# Melamine Foams Decorated with In-Situ Synthesized Gold and Palladium Nanoparticles
###### Abstract  
A versatile and straightforward route to produce polymer foams with functional surface through their decoration with gold and palladium nanoparticles is proposed. Melamine foams, used as polymeric porous substrates, are first covered with a uniform coating of polydimethylsiloxane, thin enough to assure the preservation of their original porous structure. The polydimethylsiloxane layer allows the facile in-situ formation of metallic Au and Pd nanoparticles with sizes of tens of nanometers directly on the surface of the struts of the foam by the direct immersion of the foams into gold or palladium precursor solutions. The effect of the gold and palladium precursor concentration, as well as the reaction time with the foams, to the amount and sizes of the nanoparticles synthesized on the foams, was studied and the ideal conditions for an optimized functionalization were defined. Gold and palladium contents of about 1 wt.% were achieved, while the nanoparticles were proven to be stably adhered to the foam, avoiding potential risks related to their accidental release. n pacs: 12.30. The development of polymeric nanocomposites has been identified as a promising approach to overcome these drawbacks. Incorporating the noble metal NPs into a polymer matrix allows anchoring and stabilizing the NPs, avoiding their aggregation or accidental release, and facilitates their quick recovery [5; 10; 23; 26; 27; 28; 29; 30]. However, a proper nanocomposite fabrication route is a key factor for the maintenance of the NPs functionality. Traditional polymer nanocomposite fabrication routes, such as mechanical blending processes (e.g., extrusion) or mixing in solution followed by casting, present several disadvantages. First, an optimum NPs dispersion into the polymer is difficult to achieve, and the NPs usually form aggregates unless specific functionalization procedures are adopted for the enhancement of their compatibility with the polymer matrix [29; 31; 32]. Second, most of the NPs incorporated in the composites by these procedures, are imbibed into the polymer, hindering their direct interaction with the environment, which is required for several applications such as sensoring, catalysis, and water treatment [5; 29]. Accordingly, functionalization approaches aiming to anchor or create the NPs directly onto the surface of polymeric substrates are necessary to develop efficient nanocomposites for these applications [5; 10]. Among other polymeric substrates, open-cell polymer foams offer an interconnected porous structure with a high surface area for the anchoring of NPs [5], making them excellent substrates to develop highly efficient polymer nanocomposites for diverse applications. For instance, polymer foams decorated with Ag NPs with water disinfection capability have been produced using dip-coating and in-situ NPs synthesis approaches [5; 23; 26; 27; 28]. The best results, in terms of both high anchoring stability and amount of Ag NPs on the surface of the foams, were obtained by the in-situ synthesis of the Ag NPs directly on the surface of the polymer foams struts [5; 23]. However, the functionalization of polymer foams with other noble metal NPs, such as Au or Pd, and therefore their potential use in different applications, is less studied. In the case of Au NPs, [PERSON] et al. [33] immersed polyurethane foams in dispersions of Au NPs, promoting their adsorption into the surfaces of the foam and using them as an optical sensor of organic compounds. [PERSON] et al. [34] produced polydimethylsiloxane (PDMS) sponges using hydrogel calcium alginate beads as a template for the porous structure. The incorporation of HAuCl4 into the beads allowed the in-situ formation of the Au NPs onto the surface of the cells of the PDMS sponges. [PERSON] and [PERSON] [35] followed a similar approach, adding the Au precursor directly into the PDMS formulation, obtaining nanocomposite sponges able to remove some organic compounds from polluted water. Concerning the Pd NPs, [PERSON] et al.