A seemingly small choice at the beginning of a materials-production process may determine how effectively a promising water-treatment catalyst works, according to an international research team involving scientists in Oman. The researchers found that the nitrogen-rich compound used to manufacture graphitic carbon nitride, or g-C₃N₄, substantially influenced the material’s structure, production yield and ability to break down pharmaceutical pollutants in water. Their findings suggest that melamine, urea and thiourea do not simply produce interchangeable versions of the same photocatalyst. Instead, each precursor creates a material with distinct physical, optical and electronic characteristics, affecting how it absorbs light, separates electrical charges and drives chemical reactions. The study could help guide the design of metal-free photocatalysts for treating contaminants that conventional wastewater systems may not completely remove.
Pharmaceutical residues such as acetaminophen, cephalexin and levofloxacin are increasingly detected as emerging contaminants in aquatic environments. These compounds can enter wastewater through human use, disposal and excretion, while many treatment facilities are not specifically designed to eliminate them completely. Even when concentrations are low, persistent pharmaceutical molecules and their biologically active transformation products may contribute to ecological stress and the spread of antimicrobial activity in the environment. Photocatalysis offers one possible solution. In this process, a semiconductor absorbs light and generates energetic electrons and positively charged holes. These charge carriers can react with water and dissolved oxygen to produce highly reactive species, including hydroxyl radicals and superoxide radicals, which attack complex organic molecules and progressively break them into smaller compounds.
For the new study, researchers from the University of Technology and Applied Sciences and Sultan Qaboos University in Oman collaborated with scientists at Hokkaido University in Japan and the University of South Africa. The team synthesized three forms of graphitic carbon nitride using melamine, urea and thiourea as starting materials. All three materials were produced under the same thermal conditions, allowing the researchers to compare the influence of the precursor rather than differences in manufacturing temperature or treatment time. Graphitic carbon nitride is a metal-free polymeric semiconductor built primarily from carbon and nitrogen. Its layered structure, chemical stability and ability to respond to light have made it an attractive candidate for environmental photocatalysis, although its performance depends strongly on how it is prepared.
The researchers examined the resulting materials using techniques designed to reveal their crystal structure, surface morphology and optical and electronic behavior. They then tested each catalyst in model water solutions containing acetaminophen, cephalexin and levofloxacin at a concentration of five milligrams per liter. The experiments were performed under a controlled artificial light source, with light-only samples serving as a comparison. This setup allowed the team to determine whether pollutant removal resulted from direct photolysis or from the additional catalytic activity of graphitic carbon nitride. The same experimental framework was used for the three materials, creating a controlled comparison of their degradation performance.
One of the clearest differences appeared in manufacturing yield. The melamine-derived material achieved a yield of 31.14%, while the urea-derived catalyst produced a yield of only 8.62%. Yield is more than an industrial accounting figure: it affects the amount of raw material required, the energy and cost associated with production, and the practicality of scaling a catalyst beyond the laboratory. A process that creates a larger quantity of active material under the same conditions may be easier to adapt for future water-treatment systems. The results therefore identify melamine as advantageous not only because of the performance of the final catalyst, but also because it generated substantially more product during synthesis.
The melamine-based graphitic carbon nitride also delivered the strongest overall photocatalytic performance against the three pharmaceuticals, whereas the thiourea-derived material showed the weakest activity. The researchers linked the difference to several interacting properties rather than to a single structural feature. The melamine-derived catalyst displayed greater structural uniformity and crystallinity, characteristics that can help electrons move through the material with fewer losses. It also showed more effective charge separation, reducing the likelihood that light-generated electrons and holes would rapidly recombine before participating in chemical reactions. In addition, its band gap appeared to provide a suitable balance between light absorption and the energetic force required to generate reactive species.
All three catalysts accelerated pharmaceutical degradation compared with the light-only control, demonstrating that the materials contributed actively to the process. When light reaches graphitic carbon nitride, electrons can be promoted from the valence band to the conduction band, leaving holes behind. If these charges remain separated long enough, they can initiate oxidation and reduction reactions at the catalyst surface. The holes may oxidize water or hydroxide ions, while conduction-band electrons can reduce oxygen dissolved in the solution. The resulting reactive oxygen species can attack aromatic rings, amide groups and other chemical structures found in pharmaceutical molecules. The exact reaction pathways are likely to involve multiple intermediate compounds rather than a single step, making it important to evaluate not only the disappearance of the original contaminant but also what happens to the products formed along the way.
To investigate that broader question, the researchers measured total organic carbon, a general indicator of the amount of carbon-based material remaining in the treated water. The observed decline in total organic carbon suggested that the treatment did more than transform the pharmaceuticals into other organic molecules that might remain biologically active. It contributed to the breakdown of the parent compounds and at least some of their degradation products into simpler substances. The team also examined residual antibacterial activity by exposing Escherichia coli to treated solutions. In samples containing cephalexin and levofloxacin, the zones that inhibited bacterial growth became smaller as treatment continued and were no longer detectable under the study’s test conditions after several hours. However, the researchers emphasized that this result does not prove the water became completely harmless. The assay measured antibacterial activity against one bacterial species and cannot replace a comprehensive toxicity assessment covering multiple organisms and chemical endpoints.
The study’s findings highlight precursor selection as a central design decision in the development of graphitic carbon nitride photocatalysts. Melamine, urea and thiourea supply nitrogen and carbon in different chemical environments, and their decomposition during heating can influence porosity, layer formation, defects, crystallinity and the distribution of electronic states within the final material. These microscopic differences can control how much light the catalyst absorbs, how efficiently charges migrate and how readily reactive species form at its surface. The work also suggests that a catalyst optimized for one pollutant may not automatically be the best choice for another, since molecular structure and reaction pathways influence degradation. For researchers seeking inexpensive and metal-free approaches to pharmaceutical removal, the results provide a practical reminder that synthesis chemistry and environmental performance are tightly connected.
The experiments were conducted in controlled laboratory solutions rather than real wastewater, which contains salts, dissolved organic matter, suspended particles and competing contaminants that can block light or consume reactive species. Before the technology could support large-scale treatment, researchers will need to identify all major degradation products, perform broader ecotoxicity tests, determine whether the catalyst remains stable after repeated use and establish how efficiently it can be recovered from treated water. Performance under natural sunlight will also be important, as artificial laboratory illumination may not reproduce the intensity and spectral composition available outdoors. Even with these limitations, the study offers a compelling path forward: by choosing the right precursor at the manufacturing stage, scientists may be able to produce a more uniform, higher-yielding and more effective photocatalyst for reducing pharmaceutical pollution in water.
Subject of Research: Not applicable
Article Title: Pharmaceuticals Acetaminophen, Cephalexin and Levofloxacin: Elimination and Toxicity Study via Carbon Nitride-Based Photocatalyst
News Publication Date: 25 July 2026
Web References: Sultan Qaboos University Journal for Science — https://squjs.squ.edu.om/squjs
References: DOI: 10.53539/2414-536X.1440
Image Credits: Faisal Almarzuqi, Sultan Qaboos University Journal for Science (2026)
Keywords
Graphitic carbon nitride, photocatalysis, pharmaceutical pollutants, water treatment, acetaminophen, cephalexin, levofloxacin, melamine, urea, thiourea, environmental science, materials science, nanomaterials
