Satyendra K. Das

Low temperature synthesis of Ag@anatase TiO2 nanocomposites through controlled hydrolysis and improved degradation of toxic malachite green under both ultra-violet and visible light

The nanocomposite material of titania coated silver nanoparticles (AgNPs) was prepared by employing a combination of two different synthetic routes. The proposed strategy demonstrates the utilization of a radiation chemical route to synthesize natural biopolymer gum acacia capped AgNPs at a very low pH followed by the controlled hydrolysis of Ti-tetra isopropoxide (TiPP) at low temperature for better growth of the titania shell on the AgNPs. The formation of the hybrid Ag–TiO2 nanocomposites was confirmed through UV-Vis spectroscopic analysis, which showed a red shift in the surface plasmon resonance (SPR) peak of the Ag NPs (about 15 nm) and a blue shift in the case of TiO2 (about 10 nm) with concomitant reduction in the intensity of peak of the AgNPs at 410 nm. In addition, the synthesized materials were characterized by dynamic light scattering (DLS), Fourier transform infra-red (FTIR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The as-synthesized TiO2 NPs and Ag@TiO2 nanocomposites were subsequently applied to the photochemical degradation of the toxic dye molecule, malachite green (MG), chosen as a model pollutant. The apparent photocatalytic degradation rate constants in regard to the Ag@TiO2 and TiO2 nanomaterials were calculated to be 0.25 and 0.05 min−1, respectively. The photocatalytic degradation rates of MG by the Ag@TiO2 nanocomposites under visible light illumination were found to be nearly 42 times higher than that of the TiO2 NPs implicating its great promise for the improved degradation of toxic materials such as azo dyes using visible solar light.

A nuclear hyperfine study of hafnium zirconate system

Zr-doped HfO2 system has been studied with the nuclear probe technique time differential perturbed angular correlation (TDPAC). The effect of Zr-doping on the crystal structure of HfO2 has been investigated by doping the HfO2 matrix with 20 and 50 atom% of Zr. A mild and homogeneous chemical method was followed to prepare the doped samples so that the dopant Zr-atom gets uniformly distributed throughout the HfO2 matrix. It has been observed that the incorporation of Zr-atom into the HfO2 crystal system does not affect significantly up to 50 atom%. It has been explained in terms of similar arrangement of O-atoms around both Hf and Zr atoms in their oxide crystal structure.

Enhancement of Jc by Hf-doping in the superconductor MgB2: A hyperfine interaction study

Abstract Measurements of the critical current density ( J c ) by magnetisation and the upper critical field ( H c2 ) by magnetoresistance have been performed for hafnium-doped MgB 2 . There has been a remarkable enhancement of J c as compared to that by ion irradiation without any appreciable decrease in T c , which is beneficial from the point of view of applications. The irreversibility line extracted from J c shows an upward shift. In addition, there has been an increase in the upper critical field which indicates that Hf partially substitutes for Mg. Hyperfine interaction parameters obtained from time differential perturbed angular correlation (TDPAC) measurements revealed the formation of HfB and HfB 2 phases along with the substitution of Hf. A possible explanation is given for the role of these species in the enhancement of J c in MgB 2 superconductor.

Perturbed Angular Correlation Study of the Static and Dynamic Aspects of Cadmium and Mercury Atoms Inside and Attached to a C60 Fullerene Cage

Abstract 30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on preformed targets of C60 with a thickness of 1 mg cm-2. Endofullerene compounds, viz. 111mCd@C60 and 199mHg@C60 formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds were counted for the time differential perturbed angular correlation (TDPAC) measurement using the coincidence of the 151 - 245 keV cascade of 111mCd and the 374 - 158 keV cascade of 199mHg on a six LaBr3(Ce) detector system coupled with digital electronics. The results for 111mCd@C60 indicate a single static component (27%) and a fast relaxing component (73%), the latter implying that the cadmium atom moves rapidly inside the cage at room temperature. The quadrupole interaction frequency and asymmetry parameter of the cadmium atom occupying the static site in C60 are wQ=8.21(36) Mrad s-1 and η = 0.41(9), respectively. The fast relaxation constant is 0.0031(4) ns-1. Similarly, mercury atoms also exhibit a single static and a fast component. The static site has a quadrupole frequency wQ=283.0(12.4) Mrad s-1 and η =0 with a fraction of 30%. The fast relaxation constant is 0.045(8) ns-1 with a fraction of 70%, very similar to that of cadmium.

