The study, led by Sabeela Beevi Ummalyma and colleagues at Rajagiri College of Social Sciences and the Indian Institute of Technology Guwahati, focuses on xylan because it is both abundant and chemically versatile. Xylan is a hemicellulose, a family of polysaccharides that occupies the space between cellulose fibers and lignin in plant tissues. Whereas cellulose consists largely of repeating glucose units, xylan is built mainly from xylose sugars and may carry side groups containing arabinose, acetyl or uronic acids. Its molecular structure varies according to the plant source, which affects how easily it can be extracted and broken down. Xylan is biodegradable and considered non-toxic, but humans do not efficiently digest many of its bonds. That makes it a candidate prebiotic: a compound that passes through the upper digestive tract and can be selectively metabolized by microorganisms in the colon.

The researchers compared three common agro-industrial materials with different chemical profiles. Pineapple peel contained the highest reported proportion of hemicellulose, at about 30 percent, while rice straw produced the highest xylan extraction yield, reported as 83 percent. Sugarcane bagasse, the fibrous residue left after juice is removed from sugarcane, was also investigated as a source of the polymer. These differences matter because biomass is not chemically uniform. A high hemicellulose content does not necessarily translate directly into the greatest recoverable xylan yield: cellulose, lignin, mineral content, particle structure and the accessibility of plant-cell-wall polymers can all influence processing. In practical terms, the findings suggest that pineapple waste may offer a rich raw material, while rice straw may be especially favorable for recovering xylan under the conditions tested.

Once isolated, xylan can be hydrolyzed—split by water-assisted chemical or enzymatic reactions—into smaller molecules. The study examined xylan hydrolysates containing XOS, whose chains are shorter than the original polymer. Their size and branching are important. Large xylan molecules may be difficult for microbes to transport into cells, whereas oligosaccharides can be taken up or cleaved by microbial enzymes more readily. In the gut, different bacteria possess different carbohydrate-active enzymes, so the precise pattern of xylose linkages and side groups can determine which organisms benefit. XOS are therefore not simply generic sugars. Their potential lies in being more selectively available to certain microorganisms than readily absorbed sugars such as glucose, which are usually consumed earlier in digestion and may not reach the colon in substantial quantities.

The team used Fourier-transform infrared spectroscopy, or FTIR, to examine the chemical signatures of the extracted material. FTIR works by measuring how a sample absorbs infrared radiation at frequencies associated with vibrations of particular chemical bonds. The extracted xylan displayed characteristic functional groups similar to those found in xylo-arabinoside structures, supporting the conclusion that the recovered material contained a xylan-related hemicellulose rather than being an unidentified mixture of plant compounds. The researchers also used scanning electron microscopy to inspect the material’s surface. The images showed aggregated particles with irregular morphologies, spherical forms and rough surfaces. Such physical features can influence how water and enzymes contact the substrate, potentially affecting hydrolysis and the accessibility of carbohydrate chains to fermenting microorganisms.

The most biologically striking results came from fermentation experiments with lactic acid bacteria. When the bacteria were grown with the xylan hydrolysate, the medium’s pH fell to 4.2, a sign that the organisms were metabolizing available carbohydrates and releasing acidic products. The researchers reported the strongest growth and highest short-chain volatile fatty acid production when probiotic microorganisms were supplied with the xylan-derived materials. Acetic acid reached 118.7 millimoles per millilitre as reported in the study, while propionic acid was measured at 62–74 millimoles per millilitre and lactic acid at 8.8 millimoles per millilitre. Although the units and concentration basis will require careful interpretation when comparing these values with other fermentation studies, the overall pattern indicates active microbial conversion of the plant-derived carbohydrates.

Short-chain fatty acids are among the key chemical links between diet and the gut microbiome. Acetate, propionate and butyrate are produced when bacteria ferment carbohydrates that escape digestion in the small intestine. They can serve as energy sources for intestinal cells, influence the acidity of the colon and affect microbial competition. Propionate and acetate can also enter circulation and participate in broader metabolic signaling. But the presence of an individual fatty acid in a test tube does not automatically demonstrate a health benefit in humans. Concentration, absorption, bacterial species, diet, host physiology and the balance of metabolites all matter. The current study therefore demonstrates prebiotic potential under controlled laboratory conditions, not a proven treatment for digestive disease or evidence that a supplement made from these materials will improve health in people.

The findings nevertheless fit into a rapidly expanding effort to turn lignocellulosic waste into higher-value products. Agricultural residues are attractive feedstocks because they are renewable, widely available and often generated close to processing facilities. Converting them into XOS could create value without requiring additional cropland, while reducing pressure to burn or dump waste. A commercial process would still need to address major engineering and safety questions, including consistent feedstock composition, energy and water use, removal of lignin-derived contaminants, purification, taste, storage stability and regulatory approval. It would also need to establish how the resulting XOS behave in real foods and whether they selectively support beneficial microbes in complex human gut communities rather than simply promoting fermentation in general.

