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 Characterization of Graphene oxide Polydopamine Aerogels for Contaminant Removal in Water

Graphene, a two dimensional nanomaterial with remarkable properties, often requires assembly into three dimensional (3D) macroscopic monoliths while retaining its intrinsic nanoscale properties for different functional applications including contaminant removal from water. Recently, Graphene based aerogel monolithic structures have been pursued for contaminant removal application due to porous structure and mechanical strength. However, conventional synthesis methods are unable to control shape and architecture aerogel assembly, limiting potential application in water treatment devices. In this study, we synthesized a freeze casting method with optimized graphene-oxide polydopamine (GO-PDA) to fabricate GO-PDA aerogels of controllable architecture. This approach involved fabricating molds of desired geometric structure (1 mL cube) through fused deposition model printing. A GO-PDA ink was freeze casted into molds and further freeze dried to obtain GO-PDA aerogels identical to the mold\u27s architecture. Polydopamine contributed to aerogel structure integrity through functionalization of graphene surface due to spontaneous polymerization and providing active contaminant adsorption sites. The mold assisted GO-PDA aerogel exhibited high removal capacity for methylene blue (57.29 [46.49% removal efficiency after 12 hrs], 55.49, and 52.28 mg/g respectively), Evans blue (40.96 mg/g [36.93% removal efficiency after 36 hrs]), lead (51.67 mg/g [48.36% removal efficiency after 6 hrs]), and hexavalent chromium (33.13 mg/g [28.13% removal efficiency after 24 hrs]) from aqueous solution. It also exhibited high removal capacity through recycling and regeneration (3 cycles) for methylene blue (\u3e87% removal). Characterization of GO-PDA aerogels was conducted through Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction Spectroscopy, and Raman Spectroscopy to prove functionality of polydopamine

Synthesis and Characterization of Graphene oxide Polydopamine Aerogels for Contaminant Removal in Water

Graphene, a two dimensional nanomaterial with remarkable properties, often requires assembly into three dimensional (3D) macroscopic monoliths while retaining its intrinsic nanoscale properties for different functional applications including contaminant removal from water. Recently, Graphene based aerogel monolithic structures have been pursued for contaminant removal application due to porous structure and mechanical strength. However, conventional synthesis methods are unable to control shape and architecture aerogel assembly, limiting potential application in water treatment devices. In this study, we synthesized a freeze casting method with optimized graphene-oxide polydopamine (GO-PDA) to fabricate GO-PDA aerogels of controllable architecture. This approach involved fabricating molds of desired geometric structure (1 mL cube) through fused deposition model printing. A GO-PDA ink was freeze casted into molds and further freeze dried to obtain GO-PDA aerogels identical to the mold\u27s architecture. Polydopamine contributed to aerogel structure integrity through functionalization of graphene surface due to spontaneous polymerization and providing active contaminant adsorption sites. The mold assisted GO-PDA aerogel exhibited high removal capacity for methylene blue (57.29 [46.49% removal efficiency after 12 hrs], 55.49, and 52.28 mg/g respectively), Evans blue (40.96 mg/g [36.93% removal efficiency after 36 hrs]), lead (51.67 mg/g [48.36% removal efficiency after 6 hrs]), and hexavalent chromium (33.13 mg/g [28.13% removal efficiency after 24 hrs]) from aqueous solution. It also exhibited high removal capacity through recycling and regeneration (3 cycles) for methylene blue (\u3e87% removal). Characterization of GO-PDA aerogels was conducted through Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction Spectroscopy, and Raman Spectroscopy to prove functionality of polydopamine

Mechanistic lessons learned from studies of planktonic bacteria with metallic nanomaterials: implications for interactions between nanomaterials and biofilm bacteria

Metal and metal oxide nanoparticles (NPs) are used in numerous applications and have high likelihood of entering engineered and natural environmental systems. Careful assessment of the interaction of these NPs with bacteria, particularly biofilm bacteria, is necessary. This perspective discusses mechanisms of NP interaction with bacteria and identifies challenges in understanding NP-biofilm interaction, considering fundamental material attributes and inherent complexities of biofilm structure. The current literature is reviewed, both for planktonic bacteria and biofilms; future challenges and complexities are identified, both in light of the literature and a dataset on the toxicity of silver NPs toward planktonic and biofilm bacteria. This perspective aims to highlight the complexities in such studies and emphasizes the needs for systematic evaluation of NP-biofilm interaction

Change in chirality of semiconducting single-walled carbon nanotubes can overcome anionic surfactant stabilisation: a systematic study of aggregation kinetics

