The promotion of the photocatalytic nitrogen fixation ability of nitrogen vacancy-embedded graphitic carbon nitride by replacing the corner-site carbon atom with phosphorus

Abstract

Tuning a catalyst's structure is an effective method to modify its physicochemical and electronic properties. In this work, N vacancy and phosphorus co-doped g-C₃N₄ with outstanding N₂ photofixation ability was synthesized via a two-step calcination method. XRD, UV-Vis spectroscopy, N₂ adsorption, SEM, XPS, PL spectroscopy, ESR spectroscopy and TPD studies were used to characterize the as-prepared catalysts. The results showed that the corner site C atoms in g-C₃N₄ were partially substituted by the P heteroatoms. The as-prepared co-doped g-C₃N₄ displayed an ammonium ion production rate as high as 7.5 mg·L⁻¹ h⁻¹ g_cat⁻¹, which is 2.7 and 28.8 times higher than that of individual N vacancy-doped g-C₃N₄ and neat g-C₃N₄, respectively, as well as a good catalytic stability. Experimental and density functional theory (DFT) calculation results, when compared with individual N vacancy-doping, indicated that the introduction of phosphorus could promote the activation ability of N vacancies to the adsorbed N₂ molecule, leading to the promoted N₂ photofixation performance.