Huogen Yu

Dye-Sensitization-Induced Visible-Light Reduction of Graphene Oxide for the Enhanced TiO2 Photocatalytic Performance

The reduction of graphene oxide (GO) with a large-scale production has been demonstrated to be one of the key steps for the preparation of graphene-based composite materials with various potential applications. Therefore, it is highly required to develop a facile, green, and environmentally friendly route for the effective reduction of GO. In this study, a new and effective reduced method of GO nanosheets, based on the dye-sensitization-induced visible-light reduction mechanism, was developed to prepare reduced GO (rGO) and graphene-based TiO2 composite in the absence of any additional reducing agents. It was found that the dye-sensitization-induced reduction process of GO was accompanied with the formation of TiO2-rGO composite nanostructure. The photocatalytic experimental results indicated that the resultant TiO2-rGO nanocomposites exhibited significantly higher photocatalytic performance than pure TiO2 because of a rapid separation of photogenerated electrons and holes by the rGO cocatalyst.

Highly efficient TiO2 single-crystal photocatalyst with spatially separated Ag and F− bi-cocatalysts: orientation transfer of photogenerated charges and their rapid interfacial reaction

For an efficient photocatalytic system, the rapid orientation transfer of photogenerated electron–hole pairs inside the photocatalyst and their effective interfacial catalytic reactions are significantly critical for achieving a high photocatalytic performance. However, it is quite difficult for a general photocatalyst to realize the crucial functions. In this study, the above idea was easily realized via a coupling strategy of crystal-facet engineering and spatially separated cocatalyst modification, namely, a TiO2 single-crystal photocatalyst with spatially separated Ag and F− bi-cocatalysts (Ag/F–TiO2). In this case, the F ions (as a hole cocatalyst) and Ag nanoparticles (as an electron cocatalyst) were selectively modified on the hole-rich (001) and electron-rich (101) facets of TiO2 single crystals, respectively. Photocatalytic results demonstrated that the resultant spatially separated Ag/F–TiO2 photocatalyst exhibited an obviously higher photocatalytic performance than pure TiO2, single-cocatalyst modified TiO2 (F–TiO2 and Ag/TiO2) and randomly Ag-deposited TiO2 (Ag/F–TiO2(R)). The main reason for the enhanced photocatalytic activity can be attributed to the excellent synergistic effect of orientation transfer of photogenerated charges and their rapid interfacial reaction via the efficient coupling strategy of crystal-facet engineering and cocatalyst modification, namely, the TiO2 single crystal structure can self-induce the orientation transfer of photogenerated charges to different crystal facets, while the spatially separated cocatalysts function as the effective active sites for the rapid interfacial catalytic reactions of those spatially separated charges (Ag nanoparticles on the (101) facets work as the active centres for oxygen-reduction reactions, and F ions on the (001) facets serve as the active sites for oxidation reactions of organic substances). The present coupling strategy of crystal-facet engineering and cocatalyst modification may also provide new ideas for the design and preparation of other highly efficient semiconductor photocatalysts.

Facile template-induced synthesis of Ag-modified TiO2 hollow octahedra with high photocatalytic activity

Abstract Noble metal/titania hollow nanomaterials usually exhibit excellent photocatalytic activity because of their high specific surface area, low density, good surface permeability, strong light-harvesting capacity, and rapid interfacial charge transfer. However, the present preparation methods usually include complicated and multistep procedures, which can cause damage to the hollow nanostructures. In this paper, a facile template-induced synthesis, based on a template-directed deposition and in situ template-sacrificial dissolution, was employed to prepare Ag-modified TiO2 (Ag/TiO2) hollow octahedra using Ag2O octahedra as templates and TiF4 as the precursor. In the synthetic strategy, the shells of TiO2 hollow octahedra were formed by coating TiO2 nanoparticles on the surface of Ag2O templates based on the template-directed deposition. Simultaneously, the Ag2O templates can be in situ removed by dissolving the Ag2O octahedral template in HF solution produced via the hydrolysis reaction of TiF4 in the reaction system. In addition, Ag nanoparticles were deposited on the inside and outside surfaces of TiO2 shells by effectively using the photosensitive properties of Ag2O and Ag+ ions under light irradiation, along with the formation of TiO2 hollow octahedra. The Ag/TiO2 hollow octahedra exhibited high photocatalytic activity because of their (1) short diffusion distances between photogenerated electrons and holes because of the thin shells of Ag/TiO2 hollow octahedral, (2) deposition of Ag nanoparticles on the inside and outside surfaces of TiO2 shells, and (3) rapid interfacial charge transfer between TiO2 shells and Ag nanoparticles. This work may also provide new insights into preparing other Ag-modified and hollow nanostructured photocatalysts.

