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.     

Synthesis of High‐Temperature‐Stable TiO2 and its Application on Ag+‐Activated Ceramic Tile

The main purpose of study was to provide a common synergy using Ag⁺‐doped calcium phosphate powder and high‐temperature‐stable TiO₂ for antibacterial and photocatalytic tile applications. Thermally stable SiO₂‐modified TiO₂ active layer was deposited on Ag⁺‐activated ceramic tiles by spray coating. The results showed that a nearly 100% cleanability degree was detected for SiO₂‐modified TiO₂ (TS)‐coated antibacterial tiles when compared uncoated and unmodified TiO₂‐coated tiles. Antibacterial tests and colorimetric analyses indicated that ceramic tiles provide both antibacterial and photocatalytic properties simultaneously.     

A Visible Light Photocatalyst of Carbonate‐Like Species Doped TiO2

Carbon‐doped TiO₂ nanomaterials have been successfully synthesized via an effective two‐step procedure involving hydrothermal method and followed by a low‐temperature calcination treatment process, through which a controllable amount of carbonate‐like species could be incorporated into TiO₂. First‐principles calculations suggest the TiO₂ doped with carbon in form of carbonate‐like species can effectively extend the adsorption of the material from ultraviolet region to visible light. And it is experimentally found that carbon‐doped TiO₂ nanomaterials exhibit much higher photocatalytic activity than reference P25 and TiO_2?xN_x catalysts toward the liquid‐phase degradation of organic pollutants under visible light (420 nm < λ < 800 nm) irradiation. The presence of synergic effect between carbonate‐like doping and anatase TiO₂ is believed to play an essential role in affecting the photocatalytic reactivity, and the response to the visible light is ascribed to the narrowed band gap energy controlled by carbon doping. Moreover, the roles of active species in the photocatalytic process are compared using different types of active species scavengers. Meanwhile, the degradation mechanism of the photocatalysis is proposed. It is hoped that our work could provide valuable information on the design of carbonate‐like doped semiconductor with more excellent properties and set the foundation for the further industrial application.     

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.     

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.     

Synthesis of nitropyridine‐based π‐conjugated polymers and their chemical properties

π‐Conjugated poly(3‐nitropyridine‐2,5‐diyl) ( PPy‐3‐NO₂ ), poly(3,3′‐dinitro‐2,2′‐bipyridine‐5,5′‐diyl) ( PBpy‐3,3′‐diNO₂ ), and a poly(arylene ethynylene) type polymer consisting of a 3,3′‐dinitro‐2,2′‐bipyridine unit ( PAE‐1 ) were synthesized by Cu‐promoted Ullmann coupling reaction and Pd‐catalyzed coupling reaction. PPy‐3‐NO₂ and PAE‐1 were soluble in organic solvents such as DMSO, DMF, and chloroform, and gel permeation chromatography analysis showed a number average molecular weight (M_n) of 9,300 and 12,300, respectively. PPy‐3‐NO₂ gave intrinsic viscosity, [η], of 0.53 dL g^?1 in DMF. PBpy‐3,3′‐diNO₂ had somewhat lower solubility. The polymers exhibited a UV–vis peak at about 430 nm. PPy‐NO₂ received electrochemical reduction at ?1.5 V versus Ag⁺/Ag in acetonitrile, and gave an electrochemical redox cycle in a range from 0 to ?1.1 V versus Ag⁺/Ag in an aqueous solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1763–1767, 2006     

