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Bimetallic oxides have attracted extensive attention due to their excellent photocatalytic properties. Co2NiO4 has good electrical activity which can effectively regulate the distribution of charge. The scanning electron microscope and transmission electron microscope images of Co2NiO4 showed two-dimensional uniform lamellar morphology. This kind of morphology could provide a larger specific surface area, which was conducive to improving photocatalytic water decomposing and hydrogen evolution. In addition, we combined Co2NiO4 with NiWO4 to improve the conductivity of Co2NiO4 and the position of Fermi energy level, forming a p-n-type heterojunction, effectively promoting the interface charge transfer through the internal electric field, and inhibiting the electron–hole pair recombination. The photocatalytic hydrogen production of CN/NW-3 in the sensitized system reached 341.83 μmol for 5 h, which was 19 times that of pure Co2NiO4. At the same time, UV–Vis diffuse reflection and Mott–Schottky curve were used to further determine the conduction band (CB) and valence band (VB) positions of Co2NiO4 and NiWO4, which formed a charge transport path with higher separation and transfer efficiency. This work highlights the high-efficient photocatalytic hydrogen production performance of CN/NW p-n heterojunction. Co2NiO4 and NiWO4 form p-n heterojunction, and the synergy between them provides a new hydrogen-producing active center for each. [ABSTRACT FROM AUTHOR]

Due to the poor photocatalytic hydrogen evolution ability of pure CdS, we need to develop a photocatalytic hydrogen evolution catalyst with high activity and no precious metal doping. Therefore, in this article, we used a simple hydrothermal synthesis of CdS nanoparticles, using water as a carrier, loading a small amount of amorphous CoS, by changing the loading ratio of amorphous CoS, synthesized TYPE–II type heterojunction composite catalyst CCS. The successful synthesis of the composite catalyst CCS was verified by XRD, SEM and other characterization methods. UV–vis, PL and other characterization showed that the supported amorphous CoS could significantly improve the photocatalytic activity of CdS, and the photochemical detection also showed that the performance of composite catalyst CCS was better than that of pure CdS. Using Na2S and Na2SO3 mixed solution as electron sacrificial agent, the hydrogen production performance of CCS composite catalyst was determined through hydrogen evolution experiment and cyclic stability experiment. It was found that the sacrificial agent had a great promotion effect on the hydrogen production performance of photocatalyst. It was found that the hydrogen production rate of the composite catalyst could reach 2.01 mmol·g−1·h−1, which was 6.3 times of the pure CdS. This study offers a novel approach for the design of amorphous–based nanostructures as efficient hydrogen evolution cocatalysts. First, CdS are excited by light, consuming S2− and SO32− ions in the sacrificial agent, generating a large number of electrons and holes. Due to the energy difference between the conducting band (CB) of CdS and amorphous CoS, the electrons are transferred from the surface of CdS to the conducting band (CB) of amorphous CoS, while the electrons obtained from water and H+ in the sacrificial agent are reduced to H2. The amorphous CoS is used as the transfer medium of electron acceptor, and the synergistic effect between heterojunctions is used to improve the charge separation efficiency and electron transfer rate. Therefore, the photocatalytic hydrogen production effect of the composite catalyst CCS–7 has been greatly improved. [ABSTRACT FROM AUTHOR]

The exploration of Z-scheme heterojunction photocatalysts is considered crucial to improve the efficiency of photocatalytic hydrogen evolution. In this work, ZSN with a Z-scheme heterojunction is prepared by a two-step hydrothermal method. Through the study of the surface morphology, crystallization properties, surface chemistry and optical properties of the photocatalyst, it is known that the ZSN heterojunction can improve the visible light capture ability, prolong the service life of charges, improve the efficiency of charge separation, and improve the photocatalytic performance. Under visible light irradiation, the amount of hydrogen evolution of the optimized 2-ZSN is 74 μmol, 37 times that of the pure ZnS (2 μmol). The results of photoluminescence (PL), ultraviolet-visible (UV-Visible) and electrochemical techniques show that the Z-scheme mechanism is advantageous to the separation of photogenic carriers as well as the hole transfer and separation. This work provides a reliable strategy for constructing efficient Z-scheme heterojunction photocatalysts. [ABSTRACT FROM AUTHOR]

One of the most effective methods to improve electron-transfer efficiency and photocatalytic reaction activity is to construct a photocatalyst with a heterojunction interface. Herein, a WO3/CoS2 n–n heterojunction composite catalyst was synthesized, and used in photocatalytic hydrogen evolution, and was optimized by adjusting the pH of the triethanolamine solution, the amount of Eosin Y added, and the content of WO3 in the composite catalyst. After 5 h of photocatalytic reaction, WO3/CoS2 (WCS-2) had a H2 production of 221.15 μmol, which was 80.41 times that of single WO3 and 2.17 times that of CoS2, and had good stability. XRD, SEM, TEM, and XPS characterization results indicated that WO3/CoS2 was successfully prepared. Fluorescence test and electrochemical test results showed that the WO3/CoS2 catalyst had a higher photoelectron transfer efficiency. Finally, it is pointed out that WO3/CoS2 enhanced the photocatalytic activity, which may be due to the electron migration of WO3 and CoS2 following the Z-scheme mechanism. This work presents a new idea for constructing n–n heterojunction to enhance the activity in photocatalytic hydrogen production. [ABSTRACT FROM AUTHOR]