Enhancement of Visible-Light Photocatalytic Activity of Mesoporous Au-TiO2 Nanocomposites by Surface Plasmon Resonance

Mesoporous Au-TiO2 nanocomposite plasmonic photocatalyst with visible-light photoactivity was prepared by a simple spray hydrolytic method using photoreduction technique at 90∘C. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption-desorption isotherms. The formation of hydroxyl radicals (•OH) on the surface of visible-light illuminated Au-TiO2 nanocomposites was detected by the luminescence technique using terephthalic acid as probe molecules. The photocatalytic activity was evaluated by photocatalytic decolorization of Rhodamine-B (RhB) aqueous solution under visible-light irradiation (λ g 420 nm). The results revealed that the TiO2 could be crystallized via spray hydrolysis method, and the photoreduction technique was facilitated to prepare Au nanoparticles in the mesoporous TiO2 at 90∘C. The light absorption, the formation rate of hydroxyl radicals, and photocatalytic decolorization of Rhodamine-B aqueous solution were significantly enhanced by those embedded Au nanoparticles in the Au-TiO2 nanocomposites. The prepared Au-TiO2 nanocomposites exhibit a highly visible-light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of the pristine TiO2 nanoparticles due to the surface plasmon resonance.

Synergistic Effect of Dual Electron-Cocatalysts for Enhanced Photocatalytic Activity: rGO as Electron-Transfer Mediator and Fe(III) as Oxygen-Reduction Active Site.

For a high-performance cocatalyst-modified photocatalyst, an effective interfacial separation of photogenerated electron from its corresponding holes and its following reduction reaction at the active sites are highly required. However, it is difficult for a single-component cocatalyst to simultaneously realize the crucial functions. In this study, an effective interfacial transfer of photogenerated electrons and its following rapid oxygen-reduction can be easily realized in a dual electron-cocatalyst modified Fe(III)/rGO-TiO2 photocatalyst, where the rGO nanosheets function as an electron-transfer mediator for the effective transfer of photogenerated electrons from the TiO2 surface while the Fe(III) cocatalyst serves as an electron-reduction active site to promote the following interfacial oxygen reduction. In this case, the rGO nanosheets were firstly loaded on the TiO2 nanoparticle surface by a hydrothermal method and then the Fe(III) cocatalyst was further modified on the rGO nanosheets by an impregnation method to prepare the Fe(III)/rGO-TiO2 photocatalyst. It was found that the dual electron-cocatalyst modified Fe(III)/rGO-TiO2 photocatalyst showed an obviously higher photocatalytic performance than the naked TiO2 and single-cocatalyst modified photocatalysts (such as Fe(III)/TiO2 and rGO-TiO2) owing to the synergistic effect of rGO and Fe(III) bi-cocatalysts. The present work can provide some new insights for the smart design of high-efficiency photocatalytic materials.

硫氰根选择性吸附在g-C 3 N 4 /Ag表面增强其光催化制氢性能

Abstract Silver-modified semiconductor photocatalysts typically exhibit enhanced photocatalytic activity toward the degradation of organic substances. In comparison, their hydrogen-evolution rates are relatively low owing to poor interfacial catalytic reactions to producing hydrogen. In the present study, thiocyanate anions (SCN−) as interfacial catalytic active sites were selectively adsorbed onto the Ag surface of g-C3N4/Ag photocatalyst to promote interfacial H2-evolution reactions. The thiocyanate-modified g-C3N4/Ag (g-C3N4/Ag-SCN) photocatalysts were synthesized via photodeposition of metallic Ag on g-C3N4 and subsequent selective adsorption of SCN− ions on the Ag surface by an impregnation method. The resulting g-C3N4/Ag-SCN photocatalysts exhibited considerably higher photocatalytic H2-evolution activity than the g-C3N4, g-C3N4/Ag, and g-C3N4/SCN photocatalysts. Furthermore, the g-C3N4/Ag-SCN photocatalyst displayed the highest H2-evolution rate (3.9 μmol h−1) when the concentration of the SCN− ions was adjusted to 0.3 mmol L−1. The H2-evolution rate obtained was higher than those of g-C3N4 (0.15 μmol h−1) and g-C3N4/Ag (0.71 μmol h−1). Considering the enhanced performance of g-C3N4/Ag upon minimal addition of SCN− ions, a synergistic effect of metallic Ag and SCN− ions is proposed—the Ag nanoparticles act as an effective electron-transfer mediator for the steady capture and rapid transportation of photogenerated electrons, while the adsorbed SCN− ions serve as an interfacial active site to effectively absorb protons from solution and promote rapid interfacial H2-evolution reactions. Considering the present facile synthesis and its high efficacy, the present work may provide new insights into preparing high-performance photocatalytic materials.

