Optical Characterizations of Hot‐Pressed Erbium‐Doped Calcium Fluoride Transparent Ceramic

Nanoparticles of erbium‐doped calcium fluoride were synthesised by the coprecipitation method. Micromorphology of the obtained nanoparticles was observed by transmission electron microscopy. The nanoparticles were hot‐pressed in a vacuum environment to achieve Er:CaF₂ transparent ceramic. X‐ray diffraction analysis confirmed the crystallization of a single fluorite phase after sintered. Transmittance spectrum of Er:CaF₂ ceramic sample was measured, and the transmittance at 1200 nm reached about 87%. Microstructures were characterized using field‐emission scanning electron microscopy. The luminescence spectrum of Er:CaF₂ transparent ceramics under 488‐ and 978‐nm excitation was measured and discussed. It was evidenced that strong cross‐relaxation processes between Er³⁺ ions occur at high dopant concentration, and favoring the red emission at the expense of the green one.     

Visible‐Light‐Induced Degradation of Methylene Blue by SrBi3VO8 Nanoparticles

Nanosized particles of strontium bismuth vanadate SrBi₃VO₈ were prepared via the Pechini method on the base of citrate‐complexation route. The samples were characterized using X‐ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X‐ray spectra (EDX), X‐ray photoelectron spectroscopic (XPS), and UV–vis absorption spectrum. This bismuth‐containing vanadate presents an efficient absorption in the UV–visible light wavelength region with a narrow band‐gap energy of 2.36 eV and an indirect allowed electronic transition. It is well‐known that hybridization of the 6s and 6p orbitals of Bi³⁺ could result in lone electron pair and yield some very interesting properties. The photocatalytic activities of SrBi₃VO₈ nanoparticles were evaluated by the photodegradation of methylene blue (MB) under visible light irradiation in air atmosphere. These results indicate that SrBi₃VO₈ could be a potential photocatalyst driven by visible light. To understand the charge generation and separation process, the luminescence as well as the decay lifetimes was investigated in the same samples for photocatalysis.     

Band‐Gap Engineering and Enhanced Photocatalytic Activity of Sm and Mn Doped BiFeO3 Nanoparticles

Bi_1‐xSm_xFe_1‐yMn_yO₃ (BSFMO, x = 0.0, 0.05; y = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25) nanoparticles were synthesized by using double solvent sol–gel method. Photocatalytic activity was investigated under UV and visible‐light illumination. The structural, morphological, and optical properties were analyzed by X‐ray diffraction, scanning electron microscopy, and UV‐vis spectroscopy respectively. The crystallite size of BiFeO₃ (BFO) decreases from (57.3–17.2 nm) with the increase in Sm and Mn‐doping concentration. The surface morphology shows that the pure and Sm‐doped BFO nanoparticles are irregular in shape but changes to spherical shape after Mn‐doping up to 25%. The band‐gap engineering of BFO nanoparticles is achieved by co‐doping of Sm and Mn. The band‐gap of BFO could be tuned successfully from 2.08–1.45 eV, which may be due to the distortion induced in Fe‐O octahedron and the rearrangement of molecular orbitals. These results give rise to enhanced photocatalytic activity by degradation of organic dyes (MB, CR, and MV) under the visible‐light illumination.     

Au‐nanoparticle‐decorated SnO2 nanorod sensor with enhanced xylene‐sensing performance

In this work, pure and Au‐nanoparticle‐decorated SnO₂ nanorods were prepared via a one‐step hydrothermal method combined with a facile deposition process, and then characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy. The xylene‐sensing performance of the nanorods was also investigated. The results show that Au nanoparticles with an average diameter of 4‐6 nm were immobilized on the surface of rutile SnO₂ nanorods. As the amount of Au increased, the surface‐adsorbed oxygen species gradually increased. The 12 mol% Au‐SnO₂ nanorods exhibited the highest response to 50 ppm xylene, a lower operating temperature (279 to 255°C), favorable selectivity, and fast response‐recovery speed (3 and 4 seconds, respectively). These properties made the fabricated nanorods good candidates for xylene detection. The possible mechanism for the enhanced xylene‐sensing performance is discussed.     

