Enhanced photocatalytic performance of novel self-assembled floral β-Ga2O3 nanorods

Self-assembled monoclinic phase of novel floral β-Ga₂O₃ nanorods were prepared using reflux condensation method by controlled precipitation of metal cations with urea. The structural and morphological properties were investigated by X-ray powder diffraction, Raman spectroscopy and Scanning electron microscope. Single-crystalline nanorods with size 100 nm involved in the self-assembly process to form flowery pattern have diameter ～1 μm with surface area 40.8 m²/g confirmed from transmission electron microscope and Brunauer–Emmett–Teller analysis. The band gap energy of 4.59 eV was evaluated from the UV–vis diffuse reflectance spectrum and the photoluminescence spectrum displayed the characteristic luminescence and blue-light emission peaks. Further, the photocatalytic activity of novel β-Ga₂O₃ floral nanorods towards the photodegradation of Rhodamine B in aqueous solution under ultra violet light irradiation showed better photocatalytic activity than the commercial photocatalyst Degussa P25 TiO₂.     

A facile hydrothermal route to synthesize novel PbI2 nanorods

We report the synthesis of PbI₂ nanorods by reacting lead acetate with elemental iodine at room temperature by virtue of a wet chemical method at mild reactions. The diameters of the obtained PbI₂ nanorods are about 54 nm. The present technique may open a new doorway to one-dimensional nanosized rods from the same kind of materials with irregular shape or large size. X-ray powder diffraction (XRD), Fourier transform infrared analysis (FTIR), ultraviolet–visible–near infrared analysis (UV–vis–NIR), photoluminescence measurements (PL) and scanning electron microscopy (SEM) were used to characterize PbI₂ nanorods. The as obtained products were analyzed by X-ray powder diffraction, which confirms the formation of solid PbI₂ nanorods. From the UV–vis–NIR studies the band gap of PbI₂ nanorod was estimated. The various functional groups present in the PbI₂ nanorods were identified by FTIR analysis. Intense photoluminescence was also observed with some spectral tuning possibly giving a range of emission photon energies approximately spanning from 2.1 to 3.5 eV.     

Electronic structure and optical properties of BaMoO4 powders

Barium molybdate (BaMoO₄) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 °C for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm⁻¹, which is associated to the Mo–O antisymmetric stretching vibrations into the [MoO₄] clusters. UV–vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap.     

Preparation of highly efficient Al-doped ZnO photocatalyst by combustion synthesis

Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5–6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 °C for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy (E_g) for the AZO nanopowders were in the range of 3.12–3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light (λ ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electron–hole pair's recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders.     

Effect of Er doping on optical band gap energy of TiO2 thin films prepared by spin coating

In order to evaluate the effect of Er doping in the range of 0–1.0 mol% on optical indirect band gap energy (E_g) of the film, the Er-doped TiO₂ (Er-TiO₂) thin films were spin-coated onto fluorine-doped SnO₂ coated (FTO) glasses. Glancing angle X-ray diffraction (GAXRD) results indicated that the films whose thickness was 550 nm consisted of pure anatase and FTO substrate. The anatase (101) TiO₂ peaks became broader and weaker with the rise in Er content. The apparent crystallite size decreased from 12 nm to 10 nm with increasing the amount of Er from 0 mol% to 1.0 mol%. UV–vis spectrophotometry showed that the values of E_g decreased from 3.25 eV to 2.81 eV with the increase of Er doping from 0 to 0.7 mol%, but changed to 2.89 eV when Er content was 1.0 mol%. The reduction in E_g might be attributed to electron and/or hole trapping at the donor and acceptor levels in the TiO₂ band structure.     

