Study on the photocatalytic property of La-doped CoO/SrTiO3 for water decomposition to hydrogen

The purpose of this study is to investigate the effect of La doping on the photocatalytic property of CoO/SrTiO₃. The experimental results show that a suitable concentration of La doping greatly improved the photocatalytic activity of CoO/SrTiO₃. The activity first increased, reached a maximum, and then decreased drastically with increasing doping concentration. The physical properties of the catalyst were characterized using XRD, SEM and UV-visible diffuse reflectance spectra. The influence of loading amount of co-catalyst CoO on the photocatalytic activity of La-doped SrTiO₃ was also studied and it was found that the optimum loading amount increased with increasing doping concentration.     

Semiconductor flexoelectricity in graphite-doped SrTiO3 ceramics

Improving the flexoelectric coefficients of materials is of great significance and challenge in physics and material sciences. Herein, graphite was roughly added into a paraelectric SrTiO₃ (STO) ceramic, in order to increase the dielectric permittivity and electrical conductivity, which brings minimized variations to crystal, both structure and microstructure. More importantly, the flexoelectric coefficient of the doped STO with 20 wt% C was found to experience a jump increase by an order of magnitude relative with the pure STO, which could be well interpreted by the occurrence of an interface layer between the semiconductor surface and the electrodes, whereby under bending, a large macroscopic polarization in the paraelectric ferroelectrics was generated. The facile strategy in this paper introduces a general way to probing the semiconductor flexoelectricity in the paraelectric ferroelectrics.     

Preparation by chemical solution deposition and transparent conducting properties of LaRh1-xNixO3 thin films

Transparent conducting thin films have been widely used in lots of fields. The absence of high-performance hole-type transparent conducting thin films, however, seriously limits the wider applications. LaRhO₃ as a type of perovskite material shows hole-type conduction with semiconductor-like properties and no investigations have been carried out about transparent conducting properties on LaRhO₃ thin films. Here, LaRh_1-xNi_xO₃ (x = 0, 0.05, 0.1) thin films were firstly deposited by chemical solution deposition, showing epitaxial growth on single crystal SrTiO₃ (001) substrates with the epitaxial relationship of LaRhO₃(001)[110]||SrTiO₃(001)[110]. With the doping of Ni element, the surface morphology became denser. Hall measurements confirmed that the hole concentration was enhanced with Ni doping, resulting in the decreased resistivity. Low resistivity of 17.3 mΩ cm at 300K was obtained for the LaRh_0.9Ni_0.1O₃ thin films. The electrical transport mechanisms were investigated, showing thermal activation at high temperatures and variable range hopping model for the doped thin films at low temperatures. The transmittance within the visible range for all thin films was higher than 50%. The results will provide a feasible route to deposit hole-type transparent conducting LaRhO₃-based thin films.     

Significantly improved energy storage properties of sol-gel derived Mn-modified SrTiO3 thin films

In this paper, x mol% Mn-doped SrTiO₃ (STMx, x?=?0, 0.5, 1, 3 and 5) thin films were synthesized by a sol-gel method. The effect of Mn doping on the microstructure and electrical performance was investigated. STMx (x?≤?1) thin films shows a single cubic perovskite phase while impurity phase appears for STM3 and STM5 thin films confirmed by X-ray diffraction. X-ray photoelectron spectra reveals that STM1 thin film has the lowest concentration of oxygen vacancy. The dielectric constant and loss of STMx (x?≤?1) films display good frequency stability, while decrease with the frequency for STM3 and STM5 thin films. And all samples display excellent bias stability of dielectric constant; this is advantageous for applications in a high electric field. The ferroelectric test demonstrates that the electrical breakdown strength increases and leakage current decreases for Mn doped SrTiO₃ films. A great recoverable energy storage density of 23.8?J/cm³ with an efficiency of 69.8% at 2.286?MV/cm is obtained in STM1 thin film. Furthermore, STM1 thin film shows good frequency stability of energy storage properties. It indicates that Mn doping is a simple and effective method to improve the energy storage properties of dielectric capacitors.     

