Songmei Sun

Bi2O3 Hierarchical Nanostructures: Controllable Synthesis, Growth Mechanism, and their Application in Photocatalysis

By introducing VO(3)(-) into the reaction system, uniform hierarchical nanostructures of Bi(2)O(3) have been successfully synthesized by a template-free aqueous method at 60-80 degrees C for 6 h. The as-prepared hierarchitectures are composed of 2D nanosheets, which intercross with each other. Based on the electron microscope observations, the growth of such hierarchitectures has been proposed as an Ostwald ripening process followed by self-assembly. The nucleation, growth, and self-assembly of Bi(2)O(3) nanosheets could be readily tuned, which brought different morphologies and microstructures to the final products. Pore-size distribution analysis revealed that both mesopores and macropores existed in the product. UV-vis spectroscopy was employed to estimate the band gap energies of the hierarchical nanostructures. The photocatalytic activities of as-prepared Bi(2)O(3) hierarchitectures were 6-10 times higher than that of the commercial sample, which was evaluated by the degradation of RhB dye under visible light irradiation (lambda>420 nm).

Enhancement of visible-light photocatalysis by coupling with narrow-band-gap semiconductor: a case study on Bi2S3/Bi2WO6.

To overcome the drawback of low photocatalytic efficiency brought by electron-hole recombination and narrow photoresponse range, we designed a novel Bi(2)S(3)/Bi(2)WO(6) composite photocatalyst. The composite possesses a wide photoabsorption until 800 nm, which occupies nearly the whole range of the visible light. Compared with bare Bi(2)WO(6), the Bi(2)S(3)/Bi(2)WO(6) composite exhibits significantly enhanced photocatalytic activity for phenol degradation under visible light irradiation. On the basis of the calculated energy band positions, the mechanism of enhanced photocatalytic activity was proposed. The present study provides a new strategy to design composite materials with enhanced photocatalytic performance.

CTAB-assisted synthesis of monoclinic BiVO4 photocatalyst and its highly efficient degradation of organic dye under visible-light irradiation.

A highly efficient monoclinic BiVO(4) photocatalyst (C-BVO) was synthesized by an aqueous method with the assistance of cetyltrimethylammonium bromide (CTAB). The structure, morphology and photophysical properties of the C-BVO were characterized by XRD, FE-SEM and diffuse reflectance spectroscopy, respectively. The photocatalytic efficiencies were evaluated by the degradation of rhodamine B (RhB) under visible-light irradiation, revealing that the degradation rate over the C-BVO was much higher than that over the reference BiVO(4) prepared by aqueous method and over the one prepared by solid-state reaction. The efficiency of de-ethylation and that of the cleavage of conjugated chromophore structure were investigated, respectively. The chemical oxygen demand (COD) values of the RhB were measured after the photocatalytic degradation over the C-BVO and demonstrated a 53% decrease in COD. The effects of CTAB on the synthesis of C-BVO were investigated, which revealed that CTAB not only changed the reaction process via the formation of BiOBr as an intermediate, but also facilitated the transition from BiOBr to BiVO(4). Comparison experiments were carried out and showed that the existence of impurity level makes significant contribution to the high photocatalytic efficiency of the C-BVO.

Nanosized BiVO4 with high visible-light-induced photocatalytic activity: Ultrasonic-assisted synthesis and protective effect of surfactant

Nanosized BiVO4 with high visible-light-induced photocatalytic activity was successfully synthesized via ultrasonic-assisted method with polyethylene glycol (PEG). The BiVO4 sample prepared under ultrasonic irradiation with 1g PEG for 30 min was consisted of small nanoparticles with the size of ca. 60 nm. The effects of ultrasonic irradiation and surfactant were investigated. The nanosized BiVO4 exhibited excellent visible-light-driven photocatalytic efficiency for degrading organic dye, which was increased to nearly 12 times than that of the products prepared by traditional solid-state reaction. Besides decoloring, the reduction of chemical oxygen demand (COD) concentration was also observed in the degradation of organic dye, further demonstrating the photocatalytic performance of BiVO4. After five recycles, the catalyst did not exhibit any significant loss of photocatalytic activity, confirming the photocatalyst is essentially stable. Close investigation revealed that the crystal size, BET surface area, and appropriate band gap of the as-prepared BiVO4 could improve the photocatalytic activities.

