In addition to making currency, "coin metal" actually has these wonderful uses

On October 17, 2024, Zang Shuangquan, Vice President of Academic Affairs and Dean of the School of Chemistry of Zhengzhou University, delivered a speech entitled "Magical Coin Metals" at the "Charming Chemistry: Infinite Possibilities" theme session of the Science Popularization China Starry Sky Forum.

The following is an excerpt from Zang Shuangquan’s speech:

"Coin metal" generally refers to the metal material used to make coins. Common "coin metals" include copper, gold, silver, etc.

PART1 Chemical properties and applications of “coin metals”

Coin metals play an indispensable role in modern industry. First of all, they generally have good electrical conductivity. Copper wires and printed circuit boards can be seen everywhere in life, while silver and gold are often used to make special wires. These metals are everywhere in our mobile phones, computers and other devices. Although the price of gold is much higher than that of silver and copper, its excellent chemical stability makes gold thin films widely used in the field of microelectronics to manufacture high-precision electronic circuits and tail circuits to ensure the stable operation of electronic equipment. In addition, coin metals are also widely used in the aerospace field. Due to their high temperature and corrosion resistance, they are often used to manufacture aircraft or spacecraft components. Gold thin films can also be used to manufacture solar panels for spacecraft to improve their energy conversion efficiency and durability.

In addition to the above common properties, coin metals also have their own characteristics. For example, copper has very good thermal conductivity, so it can be used as a radiator material and applied to the manufacture of air conditioners, automobiles, electronic products, etc. Copper has also become one of the standard materials for shipbuilding due to its excellent corrosion resistance, and in daily use, copper pipes are also the most durable as traditional water pipe fittings. Silver, on the other hand, has high light reflectivity and can be used to manufacture key components such as precision optical coatings and reflectors. It is indispensable in the manufacture of microscopes and astronomical telescopes. High-purity silver powder is the main material for making silver paste, which is used in the manufacture of photovoltaic cells. Each photovoltaic cell contains about 20 grams of silver. Gold foil has the ability to strongly reflect and scatter infrared light, and can be used in the manufacture of infrared detectors and anti-missile devices.

In the field of life sciences, metals are also indispensable. For example, copper is an essential trace element for the human body. It participates in the metabolism of hemoglobin and iron, and affects the absorption and storage of iron. Therefore, when we are iron deficient, we need to supplement not only iron but also copper. Copper is also involved in the formation of many enzymes and active proteins, binds to DNA, and maintains the stability of nucleic acid structure. The total amount of copper in a normal human body is about 100-150 mg, of which about 50%-70% is in muscles and bones, 20% in the liver, 5%-10% in the blood, and a small amount exists in copper enzymes. Adults need to take 2 mg of copper per day to meet physiological needs, otherwise copper deficiency may lead to a series of serious health problems.

You may be familiar with the role of silver. It is a natural, safe and highly effective antibacterial material. In today's medical system, silver products are widely used, such as 0.5% silver nitrate solution for burn and trauma treatment, 1% silver nitrate for eye drops, 10% silver nitrate smear for the treatment of various ulcers, and silver-plated materials can be used to make sutures, catheters, dressings, water cups, etc. NASA has identified silver as the safest sterilizer and uses silver as the main material to make spacecraft drinking water containers and purifiers. More than half of the world's airlines choose pure water systems based on silver.

The application of gold in medicine also has a history of thousands of years. Its ductility, stability and biocompatibility make it widely used in the field of dentistry for tooth restoration. Implants made of gold alloys are widely used in many fields in modern medicine, including nerve repair and pacemakers. In addition, gold can also be used for disease detection. During the COVID-19 pandemic, the antigen test we used used colloidal gold modified with antibodies as the color-developing component to determine whether the characteristic markers of the new crown to be tested are present.

PART2 Chemistry brings unlimited possibilities to coin metals

With the hands of chemists, "coin metal" has been given more excellent properties.

Chemistry, also known as molecular science, is essentially like building blocks with atoms, arranging and combining them to create new molecules and obtain new properties. In our research, my research team and I used coin metal atoms to build blocks to create new coin metal clusters with diverse structures. For example, we combined six silver atoms in a regular octahedron and fixed them with small organic molecules to obtain extremely bright silver cluster molecules. This molecule has a quantum yield of up to 95% and can convert almost all absorbed light into another wavelength of light and emit it. It is a very promising luminescent material. It shows excellent application prospects in the fields of lighting display, luminescent sensing, and biological imaging, and is also one of the representative star cluster molecules prepared by our laboratory.

For another example, we combine four gold atoms in a parallelogram and fix them with organic molecules to obtain a high-brightness gold cluster molecule. Since gold is a heavy element that can effectively absorb high-energy rays, this gold cluster can not only emit light under ultraviolet light, but also emit bright green light under X-rays. This material that can convert high-energy rays into light is called a scintillator material. Due to its excellent properties, cluster scintillators have shown broad application prospects in X-ray detectors, medical radiography instruments, and even high-energy particle detection in outer space.

The previous examples are all about simple cluster molecules of coin metals. So, can we build more complex cluster structures? The answer is yes.

We first constructed a silver cluster consisting of twelve silver atoms, and connected these silver clusters together through organic molecules as bridges to obtain a cluster framework material with a three-dimensional structure, just like a high-rise building built with clusters as bricks. This is also the first cluster-based framework material reported internationally.

Interestingly, there are many holes in these cluster-based framework materials, which can accommodate molecules in the air such as oxygen and nitrogen. When oxygen does not enter the holes, the material will emit light, but once oxygen molecules enter the holes, the light emission will disappear. By testing the luminescence properties of these framework materials, we can intuitively understand the oxygen content in the environment. In other words, this cluster-based framework material is a very good oxygen sensor that can detect one part per million of oxygen in the environment.

As you can see, whether it is the elemental properties or the specific atomic combination, coin metals always bring us all kinds of surprises. From ancient times to the present, from common daily necessities to various high-tech equipment, from luminescent materials to deep space exploration, coin metals have shown infinite application possibilities. However, there are still many unknown areas for coin metals. For example, what other unknown important effects do coin metals have in the life process? How big can the volume of a single cluster be? Where is its limit? We don't know. What other exciting characteristics can coin metal clusters show as catalysts? This remains to be explored and discovered in the future!