Photoinduced Electron Spin Resonance Phenomenon in α

The photoinduced phenomenon in α-Cr2O3 nanoscaled spherical particles was investigated in the temperature range of 150 up to 315 K. An X-band electron-spin resonance spectrometry was employed to probe the magnetic behavior in α-Cr2O3 under an IR illumination in the nanosecond regime. The photoinduced effect on both low and high field ESR signals appears above 280 K and is remarkably enhanced just below Néel temperature TN. Such a photoinduced ESR phenomenon disappears in a reproducible way in the paramagnetic insulating state which occurs above TN of crystalline α-Cr2O3. In the antiferromagnetic phase, that is, below TN, the shift of the low field absorption could be attributed to the interaction of the light with specific Cr3+ ions located in strongly distorted sites correlated to strong ligand-field effect

Laser fabrication of Cu nanoparticles based nanofluid with enhanced thermal conductivity: Experimental and molecular dynamics studies

Nanofluids are engineered colloidal suspensions of solid nanoparticles in aqueous and non-aqueous base fluids with enhanced thermo-physical characteristics compared to conventional heat transfer fluids (HTFs). In this study, we report on the fabrication of copper nanoparticles-ethylene glycol (CuNPs-EG) nanofluid by using a simple one-step pulsed Nd:YAG laser ablation method to ablate the surface of a pure copper target in EG base fluid under ambient conditions. Structural and morphological analysis confirmed the fabrication of pure spherical shaped CuNPs with average diameter of ~7 nm. Thermal conductivity (k) investigations of CuNPs-EG nanofluid were conducted by using a computational approach where Equilibrium Molecular Dynamics (EMD) simulations integrated with Green-Kubo (EMD-GK) method was used. The obtained EMD-GK results for k were confirmed experimentally through a guarded hot-plate technique within the temperature ranges of 298–318 K. Interestingly, a relative enhancement (η) in the percentage of thermal conductivity of CuNPs-EG nanofluids obtained after an ablation time ta = 5 min was 15% at 318 K, while sample obtained after ta = 30 min showed an enhancement of ~24% in thermal conductivity. These obtained results confirmed the suitability of using a laser based ablation method to fabricate highly efficient nanofluids which could be used as alternatives for conventional HTFs in various heat transfer applications

Physical origin of third order non-linear optical response of porphyrin nanorods

The non-linear optical properties of porphyrin nanorods were studied using Z-scan, Second and Third harmonic generation techniques. We investigated in details the heteroaggregate behaviour formation of [H4TPPS4](2-) and [SnTPyP](2+) mixture by means of the UV-VIS spectroscopy and aggregates structure and morphology by transmission electron microscopy. The porphyrin nanorods under investigation were synthesized by self assembly and molecular recognition method. They have been optimized in view of future application in the construction of the light harvesting system. The focus of this study was geared towards understanding the influence of the type of solvent used on these porphyrins nanorods using spectroscopic and microscopic techniques

Remarkable thermal conductivity enhancement in Ag—decorated graphene nanocomposites based nanofluid by laser liquid solid interaction in ethylene glycol

We report on the synthesis and enhanced thermal conductivity of stable Ag-decorated 2-D graphene nanocomposite in ethylene glycol based nanofluid by laser liquid solid interaction. A surfactant free nanofluid of Ag nanoparticles anchored onto the 2-D graphene sheets were synthesized using a two-step laser liquid solid interaction approach. In order to understand a pulsed Nd:YAG laser at the fundamental frequency (λ = 1,064 nm) to ablate Ag and graphite composite target submerged in ethylene glycol (EG) to form AgNPs decorated 2-D GNs-EG based nanofluid. From a heat transfer point of view, it was observed that the thermal conductivity of this stable Ag-graphene/EG is significantly enhanced by a factor of about 32.3%; this is highest reported value for a graphene based nanofluid

Pulsed laser deposited Cr2O3 nanostructured thin film on graphene as anode material for lithium-ion batteries

Pulsed laser deposition technique was used to deposit Cr2O3 nanostructured thin film on a chemical vapour deposited few-layer graphene (FLG) on nickel (Ni) substrate for application as anode material for lithium-ion batteries. The experimental results show that graphene can effectively enhance the electrochemical property of Cr2O3. For Cr2O3 thin film deposited on Ni (Cr2O3/Ni), a discharge capacity of 747.8 mA h g-1 can be delivered during the first lithiation process. After growing Cr2O3 thin film on FLG/Ni, the initial discharge capacity of Cr2O3/FLG/Ni was improved to 1234.5 mA h g-1. The reversible lithium storage capacity of the as-grown material is 692.2 mA h g-1 after 100 cycles, which is much higher than that of Cr2O3/Ni (111.3 mA h g-1). This study reveals the differences between the two material systems and emphasizes the role of the graphene layers in improving the electrochemical stability of the Cr2O3 nanostructured thin film.This work was sponsored within the framework of the UNESCO UNISA Africa Chair in Nanosciences & Nanotechnology and the Nanosciences African Network (NANOAFNET) by the National Research Foundation of South Africa, the African Laser Centre (ALC), the University of South Arica (UNISA) in collaboration with the Vice-Chancellor of the University of Pretoria, the National Research Foundation (NRF) of South Africa, iThemba LABS and the Abdus Salam ICTP-Trieste, Italy.http://www.elsevier.com/locate/jalcom2016-07-31hb2016Physic