Luminescence and Quantum Efficiencies of Eu3+‐Doped Vanadate Garnets

Nondoped and 5.0 mol% Eu³⁺‐doped vanadate garnets Ca₅Mg₄(VO₄)₆, NaCa₂Mg₂[VO₄]₃, KCa₂Mg₂[VO₄]₃, and NaSr₂Mg₂[VO₄]₃ were synthesized by solid‐state reactions. The formation of single‐phase compound with garnet structure is confirmed by X‐ray diffraction. The photoluminescence (PL) and PL excitation (PLE) spectra are investigated together with color coordinates. The luminescence process is discussed on the charge‐transfer transitions in [VO₄]^3? ions and the crystal structure. The PL quantum efficiencies (QE) are measured for nondoped and Eu³⁺‐doped samples. The Eu³⁺‐doped samples have higher QEs than the corresponding nondoped ones although the energy transfer occurs from [VO₄]^3? to Eu³⁺. Broad emission band due to [VO₄]^3? with intense sharp lines due to Eu³⁺, which gives white color, is observed in Eu³⁺‐doped NaCa₂Mg₂[VO₄]₃ and NaSr₂Mg₂[VO₄]₃ under excitation with UV light. These materials are suggested to be useful for lighting under the excitation with near‐UV LED.     

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.     

Highly Efficient Room Temperature Synthesis of Silver‐Doped Zinc Oxide (ZnO:Ag) Nanoparticles: Structural,Optical, and Photocatalytic Properties

Synthesis of silver‐doped zinc oxide (ZnO:Ag) nanoparticles through precipitation method has been reported. The synthesis was conducted at room temperature and no subsequent thermal treatment was applied. ZnO nanoparticles were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), fourier transmission infrared spectroscopy (FTIR), and ultraviolet‐visible (UV–Vis) spectroscopy. Detailed crystallographic investigation was accomplished through Rietveld refinement. The effect of silver content on structural and optical properties of resultant ZnO nanoparticles has been reported. It was found that silver doping results in positional shifts for the XRD peaks and the absorption band edge of ZnO. These were attributed to the substitutional incorporation of Ag⁺ ions into Zn²⁺ sites within the ZnO crystal. In addition, higher silver incorporation resulted in smaller size for ZnO nanoparticles. The photocatalytic activity of the ZnO:Ag nanoparticles was also determined by methylene orange (MO) degradation studies and compared to that of undoped ZnO. Improved photocatalytic activity was obtained for ZnO:Ag nanoparticles. It has been shown that an optimum amount of silver dopant is required to obtain maximum photocatalytic activity.     

Electrochemically Assisted Photocatalytic Oxidation of Nitrite over Cr‐Doped TiO2 under Visible Light

To investigate the photocatalytic oxidation (PCO) of nitrite ions under visible light, Cr‐doped TiO₂ supported on a titanium plate was used as a photoelectrode operated under anodic bias potential. The results showed that applying bias potential (E_appl) played an important role in the PCO of NO₂^–. Without bias potential the PCO reaction could not be initiated due to the rapid recombination rate of the photogenerated carriers, but when the potential was larger than 1.2 V (vs. saturated calomel electrode, SCE) the removal efficiency of NO₂^– increased up to 90 % within 3 h for an initial concentration of 8 mg L^–1. Zero‐order kinetics were observed at E_appl = 0.4 V (vs. SCE), while pseudo first order kinetics were found at E_appl ≥ 0.8 V (vs. SCE). The effects of the initial concentration of NO₂^–, initial solution pH, the gas atmosphere, and cathodic reaction on the PCO of NO₂^– were studied as well. Furthermore, the PCO mechanism of NO₂^– was investigated by using tert‐butyl alcohol or benzoic acid as a diagnostic probe. It showed that the PCO of NO₂^– under visible light most probably proceeded indirectly via OH radicals, not directly via the valence‐band holes.     

