Activity,selectivity, and methanol tolerance of novel carbon-supported Pt and Pt<Subscript>3</Subscript>Me (Me = Ni,Co) cathode catalysts

The activity, selectivity, and methanol tolerance of novel, carbon supported high-metal loading (40 wt.%) Pt/C and Pt₃Me/C (Me = Ni, Co) catalysts for the O₂ reduction reaction (ORR) were evaluated in model studies under defined mass transport and diffusion conditions, by rotating (ring) disk and by differential electrochemical mass spectrometry. The catalysts were synthesized by the organometallic route, via deposition of pre-formed Pt and Pt₃Me pre-cursors followed by their decomposition into metal nanoparticles. Characteristic properties such as particle sizes, particle composition and phase formation, and active surface area, were determined by transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. For comparison, commercial Pt/C catalysts (20 and 40 wt.%, E-Tek, Somerset, NJ, USA) were investigated as well, allowing to evaluate Pt loading effects and, by comparison with the pre-cursor-based catalyst with their much smaller particle sizes (1.7 nm diameter), also particle size effects. Kinetic parameters for the ORR were evaluated; the ORR activities of the bimetallic catalysts and of the synthesized Pt/C catalyst were comparable and similar to that of the high-loading commercial Pt/C catalyst; at typical cathode operation potentials H₂O₂ formation is negligible for the synthesized catalysts. Due to their lower methanol oxidation activity the bimetallic catalysts show an improved methanol tolerance compared to the commercial Pt/C catalysts. The results indicate that the use of very small particle sizes is a possible way to achieve reasonably good ORR activities at an improved methanol tolerance at DMFC cathode relevant conditions.     

Synthesis and characterization of CaF2 nanocrystals

Calcium fluoride nanocrystals (CaF₂) were synthesized by two different techniques namely co-precipitation and hydrothermal. The synthesized nanocrystals were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared red spectroscopy (FTIR), scanning electron microscopy (SEM), optical absorption and photoluminescence (PL). The crystallite size estimated using Scherer's formula was found to be in the range 30–35 nm for nanocrystals synthesized by co-precipitation method where as in case of hydrothermally synthesized nanocrystals it is in the range 20–28 nm which is less compared to those obtained by co-precipitation method. The morphological features as studied using SEM revealed that the nanocrystals are agglomerated, crispy with porous. The SEM images of hydrothermally synthesized nanocrystals showed less agglomeration than those obtained by co-precipitation method and the images confirm the formation of nanoparticles. The optical absorption spectrum showed a strong absorption band peaked at 244 nm for nanocrystals synthesized by co-precipitation method and it is 218 nm peak in case of hydrothermally synthesized ones. The PL emission spectrum showed two prominent emission bands peaked at 330 and 600 nm when excited at 218 nm.     

Studies on microstructure and density of sintered ZnO-based non-linear resistors

Systematic studies have been made of the grain growth and density of sintered ZnO-based systems containing one or more additive oxides of the type Nb₂O₅, Bi₂O₃, Sb₂O₃, CoO, Cr₂O₃, MnO₂, NiO and Al₂O₃. These samples were characterized using such techniques as scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The influence of the nature and amount of additive oxides and sintering temperature is discussed in relation to microstructure, density and the phases present.     

The NAL-ISRO acoustic test facility

The Indian Space Programme has the goals of launching a number of communication and remote sensing satellites for various uses. The acoustic exposure testing of such space bound components and systems on ground is mandatory to check their ability to withstand the extreme noise fields encountered during the trans-atmospheric flight to their final destinations in space. This paper outlines the nature and origin of this acoustic field, need for acoustic testing, establishment of a versatile groundbased high intensity acoustic-testing facility and its performance evaluation. The facility was set up as a joint project between the National Aeronautical Laboratory (nal) and the Indian Space Research Organisation (isro).     

MgNb2O6:Dy3+ nanophosphor: A facile preparation,down conversion photoluminescence and UV driven photocatalytic properties

Series of (1–9 mol %) dysprosium (Dy³⁺) ions doped MgNb₂O₆ (MNO) nanophosphors were synthesized by chemical combustion process and their photo luminescent and photocatalytic behaviours were examined. Powder X-ray diffraction (PXRD) reveals the columbite structure and crystal structure parameters were calculated. The average crystallite size was found to be in the range of 20–30 nm as calculated by Scherrer's method. The photoluminescence (PL) of MgNb₂O₆:Dy³⁺ (λ_exc-393 nm) reflects white emission for the prepared samples as confirmed by CIE and CCT. The photocatalytic activities of these nanophosphors were probed for the decolorization of acid red 88 (AR-88) under UV light irradiation. The photocatalyst with MgNb₂O₆:Dy³⁺ (5 mol %) showed enhanced activity of 97%, attributed to effective separation of charge carriers. All the above experimental results confirm that, the optimized phosphor is quite useful for WLEDs, solid-state lighting applications and as a photocatalyst.     

