Green Synthesis and Characterisation of Iron Oxide Nanoparticles Using Rice Husk and Orange Peel Extracts and Residue Templates (RHOPTNPs) for the Adsorptive Removal of Ciprofloxacin and Ibuprofen from Aqueous Solution

Water is the lifeblood of our planet, but it is increasingly carrying a hidden burden: traces of medicines we have taken. When people take antibiotics or painkillers, the body does not absorb every molecule. What remains flows out of homes and hospitals, eventually reaching rivers and lakes. These pharmaceutical residues are dangerous because they persist in the environment and can encourage bacteria to become resistant to treatment, posing a long-term threat to public health. Traditional water treatment plants were built to remove large particles and bacteria, not these tiny, dissolved chemical traces. To solve this, scientists are turning to a different approach: using tiny particles of iron oxide, which act like microscopic sponges that can grab these medicines out of the water. However, making these particles usually requires harsh chemicals and high energy. A more sustainable path is to grow them using plants, a method known as green synthesis, which turns waste into a useful tool.

In a recent study, researchers in Nigeria explored how to make these iron oxide nanoparticles using two common types of agricultural waste: rice husks and orange peels. Instead of discarding these materials, the team combined them to create a natural template for building the nanoparticles. They took the leftover solid bits of the husks and peels, mixed them with water to create an extract, and then added iron salts to this mixture. The plant materials acted as a scaffold, guiding the iron to form into tiny, magnetic particles while also coating them with natural chemicals from the plants. The resulting material, which the researchers named RHOPTNPs, was then tested to see if it could effectively pull two specific medicines—ciprofloxacin, an antibiotic, and ibuprofen, a pain reliever—out of contaminated water.

The team first examined the physical nature of their new material to understand what they had created. They found that the nanoparticles were roughly 76 nanometers in size, a scale so small that millions could fit on the head of a pin. More importantly, the material was incredibly porous, meaning it had a vast network of tiny holes and tunnels inside. This structure gave the nanoparticles a massive surface area, allowing them to interact with a large amount of water at once. The analysis also confirmed that the particles were magnetic, a crucial feature that allows them to be easily pulled out of the water with a magnet after they have done their job, rather than needing to be filtered out. The surface of these particles was covered with organic molecules from the rice and orange, which helped stabilize the particles and likely provided the chemical "hooks" needed to catch the medicines.

When the researchers tested the material in the lab, they discovered that it worked exceptionally well under specific conditions. For the antibiotic ciprofloxacin, the nanoparticles removed nearly 99.5 percent of the drug from the water when used in the right amount and given about 40 minutes to work. The process worked best at a neutral pH level, which is similar to the acidity of pure water, and performed even better as the temperature of the water increased slightly. In contrast, the removal of ibuprofen reached about 92 percent efficiency under similar conditions, but this drug behaved differently: the nanoparticles were most effective at removing it when the water was cooler. This difference suggests that the two medicines stick to the particles through slightly different mechanisms, with one process requiring heat to proceed efficiently and the other slowing down as the water gets warmer.

The study also looked at how the material behaved over time and in real-world scenarios. The researchers found that the nanoparticles could be used repeatedly. After being washed and reused four times, the material still removed about 92 percent of the ciprofloxacin it had caught initially, showing strong durability. However, its ability to catch ibuprofen dropped more significantly after repeated use, suggesting that the binding sites for ibuprofen are harder to clean and reuse. Despite this, the material proved effective when tested on actual wastewater samples taken from hospitals and residential areas in Kaduna. In these complex mixtures, which contain many other substances besides the target medicines, the nanoparticles still managed to remove a significant portion of both drugs, with removal rates ranging from 80 to 97 percent depending on the sample and the specific medicine.

The findings indicate that turning agricultural waste into a high-tech water cleaner is a viable and promising strategy. The process is not just about removing pollution; it is about creating value from materials that would otherwise be thrown away. By using the natural chemistry of rice husks and orange peels, the researchers created a magnetic adsorbent that is cheap to make, easy to recover from water, and highly effective at cleaning up pharmaceutical contaminants. While the study confirms that the material works well in controlled settings and in real wastewater, the authors note that further testing is needed to fully understand the exact chemical interactions happening on the surface of the particles and to see how the system performs on a larger scale. Nevertheless, this work offers a concrete step toward a future where cleaning our water might rely as much on the fields that feed us as on the factories that treat our waste.