Spectromicroscopic determinations of chemical environments of Ni in MoS2-Ag-Ni ternary systems

Using heterogeneous photocatalysts for harvesting sunlight and converting it for water remediation and splitting are promising to mitigate the possible crisis of environment and energy. Among various composites, the MoS₂-based heterostructures and Ni-based systems exhibit unique electronic, optical properties and redox capabilities, enabling their roles as photocatalysts. Herein, the impacts of chemical environments on the Ni electronic structures within the MoS₂-Ag-Ni ternary systems are studied via X-ray photoemission electron spectroscopy (X-PEEM). Ni nanoparticles with two different sizes of 70 and 200 nm were loaded to MoS₂ flakes with silver buffers as bridges. Heterostructures with a nominal mol percentage of (MoS₂)₇₇Ag_3.7Ni_19.3 were synthesized through an ultrasound-assisted wet method. The oxidation states and various interfacial interactions of Ni with MoS₂ in MoS₂-Ag-Ni ternary composite are spectromicroscopically determined, combining the X-ray absorption spectroscopy near Ni L-edges and the imaging capability of the X-PEEM. Results showed that Ni mainly retrains its chemical states of metal and native oxidizations without observable electronic features subjected to bonding with the sulfur from the MoS₂ flakes. The charge migration channel set up by the Ag buffer thus contributes to electron–hole migrations that facilitate the photocatalytic performance of the ternary system eventually.