Design of Bi-functional composite core–shell SiO2@ZnAl2O4:Eu3+ array as a fluorescent sensors for selective and sensitive latent fingerprints visualization protocol

Core–shell SiO₂@ZnAl₂O₄:Eu³⁺ (5?mol%) nanophosphor (NP) with coatings up to the level IV has been prepared by a facile solvothermal route, followed by heat treatment. Scanning electron microscopy studies of fabricated core–shell particles displays good spherical shape and non-agglomeration with a narrow size distribution. The thickness of the shell increased with increase in coating cycles. Photoluminescence (PL) studies exhibited strong red emission peaks at 612?nm corresponding to the ⁵D_o?→?⁷F₂ transition of the Eu³⁺ ions. PL intensity increased with calcination temperature and coating cycles. The color coordinates of the coated NP were turned towards intense pure red emission with color purity ～95%. Powder dusting method was used to visualize latent fingerprints (LFPs) by staining uncoated and coated NP on various porous and non-porous surfaces under UV light. It was clear that core–shell NP display high sensitivity, reproducibility, selectivity, reliability, and can obtain the complete three levels of fingerprint ridge details. Judd–Ofelt (J-O) intensity parameters and radiative properties, namely transition probabilities, radiative lifetimes, branching ratios, and quantum efficiency were evaluated. The aforementioned results established that the SiO₂@ZnAl₂O₄:Eu³⁺ (5?mol%) NP can be used as an ideal candidate for multifunctional applications such as WLEDs, LFPs, anticounterfeiting etc.     

Multifunctional Dy (III) doped di-calcium silicate array for boosting display and forensic applications

Latent fingerprints (LFPs) are the major physical evidences for the identification of individuals during crime spot investigation. Till date, numerous methods were followed to visualize LFPs. However, simple, accurate, and cost-effective method has wide scope in advanced forensic field. In our work, Ca₂SiO₄:Dy³⁺ nanopowders (NPs) were fabricated via solution combustion route. The optimized sample was employed for the visualization of overlapped LFPs by the cost effective powder dusting method. The obtained results reveals the complete three levels of ridge characteristics with high sensitivity, reproducibility, selectivity, and reliability on various complex surfaces. The photoluminescence (PL) spectra consist of intense peaks at ～ 480 and 574 nm owing to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 4f transitions of Dy³⁺ ions, respectively. The photometric properties confirm that the samples exhibit intense white emission with high color purity. Therefore, the prepared NPs could be a definitive choice as an advanced luminescent NPs for forensic, solid state lighting and portable FED devices.     

Photocatalytic degradation of Rhodamine B dye under UV/solar light using ZnO nanopowder synthesized by solution combustion route

Nano-sized ZnO powder with crystallite size in the range 12 to 50 nm were prepared by solution combustion route. The product was characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Photocatalytic degradation of rhodamine B (RB) dye was carried out with ZnO nanopowder. The effect of parameters such as the crystallite size, amount of catalyst, concentration of the dye, pH and irradiation on photocatalytic degradation of RB is studied. The results reveal that the maximum decolorization (more than 95%) of dye occurred with ZnO catalyst in 8 min of stirring at basic pH under solar light irradiation. It was also found that chemical oxygen demand (COD) reduction takes place at a faster rate under solar light as compared to that of UV light. The results suggest that, the ZnO solar photocatalytic irradiation is better than the calcined ZnO/solar and UV light irradiation.     

Raman and infrared study of 100 MeV swift Ag heavy ion irradiation effects in CaSO4·2H2O single crystals

The modifications of calcium sulphate (CaSO₄·2H₂O) single crystals are investigated by means of Raman and Fourier transform infrared spectroscopy (FT-IR) using 100 MeV Ag⁸⁺ ions in the fluence range 1 × 10¹¹ to 5 × 10¹³ ions/cm². It is observed that the intensities of the Raman modes decrease with increase in ion fluence. We determined damage cross-section (σ) for all the Raman active modes and found to be different for different Raman modes. Further, FT-IR studies have been carried out to confirm surface amorphisation for a fluence of 1 × 10¹³ ions/cm². It is observed that the absorption peaks at 1132–1156 cm⁻¹ corresponds to ν₃(SO₄²⁻) mode. The decrease in Raman peaks intensity with ion fluence is attributed to degradation of ν₃(SO₄²⁻) modes present on the surface of the sample.     

Porous network ZrO2/ZnFe2O4 nanocomposite with heterojunction towards industrial water purification under sunlight: Enhanced charge separation and elucidation of photo-mechanism

This work majorly aims to synthesize and also investigate the structural, optical, magnetic and optical features of ZrO₂/ZnFe₂O₄ nanocomposite. Here, different ratios of novel hetero-junction ZrO₂/ZnFe₂O₄ were synthesized by simple and fast solution combustion route. The X-ray diffraction results showed the formation of ZrO₂ and ZnFe₂O₄ nanoparticles and ZrO₂/ZnFe₂O₄ nanocomposites without any impurity. The formation of hetero-junction effectively inhibits the photo-generated charge carrier recombination. The degradation of Indigo Carmine dye by ZrO₂/ZnFe₂O₄ photocatalyst was achieved through synergistic effects with 98% degradation and removal of 77% COD from the industrial dye waste water under Sunlight irradiation. Mixing of ferrites with zirconia greatly improves the photocatalytic activity that has been clearly proposed with the help of mechanism. ZZFO 12 NC exhibits better photocatalytic activity due to the combined facets of photo and Fenton activity. The exposure and enhancement of fingerprints in various surfaces are achieved by a modest, extremely sensitive and eco-friendly method. ZZFO12 NC offer great potential as an active photocatalyst for degradation of 54% of organic pollutant present in industrial waste water under natural Sunlight.