Abstract
Because of their peculiar nitrogen-rich structure, carbon nitrides are convenient polydentate ligands for designing single atom-dispersed photocatalysts. However, the relation between catalysts’ textural properties and their photophysical–photocatalytic properties is rarely elaborated. Herein, we report the preparation and characterization of a series of single-atom heterogeneous catalysts featuring highly dispersed Ag and Cu species on mesoporous graphitic C3N4. We show that adjustment of materials textural properties and therefore metal single-atom coordination mode enables ligand-to-metal charge transfer (LMCT) or ligand-to-metal-to-ligand charge transfer (LMLCT), properties that were long speculated in single-atom catalysis but never observed. We employ the developed materials in the degradation of organic pollutants under irradiation with visible light. Kinetic investigations under flow conditions show that single atoms of Ag and Cu decrease the number of toxic organic fragmentation products while leading to a higher selectivity toward full degradation. The results correlate with the selected mode of charge transfer in the designed photocatalysts and provide a new understanding of how the local environment of a single-atom catalyst affects the surface structure and reactivity. The concepts can be exploited further to rationally design and optimize other single-atom materials.
Highlights
Single-atom catalysts (SACs) have recently emerged as a new class of materials bridging the gap between the homogeneous and heterogeneous catalysis worlds.[1−3] These materials represent the utmost utilization of precious metals while offering more facile preparation, handling, and recovery compared to traditional catalytic systems.[4,5]
We demonstrate that photocatalyst design involving atomically dispersed metal species at mesoporous graphitic carbon nitride enables control and observation of ligand−metal charge transfer
Removal of the template by treatment with (NH4)HF2 gives the mesoporous structure of the material with a high surface area, i.e., the template replica
Summary
Single-atom catalysts (SACs) have recently emerged as a new class of materials bridging the gap between the homogeneous and heterogeneous catalysis worlds.[1−3] These materials represent the utmost utilization of precious metals while offering more facile preparation, handling, and recovery compared to traditional catalytic systems.[4,5] Due to the unsaturated coordination of the active center as well as quantum and support effects, over the past few years, SACs were improved to show extraordinary catalytic activity and selectivity toward specific products in important transformations such as hydrogenation, oxidation, carbon−carbon coupling, water-gas shift, and electrosynthesis.[6−9] the scalable construction and application of SACs have emerged as key topics important both for the academic environment and for the industry.[10−12]Deposition of stable single atoms on nitrogen-framed pores of carbon and carbon nitrides is perhaps the most successful strategy existing today to prepare SACs.[13−15] The polymeric semiconductor graphitic carbon nitride (C3N4) is, an optimal scaffold due to its nitrogen-rich structure.
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