Innovation in Nanotechnology for Water Purification — Earth Day 2021 Blog!

Saumya Soni

Innovation in Nanotechnology for Water Purification — Earth Day 2021 Blog!

It is no secret that climate change and population growth both are controversial and increasing problems today as we see these affecting global water, land, and air pollution and much more. Therefore, it is critical that we invent innovative technologies to maintain, and possibly increase, the supply of clean drinking water and reduce global water pollution. Since water is a necessity for all living things on Earth, we must level up to this growing demand for clean water. By 2020, 2/3 of the population in the world are predicted to live in water-scarce conditions (or places with a lack of purified water). Currently, areas in Africa and 50% of European countries have a deficiency of water supply. Surprisingly, even first-world countries such as the U.S. who are inventing revolutionary tech for decontaminating and saving water, are facing the difficulty of exhausted waterbodies as more water is removed than regained. The U.S. has experienced the worst drought for the past fifty years. On the other hand, in rainy areas, extreme rainfall can result in erosion and soil run-off, which leads to pathogens entering water bodies along with nutrients and soil elements. Higher temperatures in air and water can influence the hygiene of drinking water in storage systems and in drinking water pipelines, which can lead to dangerous diseases. Legionnaire’s disease, caused by legionella bacteria that reach its top population in the warm water of around 40 degrees C, can form.

Given that this trend is not likely to reverse, this poses a significant threat to more than half of the world’s communities. A lack of purification technology also makes people susceptible to health diseases from drinking toxins and microplastics. Therefore, scientists are greatly considering the use of nanotechnology currently. Nanotechnology can be used for filtering water at the molecular level. Nanomaterials contain special and distinctive size-dependent properties which relate to their large specific surface area (fast dissolution, strong sorption, high reactivity) and intermittent properties (like superparamagnetism, localized surface plasmon resonance, and quantum confinement effect). These nano-based properties and unique attributes help drive the innovation for efficiently purifying water. Current water purification processes necessitate a specific amount of water to work. Since nanotechnology purification processes work at the nano-level, they can purify to the finest amount of water. This can be particularly beneficial in the rural and isolated areas which have a higher chance of a lack of clean water.

Water can be contaminated with many materials like sediments, chemicals, salt, bacteria, heavy metals, microplastics, and more. Since each of these contaminants can be different sizes, they can be totally dissolved in the water or separate from it. Therefore, not any other filtration method can completely purify it. However, nanotechnology purifies it more efficiently and almost completely. A popular kind of nanotechnology, carbon nanotubes, are cylinder-shaped molecules that consist of carbon atoms connected in one layer. The nanotubes look like strands of wire netting and small lattices and are extremely efficient at filtering out pollutants of different sizes from the water with nanotube openings that are molecule-sized. It lets water molecules go through while collecting pollutants and pathogens.

There are many types of nanomaterials which are used for water purification such as nano-adsorbents, nano metals, and nano metal oxides, membranes and membrane processes, and more. Adsorption allows solid substances to attract close contacts around them such as their surface molecules of gases or solutions. Adsorbents are solids which adsorb, attract and enclose gases or dissolved substances, while the adsorbed substances are the adsorbates. As a result of their high specific surface area, nano-adsorbents implement a faster rate of adsorption for organic compounds in comparison with powdered activated carbon. Therefore, they are more efficient at decontamination and elimination of organic and manmade contaminants such as heavy metals and micropollutants. Along with saving adsorbent substances, this process also effectively implements water treatment technology with a lower footprint. Some examples of nano-adsorbents are carbon-based nano-adsorbents (carbon nanotubes), metal-based nano-adsorbents, polymeric nano-adsorbents, and zeolites.

Carbon nanotubes (CNT’s) are allotropes of carbon with a cylinder-like nanostructure. They can either be single-walled nanotubes or multiwalled. CNT’s have a specific surface area and they have modifiable surface chemistry. Since they have a hydrophobic surface, CNT’s have to be balanced and strengthened in aqueous suspension to evade aggregation that lowers the active surface. It’s used for recognizing contaminants and adsorption of tenacious pollutants. Metal ions are adsorbable by carbon nanotubes with electrostatic attraction and magnetism and chemical bonding. Additionally, CNT’s have antimicrobial (destroying or inhibiting the growth of microorganisms) properties by implementing oxidative stress in bacteria and demolishing their cell membranes. Even though chemical oxidation happens, there aren’t any toxic byproducts produced. They can be regenerated to fit certain conditions through slight shifts in pH and other properties. Desalination processes are energy and time consuming and technically demanding, unlike adsorption which is simple to use for purification and removal of certain salts. Yang HY created a plasma-improved ultralong CNT which features an ultrahigh adsorption capacity for salt which is 2 orders of magnitude larger than conventional carbon-based water purification methods.

These ultralong carbon nanotubes can be put into action in multifunctional membranes which can eradicate salts along with organic and metal pollutants. In the future, this innovative device is predicted to be super-efficient in the removal of salt, infection, and other pollutants. Polymeric nano-adsorbents like dendrimers (repetitious branched molecules) are effective in the removal of organics and heavy metals. Natural compounds can be adsorbed by the inside of hydrophobic shells, while the heavy metals are adsorbed by the exterior branches. Diallo MS combined the dendrimers in an ultrafiltration mechanism to separate and get rid of copper from water. Almost all of the copper ions were removed by this dendrimer-ultrafiltration device process. The adsorbent gets renewed by a slight pH level change.

Sadeghi-Kiakhani created an innovative and effective bio adsorbent for removing anionic compounds (like dye) from textile wastewater (most hazardous wastewaters) by creating a combined chitosan-dendrimer nanostructure. The bio adsorbent is very efficient as it is biodegradable, non-toxic, and biocompatible and it has proven to remove up to 99% of certain dyes in the wastewater. Water is a necessity to all living things on earth. Its value is extremely high, however, many humans take its value for granted. Therefore, we will be in need of revolutionary high-tech which can help us cope with the detrimental effects of climate change.

In both developing and industrialized countries, a growing number of contaminants like micropollutants are entering the water bodies. Conventional decontamination processes such as chlorination and ozonation consume a high number of chemical agents and furthermore can produce toxic byproducts. This is why nanotechnology will be preferred in the future over other water treatment processes such as chlorination and ozonation because nanotechnology minimizes error and byproducts during the process and maximizes validity and efficiency. The benefits of nanotechnology significantly outweigh the negative effects, so it is important to adapt to these highly advanced technologies soon as they give us new opportunities and solutions to purifying water currently and in the future. Although it will be costly, we will have to evolve to use this opportunity to provide us with clean drinking water in the future.

Sources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4294021/

www.technology.org/2019/10/11/how-nanotechnology-is-transforming-water-purification/

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