Lin Zhou

Fabrication of flower-like Bi2WO6 superstructures as high performance visible-light driven photocatalysts

A novel flower-like Bi2WO6 superstructure was successfully realized by a facile hydrothermal process without any surfactant or template. Based on the evolution of this morphology as a function of hydrothermal time, the formation mechanism was proposed to be as follows: (1) self-aggregation of nanoparticles; (2) formation of crystalline nanoplates by Ostwald ripening; and (3) organization of the in situ-formed nanoplates into spherical superstructures. The pretty flower-like superstructure of Bi2WO6 was retained after calcination at 550 °C for 4 h. Both the uncalcined and calcined Bi2WO6 exhibited excellent visible-light-driven photocatalytic efficiencies for the degradation of Rhodamine B (RhB), up to 84 and 97% within 60 minutes, respectively, which were much higher than those of TiO2 (P-25) and Bi2WO6 sample prepared by solid-state reaction (SSR-Bi2WO6). Close investigation indicated that plenty of pores with different sizes existed in the Bi2WO6 superstructures, which could serve as hierarchical transport paths for small molecules and might greatly improve their photocatalytic activities.

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).

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.

Synthesis of octahedral CuS nanocages via a solid?liquid reaction

Octahedral CuS nanocages were synthesized by a solid?liquid reaction between solid Cu2O octahedra and thiourea solution at 90??C. Octahedral Cu2O particles were used as the sacrificial cores, precursor and shape-controller. The transformation of octahedral Cu2O to hollow CuS octahedra was monitored by the TEM images and EDX spectra. A mechanism of mass diffusion followed by Ostwald ripening is proposed based on the evidence of electron microscope images. The critical size (d*) of the precursor for the formation of hollow structured CuS was estimated based on the proposed mechanism and the designed experiments.

Multilayer Graphene-GeSn Quantum Well Heterostructure SWIR Light Source

The problem of light source always prevents silicon-based photonics from achieving a final integration. Although some optical pump lasers have been reported in recent years, an electrical pumping laser is considered as the ultimate solution. To fabricate a Si-based laser, there are some crucial obstacles that need to be solved such as difficulties in material epitaxy, light absorption by metal electrodes, and compatibility with the existing complementary metal-oxide-semiconductor transistor process. Here, a multilayer graphene and GeSn/Ge quantum well (QW) heterostructure is designed and fabricated as a Si-based light source. Specially designed Ge0.9 Sn0.1 /Ge QWs are used as active layer, which achieves a photoluminescence (PL) peak at 2050 nm. Graphene, which has a high transmittance for all bands of light, lessens the burden of growing thick cladding layer and perfectly breaks the deadlock of light disappearance in metal contacts. The electroluminescence (EL) spectrum of the device is achieved at a peak of 2100 nm under an injection current density of 100 A cm-2 . Both the PL and EL measurements show the heterostructure has good performance as a short-wave infrared (SWIR) light source. Therefore, the results provides a good alternative for the light source in silicon-based photonics.