Single-walled carbon nanotubes’ (SWNT) effectiveness in applications is enhanced by debundling or stabilisation. Anionic surfactants are known to effectively stabilise SWNTs. However, the role of specific chirality on surfactant-stabilised SWNT aggregation has not been studied to date. The aggregation behaviour of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalised with three anionic surfactants – sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and sodium deoxycholate – was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and divalent (CaCl2) electrolytes as well as a 2.5 mg total organic carbon (TOC) L–1 Suwannee River humic acid were used as background chemistry. Overall, sodium dodecyl benzene sulfonate showed the most effectiveness in stabilising SWNTs, followed by sodium deoxycholate and sodium dodecyl sulfate. However, the larger diameter (7,6) chirality tubes (compared to (6,5) diameter), compromised the surfactant stability due to enhanced van der Waals interaction. The presence of divalent electrolytes overshadowed the chirality effects and resulted in similar aggregation behaviour for both the SWNT samples. Molecular modelling results elucidated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of Suwannee River humic acid under 10 mM monovalent and mixed-electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilisation of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure

Method Development for Transmission Electron Microscopy of Carbon Nanotubes and for Distributed Sensing With Triboluminescent Materials in the Premise of Sustainable Infrastructure

Cement is one of the largest contributors to the carbon footprint with approximately 3-5% share of global CO2 emission. Cement production is increasing with the increase in global population and their need for added accommodation. Moreover, the relatively short lifespan of already constructed cementitious infrastructure further inflates the demand of cement and continues to increase its carbon footprint. Thus a need for higher material strength and proactive structural health monitoring can allow for a significant reduction in overall cement usage as well as the carbon emission associated with it. The overall goal of this thesis is to develop novel techniques for evaluation of material compatibilitybetween carbonaceous nanomaterial and cementitious matricesand for distributed sensing employing fracto-luminescent materials. The developed techniques will likely allow for improvement in durability and health monitoring of cementitious composites and thus will likely contribute toward a sustainable use of cementitious material. The first half of the thesis focuses on development of a sample-preparation technique for transmission electron microscopy (TEM) of graphitic nano-reinforced cementitious (GNRC) composites. A unique colloidal suspension protocol was developed where cement materials with embedded single-walled and multiwalled carbon nanotubes (SWNTs and MWNTs) were systematically prepared and characterized. SWNT and MWNT aqueous suspensions were prepared using an acid etching technique. The suspension properties were characterized with Raman spectroscopy and time-resolved dynamic light scattering measurements. The water containing functionalized SWNTs and MWNTs were incorporated in the mix design to prepare the cement paste. Compatibility between functionalized nano-reinforcements and the cementitious matrix at the nanoscale was evaluated using high resolution TEM imaging. Preferential association of the functionalized SWNTs and MWNTs within the cement matrix was found and such novel colloidal protocol for image GNRC composites can be effectively used for characterizing such compatibility. The latter half of the thesis presents a simple however robust method for material testing in the field of damage sensing in cement mortar surfaces. Manganese-doped zinc sulfide (ZnS:Mn) triboluminescent (TL) material was used to coat 2 × 2 mortar cubes. The cubes were then tested under compression loading and crack propagation was imaged with a DSLR camera. Loading rate and concentration of TL material was systematically varied and luminescence emanating from the coated surfaces was quantified with a novel image processing technique. The image analysis technique included an image processing step where total luminescence/pixel along the cracks was quantified. Overall increase of the luminescence occurs with both increase in TL concentration and rate of loading. Quantification of crack in cement based materials through this novel technique will be useful and reliable for damage sensing in both real-systems and laboratory scale material characterization. This thesis has contributed through developing a TEM imaging technique, which is a first-of-a-kind technique, and can evaluate material compatibility of SWNTs and MWNTs with complex cement crystals. This method has potential for mechanistic understanding of nano-scale reinforcement of cementitious materials. The quantitative image analysis method developed here employing TL coatings also lays foundation for material testing in the field of distributed damage sensing and monitoring of cementitious surfaces

Synthesis and Characterization of Graphene oxide Polydopamine Aerogels for Contaminant Removal in Water

