Flexible Porous Gels Synthesized by Templating Organofoams—Ability to Selectively Absorb Oil from Water

Porous absorbents are being explored rigorously for recovering volatile organic solvents and oils from water bodies. However, most existing synthesis techniques are limited to the fabrication of small-size absorbents. These techniques are based on modifying polymer sponges towards a greater affinity to organic solvents. For large-scale manufacturing, these methods turn out to be arduous, energy-intensive, and expensive. Here, we devised a simple strategy to create porous absorbents, using an inherently hydrophobic polymer, that can be easily scaled up. Our approach involves the generation of foams in an organic monomer solution by mixing it with an aqueous acidic solution and sodium bicarbonate. The acid-base reaction produces CO₂ gas bubbles, and simultaneously, oil-in-water type emulsions are formed, with the monomers being the oil phase. Both the emulsion and bubbles are stabilized by a silicone surfactant present in the monomer solution. This foamed-emulsion solution is quickly polymerized to give a porous solid named ‘oleosponge’ or ‘oleosheet’. It retains the interconnected pores from the foam, which have an average size of 277 μm. The material is flexible and mechanically robust, withstanding several cycles of deformation. It can sustain more than 90% compression and 35% tensile strain and has a tensile modulus of 40 kPa. The material also shows a contact angle of ~130° with water and 0° with oils. When immersed in a toluene-water mixture, it selectively absorbs the toluene and expands by ~75% linearly. In solvent absorption, the oleosponge outperforms commercially available polyurethane sponges, which have been used for designing hydrophobic absorbents in many previous studies. Our material shows very high absorption for a wide range of organic solvents (> 50 g/g), and it can be reused for more than 100 cycles without showing a significant reduction in its selective absorption capacity. For large-scale clean up, we have created oleosheets with dimensions of 10 x 7 cm and a thickness of 4 mm. The sheet instantly absorbs solvent and expands when spread over a large spill. The expanded sheet is robust enough to be picked up by hand and holds solvent within when held vertically. Compared to commercial oil-absorbing sheets, our oleosheets absorb and retain a much higher volume of organic solvent. Another exciting aspect of our synthesis technique is that we can attain additional interesting properties in the oleosponge simply by adding nanoparticles of interest to the monomer solution. We have created a magnetic responsive oleosponge that can be remotely lifted up by a magnet after solvent absorption. Lastly, we designed a hybrid sheet of two distinct layers with opposite wettability for water: one side can absorb solvents and oils while the other absorbs only aqueous fluids. This type of hybrid sheet could have applications in cosmetics and household use in addition to oil spills.