## 3 Results and Discussion
### Continuous Separation of Surfactant-Stabilized Emulsions Using the GN\({}_{4}\)/PSt Composites  
The separation of emulsions is much more difficult than the separation of immiscible water/oil mixtures, and the separation of surfactant-stabilized microemulsions with small droplet sizes and lower content of dispersive phase is especially challenging [59]. To test the feasibility of separating oil/water emulsions using the GN\({}_{4}\)/PSt foams, three surfactant-stabilized water-in-oil emulsions with micro-nano particle sizes were prepared, and the separation of Span 80-stabilized water-in-petroleum ether emulsions are discussed as an example. As shown in Figure 7a and Video S2, after the milky white emulsion was pumped through the monolith, the filtrate was clear and transparent indicating that in situ demulsification and continuous oil/water separation were realized. Moreover, optical micrographs and digital photographs of the as-prepared water-in-oil emulsions before and after separation using the GN\({}_{4}\)/PSt foams are shown in Figure 7b-d. While numerous dispersed droplets were seen in the feed solutions, no droplets were observed in the filtrate using an optical microscope, further highlighting the high-efficiency separation performance of the GN\({}_{4}\)/PSt foams. Furthermore, the droplet size of the feed emulsions and filtrates were measured using the dynamic light scattering. The initial emulsions  
Figure 6: Photographs showing the use of GN\({}_{4}\)/PSt composite materials for selective oil/water separation. (**a**) Petroleum ether/water and (**b**) chloroform/water, (**c**) the saturated oil absorption capacity of GN\({}_{4}\)/PSt foam for a variety of organic solvents, (**d**) images of the continuous separation of light oil/water/heavy oil mixtures using the GN\({}_{4}\)/PSt foams and corresponding (**e**) separation efficiencies for different oil/water mixtures.  
contained a wide size distribution of droplets ranging from 30 nm to 7 \(\upmu\)m (Figure 7e). In comparison, the droplets in the filtrate were smaller than 100 nm (Figure 7f), and the particle sizes were similar to those seen in a solution of the Span 80 surfactant in oil (Figure 7g). Based on these results, we speculate that the filtrate was composed of a small number of nano-sized emulsified water droplets and surfactant micelles [56; 60].  
To more quantitatively assess the demulsification efficiency of the GN\({}_{4}\)/PSt foams, the moisture contents of the emulsions before and after the separation were measured using a Karl Fischer moisture meter, and the results are shown in Figure 8. The separation efficiencies of the GN\({}_{4}\)/PSt composites for the three emulsions were 98.2%, 98.5% and 98.2%, respectively. This high separation efficiency is due to a combination of size-sieving filtration in the GN\({}_{4}\)/PSt foams as well as the completely opposite wettability towards oil and water. The long and tortuous micro-nano permeation channels in the foams were also crucial in the emulsion separation process [35; 61; 62]. In summary, the as-prepared superhydrophobic GN\({}_{4}\)/PSt porous materials could be used for the efficient, large-scale and continuous separation of emulsions to achieve rapid treatment of emulsified oil sewage.  
Figure 7: (**a**) Photographs of the setup using GN\({}_{4}\)/PSt composites for the continuous separation of water-in-petroleum ether emulsions and corresponding optical microscopy images and digital photos of the emulsions before and after separation, (**b**) water-in-petroleum ether emulsions, (**c**) water-in-toluene emulsions, (**d**) water-in-chloroform emulsions, (**e**) droplet size distributions in the water-in-petroleum ether emulsion, (**f**) droplet size distribution in the filtrate, and (**g**) droplet size distribution in a solution of 1 g/L Span 80 surfactant in petroleum ether.