Photocatalytic activity of nitrogen doped rutile TiO2 nanoparticles under visible light irradiation

This work provides the design and synthesis of nitrogen doped rutile TiO₂ nanoparticles working as efficient photocatalysts under visible light irradiation. Nitrogen doped rutile TiO₂ nanoparticles are synthesized through the surface nitridation of rutile nanoparticles, which have been prepared in advance. The experimental results show that the nitrogen element is easily doped into the lattice of TiO₂ nanoparticles and its doping amount increases with the decrease of nanocrystallite size. The photocatalytic activity of the nanoparticles under visible light irradiation is correlated not only with the amount of doped nitrogen element but also with the morphology and crystallinity of nanoparticles.     

Phase selection and visible light photo-catalytic activity of Fe-doped TiO2 prepared by the hydrothermal method

It is necessary to extend the absorption range of TiO₂ based materials from the ultraviolet to the visible light region for most photo-catalytic applications of TiO₂ under solar irradiance or indoor lighting. Also, the ability to control the structural evolution, particularly the competition and transformation between different phases (anatase or rutile), is extremely important for the preparation of high efficiency TiO₂ based photo-catalysts. In this work, we have systematically studied the effects of various processing factors on the phase selection process/outcome of nanocrystalline Fe-doped TiO₂, which includes the level of doping ions, annealing temperature, solution pH and the addition of acidic anions, using a low temperature hydrothermal method. Both Fe-doped rutile and anatase TiO₂ phases were obtained via varying the processing conditions. The visible-light photo-catalytic activity of doped materials was significantly improved over that of the pure TiO₂ nanopowders, which was demonstrated by effective degradation of methylene blue under visible light.     

An open-framework bimetallic chalcogenide structure K3Rb3Zn4Sn3Se13 built on a unique [Zn4Sn3Se16] cluster: synthesis, crystal structure, ion exchange and optical properties

Single crystals of K₃Rb₃Zn₄Sn₃Se₁₃ were synthesized by solvothermal method. The building block in this structure is a [Zn₄Sn₃Se₁₆]¹²⁻ cluster which consists of four ZnSe₄ and three SnSe₄ tetrahedra connected through corner-sharing of Se atoms. The 3D network contains intersecting channels running parallel to the crystallographic [2 1 1], [1-1-1] and [12-1] directions. The disordered K⁺ and Rb⁺ cations reside in these channels. Ion exchange of Cs⁺ with disordered Rb⁺/K⁺ ions in the structure showed a partial replacement of 15.8%. Optical diffuse reflectance experiments were carried out and gave a sharp absorption edge at 2.6 eV.     

Microwave hydrothermal synthesis of AgInS2 with visible light photocatalytic activity

AgInS₂ nanoparticles with superior visible light photocatalytic activity were successfully synthesized by a microwave hydrothermal method. This method is a highly efficient and rapid route that involves no organic solvents, catalysts, or surfactants. The photocatalytic activity of AgInS₂ nanoparticles was investigated through the degradation of dyes under visible light irradiation. Compared with TiO_2−xN_x, AgInS₂ has exhibited a superior activity for photocatalytic degradation MO under the same condition. The experiment results showed that superoxide radicals (O₂⁻), hydrogen peroxides (H₂O₂) and holes (h⁺) were the mainly active species for the degradation of organic pollutants over AgInS₂. Through the determination of flat band potential, the energy band structure of the sample was obtained. A possible mechanism for the degradation of organic pollutant over AgInS₂ was proposed.     

Fabrication and efficient photocatalytic degradation of methylene blue over CuO/BiVO4 composite under visible-light irradiation

CuO/BiVO₄ composite photocatalysts were prepared by solution combustion synthesis method and impregnation technique. X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scan electron microscopy and UV-vis diffusion reflectance spectra were used to identify the physical properties and photophysical properties of CuO/BiVO₄ composite photocatalysts. The photocatalysts exhibit the enhanced photocatalytic properties for degradation of methylene blue under visible-light (λ > 420 nm). The mechanism of improved photocatalytic activity is also discussed.     

Photocatalytic properties of BiVO4 prepared by the co-precipitation method: Degradation of rhodamine B and possible reaction mechanisms under visible irradiation

Bismuth vanadate (BiVO₄) was synthesized by the co-precipitation method at 200 °C. The photocatalytic activity of the oxide was tested for the photodegradation of rhodamine B under visible light irradiation. The analysis of the total organic carbon showed that the mineralization of rhodamine B over a BiVO₄ photocatalyst (∼40% after 100 h of irradiation) is feasible. In the same way, a gas chromatography analysis coupled with mass spectroscopy revealed the existence of organic intermediates during the photodegradation process such as ethylbenzene, o-xylene, m-xylene, and phthalic anhydride. The modification of variables such as dispersion pH, amount of dissolved O₂, and irradiation source was studied in order to know the details about the photodegradation mechanism.     

