Video Transcript
How do nanoparticulate coatings on self-cleaning windows work? (A) The nanoparticulate coatings generate electricity that powers wipers supported on the windows. (B) The nanoparticles in the nanoparticulate coatings move left and right, wiping the glass. (C) The nanoparticulate coatings are nonstick coatings that stop the dirt from adhering to the glass. (D) The nanoparticulate coatings catalyze the breakdown of dirt in the presence of sunlight.
Nanoparticulate coatings consist of a thin layer of nanoparticles coated onto the surface of material for a specific purpose, for example, to make windows self- cleaning. Nanoparticles are particles one to 100 nanometers in size or diameter. Their very small size or large surface area relative to their volume ratio gives them unique properties. A high-surface-area-to-volume ratio means that there is a large surface area exposed. In other words, the smaller the particles are, or the smaller their volume is, the more surface area is exposed to surroundings and to reacting particles that might react with or interact with nanoparticles.
Since nanoparticles have a high-surface-area-to-volume ratio, they can interact with reactants at a fast rate and increase the rate of a chemical reaction. So nanoparticles can act as a catalyst. A catalyst is any substance that increases the rate of a reaction without undergoing a permanent chemical change itself. There are many types of nanoparticles that can act as a catalyst, and some are made of a metal oxide compound and are known as metal oxide nanoparticles.
And a specific example of a metal oxide nanoparticle is TiO2, titanium dioxide. Titanium dioxide nanoparticulate coatings are sometimes put onto windows to make them self-cleaning. You might know titanium dioxide from other things like shiny paints, toothpaste, and many other shiny products.
So how do these nanoparticles help to self-clean a window? In the glass industry, if a thin layer of titanium dioxide nanoparticles are coated onto a glass window, these particles can act like catalysts. When the particles interact with ultraviolet radiation or sunlight, they produce electrons. These electrons then convert water molecules from the air into hydroxyl radicals, which are similar to a hydroxy group or hydroxyl group, except that one of oxygen’s electrons remains unpaired. The hydroxyl radicals then interact with and break down carbon-based grime on windows. And large dirt particles are broken into smaller dirt particles. These smaller particles are washed away by rain much easier than if they had not been broken down.
As we can see, the only answer choice that matches this description is answer choice (D). Titanium dioxide nanoparticles catalyze the breakdown of dirt in the presence of sunlight. Titanium dioxide nanoparticles cannot create electricity. So answer choice (A) is wrong. Titanium dioxide nanoparticles do not move from side to side, so answer choice (B) is wrong. Titanium dioxide coatings are hydrophilic when exposed to UV light and are not nonstick or hydrophobic, so answer choice (C) is also not correct.
How do nanoparticulate coatings on self-cleaning windows work? The answer is (D): the nanoparticulate coatings catalyze the breakdown of dirt in the presence of sunlight.
