Graphene/reduced graphene oxide (rGO) modification has been demonstrated to be an efficient route to improve the photocatalytic performance of various photocatalysts by promoting the effective separation of photogenerated electrons and holes. It is highly required to develop facile and environmental-friendly methods for the preparation of graphene-based photocatalytic materials. In this study, the Ag/AgCl/rGO heterostructure photocatalyst was fabricated by a mild oxidization reaction of hydrothermally prepared Ag/rGO in FeCl3 solution. It was found that the reduction of graphene oxide (GO) was accompanied with the in situ formation of metallic Ag in a Ag[(NH3)2]+-immobilized GO solution during hydrothermal treatment, while the following in situ oxidation of metallic Ag by FeCl3 solution resulted in the formation of strongly coupled Ag/AgCl/rGO heterostructure photocatalyst. The photocatalytic experimental results indicated that all the resultant Ag/AgCl/rGO nanocomposite photocatalysts exhibited a much higher photocatalytic activity than the Ag/AgCl and physically mixed Ag/AgCl/rGO composite, and the Ag/AgCl/rGO (3.2 wt % rGO) showed the highest photocatalytic performance. The enhanced photocatalytic performance of Ag/AgCl/rGO heterostructures can be attributed to the cooperation effect of the effective separation of photogenerated carriers via strongly coupled rGO cocatalyst and the enrichment of organic molecules on the rGO nanosheets. Considering the facile preparation and its high photocatalytic activity, it is possible for the present Ag/AgCl/rGO nanocomposites to be widely applied in various fields such as air purification and wastewater treatment.Keywords: Ag/AgCl; graphene; heterostructure; interface; photocatalysis;

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.Keywords: dye-sensitization-induced; graphene; interface; photocatalysis; TiO2-rGO;

AgI is instable under light irradiation owing to its photosensitive properties, while a supported Ag–AgI composite has been demonstrated to be a stable photocatalyst. However, seldom investigations have been focused on the photocatalytic activity (including deactivation) and photoinduced stability of the photosensitive AgI materials. In this study, the AgI nanoparticles were immobilized on the surface of Ag8W4O16 nanorods by an anion-exchange route and their photocatalytic activities were evaluated by photocatalytic decomposition of methyl orange and phenol solutions under visible-light irradiation. A photoinduced self-stabilizing mechanism of the AgI nanoparticles was proposed to account for the formation of a stable Ag–AgI photocatalyst, namely, instable AgI can transform into a stable Ag–AgI photocatalyst after in situ formation of partial Ag on the surface of AgI nanoparticles. The photocatalytic performance of the immobilized AgI photocatalyst was greatly influenced by the formation of metallic Ag. With increasing repetitions of photocatalytic experiments, the initial deactivation was accompanied by the rapid increase of metallic Ag owing to the reduction of lattice Ag+, while the subsequently stable activity corresponds to the formation of a stable Ag–AgI composite photocatalyst. Compared with the un-immobilized AgI photocatalyst, the immobilized AgI nanoparticles exhibited a higher and more stable photocatalytic performance.

Ag modification has been demonstrated to be an efficient strategy to improve the photocatalytic performance of TiO2 photocatalysts. However, the previous studies about the Ag modification are only restricted to the surface loading of metallic Ag or Ag(I) doping, investigations have seldom been focused on the simultaneously deposited and doped Ag/Ag(I)-TiO2 photocatalyst. In this study, Ag/Ag(I)-TiO2 photocatalyst was prepared by a facile impregnated method in combination with a calcination process (450 °C) and the photocatalytic activity was evaluated by the photocatalytic decomposition of methyl orange and phenol solutions under both UV- and visible-light irradiation, respectively. It was found that Ag(I) doping resulted in the formation of an isolated energy level of Ag 4d in the band gap of TiO2. On the basis of band-structure analysis of Ag/Ag(I)-TiO2 photocatalyst, a possible photocatalytic mechanism was proposed to account for the different UV- and visible-light photocatalytic activities. Under visible-light irradiation, the isolated energy level of Ag 4d contributes to the visible-light absorption while the surface metallic Ag promotes the effective separation of the following photogenerated electrons and holes in the Ag/Ag(I)-TiO2 nanoparticles, resulting in a higher visible-light photocatalytic activity than the one-component Ag-modified TiO2 (such as Ag(I)-TiO2 and Ag/TiO2). Under UV-light irradiation, the doping energy level of Ag(I) ions in the band gap of TiO2 acts as the recombination center of photogenerated electrons and holes, leading to a lower photocatalytic performance of Ag-doped TiO2 (such as Ag/Ag(I)-TiO2 and Ag(I)-TiO2) than the corresponding undoped photocatalysts (such as Ag/TiO2 and TiO2). Considering the well controllable preparation of various Ag-modified TiO2 (such as TiO2, Ag/TiO2, Ag(I)-TiO2, and Ag/Ag(I)-TiO2), this work may provide some insight into the smart design of novel and high-efficiency photocatalytic materials.

