Water-stable methyl-modified MOF and mixed matrix membrane for efficient adsorption and separation of cationic dyes

The water stability of typical metal–organic frameworks (MOFs) limits the practical applications in water, such as pollutants adsorption. In this work, through the pre-functionalization of hydrophobic methyl groups on the ligand, anionic Bio-MOF-1 was transformed into Bio-MOF-2Me which has excellent water stability, even in acidic and boiling water environments. Bio-MOF-2Me also keeps the negative Zeta potential, enabling it to efficiently adsorbing and separating targeted dyes in mixed aqueous solution of cationic/anionic dyes, with high removal rates of around 99%. According to the Langmuir isotherm model, the maximum adsorption capacity of Bio-MOF-2Me for cationic methyl violet could reach up to 310.2 mg⋅g−1. In order to improve the portability and recyclability of Bio-MOF-2Me-based adsorbents, a mixed matrix membrane (MMM) of Bio-MOF-2Me (Bio-MOF-2Me-MMM) was manufactured. Bio-MOF-2Me-MMM inherits the preferential adsorption and separation properties of Bio-MOF-2Me, which has a maximum adsorption capacity of 157.1 mg⋅g−1 for cationic methyl violet. The adsorption abilities of both Bio-MOF-2Me and Bio-MOF-2Me-MMM own good cyclic reversibility, and the removal efficiency respectively retained 82% (Bio-MOF-2Me) and 72% (Bio-MOF-2Me-MMM) even after five adsorption–desorption cycles. The water stability, good adsorption/separation ability, portability and reusability make ionic Bio-MOF-2Me-MMM a promising candidate for dye wastewater treatment.