Mechanistic Insight on the Formation of GaN:ZnO Solid Solution from Zn–Ga Layered Double Hydroxide Using Urea as the Nitriding Agent
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A solid solution of GaN and ZnO (GaN:ZnO) is promising as a photocatalyst for visible light-driven overall water splitting to produce H2. However, several obstacles still exist in the conventional preparation procedure of GaN:ZnO. For example, the atomic distributions of Zn and Ga are non-uniform in GaN:ZnO when a mixture of the metal oxides, i.e., Ga2O3 and ZnO, is used as a precursor. In addition, GaN:ZnO is generally prepared under harmful NH3 flow for long durations at high temperatures. Here, a facile synthesis of GaN:ZnO with homogeneous atomic composition via a simple and safe procedure is reported. A layered double hydroxide (LDH) containing Zn2+ and Ga3+ was used to increase the uniformity of the atomic distributions of Zn and Ga in GaN:ZnO. We employed urea as a nitriding agent instead of gaseous NH3 to increase the safety of the reaction. Through the optimization of reaction conditions such as heattreatment temperature and content of urea, single-phase GaN:ZnO was successfully obtained. In addition, the nitridation mechanism using urea was investigated in detail. NH3 released from the thermal decomposition of urea did not directly nitride the LDH precursor. X-ray absorption and infrared spectroscopies revealed that Zn(CN2)-like intermediate species were generated at the middle temperature range and Ga–N bonds formed at high temperature along with dissociation of CO and CO2.
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This work was supported by JSPS KAKENHI Grant Number JP16H06438, JP16H06441, JP17H05483, JP17H03392. This work was partly supported by the Center for Functional Nano Oxide at Hiroshima University. The synchrotron radiation experiments were performed at the BL01B1 beamline of SPring-8 with the approval of the Japan Synchrotron Radiation Research 32 Institute (JASRI) (Proposal No. 2017B1043 and 2018A1749).
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in 'Inorganic Chemistry', copyright c American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.8b02498.
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