Synthesis and visible‐light‐derived photocatalysis of titania nanosphere stacking layers prepared by chemical vapor deposition

BACKGROUND: In this study, visible‐light‐derived photocatalytic activity of metal‐doped titanium dioxide nanosphere (TS) stacking layers, prepared by chemical vapor deposition (CVD), was investigated. The as‐grown TS spheres, having an average diameter of 100–300 nm, formed a layer‐by‐layer stacking layer on a glass substrate. The crystalline structures of the TS samples were of anatase‐type. RESULTS: Ultraviolet (UV) absorption confirmed that metallic doping (i.e. Co and Ni) shifted the light absorption of the spheres to the visible‐light region. With increasing dopant density, the optical band gap of the nanospheres became narrower, e.g. the smallest band gap of Co‐doped TS was 2.61 eV. Both Ni‐ and Co‐doped TS catalysts showed a photocatalytic capability in decomposing organic dyes under visible irradiation. In comparison, Co‐doped TiO₂ catalyst not only displays the adsorption capacity, but also the photocatalytic activity higher than the N‐doped TiO₂ catalyst. CONCLUSION: This result can be attributed to the fact that the narrower band gap easily generates electron–hole pairs over the TS catalysts under visible irradiation, thus, leading to the higher photocatalytic activity. Accordingly, this study shed some light on the one‐step efficient CVD approach to synthesize metal‐doped TS catalysts for decomposing dye compounds in aqueous solution. Copyright © 2010 Society of Chemical Industry     

Influence of the Eu2+ on the Silver Aggregates Formation in Ag+–Na+ Ion‐Exchanged Eu3+‐Doped Sodium–Aluminosilicate Glasses

Europium‐doping sodium–aluminosilicate glasses are prepared by melt‐quenching method, in which europium ions were spontaneously reduced from their trivalent to divalent state. The silver was introduced into glasses by Ag⁺–Na⁺ ion exchange and the interactions between europium ions and silver species were investigated. Owing to energy transfer (ET) from Ag⁺/silver aggregates to Eu³⁺, significant enhancements of Eu³⁺ emission were observed for 285/350‐nm excitation, respectively. The divalent europium ions promote the formation of silver aggregates in the process of ion exchange.     

Ferroelectric properties of Li‐doped BaTiO3 ceramics

We prepared 3 kinds of Li⁺‐doped BaTiO₃ ceramics by the solid‐state reaction method: (i) (Ba_1?xLi_x)TiO_3?x/2 having A‐site Li⁺, (ii) Ba(Ti_1?xLi_x)O_3?3x/2 having B‐site Li⁺, and (iii) x/2 Li₂CO₃+BaTiO₃ mixed one, for which we investigated the stable site of Li. The density of all prepared ceramics is above 95%. The results show that the lattice structure, the grain size, and the electric properties of Li⁺‐doped BaTiO₃ ceramics are dependent on Li⁺ site. According to the increase in Li content, the cell volume of Ba_1?xLi_xTiO_3?x/2 decreases, but that of BaTi_1?xLi_xO_3?3x/2 increases. That of x/2Li₂CO₃+BaTiO₃ decreases by the small addition of Li, but increases by the large addition of Li. All Li⁺‐doped ceramics show antiferroelectric‐like double hysteresis loops. The shape of loops and the dielectric properties are also dependent on the Li site. We suggest that the role of oxygen vacancy accompanied by the Li‐doping is important. By comparison with the results of 3 type ceramics, it is concluded that at x/2Li₂CO₃+BaTiO₃ ceramics, the Li⁺ prefers to favorably substitute Ba²⁺ at A site for the low concentration of Li but its location was changed to Ti⁴⁺ site for the high concentration of Li.     

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.     

The adsorption feature and photocatalytic oxidation activity of K1−2xMxTiNbO5 (M = Mn,Ni) for methyl mercaptan in methane

The novel photocatalytic ceramics material K_1?2xM_xTiNbO₅ (M = Mn, Ni) were prepared through Mn²⁺ and Ni²⁺ ion-exchange of KTiNbO₅, which was synthesized by a hydrothermal method. The influence of the ion-exchange process on the structure and morphology of prepared ceramics material were investigated by such physicochemical methods as powder X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS) and Fourier-transform infrared (FT-IR) microscopy. The adsorption and photocatalytic oxidation of methyl mercaptan (MM) in methane were used to evaluate the catalytic performance of different constitutes. The results revealed that K_1?2xNi_xTiNbO₅ exhibited better adsorption and photocatalytic oxidation activity for MM in methane under both visible and UV light radiation. While the photocatalytic oxidation activity of K_1?2xMn_xTiNbO₅ is similar to that of K_1?2xNi_xTiNbO₅, however it has little adsorption activity for MM in dynamic state.     

