Sinteza, karakterizacija i primena funkcionalizovanih ugljeničnih nanocevi

Synthesis, Characterization and Application of Functionalized Carbon Nanotubes

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(metal 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.
Komercijalne višeslojne ugljenične nanocevi (Sigma–Aldrich i Sun Nanotech) i ugljenik XC-72R (Vulcan®, Cabot Corporation) ispitivani su netretirani i oksidovani. Rezultati elektrohemijske karakterizacije pokazuju da se posle oksidacije povećava elektrohemijski aktivna površina i kapacitivnost ugljeničnih uzoraka, kao i da se poboljšavaju svojstva prenosa naelektrisanja koja su ispitivana na osnovu reverzibilnosti Fe(CN)63–/Fe(CN)64– reakcije. Ugljenične nanocevi pokazuju bolja elektrohemijska svojstva u odnosu na ugljenik XC-72R. Morfologija ugljeničnih nanocevi ima veliki uticaj na elektrohemijska svojstva. Nanocevi sa naboranim zidovima pokazale su bolja svojstva prenosa naelektrisanja i veću pseudokapacitivnost od nanocevi sa glatkim zidovima, što je posledica većeg udela ivica grafena i defektnih mesta u ugljeničnom materijalu. Iz tog razloga su za dalju modifikaciju korišćene oksidovane nanocevi proizvođača Sigma–Aldrich.
Elektrohemijska svojstva višeslojnih ugljeničnih nanocevi modifikovanih etilendiaminom ispitivana su cikličnom voltametrijom i upoređena su sa oksidovanim ugljeničnim nanocevima. Pokazano je da modifikacija ugljeničnih nanocevi etilendiaminom dovodi do značajnog opadanja elektrohemijske aktivnosti grupa koje sadrže kiseonik, što je posledica reakcije sa etilendiaminom. Nakon modifikacije vidno je smanjenje prividne kapacitivnosti, kao i blago smanjenje svojstava prenosa naelektrisanja koja su ispitivana na osnovu reverzibilnosti Fe(CN)63–/Fe(CN)64– reakcije. Ovo je prouzrokovano smanjenjem pristupačnosti elektrolita ukupnoj površini ugljeničnih nanocevi modifikovanih etilendiaminom.
Na oksidovane i etilendiaminom modifikovane ugljenične nanocevi nanesene su nanočestice Pt koje su sintetizovane poliolnom metodom uz pomoć mikrotalasa. Količina adsorbovanih Pt nanočestica na e-MWCNT značajno je veća nego na oksidovanim nanocevima. Raspodela Pt nanočestica na EDA-modifikovanim ugljeničnim nanocevima je homogena, a srednja veličina čestica iznosi 2,5 ± 0,5 nm. Elektrohemijska merenja su pokazala da Pt nanočestice na nosaču od e-MWCNT imaju visoku vrednost elektrohemijski aktivne površine. 
U okviru disertacije izvršena je modifikacija MWCNT dapsonom koji se koristi kao anti-mikrobski i anti-zapaljenski lek. Dapsonom-modifikovane višeslojne ugljenične nanocevi (dap-MWCNT) koje su disperzibilne u vodi, pripremljene su hemijskom modifikacijom karboksilnih grupa na površini nanocevi koristeći N-HATU i DIEA. Modifikacija je potvrđena različitim tehnikama, kao što su: FTIR, TEM, TGA i elementarna analiza. Biološki efekat dap-MWCNT testiran je na makrofagama izolovanim iz peritoneuma (PMØ) pacova. Konfokalnom laserskom mikroskopijom i protočnom citometrijom pokazano je da su PMØ brzo fagocitovale dap-MWCNT kao i oksidovane (o)-MWCNT koje su upotrebljene kao kontrolni uzorak. Viabilnost PMØ nije promenjena ni sa dap-MWCNT pri malim koncentracijama (50 μg/ml i manje), kao ni sa o-MWCNT pri ekvivalentnim koncentracijama, dok veće koncentracije (50 μg/ml i više) izazivaju programiranu ćelijsku smrt, apoptozu. Apoptoza PMØ koja je izazvana pomoću kontrolnih uzoraka o-MWCNT je veća od apoptoze izazvane sa dap-MWCNT i povezana je sa pojavom oksidativnog stresa. Nasuprot tome, dap-MWCNT nisu aktivirale oksidativni stres, već su prouzrokovale apoptozu PMØ, i to najviše nakon produžene kultivacije od 3 dana. Ekvivalentne koncentracije rastvornog dapsona, iako su izazvale oksidativni stres, nisu indukovale apoptozu. Celokupni rezultat pokazuje kompleksnost dap-MWCNT/PMØ interakcija i sugeriše da se ovaj konjugat može ispitati za tretman unutar-ćelijskih mikroorganizama koji su osetljivi na dapson kao i za zapaljenske procese kod kojih se dapson koristi kao lek.
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.
