Sundaramurthy Jayaraman

Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

In this manuscript, a dramatic increase in the energy density of ~ 69 Wh kg−1 and an extraordinary cycleability ~ 2000 cycles of the Li-ion hybrid electrochemical capacitors (Li-HEC) is achieved by employing tailored activated carbon (AC) of ~ 60% mesoporosity derived from coconut shells (CS). The AC is obtained by both physical and chemical hydrothermal carbonization activation process, and compared to the commercial AC powders (CAC) in terms of the supercapacitance performance in single electrode configuration vs. Li. The Li-HEC is fabricated with commercially available Li4Ti5O12 anode and the coconut shell derived AC as cathode in non-aqueous medium. The present research provides a new routine for the development of high energy density Li-HEC that employs a mesoporous carbonaceous electrode derived from bio-mass precursors.

Exceptional Performance of TiNb2O7 Anode in All One-Dimensional Architecture by Electrospinning

We report the extraordinary performance of an Li-ion battery (full-cell) constructed from one-dimensional nanostructured materials, i.e. nanofibers as cathode, anode, and separator-cum-electrolyte, by scalable electrospinning. Before constructing such a one-dimensional Li-ion battery, electrospun materials are individually characterized to ensure its performance and balancing the mass loading as well. The insertion type anode TiNb2O7 exhibits the reversible capacity of ∼271 mAh g(-1) at current density of 150 mA g(-1) with capacity retention of ∼82% after 100 cycles. Under the same current density, electrospun LiMn2O4 cathode delivered the discharge capacity of ∼118 mAh g(-1). Gelled electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) nanofibers membrane is used as the separator-cum-electrolyte in both half-cell and full-cell assembly which exhibit the liquid like conductivity of ∼2.9 mS cm(-1) at ambient conditions. Full-cell, LiMn2O4|gelled PVdF-HFP|TiNb2O7 is constructed by optimized mass loading of cathode with respect to anode and tested between 1.95 and 2.75 V at room temperature. The full-cell delivered the reversible capacity of ∼116 mAh g(-1) at current density of 150 mA g(-1) with operating potential and energy density of ∼2.4 V and ∼278 Wh kg(-1), respectively. Further, excellent cyclability is noted for such configuration irrespective of the applied current densities.

Synthesis of porous LiMn2O4 hollow nanofibers by electrospinning with extraordinary lithium storage properties

We report the extraordinary lithium storage performance of porous LiMn2O4 hollow nanofibers synthesized by electrospinning technique. The electrospun LiMn2O4 hollow nanofibers retained 87% of initial reversible capacity after 1250 cycles at the 1 C rate. Further, excellent cycling profiles at 55 °C and cubic spinel to tetragonal phase transformation are also noted.

Hydrothermal pre-treatment for mesoporous carbon synthesis: enhancement of chemical activation

This work presents a resource-friendly process to produce high surface area mesoporous activated carbons from biomass. ZnCl2 as an activating agent was incorporated into the biomass (coconut shells) during a hydrothermal pre-treatment step. The pre-treatment was followed by pyrolysis accompanied by physical activation. The resultant mesoporous activated carbons possessed a higher total surface area and a greater degree of mesoporosity compared to the biomass that was pyrolysed without hydrothermal treatment. The cause of higher mesoporosity is inferred to be the more conducive environment for accessibility of ZnCl2 due to reduced diffusion resistance to the biomass provided by the hydrothermal treatment. In addition, the hydrothermal environment facilitated the generation of oxygen-containing functional groups that contributed to the enhanced activity of ZnCl2. Up to 67% increase in the mesoporous surface area was achieved with the inclusion of the pre-treatment step. Analogously, 50% more ZnCl2 was required to deliver the same performance in the absence of the pre-treatment step. The mesoporous activated carbons were tested for adsorption of textile dyes and possessed high adsorption capacities of up to 526 mg and 630 mg per g of carbon for methylene blue and erythrosine red, respectively. The incorporation of the hydrothermal pre-treatment is an important step in developing processes for converting biomass that make efficient and effective use of activating agents.

Electrospun ZnO Nanowire Plantations in the Electron Transport Layer for High-Efficiency Inverted Organic Solar Cells

Inverted bulk heterojunction organic solar cells having device structure ITO/ZnO/poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61 butyric acid methyl ester (PCBM) /MoO3/Ag were fabricated with high photoelectric conversion efficiency and stability. Three types of devices were developed with varying electron transporting layer (ETL) ZnO architecture. The ETL in the first type was a sol-gel-derived particulate film of ZnO, which in the second and third type contained additional ZnO nanowires of varying concentrations. The length of the ZnO nanowires, which were developed by the electrospinning technique, extended up to the bulk of the photoactive layer in the device. The devices those employed a higher loading of ZnO nanowires showed 20% higher photoelectric conversion efficiency (PCE), which mainly resulted from an enhancement in its fill factor (FF). Charge transport characteristic of the device were studied by transient photovoltage decay and charge extraction by linearly increasing voltage techniques. Results show that higher PCE and FF in the devices employed ZnO nanowire plantations resulted from improved charge collection efficiency and reduced recombination rate.

