Highly Enhanced Visible Light Photocatalytic Performance of BiOCl/X (X = Br, I) Nanocomposites with Controllable-Exposed {001} Facets.

A series of BiOClyX1-y (X = Br, I.) with controllable-exposed {001} facets have been prepared by a facile liquid preparation method, using NaBiO3, HX (X = Br, I) and hydroxylamine hydrochloride (HONH2 · HCl) as the raw materials. The fundamental properties of the as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), FT-IR spectrophotometer and UV-Vis absorption spectrometry. The photocatalytic activities of these as-prepared photocatalysts were investigated by photodegradation of Rhodamine B (RB) under visible light irradiation. BiOCl0.5Br0.5 and BiOCl0.75I0.25 nanocomposites show the best photocatalytic performance for removal of RB in individual system, respectively. A possible photocatalytic mechanism has been discussed on the basis of the results of photocatalytic experiments.

Nano BEA zeolite catalysts for the selective catalytic cracking of n-dodecane to light olefins.

Nano BEA zeolite catalysts were synthesized and modified by desilication and then ion-exchanged with Co. The desilication was carried out using 0.1 M of NaOH. The synthesized and modified nano BEA catalysts were characterized via different characterization techniques. Ammonia temperature program desorption (NH3-TPD) and the pyridine Fourier transform infrared (pyridine-FTIR) were utilized to investigate the acidity of catalysts. X-ray diffraction (XRD), 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy techniques were used to examine the structure of the catalysts. The XRD patterns of the as-synthesized nano BEA catalysts were identical to that of the reference, while the NMR analysis revealed the distribution of silicon and aluminum in the BEA structure. The scanning electron microscope (SEM) analysis confirmed that the fabricated catalysts were less than 100 nm. The desilication and Co ion-exchange altered the acidity of the catalyst. The catalysts were evaluated in the cracking of sssssss to light olefins in the temperature range from 400 °C to 600 °C. The conversion increased with the increase in the reaction temperature for both catalysts; the conversion was above 90% for the Co-BEA catalyst at a temperature above 450 °C. The yield of light olefins also increased at higher temperatures for both catalysts, while at a lower temperature the yield to light olefins was ca. 40% over that of Co-BEA.

Laser-induced photoacoustic detection of ozone at 266 nm using resonant cells of different configuration.

A highly sensitive pulsed photoacoustic (PA) spectrometer with different PA cell geometries was designed and fabricated in our laboratory to determine ozone detection at ppb level. The comparative performance and merits of these custom made cells were studied. The excitation source of PA spectrometer is a nanosecond pulsed laser at 266 nm (fourth harmonic of Nd:YAG laser) and a sensitive electret microphone as a photoacoustic detector. The sensitivity optimization of the PA system with different experimental parameters including the resonant acoustic modes of the 3 PA cells was carried out for the detection of ozone. The minimum detection limit for ozone achieved under our experimental conditions, with 3 PA cells were 10, 31 and 26 ppbV for cells designated as cell # 1, cell # 2 and cell # 3, respectively. This limit of ozone detection achieved in our work is quite appreciable to be able to detect ozone under safe permissible limits and the sensitivity achieved in our case is an order of magnitude better than earlier reports using sophisticated laser system like quantum cascade laser.

A Rapid and Cost-Effective Laser Based Synthesis of High Purity Cadmium Selenide Quantum Dots.

A rapid and cost effective method is developed to synthesize high purity cadmium Selenide (CdSe) quantum dots in acetone medium using second harmonic of Nd:YAG nanosecond pulsed laser of 532 nm wavelength. The thermal agglomeration due the nanosecond pulse duration of the laser was successfully eliminated by using unfocussed laser beam and thereby providing a favorable conditions for the synthesis of quantum dots having the grain size of 3 nm. The morphological and optical characterizations like XRD, HRTEM, optical absorption of the synthesized CdSe quantum dots, reveal that the material possesses the similar characteristics of the one synthesized through cumbersome wet chemical methods. Relative to the CdSe bulk material, the synthesized CdSe quantum dots showed a blue shift in the measured band gap energy from near infrared spectral region to visible region, making this material very attractive for many solar energy harvesting applications like photo-catalysis and solar cells.

Single-Pot Synthesis of ⟨001⟩-Faceted N-Doped Nb2O5/Reduced Graphene Oxide Nanocomposite for Efficient Photoelectrochemical Water Splitting.

Due to exciting catalytic activity and selectivity, tailoring of nanocatalysts consisting of preferred crystal facets and desired structural properties remains at the forefront of materials engineering. A facile one-step nonhydrolytic solvothermal synthesis of a nanocomposite of reduced graphene oxide and one-dimensional nitrogen-doped Nb2O5 (N-NbOx) with exposed ⟨001⟩ facet is described. Triethylamine performed the dual role as nitrogen source and capping agent to control the size and unidirectional growth of Nb2O5 nanocrystallites. The nanocomposite showed efficient visible-light-mediated (λ > 420 nm) water splitting in a photoelectrochemical cell. A plausible mechanism for the formation of N-NbOx nanorods and improved photoelectrochemical efficacy in terms of their oriented growth is proposed.

