Environmental implications of higher order fullerenes and conjugated nanostructures

In quest of harnessing emergent properties and achieving multifunctionality in the materials realm, synthesis and manipulation at the nano-scale has moved its focus from simple passive nanomaterials (NMs) to hierarchical nanostructures. Such nanostructures include higher order fullerenes (HOFs), carbon allotropes composed of more than 60 carbon atoms per fullerene cage, and conjugated nanohybrids (NHs), prepared from materials of multiple chemical origin. The advantages in their electronic, optical, physicochemical, and magnetic properties have inspired their research and use in photovoltaics, nano-electronics, biomedical imaging and drug delivery, catalysis, energy generation and storage, and environmental remediation and sensing. Not only as research grade materials, a global market of bio-imaging and fuel-cell applications have been integrating use of HOFs, and NHs, respectively. Thus it is an exciting time for materials engineering to expand the spectrum of these ‘horizon materials’ by putting together a variety of chemical ‘building blocks’ and build a wide range of multifunctional hierarchical structures. However, such conjugation leading to complex hierarchical structures also introduces unknown environmental risks. The emergent properties of these hierarchical structures necessitate careful assessment of their environmental health and safety. This dissertation is one of the first organized efforts to identify hierarchical nanostructures and assess their environmental implications. This research, through extensive literature review of these novel nanostructures, proposes a working definition of NH from environmental perspective, classifies a wide array of NHs based on chemical origin, and identifies their emerging and altered physicochemical properties with potential to generate unprecedented environmental fate, transport, transformation, and toxicity. Furthermore, this dissertation makes an effort to address three major data gaps: i.e., a) challenges in aqueous solubilization of HOFs, b) possible correlation of carbon numbers on fullerene molecules with their aggregation behavior, and c) influence of hybridization on aggregation kinetics and antimicrobiality of an important electrocatalyst NH (metal-carbon). To address the first data gap, aqueous suspensions of nC₆₀, nC₇₀, nC₇₆, and nC₈₄ were prepared using a calorimetry-based solvent exchange method. Non-aggregating and size-specific aqueous nC₆₀ and nC₇₀ fullerene clusters also were prepared using a non-ionic polymer, pluronic acid (PA). The environmental processes section of this research assessed aggregation kinetics of nHOFs and NHs as well as antimicrobiality of TiO₂ conjugated oxidized multiwalled carbon nanotube (OMWNT-TiO₂) NH. Aqueous solubilization of C₇₀, C₇₆, and C₈₄ was performed being guided by molecular dynamics (MD) simulations. Increased energy demand reflects favorability of HOF-water interaction. The experimental findings suggest that nHOF clusters obtained via solvent-exchange solubilization method remains stabilized by electrostatic repulsion. Similarly, non-ionic triblock co-polymer PA F-127 stabilized aqueous C₆₀ and C₇₀s were prepared. Experimental results suggest that size uniformity of aqueous fullerenes increased with the increase in PA concentration, yielding optimum 58.8±5.6 and 61.8±5.6 nm nC₆₀s and nC₇₀s, respectively (0.10 %w/v PA). Fullerene aqueous suspensions also manifested colloidal stability even in presence of 1 M NaCl or in biological media, i.e., DMEM and RPMI. MD simulations results indicate encapsulation of fullerene clusters by PA molecules and subsequent steric stabilization. The results from this study may facilitate mechanistic environmental and toxicological studies with size-specific fullerenes that do not aggregate in high ionic strength biological media. Aqueous suspensions of nC₆₀ and three nHOFs (i.e., nC₇₀, nC₇₆, and nC₈₄) obtained via solvent-exchange method were systematically studied to determine their aggregation kinetics in a wide range of mono- (NaCl) and divalent (CaCl₂) electrolytes. Experimentally obtained critical coagulation concentration (CCC) values of nC₆₀ and nHOFs displayed a strong negative correlation with the carbon number in fullerenes. The aggregation mechanism was dominated by van der Waals interaction as enumerated via MD simulation and modified Derjaguin-Landau-Verwey-Overbeek (DLVO) model. Natural macromolecules profoundly stabilized all fullerene clusters, even at 100 mM NaCl concentration. The results from this study can be utilized to predict aggregation kinetics of nHOFs other than the ones studied here. To understand the aggregation behavior of carbon-metal NHs, oxidized MWNTs were hybridized sequentially with undoped or Nb-doped TiO₂ and Pt NPs. OMWNT-TiO₂, OMWNT-TiNbO₂, OMWNT-TiO₂, and OMWNT-TiNbO₂-Pt and the component materials were characterized and their aggregation behavior was studied systematically. Experimental findings show that CCC values OMWNT were reduced by TiO₂ attachment; however, Nb-doping and Pt attachment increased their colloidal stability and CCC values. The aggregation mechanism was elucidated by modified DLVO energy calculations using composition-averaged Hamaker constants for NHs. Natural macromolecules stabilized all the NHs and the component materials. Antimicrobiality of OMWNT-TiO₂ NH was studied via in vitro cell viability tests. Opportunistic pathogen Pseudomonas aeruginosa PAO1 strain was exposed to OMWNT, TiO₂, and OMWNT-TiO₂ NH at different concentrations in dark and UV-irradiated conditions. OMWNT-TiO₂ NH showed higher antimicrobial activity compared to the component materials under UV-irradiation. Extracellular reactive oxygen species (ROS) measurement by using fluorescence molecular probes for H₂O₂ identifies UV-induced enhanced ROS generation by the NH as a likely antimicrobial mechanism. The research presented in this dissertation takes the first attempt toward EHS assessment of complex and hierarchical nanostructures. The research findings present new insights into these ‘horizon materials’ and likely will spark interests on this necessary line of research to better understand the environmental fate, transport, and effects of HOFs and NHs. As nanotechnology is advancing from passive singular nanostructures to active and complex nano-systems; such undertakings become imperative to evaluate implications of material complexity at the environmental interface.Civil, Architectural, and Environmental Engineerin

