Versatile CO₂-responsive Sponges Decorated with ZIF-8 for Bidirectional Separation of Oil/Water and Controllable Removal of Dyes

The complex wastewater containing water-soluble dyes and water-insoluble oils has given rise to significant environmental concerns that demand urgent remediation. Herein, a novel “smart” multifunctional sponge (ZIF-8@PMS) stepwise decorated with ZIF-8 nanoparticles and CO 2 -responsive copolymer (poly(2-(diethylamino) ethyl methacrylate- co -3-(trimethoxysilyl)propyl acrylate- co -stearyl methacrylate) was successfully prepared for CO 2 controllable oil/water separation and dyes removal. The results revealed that the sponge coated with CO 2 -responsive copolymer for three cycles (ZIF-8@PMS-3) exhibited optimal comprehensive properties. The ZIF-8@PMS-3 had excellent compressive-resilient characteristics and chemical stability. As expected, it displayed tunable wettability and charged state under the regulation of CO 2 . Based on these features, ZIF-8@PMS-3 presented highly efficient removal of oil and dyes, even for the dye-containing oil/water emulsions, via a synergistic combination of adsorption and separation methods. The adsorption capacity for oil and various organic solvents ranged from 21.3 to 50 g g –1 . The maximum adsorption capacities toward anionic dyes: methyl orange with 1205.89 mg g –1 and methyl blue with 880.00 mg g –1 in the presence of CO 2 through electrostatic interaction. In the absence of CO 2, it achieved maximum adsorption capacities for cationic dyes, including malachite green with 1246.15 mg g –1 and rhodamine B with 203 mg g –1, primarily driven by π–π interactions. According to distinct adsorption mechanisms, ZIF-8@PMS-3 could selectively adsorb either anionic or cationic dyes by exploiting CO 2 as a trigger. Furthermore, the separation efficiencies for both types of oil/water emulsions surpassed 99.9%, with respective fluxes of 1566.99 L m –2 h –1 (water-in-oil emulsion) and 310.37 L m –2 h –1 (oil-in-water emulsion). Additionally, the as-prepared sponges exhibited remarkable antibacterial properties and exceptional recyclability. Therefore, the ZIF-8@PMS-3 holds substantial promise for potential applications in practical industrial wastewater treatment.