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biosorption process is a rather complex process. The understanding of the mechanism for the binding of metal to biomass involves identifying the functional groups
present in the biomass.
Cell wall of the biomass or waste fruit cortex contains the necessary functional
groups that are involved in heavy metal binding. The structure of plant cell wall is
built by cellulose molecules that are arranged in microfibrils which are enclosed by
hemicellulosic materials: xylans, mannans, glucomannas, galactans, arabinogalactans, lignin, pectin, and protein (Al-Asheh and Duvnjak 1997; Demirbas 2008;
Nobel 2009). Cellulose that are mostly located in secondary cell wall behaves
according to the degree of crystallinity, specific surface area, and degree of polymerization of the fibers (Lee et al. 1983).
The cellulose molecules are bundled together and are usually found in the form
of microfibrils with crystalline and amorphous regions. The crystalline regions are
more orderly while the amorphous regions are less ordered. The proportion of these
two regions in cellulose varies on the type of sample (Demirbas 2008).
Due to the structure of plant cell wall, water permeates into the amorphous
regions, hemicellulose, and lignin. The absorption of the water by plant cell wall is
carried along the heavy metals bringing into contact with the functional groups
present in the cortexes (Acemioglu and Alma 2001). The structure of the cell wall
of plants plays an important factor in fruit cortexes in the adsorption of heavy metals. The structure of cellulose and pectin is shown in Fig. 13.4.
The polysaccharide-rich cell walls are mainly composed of cellulose and pectin
compounds such as galacturonic acid polymers (Fry 2004). When these pectin-like
compounds are ionized through alkaline treatment, negative charges are generated
which binds metallic cations.
Pectin is an important element from waste fruit cortexes that is involved in the
removal of heavy metals. A study was done to determine the role of pectin in biosorption by comparing the adsorption capacity of orange peels, depectinated orange
peels, and pectic acid. Similar to cellulose, the two main functional groups that are
responsible in the metal biding are the carboxyl and hydroxyl groups. The metabinding ability of pectic acid was found to be the highest mean, while depectinated
peels showed the lowest (Schiewer and Patil 2008).
Kiwi and tangerine peels were found to contain lesser amounts of starch, cellulose (Abdul Khalil et al. 2006), and pectin-type compounds (Yapo et al. 2007) compared to banana cortex. The differences in the cortexes of banana and citrus were
apparent in the biosorption capacity of Cd and Cr. The higher amount of starch and
cellulose in banana cortex helps in the binding of Cr and Cd compared to other metals (Al-Qahtani 2016).
The adsorption mechanism of heavy metals on the fruit cortexes is due to the
presence of the carboxyl and hydroxyl groups on the pores’ surfaces. The functional groups coordinate with metal ions to form metal complexes (Abdul Khalil
et al. 2006). The role of the carboxyl and hydroxyl groups is depicted in Fig. 13.5.
Alkalinization process creates active sites when it reacts with the cellulose- and
pectin-like compounds in the fruit cortexes. The active sites will be negatively
charged, hence accepting the metallic ions in the solution. The adsorption
S. Ganesan
biosorption process is a rather complex process. The understanding of the mechanism for the binding of metal to biomass involves identifying the functional groups
present in the biomass.
Cell wall of the biomass or waste fruit cortex contains the necessary functional
groups that are involved in heavy metal binding. The structure of plant cell wall is
built by cellulose molecules that are arranged in microfibrils which are enclosed by
hemicellulosic materials: xylans, mannans, glucomannas, galactans, arabinogalactans, lignin, pectin, and protein (Al-Asheh and Duvnjak 1997; Demirbas 2008;
Nobel 2009). Cellulose that are mostly located in secondary cell wall behaves
according to the degree of crystallinity, specific surface area, and degree of polymerization of the fibers (Lee et al. 1983).
The cellulose molecules are bundled together and are usually found in the form
of microfibrils with crystalline and amorphous regions. The crystalline regions are
more orderly while the amorphous regions are less ordered. The proportion of these
two regions in cellulose varies on the type of sample (Demirbas 2008).
Due to the structure of plant cell wall, water permeates into the amorphous
regions, hemicellulose, and lignin. The absorption of the water by plant cell wall is
carried along the heavy metals bringing into contact with the functional groups
present in the cortexes (Acemioglu and Alma 2001). The structure of the cell wall
of plants plays an important factor in fruit cortexes in the adsorption of heavy metals. The structure of cellulose and pectin is shown in Fig. 13.4.
The polysaccharide-rich cell walls are mainly composed of cellulose and pectin
compounds such as galacturonic acid polymers (Fry 2004). When these pectin-like
compounds are ionized through alkaline treatment, negative charges are generated
which binds metallic cations.
Pectin is an important element from waste fruit cortexes that is involved in the
removal of heavy metals. A study was done to determine the role of pectin in biosorption by comparing the adsorption capacity of orange peels, depectinated orange
peels, and pectic acid. Similar to cellulose, the two main functional groups that are
responsible in the metal biding are the carboxyl and hydroxyl groups. The metabinding ability of pectic acid was found to be the highest mean, while depectinated
peels showed the lowest (Schiewer and Patil 2008).
Kiwi and tangerine peels were found to contain lesser amounts of starch, cellulose (Abdul Khalil et al. 2006), and pectin-type compounds (Yapo et al. 2007) compared to banana cortex. The differences in the cortexes of banana and citrus were
apparent in the biosorption capacity of Cd and Cr. The higher amount of starch and
cellulose in banana cortex helps in the binding of Cr and Cd compared to other metals (Al-Qahtani 2016).
The adsorption mechanism of heavy metals on the fruit cortexes is due to the
presence of the carboxyl and hydroxyl groups on the pores’ surfaces. The functional groups coordinate with metal ions to form metal complexes (Abdul Khalil
et al. 2006). The role of the carboxyl and hydroxyl groups is depicted in Fig. 13.5.
Alkalinization process creates active sites when it reacts with the cellulose- and
pectin-like compounds in the fruit cortexes. The active sites will be negatively
charged, hence accepting the metallic ions in the solution. The adsorption
S. Ganesan