Determination of the modulated structure of the misfit layer compound (LaS)1.196VS2

Single crystal X-ray diffraction was used to determine the modulated structure of the misfit layer compound (LaS)_1.196VS₂. This compound crystallizes in the triclinic system with cell parameters: a_s = 3.410 (1) Å, b_s = 5.845(1) Å, c_s = 11.191(2) Å, α ≈ 95.15(4), β ≈ 84.79(2)°, and γ ≈ 89.98(2)°, q = 0.5978(4)a_s^* − 0.002(1)b_s^* + 0.004(2)c_s^*, and V_s = 221.2(1) Å³. A (3 + 1)D superspace group, X(α,β,γ), was used to analyze the complete structure (X is referring to a pseudo C centering). The largest modulation amplitudes are observed for La-S (between La (subsystem 2) and S (subsystem 1)), as well as V-V distances. In connection with the large V-V modulation, we observed the formation of “linear vanadium clusters” that may impact on the transport properties.     

Structural characterization and photocatalytic properties of novel Bi2YVO8

Bi₂YVO₈ was prepared by solid-state reaction for the first time. The structural and photocatalytic properties of Bi₂YVO₈ were studied. The results showed that this compound has the tetragonal crystal system with space group I4/mmm. The band gap of Bi₂YVO₈ was estimated to be about 2.09 eV by plotting (αhν)² versus hν and obtaining the hν axis intercept value according to Tauc's equation. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water with Bi₂YVO₈ as the photocatalyst under ultraviolet light irradiation (wavelength = 390 nm). Degradation of aqueous methylene blue photocatalyzed by this compound was investigated under visible light irradiation. Bi₂YVO₈ showed higher photocatalytic activity compared to Bi₂YTaO₇, Bi₂InTaO₇ or TiO₂ (P-25). Complete removal of aqueous methylene blue was achieved after visible light irradiation for 170 min. The decrease of the total organic carbon and the formation of inorganic products such as SO₄²⁻ and NO₃⁻ revealed the continuous mineralization of aqueous methylene blue during photocatalytic reaction.     

Photoluminescence study of PVP capped CdS nanoparticles embedded in PVA matrix

Photoluminescence properties of polyvinyl pyrrolidone (PVP) capped cadmium sulphide (CdS) nanoparticles embedded in polyvinyl alcohol matrix (PVA) are reported. The PVP-CdS nanoparticles are prepared by non-aqueous method wherein cadmium nitrate is used as the cadmium source and hydrogen sulphide as the sulphur source. The synthesized nanoparticles are dispersed in polyvinyl alcohol (PVA) matrix and cast as self-standing flexible (PVP-CdS)-PVA films. The nanocomposites are characterized by optical absorption spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. XRD and TEM studies show the formation of cubic CdS particles with average size ∼3-5 nm. Thermal studies, carried out to observe the changes in PVA matrix due to the incorporation of PVP-CdS nanoparticles show strong interaction between the polymer matrix and nanoparticles. The photoluminescence emission spectra of the nanocomposites show two peaks, at 502 and 636 nm, which are attributed to the band edge and surface defects respectively, of CdS nanoparticles. Effective surface capping with optimum concentration of polyvinyl pyrrolidone leads to the quenching of surface defect-related emission.     

Preparation of Fe-doped TiO2 nanotube arrays and their photocatalytic activities under visible light

Fe-doped TiO₂ nanotube arrays have been prepared by the template-based liquid phase deposition method. Their morphologies, structures and optical properties were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV-vis absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light. The UV-vis absorption spectra of the Fe-doped TiO₂ nanotube arrays showed a red shift and an enhancement of the absorption in the visible region compared to the undoped sample. The Fe-doped TiO₂ nanotube arrays exhibited good photocatalytic activities under visible light irradiation, and the optimum dopant amount was found to be 5.9 at% in our experiments.     

