Subbiah Alwarappan

Facile and green synthesis of graphene

Herein, we report a simple, facile, green and cost effective strategy for the synthesis of graphene using naturally available anti-oxidants such as carotenoids present in vegetable (carrot, sweet potato, etc.) extracts. In this work, we have employed carrot extract to reduce graphene oxide to reduced graphene oxide. A red shift (in the λmax from 230 nm to 270 nm) during the course of the reduction of GO clearly indicates the effective restoration of the sp2 graphitic carbons. In addition, we have also noticed the colour change of the reaction mixture from yellowish brown to black after 1 hour, thereby indicating the reduction of GO to reduced graphene oxide (Ct-RGO). Further, an increase in the D/G ratio value of GO from 0.979 to 1.198 after the complete reduction indicated the effective restoration of the in plane sp2 domains in the Ct-RGO. The morphology and conductivities of the Ct-RGO are characterized by several characterization techniques such as UV, FT-IR, Raman, XRD, XPS, SEM, TEM, AFM and EIS. The green synthesis reported in this work is expected to yield a biocompatible graphene material suitable for futuristic biological applications.

A Single step electrochemical synthesis of luminescent WS2 quantum dots

Transition-metal dichalcogenide quantum dots (TMDQDs) with few layers are in the forefront of recent research on tailored 2D layered materials owing to their unique band structure. Such quantum dots (QDs) draw wide interest as potential candidates for components in optoelectronic devices. Although a few attempts towards single step synthesis of MoS2 QDs have been demonstrated, limited methods are available for WS2 QDs. Herein, we demonstrate a one-step electrochemical synthesis of luminescent WS2 QDs from their bulk material. This is achieved by a synergistic effect of perchlorate intercalation in non-aqueous electrolyte and the applied electric field. The average size of the WS2 QDs is 3u2005 ±1u2005nm (N=102) with few layers. The QDs show a higher photoluminescence (PL) quantum efficiency (5u2009%) and exhibit an excitation wavelength-dependent photoluminescence. This unprecedented electrochemical avenue offers a strategy to synthesize size tunable WS2 nanostructures, which have been systematically investigated by various characterization techniques such as transmission electron microscopy (TEM), photoluminescence and UV/Vis spectroscopies, and X-ray diffraction (XRD). Time-dependent TEM investigations revealed that time plays a vital role in this electrochemical transformation. This electrochemical transformation provides a facile method to obtain WS2 QDs from their bulk counterpart, which is expected to have a greater impact on the design and development of nanostructures derived from 2D materials.

Cerium doped nickel-oxide nanostructures for riboflavin biosensing and antibacterial applications

A sensitive electrochemical method for riboflavin (RF) detection based on Ce–NiO nanostructures was developed using a hydrothermal assisted chemical route. The created several oxygen vacancies on Ce doping are considered as the key factor for the magnificent electrocatalytic behavior of the Ce–NiO sample. The same oxygen vacancies also play an important role in antibacterial applications. Hence dual behavior of this Ce–NiO sample was investigated: (i) RF sensing was characterized by XRD, SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) using [Fe(CN)6]3−/4− and phosphate buffer solution (PBS) for probing the binding interaction between the Ce–NiO and RF. The Ce ions doped into the NiO nanostructure exhibit an excellent performance towards the detection of RF over a wide linear range from 1 mM to 50 nM, with a detection limit of 0.676 nM (3σ/b). (ii) Investigation of antibacterial activity using both Gram negative and positive bacterial strains. The minimal inhibitory concentration and minimal bactericidal concentration against B. Subtilis is found to be 10 μg ml−1. The diameter of the zone of inhibition for B. subtilis and S. aureus is quantified to be 22 and 18 mm respectively. Our results confirmed that Ce-doped NiO nanomaterial is a useful platform for electrocatalytic and biomedical applications.

