▎ 摘　　要

Substrate-supported single atoms have been of interest in many fields, such as magnetism, semiconductors, catalysis, and others. As far as single-atom catalysts (such as Pt, Pd, and Au atoms) are concerned, the substrates play vital roles for the stability and activity of single-atom states. A carbon-based two-dimensional material (such as graphene) is one sort of potential substrates for single-atom catalysis. Recently, C3N, as a new carbon-based two-dimensional material, has been synthesized and attracted broad attention. We use single-atom Pt load as a probe to compare the differences of graphene and C3N substrates. It is found that C3N substrates have interesting physicochemical properties and significant superiorities. On graphene, the aggregation of Pt atoms easily occurs. However, on C3N, Pt can remain separated from each other with a single-atom state even at a high temperature. On graphene, single-atom Pt is always positively charged (Pt+). In contrast, both Pt- and Pt+ are observed on perfect and defective C3N, respectively, which significantly affect molecule adsorption. Our calculations suggest that different gas molecules prefer different charge states of Pt. Additionally, Pt-modified defective graphene and C3N are confirmed to have different magnetism. The former is paramagnetic; the latter, conversely, has nonzero magnetic moment. These are instructive to design single-atom nanomaterials and nanodevices.