The carbon yield showed a gradual decrease from 58.6% at 5min
to 45.3% at 30 min, due to the continuous loss of weight with the
increase of activation time. The same trend was found by Li et al.
(2008) andDenget al. (2009) in the preparation of activated carbons
from tobacco stems and cotton stalk under microwave radiation.
In most cases, the weight loss went along with the development The various free acidic groups were determined with the assumption
that NaOH neutralizes carboxyl, lactone and phenolic groups,
Na2CO3 neutralizes carboxyl and lactone groups and NaHCO3 neutralizes
carboxyl groups.