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.

First-Order Melting of a Weak Spin-Orbit Mott Insulator into a Correlated Metal.

The electronic phase diagram of the weak spin-orbit Mott insulator (Sr(1-x)La(x))(3)Ir(2)O(7) is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. As the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.

Structural and Magnetic Phase Transitions near Optimal Superconductivity in BaFe2(As(1-x)Px)2.

We use nuclear magnetic resonance (NMR), high-resolution x-ray, and neutron scattering studies to study structural and magnetic phase transitions in phosphorus-doped BaFe2(As(1-x)P(x)2. Previous transport, NMR, specific heat, and magnetic penetration depth measurements have provided compelling evidence for the presence of a quantum critical point (QCP) near optimal superconductivity at x=0.3. However, we show that the tetragonal-to-orthorhombic structural (T{s}) and paramagnetic to antiferromagnetic (AF, TN) transitions in BaFe2(As(1-x)Px)2 are always coupled and approach T{N}≈T{s}≥T{c} (≈29 K) for x=0.29 before vanishing abruptly for x≥0.3. These results suggest that AF order in BaFe_{2}(As(1-x)Px)2 disappears in a weakly first-order fashion near optimal superconductivity, much like the electron-doped iron pnictides with an avoided QCP.

Avoided quantum criticality and magnetoelastic coupling in BaFe(2-x)Ni(x)As2.

We study the structural and magnetic orders in electron-doped BaFe(2-x)Ni(x)As2 by high-resolution synchrotron x-ray and neutron scatterings. Upon Ni doping x, the nearly simultaneous tetragonal-to-orthorhombic structural (T(s)) and antiferromagnetic (T(N)) phase transitions in BaFe2As2 are gradually suppressed and separated, resulting in T(s)>T(N) with increasing x, as was previously observed. However, the temperature separation between T(s) and T(N) decreases with increasing x for x≥0.065, tending toward a quantum bicritical point near optimal superconductivity at x≈0.1. The zero-temperature transition is preempted by the formation of a secondary incommensurate magnetic phase in the region 0.088≲x≲0.104, resulting in a finite value of T(N)≈T(c) + 10 K above the superconducting dome around x≈0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both the normal and superconducting states.

Effect of uniaxial strain on the structural and magnetic phase transitions in BaFe2As2.

We report neutron scattering experiments probing the influence of uniaxial strain on both the magnetic and structural order parameters in the parent iron pnictide compound, BaFe2As2. Our data show that modest strain fields along the in-plane orthorhombic b axis can affect significant changes in phase behavior simultaneous to the removal of structural twinning effects. As a result, we demonstrate in BaFe2As2 samples detwinned via uniaxial strain that the in-plane C4 symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures. Surprising changes in the magnetic order parameter of this system under relatively small strain fields also suggest the inherent presence of magnetic domains fluctuating above the strain-free ordering temperature in this material.

Competing ferri- and antiferromagnetic phases in geometrically frustrated LuFe2O4.

We present a detailed study of magnetism in LuFe(2)O(4), combining magnetization measurements with neutron and soft x-ray diffraction. The magnetic phase diagram in the vicinity of T(N) involves a metamagnetic transition separating an antiferro- and a ferrimagnetic phase. For both phases the spin structure is refined by neutron diffraction. Observed diffuse magnetic scattering far above T(N) is explained in terms of near degeneracy of the magnetic phases.

An inelastic neutron scattering investigation of holmium orthoferrite.

The inelastic neutron scattering spectra recorded in this study and elsewhere provide a useful set of crystal-field (CF) energy levels for the groundJ= 6 term of Ho3+in HoFeO3. The resolution of the low-energy, temperature-dependent pseudo-quadrupole ground state splitting and magnon peaks is consistent with the self-ordering of the Ho3+sublattice atTHo∼ 8-10 K and supports earlier electron spin resonance investigations of the Ho3+magnon behaviour. Systematic analysis of the grouped singlet CF levels of Ho3: HoFeO3, in conjunction with the CF Kramers doublet levels of the neighbouring Er3+: ErFeO3, has yielded possible sets of CF parameters for the two systems.

Magnetic ordering in the Ising antiferromagnetic pyrochlore Nd2ScNbO7.

The question of structural disorder and its effects on magnetism is relevant to a number of spin liquid candidate materials. Although commonly thought of as a route to spin glass behaviour, here we describe a system in which the structural disorder results in long-range antiferromagnetic order due to local symmetry breaking. Nd2ScNbO7is shown to have a dispersionless gapped excitation observed in other neodymium pyrochlores belowTN= 0.37 K through polarized and inelastic neutron scattering. However the dispersing spin waves are not observed. This excited mode is shown to occur in only 14(2)% of the neodymium ions through spectroscopy and is consistent with total scattering measurements as well as the magnitude of the dynamic moment 0.26(2)µB. The remaining magnetic species order completely into the all-in all-out Ising antiferromagnetic structure. This can be seen as a result of local symmetry breaking due disordered Sc+3and Nb+5ions about theA-site. From this work, it has been established thatB-site disorder restores the dipole-like behaviour of the Nd+3ions compared to the Nd2B2O7parent series.

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.

Itinerant spin excitations near the hidden order transition in URu(2)Si(2).

By means of neutron scattering we show that the high temperature precursor to the hidden order state of the heavy fermion superconductor URu(2)Si(2) exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of the long-lived longitudinal f spin excitations that appear below T(0). This suggests that there is a strongly hybridized character to the itinerant excitations observed previously above the hidden order transition. Here we present evidence that the itinerant excitations, like those in chromium, are due to Fermi surface nesting of hole and electron pockets; hence the hidden order phase probably originates from a Fermi surface instability. We identify wavevectors that span nested regions of a f-d hybridized band calculation and that match the neutron spin crossover from incommensurate to commensurate on approach to the hidden order phase.

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.

Carrier localization and electronic phase separation in a doped spin-orbit-driven Mott phase in Sr3(Ir(1-x)Ru(x))2O7.

Interest in many strongly spin-orbit-coupled 5d-transition metal oxide insulators stems from mapping their electronic structures to a J(eff)=1/2 Mott phase. One of the hopes is to establish their Mott parent states and explore these systems' potential of realizing novel electronic states upon carrier doping. However, once doped, little is understood regarding the role of their reduced Coulomb interaction U relative to their strongly correlated 3d-electron cousins. Here we show that, upon hole-doping a candidate J(eff)=1/2 Mott insulator, carriers remain localized within a nanoscale phase-separated ground state. A percolative metal-insulator transition occurs with interplay between localized and itinerant regions, stabilizing an antiferromagnetic metallic phase beyond the critical region. Our results demonstrate a surprising parallel between doped 5d- and 3d-electron Mott systems and suggest either through the near-degeneracy of nearby electronic phases or direct carrier localization that U is essential to the carrier response of this doped spin-orbit Mott insulator.

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.

Three-dimensional magnetic correlations in multiferroic LuFe2O4.

We present single crystal neutron diffraction measurements on multiferroic LuFe(2)O(4). Magnetic reflections are observed below transitions at 240 and 175 K indicating that the magnetic interactions in LuFe(2)O(4) are three-dimensional in character. The magnetic structure is refined as a ferrimagnetic spin configuration below the 240 K transition. Below 175 K a significant broadening of the magnetic peaks is observed along with the buildup of a diffuse component to the magnetic scattering.

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.