Chapter 20: CAN CO₂ GAS BE CONVERTED INTO USEFUL PRODUCTS?
Can Carbon Dioxide Gas Be Converted into Useful Products?
A group of researchers is working on methods that can convert greenhouse gases originating from human activities, primarily carbon dioxide (CO₂), into useful products.
In today's modern world, the amount of greenhouse gases released into the atmosphere as a result of human activities is rapidly increasing. Although the most common greenhouse gas, CO, is one of the gases that causes global warming, it can be a raw material for the production of many useful chemicals and fuels. However, the recycling process of CO, gas has been an unsolved problem for more than 150 years. Because the reactions required for this process require high temperatures and pressures and some special materials, it is not easy to do.
Until now, research to recycle CO2 gas has focused primarily on understanding the energy-intensive conversion reaction in water-based electrolytes. However, a major problem was that water-based systems had limited CO2 retention capacity. In addition, unwanted byproducts such as hydrogen gas were produced as a result of the reaction. Researchers at Case Western Reserve University have succeeded in effectively converting CO2 gas through electrochemical processes thanks to the ionic liquids they developed.
These ionic liquids, which can be in liquid form at room temperature, are unique in that they have high CO2 retention capacity and can maintain electrochemical stability. At the same time, these liquids activate the reduction reaction of CO2 gas on the copper electrode surface, requiring less energy to start the reaction. It is also stated that industrially useful products can be produced instead of unwanted by-products as a result of the reaction.
The research team continues its work to advance the electrochemical processes for recycling carbon dioxide gas and to better control the reaction products.
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Is Evaporation Possible Without Heat?:
Evaporation, as we know it, occurs through heat transfer: When the molecules within a substance gain enough energy by interacting with their environment, they can manage to detach themselves from the material. However, recent scientific studies show that water molecules can evaporate under certain conditions without receiving heat from their environment.
In recent scientific studies, it has been noticed that the water held in hydrogels can evaporate much faster than expected due to the amount of heat it receives. The evaporation that occurs might not be directly proportional to the amount of heat it receives. A group of researchers tried to study this phenomenon under different conditions. From their study, they explained how this situation occurs and came to the conclusion that evaporation occurs under the influence of light. One of the most important results obtained was that the evaporation rate of water in the hydrogels on which light fell changed depending on the color of the light. This result cannot be explained by the heat effect. In addition, when the experiments are carried out in a light-free environment, keeping all variables the same, the results obtained begin to be compatible with theoretical predictions. This confirms the idea that light is the factor that increases the evaporation rate.
It is surprising that the water in hydrogels evaporates under the influence of light. Because both water and hydrogels have a low light absorption rate. When you look at a lake from above, you see the water deep down because water absorbs very little light. Similarly, hydrogels do not have a high light absorption rate. However, the results obtained show that when these two materials come together, contrary to expectations, the water molecules on the surface of the hydrogel can evaporate with the energy they receive from light.
The ejection of electrons by photons from atoms is called the photoelectric effect. The newly discovered phenomenon, in which photons tear molecules from liquids, was called the "photomolecular phenomenon". It is thought that photomolecular phenomenon can be used in many areas.
For example, the process of obtaining drinking water from salt water is two-staged: First, the salt water is heated to evaporate the water, then the water vapor is condensed to obtain fresh water. The process of obtaining fresh water from salt water can be made more efficient by taking advantage of the photomolecular phenomenon. Another application area of the photomolecular phenomenon could be processes where desiccant materials are used to remove moisture from the environment.
Dr. Yaodong Tu et al., from the Massachusetts Institute of Technology, published the results of the research conducted under the leadership of Prof. Dr. Gang Chen were published in the "Proceedings of The National Academy of Sciences (USA)"
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Thermal Transistors Developed to Control Heat Flow
One of the biggest problems facing the electronics industry today is overheating. In fact, a significant portion of the energy consumed by devices such as smartphones and computers is spent to keep the chips cool.
A subject that has been studied for many years to prevent overheating of electronic circuits is developing electronic devices that can control heat flow. A group of researchers led by Prof. Dr. Yongjie Hu from the University of California Los Angeles announced in an article published in Science that they have developed thermal transistors that can solve the heating problem in electronic circuits. Transistors, billions of which are found in an ordinary computer chip, are three-terminal circuit elements. The main function of one end of these devices is to control the flow of electricity between the other two ends. The newly developed thermal transistors are similarly three-terminal devices. The main function of one end of these devices is to control the heat flow between the other two ends.
Whether thermal transistors will allow heat flow is controlled by external electric fields. The applied external electric fields cause the chemical bonds that hold the atoms in the device to strengthen or weaken. Thus, the electrons in the chemical bonds gain or lose freedom of movement. This causes the thermal conductivity of the device to change. Thermal transistors are expected to be especially useful in preventing computer chips from overheating. It may even be possible to collect and use the excess heat generated with the help of thermal transistors. It is also estimated that these devices may have applications in the field of health. For example, thermal transistors can be used to kill cancer cells without harming healthy cells with the help of heat. It is stated that work is still needed for thermal transistors to be used in devices we encounter in daily life. The researchers state that their next goal is to develop hybrid devices that contain transistors that control both electric current and heat flow.
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Semiconductor Produced from Graphene
Researchers from the Georgia Institute of Technology have succeeded in obtaining a functional semiconductor from graphene that can be used in electronic circuits.
In solid materials, the energy levels in which electrons can be found are concentrated in two energy bands, one called the valence band and the other called the conduction band. The main feature of semiconductor materials, which have a very important place in the electronics industry, is that the energy difference (band gap) between the valence band and the conduction band is relatively small. This allows the conductivity properties of semiconductor materials to be easily changed. For example, transistors control electric current thanks to the semiconductor properties of silicon in their structures. One of the materials that is thought to be potentially useful in the electronics industry is graphene. This material, in which carbon atoms are arranged in a single layer, can carry high current without overheating and without deteriorating its structure. However, graphene does not have a band gap like semiconductors. Graphene is essentially an example of a material called a semimetal. In such solids, the valence and strength bands overlap to some extent.
Prof. Dr. Walter de Heer and his colleagues from Georgia Institute of Technology had previously developed a new method to produce graphene on silicon carbide sheets. One of the most important results obtained by the researchers was the discovery that graphene, which was chemically bonded to silicon carbide, began to exhibit semiconductor properties. This meant that graphene could be used to develop new generation transistors.
However, in order to obtain a functional transistor from a semiconductor, the semiconductor must undergo various processes, and this may cause the properties of the material to change.
In their latest article published in Nature, the researchers write that graphene produced on silicon carbide retains its semiconductor properties after undergoing processes that will enable it to be used in transistors. Moreover, measurements show that the mobility of the semiconductor graphene (how fast electrons can move through the material when an electric field is applied) is ten times that of silicon.
This result suggests that graphene could be used to develop next-generation transistors that enable much faster calculations.
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