The study took a deliberately straightforward route for converting a woodworking residue into a functional treatment material. Sawdust was washed, dried at 120 °C and carbonized at 300, 500 or 700 °C. A second series was prepared from sawdust carbonized at 500 °C and combined with ferrocene at nominal loadings ranging from 0.05 to 250 weight percent. The mixtures were dried and calcined, during which ferrocene decomposed and formed iron-containing phases associated with the carbon matrix. This route avoided the lignin isolation, chemical activation and elaborate pore engineering employed in some other biomass-to-carbon processes, although pyrolysis still required thermal energy and the resulting materials had comparatively low measured surface areas.

The optimum formulation differed between the two pollutants, showing that one loading cannot be assumed to optimize every contaminant. S6, the composite containing 25 weight percent ferrocene, produced the steepest pseudo-first-order decline for Brilliant Blue and was associated with an apparent rate constant of 0.022 per minute, nearly an order of magnitude higher than the unmodified carbon control. For amoxicillin, the apparent rate constants were lower and occupied a narrower range of 0.010–0.023 per minute. S4, containing 0.05 weight percent ferrocene, gave the strongest reported antibiotic performance. The authors associated the decline at excessive ferrocene loading with aggregation, light shielding and reduced access to active sites, helping explain why the material with the greatest precursor loading was not the most effective catalyst.

Infrared spectroscopy and X-ray diffraction helped connect those performance differences to changes in the material. Raising the carbonization temperature from 300 to 700 °C weakened hydroxyl and aliphatic carbon-hydrogen bands, increased the relative contribution of aromatic structures and progressively ordered the carbon. The 300 °C material had a broad diffraction halo near 2θ of 23 degrees, characteristic of poorly organized turbostratic carbon, while the 500 and 700 °C samples showed clearer graphitic reflections. Quantitative analysis indicated that carbon crystallite size increased from 0.85 nanometres at 300 °C to 1.40 nanometres at 500 °C and 1.94 nanometres at 700 °C, accompanied by lower calculated lattice strain and dislocation density.

Ferrocene introduced a separate evolution in the diffraction patterns. Weak, broad iron-related reflections at low loadings became sharper as the loading increased, consistent with larger and more crystalline iron-containing nanophases. At the highest loading, the iron-rich phase dominated the pattern and the reported crystallite size reached 33.4 nanometres, with much lower strain and dislocation density than in the unmodified carbon. The authors interpret these changes as evidence that iron species generated during ferrocene decomposition can catalyze rearrangement of disordered carbon into larger graphitic domains. The exact iron compound was not assigned conclusively without comparison to reference diffraction cards, leaving iron oxides, carbides or related phases as alternatives.

Scanning electron microscopy showed that the carbon matrix remained rough and heterogeneous after functionalization, with irregular particles, cavities, fractures and localized accumulations. At low ferrocene loading, fine particles were dispersed across the rough surface and within structural imperfections. As the concentration increased, deposits became more localized and aggregated, obscuring much of the original fibrous sawdust structure. At the highest loading, the surface was dominated by densely connected fine particles measuring roughly 111–220 nanometres. The micrographs therefore indicated that ferrocene-derived material was attached unevenly rather than forming a smooth, uniform coating, although contrast in the images alone could not conclusively identify each feature as ferrocene-derived phase.

Despite the researchers’ use of “activated carbon” terminology in parts of the description, the composites were not high-surface-area porous carbons in the conventional sense. Nitrogen adsorption measurements produced small specific surface areas, including reported values of 0.52056 square metres per gram for one 300 °C sample and 0.08987 square metres per gram for another carbonized material. Their performance therefore cannot be attributed to a highly developed network of accessible micropores. Instead, the study points to a combination of adsorption at the rough carbon surface and photochemical processes involving iron-containing centers. The carbon matrix can concentrate pollutant molecules near reactive sites, while iron phases may support light harvesting, redox cycling and interfacial charge transfer.

The proposed mechanism begins with photon absorption and the generation of electron-hole pairs in the composite. The authors suggest that charge carriers can move toward the surface, where adsorbed water and oxygen may participate in reactions that generate reactive oxygen species. Those species could then attack adsorbed contaminants and produce smaller intermediates. The carbonaceous component is proposed to increase adsorption and interfacial contact, while the iron-containing phase contributes photoactivity and electron transfer. This pathway is a mechanistically reasonable interpretation, not a conclusively demonstrated mechanism: the researchers did not conduct radical-scavenging tests or directly detect individual reactive oxygen species, so they could not determine the precise contributions of hydroxyl radicals, superoxide radicals or other intermediates.

Pollutant removal was quantified from changes in ultraviolet-visible absorbance. The Brilliant Blue band near 550–560 nanometres was used to track destruction of the dye chromophore, while amoxicillin bands in the near-ultraviolet were followed as indicators of structural alteration. A decline in these bands does not by itself establish complete conversion to carbon dioxide, water and inorganic products, because low-molecular-weight or soluble intermediates can remain. The reported percentages should therefore be understood as light-assisted degradation or color loss in model solutions, not as proof of full mineralization. The binary amoxicillin–Brilliant Blue tests also showed simultaneous attenuation of characteristic bands, but the experiment did not identify all reaction products or determine whether their toxicity was reduced.

Reuse tests showed operational stability over five consecutive cycles. The S6 composite’s Brilliant Blue removal fell gradually from about 99% in the first cycle to approximately 92% in the fifth. The S4 material’s amoxicillin removal declined from around 95% to about 87% over the same sequence. The authors attributed the small losses to possible catalyst loss during recovery and washing and to residual pollutants or intermediates blocking some active sites. The experiment supports repeated use of the composites under the tested conditions, but it does not establish long-term durability, chemical leaching behavior or performance after extended operation.

Overall, the work presents a comparatively low-process-complexity route for turning sawdust into visible-light-responsive carbon composites, with the best ferrocene loading depending on whether the target is Brilliant Blue or amoxicillin. Its strongest contribution is the combination of direct biomass carbonization, ferrocene functionalization and photocatalytic testing at room temperature under visible or simulated solar illumination. The materials remained far from performance-maximized porous carbons, and the experiments used synthetic water, model pollutant concentrations, controlled stirring and small laboratory volumes. The study therefore establishes proof-of-concept removal in laboratory model solutions rather than a ready-made wastewater treatment system, and its results do not resolve performance in real matrices containing competing dissolved substances, catalyst recovery, iron release, pollutant by-products or the energy and economic demands of scale-up.

Subject of Research: Laboratory development of ferrocene-functionalized sawdust carbon photocatalysts for dye and antibiotic removal from model water

Article Title: Eco-friendly valorization of agricultural sawdust waste for efficient elimination of dye and antibiotic contaminants from aquatic environments

Article References: Fouda, S. R., Alnasser, A. S., Radwan, M., & Abbas, M. M. M. (2026). Eco-friendly valorization of agricultural sawdust waste for efficient elimination of dye and antibiotic contaminants from aquatic environments. Scientific Reports, 16(1), Article 33012. https://doi.org/10.1038/s41598-026-71775-w

Image Credits: AI Generated

DOI: 10.1038/s41598-026-71775-w

Keywords: sawdust valorization, ferrocene carbon composite, photocatalytic water treatment, amoxicillin degradation, Brilliant Blue R-250, biomass carbon, visible-light catalysis, iron-containing phases, waste reuse, model-water testing, Eco-friendly, valorization