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He et al. Soft Sci 2024;4:37 https://dx.doi.org/10.20517/ss.2024.32 Page 11 of 27

addressed the challenges of composite membranes in water treatment by creating a polyvinyl alcohol/
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polydopamine (PVA/PDA) hybrid layer combined with ZIF-8 . This PVA/PDA@ZIF-8 forward osmosis
membrane overcomes the low permeability and fouling issues seen in traditional systems. Its porous
structure provides additional channels for water transport while reducing salt diffusion. With fewer surface-
charged groups, it minimizes interactions with contaminants, enhancing both water flux and selectivity.
Dynamic fouling tests confirmed the membrane’s excellent antifouling properties and recovery
performance. Wang et al. took a different approach, reporting a MOF-based hydrogel with high mechanical
strength, achieved by leveraging the reaction between alginate and metal ions to form MOF nuclei,
preventing the growth of large particles . This strengthens the polymer chains within or on the surface of
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the MOFs [Figure 6A]. The resulting stretchable MOF-based hydrogel tube demonstrated superior dye
removal from water, particularly effective in wastewater treatment and oil-water separation. The
hydrophilic membrane formed on the composite’s surface not only prevents oil penetration but also
improves the durability of the nano-photocatalyst powders. Addressing common challenges such as
mechanical instability and low water flux in oil-water separation, Gao et al. synthesized a superhydrophobic
MOF-based hydrogel by immersing 2D Ni-Fe MOF-halloysite nanotube (HNT) composites into PVA
hydrogels . The resulting material exhibits underwater super-oleophobicity, allowing efficient oil-water
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separation even after ten cycles [Figure 6B]. The nanosheets on the outer nanotubes enhance the
composite’s pore structure and mechanical strength, ensuring long-term performance.

Addressing the need for selective absorption, Biswas et al. fabricated MOF-gelatin nanocomposite materials
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by integrating UiO-66 or MOF-801 with gelatin and hydrogels . Due to high physicochemical
compatibility, MOF particles distribute uniformly within the gelatin matrix without affecting the material’s
porosity. Under appropriate humidity, these composites selectively absorb acetic acid, with an absorption
ratio of 260 µg·dm , making them potentially useful for protecting cultural heritage artifacts. The overuse of
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antibiotics poses a significant threat to human health, and MOFs, known for their large surface area and
tunable pore structures, are effective adsorbents for these pollutants. Luo et al. designed aluminum-based
MOF hydrogel microspheres as adsorbents for bisphenol A. By adding chitosan (CS), they increased the
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porosity, resulting in microspheres with higher specific surface area and total pore volume . Batch
experiments confirmed enhanced adsorption performance, with results following the pseudo-second-order
kinetic model and the Freundlich isotherm. Notably, these microbeads can be easily regenerated with
methanol, maintaining over 96% adsorption efficiency even after five cycles. Chai et al. developed ZIF-8/
hydrogel composite beads for the adsorption and detection of fluoroquinolone antibiotics using an in-situ
one-pot method . This approach avoids common issues such as particle agglomeration and particle-
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polymer interaction. The composite beads achieved a pollutant adsorption capacity of up to 2,887 mg·g ,
demonstrating excellent mechanical stability after seven days in water and retaining high performance after
three cycles. This study highlights the potential of MOF-based hydrogels for addressing pharmaceutical
industry pollutants. To enhance the stability and durability of MOFs, the 3D interconnected reduced
graphene oxide framework has gained popularity for its multifunctional properties and mechanical support.
In pursuit of effective water purification, Mao et al. introduced a one-step self-assembly process for ZIF-8-
based hydrogels, which transform into aerogels upon drying . These ZIF-8 hybrid aerogels exhibit high
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porosity, superhydrophobicity, and superior absorption properties, along with photocatalytic dye
degradation capabilities. This makes them effective in removing harmful dyes, heavy metal ions, and
benzene pollutants from water. The synthetic strategy has also shown potential for fabricating other
functional hydro/aerogels.

Dye wastewater, which always appears around paper, textile, and plastic factories, is expanding the impact
on the ecosystem. Chen et al. developed polyethyleneimine-modified MOF-based hydrogels via an ex-situ