BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 4

TABLE 1.1 Technical Advantages and Disadvantages of Existing Modification

Techniques.

Modification Treatment Advantages Disadvantages

Chemical
characteristics

Acidic Increases acidic

functional groups on
AC surface. Enhances
chelation ability with
metal species

May decrease BET surface
area and pore volume, May
give off undesired SO 2
(treatment with H 2 SO 4 ) or
NO 2 (treatment with HNO 3 )
gases, Has adverse effect on
uptake of organics

Basic Enhances uptake of

organics

May, in some cases, de-
crease the uptake of metal
ions

Impregnation
of foreign
material

Enhances in-built
catalytic oxidation
capability

May decrease BET surface
area and pore volume

Physical char-
acteristics

Heat Increases BET surface

area and pore volume

Decreases oxygen surface
functional groups

Biological
characteristics

Bioadsorption Prolongs AC bed life

by rapid oxidation of
organics by bacteria
before the material
can occupy adsorption
sites

Thick biofilm encapsulating
AC may impede diffusion
of adsorbate species

While these characteristics are reviewed separately as reflected by numerous
AC modification research, it should be noted that there were also research with the
direct intention of significantly modifying two or more characteristic and that the
techniques reviewed are not intended to be exhaustive. The adsorption capacity
depends on the accessibility of the organic molecules to the microporosity, which
is dependent on their size [5]. Activated carbon can be used for removing taste
and odor (T&O) compounds, synthetic organic chemicals (SOCs), and dissolved
natural organic matter (DOM) from water. PAC typically has a diameter less than
0.15 mm, and can be applied at various locations in a treatment system GAC, with
diameters ranging from 0.5 to 2.5 mm, is employed in fixed-bed adsorbents such
as granular media filters or post filters. Each of these factors must be properly
evaluated in determining the use of activated carbon in a practical application.
The primary treatment objective of activated carbon adsorption in a particular
water treatment plant determines the process design and operation; multiple ob-
jectives cannot, in most cases, be simultaneously optimized [5, 35].