Antiferromagnetic-ferromagnetic transition in Bi-doped LaFeO3 nanocrystalline ceramics

A series of nanocrystalline La_1-xBi_xFeO₃ (0.0≤x ≤ 0.5) ceramic powders were successfully prepared by the sol-gel method. X-ray diffraction and transmission electron microscopy were used to investigate the crystal structure evolution and hyperfine interactions of the samples. The average diameter of the powders was revealed to be approximately 80 nm. All the samples were crystallized into an orthorhombic crystal structure (space group Pnma) with no second phase. The magnetization of the Bi-doped samples obviously improved with increasing Bi content. A remarkable antiferromagnetic/ferromagnetic transition was detected at x ≥ 0.2, and a high coercive field of 23.05 kÖe was obtained with x = 0.5. The high correlation between the magnetization parameters and bonding characteristics indicated that significant stretching of the Fe³⁺-O_d^2- bonds and a decrease in Fe³⁺-O_d^2--Fe³⁺ linkage angles were the main origins of the strong ferromagnetism in the Bi-doped systems.     

TiO2涂层的溶胶—凝胶法制备及其光催化性能

用溶胶-凝胶法在釉面砖上制备了均匀的TiO_2涂层,讨论了影响TiO_2涂层质量的某些因素,用X射线光电子能谱仪研究了釉面涂层的化学组成.在紫外线及日光照射下,TiO_2涂层可以对敌敌畏光催化降解.     

Reduced formation of undesirable by-products from photocatalytic degradation of trichloroethylene

Photocatalytic degradation of trichloroethylene (TCE) was investigated using a tubular photoreactor packed with TiO₂ powders prepared by sol–gel techniques. Powders of the following metals: Cr, Fe, Ni, Cu and Pt, or Ca(OH)₂ were uniformly mixed with the TiO₂ powders and then their effect on the formation of COCl₂, CHCl₃, and CHCl₂COCl as by-products was examined. Concentrations of COCl₂ and CHCl₃ were determined in a product gas stream by GC/MS while CHCl₂COCl accumulated on the catalyst surface. When the catalysts were immersed in water after TCE photodegradation, the formation of Cl^- and CHCl₂COO⁻ ions was confirmed by ion-chromatography. Of the chemicals tested, only Cu and Ca(OH)₂ inhibited the formation of the chlorinated by-products. With increasing Cu and Ca(OH)₂ content, TCE conversion decreased while the stoichiometric ratio ([CO₂]_formed/[TCE]_degraded) increased. Concentrations of COCl₂, CHCl₃, and CHCl₂COCl decreased with increasing Cu and Ca(OH)₂ content. Especially, the formation of COCl₂ was remarkably suppressed with Ca(OH)₂.     

Synthesis and photocatalytic activity of TiO2-hectorite composites

TiO₂-hectorite composites were synthesized and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Diffraction Spectrum (EDS) techniques. The course of composite formation, TiO₂ particles were intercalated into hectorite. The specific surface areas of the samples were determined by nitrogen adsorption. The composite with a Ti content 2.5% (m/m) had a higher specific surface area than other composites. Photocatalytic properties were tested in photooxidation of methylene blue (MB).     

Hydrothermal preparation of Nb-doped NaTaO3 with enhanced photocatalytic activity for removal of organic dye

The construction of efficient photocatalysts has received much attention in wastewater treatment. In this study, Nb-doped NaTaO₃ was prepared with different doping ratio by a facile hydrothermal method. The prepared catalysts were analyzed by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller (BET) theory, ultraviolet–visible diffuse reflectance spectroscopy. Then the synthesized catalysts were employed to degrade a model pollutant, methylene blue (MB), under a 250 W mercury lamp. The characterization tests confirm that Nb was successfully doped into the crystal structure of NaTaO₃ and the modified NaNb_xTa_1-xO₃ (x is the doping ratio; x = 0.25, 0.5, 0.75) samples were formed, which were in regular cubic shapes just like pure NaTaO₃. The synthesized NaNb_xTa_1-xO₃ (x = 0.25, 0.5, 0.75) had improved specific surface area and narrowed band gaps compared with pure NaTaO₃. In photocatalytic degradation experiments, NaNb_0.75Ta_0.25O₃ presented the best photocatalytic activity ascribed to the narrow band gap and the high surface area, degradating 95.7% of MB after 180 min of reaction, which was even twice the ability of pure NaTaO₃. Besides, the effects of possible inorganic anions and cations in wastewater on photocatalytic degradation were investigated. Electron spin resonance (ESR) tests and capture experiments were also conducted and a possible photocatalytic mechanism was proposed. This work provides a direction for constructing superior NaTaO₃-based photocatalysts to be widely utilized in environmental protection.     

