Photoluminescence Quenching in Single-Layer MoS₂ via Oxygen Plasma Treatment

By creating defects via oxygen plasma treatment, we demonstrate optical properties variation of single-layer MoS₂. We found that, with increasing plasma exposure time, the photoluminescence (PL) evolves from very high intensity to complete quenching, accompanied by gradual reduction and broadening of MoS₂ Raman modes, indicative of distortion of the MoS₂ lattice after oxygen bombardment. X-ray photoelectron spectroscopy study shows the appearance of the Mo⁶⁺ peak, suggesting the creation of MoO₃ disordered regions in the MoS₂ flake. Finally, using band structure calculations, we demonstrate that the creation of MoO₃ disordered domains upon exposure to oxygen plasma leads to a direct-to-indirect bandgap transition in single-layer MoS₂, which explains the observed PL quenching

Low-Temperature and Gram-Scale Synthesis of Two-Dimensional Fe–N–C Carbon Sheets for Robust Electrochemical Oxygen Reduction Reaction

The Fe–N–C-based carbon materials, which are generally formed by high-temperature annealing, have been highlighted as a promising alternative to expensive Pt electrocatalysts for oxygen reduction reaction. However, the delicate formation of active sites remains an issue because of decomposition and transformation of the macrocycle during heat treatment. Accordingly, we developed a low-temperature and gram-scale approach to synthesizing iron phthalocyanine (Pc)-embedded two-dimensional carbon sheets by annealing at 450 °C. The low-temperature annealing process, which is motivated by the synthesis of carbon nanoribbons, is suitable for maintaining the Fe–N–C structure while enhancing coupling with carbon. Our two-dimensional carbon sheets show higher ORR activity than commercial Pt catalyst in alkaline media. Furthermore, the feasibility of real application to alkaline membrane electrolyte fuel cell is verified by superior volumetric current density. In durability point of view, the initial activity is retained up to 3000 potential cycles without appreciable activity loss; this excellent performance is attributed to the structural stabilization and electron donation from the carbon sheet, which occurs via strong electronic coupling. We believe that this low-temperature and large-scale synthesis of a carbon structure will provide new possibilities for the development of electrochemical energy applications

Hollow Microporous Organic Networks Bearing Triphenylamines and Anthraquinones: Diffusion Pathway Effect in Visible Light-Driven Oxidative Coupling of Benzylamines

Hollow microporous organic networks were prepared by using silica spheres as the template and tris­(4-ethynylphenyl)­amine and 2,6-diiodo-9,10-anthraquinone as the building blocks for the Sonogashira coupling. The resultant materials bearing triphenylamine and anthraquinone moieties showed efficient visible light absorption and catalytic activities in the photochemical oxidative coupling of benzylamines. Through the comparison studies of hollow and nonhollow catalytic materials, the diffusion pathway effect of the substrates was clearly observed in the photochemical conversion of benzylamines

Microporous Organic Network Hollow Spheres: Useful Templates for Nanoparticulate Co₃O₄ Hollow Oxidation Catalysts

Hollow microporous organic networks (<b>H-MON</b>s) were prepared by a template method using silica spheres. The shell thickness was delicately controlled by changing the synthetic conditions. The <b>H-MON</b>s were used as a template for the synthesis of nanoparticulate Co₃O₄ hollows which showed excellent catalytic performance in H₂O₂ oxidation