This thesis focuses on the development and evaluation of photocatalytic systems dedicated to CO₂ reduction and valorisation, while also exploring complementary environmental remediation applications, particularly water treatment. Conducted within the framework of the multidisciplinary DefiCO₂ project, this work was guided by the Safe-and-Sustainable-by-Design (SSbD) framework, with the objective of developing self-supported Cu₂O-based photocatalytic membranes designed as reusable and sustainable systems compatible with large-scale deployment.

Cu₂O, a p-type semiconductor that is abundant, non-toxic, and capable of absorbing visible light, was synthesized in the form of high-aspect-ratio nanowires through a simple hydrothermal approach based on Fehling’s reaction, carried out under low-pressure and low-temperature conditions using glucose as a bioreducing agent. The membranes were subsequently fabricated through a simple, low-cost process adaptable to industrial-scale production, based on vacuum filtration on a porous support followed by a peel-off step to obtain self-supported structures.

To improve photocatalytic performance, TiO₂ nanoparticles synthesized via a combined sol–gel and hydrothermal route were incorporated to form p–n heterojunctions promoting charge-carrier separation. The influence of different TiO₂ loadings on membrane properties and performances was investigated through their evaluation for the photocatalytic reduction of CO₂ into CO and CH₄, as well as for water treatment applications, particularly through the degradation of organic pollutants such as Orange G. Mechanistic investigations also provided valuable insights into the charge transfer mechanisms within the heterojunction, the processes governing the photocatalytic activity, and the associated reaction pathways.

Finally, a life cycle assessment (LCA) was conducted to evaluate the potential environmental impacts and benefits of the developed materials with a view to their future large-scale deployment. The results demonstrated their alignment with the Safe and Sustainable by Design (SSbD) framework. In parallel, a methodology combining life cycle assessment and emerging machine learning (ML) tools was developed to extend the framework of this thesis to a broader range of metal oxide nanowires.

Overall, this thesis contributes to the development of multifunctional photocatalytic membranes for CO₂ reduction and valorisation, as well as environmental remediation. It also opens promising perspectives for the development of more sustainable, reusable, and scalable processes and for extending this approach to other materials.

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