Weirdly Specific Questions I Want Answers to in Meta-science, part 1

Using “meta-science” as a somewhat expansive term for history, philosophy, and sociology of science. And using my blog as a place to write about something besides the physical chemistry of carbon nanomaterials in various liquids.

  • To what extent is sloppy/misleading terminology an attempt to cash in on buzzwords? Clearly, we know that motive exists – there aren’t two major papers trying to narrow down precise definitions of graphene-related terms for nothing. But as the papers also suggest, at what point is it a legitimate debate in the community about setting a definition? “Graphene” was a term that described a useful theoretical construct for decades before anyone ever thought someone could make a real sheet of it, so maybe it isn’t unreasonable that people started using to describe a variety of physical things related to the original idea.
    • This contains a sort of follow-up: What properties do people use in clarifying these definitions and how much does it vary by background? Personally, I would say I’m way closer to the ideal of “graphene” than lots of people working with more extensively chemically modified graphene derivatives and am fine with using it for almost anything that’s nearly all sp2 carbon with about 10 layers or less. But would a physicist who cares more about the electronic properties, and which vary a lot based on the number of layers even in the lower limit, consider that maddening?
  • Nanoscience is very interdisciplinary/transdisciplinary, but individual researchers can be quite grounded in just one field. How much work is being done where researchers are missing basic knowledge of another field their work is now straddling?
    • For instance, when reading up on polymer nanocomposites, it seems noted by lots of people with extensive polymer science backgrounds that there are many papers that don’t refer to basic aspects of polymer physics. My hunch is that a lot of this comes from the fact that many people in this field started working on the nanoparticles they want to incorporate into the composites and then moved into the composites. They may have backgrounds more in fields like solid-state physics, electrical engineering, or (inorganic/metallic/ceramic) materials science, where they would have been less likely to deal with polymer theory.
    • Similarly, it was noted in one paper I read that a lot of talk about solutions of nanoparticles probably would be more precise if the discussion was framed in terminology of colloids and dispersions.

Oh my gosh, I made fun of the subtitle for like two years, but it’s true

  • Is the ontological status of defects in nanoscience distinct from their treatment in bulk studies of materials? This is a bit related to the first question in that some definitions would preclude the existence of some defects in the referent material/structure.
    • On the other hand, does this stricter treatment make more sense in the few atom limit of many nanomaterials? Chemists can literally specify the type and location of every atom in successful products of well-studied cluster reactions, though these are even pushing the term “nano”.
    • Is this a reflection of applications of defects at the different scales? (More philosophically worded, are defects treated differently because of their teleological nature?) At the bulk level, we work to engineer the nature of defects to help develop the properties we want. At the nanoscale, some structures can basically be ruined for certain applications by the mislocation of a single atom. Is this also a reflection of the current practical process of needing to scale up the ability to make nanomaterials? E.g. as more realistic approaches to large-scale nanotech fabrication are developed, will the practical treatment of defects in nanomaterials converge to that of how we treat defects in the bulk?

Using Plants to Turn Pollution into Profits

Once again, I may prove why I’m a poor writer, by burying a lede. But bear with me here, because this will come full circle and yield some fruit. You probably know that urban farming has become more popular over the last decade or so as local eating became trendy. As city dwellers started their own plots, people realized there might be a unique challenge to urban areas: avoiding lead poisoning. (Although a more recent study evidently suggests you’re getting less lead than people expected.) We used lead in lots of things throughout the 20th century, and it easily accumulated in the soil in areas exposed to high doses of some sources – so cities and areas by busy highways have lead from old gas emissions, old lots have lead from old paint, and even old lead pipes and batteries can leach lead into soils. There are other pollutants that can leach into soils in other places. Mercury and cadmium can build up in places where significant amounts of coal are burned, and many mining practices can result in a lot of the relevant metal leaking out into the environment.

Traditionally, the way to deal with polluted soil is to literally dig it all up. This has a major drawback, in that completely replacing a soil patch also means you throw out some nice perks of the little micro-ecosystem that was developed, like root systems that help prevent erosion or certain nutrient sources. Recently, a new technique called phytoremediation has caught on, and as the NYT article points out, it takes advantage of the fact that some plants are really good at absorbing these metals from the soil. We now know of so-called hyperaccumulators of a lot of different metals and a few other pollutants. These are nice because they concentrate the metals for us into parts of the plants we can easily dispose of, and they can help preserve aspects of the soil we like. (And roots can help prevent erosion of the soil into runoff to boot.) Of course, one drawback here is time. If you’re concerned that a plot with lead might end up leaching it into groundwater, you may not want to wait for a few harvests to go by to get rid of it.

But a second drawback seems like it could present an opportunity. A thing that bugged me when I first heard of hyperaccumulators was that disposing of them still seemed to pose lots of problems. You can burn the plants, but you would need to extract the metals from the fumes, or it just becomes like coal and gas emissions all over again. (Granted, it is a bit easier when you have it concentrated in one place.) Or you can just throw away the plants, but again, you need to make sure you’re doing it in a place that will safely keep the metals as the plants break down. When I got to meet someone who studies how metals accumulate in plants and animals last summer, I asked her if there was a way to do something productive with those plants that now had concentrated valuable metals. Dr. Pickering told me this is called “phytomining”, and that while people looked into it, economic methods still hadn’t been developed.

That looks like it may have changed last month, when a team from China reported making multiple nanomaterials from two common hyperaccumulators. The team studied Brassica juncea, which turns out to be mustard greens, and Sedum alfredii, which is a native herb, and both of which are known to accumulate copper and zinc. The plants were taken from a copper-zinc mine in Liaoning Province, China.  The plants were first dissolved in a mix of nitric and perchloric acid, but literally just heating the acid residue managed to make carbon nanotubes. Adding some ammonia to the acid residue formed zinc oxide nanoparticles in the Sedum, and zinc oxide with a little bit of copper in the mustard greens. What’s really interesting is that the structure and shape of the nanotubes seemed to correlate to the size of the vascular bundles (a plant equivalent to arteries/veins) in the different plants.


A nanotube grown from the mustard greens. Source.

But as Dr. Pickering said to me, people have been looking into to this for a while (indeed, the Chinese team has similar papers on this from 5 years ago). What’s needed for phytomining to take off is for it to be economical. And that’s where the end of the paper comes in. First, the individual materials are valuable. The nanotubes are strong and conductive and could have lots of uses. The zinc oxide particles already have some use in solar cells, and could be used in LEDs or as catalysts to help break down organic pollutants like fertilizers. The authors say they managed to make the nanotubes really cheaply compared to other methods: they claimed they could make a kilogram for $120 while bulk prices from commercial suppliers of similar nanotubes is about $600/kg. (And I can’t even find that, because looking at one of my common suppliers, I see multiwalled nanotubes selling on the order of $100 per gram.) What’s really interesting is they claim they can make a composite between the nanotubes and copper/zinc oxide particles that might be even more effective at breaking down pollutants.

I imagine there will be some unforeseen issue in attempting to scale this up (because it seems like there always is). But this is an incredibly cool result. Common plants can help clean up one kind of pollution and be turned into valuable materials to help clean up a second kind of pollution. That’s a win-win.