KCl flux-induced growth of isometric crystals of cadmium-containing early transition-metal (Ti4+, Nb5+, and Ta5+) oxides and nitridability to form their (oxy)nitride derivatives under an NH3 atmosphere for water splitting application

Mirabbos Hojamberdiev, Hajime Wagata, Kunio Yubuta, Kenta Kawashima, Junie Jhon M. Vequizo, Akira Yamakata, Shuji Oishi, Kazunari Domen, Katsuya Teshima

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23 Citations (Scopus)

Abstract

In this study, we have attempted to experimentally validate the results of previous theoretical calculations predicting the possible formation of the CdTiO3-xNy, CdNbO2N, and CdTaO2N phases by applying conventional one- and two-step fabrication methods under an NH3 flow. For the two-step method, CdTiO3, Cd2Nb2O7, and Cd2Ta2O7 crystals were first grown by a KCl flux method, and the effects of solute concentration and cooling rate on the crystal growth were studied. The formability of their (oxy)nitride derivatives was investigated by changing the nitridation temperature (750-950°C) and time (1-10h) of oxide precursors. It was found that the CdTiO3-xNy, CdNbO2N, and CdTaO2N phases cannot be formed by the applied conventional methods due to the low volatilization temperature of cadmium and the susceptibility of titanium and niobium to reduction under an NH3 atmosphere. Under high-temperature NH3 atmosphere, only Cd2Ta2O7 was fully converted to single-phase Ta3N5. The results from the photocatalytic O2 evolution test of bare and CoOx-loaded Ta3N5 crystalline structures, converted from Cd2Ta2O7 (Cd-Ta3N5) and Na2CO3-treated Ta2O5 (Na-Ta3N5) and Cd2Ta2O7 (Na-Cd-Ta3N5) crystals by nitridation at 850°C for 20h under an NH3 flow, revealed that the CoOx-loaded Ta3N5 showed more than two times higher O2 evolution rate (655μmol), whereas the CoOx-loaded Cd-Ta3N5 and Na-Cd-Ta3N5 exhibited nearly four (501μmol) and three (422μmol) times higher O2 evolution rates at 5h compared with their bare counterparts. An improved photocatalytic activity for O2 evolution is related to the higher density of nucleation centers of CoOx nanoparticles in the form of dangling bonds in porous Ta3N5 structures and long-lived photogenerated holes, as attested by time-resolved absorption spectroscopy.

Original languageEnglish
Pages (from-to)626-635
Number of pages10
JournalApplied Catalysis B: Environmental
Volume182
DOIs
Publication statusPublished - 2016 Mar 1

Keywords

  • Flux growth
  • Oxynitride
  • Transition metal oxides
  • Visible light photocatalyst
  • Water splitting

ASJC Scopus subject areas

  • Catalysis
  • Environmental Science(all)
  • Process Chemistry and Technology

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