Synthesis,crystal structure,spectroscopic characterization and optical properties of bis(4-acetylanilinium) tetrachlorocobalt (II)

The chemical preparation, crystal structure, spectroscopic investigations and optical features are given for a novel organic–inorganic hybrid material [C₈H₁₀NO]₂CoCl₄.The compound is crystallized in the orthorhombic space group Cmca, with the following unit cell parameters: a=19.461(2) Å, b=15.523(2) Å, c=13.7436(15) Å, and Z=8. The atomic arrangement shows an alternation of organic and inorganic layers along the b-axis. The cohesion between these entities is performed by N–H…Cl and N–H…O hydrogen bonds and π–π stacking interactions.Infrared and Raman spectra at room temperature are recorded in the 4000−400 and 4000−0 cm⁻¹ frequency regions, respectively and analyzed on the basis of literature data. This study confirms the presence of the organic cation [C₈H₁₀NO]⁺ and of the [CoCl₄]²⁻ anion. UV–vis spectroscopy results showed the indirect transition with band gap energy 2.98 eV.     

Energy structure and absorption spectra of colloidal CdS nanocrystals in gelatin matrix

We investigate the energy structure of colloidal CdS nanocrystals by measuring the UV–vis absorption spectra. Nanocrystals were synthesized by sol–gel method in a gelatin matrix in the size range from 2.5 to 3.9 (±0.2) nm. In order to interpret the UV–vis absorption spectra we calculate the energy spectrum of electron quasi-stationary states using the model of open nanocrystal as well as the hole stationary spectrum in a two-band approach. It is shown that the main contribution to the absorption spectrum is made by interband transitions 1S_3/2→1S_e and 1P_3/2→1P_e, and its shape is determined by the size distribution of nanoparticles. For this system the estimated values of the effective masses of the heavy hole and light hole are 1.44m₀ and 0.28m₀, respectively.     

Large piezoelectric strain observed in sol–gel derived BZT–BCT ceramics

High performance lead (Pb)-free piezoelectric ceramics with excellent piezoelectric properties is in great demand for sensor and actuator applications. Barium zirconate titanate–barium calcium titanate [xBZT–(1 − x)BCT] (x = 0.5) is one such lead free system, which exhibits high piezoelectric properties similar to lead zirconate titanate (PZT). In this study we report the synthesis and characterization of this lead free [xBZT–(1 − x)BCT] (x = 0.5) via wet chemical sol–gel method. Calcination of the BZT–BCT precursor only at 1000 °C (against 1300 °C reported in the literature) for 4 h resulted in formation of single phase nanoparticles (<50 nm) as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. Highly dense and homogenous microstructure with 95% of the theoretical density was obtained by solid-state sintering of the green pellets at 1550 °C. Remanent polarization (Pr) of 11.55 μC/cm² and relative permittivity of 20,020 at the Curie temperature of 95 °C were obtained. Electrically poled BZT–BCT ceramics samples exhibited high piezoelectric charge coefficients, d₃₃ ∼ 530 pC/N, d₃₃* ∼ 942 pm/V, large electromechanical coupling coefficient k_p ∼ 0.45 and a large strain of 0.15%, which are comparable to those of lead based piezoelectric ceramics. The excellent piezoelectric properties of this sol–gel derived BZT–BCT system has been analyzed and correlated to its structure in this report.     

Synthesis and characterization of nanostructural CuS–ZnS binary compound thin films prepared by spray pyrolysis

We have investigated the effect of zinc concentration ([Zn]/[Cu]=0–100 at%) on nanostructural, optical and electrical properties of CuS–ZnS binary thin films grown on glass substrate by the spray pyrolysis technique. X-ray diffraction analysis showed that the films were crystallized with mixed structures of CuS hexagonal and ZnS cubic structure. UV–vis optical measurements analysis showed that these binary films have a relatively high absorption coefficient (～10⁵ cm^?1) in the visible spectrum with a direct band gap in the range of 2.57–2.45 eV in agreement with the corresponding room temperature PL spectra. The electrical studies showed that all these samples have a p-type conductivity and the free hole density decreases with increasing [Zn]/[Cu] molar ratio, in agreement with the reflectance spectra of the layers, originating from plasma oscillations.     

