The research is published online today in the journal Science.

The research follows government and industry investment to create infrastructure and markets for carbon-free liquid ammonia fuel that will not contribute to greenhouse warming. Liquid ammonia is easy to transport and packs a lot of energy, with one nitrogen and three hydrogen atoms per molecule. The new catalyst breaks those molecules into hydrogen gas, a clean-burning fuel, and nitrogen gas, the largest component of Earth’s atmosphere. And unlike traditional catalysts, it doesn’t require heat. Instead, it harvests energy from light, either sunlight or energy-stingy LEDs.

The pace of chemical reactions typically increases with temperature, and chemical producers have capitalized on this for more than a century by applying heat on an industrial scale. The burning of fossil fuels to raise the temperature of large reaction vessels by hundreds or thousands of degrees results in an enormous carbon footprint. Chemical producers also spend billions of dollars each year on thermocatalysts — materials that don’t react but further speed reactions under intense heating.

“Transition metals like iron are typically poor thermocatalysts,” said study co-author Naomi Halas of Rice. “This work shows they can be efficient plasmonic photocatalysts. It also demonstrates that photocatalysis can be efficiently performed with inexpensive LED photon sources.”

“This discovery paves the way for sustainable, low-cost hydrogen that could be produced locally rather than in massive centralized plants,” said Peter Nordlander, also a Rice co-author.

The best thermocatalysts are made from platinum and related precious metals like palladium, rhodium and ruthenium. Halas and Nordlander spent years developing light-activated, or plasmonic, metal nanoparticles. The best of these are also typically made with precious metals like silver and gold.

Following their 2011 discovery of plasmonic particles that give off short-lived, high-energy electrons called “hot carriers,” they discovered in 2016 that hot-carrier generators could be married with catalytic particles to produce hybrid “antenna-reactors,” where one part harvested energy from light and the other part used the energy to drive chemical reactions with surgical precision.

Halas, Nordlander, their students and collaborators have worked for years to find non-precious metal alternatives for both the energy-harvesting and reaction-speeding halves of antenna reactors. The new study is a culmination of that work. In it, Halas, Nordlander, Rice alumnus Hossein Robatjazi, Princeton engineer and physical chemist Emily Carter, and others show that antenna-reactor particles made of copper and iron are highly efficient at converting ammonia. The copper, energy-harvesting piece of the particles captures energy from visible light.

“In the absence of light, the copper-iron catalyst exhibited about 300 times lower reactivity than copper-ruthenium catalysts, which is not surprising given that ruthenium is a better thermocatalyst for this reaction,” said Robatjazi, a Ph.D. alumnus from Halas’ research group who is now chief scientist at Houston-based Syzygy Plasmonics. “Under illumination, the copper-iron showed efficiencies and reactivities that were similar to and comparable with those of copper-ruthenium.

Syzygy has licensed Rice’s antenna-reactor technology, and the study included scaled-up tests of the catalyst in the company’s commercially available, LED-powered reactors. In laboratory tests at Rice, the copper-iron catalysts had been illuminated with lasers. The Syzygy tests showed the catalysts retained their efficiency under LED illumination and at a scale 500 times larger than lab setup.

“This is the first report in the scientific literature to show that photocatalysis with LEDs can produce gram-scale quantities of hydrogen gas from ammonia,” Halas said. “This opens the door to entirely replace precious metals in plasmonic photocatalysis.”

“Given their potential for significantly reducing chemical sector carbon emissions, plasmonic antenna-reactor photocatalysts are worthy of further study,” Carter added. “These results are a great motivator. They suggest it is likely that other combinations of abundant metals could be used as cost-effective catalysts for a wide range of chemical reactions.”

Halas is Rice’s Stanley C. Moore Professor of Electrical and Computer Engineering and a professor of chemistry, bioengineering, physics and astronomy, and materials science and nanoengineering. Nordlander is Rice’s Wiess Chair and Professor of Physics and Astronomy, and professor of electrical and computer engineering, and materials science and nanoengineering. Carter is Princeton’s Gerhard R. Andlinger Professor in Energy and Environment at the Andlinger Center for Energy and the Environment, senior strategic adviser for sustainability science at the Princeton Plasma Physics Laboratory, and professor of mechanical and aerospace engineering and of applied and computational mathematics. Robatjazi is also an adjunct professor of chemistry at Rice.

