As featured in the upcoming 2020 September/October Gold Prospectors Magazine

By Alexandra Porto

Have you ever stopped to think about the water that flows from your faucet? While we might take clean water for granted, it is a lot harder to access than you might realize. It’s also one of the most fundamental elements needed for survival. Our bodies are made up of 60% water, flowing through our organs and transporting nutrients into our cells. When pollutants enter our drinking water, the effects can be deadly and lead to gastrointestinal issues or chronic diseases like cancer.

According to Charity: Water, nearly 1 in 10 people worldwide live without clean water. Due to rigorous U.S. standards, this is a problem we don’t frequently encounter in our daily lives. EPA Administrator Andrew Wheeler explained to CBS News that "we have the safest drinking water in the world” with 92% of drinking water meeting safety regulations. However, stories like the crisis in Flint, Michigan, show this can be a modern-day challenge even for us.

Caption: Effective filtration of micropollutants is a challenge.

Photo Credit: Nevit Dilmen, Creative Commons BY-SA 3.0

Much of the problem is due to what is known as trace contaminants. By the time water reaches your faucet, it has been through a series of conventional filtration systems. While these purification methods help meet safety standards for drinking water, they do not completely eradicate contaminants. Some of the most common micropollutants that remain are pesticides, pharmaceuticals, and perfluorooctanoic acid.

As Yale News reports, long-term exposure to these trace contaminants can pose significant health risks. Unfortunately, they have continued to elude conventional water filtration processes for years. Alternative chemical processes using ozone, hydrogen peroxide, or UV light are effective but too expensive and labor-intensive to be practical solutions. A recent gold nanoparticle discovery could now present a viable option.

Caption: This discovery has the potential to improve lives worldwide.

Photo Credit: Axelsaffran, Creative Commons BY-SA 3.0

U.S. Scientists Have Made a Breakthrough using Gold Nanoparticles.

Scientists from Yale, Rice University, Arizona State University, and the University of Texas-El Paso have developed a new gold nanoparticle that can remove trace contaminants from drinking water. On June 22, the joint effort known as Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) published their findings, opening the possibility for a revolutionary water purification method.

According to Tech Explorist, it is the gold nanoparticle’s unique photothermal properties to convert light into heat and its photocatalytic ability to use light to activate a chemical process that makes it highly appealing to scientists. While gold nanoparticles have successfully been used in numerous medical applications, their application for water filtration has been limited. To date, not much has been studied beyond water desalination or vapor disinfection technologies. That is, until now.

Yale News reports the shortage of research on this topic is due to the “difficulty of dispersing nanoparticles in water without stabilizing agents.” According to the research team, conventional nanostructure designs often lead to poor stability or inefficiencies with photothermal conversions. Recently, the NEWT researchers were able to innovate a new design that conquers this aqueous stabilization challenge.

Developing the “Janus” Nanorods was a Collaborative Effort.

The team was led by Yale’s Jaehong Kim, the Henry P. Becton Sr. Professor and chair of Chemical & Environmental Engineering, in collaboration with Rice University’s Naomi Halas. Together, they found a way to stabilize the gold nanoparticles by designing and developing critical “Janus” gold nanorods.

Solving this challenge required a multidisciplinary approach. According to Nano Werk, “Halas, Rice’s Stanley C. Moore Professor of Electrical and Computer Engineering and director of Rice’s Laboratory for Nanophotonics, played the key role of elucidating the complex mechanisms of how the photothermal and photocatalytic reactions occur on this unique nanoparticle.”

By testing a series of different nanorod designs, some with or without a chemical coating, against a control nanorod fully coated in silica, the researchers were able to prove their hypothesis. As they predicted, the “Janus” nanorod half-coated in silica was successful in heating visible-wavelength sunlight and producing free radicals that could destroy organic water pollutants.

Pedro Alvarez, founding director of NEWT, called this team effort “a great example of how researchers in two different fields of study come together under the roof of NEWT to develop highly unconventional ideas to solve difficult problems.”

Caption: “Janus” gold nanorods are the key to this filtration method.

Photo Credit: National Institute of Standards and Technology, CC0 Public Domain

How this New Purification Technology Works:

“With this partial coating, the nanorods get dispersed in water really well, and that’s very useful for this kind of application” said Kim in Yale News. This allows the gold nanorods to remain separated from each other while staying suspended in the water, which is vital for it to be used for water purification purposes.

According to the study, these half-coated “Janus” nanorods overcome stability obstacles while also providing enough of an active surface for chemical processes like photocatalysis to occur. They work by absorbing intense rays of sunlight and converting it to heat on the water’s surface. It then acts as an electron-transfer catalyst to activate ions that produce sulfate radicals. These free radicals lead to oxidative stress that destroys trace contaminants in the water.

This newly discovered filtration method is sustainable and cost-effective since it relies primarily on solar energy. Its innovative nanorod design has the potential to open the doors to more low-cost water purification methods in the future.

This Study Paves the Way Toward Purer, More Accessible Drinking Water.

Gold nanoparticles are proving more and more useful in unlocking the keys to some of science and medicine’s greatest challenges. Alvarez called this study “a great example of how forefront advances in nanotechnology can pave a new way to solve water challenges.” By overcoming the aqueous stability challenge, this research team has made it easier for others to pursue further water purification research. It even has the potential to be applied to technologies addressing other environmental concerns.

However, Kim believes this is only the start as “more work is needed to scale up the nanoparticle for real-world application.” While this new purification method is more practical than the limited chemical processes currently available, the rising cost of gold has Kim concerned. He said the next step would be to find a material less expensive than gold but with similar photothermal and photocatalytic characteristics.

Caption: New gold nanoparticles could improve global access to clean drinking water.

Photo Credit: Max Pixel, CC0 Public Domain

Gold’s unique qualities remain in high demand, regardless of whether or not a newer, less expensive material is used in the future. Above all, the real treasure found in this study is gold’s great range of scientific applications for improving human life in the years ahead.