While biochar is so beneficial to remediate organic contaminants,
it is important to examine how it works. Based on many published
research reports, the mechanism of organic pollutants removal can
be mainly summarized as surface adsorption and partition. Adsorption
refers to the surface interactions leading to adhesion of pollutant
molecules to biochar surfaces, whereas sorption includes both surface
adsorption as well as partition of pollutant molecules in the
micropores of biochar (without differentiating the two processes) as
shown in Fig. 2. Sorption was in relation to surface properties, for
example, surface area and pore size distribution (54). Many sorption
isotherms and sorption kinetics based on batch experiments indicated
that the sorption of organic pollutants to biochar made at the
low temperature mainly due to partition and at high-temperature
surface adsorption because partition occurs in the uncarbonized
fraction and the surface adsorption in carbonized fraction. Chen et al.
(40) studied the sorption mechanism of biochar made from pine
needle at 100e700C and found a transitional mechanism that from
partition-dominant at low pyrolytic temperatures to adsorptiondominant
at higher pyrolysis temperatures.