New findings might allow farmers in developing nations to produce their own fertilizer on demand, using sunlight and nitrogen from the air

Georgia Tech graduate research assistant Yu-Hsuan Liu places a sample of titanium dioxide into test equipment in the laboratory of assistant professor Marta Hatzell. (Credit: Rob Felt, Georgia Tech)

The solution to a 75-year-old materials mystery might one day allow farmers in developing nations to produce their own fertilizer on demand, using sunlight and nitrogen from the air.

Thanks to a specialized X-ray source at Lawrence Berkeley National Laboratory, researchers at the Georgia Institute of Technology have confirmed the existence of a long-hypothesized interaction between nitrogen and titanium dioxide (TiO2) – a common photoactive material also known as titania – in the presence of light. The catalytic reaction is believed to use carbon atoms found as contaminants on the titania.

If the nitrogen-fixing reaction can be scaled up, it might one day help power clean farm-scale fertilizer production that could reduce dependence on capital-intensive centralized production facilities and costly distribution systems that drive up costs for farmers in isolated areas of the world. Most of the world’s fertilizer is now made using ammonia produced by the Haber-Bosch process, which requires large amounts of natural gas.

“In the United States, we have an excellent production and distribution system for fertilizer. However, many countries are not able to afford to build Haber-Bosch plants, and may not even have adequate transportation infrastructure to import fertilizers. For these regions, photocatalytic nitrogen fixation might be useful for on-demand fertilizer production,” said Marta Hatzell, an assistant professor in Georgia Tech’s Woodruff School of Mechanical Engineering. “Ultimately, this might be a low-cost process that could make fertilizer-based nutrients available to a broader array of farmers.”

Hatzell and collaborator Andrew Medford, an assistant professor in Georgia Tech’s School of Chemical and Biomolecular Engineering, are working with scientists at the International Fertilizer Development Center (IFDC) to study the potential impacts of the reaction process. The research was reported October 29 in the Journal of the American Chemical Society.

The research began more than two years ago when Hatzell and Medford began collaborating on a materials mystery that originated with a 1941 paper published by Seshacharyulu Dhar, an Indian soil scientist who reported observing an increase in ammonia emitted from compost subjected to light. Dhar suggested that a photocatalytic reaction with minerals in the compost could be responsible for the ammonia.

Since that paper, other researchers have reported nitrogen fixation on titania and ammonia production, but the results have not been consistently confirmed experimentally.

Medford, a theoretician, worked with graduate research assistant Benjamin Comer to model the chemical pathways that would be needed to fix nitrogen on titania to potentially create ammonia using additional reactions. The calculations suggested the proposed process was highly unlikely on pure titania, and the researchers failed to win a grant they had proposed to use to study the mysterious process. However, they were awarded experimental time on the Advanced Light Sourceat the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, which allowed them to finally test a key component of the hypothesis.

Specialized equipment at the lab allowed Hatzell and graduate student Yu-Hsuan Liu to use X-ray photoelectron spectroscopy (XPS) to examine the surface of titania as nitrogen, water and oxygen interacted with the surfaces under near-ambient pressure in the dark and in the light. At first, the researchers saw no photochemical nitrogen fixation, but as the experiments continued, they observed a unique interaction between nitrogen and titania when light was directed at the minerals surface.

What accounted for the initial lack of results? Hatzell and Medford believe that surface contamination with carbon – likely from a hydrocarbon – is a necessary part of the catalytic process for nitrogen reduction on the titania. “Prior to testing, the samples are cleaned to remove nearly all the trace carbon from the surface, however during experiments carbon from various sources (gases and the vacuum chamber) can introduce trace amount of carbon back onto the sample,” Hatzell explained. “What we observed was that reduced nitrogen species only were detected if there was a degree of carbon on the sample.”

The hydrocarbon contamination hypothesis would explain why earlier research had provided inconsistent results. Carbon is always present at trace levels on titania, but getting the right amount and type may be key to making the hypothesized reaction work.

“We think this explains the puzzling results that had been reported in the literature, and we hope it gives insights into how to engineer new catalysts using this 75-year-old mystery,” Medford said. “Often the best catalysts are materials that are very pristine and made in a clean room. Here you have just the opposite – this reaction actually needs the impurities, which could be beneficial for sustainable applications in farming.”

The researchers hope to experimentally confirm the role of carbon with upcoming tests at Pacific Northwest National Laboratory (PNNL), which will allow them to directly probe the carbon during the photocatalytic nitrogen fixation process. They also hope to learn more about the catalytic mechanism so that they can better control the reaction to improve efficiency, which is currently less than one percent.