Laser-induced efficient reduction of Cr(VI) catalyzed by ZnO nanoparticles.

The present study demonstrates the complete removal of Cr(VI) in aqueous suspensions of zinc oxide nanoparticles using a novel laser-induced photocatalytic process without the use of any additive. The study showed that ∼95% Cr(VI) was removed within short time (60 min) of laser exposure in the presence of ZnO. However, the removal of chromium using conventional setup under identical conditions was found to be negligible. Effect of critical parameters, such as laser energy, catalyst concentration, chromium concentration, and added electron donor and acceptor on the photocatalytic reduction process was also investigated. The data regarding temporal behavior of metal removal was fitted to first-order kinetic and reaction rate was computed.

Laser induced photocatalytic degradation of hazardous dye (Safranin-O) using self synthesized nanocrystalline WO3.

The photocatalytic degradation of Safranin-O (known as Basic Red 2) in water using locally synthesized nanocrystalline WO(3) as a photocatalyst was investigated under UV laser irradiation. The photo-oxidation removal of the dye was monitored by UV-vis spectrophotometer. The blank experiments for either laser irradiated only Safranin-O solution or the suspension containing WO(3) and Safranin-O in the dark showed that both laser illumination and the photocatalyst were essential for the removal of Safranin-O. The effect of experimental parameters including laser energy, catalyst loading, solution pH and the initial dye concentration on photocatalytic degradation of Basic Red 2 were also investigated. Results indicate that the rate of reaction is strongly influenced by the adsorption of an azo dye into the surface of the photocatalyst materials and suggests an optimum catalyst loading and dye concentration for the degradation reaction. It was investigated that the adsorption of the dye decreases at higher alkaline pH because both catalyst and substrate are negatively charged, developing repulsive forces between them. Kinetic data obtained reveals that the rate of the reaction obeys the first-order kinetics.

On-line monitoring of remediation process of chromium polluted soil using LIBS.

Due to large growth in leather and textile industries to cater for the needs of a growing world population, contamination of soil and water resources by chromium has become a great threat for humans and animals. In this work, Laser Induced Breakdown Spectroscopy (LIBS) was applied to monitor the remediation process of soil contaminated with Chromium metal. This study was conducted at a laboratory scale by setting up an experiment in a container holding soil contaminated with chromium. This setup represents actual field conditions where remediation process could be applied and monitored for the removal of toxic metals like Cr. For generation of LIBS spectrum, the plasma was produced by focusing a pulsed Nd: YAG laser at 1064 nm on the soil contaminated with chromium under remediation process. The evaluation of the potential and capabilities of LIBS as a rapid tool for remediation process of contaminated sites is discussed in detail. Optimal experimental conditions were evaluated for improving the sensitivity of our LIBS system for monitoring of remediation process through parametric dependence study. The minimum detection limit of our spectrometer for chromium in soil matrix was 2 mg Kg(-1).

Laser-induced removal of a dye C.I. Acid Red 87 using n-type WO3 semiconductor catalyst.

Water contamination by organic substances such as dyes is of great concern worldwide due to their utilization in many industrial processes and environmental concerns. To cater the needs for waste water treatment polluted with organic dyes, laser-induced photocatalytic process was investigated for removal of a dye derivative namely Acid Red 87 using n-type WO3 semiconductor catalyst. The degradation was investigated in aqueous suspensions of tungsten oxide under different experimental conditions using laser instead of conventional UV lamp as an irradiation source. The degradation process was monitored by measuring the change in dye concentration as a function of laser irradiation time by employing UV spectroscopic analysis. The degradation of dye was studied by varying different parameters such as laser energy, reaction pH, substrate concentration, catalyst concentration, and in the presence of electron acceptors such as hydrogen peroxide (H2O2), and potassium bromate (KBrO3). The degradation rates were found to be strongly dependent on all the above-mentioned parameters. Our experimental results revealed that the dye degradation process was very fast (within few minutes) under laser irradiation as compared to conventional setups using broad spectral lamps (hours or days) and this laser-induced photocatalytic degradation method could be an effective means to eliminate the pollutants present in liquid phase. The experience gained through this study could be beneficial for treatment of waste water contaminated with organic dyes and other organic pollutants.

Highly sensitive electronically modulated photoacoustic spectrometer for ozone detection.

