Bottom-up assembly of graphene-decorated d-MXene nanoarchitecture for enhanced antibacterial activity against Escherichia coli and Bacillus cereus

A bottom-up ultrasonication-assisted strategy was employed for the assembly of graphene-decorated d-MXene nanoarchitectures, and their antibacterial activity against Escherichia coli and Bacillus cereus was systematically investigated. The formation of the nanoarchitecture was confirmed through complementary morphological, structural, spectroscopic, and surface charge analyses. Scanning electron microscopy, elemental mapping, and high-resolution transmission electron microscopy observations revealed the uniform decoration of graphene nanosheets over layered d-MXene sheets, resulting in a structurally open architecture with suppressed nanosheet restacking. Powder X-ray diffraction (PXRD) analysis exhibited peak broadening, intensity variation, and modification of the low-angle (002) reflection, while comparative PXRD analysis with a composition-matched physical mixture further demonstrated disruption of the d-MXene stacking order following ultrasonication-assisted assembly. Raman spectroscopy exhibited the coexistence of graphene D (1339 cm −1 ) and G (1581 cm −1 ) bands together with the characteristic d-MXene vibrational mode at 153 cm −1 confirming preservation of defect-associated graphene domains within the assembled nanoarchitecture. Comparative Raman analysis further revealed systematic shifts in the characteristic graphene and d-MXene bands and a decrease in the I D / I G ratio from 1.83 for the physical mixture to 1.27 for the nanoarchitecture, supporting intimate interfacial organization. X-ray photoelectron spectroscopy analysis revealed the coexistence of sp 2 C=C (284.1 eV), sp 3 C–C (284.7 eV), Ti–C (282.5 eV), and Ti–O (530.5 eV) bonding states, suggesting effective interfacial coupling and defect enriched surface regions after nanoarchitecture formation. Zeta potential analysis demonstrated enhanced colloidal stability of the graphene-decorated d-MXene nanoarchitecture with a highly negative surface charge value of −84.04 mV compared to graphene nanosheets (−54.7 mV) and d-MXene (−44.98 mV), indicating enhanced electrostatic stabilization and improved dispersion stability after nanoarchitecture formation. Dynamic light scattering analysis additionally revealed a reduction in average hydrodynamic size from 1658 nm for pristine d-MXene to 1211 nm after graphene incorporation, confirming suppression of nanosheets agglomeration within the assembled nanoarchitecture. The antibacterial activity was evaluated using colony-forming unit (CFU) and OD 600 growth assays. The graphene-decorated d-MXene nanoarchitectures exhibited concentration-dependent antibacterial activity, reducing bacterial viability from 4.00 × 10 5 /4.20 × 10 5 to 1.80 × 10 4 /2.10 × 10 4 CFU/mL after 24 h at 500 µg/mL. Similarly, bacterial growth was significantly suppressed, with OD 600 decreasing from 2.54/2.80 for untreated E. coli / B. cereus to 0.54/0.59 after treatment. Compared to a recent report (Ag/Ti 3 CNT x ), the present system shows ≈39% relative reduction in E. coli viability without requiring silver doping. The enhanced activity is attributed to the cooperative contribution of improved nanosheet accessibility, membrane contact probability, exposed active interfacial domains, and a possible additional ROS-mediated pathway.