Preparation of ordered mesoporous Ag/WO3 and its highly efficient degradation of acetaldehyde under visible-light irradiation.

A highly active photocatalyst, silver loaded mesoporous WO(3), was successfully synthesized by an ultrasound assisted insertion method. The photodegradation of a common air pollutant acetaldehyde was adopted to evaluate the photocatalytic performance of the as-prepared sample under visible-light irradiation. The photocatalytic activity was about three and six times higher than that of pure mesoporous WO(3) and nitrogen-doped TiO(2), respectively. The photocatalytic mechanism was investigated to understand the much enhanced photocatalytic activity, which was mainly attributed to the largely improved electron-hole separation in the Ag-WO(3) heterojunction.

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.

A novel BiVO4 hierarchical nanostructure: controllable synthesis, growth mechanism, and application in photocatalysis

A novel BiVO4 hierarchical nanostructure assembled by nanorods was realized via a facile and additive-free solvothermal method. Based on the electron microscope observations, the growth of such architectures with “rod to dumbbell to sphere” transformation has been proposed as a crystal splitting growth process. Ethylene glycol (EG) instead of organic surfactant played an important dual role during the process. Different shapes were obtained by controlling the synthetic parameters. The as-prepared BiVO4 hierarchical nanostructures exhibited excellent visible-light-driven photocatalytic efficiency, which was increased to nearly 20 times than that of the products prepared by traditional solid-state reaction (SSR) and the nitrogen doped TiO2 (N–TiO2). Moreover, the photocatalyst could settle immediately, which is beneficial for the separation and recycle considering their future applications in waste water treatment.

A practical visible-light-driven Bi2WO6 nanofibrous mat prepared by electrospinning

An electrospinning technique was first developed to fabricate Bi2WO6 nanofibrous mat with excellent photoactivity under visible light. The nanofibers are made of single-crystalline Bi2WO6nanoparticles about 100 nm in size. The diameters of the nanofibers can be controlled by simply tuning the weight ratio of Bi2WO6 to poly(vinyl pyrrolidone) (PVP) (R). With the value of R increasing, the average diameter of the nanofibers was decreased. In addition to the favorable recycling characteristics, the mat with R = 2 exhibits higher photocatalytic activity in the decomposition of acetaldehyde (CH3CHO) and aqueous ammonia than that of the sample prepared by solid-state reaction (SSR) and the nanoparticles. Such an advantageous electrospinning route, which not only brings effective improvement in the photocatalytic activity of catalysts but also provides a solution to the separation problem for conventional catalysts that are small in size, is worth considering for the preparation of other photocatalysts.

General Strategy for a Large-Scale Fabric with Branched Nanofiber–Nanorod Hierarchical Heterostructure: Controllable Synthesis and Applications

The preparation and characterization of a branched nanofiber-nanorod hierarchical heterostructure fabric (TiO(2)/NiO, TiO(2)/ZnO, and TiO(2)/SnO(2)) are described. The nanomaterial was synthesized on a large scale by an inexpensive, generalizable, facile, and controllable approach by combining the electrospinning technique with a hydrothermal method. The controllable formation process and factors (assistance by hexamethylenetetramine and metal oxide nuclei) influencing the morphology of the branched hierarchical heterostructure are discussed. In addition, photocurrent and photocatalytic studies suggest that the branched hierarchical heterostructure fabric shows higher mobility of charge carriers and enhanced photocatalytic activity relative to a bare TiO(2) nanofibrous mat and other heterostructures under irradiation by light. This work demonstrates the possibility of growing branched heterostructure fabrics of various uniform, one-dimensional, functional metal oxide nanorods on a TiO(2) nanofibrous mat, which has a tunable morphology by changing the precursor. The study may open a new channel for building hierarchical heterostructure device fabrics with optical and catalytic properties, and allow the realization of a new class of nano-heterostructure devices.