The nucleophilic superoxide radical (O2•–)-based dehalogenation reaction shows great potential to degrade the toxic halogenated organic compounds (HOCs). But such an O2•–-mediated reductive reaction often suffers from the competition of the secondary oxidative species (e.g., •OH), leading to inferior electron efficiency and possible disinfection byproduct formation. Here, an O2•–-dominant ultrafast dehalogenation system is developed via molecular O2 activation by the oxygen vacancy (OV)-rich CuO nanoparticles (nCuO). The nCuO delivers a remarkable dechlorination rate constant of 3.92 × 10–2 L min–1 m–2 for 2,4-dichlorophenol, much higher than that of the conventional zerovalent (bi)metals. The absorbed O2 on the nCuO surface is exclusively responsible for O2•– generation, and its reactivity increases with the elevated OV content because of the enhanced orbital hybridization between the O p- and Cu d-orbitals. More importantly, the ubiquitous carbonate species firmly bound to the surface OVs block the formation of the secondary oxidative species via H2O2 activation, assuring the dominant role of the in situ generated O2•– for the selective HOC dehalogenation. The carbonate-deactivated OVs of the nCuO can be feasibly recovered via air annealing for sustainable dehalogenation. This work provides a new opportunity for selective O2•– generation via interfacial defect engineering for dehalogenation and other environmental applications.
Li Zhijun,Zhang Mingyang,Zhang Lili,Dong Xiuli,Leng Leipeng,Horton J. Hugh,Wang Jun
Tuning the electronic properties of single atom catalysts (SACs) between the central metal and the neighboring surface atoms has emerged as an efficient strategy to boost catalytic efficiency and metal utilization. Here we describe a simple and efficient approach to create atomically dispersed palladium atoms supported over defect-containing porous ceria nanorod containing palladium up to 0.26 wt.%. The existence of singly dispersed palladium atoms is confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements. This catalyst shows excellent efficiency in hydrodehalogenation reactions at low H 2 pressure under mild conditions, along with satisfactory recyclability and scalability. Density functional theory (DFT) calculations reveal that the high activity stems from the spatial isolation of palladium atoms and the modified electronic structure of palladium confined in defect-containing ceria nanorod. This work may lay the foundation for the facile creation of single atom catalysts within the synthetic community and shed light on the possibility for scale-up production.
Two-dimensional covalent organic frameworks (2D-COFs) with permanent porosity, structural controllability, and excellent stability, are receiving ongoing attention in metal-free heterogeneous photocatalysis of organic conversions. In order to construct high optical performance COFs for selective organic transformation, herein, 2D porphyrin-based donor-acceptor (D-A) type COFs were prepared by adjusting the morphology and structure. The as-synthesized COFs facilitate charge transfer and separation of photogenerated electron-hole pairs, efficaciously producing superoxide radical anions as mediates for selective oxidation of sulfides (97% conversion and 99% of selectivity) and reductive dehalogenation of 2-bromoacetophenone (up to 99% conversion and 82% of yield). The COFs have excellent stability and recyclability , demonstrating that the 2D D-A type COFs are attractive as heterogeneous photocatalyst for visible light driven organics transformation.
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