Construction of a 2D/2D g-C3N5/NiCr-LDH Heterostructure to Boost the Green Ammonia Production Rate under Visible Light Illumination

Abstract

Photocatalytic N2 fixation has emerged as one of the most useful ways to produce NH3, a useful asset for chemical industries and a carbon-free energy source. Recently, significant progress has been made toward designing efficient photocatalysts to achieve this objective. Here, we introduce a highly active type-II heterojunction fabricated via integrating two-dimensional (2D) nanosheets of exfoliated g-C3N5 with nickel–chromium layered double hydroxide (NiCr-LDH). With an optimized loading of NiCr-LDH on exfoliated g-C3N5, excellent performance is realized for green ammonia synthesis under ambient conditions without any noble metal cocatalyst(s). Indeed, the g-C3N5/NiCr-LDH heterostructure with 2 wt % of NiCr-LDH (CN-NCL-2) exhibits an ammonia yield of about 2.523 mmol/g/h, which is about 7.51 and 2.86 times higher than that of solo catalysts, i.e., NiCr-LDH (NC-L) and exfoliated g-C3N5 (CN-5), respectively, where methanol is used as a sacrificial agent. The enhancement of NH3 evolution by the g-C3N5/NiCr-LDH heterostructure can be attributed to the efficient charge transfer, a key factor to the photocatalytic N2 fixation rate enhancement. Additionally, N2 vacancies present in the system help adsorb N2 on the surface, which improves the ammonia production rate further. The best-performing heterostructure also shows long-term stability with the NH3 production rate remaining nearly constant over 20 h, demonstrating the excellent robustness of the photocatalyst.