Preparation and Characterization of Silver‐Doped Cu(In,Ga)Se2 Films via Nonvacuum Solution Process

Cu(In,Ga)Se₂ films doped with different contents of silver ions (Ag⁺) were successfully prepared using nonvacuum spin coating followed by selenization at elevated temperatures. Increasing the Ag⁺ ion content increased the lattice parameters of the chalcopyrite structure, and shifted the A1 mode in the Raman signals to low frequencies. The band gaps of the prepared (Ag,Cu)(In,Ga)Se₂ (ACIGS) films were considerably increased, thereby increasing the open‐circuit voltage (V_oc) of the solar cells. As Ag⁺ ion content increased, the microstructures of ACIGS films became densified because the formed (Cu,Ag)₂In alloy phase with a low melting point facilitated liquid‐phase sintering. The evaporation of selenium species was correspondingly suppressed in the films during selenization, thereby reducing the selenium vacancies. The improvement in the microstructures and the defects of ACIGS films increased short‐circuit current (J_sc) and fill factor of the solar cells. The spectral response of the solar cells was also enhanced remarkably. This study demonstrated that incorporation of Ag⁺ ions into Cu(In,Ga)Se₂ films substantially improved the efficiency of the solar cells.     

Preparation and characterization of cerium‐doped titanium dioxide/ultrahigh‐molecular‐weight polyethylene porous composites with excellent photocatalytic activity

Porous ultrahigh‐molecular‐weight polyethylene (UHMWPE)‐based composites filled with surface‐modified Ce‐doped TiO₂ nanoparticles (Ce–TiO₂/UHMWPE) were prepared by template dissolution. The composites were characterized by Fourier transform infrared spectroscopy, ultraviolet (UV)–visible spectroscopy, diffuse reflectance spectra, and scanning electron microscopy); the photocatalytic activity was also evaluated by the decomposition of methyl orange under UV exposure. The results demonstrate that the severe aggregation of Ce–TiO₂ nanoparticles could be reduced by surface modification via a silane coupling agent (KH570). The Ce–TiO₂/UHMWPE porous composites exhibited a uniform pore size. Doping with Ce⁴⁺ effectively extended the spectral response from the UV to the visible region and enhanced the surface hydroxyl groups of the TiO₂ attached to the matrix. With a degradation rate of 85.3%, the 1.5 vol % Ce–TiO₂/UHMWPE sample showed the best photocatalytic activity. The excellent permeability of the porous composites is encouraging for their possible use in wastewater treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ce3+‐ and Dy3+‐Doped Oxyfluoride Borosilicate Glasses with Near White Luminescence

A series of Ce³⁺/Dy³⁺‐doped oxyfluoride borosilicate glasses prepared by melt‐quenching method are investigated for light‐emitting diodes applications. These glasses are studied via X‐ray diffraction (XRD), optical absorption, photoluminescence (PL), color coordinate, and Fourier transform infrared (FT‐IR) spectra. We find that the absorption and emission bands of Ce³⁺ ions move to the longer wavelengths with increasing Ce³⁺ concentrations and decreasing B₂O₃ and Al₂O₃ contents in the glass compositions. We also discover the emission behavior of Ce³⁺ ions is dependent on the excitation wavelengths. The glass structure variations with changing glass compositions are examined using the FT‐IR spectra. The influence of glass network structure on the luminescence of Ce³⁺/Dy³⁺ codoped glasses is studied. Furthermore, the near‐ideal white light emission (color coordinate x = 0.32, y = 0.32) from the Ce³⁺/Dy³⁺ codoped glasses excited at 350 nm UV light is realized.     

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.