Catalysts and advanced materials from waste: diversifying biochar applications towards the implementation of a circular and bio-based economy.

Abstract

Biochar is a bio-sourced and carbon-based material produced from the thermochemical processing of wood residues. Besides presenting remarkable chemical and physical properties, biochar is a tool for carbon dioxide (CO₂) sequestration. Unfortunately, it has been mainly employed in low value-added fields in pollutant removal and soil amendment. The diversification of biochar applications is aligned with the Principles of Green Chemistry and could help to tackle our society’s current environmental challenges through the achievement of the United Nations Sustainable Development Goals. The use of a material obtained from waste with recognized carbon sink potential for the further production of energy and chemicals can reduce the impacts of consumption, contribute to our good health and well-being, and also mitigate devastating climate change consequences. A true sustainable future can only be achieved if interdisciplinary and collaborative approaches are considered. In this thesis, strategies in the areas of CO₂ transformation, layered materials exfoliation, polymer composites reinforcement, catalysis, and their respective applications in biochar research are discussed. Biochar after functionalization could be applied as catalyst for the synthesis of cyclic carbonates from epoxides using CO₂ as a feedstock. Besides presenting good efficiency (i.e. conversions higher than 78.5%) and having a wide substrate scope, the catalytic system proposed could be re-used at least five times without any loss in its activity. The same material could be applied in liquidphase exfoliation processes to produce biochar nanostructures with improved chemical and physical properties. Although greener environments for the exfoliation of biochar were obtained and studied through extensive solvent screening, the functionalization of this carbon-based material was able to further increase the yield of nanostructures obtained in benign solvents to human health and the environment. Using different catalysts, the functionalized biochar produced could then be applied as a polymer additive for the production of biodegradable poly(e-caprolactone) composites with increased stiffness, crystallinity and conversions. Preliminary degradation studies also showed a positive effect of the exfoliated functionalized material in the degradation of poly(ecaprolactone) under different conditions. Functionalized biochar also showed good activity (i.e. 75.2% conversion) as the first carbon-based catalyst used for the synthesis of cyclic ethers via ring-closing C-O/C-O metathesis of their aliphatic counterparts, and as an efficient alternative system for the synthesis of terpene esters from terpene alcohols and acetic anhydrides (i.e. conversions higher than 84.3%) under mild conditions.