Enhanced visible‐light‐driven photocatalytic activities of LiInO2 by Mo6+‐doping strategy

A novel visible‐light‐driven photocatalyst of Mo‐doped LiInO₂ nanocomposite was successfully synthesized through a sol‐gel method. The effect of Mo‐doping concentrations on the microstructures and properties of LiInO₂ was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy, photoluminescence, and ultraviolet‐visible absorption spectra. The photocatalytic properties of the as‐prepared samples were evaluated by the photocatalytic degradation of methylene blue (MB) dye under visible‐light irradiation. The results demonstrated that the photocatalytic activity of 6% Mo‐LiInO₂ reached to 98.6%, which was much higher than that of the undoped photocatalyst LiInO₂ (only 46.8%). The enhanced photocatalytic activity is ascribed to Mo‐doping strategy. The holes play an important role in the process of the photodegradation of MB. The superior photocatalytic activity of the as‐prepared Mo‐LiInO₂ nanocomposites suggests a potential application for organic dye degradation of wastewater remediation. This work provides a further understanding on tailoring the band structure of semiconductor photocatalyst for enhancing visible‐light absorption and promoting electron‐hole separation by Mo‐doping strategy.     

Synthesis of Ni2+‐doped ZnAl2O4/ZnO Composite Phosphor Film with Largely Enhanced Polychromatic Emission via a Single‐Source Precursor

Ni²⁺‐doped ZnAl₂O₄/ZnO composite films were successfully fabricated on single crystal silicon substrates through a single‐source precursor route, which mainly involved slurry coating of Ni–Zn–Al‐layered double hydroxide precursor followed by calcination at elevated temperatures. Material characterization has been presented using a combination of X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectra, Raman spectra, UV–vis diffuse reflectance spectra, and fluorescence spectroscopy measurements. The results showed that Ni²⁺ ions could be uniformly doped in the two‐phase ZnO and ZnAl₂O₄ lattices. A broadened and intense polychromatic emission peak covering the whole visible region was obtained over 4.3 mol% Ni²⁺‐doped ZnAl₂O₄/ZnO composite film, which was attributed to the presence of an appropriate number of luminescent Ni²⁺centers in the ZnO and ZnAl₂O₄ double host matrix, thus largely enhancing the related transition. We believe that such unique ZnAl₂O₄/ZnO films can open up a new opportunity for advanced applications of composite phosphors.     

Photocatalytic Activity and Electronic Structure Analysis of N‐doped Anatase TiO2: A Combined Experimental and Theoretical Study

N‐Doped TiO₂ photocatalysts were prepared by a hydrothermal method with tetra‐n‐butyl titanate (TTNB) and triethanolamine as precursors. The obtained samples were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and UV‐visible diffuse reflectance spectra (DRS), respectively. Photocatalytic activities of the anatase products were investigated on the degradation of methyl orange (MO). The incorporation of nitrogen impurity in anatase TiO₂ was studied by the first‐principles calculations based on the density functional theory (DFT). The calculated electronic band structures for substitutional and interstitial N‐doped TiO₂ indicated the formation of localized states in the band gap, which lied above the valence band. Excitation from the impurity states of N 2p to the conduction band could account for the optical absorption edge shift toward the lower energies. It was consistent with the experimentally observed absorption of N‐doped samples in the visible region.     

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.     

