On Structure,Optical Properties and Photodegradated Ability of Aurivillius‐Type Bi3TiNbO9 Nanoparticles

Bi₃TiNbO₉ nanoparticles with an acceptor dopant of Ni²⁺ ion were prepared by the conventional Pechini sol–gel synthesis. The X‐ray polycrystalline diffraction measurements (XRD) and the Rietveld refinements of Bi₃TiNbO₉ samples were completed. The surface property of Bi₃TiNbO₉ nanoparticles was investigated by transmission electron microscope, scanning electron microscope), and N₂ adsorption–desorption isotherms. Bi₃TiNbO₉ nanoparticles showed an optical band gap with energy of 3.1 eV in the UV region. While the Ni²⁺‐doping could greatly reduce the band energy of Bi₃TiNbO₉:xNi²⁺ nanoparticles to 2.79 eV (x = 0.05) and 2.61 eV (x = 0.1). This indicates that the Ni‐doped samples could be excited by UV–visible light. The photocatalytic abilities were tested by the photodegradation on methylene blue solution (MB) and phenol solutions excited by visible light. Accordingly, the photocatalytic activity was improved by the Ni‐doping in B‐sites in this Aurivillius‐type structure. The results concluded that Bi₃TiNbO₉:Ni²⁺ would be a possible candidate as a visible light‐driven photocatalyst. The effective photocatalysis was discussed on the structure characteristic and experiment such as polarized Aurivillius (Bi₂O₂)²⁺ layers, luminescence, and decay lifetimes, etc.     

Raman Vibrations,Domain Structures,and Photovoltaic Effects in A‐Site La‐Modified BiFeO3 Multiferroic Ceramics

Micro‐Raman spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy (TEM), oxygen vacancies, synchrotron X‐ray absorption spectroscopy, magnetizations, optical band gaps, and photovoltaic (PV) effects have been studied in (Bi_1?xLa_x)FeO₃ (BFO100xL) ceramics for x = 0.0, 0.05, 0.10, and 0.15. XRD, Raman spectra, and TEM confirm a rhombohedral R3c symmetry with the tilted FeO₆ oxygen octahedra in all compounds. The low‐frequency Raman vibrations become broader and shift toward higher frequency as La³⁺ increases. Fe K‐edge synchrotron X‐ray absorptions reveal that Fe³⁺ valence and Fe–O–Fe bond angle are not modified by the La³⁺ substitution. All compounds exhibit a linear antiferromagnetic feature. Optical transmission reveals band gaps in the range of 2.22–2.24 eV. The heterostructures of indium tin oxide (ITO) film/(Bi_1?xLa_x)FeO₃ ceramics/Au film show a p–n junction‐like I–V characteristic behavior. The maximal PV power conversion efficiency can reach 0.19% in ITO/BFO15L/Au under illumination of λ = 405 nm. A junction‐like theoretical model can reasonably describe open‐circuit voltage and short‐circuit current as a function of illumination intensity.     

Phase Evolution,Magnetic, Optical,and Dielectric Properties of Zr‐Substituted Bi0.9Gd0.1FeO3 Multiferroics

Polycrystalline BiFeO₃ (BFO) and Bi_0.90Gd_0.10Fe_1?xZr_xO₃ (x = 0.0–0.10; BGFZ_x) ceramics were synthesized by solid‐state reaction method. Rietveld analysis of X‐ray diffraction patterns showed that BFO and BGFZ_x = 0.0 samples are stabilized in rhombohedral structure (space group R3c), whereas a small fraction of orthorhombic phase (space group Pn2₁a) is observed for BGFZ_{x = 0.03–0.10} samples. Suppression and disappearance of some Raman modes indicated a structural phase transition with addition of Zr dopant at Fe site. Magnetic measurements exhibited weak ferromagnetic behavior of BGFZ_x samples with increasing Zr⁺⁴ concentrations. The insertion of Gd⁺³ ions at Bi⁺³ sites and nonmagnetic Zr⁺⁴ ions at Fe⁺³ sites in Fe–O–Fe network suppressed the spin cycloid structure of BFO which in turn enhanced the magnetization of these ceramics. Electron spin resonance spectra revealed the breaking of spin cycloid of BFO due to the development of free spins with addition of Zr⁺⁴ dopants at Fe sites. UV–Visible diffuse reflectance spectra showed one d–d crystal field transition and two charge‐transfer (C–T) transitions along with a sharp absorption of light in visible region for all samples. Almost frequency‐independent dielectric constant and dielectric loss along with very low values of dielectric loss indicated greatly improved dielectric properties for BGFZ_{x = 0.03–0.10} samples.     