An ozone (O(3)) gas sensor with a sensitivity of parts per 10(9) (ppb) level and a high level of selectivity based on the resonant photoacoustic effect was developed using an electronically modulated cw CO(2) laser beam. Quite different from the standard chopper modulation of a laser beam, here the laser source was electronically modulated to overcome the inherent problem of frequency instability associated with chopper modulation. With electronic modulation, in conjunction with the fast Fourier transform (FFT) of transient signals, we were able to improve significantly the sensitivity of the photoacoustic (PA) system for the detection of O(3). In addition to the improved sensitivity, our method proved that the FFT of a laser modulated PA signal could suppress the noise signal generated by spurious window diffused absorption, which in the case of most commonly used lock-in techniques is rather unavoidable. The dependence of the PA signal on various experimental parameters such as buffer gas, laser power, modulation frequency, and trace gas concentration was investigated. In the case of buffer gas, argon proved to be more suitable than nitrogen and helium in terms of enhancing the sensitivity of the system. The limits of detection of O(3) using the 9 P(14) CO(2) laser line in our PA system are 5 parts per 10(9) by volume (ppbv) and 14 ppbv with electronic and standard chopper modulation, respectively. This detection limit of O(3) is quite applicable for detection of safe levels of O(3), at ground level.

Measurement of nutrients in green house soil with laser induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) has been applied for the determination of nutrients in the green house soil samples. We determined appropriate spectral signatures of vital nutrients and calibrated the method to measure the nutrients in a naturally fertilized plot, cultivated with tomato and cucumber plants. From the calibration curves we predicted the concentrations of important nutrients such as Ca, K, P, Mg, Fe, S, Ni and Ba in the soil. Our measurements proved that the LIBS method rapidly and efficiently measures soil nutrients with excellent detection limits of 12, 9, 7, 9, 7, 10, 8 and 12 mg/kg for Ca, K, P, Mg, Fe, S, Ni and Ba respectively with a precision of approximately 2%, The unique features of LIBS for rapid sample analysis demonstrated by this study suggests that this method offers promise for precision measurements of soil nutrients as compared to conventional methods in short span of time.

Study of hazardous metals in iron slag waste using laser induced breakdown spectroscopy.

Laser Induced Breakdown Spectroscopy (LIBS) was applied for quantitative elemental analysis of slag samples collected from a local steel plant using an Nd: YAG laser emitting radiation at 1064 nm wavelength. The concentration of different elements of environmental significance such as cadmium, calcium, sulfur, magnesium, chromium, manganese, titanium, barium, phosphorus and silicon were 44, 2193, 1724,78578, 217260, 22220, 5178, 568, 2805, 77871 were mg Kg-1, respectively. Optimal experimental conditions for analysis were investigated. The calibration curves were drawn for different elements. The concentrations determined with our Laser-Induced Breakdown Spectrometers were compared with the results obtained using Inductively Coupled Plasma (ICP) emission spectroscopy. Our study demonstrates that LIBS could be highly appropriate for rapid online analysis of iron slag waste. The relative accuracy of our LIBS system for various elements as compared with ICP method is in the range of 0.001-0.049 at 2.5% error confidence. Limits of detection (LOD) of our LIBS system were also estimated for the elements noted here. The hazardous effects of some of the trace elements present in iron slag exceeding permissible safe limits are also discussed.

The role of various binding materials for trace elemental analysis of powder samples using laser-induced breakdown spectroscopy.

Study of various binding materials like potassium bromide, poly(vinyl alcohol), starch, silver and aluminum has been carried out using laser-induced breakdown spectroscopy (LIBS). The role of matrix effects using these five binders on LIBS signal intensity was investigated for better performance of LIBS technique as a quantitative analytical tool. For comparative study of different binders, the signal intensity of different Mg lines at 518.3, 517.2, 383.8 and 279.5nm wavelengths were recorded for pellets prepared with known concentrations of Mg in these binders. The influence of laser energy on ablated mass under different binding materials and its correlation with LIBS signal intensity has been explored. Optical scanning microscopy images of the ablated crater were studied to understand the laser ablation process. The study revealed that the binding material plays an important role in the generation of LIBS signal. The relative signal intensity measured for a standard Mg line (at 518.3nm) were 735, 538, 387, 227 and 130 for potassium bromide, starch, poly(vinyl alcohol), silver and aluminum as binders, respectively. This indicates clearly that potassium bromide is better as a binder for LIBS studies of powder samples.

Detection of heavy metals in Arabian crude oil residue using laser induced breakdown spectroscopy.

Laser induced breakdown spectroscopy (LIBS) was applied for the elemental analysis of Arabian crude oil residue samples. The spectra due to trace elements such as Ca, Fe, Mg, Cu, Zn, Na, Ni, K and Mo were recorded using this technique. The dependence of time delay and laser beam energy on the elemental spectra was also investigated. Prior to quantitative analysis, the LIBS system was calibrated using standard samples containing these trace elements. The results achieved through this method were compared with conventional technique like inductively coupled plasma.