Synthesis and Structure-Photophysical Property Relationships of T8, T10, T12 and Oligomeric Organic Functionalized Silsesquioxanes.

Silsesquioxanes with conjugated organic tethers (chromophores) offer high orders of functionality (> 8 tethers), unusual enhanced absorption, emission and charge separation over free chromophores, excited state electron delocalization, and high thermal stability. This dissertation presents the synthesis and characterization of organic functionalized T10 and T12 [RSiO1.5]10,12 molecules, with emphasis on their synthesis by fluoride catalyzed rearrangement from [RSiO1.5]n and an understanding of their unique photophysical properties targeting components in optoelectronic devices. Initial discussion focuses on the synthesis of silsesquioxanes from silica via conversion of rice hull ash (RHA) silica to spirosiloxanes [i.e. Si(2-methyl-2,4-pentane-diolato)2] by reaction with 2-Me-2,4-pentanediol and catalytic NaOH. The resulting spirosiloxane reacts with selected arylLi reagents to form mono-aryl-spirosiloxane, suggesting a pentacoordinate silicon based mechanism. These aryl-spirosiloxanes are then converted through fluoride catalysis to novel aryl-silsesquioxanes [RSiO1.5]8,10,12. Thereafter we detail the development of [RSiO1.5]10,12 materials by fluoride catalyzed rearrangement and its mechanisms. F--catalyzed rearrangement of polymeric and octameric SQs is indispensable to the synthesis of [RSiO1.5]10/12, and mixed [R1R2SiO1.5]10,12 molecules in up to 95% yield. [PhSiO1.5]10 is synthesized in the highest reported yield to date (~50%), and is used as a model system for mechanism studies. The likely mechanistic paths taken to form T10 and T12 SQs are analyzed by experiment with MALDI/NMR to identify intermediates and computational modeling for the most likely pathways. The most favorable pathway to T10 from T8 involves coincidental participation of fluoride and water with a net enthalpy of ~-24 kcal/mol. We also explore in detail the photophysical properties of [StilbenevinylSiO1.5]8,10,12, which show similar absorption and emission in solution, but decreasing fluorescence quantum efficiencies with increasing cage size, suggesting more chromophore interactions and non-radiative decay. [StilbenevinylSiO1.5]10 shows the highest two-photon absorption cross-section of this series (5.7 GM/chromophore), offering the best polarization and charge transfer character. Fluorescence upconversion fluorescence lifetime studies on [StilbenevinylSiO1.5]8,10,12 find ultrafast charge transfer dynamics (<1 ps) indicative of chromophore-chromophore interactions in the excited state, unobserved for stilbenvinylSi(OEt)3, suggesting excited state charge delocalization.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111393/1/furgaljc_1.pd

