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

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 N-2 photofixation ability was synthesized via a two-step calcination method. XRD, UV-Vis spectroscopy, N-2 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 center dot 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 N-2 molecule, leading to the promoted N-2 photofixation performance.