Showing papers by "Ying Dai published in 2014"
TL;DR: Recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.
Abstract: Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.
952 citations
TL;DR: This work reviewed briefly the progress of the strategies on extending the light absorption spectra of photocatalysts from the aspect of solar energy harvesting, and the mechanisms, advantages and disadvantages of these strategies were reviewed.
Abstract: Photocatalysis has attracted a lot of attention owing to its great potential to solving energy and environmental problems. Although great efforts have been made in the last few decades, the poor efficiency still fails to meet the requirement of practical applications. With the aim to improve further the photocatalytic efficiency and promote their practical applications, in this work we reviewed briefly the progress of the strategies on extending the light absorption spectra of photocatalysts from the aspect of solar energy harvesting. Based on the analyses and discussions of photocatalytic performances, and the mechanisms, advantages and disadvantages of these strategies, some perspectives and interpretations of the future development of photocatalysis were proposed based on our own understanding and experience. We hope it will be helpful for our colleagues that work in the field of photocatalysis.
168 citations
TL;DR: The research demonstrates that graphene on g-C3N4 with a tunable band gap and high carrier mobility may provide a novel way for fabricating high-performance graphene-based nanodevices.
Abstract: The layered graphene/g-C3N4 composites show high conductivity, electrocatalytic performance and visible light response and have potential applications in microelectronic devices and photocatalytic technology. In the present work, the stacking patterns and the correlations between electronic structures and related properties of graphene/g-C3N4 bilayers are investigated systematically by means of first-principles calculations. Our results indicate that the band gap of graphene/g-C3N4 bilayers can be up to 108.5 meV, which is large enough for the gap opening at room temperature. The calculated charge density difference unravels that the charge redistribution drives the interlayer charge transfer from graphene to g-C3N4. Interestingly, the investigation also shows that external electric field can tune the band gap of graphene/g-C3N4 bilayers effectively. Our research demonstrates that graphene on g-C3N4 with a tunable band gap and high carrier mobility may provide a novel way for fabricating high-performance graphene-based nanodevices.
138 citations
TL;DR: In this article, the title compound was prepared by adding an aqueous Na2SiO3 solution to an AgNO3 solution and characterized by powder XRD, XPS, UV/VIS diffuse reflectance spectroscopy, and DFT calculations.
Abstract: The title compound is prepared by addition of an aqueous Na2SiO3 solution to an AgNO3 solution and characterized by powder XRD, XPS, UV/VIS diffuse reflectance spectroscopy, and DFT calculations.
126 citations
TL;DR: Anatase phase Ti 3+ self-doped TiO 2−x nanoparticles (NPs) have been successfully synthesized by a simple interface ion diffusion-redox reaction using TiH 2 and H 2 O 2 as precursors as discussed by the authors.
103 citations
TL;DR: In this article, the authors summarize recent developments in the synthesis, activity, and mechanism of plasmonic photocatalysts, with the aim of stimulating improvements in photocatalysis activities and promoting the development of the future technologies.
Abstract: Plasmonic photocatalysts, which have intensive light absorption and high charge‐separation efficiencies, are regarded as promising candidates to solve energy and environmental issues in the future. In this Review, we summarize recent developments in the synthesis, activity, and mechanism of plasmonic photocatalysts, with the aim of stimulating improvements in photocatalytic activities and promoting the development of photocatalysis. The materials systems, energy‐transfer mechanisms, and factors that influence the photocatalytic activities of plasmonic photocatalysts are discussed. Some perspectives for the future development of the design of highly efficient plasmonic photocatalysts are proposed.
96 citations
TL;DR: Bi2WO6 with O vacancies is desirable for having better near-infrared photocatalytic performance than Bi2MoO6 due to the larger mobility of photogenerated holes.
