Environmental Engineering Reference
In-Depth Information
surface reactivity. The adsorption capacity of ACFs depends on many kinds of factors, such
as raw materials, activation process, the nature of the pore structure, and the surface func-
tionality. Nevertheless, problems still remain when the ACFs are used to purify drinking
water because bacteria preferably adhere to solid supports made of carbon materials. It
has been reported that bacteria that attach to carbon particles are highly resistant to dis-
infection processes owing to bioilm formation, which causes the carbon itself to become
a source of bacterial contamination.
61
Water treatment systems comprising of powdered
AC fail in the removal of bacterial pathogens from water. Unlike chemical contaminants,
most biological adsorbates (e.g., bacteria and virus) have sizes larger than the pore size of
the microporous adsorbents like AC. This size difference makes the majority of pore sur-
face area inaccessible to the biological adsorbates, thereby limiting their removal. Hence,
it would be advantageous if the AC also possessed antibacterial activity to kill airborne or
waterborne bacteria.
In general reports, the antibacterial activities of ACs are available as ACs or ACFs sup-
ported with silver (AC/Ag or ACF/Ag). Silver nanoparticles deposited over AC by electro-
chemical deposition methods have been reported in controlling microorganisms in water.
Comparison of the antibacterial activity of the Ag/C catalyst prepared by an electrochemi-
cal deposition method with that of the Ag/C catalyst prepared by a conventional impreg-
nation technique indicates that lower amounts of the former is suficient in controlling
the microorganism, which is not the case with the latter. The main advantage of the Ag/C
catalyst prepared by electrochemical deposition is that no pretreatment conditions like
reduction are required for deactivation of microorganisms in water, which is not the case
with the catalysts prepared by impregnation techniques.
62
Viscose-based AC iber com-
posite supporting silver (ACF (Ag)) containing 0.065 wt% of silver exhibited strong anti-
bacterial activity against
E. coli
and
S. aureus
. The results of antibacterial tests for the ACF
(Ag) with varying silver content showed that the ACF did not show antibacterial proper-
ties against any bacteria, but all ACF (Ag) samples exhibited strong antibacterial proper-
ties against
E. coli
and
S. aureus
. It should be mentioned that after washing for 120 h, the
ACF (Ag) samples of 0.065 wt% Ag (with an initial silver content of 1.44 wt%) still exhibited
strong antibacterial activity against both bacteria.
63
In the last few years, there has been
growing interest in the CM as an alternative to conventional carbon materials. CMs can be
produced with the desired shape and morphology with controlled composition, structure,
and porosity. The potential of using a cylindrical CM containing impregnated silver with
longitudinal capillary channels as a ilter for water puriication has been demonstrated.
64
Carbon monolith samples with a silver coating showed good antimicrobial activity against
E. coli
,
S. aureus
,
and
Candida albicans
, and are therefore suitable for water puriication, par-
ticularly as POU systems in developing nations.
64
Graphene is another carbon material that
has been extensively used for water treatment.
65
Graphene and derivative analogs have
potential applications in water disinfection owing to their inexpensive preparation from
natural sources like sugar and graphene composites. They can be prepared by impregnat-
ing inorganic materials like silver that makes them antibacterial.
12.3.2 AC with Biocidal Quaternary Ammonium Groups
As shown above, in the preparation of antibacterial ACs, much effort has been devoted to
the impregnation of silver in ACs. Although silver has attractive antibacterial activities, their
primary shortcoming is that the particles are easily washed out since they are just deposited
on the surface of the AC. Furthermore, with increasing silver content, the speciic surface
area of the carbon decreases greatly, resulting in reduced adsorption capability. A number