Decomposition kinetics of polymer-nanocomposite materials

The synthesis of polythiophenes functionalized with an alkyl group such as coumarin and naphthol were performed successfully. A previously - described technique of WS2 synthesis from thiourea and tungstic acid was utilized to synthesize exfoliated WS2, which was employed to synthesize nanocomposite materials. Also, novel exfoliated polythiophene and poly(3-alkylthiophene) with naphthol nanocomposites using various percentages of tungsten disulfide were prepared using in-situ polymerization of the monomer with iron (III) chloride in the presence of exfoliated WS2. Additionally, the exfoliated nanocomposites of polyaniline were synthesized by an in-situ polymerization reaction of aniline with ammonium peroxydisulfate in the presence of exfoliated WS2. The poly(3-alkylthiophene) decorated with naphthol was characterized by using techniques such as NMR, FTIR, and TGA. These techniques were utilized to determine the difference between the monomers and their polymers. Both polymers displayed a noticeable improvement in thermal stability. The exfoliated nanocomposites of PThN-WS2 were also characterized using techniques such as FT-IR and XRD.The results obtained suggest that there is an interaction between the polymer and the WS2 due to the vibrational change in the IR spectrum. Ozawa's method was applied to determine the decomposition kinetics of these exfoliated nanocomposites using the Thermogravimetric Analysis (TGA). The activation energies for PTh and their six different compositions of WS2 were measured under air. Each sample was studied using four selected heating rates: 5, 10, 20 and 40 o C/min. The similar procedures were followed to compute Ea for PThN-WS2 nanocomposites. The results demonstrated that the incorporation of nanofillers has improved the Ea value for PTh-WS2 and PThN-WS2 nanocomposites. It was found that the presence of alkyl group (naphthol) on the thiophene ring has enhanced the Ea by approximately 65 kJ/mol compared to pure PTh with around 79.9 kJ/mol. Furthermore, the values of the Ea for exfoliated PT-WS2 and PThN-WS2 compositions were increased by incorporating higher percents of WS2 in comparison to that of pure PT or PThN. Ozawa's method was also applied to determine the activation energies for the pure polyaniline and their nanocomposites with WS2. All experiments were carried out in a TGA at four different heating rates under a nitrogen atmosphere. It was demonstrated that the incorporation of exfoliated WS2 in polyaniline showed an enhancement in the Ea values. Also, 12.5% of WS2-PANI composition recorded the highest Ea with 165 kJ/mol compared to that of Ea of pristine PANI with 129.8 kJ/mol

Tailored carbon based nanostructures as components of flexible thermoelectric and other devices

