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▶ 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.
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 30nm 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.
•Ag/AgCl photocatalysts with different amounts of metallic Ag were prepared.•Metallic Ag has a great effect on the stability and photoactivity of Ag/AgCl.•The stable performance is due to the ...formation of stable Ag–AgCl structure.
Recently, Ag/AgCl has been demonstrated to be a stable and highly efficient photocatalytic material. However, considering the strong photosensitive property of AgCl phase without Ag, it is clear that the metallic Ag plays an important role on the photoinduced stability of Ag/AgCl composite, which has a great effect on its photocatalytic performance. In this study, the Ag/AgCl photocatalysts with different amounts of metallic Ag were prepared by a facile hydrothermal method (30–160°C) to reveal the dependence of metallic Ag on the photoinduced stability and photocatalytic activity of Ag/AgCl photocatalyst. It was found that the amounts of metallic Ag in the Ag/AgCl could be easily controlled by adjusting the hydrothermal temperature, and the Ag amounts (0–9.8at%) gradually increased with the hydrothermal temperature from 30 to 160°C. Photocatalytic results indicated that the metallic Ag had a great effect on the photoinduced stability and photocatalytic activity of Ag/AgCl photocatalysts. As for the AgCl-30 photocatalyst (without metallic Ag), with increasing repetitions of photocatalytic reactions, the photocatalytic performance firstly decreased owing to the rapid increase of metallic Ag via the reduction of lattice Ag+ on AgCl surface, while the subsequently stable performance corresponded to the formation of a stable Ag–AgCl composite structure. For the Ag/AgCl (160°C) photocatalyst, the sample always exhibited a comparable and stable photocatalytic performance due to the initial existing of some metallic Ag (ca. 9.8at%). Therefore, a certain amount of metallic Ag on the AgCl surface can greatly improve the photoinduced stability of Ag/AgCl photocatalyst in addition to maintaining its stable photocatalytic activity.
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•Metallic Bi was deposited on the TiO2 surface by a direct photoinduced method.•Bi/TiO2 photocatalyst display an improved photocatalytic H2-production activity.•Metallic Bi works as ...an effective H2-evolution cocatalyst for TiO2 photocatalyst.•An electron cocatalyst-mediated mechanism of Bi is proposed for H2 evolution.
Exploiting novel non-noble metal cocatalysts and their facile synthetic strategies are quite crucial to develop high-performance H2-production photocatalysts. Here, metallic Bi nanoparticle as a new H2-evolution cocatalyst was deposited on the TiO2 surface to significantly enhance its H2-evolution activity by a direct photoinduced method in a Bi(III)-EG complex system. Photocatalytic H2-production experimental results suggested that all the resultant Bi/TiO2 photocatalyst display a dramatically higher photocatalytic H2-production performance than the pure TiO2. Specifically, the Bi/TiO2(1 wt%) photocatalysts exhibited the highest H2-evolution activity (37.10 μmol h−1), which is higher than the naked TiO2 photocatalyst (0.35 μmol h−1) by a factor of 106 times. In addition to the TiO2, the metallic Bi nanoparticles can also serve as an effective cocatalyst to significantly improve the H2-evolution performance of the well-known visible-light responded g-C3N4 and CdS photocatalysts. According to the above result, an electron cocatalyst-mediated mechanism of metallic Bi is proposed for the enhanced H2-production activity, where the metallic Bi cocatalyst works as an electron capturer to rapidly accept photogenerated electrons from the TiO2 surface and subsequently functions as a H2-evolution active site to promote H2 formation. Compared with the widely used noble metals (such as Pt), the present promising Bi cocatalyst is one of the very important cocatalysts for the synthesis of highly efficient photocatalytic materials due to its low cost and abundance.