Cellulose Acetate-Poly(N-isopropylacrylamide)-Based Functional Surfaces with Temperature-Triggered Switchable Wettability.

Temperature-triggered switchable nanofibrous membranes are successfully fabricated from a mixture of cellulose acetate (CA) and poly(N-isopropylacrylamide) (PNIPAM) by employing a single-step direct electrospinning process. These hybrid CA-PNIPAM membranes demonstrate the ability to switch between two wetting states viz. superhydrophilic to highly hydrophobic states upon increasing the temperature. At room temperature (23 °C) CA-PNIPAM nanofibrous membranes exhibit superhydrophilicity, while at elevated temperature (40 °C) the membranes demonstrate hydrophobicity with a static water contact angle greater than 130°. Furthermore, the results here demonstrate that the degree of hydrophobicity of the membranes can be controlled by adjusting the ratio of PNIPAM in the CA-PNIPAM mixture.

Stable Organic Monolayers on Oxide-Free Silicon/Germanium in a Supercritical Medium: A New Route to Molecular Electronics

Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

Polythiophene-gold nanoparticle hybrid systems: Langmuir-Blodgett assembly of nanostructured films†

In this work, we demonstrate a simple method of synthesizing nanoscale polythiophene-gold nanoparticle (AuNP) hybrid systems assembled by the Langmuir-Blodgett (LB) method. Regio-regular poly(3-(2-methoxyethoxy)ethoxymethyl)thiophene-2,5-diyl (PMEEMT) and poly(3-dodecylthiophene) (PDDT) were employed as the polymeric constituents. The presence of PDDT improved the amphiphilicity of PMEEMT by addressing the phase separation that occurred due to convective hydrodynamic instability on the substrate. 4 layer stacks of 90% and 99% PMEEMT films exhibited uniform film structure with a significant reduction in phase separation. A detailed mechanism for minimization of the surface effect has been proposed based on the interaction of polythiophenes with the substrate. For the first time, an ex situ approach has been adopted to incorporate AuNPs into LB films without affecting the film morphology and uniformity. The incorporation of AuNPs into the polythiophene matrix, aided by the affinity of sulphur for gold, was strongly dependent on the molecular arrangement of the matrix, which in turn depended on the composition of the matrix. The hybrid polythiophene films exhibited enhanced conductivity and can be applied in sensors, photovoltaics and memory devices.

One-step fabrication of robust and optically transparent slippery coatings

The fabrication of lubricants-infused textured surfaces has opened up a new route towards omniphobicity. However, achieving a homogeneous thin film of lubricating material on a flat/smooth surface still remains a challenge. This work shows the successful fabrication of a thin, transparent, and homogeneous coating of perfluoropolyether (PFPE, a lubricating material) on a smooth glass surface by the electrospraying technique. The sol–gel solution for electrospraying was prepared by adding a small amount of (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichlorosilane (FTS) with PFPE which was subsequently electrosprayed on a glass substrate. After curing the coated samples at 80 °C, a transparent, homogeneous, and slippery coating with a low surface energy (12.5 mN m−1) was obtained. It was observed that the presence of FTS with PFPE, assisted significantly in the stacking of PFPE on the substrate resulting in the formation of smooth, uniform blended (PFPE + FTS) films. The surface nature of the blended films was characterized by spectroscopy and microscopy. The blended surface exhibited omniphobic properties. The surface contact angles and slipping angles made by water and acetone droplets were measured to be (116°, 40.8°) and (6°, 10°), respectively. Furthermore, the coating showed good optical (transmittance – 91%) and mechanical properties with strong adherence to glass surfaces, thus revealing the potential for applications in windows and solar modules.

Antibacterial, electrospun nanofibers of novel poly(sulfobetaine) and poly(sulfabetaine)s

Polymers capable of forming hydration layers have gained increasing attention due to their ability to form environmentally friendly antifouling surfaces. Zwitterionic polymers are an important class of materials under this category. However, the effectiveness of many zwitterionic polymers for long-term applications is compromised because of their solubility in sea water, poor hydrolytic stability and deteriorating mechanical integrity upon wetting. This study reports on the preparation and characterization of electrospun fibers derived from novel polysulfobetaine and polysulfabetaines (PSBs) composed of polyvinylbenzyl backbones. The morphology of the electrospun nanofibers was elucidated with the help of a scanning electron microscope. Hydration studies were conducted in deionized water and artificial sea water. Antifouling performance of the electrospun nanofibers was evaluated by studying the adhesion and growth of bacteria in natural, and filtered sea water. Terminal restriction fragment length polymorphism (TRFLP) fingerprinting was performed to determine the nature of the bacterial community attached to the electrospun fibers. Some of the PSBs prevented bacterial growth without showing any biocidal nature. Thus the findings of this study are potentially relevant for current trends seeking environmentally friendly antifouling solutions.