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He et al. Soft Sci 2024;4:37 https://dx.doi.org/10.20517/ss.2024.32 Page 13 of 27

model to create MOF-alginate composites for dye removal, maintaining the shape of the original hydrogels
[83]
and allowing control over macroscopic forms . This simple synthesis method facilitates the use of MOF
materials in various practical applications. In addition to dyes, heavy metal ions released by industries cause
significant environmental harm, but they also hold potential for recycling. Bai et al. fabricated ZIF-67/
SAP0.45 MOF-based hydrogels with positively charged polyethyleneimine and negatively charged sodium
[84]
alginate chains, providing porosity, anti-biofouling properties, and mechanical strength [Figure 6C] .
These hydrogels demonstrated high uranium uptake capacity and retained efficiency after five adsorption-
desorption cycles in real seawater. Song et al. further developed MOF-based hydrogels capable of selectively
adsorbing U(VI) from seawater . By incorporating MOFs into the hydrogel network via coordination
[85]
bonds, they achieved excellent mechanical strength and U(VI) adsorption capacity of up to 159.56 mg·g ,
-1
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with continuous uranium uptake at 0.21 mg·g ·day in natural seawater. For the detection of uranium ions,
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Cui et al. designed a sensor/adsorbent composite using terbium(III) as a crosslinker to hybridize a
[86]
luminescent MOF with sodium alginate gel . This MOF-based hydrogel features multiple luminescence
centers and binding sites, offering ultra-high sensitivity, a wide quantification range, and excellent anti-
interference capabilities. The composite performs well without requiring complex sample preparation and
shows high accuracy in detecting uranium contamination in drinking water. While copper ions are not
radioactive, overexposure can damage the liver and kidneys. To develop effective copper adsorbents, Zhang
et al. reported a ZIF-8-alginate hybrid hydrogel (PVS/SA@ZIF-8) with amine functional groups that
[87]
enhance heavy metal ion adsorption through chelation . This hybrid exhibits excellent adsorption capacity
for Cu(II) (165.17 mg·g ), with improved mechanical properties and recyclability. Additionally, Mahmoud
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et al. synthesized a pectin hydrogel-MOFs (PHM) composite material from citrus peel by-products using
calcium chloride as a crosslinker . Adsorption studies confirmed that the material follows a pseudo-
[88]
second-order kinetic model and the Langmuir isotherm, effectively removing heavy metal ions from tap
water, seawater, and wastewater.

In summary, from oily water treatment to adsorption of anionic dyes and heavy metal ions, MOFs-based
hydrogels exhibit exceptional capabilities in addressing critical environmental challenges. The incorporation
of MOFs into hydrogel matrices not only enhances mechanical strength but also introduces unique
functionalities, such as superhydrophobicity, superoleophobicity, and excellent adsorption properties. The
ability to selectively remove pollutants, resist fouling, and withstand harsh conditions makes these
composites highly promising for widespread use, especially in underdeveloped areas. The demonstrated
effectiveness in uranium removal, dye adsorption, and separation of oil and water highlights the versatility
and practicality of MOFs-based hydrogels in tackling diverse water treatment scenarios. As researchers
continue to explore innovative synthesis methods and tailor these materials for specific applications, the
future holds great potential for the development of even more sustainable water treatment technologies.

Detection and sensors
In the field of chemical sensing, the pursuit of specific and efficient detection methods has spurred
significant research. MOFs have emerged as promising materials for biosensing due to their exceptional
properties. Lian et al. demonstrated a MOF-based hybrid hydrogel for the detection of β-lactamase, a
marker for penicillin allergy . By crosslinking the MOF matrix with alginate hydrogels [Figure 7A], they
[89]
achieved a selective and efficient detection mechanism for β-lactamase. Chemotherapy drugs such as
daunorubicin, adriamycin, and mitoxantrone are essential for cancer treatment but often cause adverse
effects. Mitoxantrone, in particular, has significant cardiotoxic effects and reduces platelet levels, making
dose detection crucial for managing side effects. Yu et al. developed a lanthanide MOF with high selectivity
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for detecting ofloxacin, achieving a detection limit of 1.1 × 10 M and a rapid response time of six
[90]
seconds . This study highlights the potential of MOF materials and MOF-based membranes in
applications such as detection and anti-counterfeiting.