A Novel Series of the New Visible-Light-Driven Photocatalysts MCo1/3Nb2/3O3 (M = Ca, Sr, and Ba) with Special Electronic Structures

In Situ Formation of Ba3CoNb2O9/Ba5Nb4O15 Heterostructure in Electrolytes for Enhancing Proton Conductivity and SOFC Performance

The in situ formation of a heterostructure delivers superior electrochemical properties as compared to the mechanical mixing, which shows great promise for developing new electrolytes for solid oxide fuel cells (SOFCs). Herein, in an SOFC constructed by the Ba5Nb4O15 electrolyte and Ni0.8Co0.15Al0.05LiO2-δ anode, an in situ formation of Ba3CoNb2O9/Ba5Nb4O15 heterostructure is designed by Co-ion diffusion from the anode to the electrolyte during cell operation, resulting in improved ion conductivity and fuel cell performance. An abnormal phenomenon is observed that the SOFC based on the Ba3CoNb2O9/Ba5Nb4O15 electrolyte delivered a peak power density of 703 mW/cm2 at 510 °C, which is higher than that at 550 °C. Characterization in terms of X-ray photoelectron spectroscopy and X-ray diffraction verifies that the operating temperature affected the Co doping concentrations, leading to different conducting behaviors of the heterostructure. Furthermore, it is found that the heterojunction of Ba3CoNb2O9 and Ba5Nb4O15 can restrict the electron migration to avoid current leakage of the cell and simultaneously enhance the proton conductivity. These findings manifest the developed in situ Ba3CoNb2O9/Ba5Nb4O15 heterostructure as a promising electrolyte for SOFCs.

Probing into the conduction band and type of carriers/traps on red/orange persistent phosphors in vacancy & solid-solution induced (Sr/Ba)1-xCaxGe4-yO9:Mn2

Long-wavelength afterglow has been a key issue in the investigation of afterglow materials. Herein, the orange/red (Sr/Ba)1-xCaxGe4-yO9:0.01Mn2+ is prepared by the introduction of vacancy induction and solid solution. The (Sr/Ba)Ge4O9:Mn2+ hardly possesses an afterglow phenomenon and exhibits only red/orange photo-luminescence (PL) attributed to the d-d transition of Mn2+, while samples with reduction of the Ge4+ content and with replacement by Ca2+ show bright afterglow emission with the peak located at about 612 nm/620 nm. The emerging broadband peak comes from charge transfer involving Mn2+ and nearby defect clusters and the bottom of the conduction band (CB). The introduction of V''''Ge creates a defective energy level above the valence band, but the ground state energy difference with Mn2+ is too large (>1 eV) to allow hole transfer, which was confirmed by ultraviolet photoelectron spectroscopy (UPS), spherical aberration-corrected transmission electron microscopy (AC-STEM), charge differential density (CDD) analysis, electron paramagnetic resonance (EPR) analysis, etc. With this achievement, we propose an original design strategy for long-wavelength afterglow and a more reasonable afterglow mechanism, which is of great importance for the investigation of long-wavelength afterglow materials.

Reactive species specific RhB assisted collective photocatalytic degradation of tetracycline antibiotics with triple-layer Aurivillius perovskites

Triple-layer Aurivillius perovskites degrade tetracycline antibiotic and rhodamine B together in acidic aqueous solution. Primarily the superoxide radical generated via a semiconductor assisted dye sensitization process degrades the tetracycline.

Targeted synthesis of a CrIII–O–VV core oxo-bridged complex: spectroscopic, magnetic and electrical properties

The results of vibrational, electronic, structural, thermal, magnetic and impedance spectroscopy studies are presented in the first reported compound with a Cr^III–O–V^V bridge.

Visible light activity of BaFe1-xCuxO3-δ as photocatalyst for atrazine degradation

Nanosized BaFe_1-xCu_xO₃ powders were prepared using the Pechini method. To limit grain growth and agglomeration, the temperature of calcination was limited to 800 °C. For all samples, the cubic form of BaFeO_2.75 was predominant with minor additional phases. Cu doping was found to have a remarkable effect on the structural cubic unit cell parameter as the Cu concentration increased. As shown by XRD,the samples were in the nanometer size range (17-63 nm). However, as the Cu concentration increases, the agglomeration increases with the highest surface area for the BaFe_0.95Cu_0.05O₃ composition, which also displays the highest photocatalytic atrazine degradation. For this sample, more than 90% degradation of atrazine was obtained at the optimum conditions (120 min irradiation under visible light at pH 11 using 0.75 mg of the catalyst). The Atrazine degradation was found to follow the pseudo-order kinetics. GC/MS was used to detect the intermediates and the reaction pathways. All the prepared samples and produced waters at the end of the experiment were found to be nontoxic.

