First attempt at Au separations with carbonized membranes
Today I tried to pass 5 nm gold through three different membranes with similar cut-offs but distinct mean diameters and porosities. All the samples I used were ozoned yesterday and tested for water permeability.
Based on the absorbance measurements, it seems that the 5 nm Au passes through 582 and 558 but not the carbonized 582 membrane.
I would like to see whether or not carbonization reduces the charge interactions between the Au and pore wall, but right now I’m forced to ozone treat everything to wet the pores. Up to this point, I’ve been unsuccessful at wetting all the pores in a carbonized sample. I will try soaking in ethanol for an extended period time next.
Just to be clear: When you say you are not “wetting all the pores,” you really mean that your agreement with theory isn’t checking out, right?
Also, did you try any larger gold?
Can you add a scan of your stock Au solution that was applied to your membranes on the graph above, so we can judge how much the gold NPs were hindered? Were the flow rates substantially reduced by the gold? Was the reduction in flow rate uniform across the samples or more significant in the carbonized sample?
Were these samples that were flow tested the previous day and allowed to dry? I’m curious if the flow testing could have changed the membranes slightly and influenced these results.
It’s curious that there is such a difference in gold passage through 582 and 558. 582 has slightly larger pores, which makes sense, but the difference is not large enough to fully explain the 2X difference in gold passage, right?
@Jim: Yes, I get inconsistent permeability when I do not ozone treat. I’m guessing it’s because of a wetting problem. I have tried larger gold, but I ran out of samples before I could complete my experiment.
@Chris: I wasn’t rigorous with keeping the volume passed the same in all the trials so the concentration was different for these samples. I was mainly concerned with determining if any amount of gold passed through.
Yes – these samples were first used to test permeability and allowed to dry overnight.
I will re-do this experiment again with fresh samples and keep track of volume passed so that we can determine the effects of pore size/porosity on transport.