Plant extracts peel MoS2 into few-layer nanosheets in a greener route

Molybdenum disulfide has become one of the most closely watched two-dimensional materials in modern nanoscience. As a transition metal dichalcogenide, it stacks molybdenum atoms between pairs of sulfur atoms in layers held together only by weak van der Waals forces, and its optical, electrical, and catalytic properties change dramatically with layer number. That layer dependence underpins applications from flexible electronics and energy storage to biosensing and photocatalysis. Yet the standard ways of making few-layer MoS2 often depend on harsh solvents, high energy input, and hazardous precursors, raising health and ecological concerns that have grown alongside the material’s popularity.

A new study from the School of Electronics Engineering at Vellore Institute of Technology in Tamil Nadu, India, published in Frontiers in Nanotechnology, offers an alternative. Hariprasad Ramachandran and Sharmila Nageswaran exfoliated bulk MoS2 using aqueous extracts of three medicinal plants: Cissus quadrangularis, Ocimum sanctum, and Lawsonia inermis. The work, conducted under mild ambient conditions, demonstrates that common phytochemicals can do the job of aggressive chemical exfoliating agents while leaving the crystalline structure of the material intact.

The choice of plants was deliberate. Cissus quadrangularis, a succulent creeper, contains flavonoids, phenolic acids, tannins, saponins, and glycosides. Ocimum sanctum, holy basil, is rich in flavonoids, terpenoids, and phenolic acids. Lawsonia inermis, henna, carries lawsone, a redox-active naphthoquinone, alongside tannins and alkaloids. In the proposed mechanism, flavonoids and phenolic acids weaken the interlayer van der Waals forces during sonication, promoting delamination, while saponins, glycosides, tannins, and alkaloids adsorb onto the newly exposed flake surfaces, acting as natural capping agents that prevent restacking and maintain colloidal stability.

The procedure itself was straightforward. Fresh plant material was boiled in distilled water for thirty minutes, filtered, and stored cold. Bulk MoS2 powder was then dispersed in each extract and bath sonicated for twelve hours at room temperature, followed by centrifugation, washing, and vacuum drying. A control sample was prepared identically in N-methyl-2-pyrrolidone, the solvent most commonly used for liquid phase exfoliation of layered materials because its surface energy matches that of MoS2. Every sample was authenticated botanically by the Botanical Survey of India, and the extract compositions were cross-verified against the IMPPAT phytochemical database.

X-ray diffraction confirmed the hexagonal 2H phase in all samples, with characteristic reflections indexed near 14.3, 33.5, 39.5, 49.8, and 58.5 degrees two-theta. The solvent-exfoliated control showed sharp, well-defined peaks indicating good crystallinity. The plant-mediated samples preserved the same phase but displayed peak broadening and reduced intensity, consistent with smaller crystallite size, lattice strain, or residual organic moieties on the surface. Ocimum sanctum produced the most crystalline plant-mediated product, while the henna-derived sample showed semi-crystalline character, suggesting that the phytochemical profile of each extract leaves a distinct fingerprint on the growing or exfoliating crystals.

Raman spectroscopy provided the clearest evidence of exfoliation. The separation between the in-plane E1 2g mode and the out-of-plane A1g mode is a well-established indicator of layer number in MoS2. Bulk material showed a separation of 28 per centimeter, and the plant-mediated samples from Cissus quadrangularis and Ocimum sanctum both showed 27 per centimeter, with redshifts in the mode positions indicating weaker interlayer interactions and thinner flakes. The authors compared their result with a previous study that used the same creeper plant and reported a smaller separation of 24.6 per centimeter, pointing to sonication duration, extract concentration, and exfoliation medium as parameters that could push the present process toward even thinner products.

Ultraviolet-visible spectroscopy showed that all processed samples retained the A and B excitonic absorption features of layered MoS2, confirming that the electronic structure survives processing. The creeper-derived sample showed the smallest exciton shift from bulk, suggesting it perturbs the native electronic structure least, while the solvent control showed the largest. Scanning electron microscopy revealed striking morphological differences: the holy basil sample formed loosely interconnected thin sheets, the henna sample produced fragmented, crumpled flakes with smaller lateral dimensions, and the creeper sample assembled into rose-like, flower-shaped clusters with curled edges that could enhance electrochemical performance through increased edge sites. Energy-dispersive X-ray spectroscopy confirmed molybdenum and sulfur in every sample, along with carbon and oxygen signatures from residual surface-bound phytochemicals.

Dynamic light scattering quantified the dispersion quality. The henna-derived sample showed the smallest hydrodynamic diameter, roughly 2.4 micrometers, while the holy basil sample showed the narrowest polydispersity index at 0.245. All samples fell below 0.4, indicating acceptable colloidal stability. Electrical measurements using a four-point probe revealed semiconducting behavior throughout, but with an important trade-off: the solvent-exfoliated control showed the lowest sheet resistance at 5.5 kiloohms per square, outperforming all plant-mediated samples, which ranged from 6.0 to 6.5 kiloohms per square. The authors attribute this to insulating organic residues at inter-flake junctions, a pattern consistent with the infrared evidence of hydroxyl and amine groups bound to the creeper-derived surfaces.

The study is candid about its limitations. All measurements represent single determinations per sample, and the authors note that batch-to-batch variability in phytochemical concentration is a genuine scale-up challenge that would require standardization of extract potency, for instance through quantification of total phenolic content before use. Zeta potential measurements, triplicate batch preparation, and transmission electron microscopy-based layer counting are identified as priorities for future validation. Direct cytotoxicity and biocompatibility testing would also be needed before any biomedical application.

Even so, the work demonstrates that three common medicinal plants can serve as tunable, multifunctional agents in the exfoliation of one of the most important two-dimensional materials, replacing toxic solvents with water and ambient conditions. The trade-off between colloidal stability and electrical conductivity is now clearly mapped, giving future researchers a rational basis for optimizing plant-mediated MoS2 toward flexible electronics, catalysis, and sensing applications where sustainability matters as much as performance.

Subject of Research: Nanotechnology

Article Title: Plant extract mediated liquid phase exfoliation of MoS2: a sustainable approach to micro and nanostructured material preparation

Article References: Ramachandran, H., & Nageswaran, S. (2026). Plant extract mediated liquid phase exfoliation of MoS2: a sustainable approach to micro and nanostructured material preparation. Frontiers in Nanotechnology, 8, Article 1906127. https://doi.org/10.3389/fnano.2026.1906127

Image Credits: AI Generated

DOI: 10.3389/fnano.2026.1906127

Keywords: MoS2, green synthesis, liquid phase exfoliation, two-dimensional materials, nanotechnology, sustainable materials, Plant, extract, mediated, liquid, phase, exfoliation