Photocatalytic activity of Li-Rb-Y doped or codoped TiO2 under sunlight irradiation

Doped TiO₂ particles were synthesized by solid grinding and sol-gel methods. The ensuing powders were analysed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ground state diffuse reflectance absorption spectroscopy (GSDR). The doped samples prepared by solid grinding at 400 °C were in the anatase form, while those synthesised via sol-gel method and calcinated at the same temperature were dominated by the rutile phase. The X-ray photoelectron spectroscopy (XPS) revealed a surface segregation of the doping elements namely for Y, Rb and Rb-Y. The photocatalytic activity of the prepared catalysts, under sunlight irradiation, was evaluated using 2-naphthol as a pollutant model. Results showed a great enhancement in the photocatalytic efficiency with incorporation of Y in samples prepared by solid grinding, while in samples prepared via sol-gel process both Rb and Y dopants greatly improve the photocatalytic activity. The Langmuir-Hinshelwood model was used to describe the photocatalytic reactions from which a pseudo-first-order kinetics was established. The repeatability of photocatalytic activity was also tested for several degradation cycles.     

Decomposition of water by a CaTiO3 photocatalyst under UV light irradiation

Platinized CaTiO₃ powder (band gap 3.5 eV) had a high photocatalytic activity of decomposing water into H₂ and O₂ under the irradiation of UV light, especially with photon energies above 3.8 eV. The existence of this photocatalytic activity is further supported on electrochemical grounds in that the photoinduced current spectrum measured between a CaTiO₃ single crystal and a Pt electrode without applied voltage in water showed a maximum near 4.1 eV. This result indicates that the direct measurement of the spectrum corresponding to the efficiency of water decomposition is an effective method to survey photocatalytic activities of materials.     

Micro-emulsion-assisted synthesis of ZnS nanospheres and their photocatalytic activity

ZnS nanospheres with rough surface were synthesized by using a micro-emulsion-assisted solvothemal process. The molar ratio of [water]/[surfactant] played an important role in controlling the size of the ZnS nanospheres. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field emission-scanning electron microscope (FE-SEM), and selected area electron diffraction (SAED) were used for the characterization of the resulting ZnS nanospheres. A possible formation mechanism was proposed. These ZnS nanospheres exhibited a good photocatalytic activity for degradation of an aqueous p-nitrophenol solution and the total organic carbon (TOC) of the degradation product has also been investigated.     

dc conduction properties of TlSbSe2 crystals

TlSbSe₂ samples used for electrical measurements were cleaved from larger crystals grown by using the Bridgman-Stockbarger method. Electrical properties of TlSbSe₂ have been carried out as a function of temperature (203-258 K) at different dc electric fields. The dc studies revealed the non-ohmic type of conduction (log I versus log V plot). The field lowering coefficientβ is evaluated from log I versus E^1/2 plot. It is found that the dominant conduction mechanism in these samples is Poole-Frenkel type. The activation energies are also calculated at different voltages. It is seen that the activation energy decreases with increase of applied voltage.     

Surfactant-free synthesis of Bi2WO6 multilayered disks with visible-light-induced photocatalytic activity

The synthesis of bismuth tungstate (Bi₂WO₆) multilayered disk which was constructed by oriented square nanoplates was easily realized via a simple surfactant-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to investigate the as-obtained product. The results indicated that the three-dimensional (3D) Bi₂WO₆ multilayered disk was constructed by self-assembly of square nanoplates via a perfect oriented manner. The formation mechanism of the product was carefully investigated on the basis of the results of time-dependent experiments. In addition, studies of the photocatalytic property demonstrated that the as-obtained Bi₂WO₆ could exhibit excellent visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB).     

Characterization and photocatalytic activity of Bi3TiNbO9 nanocrystallines synthesized by sol-gel process

Nanocrystalline Bi₃TiNbO₉ powders were synthesized by a sol-gel process, based on a colloid solution of bismuth acetate, titanium butoxide and niobium ethoxide. X-ray diffraction analysis revealed that pure Aurivillius phase of Bi₃TiNbO₉ could be prepared at a calcination temperature of 500 °C. By using scanning electron microscopy and gas adsorption method, the morphology and the specific surface area of the powders were examined. The photophysical properties of Bi₃TiNbO₉ were investigated by means of the UV-visible diffuse reflectance spectrum, from which a band gap ∼3.2 eV was empirically calculated. The as-prepared Bi₃TiNbO₉ powders were applied in the photodegradation of organic contaminant for the first time, and they showed effective photocatalytic activity for the complete decomposition of methyl orange under UV light irradiation.     

