Novel Ternary MoS₂/C-ZnO Composite with Efficient Performance in Photocatalytic NH₃ Synthesis under Simulated Sunlight

This paper was designed to realize the efficient photoreduction of N2 to NH3 over a novel ternary MoS2/C-ZnO composite which was prepared via a combination of hydrothermal and photodeposition methods. The as-prepared composite was characterized by multiple techniques including X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS), N2 adsorption, transient photocurrent response (PC), and electrochemical impedance spectroscopy (EIS). The obtained results indicated that carbon was not doped into the ZnO lattice but loaded on the surface of ZnO and acted as an electron trapper to hamper the recombination of charge carriers. The thermal treatment of C-ZnO can modify the carbon content and thus improves the charge separation efficiency. The optimal calcination temperature is determined to be 300 °C. Photodeposition of MoS2 nanoparticles on the C-ZnO-300 sample can further improve the separation of electron–hole pairs via trapping the electrons on the carbon layer. Under simulated sunlight irradiation, the optimal 1% MoS2/C-ZnO-300 composite presents the fastest NH3 generation rate of 245.7 μmol·L–1g–1·h–1, which is 9.3 and 4.0 times higher than that of ZnO and C-ZnO, respectively. Under visible light, however, C-ZnO exhibits the highest performance with a NH3 generation rate of 28.8 μmol·L–1g–1·h–1, indicating the composite follows another mechanism. The carbon layer was believed to play the role of photosensitizer to transfer electrons to ZnO or MoS2. The suggested mechanisms have been confirmed by EIS and PC analyses. Finally, the loading of carbon layer and MoS2 nanoparticles on ZnO increase the BET area. The enhanced surface area may be partially responsible for the enhanced photocatalytic performance.