Phase formation and electrical properties of BNLT–BZT lead-free piezoelectric ceramic system

Phase formation study in lead-free piezoelectric ceramics based on lanthanum doped bismuth sodium titanate (Bi_0.4871Na_0.4871La_0.0172TiO₃:BNLT) and zirconium doped barium titanate (BaZr_0.05Ti_0.95O₃:BZT), has been carried out in the system of (1−x)BNLT–xBZT where x = 0.0–1.0, by two-step mixed oxide method. It was observed that the addition of BZT in the BNLT ceramics developed the dielectric and piezoelectric properties of the ceramics with the optimum piezoelectric constant (d₃₃) and dielectric constant (ε_r) at room temperature of about 138 pC/N and 1651, respectively, from the 0.2 BNLT to 0.8 BZT ceramic sample. The Curie temperature (T_C) of this ceramic was found at 295 °C which is 195 °C higher than that of pure BZT ceramics, promising the use of this ceramic in a higher range of temperature.     

Synthesis,crystal growth and characterization of a semiorganic material: Calcium dibromide bis(glycine) tetrahydrate

Single crystals of semiorganic material calcium dibromide bis(glycine) tetrahydrate were grown from aqueous solution. The crystal belongs to monoclinic system, with a = 13.261(5) Å, b = 6.792(2) Å, c = 15.671(9) Å and β = 91.68(4)°. The presence of the elements in the title compound was confirmed by energy dispersive X-ray analysis. The solubility and metastable zone width were found. The grown crystals were tested by powder XRD, FTIR, Thermo Gravimetric and Differential Thermal Analysis, UV–vis–NIR analysis, dielectrical and mechanical studies. The transmittance of calcium dibromide bis(glycine) tetrahydrate crystal has been used to calculate the refractive index n, the extinction coefficient K and both the real ɛ_r and imaginary ɛ_i components of the dielectric constant as functions of wavelength. The optical band gap of calcium dibromide bis(glycine) tetrahydrate is 3.23 eV.     

Effective growth and characterization of piperazinium orthophthalate single crystal yielding high second harmonic generation efficiency

Good quality organic non-linear optical single crystal of piperazinium orthophthalate (PPA) was grown successfully by solution growth at room temperature by achieving the supersaturation state in slow evaporation method. The powder XRD analysis confirms the crystalline nature and structural parameters of the grown PPA crystal. The FTIR and Raman spectra confirm the existence of acid-base functional groups along with their vibrational mode exhibited, present in the grown PPA crystal. UV–Vis spectrum exhibits better transparency in the visible region with cut-off wavelength of 330 nm and the energy band gap (E_g) is analyzed to be 3.8 eV. Photoluminescence spectra shows good optical property with the excitation of 342 nm and two emission peaks in near edge UV band with blue emission at 364 and the energy transition in deep level defect states in crystals by exhibiting the green emission at 533 nm respectively. The thermal stability and the thermal absorption of the PPA crystal were identified by the TG - DTA analysis and obtained thermal stability was up to 88 °C. Vickers micro hardness test illustrates the mechanical stability of the grown PPA crystal and it belong to soft category (n = 4.6). Etching studies illustrates the growth pattern of the grown crystal using water as etchant. FE-SEM analysis shows the perfect smooth morphology of the grown PPA crystal. Second harmonic generation study illustrates the grown PPA crystal (λ = 532 nm) exhibit good nonlinear optical response.     

Lattice Compatibility Theory LCT investigations on physical and optical constants of antimony processed antimonite nano-films

Antimonite (Sb₂S₃) thin films have been synthesized through an annealing process in sulfur vapors at 300 °C of Sb thermal evaporated films. Deposited films have been characterized by X-ray diffraction, scanning electron microscopy and UV–vis–NIR spectroscopy. X-ray diagrams of these films have confirms that they were well crystallized in orthorhombic structure and some parameters such as the lattice parameter, crystallite size, microstrain and degree of preferred orientation have been reported and correlated with the effect of crystallite size. Optical properties of Sb₂S₃ films have been characterized by solid-state UV–visible absorption spectroscopy, and the band gap E_g was between 1.75 and 2.23 eV. Moreover, additional opto-thermal investigation and analyses within the framework of the Lattice Compatibility Theory provided plausible explanation for thickness-dependent incorporation of sulfur element inside antimony elaborated matrices.     