Halas and Nordlander are Syzygy co-founders and hold an equity stake in the company.

The research was supported by the Welch Foundation (C-1220, C-1222), the Air Force Office of Scientific Research (FA9550-15-1-0022), Syzygy Plasmonics, the Department of Defense and Princeton University.

Additional co-authors include Yigao Yuan, Jingyi Zhou, Aaron Bales, Lin Yuan, Minghe Lou and Minhan Lou of Rice, Linan Zhou of both Rice and South China University of Technology, Suman Khatiwada of Syzygy Plasmonics, and Junwei Lucas Bao of both Princeton and Boston College.

“The science has never supported the old eight glasses thing as an appropriate guideline, if only because it confused total water turnover with water from beverages and a lot of your water comes from the food you eat,” says Dale Schoeller, a University of Wisconsin-Madison emeritus professor of nutritional sciences who has been studying water and metabolism for decades. “But this work is the best we’ve done so far to measure how much water people actually consume on a daily basis — the turnover of water into and out of the body — and the major factors that drive water turnover.”

That’s not to say the new results settle on a new guideline. The study, published today in the journal Science, measured the water turnover of more than 5,600 people from 26 countries, ages ranging from 8 days to 96 years old, and found daily averages on a range between 1 liter per day and 6 liters per day.

“There are outliers, too, that are turning over as much as 10 liters a day,” says Schoeller, a co-author of the study. “The variation means pointing to one average doesn’t tell you much. The database we’ve put together shows us the big things that correlate with differences in water turnover.”

Previous studies of water turnover relied largely on volunteers to recall and self-report their water and food consumption, or were focused observations — of, say, a small group of young, male soldiers working outdoors in desert conditions — of questionable use as representative of most people.

The new research objectively measured the time it took water to move through the bodies of study participants by following the turnover of “labeled water.” Study subjects drank a measured amount of water containing trackable hydrogen and oxygen isotopes. Isotopes are atoms of a single element that have slightly different atomic weights, making them distinguishable from other atoms of the same element in a sample.

“If you measure the rate a person is eliminating those stable isotopes through their urine over the course of a week, the hydrogen isotope can tell you how much water they’re replacing and the elimination of the oxygen isotope can tell us how many calories they are burning,” says Schoeller, whose UW-Madison lab in the 1980s was the first to apply the labeled-water method to study people.

More than 90 researchers were involved in the study, which was led by a group that includes Yosuke Yamada, a former UW-Madison postdoctoral researcher in Schoeller’s lab and now section head of the National Institute of Biomedical Innovation, Health and Nutrition in Japan, and John Speakman, zoology professor at the University of Aberdeen in Scotland. They collected and analyzed data from participants, comparing environmental factors — such as temperature, humidity and altitude of the participants’ hometowns — to measured water turnover, energy expenditure, body mass, sex, age and athlete status.

The researchers also incorporated the United Nations’ Human Development Index, a composite measure of a country that combines life expectancy, schooling and economic factors.

Water turnover volume peaked for men in the study during their 20s, while women held a plateau from 20 through 55 years of age. Newborns, however, turned over the largest proportion daily, replacing about 28 percent of the water in their bodies every day.

Physical activity level and athletic status explained the largest proportion of the differences in water turnover, followed by sex, the Human Development Index, and age.

All things equal, men and women differ by about half a liter of water turnover. As a baseline of sorts, the study’s findings expect a male non-athlete (but of otherwise average physical activity) who is 20 years old, weighs 70kg (154 pounds), lives at sea level in a well-developed country in a mean air temperature of 10 degrees C (50 Fahrenheit) and a relative humidity of 50%, would take in and lose about 3.2 liters of water every day. A woman of the same age and activity level, weighing 60 kg (132 pounds) and living in the same spot, would go through 2.7 liters (91 ounces).

