Atomically dispersed s-block metal calcium site modified mesoporous g-CN for boosting photocatalytic N reduction

Alkaline-earth metal elements in the s-block of the periodic table have rarely been studied as active sites for nitrogen (N 2 ) photofixation. Herein, we report a single-atom calcium (Ca)-modified mesoporous g-C 3 N 4 (Ca/m-g-C 3 N 4 ) for promoting the photocatalytic N 2 reduction reaction (pNRR) under ambient conditions. Moreover, the atomically dispersed Ca as active sites of Ca/m-g-C 3 N 4 could achieve high adsorption of N 2 molecules, which could be confirmed by nitrogen temperature-programmed desorption test (N 2 -TPD). In this regard, Ca single atoms can not only serve as the active centers of N 2 but also optimize the energy band structure of m-g-C 3 N 4 , facilitating the photocatalytic synthesis of ammonia (NH 3 ). Therefore, the optimal 0.5 Ca/m-g-C 3 N 4 demonstrates a remarkable NH 3 generation amount of 42.23 μg g cat. −1 h −1 , which is 2.1 times that of pure g-C 3 N 4 (20.41 μg g cat. −1 h −1 ). Furthermore, the present 0.5 Ca/m-g-C 3 N 4 demonstrates good stability, and the NH 3 production is still remarkably unvaried after four cycling tests. More interestingly, it was also found that other alkaline earth metal elements, including magnesium (Mg), strontium (Sr), and barium (Ba), can also activate N 2 molecules. Accordingly, the photocatalytic NH 3 synthesis yield of Ba/m-g-C 3 N 4 is 29.52 μg g cat. −1 h −1 , slightly more than that of Mg/m-g-C 3 N 4 (20.52 μg g cat. −1 h −1 ) and Sr/m-g-C 3 N 4 (20.88 μg g cat. −1 h −1 ). We hope that this work could provide a novel insight for developing other high-performance N 2 -photofixation systems based on low-cost s-block alkaline-earth metal materials in the future. Alkaline-earth metal elements in the s-block of the periodic table have rarely been studied as active sites for nitrogen (N 2 ) photofixation.