M.A. Dastageer

Highly-active direct Z-scheme Si/TiO2 photocatalyst for boosted CO2 reduction into value-added methanol

In the present study, direct Z-scheme Si/TiO2 photocatalyst was synthesized via a facile hydrothermal reaction using tetrabutyl titanate and Si powder prepared from magnesiothermic reduction of SiO2 nanospheres. The Si/TiO2 nanospheres were composed of porous Si nanospheres with a diameter of ∼300 nm and TiO2 nanosheets with a diameter of 50 nm and thickness of 10 nm, and demonstrated superior visible light harvesting ability to either Si nanospheres or TiO2 nanosheets. CO2 photocatalytic reduction proved that Si/TiO2 nanocomposites exhibit high activity in conversion of CO2 to methanol with the maximum photonic efficiency of 18.1%, while pure Si and TiO2 catalyst are almost inactive, which can be ascribed to the integrated suitable band composition in the Si/TiO2 Z-scheme system for CO2 reduction. The enhanced photocatalytic property of Z-scheme Si/TiO2 nanospheres was ascribed to the formation of Si/TiO2 Z-scheme system, which improved the separation efficiency of the photogenerated carriers, prolonged their longevity, and therefore boosted their photocatalytic activity.

Detection of carcinogenic chromium in synthetic hair dyes using laser induced breakdown spectroscopy

A laser induced breakdown spectroscopic (LIBS) system, consisting of a pulsed 266 nm laser radiation, in conjunction with a high-resolution spectrograph, a gated intensified charge coupled device camera, and a built-in delay generator were used to develop a sensitive detector to quantify the concentration of toxic substances such as chromium in synthetic hair dyes available on the local market. The strong atomic transition line of chromium (Cr I) at 427.5 nm wavelength was used as a fingerprint wavelength to calibrate the detection system and also to quantify the levels of chromium in the hair dye samples. The limit of detection achieved by our LIBS detection system for chromium was 1.2 ppm, which enabled us to detect chromium concentration in the range of 5-11 ppm in the commercial hair dyes available on the local market. The concentrations of chromium in the hair dyes measured using our system were validated using a standard analytical technique such as inductively coupled plasma mass spectrometry (ICPMS), and acceptable agreement (nearly 8%) was found between the results obtained by the two methods (LIBS and ICPMS). This study is highly significant for human health, specifically for people using synthetic hair dyes for changing the color of their hair.

Response tests of a LaCl3:Ce scintillation detector with low energy prompt gamma rays from boron and cadmium

The yield of 478 and 558 keV gamma-rays have been measured from water samples containing 0.031-0.500 wt. % boron and 0.0625-0.500 wt. % cadmium, respectively, using a cylindrical 76 mm × 76 mm (height × diameter) LaCl(3):Ce detector. Inspite of interferences between detector-associated and the sample-associated prompt gamma rays, the LaCl(3):Ce detector has excellent resolution for the low energy prompt gamma-rays. An excellent agreement has been observed between the experimental and calculated yield of boron and cadmium prompt gamma ray from water samples.

Synthesis, characterization and visible light photocatalytic activity of Cr3+, Ce3+ and N co-doped TiO2 for the degradation of humic acid

The synthesis, characterization and photocatalytic activity of Cr3+ and Ce3+ co-doped TiON (N-doped TiO2) for the degradation of humic acid with exposure to visible light is reported. The synthesized bimetal (Cr3+ + Ce3+) modified TiON (Cr–Ce/TiON), with an evaluated bandgap of 2.1 eV, exhibited an enhanced spectral response in the visible region as compared to pure and Ce3+ doped TiON (Ce/TiON). The XRD analysis revealed the insertion of Cr3+ and Ce3+ in the crystal lattice along with Ti4+ and N that resulted in the formation of a strained TiON anatase structure with an average crystallite size of ∼10 nm. Raman analysis also supported the formation of stressed rigid structures after bimetal doping. HRTEM confirmed the homogeneous distribution of both the doped metallic components in the crystal lattice of TiON without the formation of surface oxides of either Cr3+ or Ce3+. Electron energy loss spectroscopy (EELS) analysis revealed no change in the oxidation of either Cr or Ce during the synthesis. The synthesized Cr–Ce/TiON catalyst exhibited appreciable photocatalytic activity for the degradation of humic acid on exposure to visible light. Additionally, a noticeable mineralization of carbon rich humic acid was also witnessed. The photocatalytic activity of the synthesized catalyst was compared with pristine and Ce3+ doped TiON.

Fabrication of Water Jet Resistant and Thermally Stable Superhydrophobic Surfaces by Spray Coating of Candle Soot Dispersion

A facile synthesis method for highly stable carbon nanoparticle (CNP) dispersion in acetone by incomplete combustion of paraffin candle flame is presented. The synthesized CNP dispersion is the mixture of graphitic and amorphous carbon nanoparticles of the size range of 20–50 nm and manifested the mesoporosity with an average pore size of 7 nm and a BET surface area of 366 m2g−1. As an application of this material, the carbon nanoparticle dispersion was spray coated (spray-based coating) on a glass surface to fabricate superhydrophobic (water contact angle > 150° and sliding angle < 10 °) surfaces. The spray coated surfaces were found to exhibit much improved water jet resistance and thermal stability up to 400 °C compared to the surfaces fabricated from direct candle flame soot deposition (candle-based coating). This study proved that water jet resistant and thermally stable superhydrophobic surfaces can be easily fabricated by simple spray coating of CNP dispersion gathered from incomplete combustion of paraffin candle flame and this technique can be used for different applications with the potential for the large scale fabrication.

