Browsing by Author "Wang, Hao"

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    Nuclear magnetic resonance study of ion adsorption on microporous carbide-derived carbon
    (Cambridge : Royal Society of Chemistry, 2013) Presser, Volker; Forse, Alexander C.; Griffin, John M.; Wang, Hao; Trease, Nicole M.; Gogotsi, Yuri; Simon, Patrice; Grey, Clare P.
    A detailed understanding of ion adsorption within porous carbon is key to the design and improvement of electric double-layer capacitors, more commonly known as supercapacitors. In this work nuclear magnetic resonance (NMR) spectroscopy is used to study ion adsorption in porous carbide-derived carbons. These predominantly microporous materials have a tuneable pore size which enables a systematic study of the effect of pore size on ion adsorption. Multinuclear NMR experiments performed on the electrolyte anions and cations reveal two main environments inside the carbon. In-pore ions (observed at low frequencies) are adsorbed inside the pores, whilst ex-pore ions (observed at higher frequencies) are not adsorbed and are in large reservoirs of electrolyte between carbon particles. All our experiments were carried out in the absence of an applied electrical potential in order to assess the mechanisms related to ion adsorption without the contribution of electrosorption. Our results indicate similar adsorption behaviour for anions and cations. Furthermore, we probe the effect of sample orientation, which is shown to have a marked effect on the NMR spectra. Finally, we show that a 13C → 1H cross polarisation experiment enables magnetisation transfer from the carbon architecture to the adsorbed species, allowing selective observation of the adsorbed ions and confirming our spectral assignments.
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    Phase-enabled metal-organic framework homojunction for highly selective CO2 photoreduction
    (London : Nature Publishing Group, 2021) Liu, Yannan; Chen, Chuanshuang; Valdez, Jesus; Meira, Debora Motta; He, Wanting; Wang, Yong; Harnagea, Catalin; Lu, Qiongquiong; Guner, Tugrul; Wang, Hao; Liu, Cheng-Hao; Zhang, Qingzhe; Huang, Shengyun; Yurtsever, Aycan; Chaker, Mohamed; Ma, Dongling
    Conversion of clean solar energy to chemical fuels is one of the promising and up-and-coming applications of metal–organic frameworks. However, fast recombination of photogenerated charge carriers in these frameworks remains the most significant limitation for their photocatalytic application. Although the construction of homojunctions is a promising solution, it remains very challenging to synthesize them. Herein, we report a well-defined hierarchical homojunction based on metal–organic frameworks via a facile one-pot synthesis route directed by hollow transition metal nanoparticles. The homojunction is enabled by two concentric stacked nanoplates with slightly different crystal phases. The enhanced charge separation in the homojunction was visualized by in-situ surface photovoltage microscopy. Moreover, the as-prepared nanostacks displayed a visible-light-driven carbon dioxide reduction with very high carbon monooxide selectivity, and excellent stability. Our work provides a powerful platform to synthesize capable metal–organic framework complexes and sheds light on the hierarchical structure-function relationships of metal–organic frameworks.