Studies on the synthesis of electrospun PAN‐Ag composite nanofibers for antibacterial application

We have successfully synthesized polyacrylonitrile (PAN) nanofibers impregnated with Ag nanoparticles by electrospinning method at room temperature. Briefly, the PAN‐Ag composite nanofibers were prepared by electrospinning PAN (10% w/v) in dimethyl formamide (DMF) solvent containing silver nitrate (AgNO₃) in the amounts of 8% by weight of PAN. The silver ions were reduced into silver particles in three different methods i.e., by refluxing the solution before electrospinning, treating with sodium borohydride (NaBH₄), as reducing agent, and heating the prepared composite nanofibers at 160°C. The prepared PAN nanofibers functionalized with Ag nanoparticles were characterized by field emission scanning electron microscopy (FESEM), SEM elemental detection X‐ray analysis (SEM‐EDAX), transmission electron microscopy (TEM), and ultraviolet‐visible spectroscopy (UV‐VIS) analytical techniques. UV‐VIS spectra analysis showed distinct absorption band at 410 nm, suggesting the formation of Ag nanoparticles. TEM micrographs confirmed homogeneous dispersion of Ag nanoparticles on the surface of PAN nanofibers, and particle diameter was found to be 5–15 nm. It was found that all the three electrospun PAN‐Ag composite nanofibers showed strong antibacterial activity toward both gram positive and gram negative bacteria. However, the antibacterial activity of PAN‐Ag composite nanofibers membrane prepared by refluxed method was most prominent against S. aureus bacteria. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of the electrolyte content on the electrical permittivity,thermal stability,and optical dispersion of poly(vinyl alcohol)–cesium copper oxide–lithium perchlorate nanocomposite solid‐polymer electrolytes

Solid‐polymer electrolytes (SPEs) in the form of poly(vinyl alcohol) (PVA) doped with various amounts (5, 10, and 15 wt %) of lithium perchlorate trihydrate (LiClO₄·3H₂O) and 2 wt % cesium copper oxide (Cs₂CuO₂) nanoparticles were fabricated by a solvent intercalation method. The obtained nanocomposites were evaluated for their chemical structure and microstructural and morphological behaviors via Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy methods, respectively. The obtained dielectric behaviors, alternating‐current conductivity, dielectric modulus, and dielectric relaxation of the SPEs depended on the volume fraction of the electrolyte. Linear behavior of the current–voltage characteristics for all of the SPE films was observed with a slight deviation at a higher voltage. The thermal behaviors of the PVA–Cs₂CuO₂–LiClO₄ films were evaluated by differential scanning calorimetry and thermogravimetric analysis. The refractive index, band‐gap energy, and optical dispersion were examined with UV–visible spectroscopy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45852.     

Effect of BaTiO3 on the microwave absorbing properties of Co‐doped Ni‐Zn ferrite nanocomposites

Coprecipitation and hydrothermal method were utilized for the synthesis of Co‐doped Ni‐Zn ferrite and barium titanate nanoparticles. The microwave absorption properties of Co‐doped Ni‐Zn ferrite/barium titanate nanocomposites with single layer structure were studied in the frequency range of 8.2–12.4 GHz.The spectroscopic characterizations of the nanocomposites were examined using X‐ ray diffraction, scanning electron microscopy, transmission electron microscopy and dynamic light scattering measurement. Thermogravimetric analysis indicated the high thermal stabilities of the composites. The composite materials showed brilliant microwave absorbing properties in a wide range of frequency in the X‐band region with the minimum return loss of ?42.53 dB at 11.81 GHz when sample thickness was 2 mm and the mechanisms of microwave absorption are happening mainly due to the dielectric loss. Compared with pure Co‐doped Ni‐Zn ferrite, Co‐doped Ni‐Zn ferrite/BaTiO₃ composites exhibited enhanced absorbing properties. The microwave absorbing properties can be modulated by controlling the BaTiO₃ content of the absorbers and also by changing the sample thicknesses. Therefore, these composites can be used as lightweight and highly effective microwave absorbers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39926.     

