# Melamine Foams Decorated with In-Situ Synthesized Gold and Palladium Nanoparticles
## 3 Results and Discussion
### ME/PDMS/Au and ME/PDMS/Pd Foams  
The treatment of ME/PDMS foams with the HAuCl4 solutions induced an evident change in the color of the foams, from the light gray of ME/PDMS (Figure 2a,b) to red (Figure 2c,d), a clear indication of the presence of Au NPs [33; 34; 35]. As shown by the photographs (Figure 2c) and the optical micrographs (Figure 2d), the coloration of the foams is homogeneous, which is an indication that the expected presence of Au NPs is throughout the porous structure of the foams. On the other hand, the treatment of the ME/PDMS foams with Na2 PdCl4 solutions also induced a color change, with the ME/PDMS/Pd foams showing a uniform dark grey-blackish color (Figure 2e,f), related to the presence of Pd NPs [36]. Figure 1: High-resolution Scanning Electron Microscopy (HRSEM) micrographs of the untreated Melamine (ME) (**a**) and ME/Polydimethylsiloxane (PDMS) cured at 80 \({}^{\circ}\)C (**b**). HRSEM image of a strut of the ME/PDMS foam (**c**) and the corresponding energy-dispersive spectroscopy (EDS) map (**d**) showing a homogeneous distribution of the Si corresponding to the PDMS (red). EDS spectra of ME and ME/PDMS foams (**e**). Figure 2: _Cont._No significant weight changes were found during the production of the ME/PDMS/Au and the ME/PDMS/Pd foams from the ME/PDMS foams, so moderate Au or Pd loads are expected on these samples. This amount of Au or Pd transferred to the foams, upon dipping to the precursor solutions of different concentrations and for different time intervals, was accurately determined by the ICP-OES analysis of the ME/PDMS/Au and ME/PDMS/Pd foams. After 48 h of immersion of the foams in solutions with HAuCl\({}_{4}\) concentrations ranging from 0.175 to 1.400 mg/mL, the transferred Au to the foams was ranging from c.a. 0.6 to 1.0 wt.%. For the precursor concentration of 0.350 mg/mL, the Au transfer already reached c.a. 1 wt.%, and this concentration was chosen for the further analysis of the kinetics of the Au transfer onto the foams. Similarly, ME/PDMS/Pd foams obtained after 48 h of immersion in solutions with Na\({}_{2}\)PdCl\({}_{4}\) concentrations ranging from 0.250 to 2.000 mg/mL showed Pd contents ranging from 0.8 to 1.2 wt.%. Additionally, an intermediate concentration of 0.500 mg/mL, which provides a Pd transfer c.a. 1.1 wt.%, was chosen to study the kinetics of the procedure. It should be noticed that this concentration is also equivalent to the selected Au concentration (i.e., 0.350 mg/mL) in terms of the noble metal ions availability, about 0.200 mg/mL. Thus, a direct comparison between the ME/PDMS/Au and ME/PDMS/Pd foams can be performed. In particular, ME/PDMS/Au and ME/PDMS/Pd foams were produced upon the dipping of the ME/PDMS foams in the HAuCl\({}_{4}\) or Na\({}_{2}\)PdCl\({}_{4}\) solutions for time intervals ranging from 1 to 120 h. As shown in Figure 3, both the Au and Pd amounts transferred to the foam increased with the reaction time increase, starting from about 0.1 wt.% Au and 0.5 wt.% Pd after 1 h of reaction time and reaching a stable value of about 1 wt.% Au and 1.1 wt.% Pd after 48 h. According to these values, the Pd transfer seems to be faster in the beginning, reaching almost 50% of the final load in just 1 h, while the Au transfer reaches about 10% at the same time. However, after 15 h, the transferred amounts of both noble metals became similar. Figure 3: Au and Pd content (wt.%) measured by Inductive Couple Plasma-Optical Emission Spectroscopy (ICP-OES) in the treated ME/PDMS/Au and ME/PDMS/Pd foams obtained after different immersion times in 0.35 mg/mL of HAuCl\({}_{4}\) and 0.50 mg/mL of Na\({}_{2}\)PdCl\({}_{4}\) in ethanol, respectively. Figure 2: Photographs of the untreated ME (**a**) and treated ME/PDMS/Au (**c**) and ME/PDMS/Pd (**e**) foams. Optical micrographs (40\(\times\)) of the untreated ME (**b**) and treated ME/PDMS/Au (**d**) and ME/PDMS/Pd (**f**) foams showing the homogenous color of the struts of the foams.