Researchers Create Catalyst That Cleans Dirty Water And Produces Hydrogen
- Oregon State University has developed a dual-purpose catalyst that cleans water polluted with herbicides while producing hydrogen.
- The catalyst is made up of semiconducting materials like titanium dioxide.
- The catalyst is capable of photocatalysis, which absorbs light to break down the organic contaminants.
The project, which included researchers from the OSU College of Engineering and HP Inc. is important because water pollution is a major global challenge, and hydrogen is a clean, renewable fuel.
OSU’s Kyriakos Stylianou said, “We can combine oxidation and reduction into a single process to achieve an efficient photocatalytic system. Oxidation happens via a photodegradation reaction, and reduction through a hydrogen evolution reaction.”
A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
Photocatalysts are materials that absorb light to reach a higher energy level and can use that energy to break down organic contaminants through oxidation. Among photocatalysts’ many applications are self-cleaning coatings for stain- and odor-resistant walls, floors, ceilings and furniture.
Stylianou, assistant professor of chemistry, led the study, which involved titanium dioxide photocatalysts derived from a metal-organic framework, or MOF.
Made up of positively charged metal ions surrounded by organic “linker” molecules, MOFs are crystalline, porous materials with tunable structural properties and nanosized pores. They can be designed with a variety of components that determine the MOF’s properties.
Upon MOFs’ calcination – high heating without melting – semiconducting materials like titanium dioxide can be generated. Titanium dioxide is the most commonly used photocatalyst, and it’s found in the minerals anatase, rutile and brookite.
Stylianou and collaborators including Líney Árnadóttir of the OSU College of Engineering and William Stickle of HP discovered that anatase doped with nitrogen and sulfur was the best “two birds, one stone” photocatalyst for simultaneously producing hydrogen and degrading the heavily used herbicide glyphosate.
Glyphosate, also known as N-phosphonomethyl glycine or PMG, has been widely sprayed on agricultural fields over the last 50 years since first appearing on the market under the trade name Roundup.
Stylianou observed, “Only a small percentage of the total amount of PMG applied is taken up by crops, and the rest reaches the environment,” Stylianou said. “That causes concerns regarding the leaching of PMG into soil and groundwater, as well it should – contaminated water can be detrimental to the health of every living thing on the planet. And herbicides leaching into water channels are a primary cause of water pollution.”
Among an array of compounds in which hydrogen is found, water is the most common, and producing hydrogen by splitting water via photocatalysis is cleaner and more sustainable than the conventional method of deriving hydrogen – from natural gas via a carbon-dioxide-producing process known as methane-steam reforming.
Hydrogen serves many scientific and industrial purposes in addition to its energy-related roles. It’s used in fuel cells for cars, in the manufacture of many chemicals including ammonia, in the refining of metals and in the production of plastics.
“Water is a rich hydrogen source, and photocatalysis is a way of tapping into the Earth’s abundant solar energy for hydrogen production and environmental remediation,” Stylianou said. “We are showing that through photocatalysis, it is possible to produce a renewable fuel while removing organic pollutants, or converting them into useful products.”
The collaboration that included graduate student Emmanuel Musa, postdoctoral researcher Sumandeep Kaur and students Trenton Gallagher and Thao Mi Anthony also tested its photocatalyst against water tainted by two other often-used herbicides, glufosinate ammonium and 2,4-dichlorophenoxyacetic acid. It worked on water containing them as well – even water with those two compounds plus PMG.
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Its quite unusual to see a catalyst that works in dual mode offering two benefits. The “degradation” is offered as the PMG result, with the formation of glycine, formic acid, and phosphoric acid as the major degradation products.. Those are useful chemicals that will still need separated out from the water. Perhaps the research team is working on that.
The hydrogen production action isn’t clear about the water’s oxygen. The press release and paper aren’t real clear on that. Hopefully the process isn’t simply making a mixture of oxygen and di hydrogen gas.
For now this work is just proven to function. To get to process engineering, there is a path that will need worked through. One does hope the work continues. All three herbicides are out in the environment and in some places really need the cleaning done.
FYI, 2,4-dichlorophenoxyacetic acid is commonly seen as 2,4,-D and glufosinate ammonium is usually seen as a component of herbicide compound products.
This is progress in the catalyst field. It seems the prime motivator is herbicide treatment with hydrogen production a side benefit. One wonders if the priorities reversed would offer a worthy benefit. These herbicides are used worldwide and the cleanup where high concentrations are located is a worthy enterprise. The duel action discovery might make a contribution to the hunt for ever more energy efficient catalysts.
Nature Inspires Breakthrough In Energy Efficiency
- Cambridge University researchers have created an eco-friendly plant-based film, utilizing cellulose nanocrystals and reflective layers, that could cool buildings, cars and other structures without requiring excessive external energy.
