Nanoparticles of CuO, Cu2O and Cu were synthesized using urea, citric acid and hexamethylenetetramine through the solution combustion method. The effect of fuel type and fuel to oxidizer ratio (F/O) was studied on the composition, size, morphology, and antibacterial behavior of the products to investigate their correlation. The synthesized nanoparticles were characterized by X-ray diffraction analysis, dynamic light scattering, field emission scanning electron microscopy, and antibacterial testing via the broth dilution method. Thermodynamic calculations revealed that the adiabatic temperature of the synthesis systems decreases as the F/O ratio increases beyond a certain threshold. This reduction in temperature slows the reaction rate, promoting re-oxidation of the products during synthesis. The results demonstrated that citric acid provided the most reductive conditions allowing for the formation of Cu2O at lower F/O ratios. Additionally, products in this system were finer (~ 30 nm) and more porous. A detailed correlation is discussed between compositional and morphological characteristics and synthesis parameters including fuel type, F/O ratio, adiabatic temperature, and the volume of combustion gas produced. Moreover, antibacterial behavior of the products was evaluated against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains. Findings indicated that the samples with the highest Cu2O content, obtained at specific F/O ratios, exhibited the most effective growth inhibition against both bacterial strains, with a particularly strong effect against Gram-negative strain (e.g., E. coli). The minimum inhibitory concentrations of Cu2O were 40.9 and 96.5 μg/mL for E. coli and S. aureus, respectively. Although the influence of the fuel type was not found to be significant on the inhibitory behavior, the products of the citric acid system showed evidences of superior inhibition against S. aureus.

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