Effect of calcination temperature on phase transformation,structural and optical properties of sol–gel derived ZrO2 nanostructures

Zirconia (ZrO₂) nanostructures of various sizes have been synthesized using sol–gel method followed by calcination of the samples from 500 to 700 °C. The calcined ZrO₂ powder samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infra-red spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis.), Raman spectroscopy (RS) and thermogravimetric analysis (TGA). The phase transformation from tetragonal (t) to monoclinic (m) was observed. The average diameter of the ZrO₂ nanostructures calcined at 500, 600 and 700 °C was calculated to be 8, 17 and 10 nm, respectively. The ZrO₂ sample calcined at 500 °C with tetragonal phase shows a direct optical band gap of 5.1 eV. The value of optical band gap is decreased to 4.3 eV for the ZrO₂ calcined at 600 °C, which contains both tetragonal (73%) and monoclinic (27%) phases. On further calcination at 700 °C, where the ZrO₂ nanostructures have 36% tetragonal and 64% monoclinic phases, the optical band gap is calculated to be 4.8 eV. The enhancement in optical band gap for ZrO₂ calcined at 700 °C may be due to the rod like shape of ZrO₂ nanostructures. The tetragonal to monoclinic phase transformation was also confirmed by analyzing Raman spectroscopic data. The TG analysis revealed that the ZrO₂ nanostructure with dominance of monoclinic phase is found to be more stable over the tetragonal phase. In order to confirm the phase stability of the two phases of ZrO₂, single point energy is calculated corresponding to its monoclinic and tetragonal structures using density functional theory (DFT) calculations. The results obtained by theoretical calculations are in good agreement with the experimental findings.     

Properties of hydrothermally processed multi-walled titania nanotubes

We report here, the production principle and optical characteristics of TiO₂ nanotubes (TNTs) grown via a hydrothermal route. As compared to TiO₂ nanoparticles (TNPs), X-ray diffraction study of TNTs exhibited weak diffraction signals along with a characteristic peak at 2θ=9.2°. The morphological study of TNTs was carried out by high resolution transmission electron microscopy (HRTEM) which revealed that each of the TNTs is made of 5–7 walls having an average wall-spacing of 0.36 nm. From the UV–vis optical absorption spectroscopy studies, the optical band gap was estimated to be 3.16 eV, for TNTs and 3.22 eV, for TNPs. The Fourier transform infrared spectroscopy study of TNTs has indicated the presence of Ti–O–Ti stretching vibrations in the range 400–800 cm⁻¹. The electron–phonon coupling parameter was found to be smaller for TNTs (S=0.7) than TNPs (S=1.3). The production of submicron sized long multiwall nanotubes would find scope in nanofluidic and other hybrid devices.     

Preparation and efficient visible light-induced photocatalytic activity of m-BiVO4 with different morphologies

The monoclinic scheelite BiVO₄ crystals with peanut-like, oval, twin-quadrangle and twin-four-pointed star morphologies were synthesized via a facile one step hydrothermal method by using sodium citrate as the chelating agent. The X-ray diffraction and scanning electron microscopy were employed to elucidate the structures and mophologies of the as-prepared BiVO₄ samples. The results showed that the formation of m-BiVO₄ with different morphologies relied on the pH value of the precursor solution. The band gaps values (E_g) of all the BiVO₄ samples were around 2.37–2.45 eV according to the UV–vis diffuse reflectance spectrum, which indicated that samples could strongly absorb in the visible light region. The photocatalytic activities of BiVO₄ crystals were evaluated by degradation of MB in aqueous solution under artificial solar-light. The BiVO₄ samples obtained at different pH values showed different photocatalytic activities during the sunlight-driven photodegradation of methylene blue (MB). The sample with peanut-like-shape prepared at pH=1 exhibited the highest activity, and the photocatalytic conversion could reach above 90% after 3 h of irradiation. The result suggested that m-BiVO₄ with peanut-like-shape could be used as an effective photocatalyst in practical application for organic pollutants degradation.     

