Effective Cascade Modulation of Charge-Carrier Kinetics in the Well-Designed Multi-Component Nanofiber System for Highly-Efficient Photocatalytic Hydrogen Generation
Na Lu,Xuedong Jing,Yao Xu,Wei Lu,Kuichao Liu,Zhenyi Zhang.Effective Cascade Modulation of Charge-Carrier Kinetics in the Well-Designed Multi-Component Nanofiber System for Highly-Efficient Photocatalytic Hydrogen Generation[J].Acta Physico-Chimica Sinica,2023,39(4):2207045-0.
Key Laboratory of New Energy and Rare Earth Resource Utilization of State Ethnic Affairs Commission; Key Laboratory of Photosensitive Materials and Devices of Liaoning Province, School of Physics and Materials Engineering, Dalian Minzu University, Dalian 116600, Liaoning Province, China
Abstract:
The photocatalytic reduction of water to hydrogen (H2) over semiconductors potentially offers an economic way to alleviate the global energy crisis and environmental pollution. Optimal modulation of charge-carrier kinetics is of great importance for enhancing the photocatalytic activity of semiconductors for reducing water to green H2. The design and manufacture of semiconductor-based heterostructure systems have emerged as promising tactics for modulating charge-carrier kinetics based on sensitization either via the semiconductor heterojunction effect or localized surface plasmon resonance. However, the cascade modulation of charge-carrier kinetics is still difficult to achieve through rationally coupling the abovementioned sensitization processes in well-designed heterostructures for highly-efficient photocatalytic H2 generation. In this study, we developed a novel quaternary hetero-component nanofibers (HNFs) system by assembling plasmonic Ag nanoparticles (NPs) and two different semiconductors of Ag2S NPs and g-C3N4 nanosheets (NSs) into the electrospun TiO2 nanofibers (NFs) viain situ oxidation (for g-C3N4 exfoliation and Ag2S) and reduction (for Ag) reactions. By combining time-resolved photoluminescence spectroscopy, three-dimensional finite-difference-time-domain simulation, and control experiments, we found that the overlapping absorption peak of plasmonic Ag NPs and g-C3N4 NSs could induce plasmonic resonant energy transfer from the Ag NPs to the neighboring g-C3N4, thereby improving the generation of photoinduced charge carriers of g-C3N4 in the quaternary HNFs system. Simultaneously, plasmonic hot electrons could be generated on the Ag NPs and transferred to the near-by hetero-components of TiO2, g-C3N4, and Ag2S, to boost the generation and separation of photoinduced charge carriers in the system. Furthermore, the energy band structure at the g-C3N4/TiO2 hetero-interface belongs to the "type II" heterojunction, while the energy band structure at the TiO2/Ag2S hetero-interface can be classified as a "type I" heterojunction. This way, the successive "energy band step" could be constructed at the g-C3N4/TiO2/Ag2S hetero-interface, resulting in improved separation and migration of photoinduced charge carriers through the transfer of photoinduced electrons from g-C3N4 to Ag2S across TiO2. Thus, the plasmonic resonant energy transfer, hot electron transfer, and successive energy-band-step-induced charge separation processes were integrated into the as-synthesized quaternary Ag/Ag2S/g-C3N4/TiO2 HNFs system, thereby achieving the effective cascade modulation of the generation, separation, and migration of photoinduced charge carriers. As such, the photocatalytic H2-generation rate of the optimal Ag/Ag2S/g-C3N4/TiO2 HNFs system was higher than that of the mechanically mixed TiO2 NFs, g-C3N4 NSs, Ag NPs, and Ag2S NPs, with the same amounts as the optimal Ag/Ag2S/g-C3N4/TiO2 HNFs photocatalyst, by approximately 9-fold under simulated sunlight irradiation. This interesting cascade modulation of charge-carrier kinetics might open new avenues for the development of highly active semiconductor-based heterostructure system for solar-to-fuels conversion.
