Self-Supporting 3D Carbon Nitride with Tunable n → π* Electronic Transition for Enhanced Solar Hydrogen Production.

Self-supporting 3D (SSD) carbon nitrides (UCN-X, X = 600-690; where X represents the pyrolytic temperature) consisting of curved layers, with plenty of wrinkles and enlarged size, are synthesized via a facile stepwise pyrolytic strategy. Such unique features of the SSD structure exhibiting dramatically improved charge mobility, extended π-conjugated aromatic system, and partial distortion of heptazine-based skeleton can not only keep the easier activation of the intrinsic π â†’  π* electronic transition but also awaken the n → π* electronic transition in carbon nitride. The n → π* electronic transition of UCN-X can be controllably tuned through changing the pyrolytic temperature, which can greatly extend the photoresponse range to 600 nm. More importantly, the change regularity of H2 evolution rates is highly positive, correlated with the change tendency of n → π* electronic transition in UCN-X, suggesting the positive contribution of n → π* electronic transition to enhancing photocatalytic activity. The UCN-670, with optimal structural and optical properties, presents enhanced H2 evolution rate up to 9230 µmol g-1 h-1 (Pt 1.1 wt%). This work realizes the synergistic optimization of optical absorption and exciton dissociation via fabricating an SSD structure. It offers a new strategy for the development of novel carbon nitride materials for efficient photocatalytic reactions.

Silver Single-Atom Catalyst for Efficient Electrochemical CO2 Reduction Synthesized from Thermal Transformation and Surface Reconstruction.

We report an Ag1 single-atom catalyst (Ag1 /MnO2 ), which was synthesized from thermal transformation of Ag nanoparticles (NPs) and surface reconstruction of MnO2 . The evolution process of Ag NPs to single atoms is firstly revealed by various techniques, including in situ ETEM, in situ XRD and DFT calculations. The temperature-induced surface reconstruction process from the MnO2 (211) to (310) lattice plane is critical to firmly confine the existing surface of Ag single atoms; that is, the thermal treatment and surface reconstruction of MnO2 is the driving force for the formation of single Ag atoms. The as-obtained Ag1 /MnO2 achieved 95.7 % Faradic efficiency at -0.85 V vs. RHE, and coupled with long-term stability for electrochemical CO2 reduction reaction (CO2 RR). DFT calculations indicated single Ag sites possessed high electronic density close to Fermi Level and could act exclusively as the active sites in the CO2 RR. As a result, the Ag1 /MnO2 catalyst demonstrated remarkable performance for the CO2 RR, far surpassing the conventional Ag nanosized catalyst (AgNP /MnO2 ) and other reported Ag-based catalysts.

High-Density Ultra-small Clusters and Single-Atom Fe Sites Embedded in Graphitic Carbon Nitride (g-C3N4) for Highly Efficient Catalytic Advanced Oxidation Processes.

Ultra-small metal clusters have attracted great attention owing to their superior catalytic performance and extensive application in heterogeneous catalysis. However, the synthesis of high-density metal clusters is very challenging due to their facile aggregation. Herein, one-step pyrolysis was used to synthesize ultra-small clusters and single-atom Fe sites embedded in graphitic carbon nitride with high density (iron loading up to 18.2 wt %), evidenced by high-angle annular dark field-scanning transmission electron microscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mössbauer spectroscopy. The catalysts exhibit enhanced activity and stability in degrading various organic samples in advanced oxidation processes. The drastically increased metal site density and stability provide useful insights into the design and synthesis of cluster catalysts for practical application in catalytic oxidation reactions.