Encapsulation of N-doped carbon layer via in situ dopamine polymerization endows nanostructured NaTi2(PO4)3 with superior lithium storage performance

NaTi₂(PO₄)₃ (NTP) anode with NASICON structure presents broad prospects for aqueous lithium ion battery. Nevertheless, its intrinsic poor conductivity and structure stability in aqueous solution restrict performance of materials. Herein, we used dopamine hydrochloride to fabricate N-doped carbon encapsulated NaTi₂(PO₄)₃ nanosphere via in situ dopamine polymerization under different solution environments. Composites show obvious improvement on electrochemical performance compared with NTP. Additionally, utilization of Tris-buffer solution endows N-doped carbon encapsulated NaTi₂(PO₄)₃ nanosphere with superior performance to those of composites acquired in other solution environments. Among all samples obtained in Tris-buffer, N-doped carbon encapsulated NaTi₂(PO₄)₃ nanosphere with proper carbon layer shows superb electrochemical performance with discharge capacities of 127.5, 113.8, and 90.9 mA h g⁻¹ at 0.2, 3.0, and 15C, respectively. Superb property may be due to the unique nanosphere structure. Nanospheres with better dispersion can shorten migration path of Li ions. Encapsulation of N-doped carbon layer improves stability in aqueous electrolyte and ameliorates electronic conductivity of materials. N doping enhances hydrophilicity and electronic conductivity, and also forms lots of defects on carbon layer, which contributes to Li ion intercalation/deintercalation. This work reveals that the combination of nanosphere and N-doped carbon layer offers a promising method to raise electrochemical performances of NaTi₂(PO₄)₃.     

Interfacial origin of enhanced energy density in SrTiO3-based nanocomposite films

SrTiO₃-based films doped with different Al-precursors were prepared by sol-gel methods and the dielectric strengths and leakage currents of the materials were investigated. The best performance was found in SrTiO₃ films doped with Al₂O₃ nanoparticles (nano-Al₂O₃). When 5 mol% of nano-Al₂O₃ was added to SrTiO₃ films with Al electrodes, the dielectric strength was enhanced to 506.9 MV/m compared with a value of 233.5 MV/m for SrTiO₃ films. The energy density of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films was 19.3 J/cm³, which was also far higher than that of the SrTiO₃ films (3.2 J/cm³). These results were attributed to interfacial anodic oxidation reactions, which were experimentally confirmed by cross-sectional transmission electron microscope studies and theoretically modelled based on Faraday's laws. The films with added nano-Al₂O₃ featured many conducting paths at the interfaces between the host phase and the guest nano-Al₂O₃, which promoted ion transport and contributed to the strong anodic oxidation reaction capability of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films.     

Preparation and properties of pure crystalline perovskite CeFeO3 thin films with vanadium doping

Cerium ferrite (CeFeO₃) thin films doped with vanadium (V:CeFeO₃) were grown on SiO₂ quartz glass and <100>‐oriented SrTiO₃ (STO) crystal substrates by the radio‐frequency magnetron sputtering method in this study. The effects of crystallization, substrate, and V‐doping on the quality, the magnetic property and the magneto‐optical property of as‐prepared films are investigated. V:CeFeO₃ film grown on STO substrate has better crystallinity and has better lattice integrity due to the higher lattice matching between substrate and film. The magnetic hysteresis loop and the magnetic circular dichroism spectra show that the magnetization strength and the magneto‐optical properties of V:CeFeO₃ films have the significant anisotropy. Moreover, V‐doping and the stress lead to the change in easy magnetization direction of film. It shows that the perovskite B‐site doping with transition‐metal ion has significant influence on the magnetic and the magneto‐optical properties of CeFeO₃ thin films.     

