Selective ozone oxidation of ammonium ion catalyzed by carbon nanocage-supported Co3O4: Role of oxygen vacancies and electron transfer sites

Abstract

For the effective treatment of the wastewater with low-medium concentration ammonia nitrogen and low strength COD, a high-performance Co₃O₄ catalyst supported on carbon nanocages (CNCs) was prepared. By isovolumetric im pregnation, Co₃O₄ could be uniformly dispersed on surface of CNCs, which possess tiny particle size and strong electron transfer capability. The catalytic performance of the prepared Co₃O₄/CNCs catalysts with different Co₃O₄ loadings was systematically evaluated and compared with Co₃O₄/CNTs. It is found that 20 wt.% Co₃O₄/CNCs shows the best catalytic performance, achieving an ammonia nitrogen conversion rate of 71.0 % and a nitrogen selectivity of 81.8 %. Compared to commonly used Co₃O₄, ammonia conversion and nitrogen selectivity of Co₃O₄/CNCs increased by 28.9 % and 15.8 % respectively. In the five consecutive cycles, the catalytic activity remained stable. The mechanism that CNCs support effectively increases the surface oxygen vacancies of Co₃O₄ through XPS analysis was also elucidated, and DFT calculations confirm strong electron transfer between CNCs and Co₃O₄, rendering Co₃O₄ nanoparticles as the primary catalytic active sites. The results may contribute to the development of high-performance catalytic ozone oxidation catalysts for ammonia nitrogen.