Size-controlled nanoscale octahedral HKUST-1 as an enhanced catalyst for oxidative conversion of vanillic alcohol: The mediating effect of polyvinylpyrrolidone

Abstract

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.