Sodium‐Doped ZnO Nanowires Grown by High‐pressure PLD and their Acceptor‐Related Optical Properties

Sodium‐doped ZnO (ZnO:Na) nanowires were grown with a high‐pressure pulsed‐laser deposition process on silicon substrates using sputtered gold particles as catalysts. The introduction of sodium dopants into ZnO nanowires was confirmed by both X‐ray diffraction spectrum and X‐ray photoelectron spectroscopy. The morphology and microstructural changes in ZnO nanowires due to sodium doping were investigated with scanning electron microscope, high‐resolution transmission electron microscope, and Raman spectrum. Detailed photoluminescence studies of ZnO:Na nanowires revealed characteristic sodium acceptor‐related peaks, for example, neutral acceptor‐bound exciton emission (A⁰X, 3.356 eV), free‐to‐neutral‐acceptor emission (e, A⁰, 3.314 eV), and donor‐to‐acceptor pair emission (DAP, 3.241 eV). This indicated that sodium doping induces stable acceptor level with a binding energy of 133 meV in ZnO:Na nanowires.     

Layer‐by‐layer modification of porous polybenzoxazine with silver nanoparticles for enhanced CO2 storage

Polybenzoxazine (PBZ) xerogels have been synthesized via quasi solventless method and coated with silver nanoparticles using the layer‐by‐layer (LbL) deposition method. After coating, the samples were carbonized at 800 °C to obtain high surface area porous carbon materials to be used for CO₂ storage. Evidences of the successful LbL deposition of the coating was provided by ultraviolet–visible and attenuated total reflection–Fourier transform infrared spectroscopy and the silver nanoparticles top layer was confirmed by scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy. Results showed that the samples coated with silver nanoparticles displayed an increased CO₂ capacity from 3.02 to 3.39 mmol g^?1 when compared with the plain carbon PBZ. The LbL method for the modification of the pore surface in porous PBZ is simple and allows the facile tuning of the inner PBZ pore's surface chemistry with metallic nanoparticles that could be enhanced CO₂ storage capacity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45097.     

Hydrolysis of SnCl2 on polyaniline: Formation of conducting PAni‐SnO2 composite with enhanced electrochemical properties

First time in the literature, we report that polyaniline‐EB can be doped by SnCl₂ to give conducting SnO₂ doped polyaniline novel material. The composite is characterized by Fourier transform infrared, ultraviolet‐visible, X‐ray diffraction, scanning electron micrograph, transmission electron microscopy, and electrochemical methods. The new composite exhibited improved electrochemical properties compared with the virgin polymer. The composite is also expected for its high sensitivity for recognizing volatile organic compounds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Decomposition of gas‐phase aromatic hydrocarbons by applying an annular‐type reactor coated with sulfur‐doped photocatalyst under visible‐light irradiation

BACKGROUND: Unlike many water pollution applications, visible‐light‐driven photocatalysis of gas‐phase pollutants has been reported only rarely. The present study was performed to investigate the feasibility of applying S‐doped visible‐light‐induced TiO₂ to treat gas‐phase aromatic hydrocarbons, using a continuous air‐flow annular‐type reactor. RESULTS: The prepared S‐enhanced TiO₂ powders, along with a commercially available TiO₂ powder (Degussa P‐25), were characterized using diffuse reflectance UV‐VIS‐NIR spectrophotometry, Fourier transform infrared (FTIR) spectrophotometry, X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetry (TG) analyses. A photocatalytic activity test exhibited an increasing trend in degradation reaction rates with increase in flow rate but a decreasing trend in terms of degradation efficiencies. Several experimental conditions induced reasonably high decomposition efficiencies with respect to toluene, ethyl benzene and o,m,p‐xylenes (close to or above 90%), although benzene exhibited a somewhat lower decomposition efficiency. CONCLUSIONS: The S‐doped TiO₂ and undoped P25 TiO₂ powders exhibited different catalyst characteristics. The results demonstrate that an annular‐type reactor coated with visible‐light‐activated S‐doped TiO₂ can serve as an effective tool to treat gas‐phase aromatic hydrocarbon streams. Copyright © 2009 Society of Chemical Industry     

Characterization and Photocatalytic Activities of Mesoporous Silica Containing BiVO4 or La‐BiVO4

