Application of Sustainable and Low-Cost Sludge-Based Adsorbents …
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3.2 Factors Affecting Activation of Adsorbent Preparation
3.2.1 Nature of Activating Agent
Chemical agents and carbonization temperature have an impact on the development
of the pore volume and pore formation. The activated carbon prepared by chemical
activation of lignin by Hayashi et al. [42] using ZnCl 2 and H 3 PO 4 showed an increase
in pore volume with an increase in temperature over the range 500–600 °C. At the
temperature above 600 °C, the carbon structure shrank showing the decrease in
surface area and hence the pore volume. Above 800 °C, the excess pore enlargement
induced combination of pores, resulting in an increase in mesopores for all alkali
metal salts and a decrease of micropore volume and of surface area. In a study
conducted by John Kennedy et al. [54], porous carbon was prepared from rice husk
using phosphoric acid activation through pre-carbonization and chemical activation.
The method adopted produced carbons with micro- and mesoporous structure.
A wide range of chemical agents is used in the activation of carbons. The chemical agents used in the chemical process are normally alkali and alkaline earth metal
containing substances and some acids such as KOH, K 2 CO 3 , NaOH, Na 2 CO 3 , ZnCl 2 ,
MgCl 2 and H 3 PO 4 . Although phosphoric acid is shown to be the most environmentally sound chemical for the activation processes, most studies have used zinc chloride due to its effective activating capability [97]. Also, it has been found that the
effect of some chemicals on the carbon precursor yields more char and less tar than
the untreated sample [1]. A very few carbon activation works are carried out using
sulphuric acid.
3.2.2 Impregnation Ratio
The increase in impregnation ratio intensifies the reaction of the activating agent
resulting in pore widening. Yanping and Rockstraw [120] activated pecan shell using
orthophosphoric acid and developed micropore and mesopore activated carbons. The
development of surface area and pore distribution followed the same trend with the
increase of impregnation ratio with micro- and mesopore volumes as 1.5, 1.5 and
2.0 cm
3 /g, respectively: The initial increase followed by decrease after reaching a
maximum was observed due to calcination of the developed carbon.
3.2.3 Activation Temperature
Low impregnation ratio (less than 1.5) and activation temperature (less than 300 °C)
were favourable in the formation of acidic surface functional groups, which consisted
of temperature-sensitive (unstable at high temperature) and temperature-insensitive
(stable at high temperature) parts. At an impregnation ratio of 1.5, activated carbon
with BET surface area and micropore volume as high as 861 m
2 /g and 0.289 cm
3 /g
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3.2 Factors Affecting Activation of Adsorbent Preparation
3.2.1 Nature of Activating Agent
Chemical agents and carbonization temperature have an impact on the development
of the pore volume and pore formation. The activated carbon prepared by chemical
activation of lignin by Hayashi et al. [42] using ZnCl 2 and H 3 PO 4 showed an increase
in pore volume with an increase in temperature over the range 500–600 °C. At the
temperature above 600 °C, the carbon structure shrank showing the decrease in
surface area and hence the pore volume. Above 800 °C, the excess pore enlargement
induced combination of pores, resulting in an increase in mesopores for all alkali
metal salts and a decrease of micropore volume and of surface area. In a study
conducted by John Kennedy et al. [54], porous carbon was prepared from rice husk
using phosphoric acid activation through pre-carbonization and chemical activation.
The method adopted produced carbons with micro- and mesoporous structure.
A wide range of chemical agents is used in the activation of carbons. The chemical agents used in the chemical process are normally alkali and alkaline earth metal
containing substances and some acids such as KOH, K 2 CO 3 , NaOH, Na 2 CO 3 , ZnCl 2 ,
MgCl 2 and H 3 PO 4 . Although phosphoric acid is shown to be the most environmentally sound chemical for the activation processes, most studies have used zinc chloride due to its effective activating capability [97]. Also, it has been found that the
effect of some chemicals on the carbon precursor yields more char and less tar than
the untreated sample [1]. A very few carbon activation works are carried out using
sulphuric acid.
3.2.2 Impregnation Ratio
The increase in impregnation ratio intensifies the reaction of the activating agent
resulting in pore widening. Yanping and Rockstraw [120] activated pecan shell using
orthophosphoric acid and developed micropore and mesopore activated carbons. The
development of surface area and pore distribution followed the same trend with the
increase of impregnation ratio with micro- and mesopore volumes as 1.5, 1.5 and
2.0 cm
3 /g, respectively: The initial increase followed by decrease after reaching a
maximum was observed due to calcination of the developed carbon.
3.2.3 Activation Temperature
Low impregnation ratio (less than 1.5) and activation temperature (less than 300 °C)
were favourable in the formation of acidic surface functional groups, which consisted
of temperature-sensitive (unstable at high temperature) and temperature-insensitive
(stable at high temperature) parts. At an impregnation ratio of 1.5, activated carbon
with BET surface area and micropore volume as high as 861 m
2 /g and 0.289 cm
3 /g