*2.1. Characterization*

Polyurethane sponge was used as a base material in order to be functionalized with graphene oxide. Polyurethane presents an open-hole structure, with a high porosity as well as a rich surface chemistry with surface-groups that can attract and react with di fferent molecules. Graphene oxide was embodied in the PU skeleton after the dispersion of GO in water. Graphene oxide was connected to polyurethane after chemical interactions between the GO (epoxy-groups) and polyurethane surface groups (C=O and –N–H groups). After the polyurethane functionalization with graphene oxide, the sponge prepared appeared with a black color and presented hydrophobicity that was further increased after the coating with PVA.

The XRD di ffraction patterns of the prepared graphite oxide (GO) as well as of the GO impregnated sponge before (PU-GO) and after the PVA coating (PU-GO-PVA) are presented in Figure 1. Graphite presents a sharp di ffraction peak at 26.6◦ in the XRD pattern (not presented), attributed to interlayer (002) spacing (d = 0.33 nm). The characteristic XRD peak of graphite oxide appeared at 2θ = 10.9◦; as estimated by the Bragg's law, the interlayer distance between the carbon layers, increased from 0.33 nm for graphite to 0.81 nm for GO [33]. In the XRD pattern of the GO impregnated sponge (PU-GO) the characteristic XRD peak of graphite oxide, at 2θ = 10.9◦, was not present, indicating that the layered structure of GO was destroyed. A di ffraction peak at 2θ = 21◦ could be due to PVA while the broad peaks at around 11.6◦ and 19.8◦ indicated some degree of crystallinity of the PU [34–36]. The XRD pattern for the sample after the sulfonamide adsorption (PU-GO-SA), which is also presented in Figure 2, reveals that a decrease of crystallinity was observed, evidenced by the disappearance of the peak at 2θ = 11.6◦.

**Figure 1.** X-ray diffraction (XRD) patterns of the graphite oxide (GO), the graphene oxide impregnated sponge (PU-GO), and the sponge after the adsorption of sulfonamides (PU-GO-SA).

**Figure 2.** Fourier-transform infrared (FTIR) spectra for (**a**) polyurethane-graphene oxide- polyvinyl alcohol (PU-GO-PVA) sponge raw and after (**b**) the absorption of sulfonamide's (SA's) (PU-GO-PVA-SA)-(in the inset the spectrum of GO).

FTIR spectroscopy was used in this study to identify the possible interactions between GO and PU (PU-GO), between PU-GO and PVA (PU-GO-PVA sponge) as well as between the sponge and the sulfonamides (PU-GO-PVA-SA) in order for the adsorption mechanism to be revealed. The FTIR spectra of PU-GO-PVA as well as of PU-GO-PVA after the sorption of sulfonamide (PU-GO-PVA-SA), are presented in Figure 2. The FTIR spectra of GO is presented in the inset of Figure 2. GO contains polar groups on the edges of graphite layers such as carbonyl, carboxyl, and epoxide, as well as hydroxyl groups within the basal planes of the graphene sheets. In the spectrum of GO (Figure 2a), the bands at 1050–1100 cm<sup>−</sup><sup>1</sup> and ~1716 cm<sup>−</sup><sup>1</sup> can be attributed to carboxylic groups whereas the band at ~1600 cm<sup>−</sup><sup>1</sup> can be attributed to C=C stretching mode of the sp<sup>2</sup> carbon skeletal network and/or to epoxy groups. The band at 1356 cm<sup>−</sup><sup>1</sup> is due to C–OH stretching of O–H groups, while the band at 1045 and at 1141 cm<sup>−</sup><sup>1</sup> can be also attributed to epoxy and alkoxy C–O groups, respectively.

Polyurethane (PU) is a polymer obtained after the polymerization of diisocyanate and polyol that contains C=O and –NH groups (electron donating sites); these groups are able to form hydrogen bonds with graphene oxide during the complexation. The spectra of PU-GO-PVA sponge presented peaks at 1740 and 1060 cm<sup>−</sup><sup>1</sup> attributed to carboxyl and epoxy groups, respectively, at a lower intensity compared to the relative peaks of the spectra of GO, indicating the involvement of these groups in the composite synthesis. The peaks at 1543 cm<sup>−</sup><sup>1</sup> could be attributed to amide II formation after reaction of the carboxylic groups of GO with –NH groups of PU while the peaks at about 1453 cm<sup>−</sup><sup>1</sup> could be attributed to –CH3 groups of PVA indicating the covering [37–39].

The most significant spectra alterations for the GO-PU-PVA after the SA adsorption (GO-PU-PVA-SA sample), are the new bands appearing at 1260 and 1070 cm<sup>−</sup><sup>1</sup> in addition to the diminishing of the peaks at 1191, 1130 and 1740 cm<sup>−</sup><sup>1</sup> (carbonyl) absorption bands (Figure 2). The new band at 1440 cm<sup>−</sup><sup>1</sup> can be attributed to amide I formation due to interactions between the SA amines and the sponge carboxylates, causing the diminishing of the band at 1740 cm<sup>−</sup>1. The new band at 1260 cm<sup>−</sup>1, can be attributed to hydrogen bond interaction between the GO-PU-PVA carboxyl groups and the sulfones/O=S=O groups of SA which are strong hydrogen-bond acceptors. It is obvious that the grafting of PU with extra carboxyl groups enhanced the SA adsorption owning to their reactions with the amines and the hydrogen bond with the sulfones/O=S=O groups of the SA. This was also reported for dorzolamine encapsulation to chitosan, as well as for pramipexole adsorption on activated carbon.
