Qingping Wu,Yao Cheng,Feng Huang,Xiao Li,Xiangshui Cui,Ju Xu,Yuansheng Wang
Atomic defects (e.g., Ti 3+ , oxygen vacancies) have been intenstively investigated for modifying TiO 2 in order to reach visible light active photocatalytic H 2 production. However, the atomic defects within TiO 2 could easily act as photo-generated charge-carrier recombination centers, resulting in relatively low H 2 conversion efficiency. In this paper, semicrystalline yellow TiO 2 nanoparticles rich of superoxide ions are new synthesized by a simple aqueous solution method. Instead of introducing atomic defects, we show for the first time that catalytic performance can also be significantly improved via in-situ creating lattice O O bonds within metastable semicrystalline TiO 2 . The synthesized semicrystalline yellow TiO 2 exhibits significantly enhanced photocatalytic activity for H 2 production after cycle tests. The formaldehyde in aqueous solution is used as target pollutant to simulate industrial wastewater. In-situ created elastic lattice O O bonds are proposed to improve catalytic performance through facilitating the breakage of C H bonds of HCHO. A series of internally consistent reaction equations is proposed that describes the role of in-situ created lattice O O bonds for improving the catalytic performance. This is strongly supported by that the H 2 production rate at the end of the fourth cycle test is significantly more than that of the beginning of the first cycle test.
Qingping Wu,Feng Huang,Mingshi Zhao,Ju Xu,Jiangcong Zhou,Yuansheng Wang
Blue TiO 2 (Ti 3+ defected TiO 2 ) nanoparticles have been intensively investigated for photocatalytic H 2 production. However, the Ti 3+ , with energy level ~1.0 eV below the conduction band , cannot initiate visible light driven H 2 production. Thus, Pt or NiO x is often used as a co-catalyst, which is economically unattractive and environmentally contaminative. In this paper, the ultra-small yellow TiO 2 nanoparticles (~3 nm) have been firstly synthesized without introducing any external dopants . The titanium vacancies (acceptor) and titanium interstitials (donor) that incorporated in the yellow TiO 2 are evidenced by various characterization techniques, and their formation mechanism is proposed. Photocatalytic evaluations indicate that the acceptor–donor defects play key roles in the catalytic process, not only initiating, but also promoting the visible light driven H 2 production. The improved activity is also evidenced by that the simulated solar light driven H 2 production for the yellow TiO 2 is ~3.7 fold comparing to that of the normal TiO 2 . A reasonable explanation is that the acceptor-donor defect associates form internal polarization for spontaneously separating photo-generated charge-carriers. The improved charge-carrier separation has been confirmed by photoluminescence spectra and photoluminescence emission decay profiles. Instead of the traditional TiO 2 based photocatalysts , the acceptor–donor defect engineered photocatalyst system offers a new approach for simultaneously initiating and promoting visible light driven co-catalyst free H 2 production.
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