Two samples of commercial MWCNTs (Sigma–Aldrich and Sun Nanotech) and a sample of carbon black (Vulcan XC-72R) were investigated in raw state and after the oxidation in nitric and sulfuric acid by ultrasound agitation. Atomic force microscopy revealed that oxidized Sigma–Aldrich nanotubes are straight with corrugated walls (bamboolike structure), while Sun Nanotech nanotubes are tortuous with smooth walls. Fourier transform infrared spectroscopy showed that abundance of oxygen containing functional groups was formed on both Sigma–Aldrich and Sun Nanotech carbon nanotubes, as well as on carbon black surfaces. Electrochemical properties were studied by cyclic voltammetry. It was found that the electrochemically active surface area of all carbon samples is expanded, charge storage ability is enhanced and the electron-transfer kinetics, probed by Fe(CN)63–/Fe(CN)64– redox couple, is promoted upon activation. The characteristics of MWCNTs were superior to carbon black. Morphology of the MWCNTs was found to be important; nanotubes with corrugated walls showed faster electron-transfer and pseudocapacitive redox kinetics than nanotubes with smooth walls. This was explained by the higher proportion of edge and defect sites, which are known as more electrochemically active than the walls of uniform grapheme structure. For this reason, oxidized MWCNTs obtained from Sigma-Aldrich were used for further modification. Electrochemical properties of EDA modified MWCNTs have been examined by using cyclic voltammetry in 0.1 M H2SO4 and 1.0 M KCl and compared with the oxidized MWCNTs. It was found that the modification by EDA leads to the significant decrease in activity of electrochemicaly active oxygen containing groups that was caused by amine grafting processes. The decrease in apparent capacitance and in the electron-transfer kinetics, probed by Fe(CN)63–/Fe(CN)64– redox couple, was observed upon modification. These were caused by the decrease in accessibility of electrolyte to overall surface area of EDA modified carbon nanotubes. MWCNTs, oxidized and EDA functionalized, were used as a supporting material for Pt nanoparticles prepared by the microwave-assisted polyol method. The Pt loading of Pt/o-MWCNT was only 2 mass % while the loading of Pt/e-MWCNT was 20 mass%. Much higher efficiency of Pt deposition on e-MWCNTs than on o-MWCNTs was ascribed to the shift in pHpzc value of the CNTs surface from 2.43 to 5.91 upon modification by EDA. The investigation by transmission electron microscopy (TEM) revealed that the mean diameter of Pt particles in Pt/e-MWCNT is 2.5  0.5 nm and that their distribution on the support is homogenous with no evidence of pronounced particles agglomeration. Cyclic voltammetry of Pt/e-MWCNT thin film indicated clean Pt surface with well-resolved peaks characteristic for polycrystalline Pt. Dapsone is an anti-microbial and anti-inflammatory drug. Water-dispersible dapsonemodified multi-wall carbon nanotubes (dap-MWCNTs) were prepared by chemical modification of the carboxyl groups introduced on the surface of the nanotubes using O-(7-azabenzotriazol-1-yl)-N,N,N’,N’-tetramethyluronium hexafluorophosphate (N-HATU) and N,N-diisopropylethylamine (DIEA). The modification was confirmed by Fourier-transform infrared spectroscopy, transmission election microscopy and thermogravimetric analysis. The biological effect of dap-MWCNTs was tested using rat peritoneal macrophages (PMØ). By confocal laser microscopy and flow cytometry, it was shown that the dap-MWCNTs were rapidly ingested by PMØ as were the control, oxidized o-MWCNTs. Neither dap-MWCNTs at lower concentrations (up to 50 μg/ml), nor o-MWCNTs, at equivalent concentrations, respectively affected the viability of PMØ, while higher concentrations triggered apoptosis. Apoptosis of PMØ induced by the control, o-MWCNTs, was higher than that induced by dap-MWCNTs and it correlated with the induction of oxidative stress. In contrast, dap-MWCNTs did not trigger oxidative stress but caused apoptosis of PMØ predominantly after prolonged cultivation (3 days). Although equivalent concentrations of soluble dapsone induced oxidative stress, they were anti-apoptotic. Cumulatively, the obtained results show the complexity of dap-MWCNT/PMØ interactions and suggest that this complex could be investigated for the treatment of dapsone-sensitive intracellular microorganisms or inflammatory diseases responding to dapsone therapy.

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Metadaten
Author:Goran Vuković
URL:http://www.itn.sanu.ac.rs/opus4/frontdoor/index/index/docId/308
Opac ID:COBISS.SR-ID 37199631
Publisher:University of Belgrade, Faculty of Technology and Metallurgy
Place of publication:Belgrade
Advisor:Petar Uskoković
Document Type:Doctoral Thesis
Language:srp
Date of Publication (online):05.12.2013
Year of first Publication:2010
Publishing Institution:University of Belgrade, Faculty of Technology and Metallurgy
Granting Institution:Ministry of Science of the Republic of Serbia
Date of final exam:06.01.2010
Tag:Pt nanoparticle electrocatalyst; amino-functionalization; cadmium adsorption; carbon nanotubes; cyclic voltammetry; cytotoxicity; dapsone; electrochemistry; macrophages; nanocomposites
Pagenumber:227
Institutes:University of Belgrade, Faculty of Technology and Metallurgy
Open access:
Collections:PhD Theses
Licence (English):License LogoCreative Commons - Attribution-Noncommercial-No Derivative Works 3.0 Serbia