Enhanced water stability of PVP-modified HKUST-1 for methane storage under LNG-ANG conditions

The coupling of liquefied natural gas and adsorbed natural gas charging (LNG-ANG) can effectively recover boil-off gas, with the key challenge being the development of efficient and stable adsorbents under cryogenic conditions (∼159 K). HKUST-1 is regarded as a promising methane adsorbent due to its abundant microporous structure and high specific surface area. However, its practical application is largely limited by water instability. After exposure to humid air for 10 days, the pristine HKUST-1 lost 68.17% of its specific surface area and 30.77% of its methane uptake capacity. Herein, we successfully prepared a water-stability-enhanced HKUST-1-PVP composite by grafting polyvinylpyrrolidone (PVP) onto the coordinatively unsaturated metal sites of HKUST-1. Among the samples, HKUST-1-P2 maintained a high specific surface area of 1242 m 2 g −1 (a loss of only 3.27%) and essentially unchanged methane uptake capacity even after exposure to humid air for at least 70 days. Furthermore, under LNG-ANG adsorption conditions (159 K, 6 bar), the methane uptake capacity of HKUST-1-P2 reached 234 cm 3 (STP) cm −3 , which is 2.6 times that of HKUST-1. These results indicate that the PVP modification strategy significantly enhances the structural stability of HKUST-1 and further stabilizes its methane adsorption performance. Computational simulations revealed that PVP grafting onto unsaturated Cu sites creates a barrier that blocks water access, thereby effectively enhancing the material's water stability. This work not only provides a simple and effective strategy for constructing water-stable MOF adsorbents but also advances the practical application of HKUST-1 materials in LNG-ANG technology.