[Enthalpy]

Hello you all,

I just read that, as catalysts must have a big surface but then light for photo-catalysis gets difficult to bring to them, a research group puts nanoparticles of catalyst on a foam, said foam keeping the resulting material aerial enough to allow the activating light reach everywhere.

I feel this is improvable.

Imagine an optical fibre channelling the activating light: it's thin and can be very long, so it brings much surface in little volume, and can be winded, crumpled or woven to compact dimensions. By putting the catalyst at its surface, it gets the activating light, for instance through fading waves, or because catalyst particles make the fibre cladding thinner where they adhere.

If the reaction medium is a gas, light will stay naturally in the fibre. If it's a liquid, whose index may exceed the fibre core's index, the lower-index cladding should be made thicker to limit light losses.

If the reactants need light but no solid catalyst, and are opaque, the optics fibre is also a way to bring light through the fading wave to a large volume, without a catalyst.

As an example or form, one (or more) long fibre is winded on a hollow mandrel consisting of several parallel struts. Tiny spacing between the turns is achieved directly by winding precision, or by co-winding a spacing wire that is subsequently removed, or by tiny notches machined in the struts. The reactants and products can then flow from the inner to the outer of the quasi-cylinder made of optics fibre. Several layers of winding are feasible as well; they were produced with a spacing, a long time ago, of copper wire for radio receiver coils.

Marc Schaefer, aka Enthalpy

[Enthalpy]

A few sub-sub-details and variants.

Making the catalyst particles as tiny as possible is tempting. A different option is a size that resonates at the active wavelength as quantum dots do. Then, the particles amplify the standing wave and the field without implying a propagating wave that takes power away. An added benefit is that resonating particles would couple well with the fibre though the cladding of lower index, without needing a locally thinner cladding. Keep in mind that the proximity to the fibre shifts the particle's tuning, which depends on the surrounding medium's index as well. Easier with a gas.

Though, as a long fibre as already a big surface, I believe the catalyst can be a uniform coating on the fibre. Being excited by the fading wave, it doesn't need to waste much light, even if the light is intense.

Long-distance data transmission prefers silica fibres, but catalysis has different needs. Maybe some materials can both channel light and act as a catalyst, like TiO₂? The huge index would save the need for a cladding. I expect a photocatalyst acts when photon energy is above the transparent energy domain, but:
- Some dopant in the transparent fibre (or at its surface) could make it a photocatalyst at lower photon energy. Then, dopant concentration would adjust the distance over which light is used.
- Frequency doubling or tripling in the fibre, or at its surface, would bring light from the transparent energy to the energy activating the catalyst.

Light can be pulsed. This changes radically the efficiency of frequency multipliers, and may be requested by them. It can also favour chemical reactions that need several species to be excited, making the photo-catalysis more selective, and adjustable. The optics fibre itself is already a means to bring concentrated light to the catalyst.

Marc Schaefer, aka Enthalpy