The research reported in the journal did not measure ammonia, but Hatzell and her students have since detected it in lab scale tests. Because the ammonia is currently produced at such low levels, the researchers had to take precautions to avoid ammonia-based contamination. “Even tape used on equipment can create small quantities of ammonia that can affect the measurements,” Medford added.

Though the amounts of ammonia produced by the reaction are currently low, Hatzell and Medford believe that with process improvements, the advantages of on-site fertilizer production under benign conditions could overcome that limitation.

“While this may sound ridiculous from a practical perspective at first, if you actually look at the needs of the problem and the fact that sunlight and nitrogen from the air are free, on a cost basis it starts to look more interesting,” Medford said. “If you could operate a small-scale ammonia production facility with enough capacity for one farm, you have immediately made a difference.”

Hatzell credits cutting-edge surface science with finally providing an explanation to the mystery.

“Since earlier investigators looked at this, there have been significant advances made in the area of measurement and surface science,” she said. “Most surface science measurements require the use of ultra-high vacuum conditions which do not mimic the catalytic environment you aim to investigate. The near ambient pressure XPS at Lawrence Berkeley National lab, allowed us to take a step closer to observing this reaction in its native environment.”

Learn more: Solving a 75-Year-Old Mystery Might Provide a New Source of Farm Fertilizer



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Creating fertilizer out of thin air with engineered bacteria

Himadri Pakrasi (left), led a team of researchers that has created a bacteria that uses photosynthesis to create oxygen during the day, and at night, uses nitrogen to create chlorophyll for photosynthesis. The team included Michelle Liberton (second from left), Deng Liu and Maitrayee Bhattacharyya-Pakrasi. (Photo: Joe Angeles/Washington University)
From left:
Himadri Pakrasi, Myron and Sonya Glassberg/Albert and Blanche Greensfelder Distinguished University Professor;
Michelle Liberton, Research Scientist;
Deng Liu, Postdoctoral Research Associate;
Maitrayee Bhattacharyya, Senior Research Scientist.
Liu is holding cyanobacterium synechocystis sp. PCC 6803.
Photos by Joe Angeles/WUSTL Photos

Next step could be ‘nitrogen-fixing’ plants that can do the same, reducing need for fertilizer

In the future, plants will be able to create their own fertilizer. Farmers will no longer need to buy and spread fertilizer for their crops, and increased food production will benefit billions of people around the world, who might otherwise go hungry.

These statements may sound like something out of a science fiction novel, but new research by Washington University in St. Louis scientists show that it might soon be possible to engineer plants to develop their own fertilizer. This discovery could have a revolutionary effect on agriculture and the health of the planet.

The research, led by Himadri Pakrasi, the Glassberg-Greensfelder Distinguished University Professor in the Department of Biology in Arts & Sciences and director of the International Center for Energy, Environment and Sustainability (InCEES); and Maitrayee Bhattacharyya-Pakrasi, senior research associate in biology, was published in the May/June issue of mBio.

Creating fertilizer is energy intensive, and the process produces greenhouse gases that are a major driver of climate change. And it’s inefficient. Fertilizing is a delivery system for nitrogen, which plants use to create chlorophyll for photosynthesis, but less than 40 percent of the nitrogen in commercial fertilizer makes it to the plant.

After a plant has been fertilized, there is another problem: runoff. Fertilizer washed away by rain winds up in streams, rivers, bays and lakes, feeding algae that can grow out of control, blocking sunlight and killing plant and animal life below.

However, there is another abundant source of nitrogen all around us. The Earth’s atmosphere is about 78 percent nitrogen, and the Pakrasi lab in the Department of Biology just engineered a bacterium that can make use of that atmospheric gas — a process known as “fixing” nitrogen — in a significant step toward engineering plants that can do the same.

The research was rooted in the fact that, although there are no plants that can fix nitrogen from the air, there is a subset of cyanobacteria (bacteria that photosynthesize like plants) that is able to do so. Cyanobacteria can do this even though oxygen, a byproduct of photosynthesis, interferes with the process of nitrogen fixation.

The bacteria used in this research, Cyanothece, is able to fix nitrogen because of something it has in common with people.

“Cyanobacteria are the only bacteria that have a circadian rhythm,” Pakrasi said. Interestingly, Cyanothece photosynthesize during the day, converting sunlight to the chemical energy they use as fuel, and fix nitrogen at night, after removing most of the oxygen created during photosynthesis through respiration.

The research team wanted to take the genes from Cyanothece, responsible for this day-night mechanism, and put them into another type of cyanobacteria, Synechocystis, to coax this bug into fixing nitrogen from the air, too.

To find the right sequence of genes, the team looked for the telltale circadian rhythm. “We saw a contiguous set of 35 genes that were doing things only at night,” Pakrasi said, “and they were basically silent during the day.”

