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In this work, we study the enhancement of Raman signals and photocatalytic activity of Ag/ZnO heterojunctions with an Ag content of 1 at.%, which were synthesized by photochemical deposition of Ag nanoparticles onto pre-synthesized ZnO nanorods. A strong interaction between Ag and ZnO nanocrystals were evidenced by XPS and UV-vis spectroscopy. The binding energy of Ag nanoparticles shifts toward lower energy compared to that of pure Ag nanoparticles, revealing that electrons transfer from Ag to the ZnO nanocrystals. The red shift of the plasmon absorption peak of Ag nanoparticles in Ag/ZnO heterojunctions further confirms the strong interaction between the two components. This strong interaction, arising from the coupling between Ag and ZnO nanocrystals, is responsible for the enhancement of Raman signals and photocatalytic activity of the Ag/ZnO heterojunctions. [ABSTRACT FROM AUTHOR]

A nanocrystal catalyst Ag/ZnO was successfully synthesized using a simple solvothermal method in this study. This catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that this catalyst was composed of metallic Ag and ZnO. The photodegradation of methyl orange (MO) was investigated in aqueous suspension containing Ag/ZnO catalyst under UV irradiation. Liquid chromatography coupled with electrospray ionization ion-trap mass spectrometry was applied to the analysis of the samples coming from the photocatalytic degradation of MO. The experimental results showed that there were four intermediates existing in the photocatalytic reaction. MO could be mineralized in the Ag/ZnO suspension after 60 min illumination. [Copyright &y& Elsevier]

Photocatalytic hydrogen production is considered as an ideal approach to solve global energy crisis and environmental pollution. Graphitic carbon nitride (g-C 3 N 4) has received extensive consideration due to its facile synthesis, stable physicochemical properties, and easy functionalization. However, the pristine g-C 3 N 4 usually shows unsatisfactory photocatalytic activity due to the limited separation efficiency of photogenerated charge carriers. Generally, introducing semiconductors or co-catalysts to construct g–C 3 N 4 –based heterojunction photocatalysts is recognized as an effective method to solve this bottleneck. In this review, the advantages and characteristics of various types of g–C 3 N 4 –based heterojunction are analyzed. Subsequently, the recent progress of highly efficient g–C 3 N 4 –based heterojunction photocatalysts in the field of photocatalytic water splitting is emphatically introduced. Finally, a vision of future perspectives and challenges of g–C 3 N 4 –based heterojunction photocatalysts in hydrogen production are presented. Predictably, this timely review will provide valuable reference for the design of efficient heterojunctions towards photocatalytic water splitting and other photoredox reactions. [Display omitted] • g–C 3 N 4 –based photocatalysts for solar hydrogen production are overviewed. • Heterojunction significantly improved the photocatalytic activity of g-C 3 N 4. • g-C 3 N 4 heterojunction/isotype junction can be synthesized by copolymerization. • The details for the design of g–C 3 N 4 –based heterojunctions are highlighted. • The challenges and prospects of g-C 3 N 4 photocatalysts are presented. [ABSTRACT FROM AUTHOR]

Highlights: [•] Porous ZnO/Sn1−x Zn x O2−x nanocatalysts with high photocatalytic activity were synthesized by a two-step solvothermal method. [•] Zn doping in SnO2 shows an influence on particle size, specific surface area and band gap. [•] The formation of ZnO/Sn1−x Zn x O2−x heterostructure improves the separation of photogenerated electron–hole pairs. [•] The synergistic effects of metal ion doping and semiconductor/semiconductor heterostructure are reported. [ABSTRACT FROM AUTHOR]