Carbon based nanostructures, such as fullerenes, carbon nanotubes and graphene showed a high potential for a vast of electronic and energy applications. However, properties of such materials in pristine forms can be insufficient to satisfy diverse specific demands, and tailoring their intrinsic properties is of increasing importance. In this work, different types of single-walled carbon nanotubes (SWCNTs) with controlled semiconducting fractions are p-/n-type doped by chemical doping in an attempt to tailor physical properties of the SWCNTs for the use in flexible thermoelectric (TE) devices and thermoplastic polymer-based conducting composites. Several p-/n-type doping schemes and an electronic type separation strategy have been developed to fulfill the task. A complete solution for efficient and scalable production of doped SWCNTs for the fabrication of flexible thermoelectric components is developed in this work. For p-type doping, a combined experimental and theoretical work demonstrates that boron atomic doping is an efficient way to simultaneously improve Seebeck coefficient (S) and electrical conductivity (σ) of SWCNT films, showing an increased thermoelectric power factor (S2σ) up to 255 μW/mK2 by a factor of 2.5 comparing to the pristine SWCNTs. For n-type doping, treatment of SWCNTs with potassium oxide and crown ether solution lead to a negative Seebeck coefficient of -30 μV/K and a promising S2σ up to 50 μW/mK2. A gel chromatography method has been developed to separate large-diameter (1.2-1.8nm) SWCNTs by electronic properties and to increase the purity of the sorted semiconducting carbon nanotubes (sc-SWCNTs) up to 95%. Effects of p-/n-type doping induced by different plasma treatments on the thermoelectric properties have been investigated for thin films made of sorted sc-SWCNTs. The high-purity sc-SWCNTs show significantly improved S of 125 μV/K. As the effects of p-type doping, air plasma treatments with proper duration (40s) lead to the increase of S, σ and thus S2σ up to 190 μW/mK2. The n-type doping for the SWCNT films have been performed via ammonia plasma treatment, and a negative S value of -80 μV/K has been achieved in air at 110oC, which is one of the best values ever reported for n-type carbon nanotube films. A flexible thermoelectric module was fabricated by printing ink made of the prepared boron doped SWCNTs and an organic solvent as an example for producing efficient all-carbon thermoelectric generators. At a temperature difference ΔT=60 K, the output voltage reaches 20 mV and the power output of 400 nW is obtained, although no “n”-legs are used in this module. At last, a work has been done on the development of melt mixed composites as TE materials, in which polypropylene is used as the matrix and boron-doped SWCNTs are used as conducting fillers. A percolation threshold lower than 0.25wt. % and a maximum conductivity up to 125 S/m at 5wt. % of SWCNT load have been achieved. The maximum conductivity is more than two times higher than that of the composites made with pristine SWCNTs as fillers

Solvents, Ionic Liquids and Solvent Effects

Solvents and ionic liquids are ubiquitous within our whole life since ancient times and their effects are actually being studied through basic sciences like Chemistry, Physics and Biology as well as being researched by a large number of scientific disciplines.This book represents an attempt to present examples on the utility of old and new solvents and the effects they exercise on several fields of academic and industrial interest. The first section, Solvents, presents information on bio-solvents and their synthesis, industrial production and applications, about per and trichloroethylene air monitoring in dry cleaners in the city of Sfax (Tunsia) and on the synthesis of polyimides using molten benzoic acid as the solvent. The second section, Ionic Liquids, shows information about the synthesis, physicochemical characterization and exploration of antimicrobial activities of imidazolium ionic liquid-supported Schiff base and its transition metal complexes, the technology of heterogenization of transition metal catalysts towards the synthetic applications in an ionic liquid matrix, the progress in ionic liquids as reaction media, monomers, and additives in high-performance polymers, a pre-screening of ionic liquids as gas hydrate inhibitor via application of COSMO-RS for methane hydrate, the extraction of aromatic compounds from their mixtures with alkanes from ternary to quaternary (or higher) systems and a review on ionic liquids as environmental benign solvent for cellulose chemistry. The final section, Solvent Effects, displays interesting information on solvent effects on dye sensitizers derived from anthocyanidins for applications in photocatalysis, about the solvent effect on a model of SNAr reaction in conventional and non-conventional solvents, and on solvent effects in supramolecular systems

Mesoporous materials for dental and biotechnological applications, curcumin polymers and enzymatic saccharification of biomass