Bandgap Narrowing of Lead-Free Perovskite-Type Hybrids for Visible-Light-Absorbing Ferroelectric Semiconductors

Perovskite-type hybrids (e.g., CH₃NH₃PbI₃) hold great promise in photovoltaics and optoelectronics due to their remarkable semiconducting properties and potential ferroelectricity. However, to date, conclusive evidence for the bulk ferroelectricity of CH₃NH₃PbI₃ is still lacking. In this context, it is highly desirable to assemble concrete perovskite ferroelectric hybrids with the semiconducting feature. Here we report, for the first time, a class of lead-free perovskite halides, (N-methylpyrrolidinium)₃Sb₂Cl_9-9xBr_9x (x = 0-1), showing large ferroelectric polarizations (5.2-7.6 μC/cm²) and pronounced semiconducting performances. In particular, a wide tunability of their optical bandgaps (3.31-2.76 eV) enables superior visible-light-induced photocurrents (∼10 nA/cm²), which allow for assembling of the crystal-based photodetectors. Our work paves a new way to build environmentally benign optoelectronic devices based on low-bandgap ferroelectric hybrids.

Recent Progress in Energy-Driven Water Splitting

Hydrogen is readily obtained from renewable and non-renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non-renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost-effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic-integrated solar-driven water electrolysis.

Structural dependence of the photocatalytic properties of double perovskite compounds A2InTaO6 (A = Sr or Ba) doped with nickel

Photocatalytic activity is greatly improved when there is no structural distortion, which guarantees maximal metal–oxygen–metal interactions.

Inorganic perovskite photocatalysts for solar energy utilization

This review specifically summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation.

A review on visible light active perovskite-based photocatalysts

Perovskite-based photocatalysts are of significant interest in the field of photocatalysis. To date, several perovskite material systems have been developed and their applications in visible light photocatalysis studied. This article provides a review of the visible light (λ > 400 nm) active perovskite-based photocatalyst systems. The materials systems are classified by the B site cations and their crystal structure, optical properties, electronic structure, and photocatalytic performance are reviewed in detail. Titanates, tantalates, niobates, vanadates, and ferrites form important photocatalysts which show promise in visible light-driven photoreactions. Along with simple perovskite (ABO₃) structures, development of double/complex perovskites that are active under visible light is also reviewed. Various strategies employed for enhancing the photocatalytic performance have been discussed, emphasizing the specific advantages and challenges offered by perovskite-based photocatalysts. This review provides a broad overview of the perovskite photocatalysts, summarizing the current state of the work and offering useful insights for their future development.

Bi2MoO6 nanobelts for crystal facet-enhanced photocatalysis

γ-Bi2MoO6 single-crystal nanobelts with dominant {010} facets exhibit facet-enhanced photocatalytic property for the photodegradation of dye pollutants under visible light irradiation. The charge carriers are more efficiently separated on the low-index facets due to the exposure of more photoactive sites to the reacting substrates.

Highly efficient photocatalytic hydrogen evolution of graphene/YInO3 nanocomposites under visible light irradiation

Visible-light-driven hydrogen evolution with high efficiency is important in the current photocatalysis research. Here we report for the first time the design and synthesis of a new graphene-semiconductor nanocomposite consisting of YInO3 nanoparticles and two-dimensional graphene sheets as efficient photocatalysts for hydrogen evolution under visible light irradiation. The graphene/YInO3 nanocomposites were synthesized using a facile solvothermal method in which the formation of graphene and the deposition of YInO3 nanoparticles on the graphene sheets can be achieved simultaneously. The addition of graphene as a cocatalyst can narrow the band gap of YInO3 to visible photon energy and prolong the separation and lifetime of electron-hole pairs by the chemical bonding between YInO3 and graphene. The photocatalytic reaction with this nanocomposite reaches a high H2 evolution rate of 400.4 μmol h(-1) g(-1) when the content of graphene is 0.5 wt%, over 127 and 3.7 times higher than that of pure YInO3 and Pt/YInO3, respectively. This work can provide an effective approach to the fabrication of graphene-based photocatalysts with high performance in the field of energy conversion.

