(2021) Colloids and Surfaces A: Physicochemical and Engineering Aspects_Size-controlled nanoscale octahedral HKUST-1 as an enhanced catalyst for oxidative conversion of vanillic alcohol: The mediating effect of polyvinylpyrrolidone

Li B.-C., Lin J.-Y., Lee J., Kwon E., Thanh B.X., Duan X., Chen H.H., Yang H., Lin K.-Y.A.

(Elsevier B.V.) Colloids and Surfaces A: Physicochemical and Engineering Aspects ISSN: 9277757 Vol.631 Issue. Article No.127639 DOI: 10.1016/j.colsurfa.2021.127639

While 2,2,6,6-tetramethylpiperidin-oxyl (TEMPO) accompanied with Cu is a promising oxidative catalytic process for converting vanillic alcohol (VL), to vanillic aldehyde (VE), the Cu-based metal organic frameworks (MOFs), HKUST-1, appears as a useful heterogeneous catalyst for VL conversion. Nevertheless, since the typical HKUST-1 is micrometer-scaled, it would be more advantageous to make HKUST-1 into nanoscale to increase outer surfaces of HKUST-1. Thus, the goal of this study is to develop a useful approach to prepare nanoscale HKUST-1 which can still exhibit octahedral morphology. Specifically, nano-HKUST-1 is developed here via mediation by polyvinylpyrrolidone (PVP). These PVP-mediated nano-HKUST-1 not only retains the crystalline structure of HKUST-1 but also maintains the octahedral morphology of HKUST-1. Interestingly, the introduced PVP would not just alter the size of HKUST-1 but also deposit PVP molecules into these nano-HKUST-1, increasing hydrophilicity of nano-HKUST-1 to attract VL in solvents. Thus, nano-HKUST-1 could exhibit noticeably higher VL conversion efficiencies then the conventional HKUST-1 owing to the smaller size, and the more hydrophilic surficial properties. Moreover, nano-HKUST-1 could also exhibit a high YVE = 91% with SVE = 100% at 120 °C for 120 min, outperforming many other reported values. Nano-HKUST-1 can be also reusable and exhibit stable YVE and 100% of SVE. These features all indicate that nano-HKUST-1 prapred by mediation of PVP is a more advantageous Cu-based catalyst for converting VL to VE, and the mediating effect of PVP revealed here also gives insights to further engieer MOFs materials for enhancing their applications. © 2021

This work is supported by the Ministry of Science and Technology (MOST) (110-2636-E-005-003), Taiwan, and financially supported by the “Innovation and Development Center of Sustainable Agriculture” from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE), Taiwan. The authors gratefully acknowledge the use of EA003600/SQUID000200 of MOST 110-2731-M-006-001 belonging to the Core Facility Center of National Cheng Kung University.