Thermal behavior of Al/MoO3 xerogel nanocomposites

Sol–gel process using molybdenum alkoxides was employed to prepare Al/MoO₃ xerogel nanocomposites as a thermite with better performance by improvement of interfacial contact area between the oxidizer and fuel. Micromorphology and thermite reaction characteristics of Al/MoO₃ xerogel nanocomposites were analyzed by scanning electron microscopy (SEM) and thermogravimetry/differential scanning calorimetry (TG/DSC), respectively. In the present Al/MoO₃ xerogel system, it was found that exothermic enthalpy increases as the Al/Mo mole ratio increases and then decreases when Al/Mo mole ratio is larger than 6 indicating that optimum mole ratio of Al/Mo is 6 with reaction enthalpy of 420.58 J/g.     

Structural and optical investigations of Eu3+-doped TiO2 nanopowders

This paper presents an evaluation of photoluminescent and structural properties of Eu³⁺-doped TiO₂ materials in powder form prepared by sol–gel process. The increase of heat-treatment temperature of synthesis results in the TiO₂ phase transition, obtaining anatase, rutile and sometimes brookite, examined by Raman and XRD techniques. Crystallite size as well as microstrains in the crystal structure were evaluated as a function of Eu³⁺ and heat-treatment temperature. It was found that when Eu³⁺ is introduced in anatase phase an intense color emission is observed under excitation at 394 and 463 nm. The rutile phase presents inversion center symmetry, and apparently the Eu³⁺ tends to occupy this site, which decreases the intensity of the emission assigned to the ⁵D₀→⁷F₂ transition. The materials obtained at 700 °C showed most intensity of emission in the red region, verified by the ratio between ⁵D₀→⁷F₂/⁵D₀→⁷F₁ transitions of Eu³⁺. The results showed that the materials are interesting absorber in the ultraviolet and red region and can be used for improvement of energy conversion in solar cells devices.     

Facile fabrication of ordered assembled TiO2/g-C3N4 nanosheets with enhanced photocatalytic activity

A series of assembled porous TiO₂/g-C₃N₄ (TC) powders composed of spherical nanoparticles were synthesized by controlling the molar ratio of urea to tetrabutyl titanate (TBOT) in a facile hydrothermal process. A nanosheets-constructed hierarchical structure was obtained at the molar ratio of urea to TBOT of 10:1, which possessed uniform mesopores with bimodal distribution (0.5–1.5 nm and 2–20 nm) and interconnected macropores between TC nanosheets. The specific surface area achieved 98.4 m² g^?1. X-ray diffraction (XRD) patterns and high resolution transmission electron microscope (HRTEM) analysis proved that the nanosheets are made of overlapping TC nanocomposite. Photoluminescence (PL) spectra results illustrated that a well-defined hierarchical porous structure is particularly desired for the low recombination rate of carriers. Further, the TC-decorated carbon fiber (CF) cloth was obtained based on the nanosheets assembled hierarchical structure, which showed more outstanding photocatalytic behavior with high degradation capability for Rhodamine B (RhB) (99.9%) and tetracycline hydrochloride (89.8%) at 60 min by 500 W Xe lamp irradiation. After five consecutive cycles, the degradation efficiencies of TC/CF cloth for both RhB and tetracycline hydrochloride all remained above 90% of the initial value.     

Visible light driven photocatalytic degradation of Rhodamine B and Direct Red using cobalt oxide nanoparticles

Cobalt oxide (Co₃O₄) nanoparticles were prepared by simple, facile and cost effective sol–gel route. Triethanol amine (TEA) was used as surfactant to reduce the size of the particles. The XRD patterns reveal that the crystallite size of the sample prepared without surfactant yields 69 nm and with different surfactant concentrations (5 ml, 10 ml, and 15 ml), the estimated crystallite sizes were reduced to 64 nm, 52 nm, and 32 nm respectively. The morphological and elemental composition of the samples was investigated by SEM and EDS. The optical studies revealed the possible electronic transitions which are responsible for an occurrence of two energy band gap in cobalt oxide. The photoluminescence probe for the presence of defects and the results obtained specified that the defects get reduced with the addition of surfactant TEA. Photocatalytic degradation of dyes (Rhodamine B and Direct Red 80) was investigated under visible light using cobalt oxide nanoparticles as catalyst. The effect of catalyst amount and pH of the dye solution was analyzed with the help of UV–visible absorption spectra.     

