Elio Rico’s research while affiliated with University of Alicante and other places

The efficient transformation of biomass into high-value chemicals remains a significant challenge, with surface ligand manipulation offering a promising approach to enhance catalytic performance. In this study, we investigate the role of organic ligands in the photocatalytic conversion of lignin into functionalized aromatics using cadmium sulfide (CdS) quantum dots (QDs). By tuning the hydrophilicity/hydrophobicity of ligands, we successfully form stable QD colloidal solutions, ensuring effective contact between the QDs and lignin. We determined that thiyl ligands triggered the photocatalytic conversion of lignin models. These ligand modifications, including the anchor group and alkyl chain length, are shown to play a critical role in facilitating electron transfer during photocatalysis. Furthermore, it was discovered that the mechanism of C-C and C-O bond cleavage at the β-O-4 linkages can be influenced by the substituents on the aromatic rings of lignin, a finding that has not been previously reported. Our findings not only advance the understanding of ligand-controlled catalysis but also present a new pathway for efficient lignin biomass valorization and organic transformation processes using QD-based photocatalysts.

Lignin valorization has become an urgent priority due to its status as the most abundant natural biopolymer containing aromatic structures, yet industrially unexploited. In this study, we present a photocatalytic method using a simple anthraquinone catalyst to break down lignin's recalcitrant structure into valuable monomers. Notably, this process is described under flow conditions for the first time. The monomer yields achieved are the highest reported in literature, although lignin is not fully depolymerized. However, the remaining oligomers can be effectively repurposed as polylactic acid (PLA) plasticizers, significantly enhancing PLA's mechanical properties and imparting shape-memory behavior. Thus, by processing lignin through a photochemical flow reactor, it is fully converted either into industrially relevant monomers, such as vanillin and syringaldehyde, or fragmented sufficiently for use as PLA plasticizers. This approach ensures that no wasteful by-products are generated, offering a sustainable pathway for lignin valorization.

The use of lignin as a renewable feedstock for valuable chemicals has gained significant momentum due to the ongoing depletion of fossil fuel reserves and the environmental harm caused by their overuse. However, extracting useful products from this recalcitrant biopolymer requires a highly selective fragmentation process. This article demonstrates that such a process can be effectively achieved through an electrochemical approach. While Ni- and Co-based catalysts have been previously employed for lignin electrooxidation, the optimal composition of mixed metal oxyhydroxides—crucial for achieving higher yields and faradaic efficiencies—has not been thoroughly investigated until now. This optimization was made possible by a comprehensive study beginning with lignin model compounds, which elucidated the reaction mechanism and facilitated the subsequent scaling of the reaction using organosolv pine lignin. Remarkably, this approach yielded up to 6.0 wt% vanillic acid. These unprecedented results were achieved through the meticulous design of an electrochemical flow cell, ensuring that the electrochemical production of lignin monomers is not only cost-effective and selective but also easily scalable.

Organic electrosynthesis has emerged as a unique platform for chemical manufacturing owing to not only the use of electricity as a green reagent, but especially, to its distinct reactivity. While conventional solvents are sought to remain inert and solely provide a liquid environment for the electrochemical process to occur, fluorinated alcohol solvents have been shown to redefine this concept. In fact, the singular properties of these solvents allow them to actively interact with the substrates and reaction intermediates driving dramatic changes in the chemo- and regio-selectivity as well as on the reaction yields. Given the rapid permeation of these solvents in the burgeoning field of electro-organic synthesis, this mini-review strives to provide a concise but up-to-date critical revision for the growing community of scientist working at the interface of synthetic chemistry and electrochemistry. Here, the main electrosynthetic transformations where they have been exploited besides their key role at activating certain reaction pathways will be highlighted. Finally, a forward-looking perspective on the more practical evolution and implementation of these systems will be discussed.

Covalent organic frameworks (COFs) have been extensively developed as photosensitizers for photocatalytic energy conversion over the past decade. However, current COF photocatalysts have yet to demonstrate the capability to harvest near-infrared (NIR) light (above 760 nm), which constitutes approximately 53% of the solar spectrum, for fuel or chemical conversion. In this work, we introduce a novel post-synthetic functionalization strategy for COFs by incorporating a palladacycle directly into the COF backbone, extending the light absorption of an azobenzene-based COF into the NIR region. This approach enables homogeneous, atomically-distributed Pd functionalization with a high loading amount of 12 wt% and without noticeable formation of Pd nanoparticles. The cyclopalladated COF, TpAzo-CPd, was utilized as a catalyst for photocatalytic hydrogen peroxide production under 810 nm illumination. This study represents the first implementation of COFs for NIR photocatalysis and opens the door to Pd-single-site COF catalysts for a wide range of organic transformations.