Preparation of NaBiO3 and the electrochemical characteristic of manganese dioxide doped with NaBiO3

NaBiO₃ crystal of high purity has been synthesized through chemical oxidization. The morphology and thermal stability of NaBiO₃ were examined with scanning electron microscope (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The electrochemical properties of MnO₂ electrodes with and without doping NaBiO₃ were studied through galvanostatic charge/discharge and cyclic voltammetry. The results indicate that the MnO₂ electrode doped with NaBiO₃ possesses remarkably higher discharge voltage and capacity and better reversibility than the pure MnO₂ electrode and Bi₂O₃ doping MnO₂ electrode.     

Tuning the Structural,Electronic, and Magnetic Properties of Strontium Titanate Through Atomic Design: A Comparison Between Oxygen Vacancies and Nitrogen Doping

The structural, electronic, and magnetic properties of seven sets of SrTiO_2.75 (oxygen vacancies) and SrTiO_2.75N_0.25 (nitrogen doping) models were investigated by the first principles calculations based on density functional theory. Our results indicated that oxygen vacancies tended to align in a chain sandwiched with Ti atoms, whereas doped nitrogen atoms (substituting oxygen atoms in SrTiO₃) preferred other arrangements rather than a chain. In addition, under stable arrangement, SrTiO_2.75 showed no magnetism, whereas magnetic moments appeared in other meta‐stable SrTiO_2.75 configurations as well as in SrTiO_2.75N_0.25, which is attributed to the Ti 3d orbitals and nitrogen p orbitals, respectively. Our results suggest a possible route for tuning magnetic and electronic properties of SrTiO₃ by atomic design.     

Ternary Ag@SrTiO3@CNT plasmonic nanocomposites for the efficient photodegradation of organic dyes under the visible light irradiation

In this research, carbon nanotube (CNT)-modified plasmonic silver-strontium titanate (Ag@ SrTiO₃) nanocomposites for the degradation of the organic dye were prepared by the sol-gel method. The characterization of all products was carried out using the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption test (BET), field emission-scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), and transient photocurrent (TPC) studies. It was found that the incorporation of Ag in and introducing CNT into the SrTiO₃ nanoparticles reduced the crystallite size to 21 nm and the band gap energy to 2.7 eV. The Reduced PL peak intensity, increased photocurrent value, and reduced charge transfer resistance approved that the Ag@SrTiO₃@CNT nanocomposite had a greater charge transfer efficiency than other samples. The optimal dosage of the photocatalyst, for the complete degradation of 5 ppm of the methylene blue (MB) solution after 30 min of the visible light irradiation, was decided as 0.5 g/L. Besides, in the experimental environment, the Ag@SrTiO₃@CNT sample illustrated the most significant photocatalytic performance of the degradation of methyl orange (MO) and Rhodamine B (RhB) dyes. The detailed mechanism and kinetics of the degradation procedure were clarified. Finally, the prepared system displayed increased stability and reusability in the entire cyclic degradation experiment.     

The photoelectrochemical properties of N3 sensitized CaTiO3 modified TiO2 nanocrystalline electrodes

The preparation of nanoporous TiO₂ electrodes modified with CaTiO₃ layers and their application in dye-sensitized solar cells (DSSCs) were reported. The as-prepared TiO₂/CaTiO₃ electrodes were characterized by XPS and XRD, indicating that a thin CaTiO₃ layer was formed on the surface of nanoporous TiO₂ electrodes. Compared with bare TiO₂ electrodes, CaTiO₃ modified TiO₂ electrodes presented more dye adsorption. Moreover spectroelectrochemical studies showed that the concentration of free electrons in the conduction band of TiO₂ was remarkably increased after surface modification. As a result, the photocurrent and photoelectric conversion efficiency of the modified electrodes were increased. The influence of the thickness of CaTiO₃ layer on the photoelectrochemical properties of the modified electrodes was investigated. Experiment results showed that proper thickness of the modification layer is crucial to the photoelectrochemical properties of modified electrodes. The highest conversion efficiency reaches 9.23% under irradiation of 100 mW cm⁻² white light, obtained with the electrode TiO₂/CaTiO₃(45 min), a 34% increase than that of bare TiO₂ electrodes.     

