Sundara Ramaprabhu

The most crucial part of the hydrogen economy is the development of a hydrogen storage material which will be cost effective and its hydrogen storage capacity meets US DOE target. This study is an attempt to develop an efficient hydrogen storage material from a simple, one step synthesis technique. Herein, we synthesize metal nanoparticles encapsulated (M = Co, Fe, Fe3C) nitrogen doped carbon nanotubes (M/NCNT) for the efficient hydrogen adsorption within temperature range of 25°C to 100°C and at pressures 5 to 18 bar. The phase, morphology, surface area, and composition of the encapsulated metal nanoparticles NCNT were confirmed by different characterization techniques. Fe/NCNT is observed to have the highest hydrogen storage capacity of 3.3 wt% at room temperature, ~16 bar pressure, and the highest isosteric heat of adsorption (Qst) of 13 kJmol−1, among all. B,N-CNTs reported 0.35 wt% hydrogen storage capacity at ~16 bar H2 equilibrium pressure and room temperature. The large surface area, defects produced on the CNT due to N doping as well as the presence of metal nanoparticles both inside, on the CNTs which results in the spillover mechanism for the dissociation of the hydrogen molecules into atoms and its diffusion through carbon layers within the CNT, are the factors that contribute to the enhancement of hydrogen storage capacity in M/NCNT.

Here, a rapid synthesis method for growing template-free three-dimensional hexagonal zinc oxide (ZnO) micro-rods (HZMR) using a pulsed-microwave (p-MW) irradiation technique is reported. The effects of microwave exposure time and power are shown to tune the morphology of hexagonal rods from solid to blind hole to hollow rods. X-ray diffraction (XRD) confirmed the growth of pure ZnO phase. Morphological investigations by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM), optical properties by micro-Raman, Diffuse Reflectance Spectroscopy (DRS), Attenuated Total Reflectance (ATR) and Photoluminescence (PL) spectroscopy techniques were carried out. The PL studies reveal a dominant red emission along with characteristic blue and green emissions. The resulting structures have the scope of being applied as miniature sensors or in lasing applications. The blind-holed structures can be used as miniature crucibles/pots in reactions. This template-free growth of hexagonal rods is a very simple and economical technique that can result in solid, hollow or one-end blind hexagonal rods. The paper discusses the growth mechanism of these unique hierarchical HZMR.

The emergence of vegetable oil as a promising alternative lubricant in the tribological application space has fueled research for making these oils as useful as mineral oils. Tribological modification of vegetable oil by the addition of TiO2/gC3N4 nanocomposite (as a nanoadditive) was studied here. The dispersion of the nanoadditive in the vegetable oil showed good oil dispersion stability without the addition of any surfactant. The tribological studies were conducted in a four-ball tester using ASTM standard D5183. In addition, the effect of temperature on tribological performance was also studied to understand the oxidation behavior of vegetable oil. The results showed a significant improvement in friction and wear properties of the optimized nano-oil. The mechanism behind the improvement in friction and wear properties is annotated in this paper.

Crosslinked Polyvinyl alcohol (PVA) membranes with sulfonated CNT (SCNT) fillers were synthesized using solution casting method for proton exchange membrane fuel cells (PEMFC). Sulfonated CNTs are reported to be one of the best additives in ionic membranes as they increase the ionic conductivity and mechanical strength of the membrane. CNTs are high aspect ratio carbon allotropes, and small quantities of SCNTs (0.01 wt%, 0.1 wt%, 0.5 wt%, and 1 wt%) are observed to make a significant difference in properties of membranes. These membranes were characterized for water uptake capacity, ion exchange capacity, and mechanical strength. Ionic conductivity, hydrogen pumping, polarization studies, and gas crossover studies were performed in situ under various conditions of humidity. PVA-SSA-0.1 wt% SCNT showed the maximum power density among all compositions tested while short term performance of PVA-SSA-0.5 wt% SCNT exhibited the least sensitivity to changes in reactant humidity. Nafion® 115 produced 0.33 W cm-2 at 0.4 V while PVA-SSA-0.1 wt% SCNT exhibited 0.21 W cm-2 at 0.4 V. Overpotential associated with the purity of hydrogen gas was accounted for in the polarization curve and it resulted in a distinctly improved power density of 0.4 W cm-2. Performance of PVA-SSA-SCNT membranes was compared with Nafion® 115 by various characterization techniques and the results indicate that the membranes developed are a cost-effective alternative to Nafion® with the best performing PVA-SSA-SCNT membrane costing ≈1% of the cost of the Nafion® 115 membrane for similar performance.

Vitamin D deficiency in the body is a worldwide health concern with major consequences on bone health. It is also related to cardiovascular diseases, depression, infectious diseases, autoimmune disorders, cancer, and recently even to COVID-19. In the present work, we have developed a silver-silver oxide nanoparticles-decorated carbon nanotube-modified glassy carbon electrode (AgCNT/GCE) based sensor for antibody-free, nanomolar detection of 25-hydroxyvitamin D (25OHD). The impedimetric technique was utilized to achieve high sensitivity. The sensor exhibited a linear response in the range of 20-100 nM. A remarkably low limit of detection of 7.9 nM was observed, which is lower than the deficiency level defined at 30 nM for human serum. The sensor exhibited excellent response stability, repeatability, reproducibility, and minimal interference. Excellent recovery of 1/4102% was also observed in real serum samples. The sensing mechanism and the AgCNT-25OHD interaction have also been explored by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), Fourier Transform Infrared (FTIR) spectroscopy, and UV-vis spectroscopy.

