Karthikeyan Krishnamoorthy

Graphene oxide as a photocatalytic material

The photocatalytic characteristics of graphene oxide (GO) nanostructures synthesized by modified Hummer’s method were investigated by measuring reduction rate of resazurin (RZ) into resorufin (RF) as a function of UV irradiation time. The progress of the photocatalytic reaction was monitored by change in color from blue (RZ) into pink (RF) followed by absorption spectra. It exhibited excellent photocatalytic activity, leading to the reduction of RZ in UV irradiation. The fitting of absorbance maximum versus time suggests that the reduction of RZ follow the pseudo first-order reaction kinetics. These results indicate that GO have great potential for use as a photocatalyst.

Graphene nanosheets: Ultrasound assisted synthesis and characterization.

A facile sonochemical route for the synthesis of graphene nanosheets via reduction of graphene oxide (GO) has been reported. The synthesized graphene sheets are characterized using UV-vis spectra, Fourier transform infra-red (FT-IR) spectra, transmission electron microscope, X-ray photoelectron spectra (XPS) and Raman spectroscopic techniques. The UV-vis spectroscopy results showed that the absorption peak was red shifted due to the reduction of GO into graphene. FT-IR and XPS spectra revealed the removal of oxygenated functional groups in graphene after the reduction process. Raman spectra confirmed the restoration of new sp(2) carbon domains in graphene sheets after the reduction. The sonochemical approach for the synthesis of graphene nanosheets is relatively fast, cost-effective and efficient as compared to other methods.

Mechanistic investigation on the toxicity of MgO nanoparticles toward cancer cells

Magnesium oxide nanoparticles (MgO NPs) are increasingly recognized for their applications in cancer therapy such as nano-cryosurgery and hyperthermia. The present study investigated the cytotoxic effects of magnesium oxide nanoparticles (MgO NPs) against normal lung fibroblast cells and different types of cancerous cells. MgO NPs exhibited a preferential ability to kill cancerous cells such as HeLa, AGS and SNU-16 cells. A detailed study has been undertaken to investigate the mechanism of cell death occurring in cancer cells (AGS cells) by the analysis of morphological changes, western blot analysis and flow cytometry measurements. Western blot analysis measurements suggested the role of apoptosis in cell death due to MgO exposure. MgO NPs enhanced ultrasound-induced lipid peroxidation in the liposomal membrane. Flow cytometry measurements using H2DCFDA showed that the toxicity of MgO NPs is attributed to the generation of reactive oxygen species, which further results in the induction of apoptosis in cancer cells. Our experimental results suggested the potential utility of MgO NPs in the treatment of cancer.

Graphene oxide nanostructures modified multifunctional cotton fabrics

Surface modification of cotton fabrics using graphene oxide (GO) nanostructures was reported. Scanning electron microscopic (SEM) investigations revealed that the GO nanostructure was coated onto the cotton fabric. The molecular level interaction between the graphene oxide and the cotton fabric is studied in detail using the Fourier transform infra-red (FTIR) spectra. Thermogravimetric analysis (TGA) showed that GO loaded cotton fabrics have enhanced thermal stability compared to the bare cotton fabrics. The photocatalytic activity of the GO-coated cotton fabrics was investigated by measuring the photoreduction of resazurin (RZ) into resorufin (RF) under UV light irradiation. The antibacterial activity was evaluated against both Gram-negative and Gram-positive bacteria and the results indicated that the GO-coated cotton fabrics are more toxic towards the Gram-positive ones. Our results provide a way to develop graphene oxide-based devices for the biomedical applications for improving health care.

Electrochemical performance of an asymmetric supercapacitor based on graphene and cobalt molybdate electrodes

In this article, we report the fabrication and electrochemical performance of asymmetric supercapacitors (ASCs) based on a reduced graphene oxide (rGO) negative electrode and a cobalt molybdate (CoMoO4) positive electrode. The rGO and CoMoO4 electrode materials were synthesized by hydrothermal and sonochemical methods, respectively. Physico-chemical characterization techniques such as X-ray diffraction, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and nitrogen adsorption–desorption isotherm analysis were used to characterize the electrode materials. The rGO nanosheets and CoMoO4 nanostructures delivered a specific capacitance of about 168.8 and 98.34 F g−1, respectively measured in a three electrode system. The rGO‖CoMoO4 ASC device demonstrated a maximum specific capacitance of 26.16 F g−1 (at a current density of 0.5 mA cm−2), an energy density of 8.17 W h kg−1, and a maximum working voltage of 1.5 V. The fabricated device possessed excellent capacitance retention of about 85% after 4000 cycles (at a current density of 1.0 mA cm−2) suggesting the superior cyclic stability of the fabricated ASC device.

