광촉매 작용을 이용한 수처리 방법 Photocatalytic water treatment: Facts vs. hype

 

Photocatalytic water treatment: Facts vs. hype

(Nanowerk News) More than three decades ago, when researchers began exploring photocatalysis as a way to purify water, efforts were buoyed by a wave of optimism within academia.

An abundance of research (more than 8,000 research papers since 2000), though, hasn’t yet translated to widespread industry use. To take a closer look at this gap, the Nanotechnology Enabled Water Treatment Systems center (NEWT) organized a workshop to take a hard look at the technology and assess its real-world value.

광촉매 작용을 이용한 수처리 방법  미국 예일 대학(Yale University) 등 5개 대학 연구 수행    미국 예일 대학(Yale University), 라이스 대학(Rice University), 애리조나 주립대학(Arizona State University), 클렘슨 주립대학(Clemson University), 텍사스 대학(University of Texas at El Paso)의 연구진은 광촉매 수처리에 대한 광범위한 연구를 수행했다. 과학자들은 30년 전부터 물을 정화하는데 광촉매 방법을 조사하기 시작했다. 그러나 2000년 이래로 8,000 종의 연구 논문이 발표되었지만, 아직까지 산업계에 널리 확산되지 못했다. 이번 연구에서는 오염 물질을 분해해서 수처리하는 광촉매 첨단 산화 프로세스(photocatalytic advanced oxidation process, AOP)를 집중적으로 조명했다. 기존의 AOP와는 달리, 광촉매 작용 시에 화학물질을 필요로 하지 않고, 저에너지 자외선 광만을 필요로 한다. 반도체용 재료는 이산화티타늄을 사용하고, 이것은 저렴하고 상대적으로 독성이 없다. TiO2의 개질 연구 이외에도 다른 반도체 재료들이 조사되었다. CdS와 WO3는 비교적 효과적인 가시광선 광촉매이지만 Cd와 같은 독성 성분 때문에 수처리용으로 적합하지 않다. 흑연 질화탄소(C3N4)는 조율 가능한 전기적 구조를 가지고 있어서 금속-프리(free) 가시광선 광촉매이지만 열악한 화학적 안정성을 가지고 있다. 페로브스카이트 재료는 저비용의 대량 생산을 할 수 있지만, 습식 상태일 경우에 불안정하기 때문에 수처리용으로 사용될 수 없다. 최근 몇 년 동안에 많은 연구진들은 광촉매에 대한 최초 주장 중의 많은 부분에 대해 의문을 제기했다. 그동안 광촉매용 나노물질이 많이 만들어졌지만, 이런 물질들 중에 많은 것들이 수처리에 사용될 수 없었다. 즉, 제조하기도 너무 어렵고 가격도 매우 고가였다. 또한 이러한 물질 중의 상당수가 충분히 견고하지 못했다. 실제 수처리 시스템의 조건과 실험실의 조건은 매우 달랐다. 이번 연구에서는 이 기술이 어떻게 하면 가장 잘 사용할 수 있을지를 제시하고 있다. 이 기술은 소규모로 실행 가능하다. 태양열로 구동될 수 있기 때문에 에너지 인프라가 부족한 자원-제한 지역이나 인구가 적은 지역에 적용될 수 있을 것이다. 또한 이 공정은 소모성 화학 물질을 필요로 하지 않기 때문에 화학 물질의 배출이 어려운 지역에 특히 유용할 것이다. 이 연구는 인간 생명을 보호하고 지속 가능한 경제 발전을 할 수 있는 수처리 시스템에 나노기술을 접목시킬 수 있는 새로운 길을 열어주었다. 이 연구결과는 저널 Environmental Science & Technology에 “The Technology Horizon for Photocatalytic Water Treatment: Sunrise or Sunset?” 라는 제목으로 게재되었다(DOI: 10.1021/acs.est.8b05041). ndsl.kr

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That workshop served as the basis for a paper published in Environmental Science & Technology (ES&T) that explores how to best direct research efforts in this area ("The Technology Horizon for Photocatalytic Water Treatment: Sunrise or Sunset?").

