期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 117, 期 13, 页码 6516-6524出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp312613r
关键词
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资金
- National Science Council of Taiwan [101-2221-E-006-243-MY3, 101-2221-E-006-225-MY3, 102-3113-P-006-012, 102-3113-E-006-002]
- National Cheng Kung University
Graphite oxide (GO) synthesized from the oxidation of graphite powders exhibits p-type conductivity and is active in photocatalytic H-2 evolution from water decomposition. The p-type conductivity hinders hole transfer for water oxidation and suppresses O-2 evolution. Treating GO with NH3 gas at room temperature tunes the electronic structure by introducing amino and amide groups to its surface. The ammonia-modified GO (NGO) exhibits n-type conductivity in photoelectrochemical analysis and has a narrower optical band gap than GO. Electrochemical analysis attributes the band gap reduction to a negative shift of the valence band. An NGO-film electrode exhibits a substantially higher incident photo-to-current efficiency in the visible light region than a GO electrode. Photoluminescence analyses demonstrate the above-edge emission characteristic of GO and NGO. NH3 treatment enhances the emission by removing nonirradiative epoxy and carboxyl sites on the GO. In half-reaction tests of water decomposition, NGO effectively catalyzes O-2 evolution in an aqueous AgNO3 solution under mercury-lamp irradiation, whereas GO is inactive. NGO also effectively catalyzes H-2 evolution in an aqueous methanol solution but shows less activity than GO. Under illumination with visible light (lambda > 420 nm), NGO simultaneously catalyzes H-2 and O-2 evolutions, but with a H-2/O-2 molar ratio below 2. The n-type conductivity of NGO may hinder electron transfer and form peroxide species instead of H-2 molecules. This study demonstrates that the functionality engineering of GO is a promising technique to synthesize an industrially scalable photocatalyst for overall water splitting.
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