Palaniswamy Suresh Kumar

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.

Unveiling TiNb2O7 as an Insertion Anode for Lithium Ion Capacitors with High Energy and Power Density

This is the first report of the utilization of TiNb2 O7 as an insertion-type anode in a lithium-ion hybrid electrochemical capacitor (Li-HEC) along with an activated carbon (AC) counter electrode derived from a coconut shell. A simple and scalable electrospinning technique is adopted to prepare one-dimensional TiNb2 O7 nanofibers that can be characterized by XRD with Rietveld refinement, SEM, and TEM. The lithium insertion properties of such electrospun TiNb2 O7 are evaluated in the half-cell configuration (Li/TiNb2 O7 ) and it is found that the reversible intercalation of lithium (≈3.45 mol) is feasible with good capacity retention characteristics. The Li-HEC is constructed with an optimized mass loading based on the electrochemical performance of both the TiNb2 O7 anode and AC counter electrode in nonaqueous media. The Li-HEC delivers very high energy and power densities of approximately 43 Wh kg(-1) and 3 kW kg(-1) , respectively. Furthermore, the AC/TiNb2 O7 Li-HEC delivers a good cyclability of 3000 cycles with about 84% of the initial value.

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.

Highly monodispersed Ag embedded SiO2 nanostructured thin film for sensitive SERS substrate: growth, characterization and detection of dye molecules

Highly monodispersed Ag embedded SiO2 nanostructured thin films are synthesized and their sensitivity towards SERS investigated. The possible mechanism for the formation of a highly monodispersed SiO2 nanostructured thin film and its self-assembled nanogap with Ag are discussed. It is found that the architecture of Ag embedded SiO2 (Ag@SiO2) are drastically influenced by precursor concentration and the reaction time. The morphology and monodispersity of the silica thin film were confirmed using FESEM and AFM. The crystallinity and existence of Ag on SiO2 were confirmed using XRD and XPS. The substrate shows enhanced SERS efficiency due to the reduced size (around 15 nm) of the Ag nanoparticles and the nano gap of (below 3 nm) between SiO2 and Ag. Based on the FDTD (finite-difference time-domain) simulation, the creation of hotspots was confirmed for the obtained nanogap. The prepared thin film possesses strong Surface Plasmon Resonance (SPR) with widely tunable peaks between 407–430 nm in the UV visible spectrum. The Ag@SiO2 nanosphere-based SERS platform provides highly enhanced effects and reveals a reproducible enhancement (EF = 7.79 × 108) of R6G (Rhodamine 6G), allowing a detection limit from a 10–18 mol L−1 solution. The prepared substrate was also used to detect trace levels of melamine from a 10–8 mol L−1 solution.

Superhydrophobic and H2S gas sensing properties of CuO nanostructured thin films through a successive ionic layered adsorption reaction process

Superhydrophobic surfaces of CuO were synthesized using a successive ionic-layered adsorption reaction technique by varying the number of deposition cycles followed by a thermal annealing process. The prepared superhydrophobic surface was composed of monoclinic CuO, which was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Dynamic contact angle measurements were obtained using a droplet evaporation method. The contact angles measured on CuO surfaces after 20, 40, and 60 deposition cycles were similar, all showing hydrophilicity. After the thermal treatment, the prepared films exhibit super-hydrophobicity with a high water contact angle of approximately 157°, which contributed to the stable superhydrophobic surface. A considerable increase in surface roughness (from 23.81 to 74.54 nm) and the conical-shaped CuO nanostructures led to super-hydrophobicity. Also a possible mechanism for the wettability behavior is proposed. Finally, the superhydrophobic CuO surface which was used for the detection of H2S gas showed a very fast response. These results indicate that the low temperature deposition of CuO nanostructured thin films were promising for reliable high-performance gas sensors.

Extraction and modification of cellulose nanofibers derived from biomass for environmental application

Cellulose is a natural biopolymer that is abundantly available in plant cell walls and is secreted in its pure forms by many bacteria. Due to their unique features cellulose materials are considered as efficient replacements for conventional polymers. Cellulose nanofibers (CNF) have attracted wide interest due to their nano size, ease of preparation, low cost, tuneable surface properties and enhanced mechanical properties. However, the efficiency of CNF depends on the extraction method employed from its source and their features vary from source to source. Hence, there is a need to understand the specificity of CNF extraction from its source in order to obtain highly efficient CNF with maximum potential. CNF has been extracted from plant sources using physical, chemical and enzymatic methods. Although plant derived CNF possess excellent features, the involvement of chemicals and complexity in extraction process limits their usage. Bacterial CNF overcome this limitation through its extracellular secretion which makes extraction easy. CNF is also extracted from various marine filamentous algae. The percentage of CNF obtained from algal sources is less compared to plants and bacterial sources. CNF finds wide variety of applications such as drug carriers, tissue regenerating scaffolds, water purifying membranes, electrodes, supercapacitors, fluorescent probes and flexible electronics. In this review, various extraction techniques of CNF from different plant and bacterial sources are discussed critically with special emphasis on CNF based composites.