Ramasamy Thangavelu Rajendra Kumar

In vitro bacterial cytotoxicity of CNTs: reactive oxygen species mediate cell damage edges over direct physical puncturing.

Understanding the bacterial cytotoxicity of CNTs is important for a wide variety of applications in the biomedical, environmental, and health sectors. A majority of the earlier reports attributed the bactericidal cytotoxicity of CNTs to bacterial cell membrane damage by direct physical puncturing. Our results reveal that bacterial cell death via bacterial cell membrane damage is induced by reactive oxygen species (ROS) produced from CNTs and is not due to direct physical puncturing by CNTs. To understand the actual mechanism of bacterial killing, we elucidated the bacterial cytotoxicity of SWCNTs and MWCNTs against Gram-negative human pathogenic bacterial species Escherichia coli, Shigella sonnei, Klebsiella pneumoniae, and Pseudomonas aeruginosa and its amelioration upon functionalizing the CNTs with antioxidant tannic acid (TA). Interestingly, the bacterial cells treated with CNTs exhibited severe cell damage under laboratory (ambient) and sunlight irradiation conditions. However, CNTs showed no cytotoxicity to the bacterial cells when incubated in the dark. The quantitative assessments carried out by us made it explicit that CNTs are effective generators of ROS such as (1)O2, O2(•-), and (•)OH in an aqueous medium under both ambient and sunlight-irradiated conditions. Both naked and TA-functionalized CNTs showed negligible ROS production in the dark. Furthermore, strong correlations were obtained between ROS produced by CNTs and the bacterial cell mortality (with the correlation coefficient varying between 0.7618 and 0.9891) for all four tested pathogens. The absence of bactericidal cytotoxicity in both naked and functionalized CNTs in the dark reveals that the presence of ROS is the major factor responsible for the bactericidal action compared to direct physical puncturing. This understanding of the bactericidal activity of the irradiated CNTs, mediated through the generation of ROS, could be interesting for novel applications such as regulated ROS delivery in cancer therapy and the sanitation of potable water supplies.

Effects of the crystallite mosaic spread on integrated peak intensities in 2θ–ω measurements of highly crystallographically textured ZnO thin films

We report x-ray diffraction (XRD) (2θ–ω and rocking curve) and transmission electron microscopy (TEM) measurements on crystallographically textured ZnO thin films of varying thicknesses and crystallite mosaic spread deposited by pulsed-laser deposition on Si. The integrated areas of the (0u20090u20090u20092) ZnO reflections in the 2θ–ω mode do not scale with film thickness and in some cases show discrepancies of two orders of magnitude compared with expectations based solely on sample thicknesses. Intensity differences of this type are regularly used in the literature as indications of differences in sample crystallinity or crystal quality. However TEM data of our samples show no evidence of amorphous deposits or significantly varying crystal quality in different films. X-ray rocking curves of these samples do show substantial variations in the mosaic spread of crystallites in the ZnO films which are the origin of the differences in integrated areas of the (0u20090u20090u20092) ZnO reflections in 2θ–ω measurements. We outline a generally applicable model to treat the 2θ–ω mode peak intensities which shows good agreement with the experimental data (to within an order of magnitude) and which is much simpler than utilizing a full reciprocal space map approach to understand the XRD data. We conclude that the normalized integrated intensity of the (0u20090u20090u20092) ZnO reflection in highly crystallographically textured ZnO thin films is strongly dependent on the rocking curve width in addition to the film thickness and the use of such intensities in isolation as measures of the thin film crystallinity or crystal quality, without reference to the rocking curve width, is likely to be misleading when making judgments of such aspects of the thin film structure.