Nano-photocatalytic materials: possibilities and challenges

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Visible light photo-oxidation of model pollutants using CaCu3Ti4O12: an experimental and theoretical study of optical properties, electronic structure, and selectivity

Charge transfer between metal ions occupying distinct crystallographic sublattices in an ordered material is a strategy to confer visible light absorption on complex oxides to generate potentially catalytically active electron and hole charge carriers. CaCu3Ti4O12 has distinct octahedral Ti4+ and square planar Cu2+ sites and is thus a candidate material for this approach. The sol−gel synthesis of high surface area CaCu3Ti4O12 and investigation of its optical absorption and photocatalytic reactivity with model pollutants are reported. Two gaps of 2.21 and 1.39 eV are observed in the visible region. These absorptions are explained by LSDA+U electronic structure calculations, including electron correlation on the Cu sites, as arising from transitions from a Cu-hybridized O 2p-derived valence band to localized empty states on Cu (attributed to the isolation of CuO4 units within the structure of CaCu3Ti4O12) and to a Ti-based conduction band. The resulting charge carriers produce selective visible light photodegradation of 4-chlorophenol (monitored by mass spectrometry) by Pt-loaded CaCu3Ti4O12 which is attributed to the chemical nature of the photogenerated charge carriers and has a quantum yield comparable with commercial visible light photocatalysts.

Photocatalytic degradation of C.I. Direct Red 23 in aqueous solutions under UV irradiation using SrTiO3/CeO2 composite as the catalyst

The photocatalytic degradation of C.I. Direct Red 23 (4BS) in aqueous solutions under UV irradiation was investigated with SrTiO3/CeO2 composite as the catalyst. The SrTiO3/CeO2 powders had more photocatalytic activity for decolorization of 4BS than that of pure SrTiO3 powder under UV irradiation. The effects of catalytic dose, pH value, initial concentration of dye, irradiation intensity as well as scavenger KI were ascertained, and the optimum conditions for maximum degradation were determined. Under the irradiation of a 250 W mercury lamp, the best catalytic dose was 1.5 g/L and the best pH was 12.0. Light intensity exhibited a significant positive effect on the efficiency of decolorization, whereas the initial dye concentration showed a significant negative effect. Under the conditions of a catalytic dose of 1.5 g/L, pH of 12.0, initial dye concentration of 100mg/L, light intensity of 250 W, and air flow rate of 0.15 m3/h, complete decolorization, as determined by UV-visible analysis, was achieved in 60 min, corresponding to a reduction in chemical oxygen demand (COD) of 69% after a 240 min reaction. A tentative degradation pathway based on the sensitization mechanism of photocatalysis is proposed.

Mild, quasireverse emulsion route to submicrometer lithium niobate hollow spheres

A water/ethylene glycol (H2O/EG) system has been designed to synthesize lithium niobate (LiNbO3) powders by a mild, one-step quasireverse emulsion method. A morphology transformation from initial nuclei to flowerlike structures and then to hollow spheres is confirmed by the time-dependent experiment. The as-obtained LiNbO3 hollow spheres are formed via Ostwald ripening under solvothermal conditions, and their absorption edge in UV/vis diffuse reflectance spectra can be effectively tuned by the current morphology control strategies. This facile, efficient, and economic work provides a new route to simply and mildly synthesize hollow LiNbO3 particles and is a good initiation in the morphology control study of LiNbO3 powders.

Synthesis of New Visible Light Active Photocatalysts of Ba(In1/3Pb1/3M1/3‘ )O3 (M‘ = Nb, Ta): A Band Gap Engineering Strategy Based on Electronegativity of a Metal Component

We have synthesized new, efficient, visible light active photocatalysts through the incorporation of highly electronegative non-transition metal Pb or Sn ions into the perovskite lattice of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M = Sn, Pb; M' = Nb, Ta). X-ray diffraction, X-ray absorption spectroscopic, and energy dispersive spectroscopic microprobe analyses reveal that tetravalent Pb or Sn ions exist in the B-site of the perovskite lattice, along with In and Nb/Ta ions. According to diffuse UV-vis spectroscopic analysis, the Pb-containing quaternary metal oxides Ba(In(1/3)Pb(1/3)M'(1/3))O3 possess a much narrower band gap (E(g) approximately 1.48-1.50 eV) when compared to the ternary oxides Ba(In(1/2)M'(1/2))O3 (E(g) approximately 2.97-3.30 eV) and the Sn-containing Ba(In(1/3)Sn(1/3)M'(1/3))O3 derivatives (E(g) approximately 2.85-3.00 eV). Such a variation of band gap energy upon the substitution is attributable to the broadening of the conduction band caused by the dissimilar electronegativities of the B-site cations. In contrast to the ternary or the Sn-substituted quaternary compounds showing photocatalytic activity under UV-vis irradiation, the Ba(In(1/3)Pb(1/3)M'(1/3))O3 compounds induce an efficient photodegradation of 4-chlorophenol under visible light irradiation (lambda > 420 nm). The present results highlight that the substitution of electronegative non-transition metal cations can provide a very powerful way of developing efficient visible light harvesting photocatalysts through tuning of the band structure of a semiconductive metal oxide.