[Display omitted] • The AgBr/HCCN photocatalyst was fabricated using an electric self-assembly approach. • The hybrid photocatalyst features an all-solid-state direct Z-scheme heterojunction. • The Z-scheme heterojunction improves the photogenerated charge carriers' separation. • The contact level of the heterojunction affects the performance of the photocatalyst. • The AgBr/HCCN photocatalyst exhibits a 5.4-fold enhancement in hydrogen evolution. Constructing a Z-scheme heterojunction with enhanced photocatalytic hydrogen evolution for graphitic carbon nitride-based (g-C 3 N 4) composites is challenging because integrating g-C 3 N 4 with other semiconductors, without specific band structure design, typically results in type I or type II heterojunctions. These heterojunctions have lower redox ability and limited enhancement in photocatalysis. Herein, we select highly crystalline carbon nitride (HCCN) as a proof-of-concept substrate. For the first time, we develop a AgBr nanosphere/HCCN composite photocatalyst that features an all-solid-state direct Z-scheme heterojunction for visible-light photocatalytic hydrogen evolution. The electron transfer mechanism is initially studied from the band structures and Fermi levels of HCCN and AgBr. It is subsequently confirmed by X-ray photoelectron spectroscopy (XPS), and electron microscopy. The close heterojunction contact and the built-in electron field of the Z-scheme heterojunction promote the migration and separation of photogenerated electrons and holes in the composite photocatalyst. Due to the redistribution of charge carriers, the photocatalyst shows superior redox capability and a markedly enhanced hydrogen evolution performance compared to its individual components. Combining all the advantages, AgBr nanosphere/HCCN reached an apparent quantum efficiency (AQE) of 6 % under the illumination of 410 nm, which is 4 times higher than that of the single HCCN component. [ABSTRACT FROM AUTHOR]

[Display omitted] • A sufficient and tunable ohmic junction can be built in allochroic Pt/CN. • The ohmic contact is formed by the photoconversion of semiconducting CN to metalloid. • The reversible photoconversion of CN is accompanied with a color change. • The ohmic contact between Pt and CN significantly enhances the HER activity. • The deactivation and regeneration mechanisms of the allochroic Pt/CN are proposed. The direct hybridization of Pt and g-C 3 N 4 generally forms a Schottky barrier between the two components, which unavoidably hinders the migration of photogenerated electrons from g-C 3 N 4 to the Pt cocatalyst. Herein, we report the first efficient allochroic Pt/g-C 3 N 4 photocatalyst that can form an ohmic contact through photoconversion of semiconducting g-C 3 N 4 to metalloid, accompanied with the charge carrier storage and photocatalyst color change, which is proved experimentally and theoretically. Through intermittent exposure of Pt/g-C 3 N 4 photocatalyst to air for a few minutes during photocatalysis, the photocatalyst shows the highest hydrogen evolution performances. The ohmic contacts greatly promote the electron transfer from the semiconducting g-C 3 N 4 to the Pt cocatalyst driven by the built-in electric field. In addition, the mechanism for the photocatalyst deactivation and activation is presented. The compositional tuning of the allochroic g-C 3 N 4 through light irradiation and exposure to air can control over the photocatalytic activity and long-term stability for hydrogen evolution. This report for the first time unveils the deactivation and regeneration mechanisms of SCN. [ABSTRACT FROM AUTHOR]

• The S + K-codoped g-C 3 N 4 presents excellent H 2 production (8.78 mmol g−1 h−1) under visible light. • The S + K-codoped g-C 3 N 4 inhibits the recombination of photogenerated carriers. • The S + K-codoped g-C 3 N 4 photocatalyst shows apparent quantum efficiency of 70 % at 420 nm for H 2 production. Modifying the structure of a photocatalyst to tailor its electronic and physicochemical properties is an effective approach for efficient photocatalysis. Herein, we demonstrate that co-doping non-metal (S) and metal (K) atoms into graphitic carbon nitride (g-C 3 N 4) provides excellent visible-light photocatalytic hydrogen production activity of 8.78 mmol g−1 h−1, which is 98 times higher than that of pristine g-C 3 N 4 (0.09 mmol g−1 h−1). The apparent quantum efficiency of the S+K-co-doped g-C 3 N 4 reaches 70 % at 420 nm. This outstanding photocatalytic performance attributed to an increased specific surface area from 6.78 to 74.23 cm3 g−1, which reduced the recombination of photogenerated charge carriers and enhanced conductivity. Various characterizations are undertaken to elucidate the S+K-co-doped g-C 3 N 4 photocatalytic mechanism. Our work not only demonstrates a facile, eco-friendly and scalable strategy for the synthesis of S+K-co-doped g-C 3 N 4 photocatalysts, but also opens a new avenue for the design of co-doped photocatalysts. [ABSTRACT FROM AUTHOR]