Doubling the energy a person uses will push their expected daily water turnover up by about liter, the researchers found. Fifty kilograms more body weight adds 0.7 liters a day. A 50% increase in humidity pushes water use up by 0.3 liters. Athletes use about a liter more than non-athletes.

The researchers found “hunter-gatherers, mixed farmers, and subsistence agriculturalists” all had higher water turnover than people who live in industrialized economies. In all, the lower your home country’s Human Development Index, the more water you go through in a day.

“That’s representing the combination of several factors,” Schoeller says. “Those people in low HDI countries are more likely to live in areas with higher average temperatures, more likely to be performing physical labor, and less likely to be inside in a climate-controlled building during the day. That, plus being less likely to have access to a sip of clean water whenever they need it, makes their water turnover higher.”

The measurements will improve our ability to predict more specific and accurate future water needs, especially in dire circumstances, according to Schoeller.

“Look at what’s going on in Florida right now, or in Mississippi — where entire regions have been exposed by a calamity to water shortages,” he says. “The better we understand how much they need, the better prepared we are to respond in an emergency.”

And the better we can prepare for long-term needs and even notice short-term health concerns, the researchers believe.

“Determining how much water humans consume is of increasing importance because of population growth and growing climate change,” says Yamada. “Because water turnover is related to other important indicators of health, like physical activity and body fat percent, it has potential as a biomarker for metabolic health.”

The study and access to the data was funded by agencies around the world, including the International Atomic Energy Agency, the National Science Foundation and National Institutes of Health in the United States, and the Chinese Academy of Sciences.

Grazed grassland makes up a large proportion of the British countryside and is vital to farming and rural communities. This land can be perceived as only being about food production, but this study gives more evidence that it could be key to increasing biodiversity and soil health.

Researchers at the UK Centre for Ecology & Hydrology (UKCEH) studied 940 plots of grassland, comparing randomly selected plots which sampled the range of grassland management across Great Britain; from intensively- managed land with a few sown grassland species and high levels of soil phosphorus (indicating ploughing/reseeding and fertiliser and slurry application), to grassland with higher levels of species and lower levels of soil phosphorus. The plots were sampled as part of the UKCEH Countryside Survey, a nationally representative long-term dataset.

The study counted the number of plant species in sample areas and analysed co-located soil samples for numbers of soil invertebrates and carbon, nitrogen and phosphorus levels.

Researchers found that less intensively managed grassland had greater diversity of plant species and, strikingly, this correlated with better soil health, such as increased nitrogen and carbon levels and increased numbers of soil invertebrates such as springtails and mites.

In the same study, the researchers used the same methods to examine the plant diversity and soil from grasslands on 56 mostly beef farms from the Pasture Fed Livestock Association (PFLA) — a farmer group that has developed standards to manage and improve soil and pasture health.

The researchers found that plots of land from PFLA farms had greater plant diversity — on average an additional six plant species, including different types of grasses and herbaceous flowering plants, compared to intensively farmed plots from the Countryside Survey. In addition, grassland plants on these farms were often taller, a quality which is proven to be beneficial to butterflies and bees.

Pasture Fed Livestock Association grasslands did not yet show increased soil health, but the research indicated that this may be due to a time lag between increasing numbers of plant species and changes in soil health, particularly on farms which have been intensively managed in the past.

Lead author Dr Lisa Norton, Senior Scientist at UKCEH, says: “We’ve shown for the first time, on land managed by farmers for production, that a higher diversity of plants in grasslands is correlated with better soil health. This work also tells us that the Pasture Fed Livestock Association members are on the right track to increase biodiversity, though it may take longer to see improvements in soil health.

“Grassland with different types of plants able to grow tall and flower is associated with improved soil health measures, and is beneficial for creepy crawlies below and above ground. Having this abundance of life in our grasslands can in turn support small mammals and birds of prey, and farmers have told us that they are seeing voles and mice in their fields for the first time.”

Dr Norton adds: “My hope for the future is that our grasslands can be managed less intensively — with all the improvements in plant and animal biodiversity and soil health that brings — but still remain productive for farmers.”

The study was published in the journal Ecology Solutions and Evidence on 25 November, 2022, and was funded by the UK Research and Innovation Global Food Security Programme.

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