Engineering Silicon to Porous Silicon and Silicon Nanowires by Metal-Assisted Chemical Etching: Role of Ag Size and Electron-Scavenging Rate on Morphology Control and Mechanism

We demonstrate controlled fabrication of porous Si (PS) and vertically aligned silicon nanowires array starting from bulk silicon wafer by simple chemical etching method, and the underlying mechanism of nanostructure formation is presented. Silicon-oxidation rate and the electron-scavenging rate from metal catalysis play a vital role in determining the morphology of Si nanostructures. The size of Ag catalyst is found to influence the Si oxidation rate. Tunable morphologies from irregular porous to regular nanowire structure could be tailored by controlling the size of Ag nanoparticles and H2O2 concentration. Ag nanoparticles of size around 30 nm resulted in irregular porous structures, whereas discontinuous Ag film yielded nanowire structures. The depth of the porous Si structures and the aspect ratio of Si nanowires depend on H2O2 concentration. For a fixed etching time, the depth of the porous structures increases on increasing the H2O2 concentration. By varying the H2O2 concentration, the surface porosity and aspect ratio of the nanowires were controlled. Controlling the Ag catalyst size critically affects the morphology of the etched Si nanostructures. H2O2 concentration decides the degree of porosity of porous silicon, dimensions and surface porosity of silicon nanowires, and etch depth. The mechanisms of the size- and H2O2-concentration-dependent dissociation of Ag and the formation of porous silicon and silicon nanowire are described in detail.

Influence of Fe3O4 nanoparticles decoration on dye adsorption and magnetic separation properties of Fe3O4/rGO nanocomposites

ABSTRACT Magnetite (Fe3O4) nanoparticles were prepared by solvothermal method and its composites with reduced graphene oxide namely FG1, FG2, and FG3 (changing magnetite precursor loading 0.1, 0.5, and 1 respectively) were used as adsorbents for the removal of methyl violet (MV) dye. The structural and morphological results confirm that rGO sheets were decorated with Fe3O4 and it ensures the variation of active sites toward dye removal property. The maximum adsorption capacity obtained for FG2 was 196 mg/g. The adsorption isotherms and kinetics better fit Langmuir and pseudo-second-order kinetic model for FG1 and FG2. Increasing of Fe3O4 loading on rGO reduces the dye adsorption sites and too low Fe3O4 loading affects the magnetic separation. The optimal loading of Fe3O4 on rGO is important parameter for the adsorption process and fast separation of adsorbent.

Polyaniline Anchored MWCNTs on Fabric for High Performance Wearable Ammonia Sensor

Polyaniline (PANI) functionalized multiwall carbon nanotubes (MWCNTs) were prepared via in situ chemical polymerization process of aniline, in which MWCNTs were spray coated on the fabric for wearable ammonia sensor. Structural, morphological, thermal properties and wettability were analyzed by scanning electron microscope, X-ray diffraction, Raman analysis and contact angle measurement. No substantial change in base resistance of MWCNTs/PANI fabric sensor was observed for a wide range of bending (from 90° to 270°) shows excellent wearability. The sensors were exposed to 20-100 ppm ammonia vapor at room temperature. It was observed that the sensing response of PANI coated MWCNTs was enhanced than MWCNTs and PANI. The sensor has the capability to detect ammonia with high sensitivity (92% for100 ppm), excellent selectivity quick response (9 s), and recovery time (30 s). The lower detection limit (LOD) for the MWCNTs/PANI fabric sensor was found to be 200 ppb. The influence of humidity on sensing parameters was studied. Sensing response and resistance of sensor have shown excellent stability after one month. We observed that PANI have a dual role in enhancing flexibility as well as improve the sensor performance toward ammonia. The results reveal the potential application of fabric based sensor for monitoring NH3 gas under ambient conditions.

In situ attachment and its hydrophobicity of size- and shape-controlled silver nanoparticles on fabric surface for bioapplication

ABSTRACT In situ synthesis of size- and shape-controlled silver nanoparticles (AgNPs) on fabrics was evaluated with structural and morphological characterization (scanning electron microscope, X-ray diffraction, and energy-dispersive spectroscope (EDS)). At lower concentration of NaBH4 (0.5 mM) with preferred AgNO3 (1 mM) mixtures shows uniform distribution of AgNPs on cotton fabrics. The attachment of smaller sized and discrete AgNPs on fabrics shows good antibacterial action on comparison with other aggregated and larger sized AgNPs when tested in Shigella sonnei and Bacillus subtilis species. Higher bactericidal action and relative change in hydrophobic nature (water contact angle >110°) of treated fabrics explained by decrease in surface free energy could have self-cleaning biomedical applications.

