Abstract
A magnetically recyclable Ni/NiO/g-C3N4 photocatalyst with significantly enhanced H2 evolution efficiency was successfully synthesized by a simple ethanol-solvothermal treatment. The presence of electronegative g-C3N4 is found to be the key factor for Ni0 formation in ternary Ni/NiO/g-C3N4, which provides anchoring sites for Ni2+ absorption and assembling sites for Ni0 nanoparticle formation. The metallic Ni0, on one side, could act as an electron acceptor enhancing carrier separation and transfer efficiency, and on the other side, it could act as active sites for H2 evolution. The NiO forms a p–n heterojunction with g-C3N4, which also promotes carrier separation and transfer efficiency. The strong magnetic property of Ni/NiO/g-C3N4 allows a good recyclability of catalyst from aqueous solution. The optimal Ni/NiO/g-C3N4 showed a full-spectrum efficiency of 2310 μmol·h−1·g−1 for hydrogen evolution, which is 210 times higher than that of pure g-C3N4. This ethanol solvothermal strategy provides a facile and low-cost synthesis of metal/metal oxide/g-C3N4 for large-scale application.
Highlights
Photocatalysis has attracted great attention in environmental protection and the domain of new energy application as it is an effective technique to degrade water pollutants and convert sustainable solar energy into applicable chemical energy, such as hydrogen.Carbon nitride, as a metal-free polymer material, has been widely used in photocatalytic water splitting since 2009, due to its advantages of non-toxicity, low cost, high stability, excellent optical properties, and electronic structure [1,2,3]
The photocatalytic hydrogen production experiment was performed in a vacuum quartz reactor with a cooling water system (LX-300, Beijing Zhongjiaojinyuan Co., Beijing, China)
The synthesized x-Ni/CN samples were characterized by X-ray diffraction (XRD) to distinguish the phases that formed on each catalyst (Figure 2a)
Summary
Photocatalysis has attracted great attention in environmental protection and the domain of new energy application as it is an effective technique to degrade water pollutants and convert sustainable solar energy into applicable chemical energy, such as hydrogen. The low separation and high recombination efficiency of photogenerated charge carriers limits its application in H2 evolution Loading noble metals such as Au, Ag, and Pt onto carbon nitride as co-catalysts is an effective way to solve these problems. These works reveal the advantages of nickel-based materials for photocatalytic hydrogen production, such as good stability, high activity, and earth abundance Most of these photocatalysts still suffer disadvantages, e.g., the harsh and dangerous synthetic conditions or the single phase obtained in one method. Compared with hydrogen reduction under high temperature [5], our ethanol-solvothermal-strategy (160 ◦ C) avoids the use of dangerous H2 and high temperature during preparation, and can introduce Ni/NiO onto g-C3 N4 in one step This solvothermal preparation method can be used as a universally applicable strategy for Metal/Metal-oxide/g-C3 N4 composites. Through a series of controlled trials, we have confirmed that the electronegativity of g-C3 N4 is a key factor for the formation of Ni0
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