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It is of great importance to explore and achieve a more effective approach toward the controllable synthesis of singleatom-based photocatalysts with high metal content and long-term durability. Herein, single-atom platinum (Pt) with high loading content anchored on the pore walls of two-dimensional βketoenamine-linked covalent organic frameworks (TpPa-1-COF) is presented. Aided by advanced characterization techniques of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, it has been demonstrated that atomically dispersed Pt is formed on the TpPa-1-COF support through a six-coordinated C 3 N−Pt−Cl 2 species. The optimized Pt 1 @TpPa-1 catalyst exhibits a high photocatalytic H 2 evolution rate of 719 μmol g −1 h −1 under visible-light irradiation, a high actual Pt loading content of 0.72 wt %, and a large turnover frequency (TOF) of 19.5 h −1 , with activity equivalent to 3.9 and 48 times higher than those of Pt nanoparticles/TpPa-1 and bare TpPa-1, respectively. The improved photocatalytic performance for H 2 evolution is ascribed to the effective photogenerated charge separation and migration and well-dispersed active sites of single-atom Pt. Moreover, density functional theory (DFT) calculations further reveal the role of Pt single atoms in the enhanced photocatalytic activity for H 2 evolution. Overall, this work provides some inspiration for designing single-atom-based photocatalysts with outstanding stability and efficiency using COFs as the support.

A new type of two-dimensional layered semiconductor with weak electrostatic but not van der Waals interlayer interactions, Bi2O2Se, has been recently synthesized, which shown excellent air stability and ultrahigh carrier mobility. Herein, we combined theoretical and experimental approaches to study the Raman spectra of Bi2O2Se and related bismuth oxychalcogenides (Bi2O2Te and Bi2O2S). The experimental peaks lie at 160 cm −1 in Bi2O2Se and at 147 cm −1 and 340 cm −1 in Bi2O2Te. They were fully consistent with the calculated results (159.89 cm −1 , 147.48cm −1 and 340.33 cm −1 ), and were assigned to the out-of-plane A1g, A1g and B1g modes, respectively. Bi2O2S was predicted to have more Raman-active modes due to its lower symmetry.The shift of the predicted frequencies of Raman active modes was also found to get softened as the interlayer interaction decreases from bulk to monolayer Bi2O2Se and Bi2O2Te. To reveal the strain effects on the Raman shifts, a universal theoretical equation was established based on the symmetry of Bi2O2Se and Bi2O2Te. It was predicted that the doubly degenerate modes split under in-plane uniaxial/shear strains. Under a rotated uniaxial strain, the changes of Raman shifts are anisotropic for degenerate modes although Bi2O2Se and Bi2O2Te were usually regarded as isotropic systems similar to graphene. This implies a novel method to identify the crystallographic orientation from Raman spectra under strain. These results have important consequences for the incorporation of 2D Bismuth oxychalcogenides into nanoelectronic devices.