Spatial compartmentalization of multiple active sites on arrays of interconnected porous nanotubes for cascade catalysis
Internal reference number 21/26-117
Start date 01/10/2021, end date : 30/09/2026
Multifunctional catalysts able to perform cascade reactions in a single reactor allow chemical processes intensification, while the use of nanomaterials affords energy savings, the possibility of non-thermal activation methods such as photocatalysis and localizing active sites in separated nano-compartments. Hollow nanostructures are excellent catalyst supports or nanoreactors, but so far most research efforts have concerned spherical objects. Using nanomaterials with anisotropy, such as nanotubes, offers more possibilities for materials tailoring: their inner and outer surfaces can be differentially functionalized, their open mouths make the inner surface accessible, and they can be assembled into 3D self-supported superstructures.
In this context, the present project aims at elaborating 3D networks of nanotubes with controlled dimensions and porosity, decorated with multiple active sites to allow cascade reactions. In particular, these 3D networks will be applied in photocatalytic reactions pertinent to fine chemistry.
These new systems offer unique opportunities for catalytic applications:
They allow to precisely localize active sites:
- Inside the hollow cavities vs. on the external surface of nanotubes,
- In the solution or grafted chemically onto the solid surface,
- With active sites belonging to the world of heterogeneous (nanoparticles) or homogeneous catalysis (organometallic complexes),
- With several (incompatible) active sites placed in locations well-separated from each other.
These new nanostructured reactors can be obtained with a great variety of compositions such as oxides, metals and polymers. Moreover, the size and geometrical arrangement of nanotubes can be tuned at will, and their walls can comprise a secondary porosity to improve further mass transfers.
Free standing scaffolds based on fully interconnected hollow nanotubes allow to implement flow chemistry and continuous processes.
The arrays of interconnected hollow nanotubes provide a perfect platform for systematic and thorough investigations of catalytic cascade reactions at nanoscale and, more precisely, enable to study the following fundamental questions:
- What is the effect of (nano)structuration on the activity but also the selectivity of immobilized catalysts?
- What is the effect of localizing several active sites in compartmentalized solids, to perform cascade reactions with non-compatible systems? Is this applicable to catalysts from different worlds (for example organocatalysis and photocatalysis, hybrids inorganic/organic, …)?
- Is it possible to obtain synergetic effects between solid supports and catalytically active sites? Especially in the case of photocatalysis and plasmonic activation, is it possible to give an active role to the support to harvest light?
Gold Nanorods as plasmonic photocatalyst
In addition to the elaboration of interconnected nanotubes, this project explores the development of gold nanorods as plasmonic photocatalyst via a seed-mediated method. Those nanoparticles exhibit two absorption peaks due to their anisotropy, with the second one being tunable depending on the aspect ratio of the rod (= the ratio between the longer and smaller physical dimensions).
A statistical model was built to predict the position of the second absorption peak of the nanorods based on the concentrations of the various reagents, i.e. CTAB, AgNO3, HAuCl4, hydroquinone, and the seeds. Such predictive models provide a valuable tool to optimize the synthesis process and fine-tune the optical properties of gold nanorods, which are crucial for applications in plasmonic catalysis and photonic technologies.
