the equilibrium experimental data. The maximum capacity was obtained for e-MWCNT, 25.7 mg/g, at 45 °C. The thermodynamic parameters were also deduced for the adsorption of Cd2+ ions on raw-MWCNT, o-MWCNT and e-MWCNT and the results showed that the adsorption was spontaneous and endothermic. In this study was shown that covalent amino-functionalization of MWCNTs was a powerful method for enhancing the ability to process MWCNTs and facilitating the preparation of homogenous, coherent and transparent MWCNT/Poly(methyl methacrylate) (PMMA) composites. Covalent bond formation between amino-functionalized MWCNTs and PMMA enhanced the MWCNTs dispersion in polymer and improved electrical conductivity and mechanical properties of the composite...