Tharangattu Narayanan

Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions

The establishment of covalent junctions between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize nanotube-based three-dimensional (3D) frameworks exhibiting superior material properties. Engineering such 3D structures in scalable synthetic processes still remains a challenge. This work pioneers the bulk synthesis of 3D macroscale nanotube elastic solids directly via a boron-doping strategy during chemical vapour deposition, which influences the formation of atomic-scale “elbow” junctions and nanotube covalent interconnections. Detailed elemental analysis revealed that the “elbow” junctions are preferred sites for excess boron atoms, indicating the role of boron and curvature in the junction formation mechanism, in agreement with our first principle theoretical calculations. Exploiting this material’s ultra-light weight, super-hydrophobicity, high porosity, thermal stability, and mechanical flexibility, the strongly oleophilic sponge-like solids are demonstrated as unique reusable sorbent scaffolds able to efficiently remove oil from contaminated seawater even after repeated use.

Binary and ternary atomic layers built from carbon, boron, and nitrogen.

Two-dimensional (2D) atomic layers derived from bulk layered materials are very interesting from both scientific and application viewpoints, as evidenced from the story of graphene. Atomic layers of several such materials such as hexagonal boron nitride (h-BN) and dichalcogenides are examples that complement graphene. The observed unconventional properties of graphene has triggered interest in doping the hexagonal honeycomb lattice of graphene with atoms such as boron (B) and nitrogen (N) to obtain new layered structures. Individual atomic layers containing B, C, and N of various compositions conform to several stable phases in the three-component phase diagram of B-C-N. Additionally, stacking layers built from C and BN allows for the engineering of new van-der-Waals stacked materials with novel properties. In this paper, the synthesis, characterization, and properties of atomically thin layers, containing B, C, and N, as well as vertically assembled graphene/h-BN stacks are reviewed. The electrical, mechanical, and optical properties of graphene, h-BN, and their hybrid structure are also discussed along with the applications of such materials.

Carbon nanotube-nanocup hybrid structures for high power supercapacitor applications.

Here, we design and develop high-power electric double-layer capacitors (EDLCs) using carbon-based three dimensional (3-D) hybrid nanostructured electrodes. 3-D hybrid nanostructured electrodes consisting of vertically aligned carbon nanotubes (CNTs) on highly porous carbon nanocups (CNCs) were synthesized by a combination of anodization and chemical vapor deposition techniques. A 3-D electrode-based supercapacitor showed enhanced areal capacitance by accommodating more charges in a given footprint area than that of a conventional CNC-based device.

Collagen based magnetic nanocomposites for oil removal applications

A stable magnetic nanocomposite of collagen and superparamagnetic iron oxide nanoparticles (SPIONs) is prepared by a simple process utilizing protein wastes from leather industry. Molecular interaction between helical collagen fibers and spherical SPIONs is proven through calorimetric, microscopic and spectroscopic techniques. This nanocomposite exhibited selective oil absorption and magnetic tracking ability, allowing it to be used in oil removal applications. The environmental sustainability of the oil adsorbed nanobiocomposite is also demonstrated here through its conversion into a bi-functional graphitic nanocarbon material via heat treatment. The approach highlights new avenues for converting bio-wastes into useful nanomaterials in scalable and inexpensive ways.

Transforming collagen wastes into doped nanocarbons for sustainable energy applications

Leather industry produces huge quantities of bio-waste that can be used as raw material for the bulk synthesis of carbonaceous materials. Here we report the synthesis of multifunctional carbon nanostructures from pristine collagen wastes by a simple high temperature treatment. Our studies reveal that the nanocarbons derived from the bio-waste have a partially graphitized structure with onion-like morphology and are naturally doped with nitrogen and oxygen, resulting in multifunctional properties. This synthetic route from bio-waste raw material provides a cost-effective alternative to existing chemical vapor deposition methods for the synthesis of functional nanocarbon materials and presents a sustainable approach to tailor nanocarbons for applications such as battery electrodes.

Three-Dimensional Porous Sponges from Collagen Biowastes

Three-dimensional, functional, and porous scaffolds can find applications in a variety of fields. Here we report the synthesis of hierarchical and interconnected porous sponges using a simple freeze-drying technique, employing collagen extracted from animal skin wastes and superparamagnetic iron oxide nanoparticles. The ultralightweight, high-surface-area sponges exhibit excellent mechanical stability and enhanced absorption of organic contaminants such as oils and dye molecules. Additionally, these biocomposite sponges display significant cellular biocompatibility, which opens new prospects in biomedical uses. The approach highlights innovative ways of transforming biowastes into advanced hybrid materials using simple and scalable synthesis techniques.

Mechanism of TiO2 Nanotubes Formation on the Surface of Pure Ti and Ti-6Al-4V Alloy

The present paper deals with the investigation of the mechanisms of TiO2 nanotubes formation on titanium surfaces during anodization process. The samples were made of pure Ti Grade-2 and Ti-6Al-4V alloy. They were grinded, etched with 0,5 wt. % HF acid and anodized. The anodization was done in electrolyte containing 0,5 wt. % HF acid using DC power supply with graphite electrode as cathode. The samples were investigated by SEM, EDAX and XRD analysis. The results show two different mechanisms of formation of TiO2 nanotubes on the surfaces of both materials. During the anodization process the oxide formations, obtained on the pure Ti surface after etching, are oxidized to nanorods; the area between them is also oxidized and connects them. This thin oxide layer grows in the metal depth while the nanorods are dissolved thus forming the porous sponge-like structure which is further transformed in tubular. While on the surface of Ti-6Al-4V alloy oxide nanonuclei originate which transform their shape from nanoseed to bowl-like with clearly pronounced bottom and walls, growing in tubular structures. The type of the material defines the surface morphology after etching. Thus obtained morphology influences on the processes running rate in different micro-regions determining origination of the titanium nanotubes on different stage as well as by different mechanism. The field-enhanced oxidation and field-enhanced dissolution are the main processes for formation of TiO2 nanotubes during anodization. In the regions with prevalent oxidation processes the TiO2 nanotubes are formed earlier while in the regions with dominant dissolution processes the TiO2 nanotubes are formed on the later stage.

Recent advances in optical limiting properties of fluorinated graphene oxides

There is a substantial interest in finding materials with high nonlinear optical (NLO) properties of materials because of its attractive applications in optical limiting for safety protections. In an effort to develop highly performing optical limiting materials, recently we have found that fluorination of graphene oxides leads to improvement in their NLO properties.