Facile synthesis and enhanced visible-light photocatalytic activity of Ag2S nanocrystal-sensitized Ag8W4O16 nanorods

Narrow band-gap (NBG) Ag2S nanocrystals (NCs) attaching on the surface of wide band-gap (WBG) Ag8W4O16 nanorods were prepared by employing a facile in situ anion exchange method with the reaction between S(2)(-) and WO4(2-), and the photocatalytic activity was evaluated by the photocatalytic decolorization of methyl orange solution under visible-light irradiation. It was found that in situ anion exchange could uniformly deposit Ag2S NCs on the surface of Ag8W4O16 nanorods, controllably adjust the size, distribution and amount of Ag2S NCs, and solidly connect Ag2S NCs to the Ag8W4O16 nanorods via the replacement of S(2)(-) in the solution with lattice WO4(2-) on the Ag8W4O16 surface. The photocatalytic results indicated that the as-prepared Ag2S/Ag8W4O16 composite photocatalysts exhibited obviously higher activity compared with the pure Ag8W4O16 and N-TiO2 photocatalysts. On the basis of band structures of Ag2S and Ag8W4O16 semiconductors and the quantum size effect of Ag2S NCs, a possible photocatalytic mechanism about the Ag2S nanocrystal-sensitized Ag8W4O16 nanorods was proposed to account for the effective visible-light photocatalytic activities. This present work may provide some insight into the design of novel and high-efficiency NBG semiconductor NCs coupled with WBG semiconductor composite photocatalysts.

Synthesis, characterization, properties, and applications of nanosized photocatalytic materials

1 State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122, Wuhan 430070, China 2Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44242, USA 3Department of Chemistry, School of Science, Wuhan University of Technology, Wuhan 430070, China 4 School of Chemistry and Environment, Beijing University of Aeronautics and Astronautics, Beijing 100191, China

Amorphous Ti(IV)-modified Bi2WO6 with enhanced photocatalytic performance

Crystalline TiO2 is a well-known oxide which can be used to improve the photocatalytic performance of other photocatalytic materials by a semiconductor-coupling strategy. However, compared with crystalline TiO2, amorphous TiO2-modified semiconductors have seldom been reported. In this study, amorphous TiO2 (referred to as Ti(IV)) as a hole cocatalyst was used to modify the photocatalytic performance of a Bi2WO6 photocatalyst by a facile wet-chemical method, where metallic Pt as the electron cocatalyst was also coated on the Bi2WO6 surface to promote the interfacial electron transfer. It was found that the dual-cocatalyst modified Ti(IV)–Pt/Bi2WO6 photocatalyst exhibited an obviously higher photocatalytic performance than the blank Bi2WO6 and single-cocatalyst modified Pt/Bi2WO6 and Ti(IV)/Bi2WO6. Based on the present experimental results, we propose a synergistic effect of amorphous Ti(IV) and Pt to illustrate the enhanced photocatalytic activity of the Ti(IV)–Pt/Bi2WO6 photocatalyst, namely amorphous Ti(IV) works as a hole cocatalyst to rapidly transfer the photogenerated holes in the valence band of Bi2WO6, while Pt acts as an electron cocatalyst to rapidly transfer the photogenerated electrons on its conduction band. As a consequence, the transfer rate and the interfacial catalytic reaction of photogenerated electrons and holes were simultaneously accelerated, which resulted in improved photocatalytic performance of the Ti(IV)–Pt/Bi2WO6 photocatalyst. The above synergistic effect mechanism in Ti(IV)-modified Bi2WO6 photocatalysts can further be demonstrated by using a low-cost Fe(III) or Cu(II) electron cocatalyst. The present study suggests that amorphous Ti(IV) can act as a new and effective hole cocatalyst for the enhanced photocatalytic performance of photocatalysts, which provides an approach for the design and development of high-performance visible-light photocatalysts with amorphous oxides.

A novel functional group difference-based selective etching strategy for the synthesis of hollow organic silica nanospheres

A facile and effective “functional group difference-based selective etching” strategy has been developed to prepare organic functionalized hollow silica nanospheres (OHSNSs) with well-defined morphology and uniform size. The key point of the strategy is to introduce different organic groups into both core and shell for the purpose of changing their relative stability against etching, which results in the preferential etching of the organic functionalized inner core. In this paper, bifunctionalized core–shell silica nanospheres synthesized by using 2-cyanoethyltriethoxysilane (CTES) as the core and 3-thiocyanatopropyltriethoxysilane (TCPTES) as the shell can be easily transformed to thiocyanato group-functionalized hollow silica nanospheres (TC-HSNSs) in a Na2CO3 solution, based on the stability difference between the cyano group functionalized inner core and the thiocyanato group functionalized outer shell. Transmission electron microscopy (TEM) confirms that the formation of TC-HSNSs undergoes the process of selectively etching the inner core. Moreover, Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDS) and elemental analysis (EA) prove that only the thiocyanato group is observed in the final product. In addition, the application of TC-HSNSs in the adsorption of aspirin has also been investigated.