Abstract: The electronic structure and related photocatalytic properties of Bi2MO6 (M = W, Mo) with various intrinsic defects are studied based on the first-principles density functional theory (DFT). Our results indicate that O vacancies form easily in both Bi2WO6 and Bi2MoO6 under Bi rich/O poor conditions. The near-infrared light transitions can be realized involving electrons from the O vacancy induced impurity states within the band gap to the conduction band. Rather than acting as photogenerated carrier recombination centers, the impurity states caused by O vacancies favor the transfer of photogenerated holes and further benefit the photocatalytic process due to the delocalized nature. The spatial separation of photogenerated carriers among different layers can be realized, which reduces the carrier recombination and improves the photocatalytic activity. In addition, Bi2WO6 with O vacancies is desirable for having better near-infrared photocatalytic performance than Bi2MoO6 due to the larger mobility of photogenerated holes.
78 citations
TL;DR: It is predicted that stable BiTeX (X = Br and I) monolayers possess intrinsic large polar electric fields along the normal direction to the plane, making them two-dimensional polar systems and promising for wide applications in nanoelectronics.
Abstract: A number of graphene-like materials have been theoretically predicted and experimentally confirmed so far. Here, based on the first-principles calculations, we predict that stable BiTeX (X = Br and I) monolayers possess intrinsic large polar electric fields along the normal direction to the plane, making them two-dimensional polar systems. Moreover, we find that these novel monolayers with thicknesses of only 3.8 A can produce a giant Rashba spin splitting derived from their peculiarly polar atomic configurations. Furthermore, the Rashba parameters of BiTeX monolayers can be effectively modulated by applying strain, and are thus promising for wide applications in nanoelectronics.
70 citations
TL;DR: Electronic structures, and effective masses of electron and hole at energy band edges are theoretically investigated by employing spin-polarized density functional theory calculations and demonstrate that the separation and transfer of photogenerated carriers along the [011] direction may be more effective than other possible directions.
Abstract: Recently, Cu2(OH)PO4 was found as the first photocatalyst active in the near-infrared(NIR) region of the solar spectrum (Angew. Chem., Int. Ed., 2013, 52, 4810; Chem. Eng. News, 2013, 91, 36), motivating us to explore systemically its photocatalytic mechanism under near-infrared light and how to improve and tune its photocatalytic performance. Herein, electronic structures, and effective masses of electron and hole at energy band edges are theoretically investigated by employing spin-polarized density functional theory calculations. The calculated energy band structure supports the absorption spectra of Cu2(OH)PO4 in the NIR region corresponding to the electron excitation from the valence band to the unoccupied bands in the gap. Our charge density analysis indicates that the O atoms in the hydroxyl serves as the effective bridge for the favoring separation of the photogenerated electron–hole pairs. Furthermore, the effective masses of electron and hole analysis demonstrate that the separation and transfer of photogenerated carriers along the [011] direction may be more effective than other possible directions. A qualitative comparison of carrier transfer ability along all the directions in the specific planes is displayed by the three-dimensional band structure. Interestingly, the calculated net dipole moment for the two basic units of Cu2(OH)PO4, octahedron and trigonal bipyramid, indicate that the macroscopic dipole moment for Cu2(OH)PO4 is zero, however, the distorted octahedron unit has a net dipole moment, which enables us to tune the macroscopic dipole moment by doping. The present work provides theoretical insight leading to a better understanding of the photocatalytic performance of Cu2(OH)PO4 and it may be beneficial to prepare more efficient Cu2(OH)PO4 for NIR light photocatalysis, which will also be helpful to design and prepare novel photocatalysts.
67 citations
TL;DR: In this paper, a one-step hydrothermal method was used to synthesize Bi2O2[BO2(OH) nanosheets with an internal polar electric field in the crystal structure.
Abstract: Bi2O2[BO2(OH)] nanosheets having an internal polar electric field in the crystal structure were synthesized by a one-step hydrothermal method. Due to the existence of the internal polar electric field, the separation of photoinduced carriers can be enhanced, resulting in the high photocatalytic activity of Bi2O2[BO2(OH)] nanosheets under irradiation of UV light.
