Browsing by Author "Ajayan, Pulickel M."

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    Advanced Three-Dimensional Structural Carbon Nanomaterials
    (2016-08-17) Ozden, Sehmus; Ajayan, Pulickel M.
    Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, are most intensively investigated carbon allotropes because of their outstanding physical and chemical properties. Recently, it has been realized that threedimensional (3D) carbon-based structures with nanoscale interconnection provide the remarkably improved properties required for critically needed applications. The properties of 3D-CNTs and graphene architectures can be tweaked for various applications. Therefore, 3D carbon-based solids with nanoscale intermolecular junctions present an exciting research area and provide opportunities for fabrication of various 3D-macroscopic architectures with unexpected properties. The creation of nanoengineered 3D-macroscopic structures in a scalable synthetic process still remains a challenge. The fundamental problem is the difficulty in introducing atomic-scale junctions between individual nanoscale structures so that they can be organized as covalently interconnected nanostructured networks with controllable physical characteristics, such as density and porosity. Here, 3D structures have been created using chemical vapor deposition method, solutionbased chemistry technique and welding method via hypervelocity impact method to generate atomic-scale junction between carbon nanostructures. The scalable fabrication of 3D macroscopic scaffolds with different hierarchical interconnected structures and soldering-like junctions between CNTs using chemical vapor deposition (CVD) technique is reported. These intermolecular junctions of CNTs result in a high thermal stability, high electrical conductivity, excellent mechanical properties, as well as excellent structural stability in a concentrated acid, base, and organic solvents. The CNT solids with such tremendous properties represent the next generation of carbon-based materials with a broad range of potential applications; we demonstrate here a couple such utility impact damping, removal oil from contaminated water and as a marker for the oil industry. Additionally, in situ nano-indentation inside a scanning electron microscopy (SEM) were used to determine the mechanical response of individual covalent junction, formed in different configurations such as “X”, “Y” and “” shapes between individual CNTs. Fully atomistic reactive molecular dynamics simulations are used to support the experimental results as well as to study the deformation behavior of junctions. Vertically aligned multiwall carbon nanotube forests (NTF) synthesized by water assisted CVD method and both sides functionalized with different functionalities as hydrophobic and hydrophilic. The produced hygroscopic nanotube forest demonstrate for water harvesting from air. The second approach has been used in this work is solution chemistry to generate crosslinking nanotube structures. The scalable synthesis of 3D macroscopic solids made of covalently connected nanotubes via Suzuki cross-coupling reaction, a well-known carbon-carbon covalent bond forming reaction in organic chemistry. The resulting CNTs solids are made of highly porous, interconnected structures made of chemically crosslinked carbon nanotubes after freeze-drying process. CNTs solids demonstrated one such utility in the removal of oil from contaminated water. In another approach hypervelocity impact method was used to investigate mechanical behavior of CNTs. The hypervelocity impact of CNT bundles against metallic targets resulted their unzipping along the tube axis, which leads to the formation of graphene nanoribbons, nanodiamonds and covalently interconnected carbon nanostructures depending on the velocity and impact geometry. This new process can produce chemical-free, high-quality graphene nanoribbons. The experimental results supported by fully atomistic reactive molecular dynamics simulations were used to gain further insights of the pathways and deformation and fracture mechanisms
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    Green Recycling of Lithium-ion Batteries
    (2024-04-19) Alhashim, Salma Hashim; Ajayan, Pulickel M.
    Lithium-ion batteries (LiBs) manifest themselves as an important building block in the move towards a net-zero carbon emission economy, and they have been crucial in defining national and international energy policies. Globally, the use of LiBs is projected to increase by almost three folds from 250 million units in 1998 to 700 million units in 2030. This has created two challenges, namely LiB waste management and supply of critical materials (e.g., cobalt, nickel, lithium, and manganese). This PhD work explores viable approaches for green recycling of LiBs. Deep Eutectic Solvents (DESs) are green lixiviants that show immense potential in the efficient hydrometallurgical recycling of LiBs owing to their polarity and non-toxic nature. However, there have been very few attempts to understand and investigate the leaching mechanisms of transition metals and Li from LiB cathode materials using DESs, which is essential in formulating large-scale procedures for industrial-scale battery recycling. In my work, I have tried to understand how the various reaction parameters including temperature, time, solid-to liquid ratio and DES composition affects the leaching efficiencies from common cathode materials (such as NCA, NMC811, and NMC111) using an ethylene glycol (EG): choline chloride (ChCl) based DES. The use of spectroscopy coupled with theoretical calculations revealed a hydrogen-bond mediated leaching mechanism that is heavily reliant on the DES composition. Furthermore, there is a quest for innovative metal recovery strategies to address concerns over expediting the leaching step and reducing energy consumption. This work showcases microwave-assisted cathode leaching leading to a rapid Li extraction (>50% in 30 sec) for varying cathode compositions. Nearly 100% Li leaching efficiency is obtained in just 30 minutes, holding a great potential for facilitating time-efficient selective Li recovery.