Gas sensing property of lithium tetraborate clad modified fiber optic sensor

The micro structured plate-like lithium tetraborate, Li₂B₄O₇ (1 μm in diameter) has been prepared by sol–gel method and characterized structurally by X-ray diffraction and morphologically by scanning electron microscopy. UV–Vis spectrum shows about 60% transparency in the visible region and the optical energy band gap is found to be 3.5 eV which is also confirmed by strong near band edge emission from luminescence spectrum. The spectral characteristics of the cladding modified fiber optic sensor coated with microcrystalline Li₂B₄O₇ are studied for various concentrations of ethanol, methanol and ammonia (50–500 ppm). At 298 K, the sensitivity for ethanol is ?10 counts/ppm which is relatively higher than ammonia (?4 counts/ppm) and methanol (?3 counts/ppm). The time response of the sensor is presented for pure Li₂B₄O₇ with ethanol gas.     

Structural,dielectric and optical properties of sol–gel synthesized 0.55Ba(Zr0.2Ti0.8)O3–0.45(Ba0.7Ca0.3)TiO3 ceramic

Lead-free polycrystalline ceramic 0.55Ba(Zr_0.2Ti_0.8)O₃–0.45(Ba_0.7Ca_0.3)TiO₃ (0.55BZT–0.45BCT) was synthesized by sol–gel method and the dielectric, impedance and optical properties of this ceramic were studied. X-ray diffraction analysis revealed the formation of pure perovskite phase with the coexistence of tetragonal and rhombohedral structures. The high value of dielectric constant (~6,985) with low dielectric loss (~0.013) was obtained at room temperature. Bulk and grain boundary resistances were measured by impedance analysis, which revealed negative temperature coefficient of resistance behaviour in this ceramic. The estimated value of optical band gap was found to be ~3.16 eV, which is related to the presence of intermediate energy levels. Two emission bands one at ~365 nm (UV region) and another at ~465 nm (blue region) were observed in photoluminescence spectrum at room temperature.     

Influence of electron beam irradiation on structural and optical properties of α-Ag2WO4 nanoparticles

The influence of 8 MeV electron beam irradiation on the structural and optical properties of silver tungstate (α-Ag₂WO₄) nanoparticles synthesized by chemical precipitation method was investigated. The dose dependent effect of electron irradiation was investigated by various characterization techniques such as, X-ray diffraction, scanning electron microscopy, UV–vis absorption spectroscopy, photoluminescence and Raman spectroscopy. Systematic studies confirm that electron beam irradiation induces non-stoichiometry, defects and particle size variation on α-Ag₂WO₄, which in turn results changes in optical band gap, photoluminescence spectra and Raman bands.     

Cadmium sulfide quantum dots stabilized by castor oil and ricinoleic acid

Castor oil and ricinoleic acid (an isolate of castor oil) are environmentally friendly bio-based organic surfactants that have been used as capping agents to prepare nearly spherical cadmium sulfide quantum dots (QDs) at 230, 250 and 280 °C. The prepared quantum dots were characterized by Ultra violet–visible (UV–vis), Photoluminescence (PL), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM) and X-ray diffraction (XRD) giving an overall CdS QDs average size of 5.14±0.39 nm. The broad XRD pattern and crystal lattice fringes in the HRTEM images showed a hexagonal phase composition of the CdS QDs. The calculated/estimated average size of the prepared castor oil capped CdS QDs for various techniques were 4.64 nm (TEM), 4.65 nm (EMA), 5.35 nm (UV–vis) and 6.46 nm (XRD). For ricinoleic acid capped CdS QDs, the average sizes were 5.56 nm (TEM), 4.78 nm (EMA), 5.52 nm (UV–vis) and 8.21 nm (XRD). Optical properties of CdS QDs showed a change of band gap energy from its bulk band gap of 2.42–2.82 eV due to quantum size confinement effect for temperature range of 230–280 °C. Similarly, a blue shift was observed in the photoluminescence spectra. Scanning electron microscope (SEM) observations show that the as-synthesized CdS QDs structures are spherical in shape. Fourier transform infra-red (FTIR) studies confirms the formation of castor oil and ricinoleic acid capped CdS QDs.