Synthesis of a CoTiO3/BiOBr heterojunction composite with enhanced photocatalytic performance

A novel heterojunction CoTiO₃/BiOBr nanocomposite with enhanced photocatalytic performance was synthesized by a precipitation-deposition method. The samples were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis spectrophotometry. Moreover, the photocatalytic activities were evaluated by decomposing the dye molecule Rhodamine B under visible light irradiation. The results showed that high photocatalytic performance can be achieved on the heterojunction photocatalysts, with the 0.15CoTiO₃/0.85BiOBr composite displaying the highest activity. The results of the study concluded that it was the introduction of CoTiO₃ into the catalyst that mainly enhanced the activity of the photocatalyst by promoting the separation of the electron-hole group on the interface between BiOBr and CoTiO₃.     

Synthesis of hollow spherical WO3 powder by spray solution combustion and its photocatalytic properties

Hollow spherical WO₃ powder was prepared from mixed solution of ammonium metatungstate, glycine and ammonium nitrate by spray solution combustion synthesis (SSCS) method. The effects of fuel ratio, temperature, precursor solution concentration on the structure and morphology of as-prepared powder, and the SSCS mechanism have been discussed in detail. When precursor solution concentration is 0.10 mol/L, in which the fuel ratio is 2, and reaction temperature set to be 800 °C, the spherical WO₃ powder with smooth surface and a median diameter of 24.02 μm can be obtained, which consists of particles with a diameter of about 30 nm, and the specific surface area is 13.5 m²/g. Moreover, the as-synthesized WO₃ powder is applied to degrade RhB solution in visible light to evaluate its catalytic performance by PLS-SXE300/300UV. Only 10 mg powder can degrade 70.1% RhB solution within 2 h.     

Effect of using different precursors on electrospinning of CaCu3Ti4O12

In this study, the rheological behavior of electrospinning solutions containing different copper and calcium salts (Cu(NO₃)₂·3H₂O, CuCl₂, Ca(NO₃)₂·4H₂O and CaCl₂) were investigated. To find out the suitable electrospinning solution for producing the high purity CaCu₃Ti₄O₁₂ nanofibers, solutions containing different copper and calcium salts were prepared and CaCu₃Ti₄O₁₂ fibers with different morphological and size were produced. The results showed that the nature of the metals complexes in the ceramic solutions had an obvious effect on the rheological behavior of the electrospinning solutions. FTIR spectras of the electrospinning solutions demonstrated that the interaction between the metal ions and carbonyl groups in the polyvinylpyrrolidone unit occurred and the polyvinylpyrrolidone chains underwent conformational variations. Intensity of the interaction between the metal ions and polymer chains in chloride salts solutions is more than nitrate salts solutions in order to the viscosities of chloride solutions that are more than nitrate solutions. So, thinner high purity polycrystalline CaCu₃Ti₄O₁₂ nanofibers with diameters ranging <200 nm were successfully synthesized by selecting a novel solution containing copper and calcium nitrates after sintering at 900 °C for 4 h.     

One-pot synthesis of 3D porous Bi7O9I3/N-doped graphene aerogel with enhanced photocatalytic activity for organic dye degradation in wastewater

The compound Bi₇O₉I₃ has been considered as a promising candidate for organic dye degradation in wastewater, but it has relatively low photocatalytic activity and difficulties in the recycling processes. In this work, a novel floating 3D porous Bi₇O₉I₃/N-doped graphene aerogel (Bi₇O₉I₃/NGA) composite was successfully synthesized through a facile hydrothermal route. The Bi₇O₉I₃/NGA composite exhibited highly enhanced photocatalytic performance toward degrading rhodamine B under visible-light irradiation, which increased 6.0 and 2.3 times compared with the Bi₇O₉I₃ and Bi₇O₉I₃/GA, respectively. The enhancement of photocatalytic degradation activity could be ascribed to the extensively promoted charge generation and migration efficiency, visible light utilization ability and reactive oxygen species production. Besides, the special 3D macroscopic block structure of Bi₇O₉I₃/NGA allowed it to float, making it easy to recycle. The photocatalytic degradation efficiency of Bi₇O₉I₃/NGA composite still could reach up to 92.7% after four consecutive cycles and presented satisfactory stability and reusability. Moreover, a possible photocatalytic degradation mechanism was revealed by radical species trapping and semi-quantitative analyses experiments.     