The incorporation of heteroatoms and defects in carbonaceous material is a well-known approach to improve the electrochemical performance of the anode in a sodium-ion battery (NIB). However, previous works aimed to use either heteroatom-doped or defect-enriched carbon material. The present work focuses on nitrogen-doped, defect-induced surface-modified carbon nanotubes (MN-BCNT) having the synergy of both the effects to improve the electrochemical performance of the NIB. Initially, in situ nitrogen-doped CNTs were grown using a scalable, cost-effective and green synthesis technique. In situ nitrogen doping introduces lattice defects resulting in bamboo-shaped CNTs. The defects were further enriched by opening the ends of the tubes and also by shortening them. This structure demonstrates the high capacity of 278 mA h g-1 at a current density of 50 mA g-1, which is more than double compared to conventional CNTs. The improved performance of MN-BCNT is attributed to the improved electrical conductivity due to nitrogen doping and the availability of significant active sites as a result of tube shortening. Moreover, the designed structure shows good cyclic stability at 200 mA g-1 accompanied with excellent rate capability.

1,4-Dioxane is a carcinogenic, non-biodegradable, organic water pollutant which is used as a solvent in various industries. It is also formed as an undesired by-product in the cosmetic and pharmaceutical industry. Given its carcinogenicity and ability to pollute, it is desirable to develop a sensitive and selective sensor to detect it in drinking water and other water bodies. Current works on this sensor are very few and involve complex metal oxide composite systems. A sensitive electrochemical sensor for 1,4-dioxane was developed by modifying a glassy carbon electrode (GCE) with a reduced graphene oxide-curcumin (rGO-CM) nanocomposite synthesized by a simple solution approach. The prepared rGO-CM was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and Scanning Electron Microscopy (SEM). The rGO-CM/GCE sensor was employed for the detection of 1,4-dioxane in the range of 0.1-100 μM. Although, the detection range is narrower compared to reported literature, the sensitivity obtained for the proposed sensor is far superior. Moreover, the limit of detection (0.13 μM) is lower than the dioxane detection target defined by the World Health Organization (0.56 μM). The proposed rGO-CM/GCE also showed excellent stability and good recovery values in real sample (tap water and drinking water) analysis.

The reaction of magnesium diboride with water results in an intermediate borohydride product which leads to the simultaneous reduction of graphitic oxide (GO) and the formation of magnesium hydroxide. In this work, the thermo-optical properties of magnesium diboride modified reduced graphene oxide–based nanofluids have been explored. The study primarily focuses on the reaction mechanism of magnesium diboride and GO by using liquid exfoliation technique. Suspension after liquid exfoliation mainly consisted of a turbid supernatant and precipitate which was composed of boron-based nanosheets (CBNs) and a composite of magnesium hydroxide and reduced graphene oxide (CBNs-rGO), respectively. Nanofluids were subsequently formulated from the obtained products of the reaction. CBNs form a stable suspension in water and ethylene glycol because of its attached borohydrides and hydroxyl hydrophilic sites. CBNs nanofluids show good thermal conductivity with poor light absorption properties in the visible wavelength range. Whereas, CBNs-rGO nanofluids show ~95% attenuation in the radiation with a significant enhancement of ~30% and 20% in thermal conductivity as compared with Deionized water– and ethylene glycol–based fluids, respectively.

TiO2 nanoparticles decorated nitrogen (N) doped helical carbon nanofiber (CNF)-carbon nanotube (CNT) hybrid material is prepared by low-cost electrospinning technique followed by hydrothermal method. Morphological investigations establish helical structure of CNFs with hierarchical growth of CNTs around CNFs. The hybrid material shows a high specific surface area of 295.17 m2 g−1 with nanoporous structure. X-ray photoelectron spectroscopic studies establish Ti–O–C/Ti–C bond mediated charge transfer channel between TiO2 nanoparticles and carbon structures with the success of N doping in CNFs. The electrospun hybrid material delivered high reversible charge capacities of 316 mAh g−1 (100th cycle) and 244 mAh g−1 (100th cycle) at a current density of 75 mA g−1 and 186 mA g−1 respectively. The charge capacities obtained for different applied current densities are higher than the conventional graphitic microporous microbeads anode. Results indicate that the hybrid material reported here shows high performance compare to graphite for LIBs.

Here, we report the growth of improved quality graphene thin film by a modified method using shellac as a low-cost and eco-friendly carbon source on three different substrates. We chose stainless steel (SS 316) plates used as a solid surface, nickel foam (NiF) representative of a solid porous substrate, and carbon fiber fabric (CFF) as a porous-flexible substrate. The graphene characteristic is found to be substrate-dependent in this single-step method. Uniform multilayer graphene is grown on SS316. In the case of Ni foam, the as-synthesized graphene exhibits high quality with relatively low defects. It was troublesome to grow uniform graphene on flexible CFF due to the low wettability of precursor solution. The substrate was required to modify with a thin (∼60 nm) layer of Ni deposition. The transfer-free method of graphene on CFF was assured by etching Ni via an acid treatment. Graphene coated SS316 used as bipolar plate exhibits superior corrosion resistance with corrosion current density Icorr ∼1.2 μA/cm2 and much lower interfacial contact resistance ICR ∼7.7 mΩ cm2. Graphene coated Ni foam was utilized as electrodes in supercapacitors which show large areal capacitance ∼1.7 F/cm2. Besides, graphene coated CFF shows sheet resistance ∼50% lower than that of uncoated CFF.