인도 간디나가르 공과대학교(IITGN)는 고피나드한 칼론(Gopinadhan Kalon) 물리·재료공학과 교수팀이 염 이온 및 기타 불순물을 99% 이상 제거할 수 있는 비용효율적이고 환경친화적인 담수화 기술을 개발했다고 지난 2월 8일 밝혔다.

이는 흑연의 구조적 무결성을 손상시키지 않으면서도 수용액 내부에서 흑연을 제어 가능하게 조작할 수 있는 최초의 방법이다. 연구 결과는 국제학술지 『네이처 커뮤니케이션즈(Nature Communications)』에 게재됐다(https://www.nature.com/articles/s41467-022-28162-6).

연구팀은 모세관 현상을 이용하는 나무의 자연적인 물 섭취에서 영감을 받았다. 전기장과 염화칼륨(KCl) 이온을 활용해 흑연 결정에 물 수송 채널(water transport channels)을 만들고, 신선한 물만 결정을 통해 이동할 수 있게 하고 그 외 모든 염 이온을 차단한 것이다.

논문의 제1저자인 라리타 사이니(Ms Lalita Saini) 박사는 “천연 흑연은 물이나 양성자를 포함한 모든 이온을 흡수하지 않는다. 그러나 성질 상 흑연 결정은 물 분자가 이동할 공간이 충분하지 않기 때문에 물 분자가 통과하는 것을 허용하지 않는다”면서 “이 문제는 전기장을 사용하고 여기에 염화칼륨(KCl) 이온을 삽입하여 해결했다. 흑연 결정 내부에 약간의 공간을 만들어 물 분자를 통과시키기 위한 안정적인 구조를 제공하는 동시에 염 이온의 움직임을 방해해 마실 수 있는 물을 제공한 것이다”라고 말했다.

연구팀에 따르면, 이번 기술은 바닷물에서 염 이온 및 기타 불순물을 99% 이상 제거할 수 있어 음용하기에 안전하다. 또한 흑연과 같은 탄소 재료는 항균성이 있어 담수화 공정에 필요한 필터의 수를 줄일 수 있다.

연구팀이 제작한 2㎜×2㎜ 크기의 장치는 전기를 사용하지 않고도 RO 기술에 견줄 만한 유량을 갖는다. 여기에는 공정 필터가 더 적게 포함되기 때문에 물 낭비도 적을 것으로 예상된다.

이 기술에 사용되는 물의 증발 및 물 여과 공정은 전기를 사용하지 않으므로 가스 배출이 발생하지 않아 환경 친화적이다.

고피나드한 교수는 “우리 방법은 흑연뿐만 아니라 고성능 분리 응용 분야를 위해 탐색할 수 있는 점토와 같은 많은 수의 층상 물질에도 적용될 수 있다”면서 “풍부한 해수와 적절한 플랜트 설계 최적화를 통해 우리의 방법은 지구상의 모든 사람들이 물을 마실 수 있다는 꿈을 실현하는 밝은 미래를 제시한다”고 말했다.

현재 연구팀은 천연 흑연을 사용하지 않아도 되는 방법을 고안하고 있으며, 대중의 기술 접근성을 높이기 위해 현장에서 활용 가능한 정수 필터를 개발하기 위해 노력하고 있다.

[원문보기]

IITGN RESEARCHERS DEVELOP A COST-EFFECTIVE AND ENVIRONMENT-FRIENDLY WATER DESALINATION TECHNIQUE TO MAKE SEAWATER DRINKABLE

The research is inspired by the trees’ natural intake of water that uses capillary effect and can prove to be impactful in providing affordable and energy-efficient drinking water solutions compared to energy-intense RO technologies.

Have you ever thought of drinking seawater to quench your thirst and also save energy? Doesn’t sound very normal, right? However, this will soon be a reality as a team of researchers at IITGN have developed a cost-effective and environment-friendly water desalination technique that can successfully remove more than 99% of salt ions and other impurities with natural processing to make seawater potable. This is the first such method that could controllably manipulate graphite inside aqueous solutions without damaging the structural integrity of graphite. These findings were recently reported in Nature Communications, an international high-impact journal: https://www.nature.com/articles/s41467-022-28162-6.

