Carbon-based nanomaterials today see wide use, from electronics and energy to environmental protection and medicine, yet we still do not know enough about what happens to them once they end up in nature. When they enter water, they encounter salts and natural substances such as plant residues and proteins, and these encounters determine whether the particles remain evenly distributed or aggregate into clusters, whether they float or sink, and how long they persist in the system. Carbon dots and nanodiamonds are related carbon nanomaterials, yet they behave differently in aquatic environments.
The team’s research brings new understanding of interactions between carbon-based nanomaterials, primarily nanodiamonds, and proteins, organic matter, and fulvic acid, which is a type of natural acid formed by the breakdown of plant material.
“Understanding these interactions is important not only for assessing the environmental risks associated with nanomaterials, but also for their sustainable development and for establishing safety regulations for their use, so that in the future we can devise solutions that are more effective and environmentally friendly,” explains Assoc. Prof. Željka Fiket, PhD, head of the Laboratory for Inorganic Environmental Geochemistry and Nanoparticle Chemodynamics at the IRB Division for Marine and Environmental Research, and a corresponding author of the paper.
What the laboratory experiments looked like
To explore what happens to these tiny carbon particles when they leave the laboratory and enter natural waters, the scientists recreated river and estuary-like conditions in the lab.
They compared fresh and saline water, varied the pH, and added components that particles truly encounter in nature, such as different proteins, a sugar-like polymer, and natural organic matter from decomposed plants. They then watched for two simple signs. They observed whether the particles stayed small and separate or aggregated into clusters. At the same time, they monitored whether the mild electrostatic effect that keeps them apart weakened or persisted.
What the team observed
The result is clear. Carbon dots are more prone to mutual aggregation and cluster formation, especially in saltier conditions or when natural substances from decomposed plants and proteins bind to them. This means they will settle faster, remain dispersed for a shorter time, and behave differently from nanodiamonds.
What this means for new material development and environmental protection
If you are designing a drug-delivery system, you need particles that will not aggregate before reaching their target. If you are remediating a polluted site, you want particles that will remain dispersed long enough to have the desired effect, then behave predictably. If you are drafting safe-use rules, you must know whether the particles will remain in the water column, sink to the riverbed, or bind to natural substances. This research offers a clear guide for all these situations, helping society assess risks, encourage greener applications, and set reasonable limits.
“In this study we showed that nanodiamonds stand out as robust and adaptable, especially when associated with appropriate natural ‘coatings’, while carbon dots require additional attention and engineering solutions to prevent their aggregation in waters,” explains Maja Dutour Sikirić, PhD, head of the Laboratory for Biocolloids and Surface Chemistry and a corresponding author of the paper.
Alongside Dr. Fiket and Dr. Dutour Sikirić, the team conducting this research includes master’s student Darija Gal from the Faculty of Science, University of Zagreb, PhD candidate Marija Petrović from IRB, Vida Strasser, PhD, from IRB, Assoc. Prof. Veronika Kovač, PhD, from the Faculty of Food Technology and Biotechnology, University of Zagreb, Sanja Frka, PhD, from IRB, Neda Vdović, PhD, from IRB, and Binoy Saikia, PhD, a scientist at the CSIR-North East Institute of Science and Technology (CSIR-NEIST), Jorhat, India.
Journal recognition and cover feature
The full paper, “Stability of nanodiamonds and carbon dots in aqueous environments, insights into aggregation behavior and additive influence,” was published in Environmental Science: Nano, a Royal Society of Chemistry journal, and was included in the Recent HOT Articles collection, with an illustration featured on the cover of the August 2025 issue.
