Youven Benseghir

Développement de nouveaux catalyseurs hétérogènes basés sur les polyoxometalates et « metal-organic frameworks » pour la photoréduction du CO₂: Dans le contexte du réchauffement climatique, le développement de nouvelles sources d'énergie propres et durables est un défi sociétal majeur. La réduction du CO₂ représente une stratégie prometteuse pour stocker les énergies renouvelables. Au cours des dernières décennies, plusieurs catalyseurs pour la photoréduction du CO₂ ont été développés, cependant ces derniers souffrent souvent d’un manque de stabilité ou de problèmes de recyclabilité typiques des catalyseurs homogènes. Dans cette thèse, nous proposons de nouveaux systèmes catalytiques hétérogènes pour la photoréduction du CO2 basés sur la combinaison de catalyseurs, de polyoxométalates (POMs) et de metal-organic frameworks (MOFs). Après avoir brièvement décrit les catalyseurs pour la photoréduction du CO₂, les POMs et leur immobilisation dans les MOFs dans un premier chapitre, nous décrivons dans le second chapitre la co-immobilisation d'un catalyseur à base de rhodium et d'un POM de type Keggin dans l’UiO-67. Le composite résultant est capable de réduire le CO₂ en formate plus efficacement que l'analogue sans POM. Le chapitre 3 décrit l'application du MOF-545 (PCN-222) pour la réduction du CO₂ en formiate. L'effet de la métallation des ligands porphyrine ainsi que l’influence de la taille des particules sur la photoréduction du CO₂ est discuté. Le dernier chapitre se concentre sur les composites à base de POM et sur la synthèse de trois nouveaux matériaux de type {P4Mo6} ayant une activité de photoréduction du CO₂donnant CO et CH4. Dans l'ensemble, ce manuscrit représente un pas en avant vers le développement de catalyseurs hétérogènes efficaces pour la photoréduction du CO₂ en produits à valeur ajoutée.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) offer remarkable porosity and chemical tunability, yet their integration and shaping into binder-free, mechanically robust, and porosity-retaining architectures remains an issue. Here, we introduce reactive direct ink writing (RDIW), an additive-manufacturing strategy that utilizes the intrinsic thixotropy of high-aspect-ratio MOF nanorods to create printable inks without any polymeric binders. After extrusion of the ink into a bath of COF monomers, rapid imine condensation produces a continuous COF sheath around each filament, forming core-sheath MOF/COF aerogels that preserve the microporosity of both components. We demonstrate that this approach is general across multiple MOFs and four imine-linked COFs and produces wood-pile structured monoliths with tuneable composition and architecture. The 3D-printed aerogels exhibit over 4 times higher initial rate of adsorption h ₀ than MOF, COF, or sol–gel-derived MOF/COF analogues, while maintaining structural integrity and recyclability. RDIW establishes a scalable framework for shaping porous crystalline materials into mechanically resilient, high-surface-area monoliths, opening new opportunities in water purification, separations, and catalytic flow systems.

The incorporation of polyoxometalates (POMs) into transition metal‐based photosystems has emerged as an effective strategy to boost photocatalytic performances for CO ₂ and water reduction into renewable energy vectors. Despite significant progress in designing {POM, porous host} composites containing isolated catalytically active metal complexes, the atomic‐level understanding of their structure‐function relationship remains limited. Here, we investigate the effect of encapsulated [PW ₁₂ O ₄₀ ] ³⁻ POMs on the photocatalytic CO ₂ reduction (CRR) performance of a Rh‐catalyst, namely the pentamethylcyclopentadienyl rhodium(III) (Rh ^III Cp*), immobilized in porous organic polymers (POPs) and compare it with the Rh ^III Cp*‐functionalized UiO‐67 MOF. While the incorporated POM enhances overall activity in both systems, (POM,Rh ^III Cp*)@POPs show a stronger shift in selectivity toward the hydrogen evolution reaction (HER). By combining the high sensitivity of dynamic nuclear polarization enhanced NMR spectroscopy with atomistic computational modelling techniques, we elucidate the POMs’ location, speciation and host‐guest interactions within the amorphous POP matrices. The results reveal that in presence of solvent, electrostatic anchoring of POMs to the POP's backbone promotes the accumulation of HTEOA ⁺ proton donors near Rh active sites, favoring selectively HER up to 240% of the initial activity of catalysts without POM incorporated. The latter contrasts with the confinement of the POM within the narrower pores of UiO‐67, limiting POM···HTEOA ⁺ interactions, thus enhancing both CRR and HER activity.