According to a report from the World Health Organisation (WHO), nearly one-fifth of the world population lives in areas that are devoid of clean drinking water. The continuous increase in population and enormous energy demands has put immense pressure on conventional clean water resources. On the other hand, the widely used Reverse Osmosis (RO) technique for desalination is expensive, wastes more water, and is highly energy-intensive, which typically requires hydrostatic pressures of 60-80 bar. With rising demand for potable water and continuously shrinking freshwater resources, more and more countries will have to turn to desalination of seawater to meet the needs.

Motivated to find an alternative and affordable solution to these issues, a research team led by Prof Gopinadhan Kalon, Assistant Professor, Physics & Materials Engineering, IITGN, created controllable water transport channels in graphite crystal with the help of an electric field and potassium chloride (KCl) ions, which allowed only fresh water to move through the crystal and blocked all the salt ions. The research team includes IITGN PhD scholars Lalita Saini, Aparna Rathi, Suvigya Kaushik, and a Postdoctoral Fellow Dr Siva Sankar Nemala.

The research is inspired by the trees’ natural intake of water that uses capillary effect. Selective transport of molecules and ions is commonly observed in biological systems. Mimicking these biological channels could result in highly efficient filtration systems. The research team used capillary process in the technique, which does not cost any energy, and in fact, the evaporation of water happened spontaneously without the need of any external pressure. The evaporation rates provided a back-calculated pressure of 50-70 bar arising from the capillary and other forces that are present inside the nanoscale channels.

Explaining the technique further, first author of the paper, Ms Lalita Saini, said, “Natural graphite is not absorptive to water or any ions including Protons. However, by its nature, the graphite crystal also does not allow any water molecules to pass through it because there is not enough space for the movement of these molecules. This issue was solved by using an electric field and inserting potassium chloride (KCl) ions in it, which create some space inside the graphite crystal and provide a stable structure for easy passage of water molecules, at the same time hindering the movement of any salt ions, giving drinkable water.”

The researchers found that this technique is self-sufficient and can successfully remove more than 99% of salt ions and other impurities from seawater, making it completely safe for drinking. Moreover, carbon materials like graphite are antimicrobial, reducing the number of filters required in the desalination process.

Prof Gopinadhan Kalon, assistant Professor, Physics & Materials Engineering, IITGN said “Our method is not only limited to graphite but also to a large number of layered materials, like clays, that could be explored for high performance separation applications. With abundant seawater and appropriate plant design optimisation, our method holds a bright future in realising the dream of drinking water for everyone on the planet.”

Carbon is abundant in nature, and India is the second largest producer of graphite in the world. The current experiment has utilised natural graphite. However, the team is also devising a method that does not require the use of natural graphite; instead, they can synthesise graphene (one-unit layer of graphite) from waste, plastics, wheat, sugar, chocolate etc., and assemble it to make graphite-like structure.

The present 2mm x 2mm sized device made by the research team has flow rates comparable to RO technology, that too without using electricity. Since this involves less process filters, it is also expected to have less wastage of water. The water evaporation and water filtration processes used in this technique do not involve any electricity, and therefore it does not produce any gas emissions, making it environment-friendly. The team is now working to develop a direct point-of-use water filter using this technique to make it accessible for the masses.

Moreover, this technique can also prove to be useful in designing filters for gas purification, proton exchange in a fuel cell, chemical separation, recovery of precious metal from waste etc. It can also be suitable for dehumidification applications as expanded graphite has high water evaporation rates.

[출처 = IITGN(https://news.iitgn.ac.in/2022/02/08/iitgn-researchers-develop-a-cost-effective-and-environment-friendly-water-desalination-technique-to-make-seawater-drinkable/) / 2022년 2월 8일]