Helen Annal Therese

Design and development of Co3O4/NiO composite nanofibers for the application of highly sensitive and selective non-enzymatic glucose sensors

Cobaltosic oxide/nickel oxide (Co3O4/NiO) composite nanofibers were synthesized via an electrospinning technique and their electrocatalytic activities toward non-enzymatic glucose sensors were evaluated in detail. The Co3O4/NiO composite exhibited the homogeneously distributed nanofibers with high porosity, effective inter connectivity and an extended number of conducting channels with an average diameter of 160 nm. The diffraction patterns depicted the face centred cubic crystalline structure of Co3O4/NiO nanofibers and the purity of the composite nanofibers was further ensured by using FT-IR and UV-vis spectroscopic analyses. The electrocatalytic performances of prepared nanofibers toward the oxidation of glucose was determined by cyclic voltammetry and amperometry techniques and the experimental results showed that the Co3O4/NiO composite nanofibers exhibited a maximum electrooxidation toward glucose, owing to the synergistic effect of Co3O4 and NiO. The electrospun Co3O4/NiO nanofibers exhibited a detection limit of 0.17 μM, a wide linear range of 1 μM to 9.055 mM and a high sensitivity of 2477 μA mM−1 cm−2. The nanofibers have also exhibited favorable properties such as good selectivity, reproducibility, durability and real sample analysis, which ensured its potential applications in the clinical diagnosis of diabetes.

Morphology and phase tuning of α- and β-MnO2 nanocacti evolved at varying modes of acid count for their well-coordinated energy storage and visible-light-driven photocatalytic behaviour

A simple hydrothermal method is developed to synthesize two different phases, α and β of MnO2 nanocacti (comprising nanowires with 1–10 nm diameter self assembled by ultrathin sheets) as well as MnO2 nanorods (10–40 nm diameter) without any seed or template. Sudden addition of concentrated H2SO4 (0.3–0.4 μL) results in the formation of nanocacti while gradual addition (dropwise) of H2SO4 solution (0.3–0.4 M) results in nanorods. Besides, the α phase of MnO2 exists at relatively high acidic strength (4 pH) compared to the β phase, which is consistent at 5 pH. Thus this could be the first report exploring the possibilities of tuning morphology as well as the phase of MnO2 through simple optimizations in acidic content. We find that polymorphic MnO2 nanocacti exhibit superior photocatalytic activity and high energy capacity as an anode in Li-ion batteries than polymorphic MnO2 nanorods. The α phase of MnO2 performs better than the β phase. α-MnO2 nanocacti demonstrate high visible light driven photocatalytic activity by degrading >90% of congo red and methyl orange dyes in 40 mg L−1 organic dye aqueous solution with 0.1 g of the as-prepared sample within 25 and 70 min, respectively. We highlight the differences between the photocatalytic activities of different phases, α and β of MnO2 nanostructures, depending on the charge transport through different dimensions of the same pristine MnO2. The constant cycling stability of α-MnO2 nanocacti with capacities as low as 300 mA h g−1 at 1C rate after 50 cycles as an anode makes it a promising material for energy storage applications. We attribute the high electro- and photo-chemical activity for α-MnO2 nanocacti to their highly mesoporous structure making this one of the highest specific surface areas (271 m2 g−1) possibly ever reported for pristine MnO2.

Room temperature magnetoelectric coupling in Zn1−xCoxO/BaTiO3 bilayer system

We report on room temperature magnetoelectric coupling in Zn1−xCoxO/BaTiO3 (x = 0.02, 0.05, and 0.10) bilayer thinfilm multiferroic system (BLS) grown on SrTiO3 (100) substrate. All the BLSs exhibit room temperature ferroelectric response. The BLS with x = 0.02 is paramagnetic, while the BLS with x = 0.05 and 0.10 is weakly ferromagnetic. Increase in Co concentration of the BLS results in reduction of permittivity and electric polarization along with increase of coercive voltage, coercive field, and magnetic moment. The d33 value change from 23 pm/V to 30 pm/V with increase in external magnetic field from 1500 G to 2500 G for BLS with x = 0.05. This shows that Zn1−xCoxO/BaTiO3 is magnetoelectrically coupled at room temperature.

Electrospun CuO/NiO composite nanofibers for sensitive and selective non-enzymatic nitrite sensors

A non-enzymatic electrochemical sensor based on the use of nanofibrous CuO/NiO as a catalytic probe was developed for the effective sensing of nitrite. One dimensional and strongly interconnected nanofibers with uniformly developed ultrafine nanograins were observed for the CuO/NiO composite nanofibers. The monoclinic crystalline structure of the CuO nanofibers was preserved even after composite formation with NiO. The electrocatalytic activity of the prepared CuO/NiO nanofibers toward nitrite oxidation was investigated under neutral conditions. When utilized as a potent non-enzymatic sensor, the CuO/NiO nanofibers showed excellent amperometric performance, including a lower sensing limit, soaring sensitivity, and a broad linear array, respectively, of 0.5 μM, 282.72 μA mM−1 cm−2, and 0.001–5 mM. Furthermore, the remarkable selectivity and stability achieved for the as-fabricated sensors endorse its real sample analysis with human serum. Thus, these findings overcome the hurdles of existing non-enzymatic nitrite sensor probes and open up new possibilities in exploring an efficient and economical approach toward the development of electrochemical probes for nitrite detection.

Room temperature magnetoelectric coupling in BaTi1−xCrxO3 multiferroic thin films

We report on room temperature (RT) magnetoelectric coupling in tetragonal BaTi1−xCrxO3 thin film multiferroics (BTCO) sputter deposited on (100) SrTiO3 (where x = 0.005, 0.01, 0.02, and 0.03). As-deposited thin films are vacuum annealed by electron beam rapid thermal annealing technique. 50 nm thick BTCO with “x = 0.01” shows RT ferromagnetic and ferroelectric response with saturation magnetic moment of 1120 emu/cc and polarization of 14.7 microcoulomb/cm2. Piezoresponse/magnetic force microscope images shows RT magnetoelectric coupling in BTCO with “x = 0.01,” which is confirmed using magnetocapacitance measurement where an increase in capacitance from 17.5 pF to 18.4 pF is observed with an applied magnetic field.