2.3. Pretreatment of substrate
2.3.1. Chemical treatment of substrate
The selected substrate (50 g) were soaked in different concentration
of 2.5%KOH, 2%H2SO4, or 3%H2O2 solution at the
ratio of 1:10 (solid: liquid) for 2 h at room temperature as
described previously (Irfan et al., 2011). After that the samples
were heated at 127 C for 60 min at 20 lb psi. Then samples
were filtered and solid residues were washed up to neutrality