i always wondered why membranes. can we not drill 0.2nm holes in silicon for instance?
I think that this is interesting question, and should not be waved away with "just drill some 0.2nm holes, use a real small drill bit"
0.2nm is tiny, given that it's on a scale that impacts how H2O molecules behave.
It's also smaller than our ability to make the circuits in computer chips, which are currently > 1 mn (1).
Use a laser? Light with a comparable wavelength is x-rays. As used in the chip manufacturing (2)
This is about size of the spacing between individual atoms (3)
So it seems like a material with 0.2nm holes "drilled" into it would be a major engineering feat at least.
1) https://research.ibm.com/blog/1nm-chips-vtfet-ruthenium
Also, if you take some fritted glass and wrap it around a solid core, such that the holes don't go anywhere — i.e. they're just pits that water molecules (but not anything larger) can enter, and then get stuck there by surface tension — then you've get https://en.wikipedia.org/wiki/Molecular_sieve s.
Some people have also experimented with single and double layers of graphene with a few very small pores. Because they are so thin, you don't need as much porosity for high transport rates.
You still have fouling issues, though.
That's literally individual silicon atoms removed
"The nearest neighbour distance is 0.235 nm" https://www.princeton.edu/~maelabs/mae324/glos324/silicon.ht...
It doesn’t imply that there should be a solution but you still want to learn why it might not work. Often you can continue the conversation enough to either exclude it or think some more about the problems that are described.
Lots of curious laypersons here, and it's often a useful way to learn. Usually it's pretty easy for an expert to answer such questions.
In this case, if you ask "can we just do this" you should follow through with "how big is that actually, what's of comparable size?" We can all google this, or learn how to. It's a useful way to learn. You won't learn how to find things out, by always just asking "can't we just" questions and walking away.
In this case, soon you'd find out that 0.2nm is on the same scale as the spacing between individual atoms in a silicon crystal.
Literal "drill" bits for removing 1 atom at a time are obviously out of the question.
It is 10x smaller than the 2nm, the scale of the best x-ray lithography computer chip manufacturing processes.
Also, for membranes, it’s not only the size and shape of the ‘holes’ that count. Many have specific chemical properties that do not solely filter on particle size.
https://www.princeton.edu/~maelabs/mae324/glos324/silicon.ht...
So no, you don't get drill bits that are 1-2 atoms wide.
Also it would take a long time to "drill" a useful number of holes if you do it one by one.
Use X-ray lithography maybe? The wavelength can be short enough and it might be more feasible to do in bulk.