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    Hybrid Perovskite Materials for Stable Optoelectronics Applications
    (2018-04-20) Tsai, Hsinhan; Ajayan, Pulickel M.; Lou, Jun; Mohite, Aditya D.
    Organic-inorganic hybrid perovskites materials have grab enormous attention in the material research community. This is because of their exceptional semiconducting properties such as direct band gap, free carrier generation, broad absorption range, long diffusion length and carrier lifetime, which enable highly efficient photovoltaic device over 22%, surpassing other classical semiconductors in few years. However, one fundamental bottleneck remains in this system that mitigates such material from wide use that are reproducibility, photo- and chemical instability. These are found to be closely related to the structure of the material, such as the hydroscopic nature of the organic cation, symmetry of the crystal structure and degree of thin film crystallinity. Therefore, the focus of this thesis is to understand the basic mechanism in structure that dominate the stability of perovskites materials properties and design robust hybrid perovskite structures through organic cation engineering. Through synthetic approach, we found that the bulky organic molecules can be inserted to the perovskite lattice, forming a layered structure with quantum and dielectric confinement, called Ruddlesden-Popper (RP) perovskites. Employing our previously developed hot-casting method, we were able to obtain near single crystalline thin film with preferred orientation. With the protection of the bulky molecules, the stability of the perovskite layers is much extended. Beyond the photovoltaics, the oriented, highly crystalline thin film can facilitate the current injection in light-emitting diodes (LEDs) which had high radiance with 1 % EQE in device performance. The devices also had low turn-on voltage which can decrease the energy consumption and benefit to lighting applications. This thesis demonstrates the detail solutions for fundamental problems and the research results can help to promote technologies and push the limits in hybrid perovskites optoelectronics society.
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    Interface Driven and Bio-mimetic Design of 3D Hybrid Materials
    (2018-10-19) Owuor, Peter Samora; Ajayan, Pulickel M.; Lou, Jun
    The discovery of Graphene, carbon nanotubes and subsequent other nano-materials led to an explosion in research geared towards utilizing their intriguing mechanical, physical and chemical properties. While the physical properties of nanomaterials have been extensively explored, the assembly in a bottom-up approach to design hybrid 3D nanostructures by taking advantage of their interfacial properties still needs a deeper inquiry. This thesis scope is to answer four key questions;  What role does the interfacial region plays in macro-scale materials properties?  Is the same effect of interfacial region at macro-scale applies to the nano-scale materials?  Is there a means to modify the interface region to assemble 3D hybrid structures?  What are the resulting applications of such design in materials? To address the aforementioned questions, novel synthetic and biomimetic strategies were employed. The first detour of the thesis delves into the chemical process where functionalization and freeze-drying methods are used to fabricate porous carbon nanotubes (CNT) with self-stiffening behavior. The chemical approach is then applied to zero-dimensional SiO2 nanoparticles to fabricate three-dimensional nanostructures with improved fire-retardant capability. Next, the thesis explores the physical methods in assembling 3D structures where graphene oxide foam is chemically and physically reinforced with polymer molecule to fabricate an oil absorption and electrical resistant foam. The thesis further develops a new method to functionalize hexagonal boron nitride (h-BN) to enable their networking forming property resulting in high porous foam for CO2 absorption. The above solutions all relates to what is referred to as ‘hard interface’ therefore there was a need to explore ‘mobile interface’ like those found in nature. In this regard, a new area of study was developed; solid-liquid composite in macro-scale materials. Here, the thesis presents two new approaches; high damping composite by addition of liquid metal in a polymer matrix and optical and stiffness switching of a phase change composite. Finally, the thesis attempts to combine the two interfaces in hybrid materials. The most important contribution of this thesis is the new techniques which can be used to design advanced composites. Furthermore, a new subset of solid-liquid composites which have never been looked at in terms of mechanical properties is brought-forth. Finally, the peer-reviewed papers published should form a basis for future scientists with plans to pursue this field.