Advances of Various Heterogeneous Structure Types in Molecular Junction Systems and Their Charge Transport Properties

Molecular Heptazine-Triazine Junction over Carbon Nitride Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

Revealing the photocatalytic mechanism between various junctions and catalytic activities has become a hotspot in photocatalytic systems. Herein, an internal molecular heptazine/triazine (H/T) junction in crystalline carbon nitride (HTCN) is constructed and devoted to selective two-electron oxygen reduction reaction (2e- ORR) for efficient hydrogen peroxide (H2 O2 ) production. In-situ X-ray diffraction spectra under various temperatures authenticate the successful formation of molecular H/T junction in HTCN during the calcining process rather than physically mixing. The increased surface photovoltage and transient photovoltage signals, and the decreased exciton binding energy undoubtably elucidate that an obvious increasement of carrier density and diffusion capability of photogenerated electrons are realized over HTCN. Additionally, the analyses of in situ photoirradiated Kelvin probe force microscopy and femto-second transient absorption spectra reveal the successful construction of the strong internal built-in-electric field and the existence of the majority of long-lived shallow trapped electrons associated with molecular H/T junction over HTCN, respectively. Benefiting from these, the photocatalytic results exhibit an incredible improvement (96.5-fold) for H2 O2 production. This novel work provides a comprehensive understanding of the long-lived reactive charges in molecular H/T junctions for strengthening the driving-force for photocatalytic H2 O2 production, which opens potential applications for enhancing PCN-based photocatalytic redox reactions.

Plasma Ag-Modified α-Fe2O3/g-C3N4 Self-Assembled S-Scheme Heterojunctions with Enhanced Photothermal-Photocatalytic-Fenton Performances

Low spectral utilization and charge carrier compounding limit the application of photocatalysis in energy conversion and environmental purification, and the rational construction of heterojunction is a promising strategy to break this bottleneck. Herein, we prepared surface-engineered plasma Ag-modified α-Fe₂O₃/g-C₃N₄ S-Scheme heterojunction photothermal catalysts by electrostatic self-assembly and light deposition strategy. The local surface plasmon resonance effect induced by Ag nanoparticles broadens the spectral response region and produces significant photothermal effects. The temperature of Ag/α-Fe₂O₃/g-C₃N₄ powder is increased to 173 °C with irradiation for 90 s, ~3.2 times higher than that of the original g-C₃N₄. The formation of 2D/2D structured S-Scheme heterojunction promotes rapid electron-hole transfer and spatial separation. Ternary heterojunction construction leads to significant enhancement of photocatalytic performance of Ag/α-Fe₂O₃/g-C₃N₄, the H₂ photocatalytic generation rate up to 3125.62 µmol g^-1 h^-1, which is eight times higher than original g-C₃N₄, and the photocatalytic degradation rate of tetracycline to reach 93.6%. This thermally assisted photocatalysis strategy improves the spectral utilization of conventional photocatalytic processes and provides new ideas for the practical application of photocatalysis in energy conversion and environmental purification.