The nonsurfactant templated sol–gel route has been demonstrated to be a cost effective, green and biofriendly pathway to obtain mesoporous materials with an interconnected network ofwormhole–like pores. It involves the formation of a metal–oxide network around an inert organic molecule (e.g., sugar molecules) which functions as a template and can be later removed bysimple extraction with water or other solvents.This research describes the preparation of mesoporous zirconia and organo–functionalized silica by the acid–catalyzed nonsurfactant templated sol–gel route and also describes the use of sublimation as a method for the template removal. Mesoporous silica nanospheres with tunable particle size were also prepared by modifying the base–catalyzed Stober process with the addition of various sugar molecules as templates. The materials were characterized using TGA, nitrogen adsorption–desorption, SEM, TEM, XRD and FTIR.The application of nonsurfactant templated mesoporous materials in the area of enzyme encapsulation and stabilization is explored in this research. A novel ‘double encapsulation’approach that enables a sol–gel encapsulated protease to retain 60 % of its original activity after 4 weeks in harsh environments, such as high pH buffer and laundry detergent, is demonstrated.The need for aesthetic, as well as durable, dental restorations has led to extensive research in the area of dental composites. This study examines the use of nonsurfactant templated mesoporous materials as fillers in dental composites. Mesoporous materials of irregular morphology prepared by acid–catalyzed sol–gel routes as well as mesoporous silica spheres prepared via base–catalyzed sol–gel reactions were both employed as fillers in experimental dental composites. This research led to the development of novel ‘dental monomertemplated mesoporous materials’, which were also evaluated as fillers in dental composites. Various approaches, such as dense packing, addition of nanosilica and spherical fillers, etc., were employed to fabricate nanocomposites with improved mechanical properties. The composites were evaluated using flexural and compression testing.Curcumin, the ground rhizome of Curcuma longa, a common South Asian herb has attracted much attention due to its chemopreventive and anti–inflammatory properties. This research describes the synthesis of a series of poly [(arylenedioxy)(diorganylsilylene)]s via polycondensation between curcumin and various diorganodichlorosilanes. These novel polymersincorporate the β–diketone unit of curcumin as well as the Si–O bond in the backbone. The polymer structure was characterized by means of 1HNMR, FTIR and elemental analysis, whileGPC results showed high molecular weights. Preliminary cell culture results suggested lack of cytotoxicity, which is important for potential applications, such as implants and tissueengineering scaffold materials. The unique and interesting thermal behavior of these polymers was studied by DSC.The technology of enzymatically degrading biomass into simple sugars, such as glucose, is a critical step towards viable production of bio–based ethanol from non–food related sources.This research demonstrates the use of a biosensor–based diabetic blood glucose monitor as a rapid glucose detector and compares it to time consuming UV assays that are currently employed in research laboratories. Pretreatment of wood shavings with ferric chloride, followed by treatment in cold NaOH/urea solution was found to significantly enhance glucose production upon enzymatic hydrolysis.Finally, accounts of exploratory experiments in the areas of thermally crosslinkable high temperature elastomers and inorganic–organic hybrid materials are provided in the appendixsections of this thesis.Ph.D., Polymer Chemistry -- Drexel University, 200