Recoil Induced Room Temperature Stable Frenkel Pairs in a-Hafnium Upon Thermal Neutron Capture

Ultrapure hafnium metal (110 ppm zirconium) was neutron activated with a thermal neutron flux of 6:6 · 1012 cm-2s-1 in order to obtain 181Hf for subsequent time differential perturbed angular correlation (TDPAC) experiments using the nuclear probe 181Hf(β-) 181Ta. Apart from the expected nuclear quadrupole interaction (NQI) signal for a hexagonal close-packed (hcp) metal, three further discrete NQIs were observed with a few percent fraction each. The TDPAC spectra were recorded for up to 11 half lives with extreme statistical accuracy. The fitted parameters vary slightly within the temperature range between 248 K and 373 K. The signals corresponding to the three additional sites completely disappear after ‘annealing’ at 453 K for one minute. Based on the symmetry of the additional NQIs and their temperature dependencies, they are tentatively attributed to Frenkel pairs produced by recoil due to the emission of a prompt 5:694 MeV -ray following thermal neutron capture and reported by the nuclear probe in three different positions. These Frenkel pairs are stable up to at least 373 K.

A Comparative Time Differential Perturbed Angular Correlation Study of the Nuclear Quadrupole Interaction in HfF4·HF·2H2O Using 180mHf and 181Hf(β–)181Ta as Nuclear Probes: Is Ta an Innocent Spy?

We report on a comparative study of the nuclear quadrupole interaction of the nuclear probes 180mHf and 181Hf(β −)181Ta in HfF4・HF・2H2O using time differential perturbed angular correlations (TDPAC) at 300 K. For the first probe, assuming a Lorentzian frequency distribution, we obtained ωQ= 103(4) Mrad/s, an asymmetry parameter η = 0.68(3), a linewidth δ = 7.3(3.9)%, and full anisotropy within experimental accuracy. For the second probe, assuming a Lorentzian frequency distribution, we obtained three fractions: (1) with 56.5(7)%, ωQ= 126.64(4) Mrad/s and η = 0.9241(4) with a rather small distribution δ = 0.40(8)% which is attributed to HfF4・HF・2H2O; (2) with 4.6(4)%, ωQ = 161.7(3) Mrad/s and η = 0.761(4) assuming no line broadening which is tentatively attributed to a small admixture of Hf2OF6・H2O; (3) the remainder of 39.0(7)% accounts for a rapid loss of anisotropy and is modelled by a perturbation function with a sharp frequency multiplied by an exponential factor exp(−λ t) with λ = 0.55(2) ns−1. Whereas the small admixture of Hf2OF6・H2O escapes detection by the 180mHf probe, there is no rapid loss of roughly half the anisotropy as is the case with 181Hf(β −)181Ta. This loss could in principle be due to fluctuating electric field gradients originating from movements of nearest neighbour HF adducts and/or H2O molecules after nuclear transmutation to the foreign atom Ta which are absent for the isomeric probe. Alternatively, paramagnetic Ta ions could lead to fluctuating magnetic dipole fields which, when combined with fluctuating electric field gradients, could also lead to a rapid loss of anisotropy. In any case, Ta is not an “innocent spy” in this compound. Although 180mHf is not a convenient probe for conventional spectrometers, the use of fast digitizers and software coincidences would allow to use all γ -quanta in the stretched cascade which would greatly improve the efficiency of the spectrometer. 180mHf could also serve as a Pu analogue in toxicity studies.