From Khoi-San indigenous knowledge to bioengineered CeO2 nanocrystals to exceptional UV-blocking green nanocosmetics

Single phase CeO2 nanocrystals were bio-synthesized using Hoodia gordonii natural extract as an effective chelating agent. The nanocrystals with an average diameter of 〈Ø〉 ~ 5–26 nm with 4+ electronic valence of Ce displayed a remarkable UV selectivity and an exceptional photostability. The diffuse reflectivity profile of such CeO2 exhibited a unique UV selectivity, in a form of a Heaviside function-like type profile in the solar spectrum. While the UV reflectivity is significantly low; within the range of 0.7%, it reaches 63% in the VIS and NIR. Their relative Reactive Oxygen Species (ROS) production was found to be < 1 within a wide range of concentration (0.5–1000 μg/ml). This exceptional photostability conjugated to a sound UV selectivity opens a potential horizon to a novel family of green nano-cosmetics by green nano-processing

Effect of substrate temperature on the structure and the metal insulator transition in pulsed laser deposed V02\ films on soda lime glass

In this paper, we report the effect of soda lime substrate deposition temperature (Ts) on the crystal structure and the metal insulator transition of VO2 thin films. Samples were deposited at substrate deposition temperature ranging from 450 to 600 0C by pulsed-laser deposition and characterized by x-ray diffraction and UV-VIS spectrophotometer. At a substrate temperature of 550°C, the VO2 (100) reflection dominate the spectrum showing a change in crystalline grains orientation. The highest transition temperatures of 74 oC with the lowest hysteresis width of 11 oC were obtained on the same sample grown at a substrate deposition temperature of 500 oC and also corresponding to the largest grains size of a value of 350 nm.http://link.springer.com/journal/125962016-03-31hb201

Synthesis and characterization of porphyrin nanotubes/rods for solar radiation harvesting and solar cells

Energy transfer and electron transfer events as they occur between well arranged light harvesting antenna molecules, the reaction center and other factors determine the function of natural photosynthesis. The overall small reorganization energy and the well-balanced electronic coupling between each component bear key characters for the unique efficiency of natural photosynthesis. Such aspects permit the design and assembly of artificial systems that efficiently process solar energy, replicating the natural processes. The rich and extensive transitions seen in porphyrin-based materials hold great expectation as light harvesting building blocks in the construction of molecular architectures, allowing an efficient use of the solar spectrum. Hence in this study porphyrin nanorods are synthesized and characterized for future application in the construction of the artificial light harvesting system. Understanding the sizes and growth mechanism of porphyrins nanorods by self-assembly and molecular recognition is essential for their successful implementation in nanodevices. Spectroscopic and microscopic studies were carried out to investigate the effect that time, concentration and solvents have on the fabrication of porphyrin nanorods by ionic self-assembly of two oppositely charged porphyrins. We investigate in details the heteroaggregate behavior formation of [H 4TPPS 4] 2- and [SnTPyP] 2 mixture by means of the UVvis spectroscopy and aggregates structure and morphology by transmission electron microscopy (TEM). This study demonstrates the potential for using different concentrations and solvents to influence the physical and optical properties of porphyrin based nanorods. © 2011 Elsevier B.V. All rights reserved

Synthesis and characterization of porphyrin nanotubes/rods for solar radiation harvesting and solar cells

Energy transfer and electron transfer events as they occur between well arranged light harvesting antenna molecules, the reaction center and other factors determine the function of natural photosynthesis. The overall small reorganization energy and the well-balanced electronic coupling between each component bear key characters for the unique efficiency of natural photosynthesis. Such aspects permit the design and assembly of artificial systems that efficiently process solar energy, replicating the natural processes. The rich and extensive transitions seen in porphyrin-based materials hold great expectation as light harvesting building blocks in the construction of molecular architectures, allowing an efficient use of the solar spectrum. Hence in this study porphyrin nanorods are synthesized and characterized for future application in the construction of the artificial light harvesting system. Understanding the sizes and growth mechanism of porphyrins nanorods by self-assembly and molecular recognition is essential for their successful implementation in nanodevices. Spectroscopic and microscopic studies were carried out to investigate the effect that time, concentration and solvents have on the fabrication of porphyrin nanorods by ionic self-assembly of two oppositely charged porphyrins. We investigate in details the heteroaggregate behavior formation of [H4TPPS4]2- and [SnTPyP]2+ mixture by means of the UV–vis spectroscopy and aggregates structure and morphology by transmission electron microscopy (TEM). This study demonstrates the potential for using different concentrations and solvents to influence the physical and optical properties of porphyrin based nanorods