Surface activation of graphene oxide nanosheets by ultraviolet irradiation for highly efficient anti-bacterials

A comprehensive investigation of anti-bacterial properties of graphene oxide (GO) and ultraviolet (UV) irradiated GO nanosheets was carried out. Microscopic characterization revealed that the GO nanosheet-like structures had wavy features and wrinkles or thin grooves. Fundamental surface chemical states of GO nanosheets (before and after UV irradiation) were investigated using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Minimum inhibitory concentration (MIC) results revealed that UV irradiated GO nanosheets have more pronounced anti-bacterial behavior than GO nanosheets and standard antibiotic, kanamycin. The MIC of UV irradiated GO nanosheets was 0.125 μg ml⁻¹ for Escherichia coli and Salmonella typhimurium, 0.25 μg ml⁻¹ for Bacillus subtilis and 0.5 μg ml⁻¹ for Enterococcus faecalis, ensuring its potential as an anti-infective agent for controlling the growth of pathogenic bacteria. The minimum bactericidal concentration of normal GO nanosheets was determined to be two-fold higher than its corresponding MIC value, indicating promising bactericidal activity. The mechanism of anti-bacterial action was evaluated by measuring the enzymatic activity of β-D-galactosidase for the hydrolysis of o-nitrophenol-β-D-galactopyranoside.

Nanostructured molybdenum oxide-based antibacterial paint: effective growth inhibition of various pathogenic bacteria

The prevention of bacterial infections in the health care environment is paramount to providing better treatment. Covering a susceptible environment with an antimicrobial coating is a successful way to avoid bacterial growth. Research on the preparation of durable antimicrobial coatings is promising for both fundamental surface care and clinical care applications. Herein, we report a facile, efficient, and scalable preparation of MoO3 paint using a cost-effective ball-milling approach. The MoO3 nanoplates (synthesized by thermal decomposition of ammonium heptamolybdate) are used as a pigment and antibacterial activity moiety in alkyd resin binders and other suitable eco-friendly additives in the preparation of paint. Surface morphology, chemical states, bonding nature, and intermolecular interaction between the MoO3 and the alkyd resin were studied using Raman and x-ray photoelectron spectroscopic analysis. The antibacterial properties of a prepared MoO3 nanoplate against various bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Klebsiella pneumoniae) was determined using the microdilution method. Bacterial strains exposed to an MoO3 paint coated surface exhibit a significant loss of viability in a time-dependent manner. Fundamental modes of antibacterial activities ascribed from a biocompatible and durable MoO3 nanostructure incorporated into an alkyd resin complex are discussed. The obtained experimental findings suggest the potential utility of prepared MoO3-based paint coating for the prevention of health care associated infections.

Toxicity of Nano Molybdenum Trioxide toward Invasive Breast Cancer Cells

Current chemotherapy is limited by the nature of invasive cancer cells, which are similar to cancer stem cells. Nanomaterials provide a potential alternate mode of cancer therapy. This study investigated the cytotoxicity of molybdenum trioxide (MoO3) nanoplates toward invasive breast cancer iMCF-7 cells by analyzing morphological changes and performing Western blot and flow cytometry analyses. The findings suggested that MoO3 exposure induces apoptosis and generates reactive oxygen species (ROS) in iMCF-7 cells. This study revealed the potential utility of MoO3 for treating metastatic cancer cells, which might enable advancements in cancer therapy.

Titanium carbide sheet based high performance wire type solid state supercapacitors

Two dimensional sheets based on transition metal carbides have attracted much attention in electrochemical energy storage sectors. In this work, we demonstrated the fabrication and performance of titanium carbide based wire type supercapacitors (WSCs) towards next generation energy storage devices. The layered titanium carbide sheets were prepared via selective extraction of Al from the precursor Ti2AlC using hydrofluoric acid and are extensively characterized using X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy, Fourier transform-infrared spectroscopy, and laser Raman spectral analyses, respectively. The X-ray photoelectron spectroscopy studies confirmed the presence of oxygen and fluorinated functional groups attached on the surface of titanium carbide. The electrochemical studies of the fabricated titanium carbide WSC devices showed ideal capacitive properties with a specific length capacitance of 3.09 mF cm−1 (gravimetric capacitance of about 4.64 F g−1), and specific energy density of about 210 nW h cm−1 (in length) or 315 mW h kg−1 (in gravimetric) with excellent cycling stability. Further, a detailed examination of the capacitive and charge-transfer behavior of titanium carbide WSCs has been investigated via electrochemical impedance analysis using Nyquist and Bode plots. Additionally, we have also demonstrated the practical application of the titanium carbide WSCs, highlighting the path for their huge potential in energy storage and management sectors.

New function of molybdenum trioxide nanoplates: Toxicity towards pathogenic bacteria through membrane stress

Inorganic nanostructures are highly recognized for their potential use in the development of new functional materials for biomedical applications. In this study, we investigated the antibacterial efficiency of molybdenum trioxide (MoO3) nanoplates against four types of pathogenic bacteria. MoO3 nanoplates are synthesized by a simple wet chemical approach. X-ray diffraction and FT-IR analysis showed the presence of an orthorhombic phase of MoO3 nanoplates. Field emission scanning electron microscope studies confirmed the formation of plate-like structures of MoO3. The minimum inhibitory concentration (MIC) of MoO3 nanoplates against pathogenic bacteria was evaluated using a microdilution method. MICs such as 8μg/mL (against Escherichia coli and Salmonella typhimurium), 16μg/mL (against Enterococcus faecalis), and 8μg/mL (against Bacillus subtilis) show that MoO3 nanoplates have predominant antibacterial activity compared to the standard antibiotic, kanamycin. Evaluation of bacterial enzymatic (β-d-galactosidase) activity in the hydrolysis of o-nitrophenol and β-d-galactopyranoside suggested the disruption of the bacterial cell wall mechanism responsible for bacterial toxicity.