The longan seed activated carbon (LSAC) was prepared
according to the following procedure. The raw longan seed was
crushed and sieved to obtain desired particle size of 100 mesh,
which were dried in an oven at 100 8C for 10 h to remove the
absorbed water on the surface and then stored in silica gel
desiccators before use. The dried longan seed was subjected to
carbonization in N2 atmosphere at 300–450 8C for 1.5 h. The
carbon so formed was cooled to room temperature and crushed.
The carbonized material was mixed with sodium hydroxide
(NaOH) in a 1: (1–4) (w/w) ratio. The mixture was then activated
in N2 atmosphere at 600–800 8C for 0.5–1.5 h. The longan seed
activated carbon was cooled to room temperature and washed
with distilled water until its pH reached 7.0. The product (LSAC)
was then dried in a hot air oven at 80 8C for 24 h. The dried LSAC
was thereafter ground and sieved through a 100 mesh screen, and
stored in desiccators for use in adsorption studies. LSAC was
characterized by scanning electron microscopy (SEM) to investigate
the nature and surface characteristics. The BET surface area,
pore volumes, pore size distribution, micropore surface area and
average pore diameter (APD) of LSAC were also measured by the N2
adsorption at 77 K with surface area and pore size analyzer.
An orthogonal experimental design L9(34) was used in the
preparation of LSAC experiment as presented in Table 1, and four
influencing factors of carbonized material/NaOH ratio, activation
time, activation temperature and carbonization temperature were
chosen, and three levels were set for each factor. The equilibrium
adsorption capacity of Cr(VI) on LSAC were set as the investigation
target, to qualitatively analyze effects of the selected factors on the
preparation of LSAC.