[Show abstract][Hide abstract] ABSTRACT: In this work, bifunctional TiO2/Ag3PO4/graphene (GR) composites have been prepared via the combination of ion-exchange method and hydrothermal approach, and the fabrication of “pizza-like” three-phase TiO2/Ag3PO4/GR composites has been achieved through the electrostatic-driven assembly of positively-charged Ag+ on negatively-charged graphene oxide (GO) sheets, followed by the nucleation & controlled growth of Ag3PO4 and the deposition of Degussa P25 on the GO surface. Consequently, the hydrothermal treatment leads to the generation of TiO2/Ag3PO4/GR composites with well-defined structures. The as-prepared composites exhibited highly efficient visible light photocatalytic activity toward organic dye molecule degradation and showed excellent bactericidal performance. This is the first report on the production of bifunctional three-phase metal oxide-Ag3PO4-GR composite materials with improved photocatalytic and antibacterial properties. The improved photocatalytic activity is attributed to the effective separation of photoexcited electron-hole pairs and fast charge transfer between components in the composite, while its excellent bactericidal performance is believed to come from intrinsic bacterial inactivation of Ag3PO4 and photo-induced antibacterial activity of active oxygen-containing radicals generated in the irradiated system. The proper molar ratio of Ag3PO4/TiO2 and the added amount of GO in the precursor have been considered to play crucial roles in the formation of bifunctional composites with promising properties. The TiO2/Ag3PO4/GR composite significantly decreases the percentage of expensive Ag-containing material while it reveals better photocatalytic and antibacterial performance than Ag3PO4, providing new insights into the low-cost, large-scale production of Ag3PO4-based function materials for practical applications.
[Show abstract][Hide abstract] ABSTRACT: Cubic Ag3PO4 microcrystals were synthesized by deposition-precipitation in the presence of ammonia. As-synthesized samples were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman spectroscopy and UV-visible diffuse reflectance spectroscopy (UV-vis DSR). Visible-light-driven photocatalytic performance of the obtained Ag3PO4 was evaluated for photocatalytic degradation of typical organic dye molecules. Compared to irregular Ag3PO4 materials prepared in the absence of ammonia, the prepared cubic samples exhibited a higher photocatalytic activity, suggesting the crucial role of the ammonia in the formation of cubic Ag3PO4 microcrystals. In addition, the specific cubic morphology of Ag3PO4 sample contributes substantially to its highly efficient visible light photocatalytic performance. Moreover, photocatalytic degradation experiments of the cubic Ag3PO4 toward different organic dye molecules rhodamine B (RhB), methyl blue (MB) and methyl orange (MO) were carried out. These results show that photo-generated active oxygen-containing superoxide radicals and photo-induced holes offer the major contribution to highly efficient visible light photocatalytic activity of Ag3PO4.
Ceramics International 12/2013; 39(8):9715-9720. DOI:10.1016/j.ceramint.2013.04.044 · 2.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphene (GR)-TiO2 mesocrystal composites were prepared by a facile template-free process based on the combination of sol-gel and solvothermal methods, and were characterized using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), nitrogen absorption and electron spin resonance (ESR). Visible light photocatalytic performance of GR-TiO2 composites was evaluated for photocatalytic degradation of organic dye Rhodamine B. It was found that the amount of graphene oxide (GO) added obviously affects morphologies of TiO2 mesocrystals and photocatalytic activities of as-prepared nanocomposites. Composites prepared in the presence of different amounts of GO all exhibit higher photocatalytic activity than pure TiO2 mesocrystals and P25, the composite obtained by using 20mg GO presents the most uniform TiO2 mesocrystals in the composite and shows the highest photocatalytic efficiency. The mechanism for the generation of TiO2 mesocrystals in the GR-TiO2 composite is proposed and possible reasons for the enhancement in visible light photocatalytic efficiency are also discussed.