58 citations
TL;DR: A novel 2D material germanane (GeH), which was synthesized by an ion-exchange approach, was firstly found to exhibit photocatalytic performance in the hydrogen evolution of water splitting and decomposition of organic contaminants under illumination of visible light.
TL;DR: In this article, the authors explored how the visible-light energy absorbed by noble-metal nanoparticles (NPs) is converted to electrons and holes in the semiconductor in a visible light plasmonic photocatalyst by studying the representative system Ag@AgCl.
Abstract: We explored how the visible-light energy absorbed by noble-metal nanoparticles (NPs) is converted to electrons and holes in the semiconductor in a visible-light plasmonic photocatalyst by studying the representative system Ag@AgCl on the basis of density functional calculations and classical electrodynamics calculations. These calculations suggest that the energy transfer from the Ag NPs to the semiconductor AgCl requires the presence of midgap defect states in the semiconductor and that the surface plasmon resonance (SPR) of the Ag NPs strongly enhances the optical transitions of the semiconductor involving the defect states. We verified this suggestion experimentally by preparing Ag@AgCl samples possessing different degrees of bulk and surface defects and subsequently by carrying out photodegradation experiments using these samples.
TL;DR: Electrostatic adsorption plays an important role in the formation of BiOX/ACF composites, which show excellent cyclic properties and stable performance.
Abstract: BiOX have been grown on the surface of activated carbon fibers (ACF) as recycled photocatalysts. The analysis results illustrate that electrostatic adsorption plays an important role in the formation of BiOX/ACF composites. The photocatalytic experimental results indicate that BiOX/ACF show excellent cyclic properties and stable performance.
TL;DR: In this paper, the authors demonstrate via density functional theory that low-buckled two-dimensional (2D) Co2C18H12 lattice structure are spin-polarized.
TL;DR: In this article, a simple hydrothermal method using Zn as the reductant was used to synthesize self-doped TiO2 (A)/TiO2(R) heterojunctions with anatase and rutile nanorods, which exhibited an extended visible light absorption and higher visible-light photocatalytic activity.
Abstract: Ti3+ self-doped TiO2(A)/TiO2(R) heterojunctions comprising anatase TiO2 (TiO2(A)) nanoparticles and rutile TiO2 (TiO2(R)) nanorods were synthesized by a simple hydrothermal method using Zn as the reductant. The structure, crystallinity, morphology, and chemical state of the as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The heterojunction architectures and Ti3+ contents could be controlled by adjusting the temperature of the hydrothermal treatment. Zn acts as a reducing agent and Zn2+ stabilizes the oxygen vacancies. Meanwhile, the generated ZnO clusters promote phase transformation from TiO2(A) to TiO2(R). The visible-light photocatalytic degradation of dyes was analyzed. The Ti3+ self-doped TiO2(A)/TiO2(R) heterojunctions exhibited an extended visible light absorption and higher visible-light photocatalytic activity than that of commercial P25 TiO2 in the photodegradation of Methylene blue and Rhodamine B under visible-light irradiation (λ ≥ 400 nm). Ti3+ self-doping expanded the light-response range, and the formed heterojunctions at the interface of TiO2(A) nanoparticles and TiO2(R) nanorods efficiently reduced the recombination of photoinduced electron–hole pairs. This self-doping increased the lifetime of charge carriers by 15 times that of P25 TiO2 and enhanced the corresponding photocatalytic activity of the self-doped heterojunctions.
TL;DR: In this paper, the electronic properties of pentavalent-ion (Nb5+, Ta5+, and I5+) doped anatase and rutile TiO2 were studied using spin-polarized GGA+U calculations.