Preparation and characterization of a novel activated carbon‐supported N‐doped visible light response photocatalyst (TiO2−xNy/AC)

A photocatalyst, TiO_2?xN_y/AC (activated carbon (AC) supported N‐doped TiO₂), highly active in both the Vis and UV range, was prepared by calcination of the TiO₂ precursor prepared by acid‐catalyzed hydrolysis in an ammonia atmosphere. The powders were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, X‐ray diffraction, N₂ adsorption, Fourier transform infrared spectroscopy and phenol degradation. The doped N in the TiO₂ crystal lattice creates an electron‐occupied intra‐band gap allowing electron‐hole pair generation under Vis irradiation (500–560 nm). The TiO_2?xN_y/AC exhibited high levels of activity and the same activity trends for phenol degradation under both Vis and UV irradiation: TiO_2?xN_y/AC calcined at 500 °C for 4 h exhibited the highest activity. The band‐gap level newly formed by doped N can act as a center for the photo‐generated holes and is beneficial for the UV activity enhancement. The performance of the prepared TiO_2?xN_y/AC photocatalyst revealed its practical potential in the field of solar photocatalytic degradation of aqueous contaminants. Copyright © 2007 Society of Chemical Industry     

Direct Sunlight Catalytic Decomposition of Organic Pollutants via Sm- and Ce-Doped BiFeO3 Nanopowder Synthesized by a Rapid Combustion Technique

In the development of photocatalytic processes towards waste water treatment, we have been long faced three foremost obstacles, including catalyst mass production, photon-energy cost and finally catalyst separation process after the treatment. In this study, such problems were addressed through the development of samarium and cerium-doped BiFeO₃ (BFO) nanoparticles (NPs) (Bi_xRE_xFeO₃; RE?=?Sm, Ce, x?=?0.00, 0.01, 0.03, 0.05;) employing a rapid solution combustion synthesis (SCS). This technique is greatly capable of large scale nanopowder production at low temperature. In the SCS procedure, different amount of oxidant-to-fuel (glycine-to-nitrate ion, Gly/NO₃^?) were investigated (Gly/NO₃^??=?0.2, 0.3, 0.37, 0.56, and 0.8). Moreover, a catalytic sunlight irradiation was employed to study the effect of Sm and Ce dopant contents on the photodegradation of benzene and methyl orange (MO) in the aqueous solution. The as-synthesized catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS) and Brunauer–Emmett–Teller (BET)/Barrett-Joyner Halenda (BJH) techniques. The band gap energy of BFO decreaed from 2.14 to 2.06 eV with the increase of Sm³⁺ contents while it increased up to 2.22 eV in the case of Ce-doped BFO. The solar decomposition of the organic pollutants demonstrated the superior performance of Bi_1-xSm_xFeO₃ photocatalyst rather than using cerium in the BFO crystalline structure which is attributed to the increased surface area and visible light harvesting.

Graphic Abstract

     

Structural,dielectric, vibrational and magnetic properties of Sm doped BiFeO3 multiferroic ceramics prepared by a rapid liquid phase sintering method

Rare earth Sm substituted Bi_1−xSm_xFeO₃ with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO₃ and Sm-doped BiFeO₃. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO₃ ceramics. The magnetic hysteresis measurements at room temperature and 5 K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.     