[Show abstract][Hide abstract] ABSTRACT: A facile and effective hydrothermal method for the fabrication of the Ag3PO4-graphene (Ag3PO4-GR) visible light photocatalyst has been developed to improve the photocatalytic performance and stability of Ag3PO4, and also to reduce the high cost of Ag3PO4 for practical uses. The size and morphology of Ag3PO4 particles could be tailored by the electrostatically driven assembly of Ag+ on graphene oxide (GO) sheets and by the controlled growth of Ag3PO4 particles on the GO surface. The generation of Ag3PO4 and the transformation of GO to GR can be achieved simultaneously in the hydrothermal process. The improved photocatalytic activity of Ag3PO4-GR composites under visible light irradiation is attributed to high-surface-area GR sheets, enhanced absorption of organic dyes, and more efficient separation of photogenerated electron–hole pairs. The transfer of photogenerated electrons from the surface of Ag3PO4 to GR sheets also reduces the possibility of decomposing Ag+ to metallic Ag, suggesting an improved stability of recyclable Ag3PO4-GR composite photocatalyst. Moreover, with the advances in the large-scale production of high-quality GO, the use of GO as the starting material can also reduce the cost for the synthesis of Ag3PO4-based photocatalysts without weakening their photocatalytic activities.
[Show abstract][Hide abstract] ABSTRACT: Graphene oxide (GO)-enwrapped Ag3PO4 composites were successfully fabricated by the electrostatically-driven assembly of positively charged silver ions on the negatively charged GO sheets, followed by the controlled growth of sphere-like Ag3PO4 particles on GO sheets via an in-situ ion-exchange method. Moreover, GO–Ag3PO4 composites were fully characterized and the visible light photocatalytic performance of the GO–Ag3PO4 sample was investigated. The results indicated that the presence of GO sheets could effectively tailor the size of Ag3PO4 particles, GO–Ag3PO4 composites exhibited excellent visible-light absorption, and the photocatalytic degradation efficiency of Rhodamine B (RhB) over GO–Ag3PO4 composites is apparently higher than with pure Ag3PO4 mainly due to the photo-induced holes and the generation of irradiated active superoxide radicals.
[Show abstract][Hide abstract] ABSTRACT: Rod-like nanosized silver tungstate (Ag2WO4) was synthesised via a facile hydrothermal method and characterised by field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and electron spin resonance spectroscopy. Under ultraviolet (UV) light, nearly complete degradation of rhodamine B (RhB) was observed in Ag2WO4 suspension after irradiation for 60 min, around 15 RhB was absorbed in the dark. However, more than 60 of methyl blue was absorbed in the dark and the rest was observed to be completely degraded upon UV light irradiation for 10 min. The formed superoxide (O2-.) and hydroxyl (·OH) radicals, as well as photoinduced holes were considered to be the dominant active species in the photocatalytic process.
[Show abstract][Hide abstract] ABSTRACT: In this study, an amino acid, glutamine, has been employed as the modifier in the hydrothermal synthesis of rod-like hydroxyapatite (HAp) nanoparticles. X-ray diffractometer results confirm the formation of a typical HAp phase without impurities and microscopic results indicate that the morphology and size of the as-prepared products could be controlled by adjusting the pH value of the hydrothermal system. Owing to a variety of amino acids and characteristics of as-synthesised nano-sized HAp, the findings may have implications in the large-scale controllable synthesis of well-defined HAp nanomaterials; it may also provide a general facile and low-cost method for the preparation of uniform nanostructured HAp by utilising biomolecules as modifiers.
[Show abstract][Hide abstract] ABSTRACT: The tribological behavior of graphene oxide (GO) films deposited on a mica substrate has been investigated by atomic force microscopy, in which different voltages were applied to a tip. It was found that the frictional forces on the GO films remain unchanged in the presence of negative tip voltages, while the frictional forces increase remarkably with an increase of the voltage when positive voltages are given to the tip, and at a certain positive tip voltage the frictional forces reach a stable value with increasing number of repeated cycles. To study the influence of the tip voltage on the frictional forces of the GO films, the adhesive and electrostatic force gradients between the tip and GO films were measured. The results showed that the adhesive and electrostatic forces increased with increase of the positive tip voltages. This phenomenon is due to the polarization of charges in the GO films induced by the applied tip voltages, which causes intensive electrostatic interactions between the tip and GO films and a corresponding rise in the adhesive forces and the frictional forces.