such process are called as biosorbents. Both physical and chemical interactions
happen in biosorption.
Commonly adsorbents are carbon-based materials, zeolites, clay, alumina, sand
and natural oxides. Carbon-based materials include activated carbons, carbonized
materials, graphene-based adsorbents and carbon nanotubes.
Physisorption
Chemisorption
Non-specific
Highly specific
Occurs due to van der Waals’s force
Occurs due to chemical bonds
Activation energy is not essential
Activation energy is essential
No electron transfer, while polarization of
adsorbate occurs
Electron transfer leading to bond formation
between adsorbate and adsorbent
Rapid process
Slow process
Reversible
Irreversible
Non-surface specific
Surface specific
No dissociation of adsorbed species
May involve dissociation
Mono layer or multilayer
Monolayer only
Only significant at very low operational temperature (at higher temperature, the process of
physisorption decreases)
Possible over a wide range of temperature (with
increasing temperature, chemisorption first
increases and then decreases)
Enthalpies are in the region of À20 kJ/mol
Enthalpies are in the range of À200 kJ/mol
More liquefiable gases are adsorbed readily
Gases which form compounds with adsorbent
alone undergo chemisorption
High pressure favours the process and low
pressure causes desorption
High pressure is favourable, but low pressure
does not cause desorption
2 Biosorbents
Biosorbents are called so attributing to their biological nature. Bacteria [2], fungi [3],
algae [4, 5], agricultural wastes [6, 7], seed husks [8–10], leaves [11], stems [12],
animal shells [13], scales [14], bone powders [15] and biopolymers [16] are few of
commonly used biosorbents. Another widely used biosorbent to remove environmental pollutants is biochar which is derived from the pyrolysis of substrates
including food waste, agricultural wastes and saw dust. Biosorbents can be used as
such available (native biosorbents) or modified by physical and chemical methods
(modified biosorbents). Usually unicellular organisms are used as available [2–
5]. Agricultural wastes [7], rice husk and wood wastes [17] can be burned and
used as biochar.
Usually dead biomass is preferred over live biomass as it does not require growth
medium and growth can cause increase in the biological and chemical oxygen
demand. Also, dead biomass can be modified through various activation processes.
Regeneration of dead biomass can also be done easily. Modified biosorbents can
Material and Process Selection for Biosorption
243
happen in biosorption.
Commonly adsorbents are carbon-based materials, zeolites, clay, alumina, sand
and natural oxides. Carbon-based materials include activated carbons, carbonized
materials, graphene-based adsorbents and carbon nanotubes.
Physisorption
Chemisorption
Non-specific
Highly specific
Occurs due to van der Waals’s force
Occurs due to chemical bonds
Activation energy is not essential
Activation energy is essential
No electron transfer, while polarization of
adsorbate occurs
Electron transfer leading to bond formation
between adsorbate and adsorbent
Rapid process
Slow process
Reversible
Irreversible
Non-surface specific
Surface specific
No dissociation of adsorbed species
May involve dissociation
Mono layer or multilayer
Monolayer only
Only significant at very low operational temperature (at higher temperature, the process of
physisorption decreases)
Possible over a wide range of temperature (with
increasing temperature, chemisorption first
increases and then decreases)
Enthalpies are in the region of À20 kJ/mol
Enthalpies are in the range of À200 kJ/mol
More liquefiable gases are adsorbed readily
Gases which form compounds with adsorbent
alone undergo chemisorption
High pressure favours the process and low
pressure causes desorption
High pressure is favourable, but low pressure
does not cause desorption
2 Biosorbents
Biosorbents are called so attributing to their biological nature. Bacteria [2], fungi [3],
algae [4, 5], agricultural wastes [6, 7], seed husks [8–10], leaves [11], stems [12],
animal shells [13], scales [14], bone powders [15] and biopolymers [16] are few of
commonly used biosorbents. Another widely used biosorbent to remove environmental pollutants is biochar which is derived from the pyrolysis of substrates
including food waste, agricultural wastes and saw dust. Biosorbents can be used as
such available (native biosorbents) or modified by physical and chemical methods
(modified biosorbents). Usually unicellular organisms are used as available [2–
5]. Agricultural wastes [7], rice husk and wood wastes [17] can be burned and
used as biochar.
Usually dead biomass is preferred over live biomass as it does not require growth
medium and growth can cause increase in the biological and chemical oxygen
demand. Also, dead biomass can be modified through various activation processes.
Regeneration of dead biomass can also be done easily. Modified biosorbents can
Material and Process Selection for Biosorption
243