Functionalization of sustainable biomaterial spongin through creating new 3D composites with chromium for catalytic applications

The structural biocomposite spongin, which forms three-dimensional (3D) microporous skeletons in keratosan demosponges, known as the first multicellular organisms, belongs to sustainable biological materials. This study reports the first chromium tanning of spongin scaffolds isolated from two species of industrially used commercial sponges (Hippospongia communis and Spongia tampa) under extreme biomimetic conditions. Carbonization of the studied spongin samples followed by chromium plating led to the formation of complex multiphase structures never reported before. We use digital, and scanning electron microscopy, as well as XRD, FT-IR, XPS, thermogravimetric analysis and HR-TEM, for identification and characterization of the created 3D spongin-chromium composites. A mechanism for the interaction of chromium with the functional groups of spongin has also been proposed. Our data provide insights into the highly specific chemical and structural arrangements resulting from the Cr-tanning of diverse forms of spongin-based composite materials with perspectives of their practical applications including the hydrogen evolution reaction.