One-Step Pyrolytic Synthesis of Multiwalled Carbon Nanotubes: The Role of Resupply of Carbon Species on the Quality Control

An investigation on varying experimental parameters such as solution quantity (2.5, 5 and 7.5 mL) and reaction time (15, 30, 45 and 60 min) was carried out for the production of high-quality multiwalled carbon nanotubes (MWCNTs) in one step pyrolysis. Structural analysis revealed the uniform diameter distribution and the length of nanotubes in the range of 60-80 nm and 0.4-2 μm, respectively. Raman and X-ray diffraction analysis showed a remarkable reduction in defect density with increase in graphitization degree, upon increasing the solution volume and reaction time. MWCNTs prepared at higher solution quantity (7.5 mL) with higher reaction time (60 min) showed higher crystallinity (70% graphitization) and lower defect density (ID/IG: 0.56). The attainment in equilibrium of evaporation cum precipitation in formation of high quality nanotubes structure is evaluated. An effective resupplying of condensed precursors by re-evaporation leads for the achievement of low defect density nanotubes with higher product yield is achieved.

Impact of Oxygen Functional Groups on Reduced Graphene Oxide-Based Sensors for Ammonia and Toluene Detection at Room Temperature

The chemically reduced graphene oxide (rGO) was prepared by the reduction of graphene oxide by hydrazine hydrate. By varying the reduction time (10 min, 1 h, and 15 h), oxygen functional groups on rGO were tremendously controlled and they were named RG1, RG2, and RG3, respectively. Here, we investigate the impact of oxygen functional groups on the detection of ammonia and toluene at room temperature. Their effect on sensing mechanism was analyzed by first-principles calculation-based density functional theory. The sensing material was fabricated, and the effect of reduction time shown improved the recovery of ammonia and toluene sensing at room temperature. Structural, morphological, and electrical characterizations were performed on both RG1 and RG3. The sensor response toward toluene vapor of 300 ppm was found to vary 4.4, 2.5, and 3.8% for RG1, RG2, and RG3, respectively. Though RG1 shows higher sensing response with poor recovery, RG3 exhibited complete desorption of toluene after the sensing process with response and recovery times of approximately 40 and 75 s, respectively. The complete recovery of toluene molecules on RG3 is due to the generation of new sites after the reduction of oxygen functionalities on its surface. It could be suggested that these sites provided anchor to ammonia and toluene molecules and good recovery under N2 purge. Both theoretical and experimental studies revealed that tuning the oxygen functional groups on rGO could play a vital role in the detection of volatile organic compounds (VOCs) on rGO sheets and was discussed in detail. This study could provoke knowledge about rGO-based sensor dependency with oxygen functional groups and shed light on effective monitoring of VOCs under ambient conditions for air quality monitoring applications.

One step 'dip' and 'use' Ag nanostructured thin films for ultrahigh sensitive SERS Detection.

A simple one step galvanic displacement method which involves dipping of the silicon substrate in the AgNO3/HF solution and using it for SERS application without any further process is demonstrated. The size and shape of the Ag nanoparticles changes as the deposition time is increased. Initially the shape of the particles was nearly spherical and as it grows, becomes oblong and then coalesce to form a discontinuous film with vertically grown hierarchical Ag nanostructures. The sizes of the deposited particles were in the ranges from 30nm to a discontinuous film. It also demonstrated a highly sensitive chemical detection by surface-enhanced Raman scattering of rhodamine 6G dye, down to 10(-16)M concentration. Prepared samples were able to detect lower concentrations of Melamine. Discontinuous thin films with hierarchical Ag nanostructures were obtained for 5min Ag deposition. The formation of Hot spots between the discontinuous islands and also along the hierarchical structures is responsible for the high SERS enhancement. This simple one step, fast, non-lithographic and cost effective method can be applied for various label free detection of analytes of importance.