Light, electrons, photons and contamination

Light, electrons, photons and contamination

Light, electrons, photons. The rider is interested in light that there is no doubt. It must be why we found a chemical in the Faculty of Natural Sciences and wander with him on these issues.
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By Leonardo Moledo

-You work with and photochemical air pollution. Why am I not a bit what this is?

-Tell a little story. My first thesis in silver on the photochemical reactions between gases (molecules in the atmosphere, but in a closed container). The photo is actually the study of chemical reactions that are related to the light: I was going through various stages until finally I devoted myself to the photochemistry of solids, or systems.

- And what he is doing now?

Two things. On the one hand, the study of reactions that occur with light in ways organized or ordered and on the other, we studied the chemical reactions that occur in the atmosphere through field work: we measured the concentration of pollutants and try to make models to predict how keep the thing going and how we can improve. That brings me almost to my roots: the relationship between particles and gases back to the relationship between gases. They are two completely different projects. Our activities in atmospheric chemistry are well known. But it is not our main line of inquiry.

- And what would prefer to speak?

-What is under press ...

Talk-time of light and the sound ...

-The example of the action of light on photosynthesis is organized systems: here we have light that is irradiated on the leaves, which contain chlorophyll and other pigments that are arranged to absorb light and channel the reaction center. Then, through the action of the center, the light is converted into carbohydrates, etcetera, etcetera. While this paradigm is the action, is not what we studied. We take some of that photosynthesis to create artificial systems that allow us to harness sunlight to produce certain substances. For example: there is a cancer treatment, photodynamic therapy is that, based on the introduction of a color in the body and irradiation in the area where the cancer. The dye is introduced in a general system and then it focuses on the area where the cancer is, so that when the dye that absorbs light is accumulated there, is excited. The dye is highly reactive, so as to effectively destroy the cell.

- Is it a therapy that is used?

In many countries do, here I have no reference was being used for experimentation. Now systems are being used a lot of nanoparticles, which are either themselves against reactive to light, or they incorporate dyes that are reactive. That is quite successful in the experimental field. To make the process more efficient, there must be a lot of dye molecules together. But this is a problem: the energy absorbed being together, is dissipated as heat from the reactions that are between them. The plants have solved the problem of organizing such a way that the concentration is very large, but the interactions between molecules are prevented to the maximum. A bit that is what we do, sometimes by very simple: take a solid, put it in a dye solution and we are left with a solid color, for example. Another way is to take a glass, put glass on an electrically charged polymer, we put up a load with the opposite color, then another layer of charged polymer and so on.

A sandwich-polymer and dye.

Something like that. The technique is called self layer by layer. Many people try to put the dye molecule in the specific location, which is very valuable. But we do not do this: try to find systems in which the molecules have to fall where they fall. Those are the two ways we are exploring, to put the largest possible amount of dye in a solid, either for a photodynamic therapy or to a photovoltaic cell works by absorbing energy in different regions of the spectrum. This can be achieved with different dyes, which absorb the largest number of regions of the spectrum. That is the strategy used by plants as well.

Come-a little to the intimacy of the action of light. We have a molecule that receives a photon, a particle of light. What about the photon?

-Molecules are made up of atoms, which themselves have nuclei and electrons. The molecules themselves are orbital, the atom: diffuse regions where the electrons. Externalities are the most involved in chemical reactions: when the molecule absorbs light, stir and move to a higher orbital.

- And there, what happens? How is that a photon in a jump to the upper layer?

The photon-electromagnetic field is in motion. The light has an electric field and magnetic field. In this case we are interested in the electric field that is oscillating. This field interacts with electrons, if the energy is reached, the photon is absorbed. By then, the interaction between the electron and the electric field is achieved by a molecule with an electron in a higher state. Why is this useful? It is more energy and more energy is allowed to give certain reactions that otherwise would not or would too slowly. This opens the way to energy storage. So do plants convert light energy and use that energy to generate compounds that otherwise can not be generated. The photon activates a molecule of chlorophyll, which triggers a cascade of reactions whose reactants are carbon dioxide and water, and its products are glucose and other carbohydrates.

And the idea is ...

-The idea is to excite as many molecules as possible with the widest possible spectrum of light and use these systems as building blocks for other things. However, one can have a photoelectric cell, which when absorbed light produces a charge separation, leaving the outside, closed the circuit and generates a current. This requires light of a certain energy, the energy at which the material absorbs. If one wants the material to absorb a different range of wavelengths, in a different area of the spectrum, what is done is to put a dye that is excited by absorbing photons, delivers an electron to the electrode and the electron is given turn out. Our particulitas be building blocks for this. Another example: photocatalysis.

-What is ...

-... a process whereby a semiconductor material (such as titanium dioxide) absorbs a photon, an electron loose and creates a vacancy. This electron can go into another molecule and the semiconducting molecule can receive electrons from the other side. The ability of these electron holes get so big that it can oxidize (remove electrons from) a bunch of molecules and destroy them, doing the reverse process of photosynthesis. Grab the material and convert it into carbon dioxide and water, which is very interesting for decontamination processes.

Well, because it talked about pollution, why I do not mind a bit of the other line of inquiry?

Ago as ten or fifteen years we started to work in collaboration with the Fundación Siglo XXI. I fell there for nostalgia, because it came from relationships with photochemical gases. We have learned since then what are the most important pollutants. What we wonder, too, is why we are not as bad as Mexico City or as Santiago de Chile.

But this may not be a chemical reason but for a reason ... weather, here we are surrounded by mountains.

Yes and no. One part of a series of primary pollutants (carbon monoxide, nitrogen monoxide, hydrocarbons) that if you have time, sunlight is converted into nitrogen dioxide and ozone, which are oxidants. These are the causes of smog, which is known in Mexico or in Santiago. There is no question of Meteorology: meteorology helps disperse pollutants and do not have time to react, or react further in other conditions. Weather is what happened in April last year, from where the fires took place in Buenos Aires Tigre everything was filled with an overwhelming humareda ten days.

-What I said is that the root chemistry course is, but why are neither James nor DF is that we are in an open city.

It is well. With a little objection. One thinks that the wind just sweeps. But if the wind sweeps, creeps. And what is produced here send it there. The wind dispersed. And not just the wind. That the wind that sweeps is a half-truth, because what it does is disperse.