Water. Desalination + reuse
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Water. desalination + reuse June 2017 FAR SITE 29 Q & A A L B E R T O N A L D O N I "It might be possible to control what you want from a chemical reaction" • Plasmonics is a eld of nano photonics which is the use of nano materials that can concentrate light in nano scale volumes. This is possible because these materials sustain collective oscillation of surface electrons, which are surface plasmons. So these surface plasmons absorb solar energy, light, and concentrate this light in a very small nano metric volumes. • You can use this structure in a device like solar cell or photo electrical device which needs to convert sunlight to split water to make hydrogen and oxygen, or to produce solar fuel for CO2 reduction. The other way to use plasmonic structure is to exploit the decay of these surface plasmons which occurs in a very short time. This decay produces highly energetic electrons and holes that can be used to do chemistry which is usually only possible in very extreme conditions. So, through light you excite the materials and you have these very energetic electrons and those can drive chemical reaction more e• ciently, or in a di• erent way that is usually not possible in ambient conditions. This is exciting because you can activate molecular pathways that are di• erent from the usual pathway followed by chemical reaction. And so it might be possible to control what you want to obtain from a chemical reaction and obviously this is very interesting. • A er decay these materials produce intense local heating, so this collective oscillation of electrons coupled with lattice vibration of the material produces heating which is local on the nanostructure. So you convert solar energy into heat. This can be very interesting for chemistry to drive a thermal reaction. Using this nanostructure, you can generate a very high temperature on the nano metre scale, so on the single structure, and you can drive this chemistry without other energy input. You use solar energy and produce heat to drive chemical reaction on the structure. • Another way to use this heat is to drive a chemical separation process. You generate heat on the nanostructures, and this can be on a lm, so you can have a large area. Immerse this in water, and you can drive evaporation. You can obtain a very e• cient device based on plasmonic particles that drive very e• cient desalination. You have solar evaporation, mediated in this case by particles that concentrate light, generate local heating at high temperature, and they induce the evaporation of water, so you induce desalination. What is plasmonics? How does it apply to sustainable chemistry? How can plasmonics use solar energy in chemistry? How does it apply to desalination? Alberto Naldoni, is senior researcher, senior scientist, and co-leader of the photoelectric chemical group at the Regional Centre of Advanced Technologies and Materials at Palacky University, Olomouc, Czech Republic "It might be possible to control what 'Applying plasmonics to a sustainable future' by Alberto Naldoni, Vladimir Shalaev, and Mark Brongersma, was published in Science on 2 June 2017 a catholyte solution, and the sec- ond is to have an air cathode." He adds: "We are desalinat- ing water with very, very low energy consumption We are talking about 0.5 kWh per cube. It's radically lower than the con- sumption that we have in our RO plants of 3 to 4 kWh. And, the way of gathering this electricity from wastewater is completely new. We use the energy content of the wastewater for powering desalination." Inside the microbial desalination cell In between the pre-treatment and the reverse osmosis (RO) is the microbial desalination cell (MDC). The ion exchange membranes in the MDC receive seawater and make it brackish. The MDC enables a decrease in salinity from around 35,000 milligrams per litre, to around 5,000 milligrams per litre, owing to the electrical current that is formed between the cathode and anode inside the MDC. The geobacter is coating the cathodes; and nutrients from the wastewater stream are enabling the geobacter to survive. The concept comes from microbial fuel cells, and the innovation here is the application to ion exchange membranes, and their ability to use the electrical current to desalinate water. The innovation comes from IMDEA research centre in Madrid, Spain, where professor Abraham Esteve-Nunez was the first person to come up with the idea to apply it to desalination. The microbial desalination cell (MDC) will be operating at pre-pilot scale, which is the biggest MDC ever built in the world. Victor Monsalvo, head of eco-effi ciency, innovation and technology department, FCC Aqualia