# Gelatin-Siloxane Hybrid Monoliths as Novel Heavy Metal Adsorbents
## 1 Introduction
Among new possible routes for preparation of new materials exhibiting high removal efficiency and adsorption capacity, synthesis of organic-inorganic hybrids can be taken into consideration. Organic-inorganic hybrids represent a group of materials that combine the advantages of organic polymer (such as elasticity, formability, toughness) and inorganic compound (like hardness, strength, high chemical resistance and thermal stability) [11; 12]. According to the definition provided by IUPAC (International Union of Pure and Applied Chemistry): \"_A hybrid material is composed of an intimate mixture of inorganic components, organic components, or both types of components. The components usually interpenetrate on a scale of less than 1 \(\mu\)m_\" [13]. It is worth noting that hybrid materials represent a synergetic combination of inorganic and organic components and they are not just simple physical mixtures of their constituents. Thus, properties they reveal are not the sum of the individual contributions of both phases but are dependent on the inner interfaces between them. Depending on the nature of the interface, hybrid materials are divided into two classes: _class I_ and _class II_. In the first class, the chemical interactions between organic and inorganic compounds are weak (hydrogen, van der Waals or electrostatic interactions), while in a _class II_, the two phases are linked together through strong chemical covalent or coordinative bonds resulting in blends or interpenetrating networks [14; 15]. Organic-inorganic hybrids can be prepared using varied synthetic strategies (e.g., sol gel route) that opens the possibility for the design of materials exhibiting tailored properties. This approach makes them suitable for several applications in: textile; packaging; construction; automobile industries; micro-optics; microelectronics; as well as in the synthesis of functional coatings; and as biosensors; biocatalysts or novel materials for cosmetics or biomedical purposes. Among them, adsorbents are one of the promising options [14; 16; 17; 18]. Recently, there is a growing interest in the application of inexpensive adsorbents prepared from usable agricultural waste (e.g., egg shells, banana peels, rice husk) or common biopolymers such as alginate, gelatin, chitosan, lignocellulosic materials [6; 19]. In the scientific literature there are several examples of gelatin application for the preparation of adsorbents [20; 21; 22]. Gelatin is a biodegradable, biocompatible and non-toxic natural polymer, widely used as a gelling agent in the manufacturing processes of food, cosmetic components, and pharmaceuticals. Due to its good film-forming ability it can also be applied to the preparation of coatings or packaging materials [22; 23]. However, due to its hydrophilic nature and high moisture sensitivity it requires modification (e.g., with cross-linking agents such as glutaraldehyde, phenolic acids, flavonoids, or genipin) in order to enhance mechanical and thermal stability. Physiological properties of gelatin can also be altered by the chemical reaction of a biopolymer with organosilicon compounds [24; 25] or other biopolymers such as chitosan, alginate or polyvinyl alcohol [26; 27; 28]. [PERSON] et al. [27] described adsorbers composed of gelatin, which reveals amphoteric nature due to the presence of both positive and negative charged centers (depending on its isoelectric point and pH of the environment) and anionic polymer alginate. They reported the pH of the effluent's dependent adsorption efficiency. In this work, we describe novel porous hybrid materials based on gelatin and organomodified silicone containing epoxy-group, which can be applied for adsorption of Cu(II), Cd(II) and Pb(II) from aqueous solution. To the best of our knowledge, this is the first report concerning gelatin-siloxane porous monoliths suitable for heavy metal removal.