*3.3. Chromatography*

The mobile phase consisted of water, containing 0.1% (*v*/*v*) formic acid (A), acetonitrile (B), and methanol (C). The analytes were separated following a gradient elution program, starting at 80:3:17 (*v*/*v*/*v*), turning to 74:6:20 (*v*/*v*/*v*) in the next 7.5 min, kept isocratic for 2.5 min, and finally changing to 50:10:40 (*v*/*v*/*v*) in the last three minutes. The flow rate was set at 1.0 mL min−1, while monitoring of the analytes was set at 265 nm.

#### *3.4. Functionalization of Sponges*

A commercially available polyurethane sponge was cut into cubes, immersed into ethanol/water solution, and placed in an ultrasonic bath for 20 min. The sponge was left at room temperature to dry and then it was dipped in a GO mixture for 24 h to be stirred mechanically. The mixture was prepared by the addition of 0.12 g GO in 60 mL NH3/EtOH solution (4:1, *v*/*v*). When mechanical stirring was completed, the sponge was left to dry in room temperature. Subsequently it was rinsed with water and PVA solvent was added as a final step. The PU-GO sponge is shown in Figure 8.

**Figure 8.** Image of the polyurethane-graphene oxide (PU-GO) sponge.
