Comparative Evaluation of Fe₂O₃, CuO, ZnO and NiO Nanoparticles for Removal of Triazine Herbicides from Water and Agricultural Commodities

Every day, farmers rely on a specific class of chemicals called triazine herbicides to protect their crops from weeds. These substances, including common names like atrazine and metribuzin, are effective at keeping fields clear, but they are also stubborn. They do not break down easily in the environment, and they can travel from the soil into rivers, lakes, and groundwater. This persistence creates a double problem: it threatens the health of ecosystems and leaves residues on the food we eat, such as tomatoes, corn, and potatoes. While washing produce with water is a standard practice, these chemicals often cling tightly to the surface of plants, making them difficult to remove with a simple rinse. Scientists have long sought a way to clean both our water and our food more effectively, turning their attention to the microscopic world of nanotechnology. By using particles so small that they are measured in billionths of a meter, researchers can create materials with enormous surface areas and unique chemical abilities that might capture or break down these stubborn pollutants.

A team of researchers at St Xavier's College set out to test four different types of these microscopic particles to see which one could best remove atrazine and metribuzin from water and from fresh produce. They focused on particles made from four common transition metal oxides: iron oxide, copper oxide, zinc oxide, and nickel oxide. These materials were chosen because they are known to interact with organic chemicals in various ways, such as sticking to them or breaking them apart through chemical reactions. The researchers did not just look at how well these particles could sit in water and absorb the chemicals; they also tested whether exposing the mixture to light would help break the chemicals down faster, a process known as photocatalysis. They wanted to find out if one specific material was superior to the others and if it could be used repeatedly without losing its effectiveness.

To begin their investigation, the team prepared solutions containing the herbicides and mixed them with different amounts of each nanoparticle type. They carefully controlled the conditions, adjusting the acidity of the water and the time the particles were allowed to interact with the chemicals. They found that all four types of nanoparticles were able to remove the herbicides to some degree, but there were clear differences in their performance. The particles made of zinc oxide proved to be the most effective, removing nearly 94 percent of the atrazine and over 91 percent of the metribuzin from the water under the best conditions. Copper oxide followed as the second-best performer, while iron oxide and nickel oxide were less efficient. The researchers determined that the zinc oxide particles worked so well because they could not only stick to the herbicide molecules but also, when exposed to light, generate reactive species that actively broke the chemical bonds of the pollutants.

The study also looked at how the process worked over time. By analyzing the speed at which the herbicides were removed, the team concluded that the interaction was not just a simple physical sticking process. Instead, the data suggested a more complex chemical bonding occurred between the nanoparticles and the herbicide molecules. This finding helped explain why the removal was so efficient and why the zinc oxide particles, which have a strong ability to interact with light, performed so well. When the researchers compared the results of experiments done in the dark against those done under light, the difference was significant for zinc oxide and copper oxide. The light significantly boosted the ability of these particles to degrade the herbicides, confirming that a light-driven chemical reaction was a key part of the cleanup process.

Beyond cleaning water, the researchers wanted to know if these particles could help clean actual food. They took fresh tomatoes, corn, and potatoes and sprayed them with the herbicides to simulate real-world contamination. They then washed these samples with a suspension of the nanoparticles. The results mirrored the water tests: washing with zinc oxide removed the highest percentage of pesticide residues from all three types of produce. For tomatoes, corn, and potatoes, the zinc oxide wash reduced atrazine residues by roughly 93 percent, 85 percent, and 89 percent, respectively. While copper oxide also showed good results, it did not perform as well as the zinc oxide. The researchers noted that the smooth surface of the tomatoes allowed for slightly better cleaning than the rougher, more irregular surfaces of the corn and potatoes, which tended to hold onto the chemicals more tightly.

A crucial part of the study was determining whether these nanoparticles could be used more than once, which is essential for any practical application. The team tested the zinc oxide particles over five consecutive cleaning cycles. Even after being washed, dried, and reused, the particles maintained a high level of effectiveness, removing more than 88 percent of the herbicides by the fifth cycle. This demonstrated that the material was stable and did not degrade quickly, making it a viable candidate for repeated use. In contrast, the other materials showed different mechanisms of action; for instance, the iron oxide particles relied on a combination of surface adsorption and surface complexation, while the copper oxide particles used a redox process, which involves the transfer of electrons to break down the chemicals. The nickel oxide particles primarily worked through surface interactions but had minimal light-driven degradation, functioning mainly as an adsorbent.

The final conclusion of the research was a clear ranking of the materials based on their overall ability to clean up triazine herbicides. Zinc oxide emerged as the top choice, followed by copper oxide, then iron oxide, and finally nickel oxide. The study highlighted that zinc oxide is particularly promising because it combines high adsorption capacity with strong photocatalytic activity, meaning it can both grab the pollutants and destroy them when light is present. It also proved to be reusable and effective on real food items. While the research was conducted under controlled laboratory conditions, the findings suggest that zinc oxide nanoparticles could play a significant role in future technologies designed to protect water supplies and ensure the safety of our food supply by removing these persistent agricultural chemicals.