Improving electrochromic behavior of spray pyrolised WO3 thin solid films by Mo doping

The effects of molybdenum [Mo] doping on the electrochromic behavior of spray pyrolised tungsten trioxide [WO₃] thin films have been studied. It has been observed that the color-bleaching kinetics, coloration efficiency, and stability of electrochromic WO₃ films are closely related to molybdenum doping concentration, apart from their microstructure and crystallinity. While a nominal 6.0 at.% molybdenum doping produces best electrochromic response in WO₃ films, the electrochemical stability is highest when the nominal concentration of molybdenum is about 2.0 at.%. The improved electrochromic behavior of the Mo doped WO₃ films has been explained from the improved H⁺ ion diffusion coefficient in the films during coloration and decoloration process.     

Photoactive behavior of polyacrylonitrile fibers based on silver and zirconium co‐doped titania nanocomposites: Synthesis,characterization, and comparative study of solid‐phase photocatalytic self‐cleaning

Silver and zirconium co‐doped and mono‐doped titania nanocomposites were synthesized and deposited onto polyacrylonitrile fibers via sol–gel dip‐coating method. The resulted coated‐fibers were characterized by X‐ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, diffuse reflectance spectroscopy, thermogravimetric analysis, and BET surface area measurement. Photocatalytic activity of the TiO₂‐coated and TiO₂‐doped coated fibers were determined by photomineralization of methylene blue and Eosin Y under UV–vis light. The progress of photodegradation of dyes was monitored by diffuse reflectance spectroscopy. The XRD results of samples indicate that the TiO₂, Ag‐TiO₂, Zr‐TiO₂, and Ag‐Zr‐TiO₂ consist of anatase phase. All samples demonstrated photo‐assisted self‐cleaning properties when exposed to UV–vis irradiation. Evaluated by decomposing dyes, photocatalytic activity of Ag–Zr co‐doped TiO₂ coated fiber was obviously higher than that of pure TiO₂ and mono‐doped TiO₂. Our results showed that the synergistic action between the silver and zirconium species in the Ag‐Zr TiO₂ nanocomposite is due to both the structural and electronic properties of the photoactive anatase phase. These results clearly indicate that modification of semiconductor photocatalyst by co‐doping process is an effective method for increasing the photocatalytic activity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Photocurrent response and semiconductor characteristics of Ce-Ce2O3-CeO2-modified TiO2 nanotube arrays

We reported Ce and its oxide-modified TiO₂ nanotube arrays (TNTs) and their semiconductor properties. The TNTs were prepared by anodic oxidation on pure Ti and investigated by electrochemical photocurrent response analysis. Then, the TNT electrodes were deposited of Ce by cathodic reduction of Ce(NO₃)₃ 6H₂O. After deposition, the TNT electrodes were fabricated by anodic oxidation at E = 1.0 V_(SCE) for various electricity as Ce-Ce₂O₃-CeO₂ modification. The Ce-deposited TNTs (band gap energy E_g = 2.92 eV) exhibited enhanced photocurrent responses under visible light region and indicated more negative flat band potential (E_fb) compared with the TNTs without deposition. After anodic oxidation, the mixed Ce and its oxide (Ce₂O₃-CeO₂)-modified TNT photoelectrodes exhibited higher photocurrent responses under both visible and UV light regions than the TNTs without deposition. The photocurrent responses and E_fb were found to be strongly dependent on the contents of Ce₂O₃ and CeO₂ deposited on TNTs. A new characteristic of E_g = 2.1 ± 0.1 eV was investigated in the Ce₂O₃- and CeO₂-modified photoelectrodes. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were also employed to characterize various modified TNTs photoelectrodes.     

