Oyster and Pyramidella Shells as Heterogeneous Catalysts for the Microwave-Assisted Biodiesel Production from Jatropha curcas Oil

Figure 5

SEM images of (a) natural oyster shell, (b) calcined oyster shell, (c) natural Pyramidella shell, and (d) calcined Pyramidella shell.

(a)

(b)

(c)

(d)