The overall water splitting by solar-energy-driven photocatalysts is a crucial issue as a solution for today’s mass scale energy and environmental problems. The activity of those photocatalysts is to be improved by  their surfaces where the water splitting reactions take place. This time we report two useful tips to enhance the efficiency of LaTiO₂N, an important candidate oxynitride for photocatalysis.  One is to clean off the debris and defects on the particle surface. Domen et al.¹ reported a brief, effective aqua regia treatment was in removing surface defects of LaTiO₂N. However, aqua regia accompanies drawbacks of its severe reactivity. We need quick, elaborate washing to stop etching of the oxynitride in a contolled manner, and we need to isolate the aqua regia’s corrosive fume from the environment. More convenient and effective altanative surface treatment reagents are wanted in this sense. Two is to modify the surface of LaTiO₂N with CoO_x nanoparticles as so-called co-catalysts.  The co-catalysts are supposed to assist the separation of photogenerated charges as well as promotion of surface reactions to evolve O₂. CoO_x nanoparticles, composed of earth abundant elements, are conventionally loaded by the liquid impregnation/calcination method.²  However the process of calcination on LaTiO₂N brings about a complexity of heating in NH₃ flow to avoid surface oxidation, simultaneously introducing chances of CoO_x particle sintering and metallization. Our solutions for there problems are by rinsing in aqueous poly(4-styrenesulfonic acid) (PSS) solution followed by loading CoO_x with a microwave assisted deposition. Static treatment of the LaTiO₂N powder in PSS solution for 17 hours and microwave assisted one-pot loading of CoO_x with Co(NH₃)₃Cl₃ in Eyleneglycol solution, prior to fabrication into an electrode, increased the photoanodic current up to 8.9 mA cm^-2 at 1.23 V_RHE, which is 3 times larger than that without these reforming. We also confirmed that LaTiO₂N was treated with PSS solution conveniently and care-freely in comparison with etching in aqua regia, and cocatalyst was coated throughout the surface of LaTiO₂N particle by using microwave quick heating.

1. M. Matsukawa,  R. Ishikawa, T. Hisatomi, Y. Moriya, N. Shibata, J. Kubota, Y. Ikuhara and K. Domen, Nano Lett. 2014, 14, 1038−1041.

2. F. Zhang, A. Yamakata, K. Maeda, Y. Moriya, T. Takata, J. Kubota, K. Teshima,  S. Oishi and K. Domen, J. Am. Chem. Soc., 2012, 134, 8348−8351.