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 center dot 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-2MeMMM) 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 center dot 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.