(Invited) Designing Hybrid Nanostructures for Enhancing Photon Harvest in Photocatalysis

Harvesting photons at longer wavelengths in the visible and near infrared (NIR) ranges represents an attractive approach to improve the power conversion efficiency of photocatalysis and photovoltaics. Plasmonic and upconverting nanostructures are promising in boosting and broadening photon harvesting and have been recently explored for enhancing the efficiency of solar cells and photocatalysis. Herein, I will present some of our most recent development in plasmonic and upconverting nanostructures and their applications in photocatalysis and solar cells and [1-5]. One example is shown in Figure 1. It illustrates the synthesis of novel, plasmonic Au nanoparticle decorated NaYF4:Yb3+, Er3+, Tm3+ (denoted as NYF) – core @ porous-TiO2-shell microspheres, which can harvest solar photons over a wide spectral range from ultraviolet to NIR for efficient photocatalysis, significantly better than the benchmark Degussa P25 [1]. The enhanced activity is attributed to synergistic effects from nanocomponents arranged into the nanostructured architecture in such a way that favours the efficient charge/energy transfer among nanocomponents and largely reduced charge recombination. Recently, an even simple method was developed for combing Au nanoparticles and NYF microspheres with two-dimensional graphitic C3N4 (g-C3N4) nanosheets (Au-NYF/g-C3N4) [2]. The simple one-step synthesis of NYF in the presence of g-C3N4, which was not previously reported in the literature, leads to both high NYF yield and high coupling efficiency between NYF and g-C3N4. The Au-NYF/g-C3N4 structure exhibits excellent stability, wide photoresponse from the ultraviolet, to visible and NIR regions, and prominently enhanced photocatalytic activities compared with the plain g-C3N4 sample in the degradation of methyl orange. Very recently, by constructing a complete comparative framework, based on the similar catalysts having alloy synergistic effect or plasmonic effect, or both, we compared the plasmonic and synergistic effects. It helps answers an important, yet not previously addressed question: synergistic and plasmonic effects, which can make more important contribution to photocatalysis? On the other hand, quantum dots are also promising for photon harvesting because of their size-tunable bandgaps, even in the NIR range. I may briefly introduce the use of quantum dots in photocatalysis and solar cells [6]. References [1] Z. Xu, M. Quintanilla, F. Vetrone, A. O. Govorov, M. Chaker and D. Ma*, Adv. Funct. Mat., 2015, 25, 2950 ( Front Cover ). [2] Q. Zhang, J. Deng, Z. Xu, M. Chaker, D. Ma, ACS Catalysis, 2017, 7, 6225. [3] Z. Xu, Md G. Kibria, B. AlOtaibi, P. N. Duchesned, L. V. Besteiro, Y. Gao, Q. Zhang, Z. Mi, P. Zhang, A. O. Govorov, L. Mai, M. Chaker, D. Ma, Applied Catalysis B: Environmental, 2017, in press. [4] H. Liang, D. Rossouw, H. Zhao, S. K. Cushing, H. Shi, A. Korinek, H. Xu, F. Rosei, W. Wang, N. Wu, G. A. Botton, and D. Ma,* J. Am. Chem. Soc., 2013, 135, 9616. [5] H. Liang, H. Zhao, D. Rossouw, W. Wang, H. Xu, G. A. Botton, D. Ma, Chem. Mater. 2012, 24, 2339. [6] I. Ka, B. Gonfa, V. Le Borgne, D. Ma*, M. A. El Khakani*, Adv. Funct. Mater., 2014, 24, 4042 ( Inside Back Cover ).