Erping Gao

Heterostructured bismuth molybdate composite: preparation and improved photocatalytic activity under visible-light irradiation.

A heterostructured photocatalyst containing the same Bi, Mo, and O elements (Bi(3.64)Mo(0.36)O(6.55)/Bi(2)MoO(6)) was realized by a facile hydrothermal method. The heterostructured composite was characterized by powder X-ray diffraction, selected-area electron diffraction, scanning electron microscopy, and high-resolution electron microscopy. The Bi(3.64)Mo(0.36)O(6.55)/Bi(2)MoO(6) composite exhibited notable enhanced photocatalytic activity compared to Bi(2)MoO(6) or Bi(3.64)Mo(0.36)O(6.55) in the photocatalytic degradation of rhodamine B and phenol under visible-light irradiation. More interestingly, it is found that the heterostructured composite could mineralize organic substances into CO(2) efficiently. This study offered a clue for the design of an efficient photocatalyst in the application of environmental treatment.

Photoreduction of CO2 on BiOCl nanoplates with the assistance of photoinduced oxygen vacancies

CO2 photoreduction by semiconductors is of growing interest. Fabrication of oxygen-deficient surfaces is an important strategy for enhancing CO2 photoreduction activity. However, regeneration of the oxygen vacancies in photocatalysts is still a problem since an oxygen vacancy will be filled up by the O atom from CO2 after the dissociation process. Herein, we have fabricated highly efficient BiOCl nanoplates with photoinduced oxygen vacancies. Oxygen vacancies were easily regenerated by light irradiation due to the high oxygen atom density and low Bi-O bond energy even when the oxygen vacancies had been filled up by the O atom in the photocatalytic reactions. These oxygen vacancies not only enhanced the trapping capability for CO2, but also enhanced the efficiency of separation of electron-hole pairs, which resulted in the photocatalytic CO2 reduction under simulated solar light. Furthermore, the generation and recovery of the defects in the BiOCl could be realized during the photocatalytic reduction of CO2 in water. The existence of photoinduced defects in thin BiOCl nanoplates undoubtedly leads to new possibilities for the design of solar-driven bismuth based photocatalysts.

Enhanced photocatalytic activity of Bi2WO6 with oxygen vacancies by zirconium doping

To overcome the drawback of low photocatalytic efficiency brought by electron-hole recombination, Bi(2)WO(6) photocatalysts with oxygen vacancies were synthesized by zirconium doping. The oxygen vacancies as the positive charge centers can trap the electron easily, thus inhibiting the recombination of charge carriers and prolonging the lifetime of electron. Moreover, the formation of oxygen vacancies favors the adsorption of O(2) on the semiconductor surface, thus facilitating the reduction of O(2) by the trapped electrons to generate superoxide radicals, which play a key role in the oxidation of organics. Visible-light-induced photodegradation of rhodamine B (RhB) and phenol were carried out to evaluate the photoactivity of the products. The results showed that oxygen-deficient Bi(2)WO(6) exhibited much enhanced photoactivity than the Bi(2)WO(6) photocatalyst free of oxygen deficiency. This work provided a new concept for rational design and development of high-performance photocatalysts.

Electrospun nanofibers of Bi-doped TiO2 with high photocatalytic activity under visible light irradiation.

Bi-doped TiO(2) nanofibers with different Bi content were firstly prepared by an electrospinning method. The as-prepared nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence spectra (PL), and UV-vis diffuse reflectance spectroscopy (DRS). The results indicated that Bi(3+) ions were successfully incorporated into TiO(2) and extended the absorption of TiO(2) into visible light region. The photocatalytic experiments showed that Bi-doped TiO(2) nanofibers exhibited higher activities than sole TiO(2) in the degradation of rhodamine B (RhB) and phenol under visible light irradiation (λ>420 nm), and 3% Bi:TiO(2) samples showed the highest photocatalytic activities.

Ultrathin {001}‐Oriented Bismuth Tungsten Oxide Nanosheets as Highly Efficient Photocatalysts