Organic Thin Film Transistor Integration

This thesis examines strategies to exploit existing materials and techniques to advance organic thin film transistor (OTFT) technology in device performance, device manufacture, and device integration. To enhance device performance, optimization of plasma enhanced chemical vapor deposited (PECVD) gate dielectric thin film and investigation of interface engineering methodologies are explored. To advance device manufacture, OTFT fabrication strategies are developed to enable organic circuit integration. Progress in device integration is achieved through demonstration of OTFT integration into functional circuits for applications such as active-matrix displays and radio frequency identification (RFID) tags. OTFT integration schemes featuring a tailored OTFT-compatible photolithography process and a hybrid photolithography-inkjet printing process are developed. They enable the fabrication of fully-patterned and fully-encapsulated OTFTs and circuits. Research on improving device performance of bottom-gate bottom-contact poly(3,3'''-dialkyl-quarter-thiophene) (PQT-12) OTFTs on PECVD silicon nitride (SiNx) gate dielectric leads to the following key conclusions: (a) increasing silicon content in SiNx gate dielectric leads to enhancement in field-effect mobility and on/off current ratio; (b) surface treatment of SiNx gate dielectric with a combination of O2 plasma and octyltrichlorosilane (OTS) self-assembled monolayer (SAM) delivers the best OTFT performance; (c) an optimal O2 plasma treatment duration exists for attaining highest field-effect mobility and is linked to a “turn-around” effect; and (d) surface treatment of the gold (Au) source/drain contacts by 1-octanethiol SAM limits mobility and should be omitted. There is a strong correlation between the electrical characteristics and the interfacial characteristics of OTFTs. In particular, the device mobility is influenced by the interplay of various interfacial mechanisms, including surface energy, surface roughness, and chemical composition. Finally, the collective knowledge from these investigations facilitates the integration of OTFTs into organic circuits, which is expected to contribute to the development of new generation of all-organic displays for communication devices and other pertinent applications. A major outcome of this work is that it provides an economical means for organic transistor and circuit integration, by enabling use of the well-established PECVD infrastructure, yet not compromising the performance of electronics

Non-covalent interactions in organotin(IV) derivatives of 5,7-ditertbutyl- and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine as recognition motifs in crystalline self- assembly and their in vitro antistaphylococcal activity

Non-covalent interactions are known to play a key role in biological compounds due to their stabilization of the tertiary and quaternary structure of proteins [1]. Ligands similar to purine rings, such as triazolo pyrimidine ones, are very versatile in their interactions with metals and can act as model systems for natural bio-inorganic compounds [2]. A considerable series (twelve novel compounds are reported) of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) and 5,7-diphenyl- 1,2,4-triazolo[1,5-a]pyrimidine (dptp) were synthesized and investigated by FT-IR and 119Sn M\uf6ssbauer in the solid state and by 1H and 13C NMR spectroscopy, in solution [3]. The X-ray crystal and molecular structures of Et2SnCl2(dbtp)2 and Ph2SnCl2(EtOH)2(dptp)2 were described, in this latter pyrimidine molecules are not directly bound to the metal center but strictly H-bonded, through N(3), to the -OH group of the ethanol moieties. The network of hydrogen bonding and aromatic interactions involving pyrimidine and phenyl rings in both complexes drives their self-assembly. Noncovalent interactions involving aromatic rings are key processes in both chemical and biological recognition, contributing to overall complex stability and forming recognition motifs. It is noteworthy that in Ph2SnCl2(EtOH)2(dptp)2 \u3c0\u2013\u3c0 stacking interactions between pairs of antiparallel triazolopyrimidine rings mimick basepair interactions physiologically occurring in DNA (Fig.1). M\uf6ssbauer spectra suggest for Et2SnCl2(dbtp)2 a distorted octahedral structure, with C-Sn-C bond angles lower than 180\ub0. The estimated angle for Et2SnCl2(dbtp)2 is virtually identical to that determined by X-ray diffraction. Ph2SnCl2(EtOH)2(dptp)2 is characterized by an essentially linear C-Sn-C fragment according to the X-ray all-trans structure. The compounds were screened for their in vitro antibacterial activity on a group of reference staphylococcal strains susceptible or resistant to methicillin and against two reference Gramnegative pathogens [4] . We tested the biological activity of all the specimen against a group of staphylococcal reference strains (S. aureus ATCC 25923, S. aureus ATCC 29213, methicillin resistant S. aureus 43866 and S. epidermidis RP62A) along with Gram-negative pathogens (P. aeruginosa ATCC9027 and E. coli ATCC25922). Ph2SnCl2(EtOH)2(dptp)2 showed good antibacterial activity with a MIC value of 5 \u3bcg mL-1 against S. aureus ATCC29213 and also resulted active against methicillin resistant S. epidermidis RP62A