Kuei-Hsien Chen

Graphitic carbon nitride (CN) has emerged as a highly promising material in the photocatalysis field. However, its bulk structure suffers from a lack of active sites, limiting its practical application. Herein, a boron-doped CN (BCN) was prepared by a green gas-blowing-assisted thermal polymerization and then subjected to different exfoliation processes in order to delaminate the layered structure and tune the surface-active sites. A thorough comparative study shows that thermal exfoliation creates unsaturated nitrogen sites and induces the formation of interconnected layers that act as an electron diffusion channel for better charge transport. Furthermore, the thermally exfoliated BCN is rich in structural disorders that serve as dissociation defects for photoinduced charge carriers with a low exciton binding energy of 27 meV. Experimental results supported by theoretical calculations show that the nitrogen adjacent to boron is activated by the surrounding surface amino groups and the perforated texture to serve as an active adsorption site towards CO2 and H2O. Consequently, the exfoliated BCN acts as an outstanding bifunctional photocatalyst towards CO2 reduction into CO (40.41 μmol g−1 h−1) and prominent hydrogen evolution (4740 μmol g−1 h−1, 12.2% apparent quantum yield (AQY)).

One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO2 molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni-nanocluster loaded black TiO2 (Ni/TiO2[Vo]) with built-in dual active sites for selective photocatalytic CO2 conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO2 binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.

Layered MoS2 is considered as one of the most promising two-dimensional photocatalytic materials for hydrogen evolution and water splitting; however, the electronic structure at the MoS2-liquid interface is so far insufficiently resolved. Measuring and understanding the band offset at the surfaces of MoS2 are crucial for understanding catalytic reactions and to achieve further improvements in performance. Herein, the heterogeneous charge transfer behavior of MoS2 flakes of various layer numbers and sizes is addressed with high spatial resolution in organic solutions using the ferrocene/ferrocenium (Fc/Fc+) redox pair as a probe in near-field scanning electrochemical microscopy, i.e. in close nm probe-sample proximity. Redox mapping reveals an area and layer dependent reactivity for MoS2 with a detailed insight into the local processes as band offset and confinement of the faradaic current obtained. In combination with additional characterization methods, we deduce a band alignment occurring at the liquid-solid interface.

Abstract Application of lasers is omnipresent in modern-day technology. However, preparation of a lasing device usually requires sophisticated design of the materials and is costly, which may limit the suitable choice of materials and the lasing wavelengths. Random lasers, on the other hand, can circumvent the aforementioned shortcomings with simpler fabrication process, lower processing cost, material flexibility for any lasing wavelengths with lower lasing threshold, providing a roadmap for the design of super-bright lighting, displays, Li-Fi, etc. In this work, ultralow-threshold random laser action from semiconductor nanoparticles assisted by a highly porous vertical-graphene-nanowalls (GNWs) network is demonstrated. The GNWs embedded by the nanomaterials produce a suitable cavity for trapping the optical photons with semiconductor nanomaterials acting as the gain medium. The observed laser action shows ultralow values of threshold energy density ≈10 nJ cm?2 due to the strong photon trapping within the GNWs. The threshold pump fluence can be further lowered to ≈1 nJ cm?2 by coating Ag/SiO2 upon the GNWs due to the combined effect of photon trapping and strong plasmonic enhancement. In view of the growing demand of functional materials and novel technologies, this work provides an important step toward realization of high-performance optoelectronic devices.