XRD was used to qualitatively characterize the metals species in
the biosurfactant. Fig. 6B shows the XRD profile of the biosurfactant
from Bacillus sp. USTBa. The XRD pattern indicates that the
maximum peak intensities are at ca. 22, 24 and 30, corresponding
to the Miller indices of 113, 100, and 110, respectively. The XRD
data confirms that the biosurfactant has unique crystallinity and is
mainly composed of face-centered cubic structure of carbon, sodium,
and sulfur structure. The results obtained were in agreement
with those obtained in our previous study [18]. To best of our
knowledge, this is the first XRD study for the biosurfactant obtained
from Bacillus sp. isolated from petroleum reservoir. Further,
TG and DSC analysis were carried out to study the crystalline domain
of the biosurfactant that improves the performance over
the wide range of temperature.