published on 22 May 2016 in energy

Green chemistry

A bit of history
Chemistry accompanies man from that day long ago when coarse hands full of hope put out the first fire. Those men were unaware of it but they had just tamed a violent chemical reaction: the oxidation of cellulose contained in wood, which produces heat and light and whose by-product is carbon, the first element to be isolated artificially. From that day on, in the millenniums that followed, the history of man has been a succession of new discoveries used to meet new demands. Copper, which has been so important that it has characterised an era in history to which it has given its name, was extracted ten thousand years ago from malachite using carbon. Iron, on the other hand, was first discovered four thousand years ago when the Hittites developed techniques for the extraction of metals from ores, such as hematite. The word siderurgy, i.e. the process that extracts iron from rock, derives from the Latin word sider, meaning star, because the first iron known to man rained down on Earth in the form of meteorites. We have to wait until the third millennium B.C. for the earliest known glass objects. In his treatise on Natural History, Pliny the Elder tells us that the first techniques that resulted in this precious transparent material were developed in Phoenicia combining silica (sand), soda and lime in an oven. After a rather long period in which chemistry was considered more a form of sorcery than of science, finally the Irish scientist Robert Boyle (who described the relationship between the volume and pressure of a gas) established chemistry as a branch of science. It was the Italian Alessandro Volta’s invention of the first battery instead that marked the birth of electrochemistry. It is only at the end of the 19th Century that the era of synthetic organic compounds begins, i.e. plastic materials, which in the course of the 20th Century are indissolubly connected to technological progress and collective wellbeing.

Chemistry in our lives
Chemistry is an integral part of our daily lives: one only has to think about all the plastic objects we use every day or about the fact that ammonia, one of the most highly produced molecules in the world, is at the base of our food chain because it is used in agriculture for the production of the most common fertilisers. Even though it is so familiar, our relationship with this branch of science has never been really serene; many people, for example, use the word “chemical” as a synonym of “poisonous”. The news and everyday experience, on the other hand, are full of facts, reports and data in which chemical compounds are the cause of dramatic events. In the last few years a new approach to the science of matter has taken shape as an answer to the need for safety and for the protection of human health and the environment: green or sustainable chemistry.

New chemistry
Sustainable development, i.e. the growth model that ensures one generation to have the necessary resources to live without denying the succeeding generation the same opportunities, imposes the replacement of old technologies with more ecological and cleaner processes. The Green Chemistry Revolution is based on a series of precise manufacturing policies aimed at reducing energy costs, optimising the amount of material used, using natural raw materials and renewable energy sources, identifying micro-organisms capable of carrying out chemical reactions naturally, replacing old, polluting compounds with new, clean molecules, reducing waste materials from chemical reactions. For example, the infamous carbon dioxide, an absolutely harmless chemical compound, could replace the dangerous organic solvents used in many industrial sectors. Bacteria, instead, will be our best allies in agriculture replacing pesticides and herbicides. One of the most promising and fascinating developments of green chemistry is biomimetics, i.e. the science of imitating natural processes. In fact, nature has, over the course of millions of years, “invented” surprising technological and economic solutions at a zero environmental impact level. For example, each and every leaf on the planet contains billions of molecules that are capable of breaking down water molecules into oxygen and hydrogen with the help of sunlight. If man were to carry out a similar process it would have extremely high energy costs. A green future in which “artificial leaves” with the help of sunlight can split water into hydrogen, required to move cars, would be wonderful. Or else we can think of the plastic currently obtained from corn waste or even of the packaging material that in the future will imitate the resistant structure of the skin of some desert animals. On the market there are syringes with very thin painless needles that have been designed keeping the mosquito’s feeding apparatus in mind. Enzymes are microscopic molecular machines that are central to every chemical activity that occurs within living cells. They carry out incredibly complex processes with very low energy costs at efficiency levels still inconceivable for man. These small molecules, these protein jewels, could act as models for the development of new synthesis processes.

Even petrochemistry, i.e. the science concerned with developing synthetic materials starting from crude oil and natural gas, will have its own Green Revolution. Hydrocarbons are very precious compounds and at the moment, in addition to fuelling the combustion engines of our cars, they are at the base of complex industrial processes that result in the creation of plastics, synthetic fibres, rubber, paints, fertilisers and even medicines. But the future of hydrocarbons could be even brighter: polymer semiconductors, i.e. those plastic materials that have chemical-physical properties similar to those of silicon, are currently being used to make very light plastic solar cells that are economical and incredibly versatile. To date, the efficiency of these cells is less than that of traditional silicon cells but being new technologies there are good prospects for development. Maybe one day we will have photoelectric paints, with which we can coat houses or clothing, capable of charging portable electronic devices, such as computers.

Edited by Andrea Bellati

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