Chemical upgrading of biowaste and bio-sourced molecules through catalysis, green extraction and functional nanomaterials synthesis.

Abstract

Global challenges such as climate change and our deep reliance on finite resources force us to newly evaluate our approach to energy and material use. Facing these issues requires not only a massive reduction of waste and emissions generated but also rethinking how value can be created from what is conventionally considered waste, according to a circular economy perspective. In this framework, the present work focuses on the design of sustainable catalytic systems and biomass valorisation strategies. For instance, due to their low toxicity, cost-effectiveness and chemical robustness molybdenum catalysts can represent excellent non-noble metal alternatives to more conventional noble metal catalysts. As one of the core topics of this thesis, a multiphase heterogeneous catalytic system that exploits the potential of molybdenum supported on a bio-based carbon. This system was developed for the selective oxidation of bio-sourced alcohols into aldehydes, taking advantage of air as a green oxidant and methyltrioctyl ammonium chloride as a hydrophobic ionic liquid phase designated for catalyst confinement. This approach enabled quantitative conversions and selectivities up to 99%, while showing remarkable resilience over time and ensuring efficient catalyst reuse over multiple consecutive cycles. A different kind of investigation was conducted with the aim to optimise an environmentally friendly protocol for the isolation of a functional biopolymer, chitin, directly from fishery biowaste using water-compatible ionic liquids, such as ammonium formate. The optimised pulping method yielded high-quality chitin with physicochemical properties (DA>94%, MW 6.6 × 105 g/mol) comparable to the commercial counterpart, while significantly reducing the environmental impact compared to conventional chemical extraction. Finally, a consistent part of this work was focused on the optimisation of a synthetic protocol for the preparation of nitrogen-doped carbon nanomaterials from bio-based precursors, including chitin and chitinous biowaste, which were subsequently investigated as non-toxic and cost-effective additives in aqueous zinc-ion batteries. These nanomaterials proved effective in preventing zinc dendrite formation and promoting uniform metal deposition, enabling electrode stabilisation even at high current densities and proving efficient during consecutive zinc plating/stripping cycles.