Every time we fry our favourite foods, we create something that most of us throw away without a second thought: used cooking oil. Across Asia alone, tens of thousands of tons of this oily waste end up discarded every year, clogging drains, polluting rivers, and creating environmental hazards. But scientists have found an unexpected second life for this everyday waste. By using advanced nanotechnology, researchers are transforming discarded oil into powerful materials that could revolutionize electronics, environmental cleanup, and even renewable energy.

This story explores how waste cooking oil, something found in every home and restaurant, can be recycled into carbon nanotubes and nanocomposites. These are microscopic tubes made of carbon atoms that have extraordinary strength, conductivity, and versatility. Once considered a laboratory curiosity, carbon nanotubes are now a foundation for futuristic technologies, and their production from waste oil marks a turning point in green innovation. When cooking oil is heated repeatedly, its chemical structure changes, forming degraded fats and polymerized residues. This oil becomes unsuitable for consumption and is typically disposed of through sinks or illegal dumping. When poured down drains, it solidifies with food waste and soap, forming blockages that damage plumbing and sewage systems. Open burning of used oil, on the other hand, releases harmful smoke that contributes to air pollution and greenhouse gases.

According to research from Institute of Nanoscience and Nanotechnology (ION2), Universiti Putra Malaysia (UPM), a single country can produce tens of thousands of tonnes of waste cooking oil annually. Traditional disposal methods fail to cope with this growing waste stream. Environmental agencies classify it as hazardous due to its impact on soil, water, and aquatic life. Recycling it into biodiesel has been one solution, but the process is costly and energy-intensive. That is why scientists began searching for a more sustainable and high-value alternative. At the heart of this discovery is a process called floating catalyst chemical vapor deposition (FCCVD). In simple terms, this technique uses heat and gas flow to break down liquid hydrocarbons into carbon atoms that then assemble into nanotubes. In this case, the hydrocarbon comes from waste palm oil where the same kind used for frying food.

In the ION2, UPM laboratories, researchers filtered and purified used cooking oil, then injected it into a high-temperature furnace together with small amounts of hydrogen and argon gases. The oil vaporized and decomposed, while an iron-based compound called ferrocene acted as a catalyst, encouraging the formation of carbon nanotubes. A small quantity of thiophene, a sulfur compound, was added to promote better alignment and yield. Inside the furnace, carbon atoms began assembling into hollow cylinders just a few nanometers in diameter but thousands of times longer than they are wide. These cylinders are known as multiwalled carbon nanotubes (MWCNTs), grew like cotton fibers and collected into soft, black aerogel-like masses called CNT cotton. This material is extremely light, conductive, and strong. By optimizing the reaction conditions such as temperature, gas flow, and catalyst ratio, the team achieved high-quality nanotubes with controlled structure and minimal impurities. The ideal temperature for production was around 1150°C, yielding long and pure nanotube bundles.

Under an electron microscope, CNTs appear as networks of intertwined tubes, each made up of hexagonally arranged carbon atoms. These structures are stronger than steel but lighter than aluminum. The electrons inside them can move with little resistance, making CNTs excellent electrical conductors. When waste cooking oil is used as the carbon source, its natural triglycerides, combinations of carbon, hydrogen, and oxygen, provide an abundant supply of carbon atoms for nanotube growth. The presence of trace metals and fatty acid chains in the oil helps in nucleating (seeding) nanotube formation. Compared with fossil-based hydrocarbons like methane or acetylene, the renewable nature of cooking oil makes it a greener, cheaper, and safer choice. A major advantage of this method is that it bypasses the need for complex chemical purification. The FCCVD process yields CNT cotton that can be directly handled, pressed into sheets, or mixed into other materials without heavy solvent use. It is a form of “green nanotechnology,” where waste becomes the feedstock for advanced materials.

The journey of waste oil recycling does not end with pure carbon nanotubes. A newer branch of research has explored combining CNTs with other nanomaterials to create hybrids that have multifunctional properties. One promising example is the CNT cotton/ZnO nanocomposite developed at UPM’s Nanomaterial Synthesis and Characterization Lab. Here, the same waste cooking oil served two purposes: first as a carbon source for producing CNT cotton, and second as a biotemplate for the controlled growth of zinc oxide (ZnO) nanoparticles. When CNT cotton was immersed in a zinc acetate solution mixed with a small amount of waste oil, the fatty acids in the oil helped anchor zinc ions onto the CNT surface. After heating and hydrothermal treatment, ZnO crystals grew directly on the nanotube framework, forming a uniform nanocomposite. Analyses showed that chemical bonds formed between zinc and the oxygen-containing groups derived from the oil, giving rise to structures that combined the mechanical strength of carbon nanotubes with the photocatalytic and antibacterial capabilities of ZnO. The X-ray diffraction results confirmed the coexistence of crystalline carbon, zinc oxide, and traces of iron oxide from the catalyst. Under a microscope, researchers observed tiny ZnO rods decorating the CNT surface, creating a three-dimensional network. This hybrid material is highly versatile. It can be used for water purification, solar energy harvesting, and antimicrobial coatings. Because the entire process uses waste oil and mild synthesis conditions, it represents a sustainable route toward functional nanomaterials with low environmental footprint.