Photocatalytic,magnetic, and electrochemical properties of La doped BiFeO3 nanoparticles

We successfully prepared La_1?xBi_xFeO₃ (L_xB_1?xFO, x?=?0.01–0.1) nanoparticles using a sol-gel technique, and studied their photocatalytic, magnetic, and electrochemical properties. Structural refinement studies of the prepared nanoparticles revealed a gradual structural transition from rhombohedral to orthorhombic. The average grain size was observed to decrease with increasing the concentration of La. The photocatalytic degradation of Rhodamine B (RhB) in the presence of the prepared nanoparticles was studied under visible light irradiation. The L_0.06B_0.94FO nanoparticles showed higher degradation efficiency compared to pure BiFeO₃ (BFO) nanoparticles. Magnetic studies showed that La doping improved the magnetization of BFO due to the reduction in grain size and destruction of cycloid coupling of spins. Higher specific capacitance values were obtained for La doped BFO (LBFO) nanoparticles compared to BFO nanoparticles. A maximum specific capacitance of 219?F?g^?1 was obtained at a current density of 1?A?g^?1 for LBFO nanoparticles.     

Hydrothermal synthesis of Li co-doped Zn0.98Mg0.02O nanoparticles and their structural,optical and electrical properties

Zn_0.98−xMg_0.02Li_xO (x=0.0, 0.01, 0.02, 0.03) nanoparticles were synthesized by the hydrothermal method. The structural, optical and electrical properties of the samples were analyzed by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Diffuse Reflectance UV–vis spectroscopy, and Hall effect measurements. XRD results showed that Zn_0.98−xMg_0.02Li_xO with wurtzite structure are obtained without impurities and additional phases. The lattice parameters (a, c) initially decrease, but they increase with further Li doping. The optical measurements exhibited blue-shift of optical band edge and widening of the band gap. Temperature dependent transport measurements using Van der Pauw method showed that Li doping increased the resistivities and charge carrier density, while it decreased the Hall mobility.     

Investigation of structural,optical, dielectric and magnetic studies of Mn substituted BiFeO3 multiferroics

A series of Mn doped BiFeO₃ with composition BiMn_xFe_1−xO₃ (x = 0.0, 0.025, 0.05, 0.075, 0.1) was synthesized via a citrate precursor method. Structural, morphological, optical, electrical and magnetic properties were investigated by using various measurement techniques. XRD patterns confirmed that the materials possess distorted rhombohedral structure with space group R3c. Average crystallite size was found to be in the range 18–36 nm. A decrease in the value of lattice parameters has been observed due to contraction of unit cell volume with Mn doping. Higher tensile strain for the prepared nanoparticles was observed in Hall-Williamson Plot. Field Emission Scanning Microscopy (FESEM) showed the spherical, uniform, dense nanoparticles in the range 80–200 nm. Reduction in grain size was observed which may be due to suppression of grain growth with Mn doping. FTIR studies reported two strong peaks at 552 cm⁻¹ and 449 cm^-1 which confirmed the pervoskite structure. Dielectric properties were studied by measuring the dielectric constant and loss in the frequency range 1 kHz to 1 MHz. Magnetic hysteresis loop showed the retentivity (M_r) increasing from 0.0514 emu/g of BFO to 0.0931 emu/g of 10% Mn doping. Coercivity was found to increase upto 0.0582 T for 5% Mn doping and then reduced to 0.0344 T for 7.5% Mn doping. Saturation magnetization was observed to increase from 0.6791 emu/g for BFO to 0.8025 emu/g for 7.5% and then reduced to 0.6725 emu/g for 10% Mn doping in BFO. Improvement in dielectric and magnetic properties makes this material as a promising candidate for multifunctional device applications.     

