Publication
Gold plays a dominant role in our modern society. Initially used in coinage and jewelry, it has become an essential metal for the electronics industries. Today, more gold is consumed than mined from virgin ores. Therefore, gold recycling methods have become essential as a circular economy comes to displace linear economic pathways. To embrace this new challenge, chemical research is exploring various novel sustainable adsorbent to recover gold from Electronic waste (e-waste) efficiently and selectively. Metal organics frameworks (MOFs), due to their porous nature, have the potential to be a template for a novel generation of adsorbents. Indeed, their high surface area, large pore volume and chemical tunability make them ideal candidates to design adsorbent having exceptional capacities for precious metals recovery. Hence, this thesis will focus on a scalable synthesis and post-synthetic modification of MOFs towards the industrial recovery of gold from e-waste. In chapter 1, we explore the chemistry of gold and various leaching methods used to dissolve gold into solution. We then review the gold recovery techniques currently employed in industry, highlighting their current limitations. Lastly, we examine recent advances in adsorbent research, with a focus on gold speciation, adsorption kinetics, selectivity and capacity, placing particular emphasis on the utilization of water-stable MOFs as adsorbents. In chapter 2, building on previous research into Fe-BTC/PpPDA (poly para-phenylene diamine) polymer composites, we introduce a pioneering method for in-situ polymerization within a MOF under continuous flow conditions. This study focuses on developing an efficient, eco-friendly production process that reduces solvent usage while improving scalability and uniformity. The composite's effectiveness is tested across various industrial gold leaching solutions. After identifying the optimal solution, a continuous flow process transforms the fine composite powder into sodium alginate beads, which are then evaluated for gold recovery from e-waste. In-situ X-ray Absorption Near Edge Spectroscopy (XANES) is used to track the reduction of Au(III) to Au(0) during adsorption, marking the first use of XANES for monitoring gold adsorption in MOFs. Chapter 3 introduces post-synthesis modification (PSM) of a water-resistant MOF (Cr- BDC-NH2) to improve its adsorption kinetics and capacity. We report the covalent grafting of high-density amine functional such as ethylenediamine, diethylenetriamine or tris(2-aminoethyl)amine groups inside Cr-BDC-NH2. Stability and gold recovery tests are conducted in acidic environments, followed by selectivity tests and in-situ XANES to study gold reduction kinetics. Chapter 4 shifts the focus towards designing scalable, water-stable, large-pore MOFs based on the UiO-68 framework, featuring high amine densities to enhance gold recovery. Novel piperazine-based ligands are synthesized, and their corresponding MOFs are tested for stabil