Zeolitic Imidazolate Framework (ZIFs) glasses possess both the intrinsic porosity of Metal–Organic Frameworks (MOFs) and the melt-processability of conventional glasses, thereby representing a new class of porous materials that has already demonstrated established promise across a range of applications. However, unlike the high pore tunability in crystalline MOFs, pore engineering in MOF glasses is challenging due to pore collapse during melting and the overall amorphous structure. Therefore, developing a versatile strategy to tune pores in MOF glasses is of critical importance. This work demonstrates that vacuum-assisted heating allows Ångstrom-scale pore engineering in ZIF-62 glasses. The negative pressure dependence on ZIF-62 glass formation and porosity was systematically investigated by going from ambient pressure to high vacuum (HV, 1×10−10 bar) for heating of ZIF-62. A clear correlation between vacuum strength and final glass pore size is observed. High-Resolution Transmission Electron Microscopy (HRTEM) showed significantly larger porosity in ZIF-62 glasses formed under higher vacuum conditions, further supported by CO2 gas sorption showing an increase in CO2 uptake capacity from 0.29 mmol·g-1 for ZIF-62 to 0.94 mmol·g-1 for agZIF-62HV. Comprehensive characterization (XRD, ED, XPS, IR, Raman, DSC, TGA) confirms the preservation of the chemical environment, and gas sorption reveals changes to the porosity structure. These findings, combined with the unprecedented colorless nature of the resulting glasses, highlight the potential of negative pressure as a parameter to tune the microstructure and porosity in hybrid glasses, which in turn further advances the applicability of these materials in fields where precise structural control is of critical importance, such as catalysis, separation or capture processes, and advanced optics.

NU-1000, a pyrene-containing benchmark metal–organic framework (MOF), is well-known for its utility and potential across a wide range of applications. Although the extended π-systems in NU-1000 confer favorable properties for diverse photochemical applications, they also increase the susceptibility of the MOF to photodegradation. However, the photostability of NU-1000 has yet to be systematically studied and remains poorly understood. Herein, we report that in the presence of oxygen, water, and light of appropriate energy, extensive oxidation of the pyrene linkers of NU-1000 can occur to yield terephthalic acid as the major decomposition product. Through extensive mechanistic studies, we show that the open framework structure of NU-1000 greatly facilitates linker oxidation, with more than 25-fold greater linker decomposition from the MOF within 3 h of photoirradiation compared to a homogeneous solution of the linker, brought about by rapid generation of pyrene-centred holes. By determining the specific conditions under which the MOF remains stable, our findings offer not just valuable strategies for preserving the integrity of NU-1000 for controlled applications but also reveal its ability to decompose into benign products under ambient light and oxygen, which could provide an eco-friendly route for avoiding environmental accumulation of MOF materials for various applications.

Metal-organic frameworks (MOFs) show promising results in various fields, such as gas separation and catalysis, but they face limitations due to problems associated with their low processability. This study addresses these challenges by utilizing postsynthetic modification (PSM) of NH₂-UiO-66 and NH₂-MOF-808 with 1,3,5-benzene tricarbaldehyde (BTCA) to form hybrid aerogels consisting of MOF-loaded covalent organic framework (COF). BTCA-modified MOF nanoparticles via imine bond formation were confirmed by ¹H NMR, FTIR, and solid-state ¹³C NMR spectroscopies. MOF/COF composites were analyzed via TGA, PXRD, BET, and solid-state ¹³C NMR, showing retained crystallinity and increased porosity in comparison to the sum of the individual components. Moreover, improved aerogel mechanical properties and increased MOF loading of up to 75 wt % were achieved for covalently bound aerogels. Hybrid aerogel composites were successfully utilized as catalytic filters for the decomposition of nerve agent simulant and pesticide dimethyl-4-nitrophenylphosphate (DMNP), avoiding secondary pollution associated with MOF powder catalysis.

To achieve high catalytic activity of artificial photosystems in carbon dioxide reduction or water reduction/oxidation into renewable energy vectors, the use of sacrificial electron do-nors (SEDs) remains mandatory. Despite significant progress in artificial photocatalysis, a detailed understanding of the influence of the SEDs on the reaction mechanism is still lack-ing. We have explored the roles of triethanolamine as SED in the selective CO2 to formic acid photoreduction promoted by various pentamethylcyclopentadienyl rhodium(III)-based porous materials as model catalysts, including polyoxometalate-doped systems. In the pres-ence of anionic polyoxometalates, agglomeration of protonated triethanolamine close to the catalytically active site favours H2 evolution over CO2 reduction, which can be modulated through the degree of confinement imposed by the pores size. Radical trapping experiments and EPR spectroscopy show that triethanolamine-radicals are crucial for a high activity in CO2 reduction. Triethanolamine-radicals act as electron relays in the efficient two-electron activation of the catalyst, regardless whether a homogeneous or a heterogeneous catalyst is used. In contrast, triethylamine-radicals cause deactivation of the one-electron reduced cata-lyst, thus highlighting the effect of different SED-intermediates and underling the im-portance of an appropriate SED.

We present the development of dynamic and patternable liquid photonic crystals (LPCs) based on zeolitic imidazolate framework-8 (ZIF-8) crystals, an approach that exploits the unique optical and structural properties of metal-organic frameworks (MOFs). By utilizing monodisperse ZIF-8 particles with tunable size and morphology, our study demonstrates the formation of vibrant structural colors via reversible electric-field-induced assembly. These LPCs exhibit rapid color modulation, angle-independent coloration, and remarkable stability, surpassing the performance of traditional LPCs. A key finding lies in the observation of metamerism within MOF-based LPCs, where spectrally distinct configurations appear indistinguishable to the human eye, potentially enabling hidden optical encoding. Additionally, our patterned electrophoretic displays showcase the ability to generate dynamic color patterns, further emphasizing their versatility. This work represents the first realization of on-demand structural color control of MOF-based materials, whereby the observed metamerism of the materials could unlock new opportunities for advanced photonic applications such as anti-counterfeiting, optical encoding, and dynamic displays.