Research into catalytic materials that convert light energy into chemical energy by decomposing water still faces great difficulties. CuNi2S4 has attracted public attention due to its unique morphology; however, its high electron–hole recombination rate and weak charge separation efficiency limit its use in the field of catalysis. Herein, CoWO4 material is synthesized in situ on a CuNi2S4 surface by a hydrothermal method; the Z-type heterointerface constructed by the surface contact of the two materials under fusion shows a huge promotion effect on the catalytic ability. The performance (3754.3 μmol g−1 h−1) of the composite material (CW/CNS-12%) reached 42 and 6 times those of the two monomer materials, respectively, and the excellent catalytic ability of the composite is also reflected in its long-term stability. The experimental data proves that the modification of CuNi2S4 by building a heterostructure can improve the specific surface area of the material and the amount of carriers it generates. The charge transfer caused by the existence of the heterojunction hinders the recombination of carriers and holes; fluorescence and electrochemical characterization further confirms the charge transfer process in the Z-type heterojunction. This research provides new insights to promote catalytic performance by building heterostructures between monomer materials. [ABSTRACT FROM AUTHOR]

Overall dye-sensitized photocatalytic HER system based on g-C 3 N 4 and 2D Co MOF doped by Sm achieved effective photocatalytic H 2 evolution. • An overall dye-sensitized system was constructed for efficient photocatalytic HER. • 2D Co MOF and protonated g-C 3 N 4 formed a 2D/2D heterojunction. • Protonated g-C 3 N 4 preferentially adsorbed EY molecules. • Sm element doping 2D Co MOF further improved carrier separation. A dye-sensitive photocatalytic H 2 evolution reaction (HER) system with photogenerated carrier directed conduction was constructed. The protonated g-C 3 N 4 combines with the sheet-like Co MOF to form a 2D/2D heterojunction via electrostatic self-assembly. The protonated g-C 3 N 4 and 2D Co-MOF directionally adsorb Eosin Y (EY) and triethanolamine (TEOA) molecules through hydrogen bond and complexation to achieve a whole photocatalytic system. The integral structure effectively facilitates the utilization of dye sensitizer and hole sacrificial agent to achieve the effective and stable photocatalytic H 2 evolution capacity. The photocatalytic hydrogen evolution rate of g-C 3 N 4 after protonation is 1.88 times as high as that of the original g-C 3 N 4. On the basis of 2D/2D heterojunction, Co MOF is doped with rare earth element Sm. The 4f electrons and the difference valences (Sm3+ and Co2+) further suppress the reorganization of photogenerated excitons to achieve highly efficient photocatalytic HER. The directional coupling of sensitizer and electron sacrificial agent combined with rare earth element doping makes the photocatalytic HER rate of the composite material reached 73.42 μmol.h−1 within 5 h under simulated sunlight. [ABSTRACT FROM AUTHOR]

With the development of research on the photocatalytic water splitting and hydrogen (H 2) precipitation, cobalt ferrite and molybdate have begun to appear as catalysts for the study of photocatalytic hydrogen precipitation. In this paper, the p-n heterojunction CoFe 2 O 4 /NiMoO 4 (CFO/NMO) is prepared by hydrothermal method. The constructed p-n type (type Ⅱ) heterojunction CFO/NMO has the highest hydrogen evolution (Eosin Y as a sensitizer), which is 7.39 times and 1.95 times that of elemental CFO and NMO, respectively. After the CFO and NMO form a heterojunction, a built-in electric field is formed inside to effectively separate the photogenerated carriers. At the same time, the dense interface of the heterojunction also promotes the transfer of photogenerated carriers and promotes the reduction of H+ protons on this catalyst surface. In short, this work provides more possibilities for the field of photocatalytic hydrogen evolution from molybdate and cobalt ferrite compounds. Image 1 • High-efficiency hydrogen evolution is realized through CoFe 2 O 4 /NiMoO 4 heterojunction composite material. • The synergistic effect of magnetic CoFe 2 O 4 and NiMoO 4 improves the photocatalytic hydrogen evolution activity. • Experimental characterization to verify the photocatalytic mechanism of p-n heterojunction. [ABSTRACT FROM AUTHOR]

Photocatalytic material Zn x Cd 1-x S band gap adjustment avoids composite Z-scheme heterostructure construction. • Efficient photocatalytic H 2 evolution material NiCo 2 S 4 @Zn 0.5 Cd 0.5 S was prepared. • Zn x Cd 1-x S energy band adjustment induced the conversion of photo-generated carrier transmission path. • Direct Z-scheme heterojunction between NiCo 2 S 4 and Zn 0.5 Cd 0.5 S was constructed. The hollow sphere structure of NiCo 2 S 4 achieved uniform contact between composite material. Based on hollow spherical NiCo 2 S 4 , Zn x Cd 1-x S with adjustable band structure was used to construct a composite for photocatalytic hydrogen evolution. The hollow spherical structure of NiCo 2 S 4 gives Zn x Cd 1-x S more contact positions to form a stable heterojunction. Through the band structure adjustment for Zn x Cd 1-x S, the induced electron transfer model was transformed into Z-scheme, which effectively enhances the photo-produced carrier separation efficiency of the composite material. At the same time, the fast electron transfer is realized by the great conductivity of the hollow spherical NiCo 2 S 4. This allows the composite material to obtain a shorter average lifetime of PL (0.15 ns) compared to Zn 0.5 Cd 0.5 S (3.9 ns). The composite NiCo 2 S 4 @Zn 0.5 Cd 0.5 S with Z-scheme heterojunction exhibited excellent photocatalytic HER activity and stability due to its unique spatial structure and efficient Z-scheme electron transfer path. The optimized composite NiCo 2 S 4 @Zn 0.5 Cd 0.5 S 1:1 photocatalytic HER rate reached 233.68 μmol.h−1, which is equivalent to 5.81 times that of Zn 0.5 Cd 0.5 S (40.25 μmol.h−1). [ABSTRACT FROM AUTHOR]