- Through structural color, specific colors can be achieved without pigments which can absorb sunlight and generate too much heat, enabling a wider range of colors for the cooling film.
- The colorful bi-layered film generated over 120 Watts of cooling power per square meter, comparable to that of many types of residential air conditioning units.
Scientists will report at the American Chemical Society an eco-friendly plant based film that cools when exposed to sunlight. The material could someday keep buildings, cars and other structures cool without requiring as much external power. The film comes in many textures and bright, iridescent colors.
Silvia Vignolini, Ph.D., the project’s principal investigator at Cambridge University (U.K.), started the explanation with, “To make materials that remain cooler than the air around them during the day, you need something that reflects a lot of solar light and doesn’t absorb it, which would transform energy from the light into heat. There are only a few materials that have this property, and adding color pigments would typically undo their cooling effects.”
Passive daytime radiative cooling (PDRC) is the ability of a surface to emit its own heat into space without it being absorbed by the air or atmosphere. The result is a surface that, without using any electrical power, can become several degrees colder than the air around it. When used on buildings or other structures, materials that promote this effect can help limit the use of air conditioning and other power-intensive cooling methods.
Qingchen Shen, Ph.D., also at Cambridge University, who is presenting the work at ACS continued, “Some paints and films currently in development can achieve PDRC, but most of them are white or have a mirrored finish. But a building owner who wanted to use a blue-colored PDRC paint would be out of luck – colored pigments, by definition, absorb specific wavelengths of sunlight and only reflect the colors we see, causing undesirable warming effects in the process.”
But there’s a way to achieve color without the use of pigments. Soap bubbles, for example, show a prism of different colors on their surfaces. These colors result from the way light interacts with differing thicknesses of the bubble’s film, a phenomenon called structural color. Part of Vignolini’s research focuses on identifying the causes behind different types of structural colors in nature. In one case, her group found that cellulose nanocrystals (CNCs), which are derived from the cellulose found in plants, could be made into iridescent, colorful films without any added pigment.
As it turns out, cellulose is also one of the few naturally occurring materials that can promote PDRC. Vignolini learned this after hearing a talk from the first researchers to have created a cooling film material. “I thought wow, this is really amazing, and I never really thought cellulose could do this.”
In their recent work, Shen and Vignolini layered colorful CNC materials with a white-colored material made from ethyl cellulose, producing a colorful bi-layered PDRC film. They made films with vibrant blue, green and red colors that, when placed under sunlight, were an average of nearly 40° F cooler than the surrounding air.
A square meter of the film generated over 120 Watts of cooling power, rivaling many types of residential air conditioners.
Shen said the most challenging aspect of this research was finding a way to make the two layers stick together. On their own, the CNC films were brittle, and the ethyl cellulose layer had to be plasma-treated to get good adhesion. The result, however, was films that were robust and could be prepared several meters at a time in a standard manufacturing line.
Since creating these first films, the researchers have been improving their aesthetic appearance. Using a method modified from approaches previously explored by the group, they’re making cellulose-based cooling films that are glittery and colorful. They’ve also adjusted the ethyl cellulose film to have different textures, like the differences between types of wood finishes used in architecture and interior design, Shen explained. These changes would give people more options when incorporating PDRC effects in their homes, businesses, cars and other structures.
The researchers now plan to find ways they can make their films even more functional. According to Shen, CNC materials can be used as sensors to detect environmental pollutants or weather changes, which could be useful if combined with the cooling power of their CNC-ethyl cellulose films. For example, a cobalt-colored PDRC on a building façade in a car-dense, urban area could someday keep the building cool and incorporate detectors that would alert officials to higher levels of smog-causing molecules in the air.
Of worthy note, the researchers acknowledge support and funding from Purdue University, the American Society of Mechanical Engineers, the European Research Council, the Engineering and Physical Sciences Research Council, the Biotechnology and Biological Sciences Research Council, the European Union and Shanghai Jiao Tong University.
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This might be quite the revolution in roofing, siding and automotive finishes. So far the results are quite encouraging. Lacking an estimate of cost is still out there and the practicality of refurbishing a building or car using a plasma treatment is something of a mystery so far.
But one can be sure there will be interest. The cooling effect, plus the aesthetic potential are great motivators. An iridescent color selection is sure to light up the automobile and designer fields with innumerable ideas.
Lets hope this technology is low cost. The heat gain to buildings and the cooking of car interiors out in the sun are likely quite high unrealized costs. For them to be moderated at a possible drop of 40° F is going to save a lot of electrical power and make cars much more efficient.
By Brian Westenhaus via New Energy and Fuel
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