“We recognize the large disparity between academic research and industry application,” said Jaehong Kim, the Henry P. Becton Sr. Professor and Chair of Chemical & Environmental Engineering at Yale. For the workshop, Kim assembled a team of 14 leading researchers in the field from around the world for a daylong brainstorming session last March. They shared their ideas on potential applications of the technology, its limitations, and best real-world uses for it.

The researchers focused on photocatalytic advanced oxidation processes (AOPs), which treat water by breaking down contaminants. Unlike conventional AOPs, photocatalysis doesn’t require chemicals. And because it requires only low-energy UV light, there are potential solar applications. The standard material for semiconductors is titanium dioxide (TiO2), which is inexpensive and relatively non-toxic. These properties promised a revolutionary new way to treat water.

The ES&T paper refers to the early years of photocatalysis research as its “sunrise” phase - that is, when excitement by the subject’s potential fuels a vast body of research. Having gone beyond that phase, Kim says it is now time to take a more measured approach.

In recent years, leading researchers have questioned many of the initial claims for photocatalysis, especially regarding large-scale municipal water treatment. Kim stresses that the ES&T paper isn’t meant to discourage researchers about photocatalysis, but to serve as a “reality check” and offer some guidance on possible directions to take it.

One issue, Kim said, is that there’s a disconnect between a discovery that’s scientifically interesting compared to something that’s practically useful.

“Researchers started to make very fancy nanomaterials for photocatalysis, but a lot of these materials can’t be used for water treatment,” Kim said. That is, they’re too hard to make and too expensive. Also, many of these materials aren’t robust enough for their designated uses - the conditions for an actual water treatment system are very different from those of a lab.

“As a community, we got a little too excited about these complicated nanomaterials without really considering the potential applications in the real world,” said Kim, who has been a member of NEWT since it was established in 2015. “In this paper, we’re saying ‘Let’s realize where we are now and think about these boundaries when using photocatalysis for water treatment.”

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The researchers offer suggestions as to how the technology might be best used. Specifically, they point to niche applications, such as hydroponics and aquaculture, which are usually practiced on a small scale. Because it can be solar-powered, the technology could also be potentially used in resource-limited regions that lack energy infrastructures, particularly remote communities with small populations. And because the process doesn’t require consumable chemicals, it also has promise for places where chemicals are hard to get.

Pedro J.J. Alvarez, founding director of NEWT, said part of the center’s mission is to take an honest look at the research it’s conducting and discern between “academic hype” and work likely to produce important societal benefits, such as water security. The ES&T paper is part of that effort.

 

"There was a point where we noticed there was not enough ‘pull' from our industrial partners, despite the many high-impact papers we were generating, and decided to investigate this disconnect," said Alvarez, the George R. Brown Professor of Civil and Environmental Engineering at Rice University.

Stephanie K. Loeb, first author of the paper, said the project aimed to provide background for researchers and a candid assessment of the existing literature.

“The technology is at an interesting junction where there’s a lot of science and there’s the idea of what people want it to do - but those two aren’t necessarily coming together,” said Loeb, a Ph.D. student in Kim’s lab. “The idea behind this paper is to identify where those problems are and how we can take this technology and fill in the gaps to transition it from academics to the real world.”

The research has resonated with the community of photocatalytic researchers. The study, which features the Kim’s artwork (including the issue’s cover), has been on the website’s list of most read papers since it went online.

NEWT is an interdisciplinary, multi-institution nanosystems-engineering research center headquartered at Rice University that is applying nanotechnology to develop off-grid water treatment systems that both protect human lives and support sustainable economic development. In addition to Yale and Rice, NEWT’s leadership includes experts from Arizona State University, the University of Texas at El Paso and more than 30 industry and government partners.

Source: Yale University

https://www.nanowerk.com/nanotechnology-news2/newsid=52405.php

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