Graphene, a two dimensional nanomaterial with remarkable properties, often requires assembly into three dimensional (3D) macroscopic monoliths while retaining its intrinsic nanoscale properties for different functional applications including contaminant removal from water. Recently, Graphene based aerogel monolithic structures have been pursued for contaminant removal application due to porous structure and mechanical strength. However, conventional synthesis methods are unable to control shape and architecture aerogel assembly, limiting potential application in water treatment devices. In this study, we synthesized a freeze casting method with optimized graphene-oxide polydopamine (GO-PDA) to fabricate GO-PDA aerogels of controllable architecture. This approach involved fabricating molds of desired geometric structure (1 mL cube) through fused deposition modelling printing. A GO-PDA ink was freeze casted into molds and further freeze dried to obtain GO-PDA aerogels identical to the mold’s architecture. Polydopamine contributed to aerogel structure integrity through functionalization of graphene surface due to spontaneous polymerization and providing active contaminant adsorption sites. The mold assisted GO-PDA aerogel exhibited high removal capacity for methylene blue (57.29 [46.49% removal efficiency after 12 hrs], 55.49, and 52.28 mg/g respectively), Evans blue (40.96 mg/g [36.93% removal efficiency after 36 hrs]), lead (51.67 mg/g [48.36% removal efficiency after 6 hrs]), and hexavalent chromium (33.13 mg/g [28.13% removal efficiency after 24 hrs]) from aqueous solution. It also exhibited high removal capacity through recycling and regeneration (3 cycles) for methylene blue (\u3e87% removal). Characterization of GO-PDA aerogels was conducted through Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction Spectroscopy, and Raman Spectroscopy to prove functionality of polydopamine

Factorial Design of Experiments for Optimization of Photocatalytic Degradation of Tartrazine by Zinc Oxide (ZnO) Nanorods with Different Aspect Ratios

The photocatalytic degradation of the azo dye tartrazine using zinc oxide (ZnO) as photocatalyst under ultraviolet light was investigated using a 24 factorial design. The variables studied were the aspect ratio of ZnO nanorods, the ZnO load, the initial pH of tartrazine solution, and the H2O2 volume. These variables were studied aiming to maximize the tartrazine removal efficiency and the pseudo-1st-order rate constant of the removal process. The ZnO aspect ratio was tuned by varying the Lewis base during the synthesis, hexamethylenetetramine (HMTA) was used to prepare ZnO with low aspect ratio (ZnO_LowAR), and NaOH was used to prepare ZnO with high aspect ratio (ZnO_HighAR). The microstructural characterizations indicated that ZnO_LowAR and ZnO_HighAR nanorods have similar structural, textural and optical properties. The only exception was the dimensions of the nanorods obtained, which could result in differences in the facets exposed on each type of nanorod surface. The factorial design revealed that ZnO aspect ratio, the initial pH of tartrazine solution, and the H2O2 volume all have primary significant effects, whereas the ZnO load is not significant neither in the tartrazine removal efficiency nor in the pseudo-1st-order rate constant. Statistical models considering the coefficients of the significant interactions were obtained, leading to reasonable predicted results in comparison to the results experimentally obtained. The conditions leading to highest removal efficiency (~92%) and pseudo-1st-order rate constant (3.81 x 10-2 min-1) were carried out with ZnO_HighAR, initial pH 7, and without H2O2, which outperformed the TiO2 P-25 under the same conditions

Using Deep Eutectic Solvent for Conjugation of Fe3O4 Nanoparticles onto Graphene Oxide for Water Pollutant Removal

Deep eutectic solvents (DESs) have emerged as a substitute for ionic liquids with lower cost and enhanced biodegradability. The most common class of DES refers to a mixture of a quaternary ammonium or phosphonium salt and a hydrogen bond donor (e.g., carboxylic acid) with a melting point lower than that of individual components. DESs have recently shown promise for surface modification of graphene oxide (GO) nanosheets with different functional groups. We hypothesize that such surface functionalization of GO (and other carbon nanomaterials) with DESs can provide a new route to conjugate metallic nanoparticles onto GO surfaces (and similar). Here, we used a typical DES, based on choline chloride and urea, for the conjugation of presynthesized Fe3O4 nanoparticles onto GO nanosheets at different GO:Fe3O4 ratios. Physicochemical characterization not only confirmed the ability of DES to prepare DES/GO-Fe3O4 nanohybrids successfully, but also evidenced the influence of DES on the homogeneity and size distribution of Fe3O4 nanoparticles in these nanohybrids. DES/GO-Fe3O4 nanohybrids can perform better than both GO and Fe3O4 as adsorbents for organic dyes (methylene blue, MB) and heavy metals (Lead (II)). However, depending on the contaminant type, the contaminant removal performance varied differently for DES/GO-Fe3O4 nanohybrids with different ratios