Tamil Selvan Sakthivel

Untangling the biological effects of cerium oxide nanoparticles: the role of surface valence states

Cerium oxide nanoparticles (nanoceria; CNPs) have been found to have both pro-oxidant and anti-oxidant effects on different cell systems or organisms. In order to untangle the mechanisms which underlie the biological activity of nanoceria, we have studied the effect of five different CNPs on a model relevant aquatic microorganism. Neither shape, concentration, synthesis method, surface charge (ζ-potential), nor nominal size had any influence in the observed biological activity. The main driver of toxicity was found to be the percentage of surface content of Ce3+ sites: CNP1 (58%) and CNP5 (40%) were found to be toxic whereas CNP2 (28%), CNP3 (36%) and CNP4 (26%) were found to be non-toxic. The colloidal stability and redox chemistry of the most and least toxic CNPs, CNP1 and CNP2, respectively, were modified by incubation with iron and phosphate buffers. Blocking surface Ce3+ sites of the most toxic CNP, CNP1, with phosphate treatment reverted toxicity and stimulated growth. Colloidal destabilization with Fe treatment only increased toxicity of CNP1. The results of this study are relevant in the understanding of the main drivers of biological activity of nanoceria and to define global descriptors of engineered nanoparticles (ENPs) bioactivity which may be useful in safer-by-design strategies of nanomaterials.

Effect of amine-modified boron nitride (BN) on ammonium perchlorate decomposition

Solid propellant is an important material in space exploration. It is also used in the automobile and demolition industries as well as in ejection seats and airbags where precise control of burning rate is crucial. In the present work, a novel multiphase boron nitride (BN) material containing NH2 was synthesized and found to have a large impact on energetic materials. The reaction of the BN material with solid oxidizer ammonium perchlorate (AP) was characterized using DSC/TGA, SEM, XPS, and a high-pressure propellant strand burner. Primary amine groups on the BN material participates in a chemical reaction with the AP crystals causing a dramatic weight loss during low-temperature decomposition which is important for high-precision applications. While the burning rates of propellants containing 0.5% of the micron- and nano-sized BN materials increased by about 30% over the baseline formulation with no BN, similar propellants containing the synthesized BN material decreased the burning rate by as much 25%.

Facile nanoparticle dispersion detection in energetic composites by rare earth doped in metal oxide nanostructures

The segregation and agglomeration of nanoparticles dispersed in polymer matrices play important roles in nanocomposite performance. A method of rapid and simultaneous visualization of macroscopic and submicron particle dispersion properties is presented, based on nanoparticle luminescence induced by europium doping. The luminescence intensity of polymer composites containing Eu-doped TiO2 nanoparticle catalysts varied with the nanoparticle agglomerate size between 90 nm and 10 μm, and with concentration variations from segregation. These variations were detected by photoluminescence spectroscopy and visible-light photography, making this a facile characterization method for bulk composites without affecting the nanoparticle performance.

Synthesis and modification of mercapto-submicron scavenger for real-time extraction and preconcentration of As(III)

The gradual increase of arsenic in aquatic layers over the last decades has necessitated the early detection of low levels of arsenic on real time due to its hazardous impact on health. Here, the mercapto-submicron scavenger was synthesized and utilized for solid-phase dispersion extraction technique for real-time extraction and preconcentration of arsenite As(III). Because of particle size, they naturally dispersed without the need for any additional power. The formation of particles and the achievement of the modification of the particles were confirmed by SEM, TEM, size distributions, CHN analysis, FT-IR spectroscopy, micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), zeta potential, energy dispersive X-ray analysis and (EDX) and thermogravimetric analysis (TGA), which confirmed the formation of particles in the size of 253 ± 34 nm, the chemical implantation of the mercapto groups on the surface was successfully accomplished with a loading of 0.281 mmol g−1. The particles showed proper dispersion and stability in the aqueous phase before and after being associated with As(III). The chelating process between As(III) and mercapto groups was assessed by XPS which confirmed that the mercapto-submicron scavenger can sequestrate As(III) from water with maximum efficiency. Several factors that could optimize the process were assessed such as the effect of sorbent dose, pH, contact time, sample volumes, eluents, and matrix interference. The As(III) calibration curve showed a positive linear correlation in the range of 0–100 μg L−1 and coefficient of determination (r2 = 0.9981). Optimum recovery was obtained with an equilibrium time of 30 min at pH = 8.5. It was found that the release of As(III) from the mercapto-submicron scavenger was eluent dependent and the maximum recovery at the optimum conditions was 98 ± 3%. The average recovery of As(III) from three different ground water locations was 97.15%.