Enhancement of photocatalytic efficiency by in situ fabrication of BiOBr/BiVO4 surface junctions.

Surface junctions between BiOBr and BiVO4 were synthesized. The BiOBr/BiVO4 with 1wt.% of BiOBr exhibited the highest photocatalytic activity in the degradation of RhB under visible-light irradiation. It was found that the highly efficient adsorption of RhB molecules via the electrostatic attraction between Br- and cationic N(Et)2 group played a key role for the high photocatalytic activities of BiOBr/BiVO4. This efficient adsorption promoted the N-deethylation of RhB and thus accelerated the photocatalytic degradation of RhB. Moreover, the metal-to-metal charge transfer (MMCT) mechanism was proposed, which revealed the concrete path paved with Bi-O-Bi chains for the carrier migration in BiOBr/BiVO4. The interaction between photoexcited RhB* and the Bi3+ in BiVO4 provided the driving force for the migration of photo-generated carriers along the Bi-O-Bi chains. This work has not only demonstrated the important role of efficient adsorption in the photocatalytic degradation of organic contaminants, but also developed a facile strategy to improve the efficiency of photocatalysts.

Magnetic Properties Improvement of Die-upset Nd-Fe-B Magnets by Dy-Cu Press Injection and Subsequent Heat Treatment.

Ultrafine-grained die-upset Nd-Fe-B magnets are of importance because they provide a wide researching space to redesign the textured structures. Here is presented a route to obtain a new die-upset magnet with substantially improved magnetic properties. After experiencing the optimized heat treatment, both the coercivity and remanent magnetization of the Dy-Cu press injected magnets increased substantially in comparison with those of the annealed reference magnets, which is distinct from the reported experimental results on heavy rare-earth diffusion. To study the mechanism, we analyzed the texture evolution in high-temperature annealed die-upset magnets, which had significant impact on the improvement of remanent magnetization. On basis of the results, we find that the new structures are strongly interlinked with the initial structures. With injecting Dy-Cu eutectic alloy, an optimized initial microstructure was achieved in the near-surface diffused regions, which made preparations for the subsequent texture improvement. Besides, the Dy gradient distribution of near-surface regions of the Dy-Cu press injected magnets was also investigated. By controlling the initial microstructure and subsequent diffusion process, a higher performance magnet is expected to be obtained.

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.

Low-temperature combustion synthesis of Bi2WO6 nanoparticles as a visible-light-driven photocatalyst.

Visible-light-induced Bi(2)WO(6) photocatalyst has been successfully synthesized via a facile low-temperature combustion synthesis method, using glycine as the fuel. The photocatalytic activities of the as-synthesized samples were evaluated by the photodegradation of rhodamine B (RhB) and phenol under visible-light irradiation (lambda>420 nm). The results showed that the molar ratio of fuel to oxidizer had an important influence on the photocatalytic activities of the products. When the molar ratio of fuel to oxidizer was 1, the photocatalyst exhibited the highest degradation efficiency, which can completely degrade RhB with a concentration up to 10(-4)M within 75 min. Besides decoloring, the markable reduction of chemical oxygen demand (COD) was also observed in the degradation of RhB, further demonstrating the photocatalytic performance of Bi(2)WO(6). Additionally, the photocatalyst showed much enhanced visible photocatalytic efficiency, up to 94.2% in 4h, than the bulk Bi(2)WO(6) powder (SSR) in the degradation of phenol.

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.

Visible light-induced efficient contaminant removal by Bi5O7I.

A new visible light-driven photocatalyst, Bi5O7I, prepared by a hydrothermal method was studied. The as-prepared Bi5O7I exhibited efficient photocatalytic activity in the decomposition of a widely used dye, tetraethylated rhodamine (RhB), in water and acetaldehyde (CH3CHO) in air under visible light irradiation. Besides decoloring, the reduction of chemical oxygen demand concentration was also observed in the degradation of RhB, further demonstrating the photocatalytic performance of Bi5O7I. The results of density functional theory calculations indicated that the conduction band bottom of Bi5O7I is mainly composed of Bi 6p orbits, and the valence band top primarily consists of I 5p and O 2p orbits. The as-prepared Bi5O7I exhibited much higher photocatalytic activity than Bi2O3, which may be ascribed to the hybrid states of the valence bands as well as the internal electric fields between Bi5O7 and I slabs. According to experimental results, a possible photocatalytic mechanism of Bi5O7I was proposed.