Alkaline Earth Metal Intercalated into Carbon Nitride Nanosheets for Photocatalytic Peroxymonosulfate Removal of Refractory Organic Pollutants

Abstract

In this work, different alkaline earth metals intercalated into g-C3N4 (MCN, M = Ca, Sr, Ba) were prepared through the calcination of alkaline earth metal chlorides (MCl2, M = Ca, Sr, Ba) and melamine. The crystallite sizes of Bulk CN, BaCN, SrCN, and CaCN are 4.6, 4.8, 1.9, and 1.5 nm, respectively. In order to efficiently transfer charges among the g-C3N4 layers, the alkaline earth metal ions were designed as a “bridge”, which could chemically bond with the atoms of two adjacent layers while connecting the upper and lower layer. It is found that the cyano groups appearing on the MCN skeleton have a strong electron-attracting effect, which has a good guiding effect on promoting the separation of electrons and holes. The results of density functional theory further confirmed that BaCN had the strongest adsorption energy for peroxymonosulfate. Experiment results showed that the BaCN photocatalyst exhibited an excellent bisphenol A (BPA) degradation activity in the presence of peroxymonosulfate. The results showed that the performance of the BaCN photocatalyst to degrade BPA under visible light was 12 times that of CN. Meanwhile, the BaCN photocatalyst still had a 95% efficiency of BPA removal after four cycles of the experiment. The possible reaction mechanism in the degradation process was analyzed through electron spin resonance and capture experiments. This paper provides an idea for the comodification of g-C3N4 with alkali earth metals and cyanide groups to activate peroxymonosulfate.