The porous TiO2 film was self-assembled on the surface of electrophoretic-deposited titanate nanoribbon film without the addition of templates by using TiF4 as the precursor. It was found that the hydrolysis of TiF4 was accompanied with the self-assembly processes of TiO2 nanoparticles on the surface of electrophoretic-deposited titanate nanoribbon film, resulting in the formation of porous TiO2 structures. Titanate nanoribbon film was demonstrated to provide the active sites for the effective self-assembly of porous TiO2 nanostructures owing to a large amount of hydroxyl groups. Compared with the nonporous TiO2 film, the prepared porous TiO2 films obviously showed an enhanced photocatalytic activity, which could be attributed to the rapider diffusion and more efficient transport of various reactants and products during photocatalytic reaction in the porous structures.

Usually, it is difficult to get small AgCl nanoparticles by a conventional aqueous solution route owing to their high nucleation and growth rate. In this study, AgCl nanoparticles with a diameter of less than 30 nm were uniformly coated on the surface of Ag8W4O16 nanorods to form Ag8W4O16/AgCl-nanoparticle core–shell heterostructures by a simple in situ anion-exchange route. It was found that the ion exchange reaction between Cl− and WO42− ions was preferable to occur on the surface of Ag8W4O16 nanorods rather than in the bulk solution, resulting in the formation of core–shell nanorods. The AgCl shell layer could be easily controlled by adjusting the concentration of NaCl solution. With increasing NaCl concentration, more Ag8W4O16 phase in the core transferred into AgCl-nanoparticle shell layer while the total size of the core–shell nanorods almost remained unchanged. The photocatalytic activity experiments of methyl orange aqueous solution under fluorescence light irradiation indicated that the AgCl nanoparticles coated on the surface of Ag8W4O16 nanorods, which could be readily separated from a slurry system after photocatalytic reaction, exhibited a much higher photocatalytic activity than the bulk AgCl photocatalyst.Graphical abstractResearch highlights▶ Ag8W4O16/AgCl-nanoparticle core–shell nanorods were prepared. ▶ The AgCl nanoparticles with a diameter of less than 30 nm were obtained. ▶ AgCl-nanoparticle shell can be easily controlled by NaCl solution. ▶ AgCl nanoparticles exhibited high photocatalytic activity.

AgI is instable under light irradiation owing to its photosensitive properties, while a supported Ag–AgI composite has been demonstrated to be a stable photocatalyst. However, seldom investigations have been focused on the photocatalytic activity (including deactivation) and photoinduced stability of the photosensitive AgI materials. In this study, the AgI nanoparticles were immobilized on the surface of Ag8W4O16 nanorods by an anion-exchange route and their photocatalytic activities were evaluated by photocatalytic decomposition of methyl orange and phenol solutions under visible-light irradiation. A photoinduced self-stabilizing mechanism of the AgI nanoparticles was proposed to account for the formation of a stable Ag–AgI photocatalyst, namely, instable AgI can transform into a stable Ag–AgI photocatalyst after in situ formation of partial Ag on the surface of AgI nanoparticles. The photocatalytic performance of the immobilized AgI photocatalyst was greatly influenced by the formation of metallic Ag. With increasing repetitions of photocatalytic experiments, the initial deactivation was accompanied by the rapid increase of metallic Ag owing to the reduction of lattice Ag+, while the subsequently stable activity corresponds to the formation of a stable Ag–AgI composite photocatalyst. Compared with the un-immobilized AgI photocatalyst, the immobilized AgI nanoparticles exhibited a higher and more stable photocatalytic performance.