The team, which also included research associate Michelle Liberton, former research associate Jingjie Yu, and Deng Liu manually removed the oxygen from Synechocystis and added the genes from Cyanothece. Researchers found Synechocystis was able to fix nitrogen at 2 percent of Cyanothece. Things got really interesting, however, when Liu, a postdoctoral researcher who has been the mainstay of the project, began to remove some of those genes; with just 24 of the Cyanothece genes, Synechocystis was able to fix nitrogen at a rate of more than 30 percent of Cyanothece.

Nitrogen fixation rates dropped markedly with the addition of a little oxygen (up to 1 percent), but rose again with the addition of a different group of genes from Cyanothece, although it did not reach rates as high as without the presence of oxygen.

“This means that the engineering plan is feasible,” Pakrasi said. “I must say, this achievement was beyond my expectation.”

The next steps for the team are to dig deeper into the details of the process, perhaps narrow down even further the subset of genes necessary for nitrogen fixation, and collaborate with other plant scientists to apply the lessons learned from this study to the next level: nitrogen-fixing plants.

Crops that can make use of nitrogen from the air will be most effective for subsistence farmers — about 800 million people worldwide, according to the World Bank — raising yields on a scale that is beneficial to a family or a town and freeing up time that was once spent manually spreading fertilizer.

“If it’s a success,” Bhattacharyya-Pakrasi said, “it will be a significant change in agriculture.”

Learn more: Researchers engineer bacteria that create fertilizer out of thin air



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More efficient fertilizers using graphene as a carrier


Fertilisers with lower environmental impacts and reduced costs for farmers are being developed by University of Adelaide researchers in the world-first use of the new advanced material graphene as a fertiliser carrier.

In partnership with industry, the researchers have demonstrated effective slow release fertilisers can be produced from loading essential trace elements onto graphene oxide sheets.

Using graphene as a carrier means the fertilisers can be applied in a more targeted fashion, with overall increased fertiliser efficiency and great nutrient uptake by the plants. The graphene-based carriers have so far been demonstrated with the micronutrients zinc and copper. Work is continuing with macronutrients such as nitrogen and phosphate.

“Fertilisers that show slower, more controlled release and greater efficiency will have reduced impact on the environment and lower costs for farmers over conventional fertilisers, bringing significant potential benefit for both agriculture and the environment,” says Professor Mike McLaughlin, Head of the University of Adelaide’s Fertiliser Technology Research Centre at the Waite campus.

“Our research found that loading copper and zinc micronutrients onto graphene oxide sheets was an effective way to supply micronutrients to plants. It also increased the strength of the fertiliser granules for better transport and spreading ability.”

Professor Dusan Losic, nanotechnology leader in the University’s School of Chemical Engineering and Director of the University’s Australian Research Council (ARC) Research Hub for Graphene Enabled Industry Transformation, says: “Graphene is a novel new material only discovered in 2004 and has incredible properties, including a very high surface area, strength and adaptability to bind to different nutrients. We started exciting research on a broad range of applications of graphene four years ago – this is the first time graphene has been developed as a carrier for fertiliser nutrients.”

Learn more: Graphene promise for more efficient fertilisers


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Using sunlight to produce nitrogen-based synthetic fertilizer drastically cut the energy needed to produce it

Nanostructures made from gold concentrate light energy and boost molybdenum’s ability to pull apart the two nitrogen atoms in an N2 molecule (illustration by the researchers)

Nitrogen-based synthetic fertilizer forms the backbone of the world food supply, but its manufacture requires a tremendous amount of energy. Now, computer modeling at Princeton University points to a method that could drastically cut the energy needed by using sunlight in the manufacturing process.

Manufacturers currently make fertilizer, pharmaceuticals and other industrial chemicals by pulling nitrogen from the air and combining it with hydrogen. Nitrogen gas is plentiful, making up about 78 percent of air. But atmospheric nitrogen is hard to use because it is locked into pairs of atoms, called N2, and the bond between these two atoms is the second strongest in nature. Therefore it takes a lot of energy to split up the N2molecule and allow the nitrogen and hydrogen atoms to combine. Most manufacturers use the Haber-Bosch process, a century-old technique that exposes the N2 and hydrogen to an iron catalyst in a chamber heated to more than 400 degrees Celsius. The method uses so much energy that Science magazine recently reported that manufacturing fertilizer and similar compounds represents about 2 percent of the world’s energy use each year.

A research team led by Emily Carter, Princeton’s dean of engineering and the Gerhard R. Andlinger Professor in Energy and the Environment, wanted to know if it would be possible to use light to weaken the bond in the atmospheric nitrogen molecule. If so, it would allow manufacturers to radically cut the energy needed to split nitrogen for use in fertilizer and a wide array of other products.