White luminescence of bismuth and samarium codoped Y2O3 phosphors

In this work Sm³⁺ (0–2.0 at%) and Bi³⁺ (0–2.0 at%) doped Y₂O₃ luminescent powders were prepared by a sol–gel method from yttrium acetylacetonate, samarium and bismuth nitrates as metal sources. The as prepared powders (chemical composition is close to stoichiometric Y₂O₃) present the cubic structure from 700 °C, and at 900 °C are characterized by the presence of rounded particles with heterogeneous size of 42.9 nm. Luminescent effect of ions of Sm³⁺ and Bi³⁺ into Y₂O₃ host as was studied on heat treated powders from 800 to 1100 °C. The combination of the red luminescence from the Sm³⁺ ions and the bluish from Bi³⁺, makes the synthesized phosphors candidates to be used in fabrication of phosphor-converted light-emitting diodes (LEDs).     

Oil swollen surfactant gel based synthesis of metal oxides nanoparticles: An attractive alternative for the conventional sol gel synthesis

Metals (Zr, Zn and Cu) containing oil swollen surfactant gels have been utilized as precursors for the preparation of metal oxides (ZrO₂, ZnO and CuO) nanoparticles. No metal alkoxide, external gelating agent or any other intricate molecule have been utilized to reinforce gelation; gel stage has been achieved simply through judicial adjustment of water to surfactant ratio and salinity of the reaction mixture. Unlike, several previously published reports, in this approach surfactant has been added not to just increase the viscosity of solution but it has also formed rod shaped gelatinous micelles in response to the variation in water to surfactant ratio, which endowed mechanical strength to the gel. The effect of nature of metal salt on mechanical properties of gel has also been investigated. Zn and Cu containing cetyltrimethylammonium bromide (CTAB) gels have been found to be strongest and weakest, respectively. Metal containing CTAB gels were heat treated at various temperatures (600, 700 and 800 °C) in order to obtain metal oxides nanoparticles. The effect of calcination temperature on crystallinity, particle size and morphology of the metal oxides nanoparticles has also been investigated. A comparison between ZrO₂ nanoparticles prepared using conventional sol gel and oil swollen surfactant gel method has also been carried out in terms of crystallinity, particle size and optical property.     

Influence of multi-step annealing on nanostructure and surface morphology of Y2O3:SiO2 powder

Y₂O₃:SiO₂ powder was synthesized by a sol–gel method, using hydrous yttrium nitrate and hydrous silicon oxide as precursors and HCl as a catalyst. The dried samples were submitted to multi-step annealing schedule in air without applying pressure. A simple four-step annealing schedule with a final stage of about 900 °C for 6.0 h was followed. The samples of Y₂O₃:SiO₂ nanocomposites were obtained with well defined size and shape. Structural changes of the nanocomposites were investigated by XRD, FTIR and TEM. Multi-step annealing scheme with different ramp rates and incubation times allows recovery-relaxation processes within the boundaries and leading to a concomitant linear increase of crystallite size and densification. Almost fully dense quasi-spherical cubic-yttria nanopowder has been demonstrated with an average grain size distribution of 10–40 nm; can be uniformly dispersed in silica matrix.     

Adsorption efficiency and photocatalytic activity of fly ash-based geopolymer foam mortar

Fly ash-based geopolymer foam mortar (GFM) was used as an adsorbent material to methylene blue (MB) and also the dye removal material using the photocatalytic mechanism. The GFM, containing 50 wt% river sand aggregate, was prepared to have approximately 46% open porosity, pore size distribution between 0.01 and 3.5 mm, and water permeability of 0.2 cm/s. The variation of adsorption efficiency and adsorption capacity with the contact time of the GFM was first evaluated using various GFM dosages (10, 20, 50, 80, and 100 g/L). The adsorption efficiency at equilibrium (AE_e) was found to linearly increase, while adsorption capacity (q_ae) exponentially decayed, with an increase of loading dosages. The photocatalytic removal efficiency of ~100% was obtained with 50, 80, and 100 g/L GFM loading dosages, with a shorter time at higher dosages. The GFM could be reused, without regeneration, for 5 cycles. The AE_e and q_ae for each reused cycle did not noticeably change suggesting the reusability. The photocatalytic removal efficiency, however, was found to decrease with an increase of the reused cycle. After the 5^th cycle, the highest removal efficiency was reduced to ~70%. The attempts to treat the GFMs with hydrochloric (HCl) and phosphoric (H₃PO₄) acid to reduce the excess alkaline did not give satisfactory results as expected. The photocatalytic removal efficiency had subsided after the treatment with both acids.     