Pulse height tests of a large diameter fast LaBr3:Ce scintillation detector

The pulse height response of a large diameter fast 100 mm × 100 mm LaBr3:Ce detector was measured for 0.1-10 MeV gamma-rays. The detector has a claimed time resolution of 608 ps for 511 keV gamma rays, but has relatively poor energy resolution due to the characteristics of its fast photomultiplier. The detector pulse height response was measured for gamma rays from cobalt, cesium, and bismuth radioisotope sources as well as prompt gamma rays from thermal neutron capture in water samples contaminated with mercury (3.1 wt%), boron (2.5 wt%), cadmium (0.25 wt%), chromium (52 wt%), and nickel (22 wt%) compounds. The energy resolution of the detector was determined from full width at half maximum (FWHM) of element-characteristic gamma ray peaks in the pulse height spectrum associated with the element present in the contaminated water sample. The measured energy resolution of the 100 mm × 100 mm detector varies from 12.7±0.2% to 1.9±0.1% for 0.1 to 10 MeV gamma rays, respectively. The graph showing the energy resolution ΔE/E(%) versus 1/√Eγ was fitted with a linear function to study the detector light collection from the slope of the curve. The slope of the present 100 mm × 100 mm detector is almost twice as large as the slope of a similar curve of previously published data for a 89 mm × 203 mm LaBr3:Ce detector. This indicates almost two times poorer light collection in the 100 mm × 100 mm detector as compared to the other detector.

A study of laser-induced blue emission with nanosecond decay of silicon nanoparticles synthesized by a chemical etching method

Silicon nanoparticles (Si NPs), exhibiting a strong visible photoluminescence (PL), have found many applications in optoelectronics devices, biomedical tags and flash memories. Chemical etching is a well-known method for synthesizing orange-luminescent, hydride-capped silicon nanoparticles (H/Si NPs). However, a blueshift in emission wavelength occurs when reducing the particle size to exciton Bohr radius or less. In this paper, we attempted to synthesize and characterize H/Si NPs that emit lower wavelengths at room temperature. We proved that our method succeeded in synthesizing H/Si NPs with emission in the blue region. The wavelength-resolved and time-resolved studies of the PL were executed for H/Si NPs in methanol (MeOH), pyridine (py) and furan, using the 355 nm pulsed radiation from a Nd:YAG laser. In addition, excitation wavelength-dependent and PL studies were executed using the spectrofluorometer with a xenon (Xe) broad band light source. We noticed solvent-dependent PL spectra with sharp peaks near 420 nm and a short lifetime less than 100 ns. The morphology and particle size were investigated by high resolution transmission electron microscope (HRTEM). Particles as small as one nanometer were observed in MeOH and py suspensions while two-nanometer particles were observed in the furan suspension.

Nano-NiO as a photocatalyst in antimicrobial activity of infected water using laser induced photo-catalysis

Nano NiO photo catalyst was synthesized by sol gel method and it is used as a photo catalyst in conjunction with 355 nm laser radiation in the process of disinfecting water infected with Escherichia coli microorganism. When synthesized nano-NiO material is used as a photo catalyst, a bacteria decay rate constant of 0.35 min-1 and this rate constant is higher than the bacteria decay rate constant of 0.24 minutes−1 for TiO2 as a photo catalyst under same catalytic concentration and laser pulse energy. From the TEM study, a grain size as low as 20–40 nm was observed and the absorption study showed a band gap of 3.85 eV. The dependence of depletion rate of bacterial count in the infected water on the nano-NiO concentration and the irradiating laser pulse energy were carried out.

Enhanced photo-catalytic activity of ordered mesoporous indium oxide nanocrystals in the conversion of CO2 into methanol

ABSTRACT Ordered mesoporous indium oxide nanocrystal (m-In2O3) was synthesized by nanocasting technique, in which highly ordered mesoporous silca (SBA-15) was used as structural matrix. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halanda (BJH) studies were carried out on m-In2O3 and the results revealed that this material has a highly ordered mesoporous surface with reduced grain size, increased surface area and surface volume compared to the non porous indium oxide. The diffuse reluctance spectrum exhibited substantially improved light absorption efficiency in m-In2O3 compared to normal indium oxide, however, no considerable change in the band gap energies of these materials was observed. When m-In2O3 was used as a photo-catalyst in the photo-catalytic process of converting carbon dioxide (CO2) into methanol under the pulsed laser radiation of 266-nm wavelengths, an enhanced photo-catalytic activity with the quantum efficiency of 4.5% and conversion efficiency of 46.3% were observed. It was found that the methanol production yield in this chemical process is as high as 485 µlg−1 h−1 after 150 min of irradiation, which is substantially higher than the yields reported in the literature. It is quite clear from the results that the introduction of mesoporosity in indium oxide, and the consequent enhancement of positive attributes required for a photo-catalyst, transformed photo-catalytically weak indium oxide into an effective photo-catalyst for the conversion of CO2 into methanol.

Study of temporal evolution of electron density and temperature for atmospheric plasma generated from fluid samples using laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS), is an atomic emission based analytical technique, where laser induced plasma is analyzed after appropriate time delay allowed for plasma cooling. The selectivity and the sensitivity of the system immensely depend on the plasma parameters and hence understanding the formation and evolution of the laser induced plasma is very vital in the optimization of LIBS detection systems. In this study, laser induced plasma was generated using a laser beam of 266 nm wavelength and spectral analysis was carried out using Spectrograph ICCD system with appropriate time delay. The temporal response of the plasma existing in local thermodynamic equilibrium was investigated with respect to the important plasma parameters (temperature and electron density) computed from the LIBS spectra.