Porous materials for the recovery of precious metals

This thesis is part of the research work carried out during my PhD in Molecular Sciences at the Department of Chemical Sciences of the University of Padua (DISC), under the supervision of Professor Marco Frasconi. My PhD thesis is part of a large-scale research project funded by the National Recovery and Resilience Plan (PNRR) under the Made in Italy framework, aimed at the development of innovative porous materials and the exploration of their potential applications. The research activity was focused on the development and characterization of porous materials in the form of thin films. These systems combine the high surface area typical of porous structures with the chemical–physical, electrical, and mechanical properties of nanomaterials, meeting current needs in the fields of environmental remediation, microelectronics, and advanced sensing. The use of these materials in recovery processes is a growing field of interest, driven by the need to counteract the depletion of natural resources and the increase in global pollution. In particular, the recovery of precious metals (such as gold) from electronic waste using nanometric porous materials represents a sustainable alternative to traditional mining. This work lays the foundation for such applications by developing simple, robust, and scalable methods for the fabrication of porous films. The development of nanometric films was achieved without the use of complex approaches, such as Langmuir–Blodgett methods, or dedicated instrumentation obtaining thin and mechanically stable materials using only standard laboratory equipment. The reduced thickness of these films and the associated nanoscale confinement effects result in properties that are significantly different from those of bulk polymers. These distinctive features can be observed in both freestanding and supported configurations and influence mechanical, thermal, optical, electrical, and chemical behavior. Compared to more established characterization techniques, which mainly focus on chemical composition or morphology, the study of mechanical properties represents a frontier research area, especially in applications where reduced dimensions are essential. However, the investigation of freestanding nanometric films is often limited by technical challenges related to their extremely small size. To address this issue, the developed materials were characterized using a custom-made tensile testing platform, together with specially designed supports that allowed the polymeric films to be maintained in a freestanding configuration. In this way, the measured properties can be attributed exclusively to the material itself and can be considered realistic parameters for applications such as sensors or wearable materials, where functionality must be achieved without external supports. During my research activity, both crystalline and amorphous porous materials were investigated. The interfacial synthesis strategy proved to be highly effective for the fabrication of materials based on Covalent Organic Frameworks (COFs) and disulfide-linked films. The first research topic addressed in this dissertation concerns COFs. COFs are a class of porous polymers characterized by two- or three-dimensional pore networks formed through reactions between organic building blocks. Their structure is governed by strong dynamic covalent bonds, which provide both stability and crystallinity. Advances in topological chemistry have enabled precise synthetic control, leading to ordered nanoporous structures with preferential orientation and tunable properties through appropriate molecular design. COFs exhibit a layered structure, whose stability is strongly related to weak interlayer interactions. In the first phase of my PhD, imine- and enamine-linked COF thin films were synthesized and are described in detail in section 3 of this elaborate. For the first time in the literature, the structure of the selected COFs, specifically the imine-linke