Abstract: The electronic properties of pentavalent-ion (Nb5+, Ta5+, and I5+) doped anatase and rutile TiO2 are studied using spin-polarized GGA + U calculations. Our calculated results indicate that these two phases of TiO2 exhibit different conductive behavior upon doping. For doped anatase TiO2, some up-spin-polarized Ti 3d states lie near the conduction band bottom and cross the Fermi level, showing an n-type half-metallic character. For doped rutile TiO2, the Fermi level is pinned between two up-spin-polarized Ti 3d gap states, showing an insulating character. In addition to the Nb (Ta)-doped anatase TiO2, we propose that the I-doped anatase TiO2 can also be a potential transparent conducting oxide, which is worthy of further experimental verification. These findings clarify the long-standing controversy of whether GGA + U calculation can successfully predict the conducting property in the Nb (Ta)-doped anatase phase and the insulating property in the rutile phase. Moreover, our results show that the symmetry breaking can cause a metal-insulating transition in pentavalent-ion-doped anatase TiO2, though this symmetry breaking may not occur spontaneously because of the relatively high energy barrier.
TL;DR: The results reveal that the replacement of divalent host oxygen atoms with monovalent atoms can decrease theHEIE and proper surface treatment of semiconductor before depositing metal particles and structure optimization of the composite are suggested to improve the HEIE.
Abstract: The low hot electrons injection efficiency (HEIE) from plasmonic metal to semiconductor significantly affects the performance of metal–semiconductor composite. However, there are few reports about the origin of this low HEIE. In the present work, the factors affecting the transfer process and generation efficiency of hot electron in Au@TiO2 composite are investigated using first-principles calculations and Maxwell’s electrodynamics theory. The occupation of surface oxygen vacancies of TiO2 by gold atoms is found to increase the hot electrons transfer barrier and expand the space charge region, which decrease the HEIE. In addition, the existing Au@TiO2 structure going against the generation of large amount of hot electrons may also lead to low HEIE. Our results reveal that the replacement of divalent host oxygen atoms with monovalent atoms can decrease the HEIE and comparison with experimental results allows us to validate our predictions. Furthermore, proper surface treatment of semiconductor before depos...
TL;DR: In this paper, the effect of external electric field (E-field) on the electronic properties of wrinkled germanane based on first-principles calculations is investigated, and it is shown that a minuscule E-field can largely and continuously reduce the energy gap.
Abstract: Effective modulation of physical properties via external control is a tantalizing possibility that would bring two-dimensional material-based electronics a step closer. Following the recent experiments, we report a systematic investigation of the effect of external electric field (E-field) on electronic properties of wrinkled germanane based on first-principles calculations. Our results demonstrate that a minuscule E-field can largely and continuously reduce the energy gap of wrinkled germanane. This goes beyond all existing two-dimensional materials, since the required E-field in wrinkled germanane is only a fraction of that for most existing two-dimensional materials. More interestingly, our data show that the promising band inversion can be obtained by modulation of strength of the tiny E-field due to the modification of electron distribution. Furthermore, the possible underlying physical mechanisms are discussed in detail. These results provide a new perspective on the formation of germanane-based electronic devices.
TL;DR: In this paper, a simple hydrothermal process was used to synthesize β-AgVO3 nanowires, which provided a V source for photocatalytic properties.
Abstract: β-AgVO3 nanowires were synthesized by a simple hydrothermal process. With β-AgVO3 providing a V source, BiVO4@β-AgVO3 composites were obtained through an in situ growth process. BiVO4@β-AgVO3 composites exhibited enhanced photocatalytic properties. We discussed the possible mechanism of enhanced photocatalytic activities. The effect of content and size of BiVO4 was also studied specifically.
TL;DR: It is demonstrated that transition-metal (TM) monolayers (TM = Ti, Zr, Hf, V, Nb, or Ta), d-electron-based materials, could also hold Dirac cones and not only p-electronic materials as known before, and some TM-monolayers exhibit ferromagnetic couplings simultaneously.