Synthesis of Nanoparticulate In‐Doped BiVO4 for Enhanced Visible‐Light Photocatalytic Degradation of Dye

Indium (2.9, 3.5, and 4.9 at. %)‐doped and pristine monoclinic BiVO₄ nanoparticles were synthesized by hydrothermal method. They were characterized by high‐resolution scanning electron, field emission scanning electron, transmission electron and high‐resolution transmission electron microscopies, powder X‐ray and selected‐area electron diffractometries, energy‐dispersive X‐ray, Raman, UV‐visible diffuse reflectance, photoluminescence, and solid‐state impedance spectroscopies. The band gap and near‐band‐gap emission of 4.9% In‐doped BiVO₄ nanoparticles are larger than those of the rest of the nanomaterials. The charge‐transfer resistance of 4.9% In‐doped BiVO₄ is the least. In‐doping enhances visible‐light photocatalytic activity.     

Poly(o-toluidine dihydrochloride): Spectral Characterization and Synthesis of Eskolite Nanoparticles

Poly(o-toluidine?·?2HCl) and its doped polymers with Mn and Cr ions have been synthesized and characterized by FT-IR, UV–Vis. and thermogravimetrical analyses. Potassium dichromate has been used as an initiator and a dopant of chromium in CrPOT preparation. The effect of doping on thermal and optical properties of Poly(o-toluidine dihydrochloride) has been discussed.

CrPOT has been used as a precursor of Cr₂O₃ nanoparticles through thermal decomposition rout. The obtained nanoparticles have been characterized by X-ray diffraction and high resolution transmission electron microscope. The results indicated that Cr₂O₃ exists in hexagonal structure as mesoporous Eskolit with average particle size of 48?nm. Optical band gap measurements indicated that Eskolite nanoparticles have wider band gap than the bulk.     

Investigation of optical,structural, FTIR and magnetic properties of Sn substituted Zn0.98Mn0.02O nanoparticles

Zn_0.98Mn_0.02O and Zn_0.98−xMn_0.02Sn_xO (x=2% and 4%) nanoparticles have been successfully synthesized via sol–gel method. X-ray diffraction (XRD) confirmed the hexagonal wurtzite structure of the samples and also successful Sn doping without any secondary phases. The microstructure of ZnMnO was significantly altered where the morphology was turned from mixed plate-like structure to spherical like structure by Sn substitution which was confirmed by electron microscope images. The energy dispersive X-ray (EDX) analysis confirmed the presence of Sn and Mn in Zn–O nanoparticles. The observed narrowing of energy gap (red shift) from 3.85 eV (Sn=0%) to 3.66 eV (Sn=4%) was discussed based on size effect and generation of free carrier concentrations. The improved optical properties of Sn–Zn–Mn–O evidenced for developing opto-electronic devices with better conversion efficiency. The shift of lattice mode (position) around 527–548 cm⁻¹ and the change in shape of the band demonstrated the presence of Sn in Zn–Mn–O. The decrease of UV emission intensity and increase of defect related blue and green emissions indicated the possible generation of white light sources and display devices. The superior magnetic property of Sn doped Zn_0.98Mn_0.02O was explained by the intrinsic exchange interaction between Zn/Mn/Sn ions through the defects induced by Sn.     

Visible light induced self-cleaning performance of iron-doped TiO2 nanoparticles for surface applications

This study aimed to enhance the visible light photosensitivity of TiO₂ nanoparticles for self-cleaning applications by doping with Fe³⁺. Nanocrystalline undoped and Fe-doped TiO₂ (Ti_1 − xFe_xO₂, x = .01–.04) were synthesized via sol–gel method. The results demonstrated that Fe-doped TiO₂ nanoparticles exhibited visible light sensitivity and self-cleaning properties. An increased Fe concentration resulted in a red shift in the absorption band edge. Fe_0.03-doped TiO₂ with an average particle size of ∼21 nm, a crystallite size of ∼12 nm, and a band gap of ∼2.86 eV showed the highest photocatalytic activity (60% methylene blue degradation) and super-hydrophilicity (water droplet contact angle 9°) under visible light radiation. These findings highlight the potential of Fe-doped TiO₂ nanoparticles as a promising material for self-cleaning applications.     