One of the earliest practical demonstrations of CNTs made from waste oil was in microstrip patch antennas (MPA), a thin, flexible antennas used in communication devices. Researchers replaced conventional copper with CNT-based conductive films. Despite being lighter and flexible, these antennas maintained good signal performance. The CNT paste, prepared from nanotubes mixed with natural binders like linseed oil, was printed onto flexible substrates and tested for electrical properties. Even though copper remains more conductive, the CNT-based antennas showed promise for wearable and lightweight electronics.

Beyond antennas, CNTs derived from waste oil are also being investigated for:

• Energy storage: When used as electrodes in supercapacitors or lithium batteries, CNTs provide high surface area and excellent charge mobility.
• Environmental remediation: Their porous structure can trap oil and organic pollutants, helping to clean contaminated water.
• Sensors and catalysts: CNT composites can detect gases, light, or biological molecules, or accelerate chemical reactions.

Each of these applications turns what was once an environmental problem into a resource for cleaner technologies.

The success of these experiments marks more than a scientific achievement; it reflects a mindset shift toward a circular economy. Instead of viewing used cooking oil as waste, it becomes a renewable raw material feeding advanced manufacturing. The same oil that once fried food can now form part of an antenna, a battery, or a medical sensor. In this model, waste is minimized, and value is continuously regenerated. Small restaurants and households could, in the future, contribute their used oil to collection centers, where it is filtered and converted into carbon feedstock for nanomaterial production. This approach aligns with global sustainability goals by reducing carbon emissions, limiting waste disposal, and promoting green technology industries. Recycling waste cooking oil into CNTs and nanocomposites brings multiple benefits. Environmentally, it prevents pollution of waterways and reduces the demand for fossil hydrocarbons. Economically, it lowers production costs for nanomaterials that are otherwise expensive when synthesized from pure gases or chemicals. In Malaysia and other palm-oil-producing countries, the abundance of waste oil offers an inexpensive and steady supply of carbon feedstock. This could give rise to local industries that manufacture nanomaterials domestically instead of importing them. Moreover, this approach supports the nation’s green technology policy, integrating waste management with high-value innovation. The carbon footprint of the synthesis process is also lower. Since cooking oil already contains carbon atoms from renewable sources (plants), the net carbon emission is smaller compared to using petrochemical precursors.

The pioneering studies at ION2,  Universiti Putra Malaysia were led by research teams who saw opportunity in waste. By combining chemical engineering, materials science, and environmental sustainability, they demonstrated how local waste could drive global innovation. Graduate students and researchers worked long hours perfecting the FCCVD system, adjusting gas ratios, temperatures, and catalyst compositions to achieve consistent results. Their findings were published in journals and presented internationally, inspiring other scientists to look at everyday materials in a new light. This interdisciplinary effort reflects the evolving role of science, not only to understand the world but to repair it. Nanotechnology, once thought to belong only in high-tech laboratories, is now tied directly to community issues such as waste management and environmental protection. The idea of transforming waste cooking oil into nanotechnology products is still developing. Future studies will likely explore scaling up the process for industrial production, improving purity and yield, and integrating CNT composites into commercial devices. One exciting direction is the creation of graphenated carbon nanotubes (g-CNTs), a hybrid structure where graphene sheets grow on CNT surfaces, combining the best of both materials. Early results suggest that when waste cooking oil is carefully tuned during FCCVD synthesis, such hybrids can form naturally, leading to even higher electrical and mechanical performance. Researchers are also investigating how these nanomaterials can support the clean energy transition, such as being used in electromagnetic interference (EMI) shielding for electric vehicles, or as catalysts for hydrogen production.

Recycling waste cooking oil into nanotechnological materials represents a remarkable fusion of environmental responsibility and scientific creativity. It shows that sustainable innovation does not always require exotic resources; sometimes, it begins in the kitchen. Through controlled high-temperature reactions, simple waste oil can become the foundation for materials that conduct electricity, store energy, and protect the environment. By doing so, it closes the loop between daily life and advanced technology, proving that even waste can power the future of science. As this field advances, the humble bottle of used cooking oil may soon be recognized not as waste—but as the starting point of a cleaner, smarter world.

Written by:
Dr. Ismayadi Ismail (NSCL, ION2, UPM)

Date of Input: 12/11/2025 | Updated: 12/11/2025 | roslina_ar