Photocatalysis is a green technology to use ubiquitous and intermittent sunlight. The emerging S‐scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the ...state‐of‐the‐art progress and provides new insights into its general designing criteria. It starts with the challenges confronted by single photocatalyst from the perspective of energy dissipation by borrowing the common behaviors in the dye molecule. Subsequently, other problems faced by single photocatalyst are summarized. Then a viable solution for these problems is the construction of heterojunctions. To overcome the problems and mistakes of type‐II and Z‐scheme heterojunctions, S‐scheme heterojunction is proposed and the underlying reaction mechanism is summarized. Afterward, the design principles for S‐scheme heterojunction are proposed and four types of S‐scheme heterojunctions are suggested. Following this, direct characterization techniques for testifying the charge transfer in S‐scheme heterojunction are presented. Finally, different photocatalytic applications of S‐scheme heterojunctions are summarized. Specifically, this work endeavors to clarify the critical understanding on curved Fermi level in S‐scheme heterojunction interface, which can help strengthen and advance the fundamental theories of photocatalysis. Moreover, the current challenges and prospects of the S‐scheme heterojunction photocatalyst are critically discussed.
Emerging S‐scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the state‐of‐the‐art progress of S‐scheme heterojunction. Design principles for S‐scheme heterojunction are proposed and four types of S‐scheme heterojunctions are suggested. Direct characterization methods for electron transfer in S‐scheme heterojunction are presented. Different photocatalytic applications are summarized. Especially, the curved Fermi level in S‐scheme heterojunction interface is discussed.
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•An in situ one-step hydrothermal method was developed to prepare OG/g-C3N4.•Hydrothermal treatment greatly increase the specific surface area of bulk g-C3N4.•Hydrothermal treatment ...induce the formation of OH and CO on g-C3N4 surface.•The OG/g-C3N4 shows an obviously improved H2-evolution performance.
Surface modification of g-C3N4 is one of the most effective strategies to boost its photocatalytic H2-evolution performance via promoting the interfacial catalytic reactions. In this study, an in situ one-step hydrothermal method was developed to prepare the oxygen-containing groups-modified g-C3N4 (OG/g-C3N4) by a facile and green hydrothermal treatment of bulk g-C3N4 in pure water without any additives. It was found that the hydrothermal treatment (180°C) not only could greatly increase the specific surface area (from 2.3 to 69.8m2g−1), but also caused the formation of oxygen-containing groups (OH and CO) on the OG/g-C3N4 surface, via the interlayer delamination and intralayer depolymerization of bulk g-C3N4. Photocatalytic experimental results indicated that after hydrothermal treatment, the resultant OG/g-C3N4 samples showed an obviously improved H2-evolution performance. Especially, when the hydrothermal time was 6h, the resultant OG/g-C3N4(6h) exhibited the highest photocatalytic activity, which was clearly higher than that of the bulk g-C3N4 by a factor of ca. 7. In addition to the higher specific surface area, the enhanced H2-evolution rate of OG/g-C3N4 photocatalysts can be mainly attributed to the formation of oxygen-containing groups, which possibly works as the effective H2-evolution active sites. Considering the facie and green synthesis method, the present work may provide a new insight for the development of highly efficient photocatalytic materials.
•Fe(III) cocatalyst was loaded on the TiO2−xNx surface by an impregnation method.•Fe(III)/TiO2−xNx showed an enhanced visible-light photocatalytic activity.•Fe(III) cocatalyst promoted the rapid ...separation of photogenerated charges.•The advantage of Fe(III) as a new cocatalyst is its low cost and abundant resource.