Analysis of Moisture Content in Beetroot using Fourier Transform Infrared Spectroscopy and by Principal Component Analysis

The moisture content of beetroot varies during long-term cold storage. In this work, we propose a strategy to identify the moisture content and age of beetroot using principal component analysis coupled Fourier transform infrared spectroscopy (FTIR). Frequent FTIR measurements were recorded directly from the beetroot sample surface over a period of 34 days for analysing its moisture content employing attenuated total reflectance in the spectral ranges of 2614–4000 and 1465–1853 cm−1 with a spectral resolution of 8u2009cm−1. In order to estimate the transmittance peak height (Tp) and area under the transmittance curve

The Effect of Low Energy Nitrogen Ion Implantation on Graphene Nanosheets

({int }_{{bar{nu }}_{i}}^{{bar{nu }}_{f}}{T}_{p}dbar{nu })

Strategic Applications of Nanomaterials as Sensing Platforms and Signal Amplification Markers at Electrochemical Immunosensors

(∫ν¯iν¯fTpdν¯) over the spectral ranges of 2614–4000 and 1465–1853 cm−1, Gaussian curve fitting algorithm was performed on FTIR data. Principal component and nonlinear regression analyses were utilized for FTIR data analysis. Score plot over the ranges of 2614–4000 and 1465–1853 cm−1 allowed beetroot quality discrimination. Beetroot quality predictive models were developed by employing biphasic dose response function. Validation experiment results confirmed that the accuracy of the beetroot quality predictive model reached 97.5%. This research work proves that FTIR spectroscopy in combination with principal component analysis and beetroot quality predictive models could serve as an effective tool for discriminating moisture content in fresh, half and completely spoiled stages of beetroot samples and for providing status alerts.

Ionic liquid modified N-doped graphene as a potential platform for the electrochemical discrimination of DNA sequences

In this work, we report the adsorption kinetics of electrochemically synthesized WS2 quantum dots (QDs) (ca. 3 nm) onto a polycrystalline gold electrode. The Langmuir adsorption isotherm approach was employed to explore the temperature and adsorbate concentration dependence of the experimentally calculated equilibrium constant of adsorption ( Keq) and the free energy for adsorption (Δ Gads). Subsequently, we extract other thermodynamic parameters, such as adsorption rate constant ( Kads), desorption rate constant ( Kd), the enthalpy of adsorption (Δ Hads), and the entropy of adsorption (Δ Sads). Our findings indicate that Δ Gads is temperature-dependent and ca. -7.64 ± 0.6 kJ/mol, Δ Hads = -43.72 ± 1.7 kJ/mol, and Δ Sads = -0.126 ± 0.017 kJ/(mol K). These investigations on the contribution of the enthalpic and entropic forces to the total free energy of this system underscore the role of entropic forces on the stability of the WS2 QDs monolayer and provide new thermodynamic insights into other transition-metal dichalcogenide quantum dot (TMDQD) monolayers as well.

Nickel-Incorporated, Nitrogen-Doped Graphene Nanoribbons as Efficient Electrocatalysts for Oxygen Evolution Reaction

Herein, we report the effect 50xa0keV nitrogen ion implantation at varying fluence on the optical properties of graphene nanosheets (number of layers <u20095). Initially, graphene nanosheets synthesized by the direct liquid exfoliation of graphite layers were deposited on a cleaned Si-substrate by drop cast method. These graphene nanosheets are implanted with 50xa0keV nitrogen-ion beam at six different fluences. Raman spectroscopic results show that the D, D′ and G peak get broadened up to the nitrogen ion fluence of 1u2009×u20091015xa0ions/cm2, while 2D peak of graphene nanosheets disappeared for nitrogen-ions have fluence more than 1014xa0ions/cm2. However, further increase of fluence causes the indistinguishable superimposition of D, D′ and G peaks. Surface contact potential value analysis for ion implanted graphene nanosheets shows the increase in defect concentration from 1.15xa0×xa01012 to 1.98xa0×xa01014xa0defects/cm2 with increasing the nitrogen ion fluence, which resembles the Fermi level shift towards conduction band. XRD spectra confirmed that the crystallinity of graphene nanosheets was found to tamper with increasing fluence. These results revealed that the limit of nitrogen ion implantation resistant on the vibrational behaviors for graphene nanosheets was 1015xa0ions/cm2 that opens up the scope of application of graphene nanosheets in device fabrication for ion-active environment and space applications.Graphical Abstract