the eXternal mind

This was my final paper for my independent research project in a laboratory class, Ch 15, at Caltech. I’m currently in finals week so I have about 4 finals to take and 1 more assignment to finish.

Abstract:

Brita(R) water filters are popular personal and home water filtration systems that claim to reduce, among many impurities, the concentration of copper in tap water by at least 74% and chlorine by at least 94%. These claims and the performance of the filters were tested by filtering residential tap water and then collecting filtrated samples at various points along the filtration process up to 40 gallons (Brita(R) ’s claim of the filter’s lifespan). By using mercury electrode differential pulse cyclic voltammetry and uv-vis spectrometry (on DPD colorimetric reaction), the concentrations of copper and chlorine, respectively, were determined in unfiltrated and filtrated tap water. The results showed that there was an average of 36.10% +/- 2.43% reduction of copper and 72.49% +/- 0.03% reduction of chlorine throughout the 151 L (40 gallons) filtering of the Brita(R) water filter. There was also a detectable difference (5.48% change for copper and 17.12% change for chlorine), albeit small, between new filters and filters due to be replaced after 151 L. Under real world usage of the Brita(R) water filter (and not in prepared laboratory samples), Brita(R) ’s claims about percent reduction are overestimated by ~43% for copper and 13% for chlorine.

Full Paper: Analyzing the Effectiveness of Brita® Water Filters (PDF, 565 KB).

I’m somewhat 6-7 weeks into my SURF (summer undergraduate research fellowship) at the University of Pennsylvania (although I got the SURF from Caltech) so I figured I should post something.

The project I’m working on is slightly different than from my project proposal that I posted a few months ago. Essentially, I’m more focused on making porphyrin for conducting polymers now instead of for supercapacitors. In short, a conductive polymer is like a wire but made with organic elements (like carbon, oxygen, nitrogen atoms) instead of with metals (like copper, silver, iron, although a little bit of metal can be added). Conductive polymers are cool because they can be used to create molecular electronics (imagine wire being constructed piece by piece on a computer chip), organic electronics (such as OLEDs), supercapacitors, and generally cheaper electronics.

However, a problem that they suffer from is that their conductivities are not very high. For instance, the electrical conductivity of copper is 59.6*10^6 S-m^-1 whereas polyacetylene, a conducting polymer, has a conductivity of around 10^-7 S-m^-1 which is like 18 orders of magnitude smaller. However, a better comparison would be with silicon (which conducting polymers have a good chance of replacing) which has a conductivity of around 10^-5 S-m^-1 (I’m not too sure on this number so don’t quote me on this).

Porphyrin can be made into conductive polymers (although we are working with oligmers, really short polymers with only a few units length), and recent research (by my mentor Paul and the group) has shown that it has the potential to have conductivities at or even better than amorpous silicon!

My project consists of working with a certain class of porphyrin and synthesizing a new variant of them. This new variant will have a flatter chemical structure that will allow the porphyrin oligmers to pack more closely to each other. When they are closer to each other, then they can interact with each other better (pi-pi bonding is increased) and pass electrons (and holes) more effectively.

Well, at least that’s what my mentor and I think so far. I’m still in the process of making the porphyrin. The synthesis process is proving to be really tedious since it has around 12-15 steps which, after each step, requires one or more purification processes (mostly column chromatography). In total, I have over 24-28 steps to complete. Each step takes around a whole day so this is pretty much why I’m still in the synthesis process.

The yield is also very low (around 15-20%). The amount of material I’m currently working with is about 1 gram (I started with around 4.5g). Probably by the end of the all the steps, I’ll end up with maybe 0.2 grams of porphyrin. But those 0.2 grams are the result of over 6 weeks of labor and hundreds of dollars of materials. This is partially the reason why my mentor in recent days keeps reminding me to guard these samples (not fully synthesized yet though, but very close) with my life. Although he’s kind of joking, pretty much, if I screw up (which I’m very prone to do), I should just like give up and go into computer science or something.

The idea of manipulating matter at will (aka. Chemistry) is tremendously awesome, but it can be so tedious at times. For instance, if one comes up with an idea in chemistry, it might take weeks just to test it. That’s too long! I’m used to the computer science method is programming things at once and making modifications on the fly—instant feedback.

I actually started writing this post last week or so and didn’t get around to finishing it. Today, my mentor (he helps me do a lot of synthesis work) are almost close to completion. We have two and three these new porphyrin variants connected. Our goal is to make a pentamer (five connected porphyrins). The next reaction should give us a pentamer. After purifications and such, we should have the final product by the end of this week.