Nitrogen doped TiO2 (TiO2−xNx), one of the most promising visible-light photocatalytic materials, exhibits a low photocatalytic activity owing to the rapid recombination of photogenerated electrons and holes, which is caused by the isolated energy level of N 2p formed above the valence band of TiO2. To reduce the recombination of photogenerated charges and further improve the photocatalytic performance of TiO2−xNx, in this study, Fe(III) cocatalyst was loaded on the surface of TiO2−xNx photocatalyst by a simple impregnation method. It was found that after surface modification by Fe(III) cocatalyst, the photocatalytic performance of all the TiO2−xNx photocatalysts could be greatly improved for the decomposition of MO under visible-light irradiation. Especially, the Fe(III)/TiO1.981N0.019 photocatalyst showed the highest photocatalytic activity and its rate constant k was ca. 52.5×10−4min−1, which is higher than that of the corresponding TiO1.981N0.019 photocatalyst (9.9×10−4min−1) by a factor of 5.3 times. Based on the present experimental results, the Fe(III) was thought to be an effective cocatalyst to significantly improve the electron transfer from the conduction band of TiO2−xNx to the adsorbed oxygen, thus facilitating the rapid separation of photogenerated charges and greatly enhancing the photocatalytic activity. In addition, the direct interfacial charge transfer from the N 2p isolated energy level to Fe(III) cocatalyst can also contribute to the enhanced photocatalytic efficiency of TiO2−xNx. Considering the abundant Fe resources and its low cost, the Fe(III)-cocatalyst modification can be regarded as an effective approach for rational design and development of high-performance visible-light photocatalysts in practical applications.
•RGO-cocatalyst modification and AgCl nanonization were simultaneously realized.•AgCl nanoparticles with a size of 20–200nm are tightly grafted on the rGO surface.•Ag/AgCl-rGO photocatalyst shows an ...excellent photocatalytic activity.•Both rGO cocatalyst and AgCl nanonization contribute to an improved performance.
Usually, cocatalyst modification and nanonization of photocatalytic materials have been demonstrated to be two kinds of effective strategies to improve the photocatalytic performance. For the well-known Ag/AgCl photocatalyst, it is difficult to obtain AgCl nanoparticles by a conventional precipitation reaction in aqueous solutions. It is highly required to develop a facile and effective strategy to simultaneously realize the cocatalyst modification and nanonization of Ag/AgCl photocatalysts. In this study, cocatalyst modification and nanonization of Ag/AgCl photocatalyst were simultaneously realized via a facile reduction–reoxidization route by using graphene oxide (GO) as the cocatalyst modifier. It was found that the chemical reduction of both Ag+ and GO by NaBH4 leaded to the formation of nanoscale Ag grafted on the reduced GO (rGO), whereas the following in situ reoxidization of metallic Ag in FeCl3 solution resulted in the final formation of well-dispersed Ag/AgCl nanoparticles on the rGO surface. Owing to a good encapsulation of Ag nanoparticles by rGO nanosheets, the resultant AgCl nanoparticles could be easily controlled to be 20–200nm and were tightly grafted on the rGO cocatalyst surface. The photocatalytic experimental results indicated that all the Ag/AgCl-rGO (1–5wt% rGO) nanocomposites exhibited a much higher photocatalytic decomposition of phenol than the Ag/AgCl under visible light irradiation, and the Ag/AgCl-rGO (3wt% rGO) showed the highest performance. The enhanced photocatalytic activity of Ag/AgCl-rGO can be attributed to the cooperation effect of rGO nanosheet cocatalyst promoting the effective transfer of photogenerated electrons, and the nanonization of AgCl particles that provide more surface active sites for the decomposition of organic substances. This work may provide new insights into the fabrication of high-performance visible-light photocatalytic materials.
Mesoporous titania nanorod/titanate nanotube composites were prepared using TiF
4 and H
3BO
3 as the precursors. The prepared samples were characterized with TEM, SEM, XRD, HRTEM, and nitrogen ...adsorption–desorption isotherms. The photocatalytic activities were evaluated by photocatalytic oxidation of acetone in a gas phase and photocatalytic discolorization of methyl orange aqueous solution in an aqueous phase, respectively. The results indicated that the photocatalytic activity of the mesoporous titania nanorod/titanate nanotube composites exceeded that of P25 by a factor of about 2.5 times for the photocatalytic oxidation of acetone. This could be attributed to the fact that the former had a larger specific surface area and a higher pore volume. Moreover, the mesoporous titania nanorod/titanate nanotube composites, which could be readily separated after photocatalytic reaction in an aqueous phase, exhibited highly photocatalytic activity for the degradation of methyl orange aqueous solution.
