Figure 2.

FTIR spectra of nanoparticles obtained by the microemulsion process with different water to surfactin ratios (W/S; 250, 500, 1000 and 40,000): without calcination (a) 4000–400 cm⁻¹, (b) 1300–400 cm⁻¹; with calcination at 800 °C (c) 4000–400 cm⁻¹, (d) 1300–400 cm⁻¹.