Abstract: p-Electron-based monolayer materials have dominated the research of Dirac fermions since the first exfoliation of graphene. In the present work, the electronic and magnetic properties of d-electron-based Dirac systems are studied by combining first-principles with mean field theory and Monte Carlo approaches. From first-principles calculations, we demonstrate that transition-metal (TM) monolayers (TM = Ti, Zr, Hf, V, Nb, or Ta), d-electron-based materials, could also hold Dirac cones and not only p-electron-based materials as known before. This may shed light on the breakthrough of new nanomaterials with d-type Dirac points. Moreover, the carrier mobility near the Dirac points of these materials can be tuned regularly by isotropic strains from −5% to 5%, without breaking the Dirac cones. However, the Dirac points would disappear under anisotropic strains, indicating that a rigorous honeycomb lattice may be the main precondition for Dirac points in TM-monolayers. Furthermore, some TM-monolayers (TM = Ti, Zr, or Hf) exhibit ferromagnetic couplings simultaneously. In addition, by mean field theory and Monte Carlo methods, it is found that Curie temperatures of TM-monolayers can be higher than 580 K even to 1180 K. Our findings significantly expand the Dirac systems.
TL;DR: In this article, the authors applied a photocatalytic system to form CuO/CuSCN valence state heterojunctions, which exhibited enhanced visible light driven photocatalysis activity and, surprisingly, ultraviolet light restrained activity.
TL;DR: The present study conclusively accounts for the recent experimental results and indicates that the final electronic structures of doping system are very sensitive to the models used to conduct calculations, which can rationalize the distinct conclusions about N-doped TiO2 in previous theoretical works.
Abstract: We have carried out a theoretical study to explain the photocatalytic performance of the newly synthesized special core (pure TiO2)–shell (heavily nitrogen (N)-doped TiO2) structure of TiO2 nanocrystal using advanced first-principles calculations. The conventional N doping models by maximizing the mutual distances between dopants are found to only introduce localized gap states irrespective of doping concentrations, which is in agreement with previous theoretical results but cannot explain the experimental results. In comparison, the electronically coupled N doping of TiO2, which is almost as stable as the conventional doping models and generally overlooked in previous works, can not only narrow the overall band gap but also decrease the carrier recombination rate. In particular, in the special core–shell structure of TiO2 nanocrystal, perfect type-II-like homojunction is formed, which can further decrease the carrier recombination rate. The present study conclusively accounts for the recent experimental ...
TL;DR: In this paper, a triterpene compound derived from the Chinese medicinal plant Tripterygium wilfordii was used to synthesize CSL-modified TiO2 nanoparticles by a hydrothermal treatment method.
Abstract: In this study, celastrol (CSL), a triterpene compound which is derived from the Chinese medicinal plant Tripterygium wilfordii, was used to synthesize CSL-modified TiO2 nanoparticles by a hydrothermal treatment method. The nanoparticles phase, morphology, surface structures, as well as the visible-light photocatalytic activities were studied. The modification of CSL does not alter the crystalline structure of the TiO2 but can prevent TiO2 from further aggregating and provides photosynthesis pigments as an in situ dye-sensitizing source. Compared to pure TiO2, the resulting CSL-modified TiO2 nanoparticles exhibit enhanced visible-light photocatalytic activity and showed an excellent cyclic stability in the decomposition of methylene blue (MB). In addition, the photocatalytic degradations of MB were all demonstrated to follow a first-order kinetic model. The enlarged specific surface area and CSL-modified surface improved the visible-light photocatalytic activity of nanoparticles.
TL;DR: In this paper, the title compound was prepared by adding an aqueous Na2SiO3 solution to an AgNO3 solution and characterized by powder XRD, XPS, UV/VIS diffuse reflectance spectroscopy, and DFT calculations.
Abstract: The title compound is prepared by addition of an aqueous Na2SiO3 solution to an AgNO3 solution and characterized by powder XRD, XPS, UV/VIS diffuse reflectance spectroscopy, and DFT calculations.
TL;DR: In this article, the authors reported a giant Rashba-type spin splitting in SrFBiS2 and BiOBiS2 nanosheets originating from their hidden local polar atomic configurations, and they observed two sets of Rashba spin splittings in both materials; this is different from most of the previous studied Rashba systems, in which there is only one set of spin splitting.