High-voltage electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode materials via Al concentration gradient modification

Al₂O₃-modified LiNi_0.5Co_0.2Mn_0.3O₂ cathode material is successfully synthesized via a facile carboxymethyl cellulose (CMC)-assisted wet method followed by a high-temperature calcination process. Al concentration gradient doping and accompanying formation of Al-coating are simultaneously accomplished in the modified samples. XRD and EDS analysis demonstrate that Al element is successfully doped into the crystal lattice with concentration gradient distribution inside the particles, reducing the Li/Ni cation mixing and stabilizing the layered structure. The compact distribution of Al on the surface forms a protective layer between the electrodes and the electrolyte, prohibiting the harmful side reactions and phase transition on the interphase. Compared with the pristine, the modified material with 2000?ppm Al₂O₃ (Al-2000) shows the best high-voltage performance with the capacity retention increased by ~13.3% from 138.3 to 163.0 mAh g^?1 at 1?C in 3.0–4.6?V after 100 cycles. Even under the high current rate of 8?C (1240 mAh g^?1) after 200 cycles, the Al-2000 still exhibits a capacity retention of 88.6%, greater than 80.3% for the pristine. Furthermore, results from the cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) measurements confirm the roles of the Al₂O₃ modification in decreasing polarization and electrochemical resistances, contributing to the kinetic process of electrodes.     

Mg3Y2Ge3O12:Bi3+ UV fluorescent phosphor as the TiO2 “sensitizer” for enhancing the heavy oil viscosity reduction

Nowadays, visible fluorescent materials based on rare earth (RE) and non-RE ions doping have been extensively explored for white LEDs. As for the UV fluorescent materials, it is well known that they are not suitable for the lighting applications. As a result, when compared to the visible fluorescent materials, previous works paid little attention to the UV fluorescent materials. In this work, we report a type of Mg₃Y₂Ge₃O₁₂:Bi³⁺ UV fluorescent phosphor. To understand the crystal structural information and photoluminescence (PL) properties of samples, we have used the X-ray diffraction (XRD), scanning electronic microscope (SEM), UV–visible diffuse reflectance and PL spectra to characterize them. The structural results reveal that the Bi³⁺ doped sample show their particle size at about 30 μm. The PL results show that the Bi³⁺ doped sample upon excitation at 230 nm can show a broad emission band that can almost cover the whole UV spectral region from 290 nm to 410 nm. Since this UV fluorescent band is exactly in agreement with the UV absorption region of TiO₂ semiconductor, we have fabricated several Mg₃Y₂Ge₃O₁₂:Bi³⁺/TiO₂-based ceramic plates and proposed used them to serve as an efficient UV irradiation source for photocatalytic application. As a result, we find that the TiO₂ can exhibit the significantly enhanced photocatalytic property for the heavy oil viscosity reduction after adding the Mg₃Y₂Ge₃O₁₂:Bi³⁺ UV fluorescent phosphor.     

Enhancement of photoelectrochemical performance of BiFeO3 by Sm3+ doping

Bismuth ferrite (BiFeO₃) holds great potentials in the photoelectrocatalysis due to the advantages of low cost, narrow band gap and good chemical stability. However, the photoelectrochemical performance of BiFeO₃ is usually inhibited by the poor charge carrier transport. Here, we report the flame annealing synthesized Sm³⁺ doped BiFeO₃ photocathodes for efficient hydrogen production. Greatly enhanced water reduction activity was found in doped samples. The Bi_0.95Sm_0.05FeO₃ composition exhibited largest photocurrent density of 0.1061 mA cm^?2 at 0 V vs. RHE in 0.5 M Na₂SO₄, which was 5.6 times higher than that of the pristine BiFeO₃. Mott-Schottky analysis and electrochemical impedance spectra proved that the Bi³⁺substitution increased the charge carrier concentration and facilitated the charge migration. Incident photon-to-electron conversion efficiency (IPCE) value for Bi_0.95Sm_0.05FeO₃ film (～6.39% at 325 nm) was approximately ten times higher than that of undoped sample. The high performance can be ascribed to the rational Sm³⁺ doping, which can improve visible light absorption ability, facilitate the charge carrier transport kinetics and hinder the recombination of photogenerated carriers. Our work provides a facile cation doping with rare earth ions to improve the photoelectrochemical performances.     

