Investigation of antimicrobial effects of quince (Cydonia oblonga) and blackberry (Rubus fruticosus) extracts on bacteria applied graphitic carbon nitride (g-C₃N₄)

Nanomaterials have gained increasing attention in recent years due to their potential to provide innovative and effective solutions against the growing problem of bacterial resistance. Understanding the relationship between structural features and biological response is critical both for the design of new materials and for improving current applications. In this study, g-C₃N₄ was synthesized under controlled conditions through thermal and chemical layer separation methods, and the resulting nanoparticles were characterized using by FT-IR, SEM, BET, and Zeta potential analyses. FT-IR results revealed that the characteristic vibrations in the 1200–1600 cm⁻¹ region were more pronounced in the bulk g-C₃N₄ nanoparticles, while the broad band around 2400 cm⁻¹ indicated a weakening of structural order after layer separation processes. SEM images demonstrated that bulk g-C₃N₄ exhibited a heterogeneous surface morphology; thermal layer separation increased porosity, chemical layer separation produced a rough yet more homogeneous morphology, and thermally–chemically combined layer separation markedly improved surface organization. BET analyses showed that thermally treated g-C₃N₄ nanoparticles possessed higher surface area and pore volume, whereas bulk and chemically separated g-C₃N₄ nanoparticles exhibited more limited adsorption capacities. Zeta potential measurements indicated that bulk, thermally separated, and chemically separated nanoparticles displayed stable dispersion behavior at approximately −15 mV, while thermally–chemically combined layer separation resulted in lower stability, with a zeta potential of −10.3 mV. Additionally, extracts prepared from quince and blackberry leaves were evaluated for their bioactive potential. Phenolic profiling revealed high phenolic contents, reaching 1916,37 and 1746 mg GAE/g, respectively, while DPPH and CUPRAC assays demonstrated strong antioxidant capacities, and HPLC analysis confirmed broad phenolic diversity. In another stage of the study, g-C₃N₄ and its layer separation derivatives, alone or in combination with the plant extracts, were tested at concentrations ranging from 32 to 0,0625 mg/mL. The thermally–chemically layer separation g-C₃N₄ sample exhibited activity at 32 mg/mL particularly against Gram-positive bacteria. The plant extracts themselves showed stronger antibacterial activity at 2–8 mg/mL, although certain combined treatments resulted in antagonistic increases in optical density. Overall, the structural order, surface properties, and colloidal behavior of the g-C₃N₄ derivatives were found to be closely associated with their biological performance, while the plant extracts exhibited notable therapeutic potential due to their rich phenolic content and strong antioxidant capacity. The findings indicate that the structural features of g-C₃N₄ and its exfoliated forms directly influence antibacterial behavior, and that nanoparticles with improved surface area and morphology demonstrate greater efficacy against Gram-positive species. Quince and blackberry extracts offer significant biological potential through their high phenolic richness, and although certain combinations displayed antagonistic effects, the material–extract compatibility can be enhanced under appropriate conditions. This work provides a scientific basis for advancing g-C₃N₄-based nanostructures for biological applications and for designing new antimicrobial approaches supported by plant-derived natural compounds.