Influence of Fe3+-doping on optical properties of CeO2−y nanopowders

Ce_1?xFe_xO_2?y (0≤x≤0.05) nanopowders were synthesized using hydrothermal method at low calcination temperature and low doping regime. Structural and morphological characterization has been carried out by the X-ray diffraction method and non-contact atomic force microscopy. Vibrational properties were investigated by Raman spectroscopy. It was observed that the content of oxygen vacancies increased significantly with Fe doping up to 3 mol%. For higher dopant concentration, phase separation was detected. The optical properties of pure and Fe³⁺-doped CeO_2?y samples were investigated by spectroscopic ellipsometry. Several analytical models were applied to analyze the optical absorption onset of ceria defective structure. It was found that, Cody–Lorentz model most suitably described the sub-band gap region of CeO_2?y nanopowders and consequently gave more accurate band gap values, which are closer to the direct band gap transitions than to the indirect ones. The increased content of localized defect states in the ceria gap and corresponding shift of the optical absorption edge towards visible range in Fe-doped samples can significantly improve the optical activity of nanocrystalline ceria.     

Magnetic Properties of Mn‐doped SnO2 Thin Films Prepared by the Sol–Gel Dip Coating Method for Dilute Magnetic Semiconductors

Manganese‐doped tin oxide (SnO₂:Mn) thin films were deposited on glass substrates by the sol–gel dip coating technique. The effect on structural, morphological, magnetic, electrical, and optical properties in the films with different Mn concentrations (0–5 mol%) were investigated. X‐ray diffraction patterns (XRD) showed the deterioration of crystallinity with increase in Mn‐doping concentration. Scanning electron microscopy (SEM) studies showed an inhibition of grain growth with an increase in Mn concentration. X ray photoelectron spectroscopy (XPS) revealed the presence of Sn⁴⁺ and Mn³⁺ in SnO₂: Mn films. SnO₂: Mn films show ferromagnetic and paramagnetic behavior. These SnO₂:Mn films acquire n‐type conductivity for 0–3 mol% (SnO₂ ‐ Sn_0.97Mn_0.03O_{2) ‐}doping concentration and p type for 5 mol% Mn‐doping concentration(Sn_0.95Mn_0.05O₂) in SnO₂ films. An average transmittance of > 75% (in UV‐Vis region) was observed for all the SnO₂:Mn films. Optical band gap energy of SnO₂: Mn films were found to vary in the range 3.55 to 3.71 eV with the increase in Mn‐doping concentration. Photoluminescence (PL) spectra of the films exhibited an increase in the emission intensity with increase in Mn‐doping concentration which may be due to structural defects or luminescent centers, such as nanocrystals and defects in the SnO₂. Such SnO₂:Mn films with structural, magnetic and optical properties can be used as dilute magnetic semiconductors.     

Structural,magnetic and optical properties of Ce substituted BiFeO3 nanoparticles

Ce substituted Bi_1−xCe_xFeO₃ (x=0.03, 0.05, 0.07 and 0.10) nanoparticles were prepared by a tartaric acid based sol–gel route. X-ray diffraction patterns and Raman spectra revealed a structural phase transition from rhombohedral to orthorhombic phase for x=0.10 sample. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization with increasing Ce concentration. The improved magnetic properties due to the breaking of spin cycloid with Ce substitution have been observed from electron spin resonance (ESR) study. The measured g-values for all samples are greater than 2 and the ESR lines shift towards higher g-value with increasing Ce concentration, indicating ferromagnetic nature of these samples. UV–visible diffuse reflectance spectra showed a sharp absorption in the visible region with two d–d and three charge transfer (C-T) transitions. Prominent red shift in the band gap indicates a significant change in the band structure of the doped nanoparticles.     