Shape-controlled synthesis is a commonly employed strategy to optimize the performance of various crystalline semiconductors, because the atomic configuration and coordination of the surface inherently determine the heterogeneous reactivity. Similarly, heterogeneous photocatalytic activity is closely related to the shape and facets of a semiconductor crystal photocatalyst. This concept has been critically studied in TiO2 photocatalysts, which proved the feasibility of improving photocatalytic performance by shape control. TiO2 is well-known to only be activated by UV light, which greatly limits its practical applications. As a visible-light photocatalyst, Bi2WO6 should utilize solar energy with a higher efficiecy than TiO2. Many works have studied the development of highly active Bi2WO6 photocatalysts with various morphologies, for example, nanoplates, nanofibers, nanospheres, hierarchical nanostructures, and porous structures. However, achieving a facet-controlled synthesis of Bi2WO6 and establishing an improvement of the photocatalytic activity related to that control is still a challenge, and has only rarely been reported in previous studies. A key process for semiconductor photocatalysis is the generation of electron–hole pairs, followed by the separation of these charge carriers and their diffusion to the surface, where they take part in the photocatalytic redox reactions. In the case of Bi2WO6 as photocatalyst, the low conduction band edge results in photogenerated electrons with insufficient reductive power. Therefore, the application of Bi2WO6 as photocatalyst mainly depends on the high oxidative ability of its photogenerated holes. Thus, much attention should be paid to efficient hole transport and utilization when designing highperformance Bi2WO6 photocatalysts. Bi2WO6 has a layered structure, which comprises layers of octahedral [WO4] 2 sandwiched by [Bi2O2] 2+ layers. Previous studies on its electronic structure have shown that the valence band, for hole transport, is mainly composed of O 2p and Bi 6s levels. Upon photoexcitation, charge transfer occurs from O 2p + Bi 6s hybrid orbitals to the empty W 5d orbitals. When considering both the crystal and electronic structure, hole transport can be expected to occur mainly in the [Bi2O2] 2 + layers, and hole oxidation to occur at either a Bi or an O site. Taking this into account, Bi2WO6 photocatalysts with a terminal lattice plane parallel to the [Bi2O2] 2 + layers and with high O and Bi atom densities would exhibit excellent photocatalytic activity. Based on an analysis of atomic models of Bi2WO6 projected along different directions (Supporting Information, Figure S1), the {001} lattice planes were found to satisfy these two criteria for efficient hole oxidation. Attempting to obtain the desired Bi2WO6 shape, we designed a hydrothermal process for synthesizing {001}-oriented crystalline of Bi2WO6. By controlling the growth kinetics, {001}oriented ultrathin nanosheets of Bi2WO6 with a thickness of only 3–4 nm (about 2 unit cells along the c-axis) could be firstly realized. The growth kinetics were controlled by adjusting the pH of the reaction system. Several studies have proved that changing the pH in a hydrothermal process affects the crystallinity, morphology, and specific surface area of the product. 14] In our present work, {001}-oriented Bi2WO6 ultrathin nanosheets could be obtained under acidic reaction conditions. Figure 1 shows an X-ray diffraction (XRD) pattern of the as-prepared Bi2WO6 nanosheets. All of the diffraction peaks in Figure 1 can be indexed to the orthorhombic phase of Bi2WO6 [space group B2ab (41), Joint Committee on Powder Diffraction Standards (JCPDS) card number 73-2020] . No other likely impurities, such as Bi2O3 or WO3, were detected. The broad diffraction peaks imply that the Bi2WO6 sample is of nanocrystalline nature. The relative diffraction intensities of both the (200) and (020) peaks over the (113) peak are much higher than the

Polypyrrole/Bi2WO6 composite with high charge separation efficiency and enhanced photocatalytic activity

The recombination of photogenerated electrons and holes is a crucial factor that limits the efficiency of photocatalysis and dye-sensitized solar cells. Conducting polymers are known to have high charge carrier mobility. Herein, a polypyrrole (PPy)/Bi2WO6 composite with promoted charge separation efficiency was designed by a “photocatalytic oxidative polymerization” method. The photo-degradation of a typical model pollutant, phenol, demonstrated that the PPy/Bi2WO6 composite possessed significantly enhanced photo-activity than pure Bi2WO6 under simulated sunlight irradiation. The higher photo-activity was attributed to the synergetic effect between PPy and Bi2WO6. The photogenerated holes on the valence band of Bi2WO6 could transfer to the highest occupied molecular orbital of PPy, leading to rapid photoinduced charge separation and enhancing the photocatalytic activity. This work provided a new concept for rational design and development of highly efficient polymer-semiconductor photocatalysts for environmental purification under simulated sunlight.

Solar light photocatalysis using Bi2O3/Bi2SiO5 nanoheterostructures formed in mesoporous SiO2 microspheres

There have been significant efforts to find novel photocatalytic materials with improved properties, such as an extended absorption wavelength from the UV to the visible-light region. Among the semiconductors with high photocatalytic activities, considerable attention has been given to bismuth-based oxides with suitable band gaps, which provide an opportunity to harvest visible light. Herein, we report Bi2O3/Bi2SiO5 nanoheterostructures formed in mesoporous SiO2 microspheres. The as-prepared nanocomposite exhibited excellent photocatalytic activities for the decomposition of both bisphenol A and acetaldehyde under irradiation by simulated solar light. The enhanced photocatalytic activity is due to (i) the reduction in the electron–hole recombination rate because of the reduced dimensions of the photocatalyst, (ii) a more efficient utilization of the photogenerated electrons and holes as a result of the high surface area to bulk ratio of the mesoporous structure, and (iii) a better electron–hole pair separation due to the formation of the Bi2O3/Bi2SiO5 nanoheterostructure. The high efficiency in the degradation of organic pollutants under mild conditions makes the as-prepared mesoporous photocatalyst a promising candidate for photocatalytic environmental purification.