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

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.