A facile and novel construction of attapulgite/Cu2O/Cu/g-C3N4 with enhanced photocatalytic activity for antibiotic degradation

A high-performance photocatalyst, attapulgite/Cu₂O/Cu/g-C₃N₄ (ATP/Cu₂O/Cu/g-C₃N₄), was constructed via a one-pot redox strategy under anoxic calcination. The as-prepared composites were characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption isotherms (BET), photoluminescence emission (PL), and electrochemical impedance spectra (EIS). Results indicate that ultra-fine CuO nanoparticles on the surface of rod-like attapulgite are in-situ reduced by NH₃ gas to generate Cu and minority Cu₂O during the pyrocondensation of melamine. Meanwhile, the generated g-C₃N₄ membrane is uniformly encapsulated on the surface of attapulgite/Cu₂O/Cu to assemble Z-scheme Cu₂O/Cu/g-C₃N₄ heterostructure. ATP/Cu₂O/Cu/g-C₃N₄ shows improved visible light response ability and hole-electron suppression compared with ATP/g-C₃N₄. The photocatalytic performance and mechanism of the obtained photocatalyst for antibiotic degradation were evaluated by UV–Vis spectrometer and liquid chromatograph. ATP/Cu₂O/Cu/g-C₃N₄ can exhibit favorable photocatalytic activity and reusability for chloramphenicol. In addition, h⁺ and·OH radicals are the main active sites in the photocatalytic process, and Cu species play a vital role in separation and retarding recombination of electron-hole pairs.     

Structural,optical and photocatalytic properties of hafnium doped zinc oxide nanophotocatalyst

A series of novel hafnium (Hf) doped ZnO nanophotocatalyst were synthesized using a simple sol–gel method with a doping content of up to 6 mol%. The structure, morphology and optical characteristics of the photocatalysts were characterized by XRD, SEM, TEM, FTIR, XPS, DRS and PL spectroscopy. The successful synthesis and chemical composition of pure and doped ZnO photocatalysts were confirmed by XRD and XPS. DRS confirmed that the spectral responses of the photocatalysts were shifted towards the visible light region and showed a reduction in band gap energy from 3.26 to 3.17 eV. Fluorescence emission spectra indicated that doped ZnO samples possess better charge separation capability than pure ZnO. The photocatalytic activity of Hf-doped ZnO was evaluated by the methylene blue (MB) degradation in aqueous solution under sunlight irradiation. Parameters such as irradiation time and doping content were found effective on the photoactivity of pure ZnO and Hf-doped ZnO. The photocatalysis experiments demonstrated that 2 mol% Hf-ZnO exhibited higher photocatalytic activity as compared to ZnO, ZnO commercial and other hafnium doped ZnO photocatalysts and also revealed that MB was effectively degraded by more than 85% within 120 min. The enhanced photoactivity might be attributed to effective charge separation and enhanced visible light absorption. It was concluded that the presence of hafnium within ZnO lattice could enhance the photocatalytic oxidation over pure ZnO.     

Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Titanium dioxide nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method in hydrochloric acid solutions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectrum (XPS) and UV–vis spectra were carried out to characterize the composites with different PANI contents. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the modified catalysts. Results show that TiO₂ nanoparticles are deposited by PANI to mitigate TiO₂ particles agglomeration. The modification does not alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction patterns. UV–vis spectra reveal that PANI-modified TiO₂ composites show stronger absorption than neat TiO₂ under the whole range of visible light. The resulting PANI-modified TiO₂ composites exhibit significantly higher photocatalytic activity than that of neat TiO₂ on degradation of phenol aqueous solution under visible light irradiation (λ ≥ 400 nm). An optimum of the synergetic effect is found for an initial molar ratio of aniline to TiO₂ equal to 1/100.