Dry-pressed anodized titania nanotube/CH3NH3PbI3 single crystal heterojunctions: The beneficial role of N doping

Highly ordered, anodically grown TiO₂ nanotubes on titanium supports were annealed in ammonia atmosphere in order to incorporate nitrogen doping (≤2?at.%) in the titanium oxide lattice. FESEM micrographs revealed nanotubes with an average outer diameter of 101.5?±?1.5?nm and an average wall thickness of about 13?nm. Anatase crystals were formed inside the tubes after annealing in ammonia atmosphere for 30?min. With further annealing, rutile peaks appeared due to the thermal oxidation of the foil and rise as the duration of heat treatment was increased. The concentration and chemical nature of nitrogen in the nanotube arrays can be correlated to the optical response of dry-pressed heterojunctions of doped TiO₂/CH₃NH₃PbI₃ single crystals. The N-TiO₂/perovskite heterojunction with the highest amount of interstitial nitrogen exhibited an improved photocurrent, indicating the importance of the semiconductor doping-based heterojunction optimization strategies to deliver competitive levels of halide perovskite-based optoelectronic devices to be envisioned for urban infrastructures.     

Gradient doping of Cu(I) and Cu(II) in ZnO nanorod photoanode by electrochemical deposition for enhanced photocurrent generation

This study describes the synthesis and characterization of Cu-doped ZnO nanorods (NRs) by an electrochemical method in the presence of two different Cu precursor (Cu⁺² and Cu⁺) in order to improve photocurrent generation. Analyses of the resulting materials by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis and electrochemical photocurrent (ECP) spectroscopy confirm the formation of well-aligned ZnO Würtzite nanostructures in the form of hexagonal rods. For both doping source with a concentration of up to 0.5%, the following changes were observed: a distortion of the ZnO morphology, an increase in transmittance to 96% for ZnO doped with Cu⁺², and a reduction of the energy gap from 3.36 eV to 3.06 and 3.02 eV for ZnO doped with Cu⁺² and Cu⁺, respectively. From photoelectrochemical tests, the photo-current density was improved up to 0.05 mA cm^-2 in the presence of Cu doping, which is twelve times superior to that of undoped ZnO nanorods, which means that the incorporation of Cu+2 or Cu + significantly improves the separation efficiency of photogenerated electron-hole pairs. These results can be considered promising for optoelectronic and photocatalysis applications.     

Controlled synthesis of various SrTiO3 morphologies and their effects on photoelectrochemical cathodic protection performance

As an n-type semiconductor with typical perovskite structure, SrTiO₃ has broad research prospects in photochemical cathodic protection because of its suitable energy band structure. However, there is a lack of research on the effect of SrTiO₃ micro morphology on Photoelectrochemical cathodic protection performance. In this paper, a series of SrTiO₃ samples with controllable morphology were designed and prepared by changing the ratio of alcohol to water in the solvent, including nanoparticles (NPs), nano ball (NBs), nano rod (NRs), coral stone-like microspheres (CSLMs) and flower-like microspheres (FLMs). The experimental results show that FLMs samples have better photochemical cathodic protection performance. Under the condition of on light, the photocurrent density of FLMs samples reaches 9.2 μA. The photocurrent density of NPs samples is only 2.5 μA. The former is about 3.6 times that of the latter. The open circuit potential of FLMs samples has shifted from ?0.18 V to ?0.42 V, with a negative shift of 240 mV, while CSLMs samples have only a negative shift of 180 mV. In contrast, FLMs samples have a more negative shift of 60 mV. After four light cycle experiments, the performance of FLMs samples is stable without obvious change.