A one-step deep eutectic solvent assisted synthesis of carbon nitride/metal oxide composites for photocatalytic nitrogen fixation

Abstract

Nitrogen fixation remains a challenge from both academic and industrial perspectives. Photocatalysis based on versatile semiconductors is a promising route for nitrogen fixation under mild conditions. In this study, for the first time, a ternary deep eutectic solvent (DES) strategy was developed for scalable synthesis of g-C₃N₄/metal oxide composites. A series of g-C₃N₄/metal oxide composites were prepared by a facile one-step calcination process using a ternary DES containing urea, melamine and metal chlorides. Moreover, since a DES is a homogeneous solution, the metal oxide after pyrolysis can be uniformly supported on the g-C₃N₄ nanosheet. This greatly increases the number of sites for photocatalysis and increases the catalytic efficiency. These composites show extraordinary photocatalytic effects for the reduction of nitrogen in atmospheric environment. With g-C₃N₄/40 wt% Fe₂O₃ as the photocatalyst, the maximum efficiency for ammonia generation can reach 4380 μmol L⁻¹ h⁻¹, which is the best yield to the best of our knowledge. The highly photocatalytic activity may be attributed to the efficient interfacial interaction between the 2D g-C₃N₄ nanosheets and α-Fe₂O₃ nanoparticles, which promotes the transfer and separation efficiency of charge carriers.