Rapid Solvent‐Free Microwave‐Assisted Synthesis of 2D Nitrogen‐Doped Carbon Nanosheets: Optical, Cytotoxic, Antioxidant, and Anti‐Inflammatory Studies

ABSTRACT Developing sustainable, metal‐free fluorescent nanomaterials with controlled structure and multifunctional biological activity remains an important challenge for bioimaging and biomedical applications. In this context, a solvent‐free, one‐pot microwave‐assisted approach is presented for the synthesis of two‐dimensional (2D) nitrogen‐doped carbon nanosheets (N‐CNS) using citric acid and polyvinylpyrrolidone as carbon and nitrogen precursors. The synthesized N‐CNS exhibit a crumpled, few‐layered nanosheet morphology with an average lateral size of ∼98 nm and thickness in the range of 3–12 nm, as confirmed by TEM, FE‐SEM, and AFM analyses. Combined structural and compositional characterization using XRD, SAED, Raman, FTIR, XPS, and EDX spectroscopy confirms the formation of turbostratic, defect‐rich graphitic nanosheets, evidenced by characteristic (002) and (100) reflections, D (1365 cm − 1 ), G (1519 cm − 1 ), and 2D (2775 cm − 1 ) Raman bands with an I D /I G ratio of 1.17, the presence of oxygen‐ and nitrogen‐containing surface functional groups, and a nitrogen content of ∼9.9 at%. Nitrogen adsorption–desorption measurements reveal a specific surface area of 564.16 m 2 g − 1 with mesoporosity centered at ∼3.4 nm. Optical studies show blue photoluminescence with excitation‐dependent emission behavior and a quantum yield of ∼32%. Time‐resolved fluorescence measurements reveal biexponential decay with lifetimes of ∼2.96 and 8.88 ns, indicating contributions from defect‐related and graphitic‐domain‐mediated emissive states. In vitro cytotoxicity evaluation using MDA‐MB‐231 cells shows cell viability exceeding 90% up to a concentration of 2.5 mg mL − 1 . The N‐CNS further demonstrates antioxidant activity with an EC 50 of 19.54 µg mL − 1 and anti‐inflammatory activity with an EC 50 of 132.72 µg mL − 1 . These results indicate that the synthesized N‐CNS possess structural, optical, and biological characteristics relevant to fluorescence‐based bioimaging and related biomedical applications.