Plasmonic photocatalysis has recently facilitated the rapid progress in enhancing photocatalytic efficiency under visible light irradiation, increasing the prospect of using various light sources for environmental and energy applications such as wastewater treatment, water splitting and carbon dioxide reduction. In fact, coupled with noble metal nanoparticle and semiconductors, it has been successfully employed in various fields including artificial photosynthesis. Surface plasmon resonance (SPR) is a unique optical property which occurs on rare noble metals (gold, silver, and Copper) under light irradiation; however, the low-reserve and high-cost noble metals restrict their practical utilization in plasmonic photocatalysis.
Consequently, researchers have focused on improving some low-cost nonmetallic materials that exhibit the SPR phenomenon, through doping. In particular, WO3–x, MoO3–x and Cu2–xS have been reported to being more attractive candidates owing to their facile synthesis and strong SPR absorption in visible–near-infrared region.
One strategy of stabilizing nonmetallic plasmonic photocatalysts involves marrying them with semiconductors for constructing heterostructures. However, the construction of heterostructures with fast and continuous photoelectron injection is still a challenging endeavor. In this context, tungsten oxides with defects have been recently reported as photocatalysts for CO2 reduction, unfortunately, the effect of their SPR on CO2 reduction is still unclear and therefore ought to be studied.
In a recent publication, Associate professor Zaizhu Lou, Juan Li, Dr. Xianguang Yang and Professor Baojun Li from the Jinan University, together with Dr. Peng Zhang from the Pohang University of Science and Technology and Professor Baibiao Huang from the Shandong University, China, presented a study where they focused on constructing nonmetallic plasmonic heterostructure TiO2-mesocrystals/WO3−x-nanowires by coupling mesoporous crystal TiO2 and plasmonic WO3−x through a solvothermal procedure. Their work is currently published in the research journal, Advanced Functional Material.
In brief, nonmetallic plasmonic WO3−x nanowires (WO3−x-NWs) were loaded on the mesoporous crystal structure TiO2 (TiO2-MCs), by one-step solvothermal process, following which the heterostructures (TiO2-MCs/WO3−x-NWs) were obtained as plasmonic photocatalysts for hydrogen generation and CO2 reduction. Various characterization techniques were used, including: XRD, SEM, TEM and UV–vis micro-spectrophotometry – among others.
The authors observed that continuous photoelectron injection from TiO2 to WO3−x increased the free carrier density of WO3−x, leading to stable SPR absorption and hot electron generation for plasmonic photocatalysis, as was demonstrated by the PL study. Additionally, Photocatalytic results illustrated the dominant role of hot electrons of WO3−x for hydrogen generation under visible light irradiation.
In summary, TiO2-MCs/WO3−x-NWs were constructed by coupling mesoporous crystal TiO2-MCs and nonmetallic plasmonic WO3−x nanowires through one-step solvothermal procedure in a bid to stabilize SPR of nonmetallic plasmonic WO3−x. Generally, the study demonstrated that photoelectron injection from TiO2 to WO3−x, and the nonmetallic SPR of WO3−x plays a great role in the highly selective methane generation during CO2 photoreduction. Altogether, it was seen that the synergetic effects of photoelectron injection and nonmetallic SPR induced plasmonic hot electrons contributed to highly selective methane generation under UV–vis light irradiation.
Zaizhu Lou, Peng Zhang, Juan Li, Xianguang Yang, Baibiao Huang, Baojun Li. Plasmonic Heterostructure TiO2-MCs/WO3−x-NWs with Continuous Photoelectron Injection Boosting Hot Electron for Methane Generation. Advanced Functional Materials 2019, 1808696.