The researchers describe the extracted xylan and its hydrolysates as promising candidates for prebiotic nutraceuticals, food, feed and pharmaceutical applications. Their results provide a biochemical proof of concept: crop residues can yield a defined class of plant polymers, those polymers can be converted into shorter carbohydrate chains, and lactic acid bacteria can use the products while generating organic acids. The next step is to move beyond flask-based fermentation toward detailed compositional analysis, microbial-community studies, animal work and controlled human trials. If those investigations confirm safety, efficacy and reliable production, the humble leftovers of rice, sugarcane and pineapple could become raw materials for microbiome-focused products—linking waste reduction with the growing global demand for foods that nourish the organisms living inside us.

Green hydrogen is generally produced by electrolysis, in which electricity splits water molecules into hydrogen and oxygen. When the electricity comes from renewable sources such as wind or solar power, the process can generate hydrogen without the direct carbon emissions associated with fossil-fuel-based production. However, conventional electrolysis requires substantial amounts of electricity, and the cost and availability of low-carbon power remain significant barriers to large-scale deployment.

The Ohio State team’s approach is designed to lower that energy burden by using chemical reactions that occur during carbon capture and mineralization. Instead of treating carbon dioxide as a waste gas that must simply be compressed or stored, the process uses it as a reactive feedstock. When carbon dioxide encounters alkaline components in steel slag or coal ash, it can react to form calcium carbonate, commonly known as calcite. This reaction permanently converts the gas into a stable mineral while releasing chemical energy that can assist the electrochemical production of hydrogen.

In their first demonstration, the researchers exposed industrial by-products to carbon dioxide and showed that the gas could be incorporated into high-purity calcite. Steel slag, a residue generated during steelmaking, contains calcium-rich compounds capable of reacting with carbon dioxide. Coal ash, produced by coal combustion, can also contain alkaline minerals and reactive metal oxides. These materials are often difficult or costly to manage, but the new process treats them as chemical resources rather than unwanted residues.

Calcite is one of the most abundant minerals on Earth and has broad industrial applications. It can be used in construction materials, agricultural products, paper, plastics, paints and pharmaceuticals. By producing calcite alongside hydrogen, the researchers aim to create an economic incentive for carbon capture that does not depend entirely on carbon credits, government subsidies or environmental mandates. The mineral product could potentially offset part of the cost of operating the system.

The key technical feature of the process is its electrochemical integration. During mineralization, carbon dioxide reacts with calcium-containing compounds in the waste, producing carbonate ions that ultimately precipitate as calcite. At the same time, water electrolysis generates hydrogen at an electrode. Because the mineralization reactions alter the chemical environment and contribute energy to the overall system, less external electrical energy may be required than in conventional hydrogen production. The researchers report that this interaction allowed them to produce hydrogen using widely available grid electricity while achieving a negative-emissions outcome under their accounting framework.

A negative-emissions claim means that the process removes and permanently stores more carbon dioxide than is released throughout the relevant production pathway. In this case, the carbon is fixed into calcite rather than being released back into the atmosphere. The environmental performance of the technology would still depend on factors including the source of the electricity, the energy required to transport and process the industrial waste, and the durability and end use of the mineral product. Even so, the ability to combine waste treatment, carbon storage and fuel production in one process could provide an important advantage over systems that perform these functions separately.

The researchers estimate that the value of the calcite co-product could reduce the effective cost of hydrogen production to less than $1 per kilogram. That projected figure would place the process within the range needed to compete with hydrogen produced from fossil fuels, although commercial performance would need to be confirmed at a much larger scale. Laboratory demonstrations do not always capture the challenges of continuous operation, waste-material variability, electrode durability, gas purification, mineral separation and industrial permitting.

If deployed across interconnected steel, coal and energy sectors, the technology could prevent an estimated 500 million metric tons of carbon dioxide pollution each year, according to the study. Its potential reach extends beyond hydrogen: carbon dioxide converted into mineral form could serve as a feedstock for sustainable manufacturing of other chemicals and advanced materials. The researchers emphasize that their system does not require specialized carbon-capture materials, relying instead on abundant industrial residues that are already generated in large quantities.

The study, led by postdoctoral researcher Tomaz Neves-Garcia with senior author Robert Baker, presents the process as an example of a broader shift in climate technology: designing systems that create economic value while reducing emissions. By transforming carbon dioxide, steel slag and coal ash into hydrogen and calcite, the researchers say their approach could simplify carbon management and make clean-fuel production more attractive. The work was supported by the Camille and Henry Dreyfus Foundation, with undergraduate research fellow Corrado Masciocchi also contributing as a co-author.

Subject of Research: Electrochemical production of green hydrogen and carbon dioxide mineralization using steel slag and coal ash

Article Title: Electrochemical CO2 Mineralization and H2 Generation from Steel and Coal Waste

News Publication Date: 8 July 2026

Web References: https://climate.mit.edu/ask-mit/how-clean-green-hydrogen; https://research.cbc.osu.edu/baker.2364/employees/tomaz-neves-garcia/; https://chemistry.osu.edu/

References: ACS Energy Letters, DOI: 10.1021/acsenergylett.6c01395

Keywords: Green hydrogen, carbon dioxide mineralization, carbon capture, calcite, steel slag, coal ash, electrolysis, negative emissions, industrial waste, climate technology, sustainable chemistry, clean energy