A nanocomposite made using cyanobacterial extract broke down more crystal violet dye than a chemically synthesized version in laboratory tests. At pH 9, after 90 minutes with 0.1 g of catalyst per 50 mL, the biogenic material achieved 96.5% photodegradation, compared with 79.2% for the chemical comparator. Photodegradation means light-assisted breakdown of a pollutant.
The comparison was carried out in aqueous crystal violet solutions under ultraviolet light, not in reported samples of real wastewater. That makes the result a laboratory comparison, but it does not establish how the material would perform in a complex environmental setting or whether the resulting products would be harmless.
A biological ingredient, two different preparations
The researchers examined two nickel oxide and cobalt oxide nanocomposites. One, NiO/CoO, was made by chemical co-precipitation. The other, NiO/CoO@CM, was produced with cyanobacterial mats extract as the bioactive part of the synthesis. The study asked whether the extract-mediated route would produce different material properties and better crystal violet photodegradation.
The paper compared the materials through several forms of characterization, including surface-area measurements, ultraviolet-visible light analysis, electron microscopy, X-ray diffraction and infrared spectroscopy. X-ray photoelectron spectroscopy was also used to examine the oxidation states and surface composition of the prepared nanocomposites.
The biogenic material was reported to have a surface area of 38.97 square metres per gram, a crystallite size of 27.05 nanometres and a band-gap energy of 2.9 electronvolts, along with abundant biofunctional groups. In plain terms, the reported measurements pointed to more available surface and a smaller crystal structure, while the band gap describes the energy needed for electrons in the material to respond to light.
The gap was also seen in carbon removal
The photodegradation tests were run at room temperature with ultraviolet light at a wavelength of 365 nanometres. The vessels were kept stirring at 300 revolutions per minute, and the researchers varied pH, contact time, catalyst dose and starting dye concentration. The photocatalytic experiments were repeated three times under the same conditions, with the reported values presented as averages.
The stronger dye-colour result was accompanied by higher removal of total organic carbon, a broader measure of how much carbon-containing material remained in the solution. Within 90 minutes, removal reached 87.9% with NiO/CoO@CM and 72.6% with NiO/CoO under the same conditions.
The difference persisted, though performance fell, when the catalysts were reused. Across five successive cycles, reported degradation for the biogenic material declined from 92.8% to 75.8%. The chemically synthesized material fell from 80.5% to 65.7%.
What the measurements suggest, and what they do not
The adsorption analysis, which describes how dye molecules attach to a material’s surface, fitted the Freundlich model better than the Langmuir model for both catalysts. The reported fit values were 0.998 versus 0.83 for NiO/CoO and 0.986 versus 0.93 for NiO/CoO@CM. The Freundlich parameter Kf was also higher for the biogenic material, at 39.36 milligrams per gram compared with 14.00 milligrams per gram.
A pseudo-second-order model also fitted the results better than a pseudo-first-order model for both materials. The reported R2 values for the second-order fits were 0.982 for NiO/CoO and 0.995 for NiO/CoO@CM, compared with 0.74 and 0.61 for the first-order fits. The authors interpreted that pattern as evidence of chemisorption, meaning adsorption involving chemical interactions at the surface, although a model fit describes the pattern in these experiments rather than proving how the process would behave elsewhere.
The authors link the biogenic catalyst’s stronger reported performance to its larger surface area, smaller crystallites, biofunctional groups, improved separation of light-generated charges and the formation of reactive oxygen species. Those explanations are the authors’ interpretation of the laboratory findings. The supplied analysis does not establish a causal advantage beyond the tested conditions, because the two materials were made by different synthesis procedures.
The practical questions remain open
The study does not show complete breakdown of crystal violet: decolorization was higher than total organic carbon removal. It also does not identify all transformation products or show that the process is safe, free of harmful by-products, effective in real wastewater or protective of aquatic ecosystems. The experiments used prepared aqueous dye solutions, and the supplied analysis reports no complete mass balance.
Because the reported photocatalytic data were averages of three repeated experiments under the same conditions, they describe performance in that test setup. The supplied analysis does not report confidence intervals, standard deviations or formal statistical tests comparing the two materials. The data are stated to be included in the article and available from the corresponding author on request.
The article records receipt on 17 May 2026 and acceptance on 11 August 2026. Its disclosure says that open-access funding was provided by STDF in cooperation with EKB, while also stating that no funding was received, a distinction the supplied analysis says is not clarified. The authors declare no competing interests.
Paper data and sources
Original title: Cyanobacterial extract mediated biogenic synthesis of NiO/CoO nanocomposites for enhanced photodegradation of crystal violet dye.
Authors: Mohamed H H Ali, Mohamad S Abdelkarim, Soaad A Sabae
Journal/Repository: Scientific reports
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1038/s41598-026-66973-5
Original paper · Full text