Complete oxidation of acetaldehyde on Pt/CeO2-ZrO2-Bi2O3 catalysts

Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts for catalytic combustion of acetaldehyde, which is one of volatile organic compounds (VOCs), were prepared by a wet impregnation method in the presence of polyvinylpyrrolidone K25 (PVP). The addition of PVP in the preparation process was effective to enhance the specific surface area and the Pt²⁺ ratio on the surface. Additionally, the pore volume and size of the catalysts were modified by the PVP addition. The Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts are specific for the total acetaldehyde oxidation and CO and any acetaldehyde-derivative compounds were not observed as by-products. The catalytic activity of the Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts was significantly promoted by the PVP addition and the total oxidation temperature decreased. By the optimization of the amount of platinum, the complete oxidation of acetaldehyde was realized at a temperature as low as 140 °C on a 10 wt%Pt/CeO₂-ZrO₂-Bi₂O₃ catalyst.     

Temperature-dependent oxygen release, intercalation behaviour and catalytic properties of V2O5·xNb2O5 compounds

In order to investigate the catalytic properties, V_2,38Nb_10,7O_32,7, VNb₉O₂₅ and solid solutions of V₂O₅ in TT-Nb₂O₅ were prepared by thermal decomposition of freeze-dried oxalate precursors. The samples were characterised by X-ray diffraction and surface area determination. The crystalline samples are capable of the intercalation of sodium and lithium ions from solution. Above a temperature of about 500 °C, in dependence on the oxygen partial pressure a reversible release and uptake of oxygen without a structural variation takes place. The catalytic properties have been evaluated for the oxidative dehydrogenation (ODH) of propane and propene. There are only small differences in the catalytic activity of the different crystalline samples. Because of the relative high starting temperature, a selective catalytic oxidation of propane to propene is hardly observed.     

Properties of TiO2 prepared by acid treatment of BaTiO3

TiO₃ powders were prepared by acid treatment of BaTiO₃ and their properties were investigated. The BaTiO₃ powder was subjected to HNO₃ in concentrations ranging from 10⁻³ to 8 M at 90 °C for 0.5-6 h. Dissolution of BaTiO₃ and precipitation of TiO₂ occurred at acid concentrations of 2-5 M. BaTiO₃ dissolves completely to form a clear solution at reaction times of 0.5-1 h, but a rutile precipitate is formed after 2 h of acid treatment. By contrast, anatase is precipitated by adjusting the pH of the clear solution to 2-3 using NaOH or NH₄OH solution. The rutile crystals were small and rod-shaped, consisting of many small coherent domains connected by grain boundaries with small inclination angles and edge dislocations, giving them a high specific surface area (S_BET). With increasing HNO₃ concentration, the S_BET value increased from 100 to 170 m²/g while the crystallite size decreased from 25 to 11 nm. The anatase crystals obtained here were very small equi-axial particles with a smaller crystallite size than the rutile and S_BET values of about 270 m²/g (higher than the rutile samples). The photocatalytic activity of these TiO₂ was determined from the decomposition rate of Methylene Blue under ultraviolet irradiation. Higher decomposition rates were obtained with larger crystallite sizes resulting from heat treatment. The maximum decomposition rates were obtained in samples heated at 500-600 °C. The photocatalytic activity of the TiO₂ was found to depend more strongly on the sample crystallite size than on S_BET.     

Photoinduced charge property of nanosized perovskite-type LaFeO3 and its relationships with photocatalytic activity under visible irradiation

In this paper, ABO₃-type perovskite LaFeO₃ nanosized photocatalysts were synthesized by a sol-gel method, using citric acid (HOOCCH₂C(OH)(COOH)CH₂COOH) as complexing reagent and La(NO₃)₃·6H₂O and Fe (NO₃)₃·9H₂O as raw materials. The as-prepared samples also were characterized by several testing techniques, such as thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET), infrared spectrum (IR), ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and electrical field induced surface photovoltage spectroscopy (EFISPS). The sample activity of different LaFeO₃ nanoparticles for degrading Rhodamine B solution under visible irradiation (λ > 400 nm) was evaluated. The effects of thermal treatment temperature on photoinduced charge property and photocatalytic activity were mainly investigated, together with their relationships. The results show that the LaFeO₃ sample calcined at 500 °C exhibits higher activity, and the activity decreases with increasing calcination temperature, which is in good agreement with the characterization results. The weaker is the PL and SPS signal, the higher is the photocatalytic activity. Moreover, the activity of all as-prepared LaFeO₃ samples is higher than that of international P-25 TiO₂ under visible irradiation.