“Harnessing the energy in sunlight to activate inert molecules such as nitrogen, and greenhouse gases methane and carbon dioxide for that matter, is a grand challenge for sustainable chemical production,” said Carter, who is a professor of mechanical and aerospace engineering and of applied and computational mathematics. “Replacing traditional energy-intensive high temperature, high pressure chemical manufacturing with sunlight-driven, room temperature processes is another way to decrease our dependence on fossil fuels.”

The researchers were interested in taking advantage of the unique behavior of light when it interacts with metallic nanostructures smaller than a single wavelength of light. Among other effects, the phenomenon, called surface plasmon resonance, can concentrate light and enhance electric fields. Dr. John Mark Martirez, a post-doctoral researcher and member of the Princeton research team, said that the researchers believed it would be possible to use plasmon resonances to boost a catalyst’s power to split apart nitrogen molecules.

“It is a different method of delivering energy to break the bond,” he said. “Instead of using heat, we are using light.”

In a January 5 article in the journal Science Advances, the researchers describe how they used computer simulations to model light’s behavior in tiny structures made from gold and molybdenum. Gold is one of a class of metals, including copper and aluminum, which can be shaped to produce surface plasmon resonances. The researchers used a set of computer modeling tools to simulate nanostructures made of gold, and added molybdenum to its surface, which is a metal that can split nitrogen molecules.

“The plasmonic metal acts like a lightning rod,” Martirez said. “It concentrates a large amount of the light energy in a very small area.”

The concentrated light energy effectively boosts the molybdenum’s ability to pull apart the two nitrogen atoms.

“The interaction of light magnifies the electric field close to the surface of the catalyst, which helps break the bond,” Martirez said.

The researchers’ calculations indicate that the plasmon-resonance technique should be able to reduce substantially the energy needed to crack the atmospheric nitrogen molecules. Carter said the modeling indicates it should be possible to dissociate the nitrogen molecule at room temperature and at lower pressures than required by the Haber-Bosch process.

Simulating the process while also considering the effect of light was challenging. Most computer models that can accurately assess chemical reactions at the molecular level, and account for changes induced by light, can only simulate a few atoms at a time. While this is scientifically valuable, it does not usually suffice for evaluating industrial processes.

So the researchers turned to a technique originally developed by Carter that allows scientists to use highly accurate methods for modeling a small fragment of the surface and then extend those results to get an understanding of a wider system. The technique, called embedded correlated wave function theory, has been repeatedly verified and extensively used within the Carter group, and the researchers are confident in its application to the nitrogen-splitting problem.

Carter said her team is collaborating with Naomi Hallas and Peter Nordlander of Rice University to test the plasmon-resonance technique in the lab. The researchers have worked together on similar projects in the past, including demonstrating the dissociation of hydrogen molecules on pure gold nanoparticles.

As a next step, Carter said she would like to extend the plasmon resonance technique to other strong chemical bonds. One candidate is the carbon-hydrogen bond in methane. Manufacturers use natural gas to supply the hydrogen in fertilizer as well as other important industrial chemicals. So finding a low-energy method to break that bond could also be a boon to manufacturing.

Learn more: New process could slash energy demands of fertilizer, nitrogen-based chemicals




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Could pollen be turned into a low-cost fertilizer?

via ACS

As the world population continues to balloon, agricultural experts puzzle over how farms will produce enough food to keep up with demand.

One tactic involves boosting crop yields. Toward that end, scientists have developed a method to make a low-cost, biocompatible fertilizer with carbon dots derived from rapeseed pollen. The study, appearing in ACS Omega, found that applying the carbon dots to hydroponically cultivated lettuce promoted its growth by 50 percent.

Equipped with exceptional mechanical, thermal, optical and electrical properties, carbon nanomaterials are commonly associated with complex devices. Surprisingly, these materials could also have potential agricultural applications — some studies have shown that they increase plant growth. The problem with this concept, however, is that many carbon nanomaterials are expensive to produce and usually come with heavy metal contamination. For a safer alternative, Yingliang Liu, Bingfu Lei and colleagues turned to carbon dots, which previous studies have shown are biocompatible.

The researchers synthesized carbon dots by breaking apart and heating rapeseed pollen. The high-yield process was relatively inexpensive, costing 3 cents per gram. Testing the material as fertilizer on lettuce showed that at a concentration of 30 milligrams per liter of a nutrient solution, the plant biomass was nearly 50 percent greater in treated plants than those that didn’t receive the carbon dots. Additionally, because carbon dots are fluorescent, the researchers could track the materials under ultraviolet light. They saw that the materials were distributed mainly in the leaves. Further analysis also demonstrated that the levels of vitamin C, and soluble sugars and proteins weren’t affected.

via American Chemical Society


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