Pure monoclinic BiVO₄, La‐doped BiVO₄ catalysts, and MCM‐41 samples containing BiVO₄ and La‐doped BiVO₄ were prepared via precipitation. An improved photocatalytic activity was observed in the degradation of 2,4,6‐trichlorophenol using La‐doped samples. With higher amounts of La, a partial tetragonal crystalline phase of bismuth vanadate was found. The pure and La‐doped BiVO₄ sample were loaded onto the mesoporous silica MCM‐41. Enhanced catalytic activity was achieved in comparison with those not being loaded onto MCM‐41. The lowered band gap following the introduction of La ions and also formation of higher amounts of surface complexes with pollutant molecules are the main reasons of the improved catalytic activity. A comparison of the extent of different chlorophenols toward degradation over the prepared catalysts revealed that under current experimental conditions the samples with more chloride groups suffer higher degradation.     

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     

Niobium‐Doped Titania Photocatalyst Film Prepared via a Nonaqueous Sol‐Gel Method

Niobium‐doped Titanium dioxide (Nb:TiO₂) transparent films were successfully deposited on glass substrates using a non‐aqueous sol‐gel spin coating technique. The effect of Nb concentration on the structural and photocatalytic properties of Nb:TiO₂ films was studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV visible spectroscopy. The films with 12 at.% (atomic percent) Nb doped TiO₂ showed excellent photocatalytic activity through 97.3% degradation of methylene blue (MB) after 2 h of UV irradiation.     

Effects of an oxygen‐ion beam (O+7, 100 MeV) and γ irradiation on polypyrrole films

Nanostructured polypyrrole films doped with para‐toluene sulfonic acid were prepared by an electrochemical process, and a comparative study of the effects of swift heavy ions and γ‐ray irradiation on the structural and optical properties of the polypyrrole was carried out. Oxygen‐ion (energy = 100 MeV, charge state = +7) fluence varied from 1 × 10¹⁰ to 3 × 10¹² ions/cm², and the γ dose varied from 6.8 to 67 Gy. The polymer films were characterized by X‐ray diffraction, ultraviolet–visible spectroscopy, and scanning electron microscopy. The X‐ray diffraction pattern showed that after irradiation, the crystallinity improved with increasing fluence because of an increase in the crystalline regions dispersed in an amorphous phase. The ultraviolet–visible spectra showed a shift in the absorbance edge toward higher wavelengths, which indicated a significant decrease in the band gap of the polypyrrole film after irradiation. The scanning electron microscopy study showed a systematic change in the surface of the polymer. A similar pattern was observed with the γ irradiation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Facile Ion‐Exchange Synthesis and Visible Light Photocatalytic Studies of Cu2+, Sn2+, and Ag+‐Substituted LiMg0.5Ti0.5O2

A novel series of visible light‐sensitive Cu²⁺, Sn²⁺, and Ag⁺‐substituted LiMg_0.5Ti_0.5O₂ photocatalysts were synthesized by a facile ion‐exchange method and characterized by XRD, UV‐Vis diffuse reflectance spectra, scanning electron microscopy equipped with an X‐ray energy‐dispersive spectroscopy, Brunauer‐Emmett‐Teller surface area, inductively coupled plasma mass spectrometry, and thermal gravimetric analysis. The characterization results showed that morphology, crystallite size, and surface areas of the ion‐exchange products were almost similar to the parent compound. Absorption edges of Ag⁺‐doped (AMT), Cu²⁺‐doped (CMT), and Sn²⁺‐doped (SMT) samples were red shifted remarkably into the visible light region while parent LiMg_0.5Ti_0.5O₂ (LMT) was UV active. Photocatalytic activity of these samples was evaluated by studying the degradation of methylene blue and nitro benzene under visible light irradiation and the stability of all samples during photocatalytic experiment was also investigated. The activity of all photocatalysts was ranked accordingly as SMT ≥ AMT > CMT > LMT. The correlation between photocatalytic properties, band gap energy, rate of recombination of the charge carriers, and amount of ^●OH radicals generated during photocatalysis and the underlying reasons were discussed.