Abstract: The Rashba effect is increasingly seen as the key ingredient in the burgeoning field of spintronics. However, the lack of two-dimensional materials with a large Rashba effect hinders its practical applications. Here, with density functional theory, we report giant Rashba-type spin splitting in SrFBiS2 and BiOBiS2 nanosheets originating from their hidden local polar atomic configurations. Owing to the weak interactions between the two BiS2 layers, they hold two individual Rashba spin splittings belonging to two opposite BiS2 layers, which are degenerated because of their inversion symmetry. As a result, with small perturbations, such as a tiny electric field, we observe two sets of Rashba spin splittings in both materials; this is different from most of the previous studied Rashba systems, in which there is only one set of Rashba spin splitting. More interestingly, the strength of the Rashba effect in both nanosheets can be preserved while their bandgap can be effectively tuned by applying an external electric field.
TL;DR: The photocatalytic efficiency was evaluated by decomposing methyl orange dye under ultraviolet light irradiation, and the Ln(IO3)3 products show excellent photoc atalytic properties.
Abstract: Ln(IO3)3 (Ln = Ce, Nd, Eu, Gd, Er, Yb) polycrystals were hydrothermally synthesized using lanthanide nitrate or lanthanide oxide and iodic acid as precursors. X-ray diffraction was used to characterize the crystal structures of the Ln(IO3)3 products. Scanning electron microscopy was carried out to observe the microscopic morphologies. The lattice spacings were studied by high-resolution transmission electron microscopy and selected area electron diffraction. We evaluated the photocatalytic efficiency by decomposing methyl orange dye under ultraviolet light irradiation, and the Ln(IO3)3 products show excellent photocatalytic properties. To rule out the effect of photosensitization, 2,4-dichlorophenol was also photodegraded. As one of the key factors of photocatalysis, ultraviolet–visible diffuse reflectance spectra of the Ln(IO3)3 samples were also studied, and all products have strong absorption in the ultraviolet region.
TL;DR: In this paper, the effect of Pd decoration on the gas sensing properties of vanadium oxide nanotubes (VONTs) was investigated and the mechanism of promoting sensing properties with Pd nanoparticles was discussed.
TL;DR: In this article, a facile microwave irradiation was used to synthesize Ag nanoparticle supported on vanadium oxide nanotubes (VONTs) for gas sensing towards C2H5OH, NH3 and C6H5CH3 gases.
Abstract: A facile microwave irradiation was used to synthesize Ag nanoparticle supported on vanadium oxide nanotubes (VONTs) in this paper. The VONTs on alumina tube installed with Pt electrodes were tested for gas sensing towards C2H5OH, NH3 and C6H5CH3 gases. Detailed studies showed that the sensing capabilities were greatly enhanced in comparison to those of pure nanotubes. It was found that the Ag nanoparticles supported on VONTs sensing films exhibited a high C2H5OH selectivity compared with NH3 and C6H5CH3 gases. When the sensor is exposed to C2H5OH, the ethanol molecules interact with the preadsorbed oxygen ions on the Ag nanoparticles surface. The ethanol oxidation on the Ag nanoparticles leads to the transfer of electrons into the semiconducting VONTs and this is reflected as the change in conductance of sensor. The presence of Ag nanoparticles on the surface of VONTs serves to enhance the C2H5OH oxidation due to a higher oxygen ion-chemisorption on the conductive Ag nanoparticle surfaces.
TL;DR: In this paper, a one-step facile solvothermal method was used to synthesize a Ti3+:TiO2/TiF3 hybrid, which exhibited excellent visible-light photocatalytic reactivity.
Abstract: A Ti3+:TiO2/TiF3 hybrid was synthesized via a one-step facile solvothermal method. Due to the presence of TiF3, TiO2 contained a high concentration of Ti3+ species and Ti3+ was stabilized. The Ti3+:TiO2/TiF3 hybrid exhibited excellent visible-light photocatalytic reactivity. The electron structure of TiF3 was studied, and a photocatalytic mechanism was also proposed.