The main material that I will be working with is titanium dioxide, TiO2, often called titania. Titania has a lot of uses, most often as a white pigment in everything from paint to skim milk and makeup. This widespread use is great, because it means that titania is pretty cheap. The reason I'm investigating titania is because it also functions as a photocatalyst. The means that when UV light strikes titania, it causes changes in the material that create free radicals. These free radicals are super reactive and really want to oxidize any organic materials they come into contact with. Since sunlight contains a small UV component, this reaction is pretty easy to activate. The material can even be reused for subsequent reactions later. Here is a sort of vague schematic showing this process:
Often, these organic materials are pollutants in the water or air (as shown above), or bacteria, either airborne or on surfaces. For this reason, titania is being incorporated into a lot of building materials such as roofs and external paneling (to treat local air pollution), or internal paneling or tiles (in, say, a hospital, to reduce surface bacteria concentrations). Here's a cool picture showing a comparison between ordinary tiles (the super dirty ones) and titania coated tiles (very clean!).
My project uses titania for it's ability to break down organic pollutants in water. This sounds pretty simple: you throw the titania in the water, put it in sunlight, and the titania cleans it all up. But afterwards, how do you separate the titania from the clean water so that you can use it again? This is where my project comes in. I'm going to be synthesizing magnetic titania "core-shell" pebbles. Titania by itself is not magnetic, but what you can do it make an M&M like structure where you have a magnetic material in the core, and the titania around it as the shell. The cool thing about this is that once you've got the water all cleaned up, you simply turn on a magnetic field to separate out the titania for reuse. Easy! The magnetic core is typically iron oxide. So, in order to do this, I first have to make tiny iron oxide spheres, then coat them with titania. Because science is never simple, we have one more problem. The direct contact between the iron oxide and the titania seems to reduce the photocatalytic activity (how well it works to break down the pollutants) of the titania. So, we have to add in a "buffer" layer of silicon dixoide between the iron oxide and the titania. This adds another step to my process: make the iron oxide spheres, coat them with silica, then coat them with titania.
Just making these pebbles is not too hard - it takes time but ultimately it's not all that challenging. Now here's where the fun starts. Materials can be divided into two classes: crystalline and amorphous. Crystalline materials have a very regular, predictable structure in which each atom goes in a certain position. Amorphous ones don't. They're just all jumbled up every which way. Here is a good comparison.
Normally the way to check for crystallinity is to use x-ray diffraction, which I've talked about before. But in the case of titania, there is often a pretty significant amorphous content that doesn't show up on the x-ray diffraction spectrum. There are other ways to figure out the amorphous content, but I won't go into them right now because they're pretty complicated of course, I have to do them for this project). But what previous studies have found is that the amorphous content of the titania is possibly related to the photocatalytic activity of the material. So, part of my project will be trying to pin down this correlation. This first requires me to set a standard method for determining the amorphous content of the material (I probably get to use a synchrotron - a huge circular particle accelerator. So cool!). Then, I'll look at the photocatalytic activity and see how that corresponds to the amorphous content and what can be modified in the material synthesis to change the amorphous fraction of the material.This is probably more than enough work for nine months. Better go get started.
Update: I just tried to go get my materials to start this and they are locked up in this guy Hou Ran's cabinet and Hou Ran isn't going to back until Wednesday and no one has the keys. My postdoc just told me to go sightseeing. Hahaha Singapore is so inefficient like this.
I like best the synchrotron, and the ending. Reading through it struck me that the slow obstaclecrawl (not to be confused with the lobstercrawl, a vaunted Maine tradition, or the the monocle call, which is the sound you make when you have lost your monocle in the parlor)--anyway, the whole process strikes me as not that much unlike the slow crawl of writing beautiful verse. It takes many, many failed attempts to hit anything remotely worthwhile, anything that touches others' lives and souls and worlds. But we struggle on. What the hell else are we gonna do?
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