Synthesis of visible light-active nanostructured TiOx (x < 2) photocatalysts in a flame aerosol reactor

Titanium dioxide is a wide band gap (3.2 eV) semiconductor which is photo-active when irradiated with UV light. For wider scale use of TiO₂ as a photocatalyst, its activity needs to be extended to the visible light region (constituting 45% of total incident solar energy). A diffusion flame aerosol reactor (FLAR) with an oxygen lean environment in the particle formation zone has been used to synthesize oxygen deficient titanium suboxide (TiO_x with x < 2) nanoparticles. Using a standard-based electron energy loss spectroscopy (EELS) technique, the non-stoichiometry (x in TiO_x) in the flame synthesized particles has been quantified with high accuracy (uncertainty less than 3%). Under an oxygen lean environment in the particle formation zone, the non-stoichiometry in the TiO_x particles is a function of the flame temperature. The value of x in the flame synthesized TiO_x nanoparticles is in the range of 1.88 < x < 1.94. Diffuse reflectance spectra confirmed that the oxygen deficient TiO_x particles absorbed visible light. Visible light activity of the TiO_x particles is demonstrated by photocatalytic degradation of methyl orange solution under visible light illumination.     

Synthesis of TiO2−xNy/Ag‐PbMoO4 Composite and Their Photocatalytic Activity Under Simulated Solar Light Irradiation

TiO_2?xN_y/Ag‐PbMoO₄ composite were synthesized by sonochemical method. The results revealed that the band‐gap energy absorption edge of TiO_2?xN_y/Ag‐PbMoO₄ composite was shifted to a longer wavelength as compared to TiO₂, TiO_2?xN_y, PbMoO_4, and Ag‐PbMoO₄. The TiO_2?xN_y/Ag‐PbMoO₄ composite showed the enhanced photocatalytic activity for degradation of indigo carmine dye (ICD) under simulated solar light irradiation. The TiO_2?xN_y/Ag‐PbMoO₄ composite exhibited the highest percentage (95.4%) of degradation of ICD and the highest reaction rate constant (0.0244 min^?1) in 2 h. The results suggested that a good combination of Ag and TiO_2?xN_y nanoparticles has great influence on the photocatalytic behavior of PbMoO₄.     

Structural,Optical, and Magnetic Properties of Nickel‐Doped Tin Dioxide Nanoparticles Synthesized by Solvothermal Method

We have successfully synthesized Sn_1?xNi_xO₂ (0.05 ≤ x ≤ 0.15) solid solutions in order to study their structural, optical, and magnetic properties at different Ni concentrations. X‐ray diffraction showed monophasic and crystalline tetragonal structure. The shifting of peaks toward higher angle is attributed to the incorporation of Ni²⁺ ions in SnO₂ host lattice. Particle growth restrained upon Ni‐doping and found to be in the range of 8–12 nm. Ni‐doped SnO₂ nanoparticles show blue shift in band gap studies, which is found to be in the range of 3.9–4.1 eV. High surface areas have been achieved for these solid solutions, which come out to be 130, 200, 457, 497, and 680 m²/g, respectively. The solid solutions exhibit paramagnetic behavior along with antiferromagnetic exchange coupling.     

Catalytic and Heating Behavior of Nanoscaled Perovskites under Microwave Radiation

Perovskite powders of the types La_0.5Ca_0.5Al_yM_1–yO_3–δ (y = 0–0.8), M = Fe, Cr, Mn, Co and La_xSr_1–xMn_yCo_1–y (x = 0.5–1, y = 0–1) were prepared via a sol‐gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1000 °C for 6 h. The phase composition of the samples was established by X‐ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100 nm in size and formed agglomerates larger than 1.0 μm. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3 g of catalyst in a fixed‐bed quartz reactor (i.d. = 18 mm) under thermal‐assisted and microwave‐assisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M‐atom and its number of unpaired d‐electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods.