64 Analytical Methods in Environmental Chemistry Journal; Vol. 2 (2019)
[1]. There are various methods for the adsorption
or removal of arsenic from contaminated water
sources, the most important of which are chemical
deposition [2], reduction by electron ultrafiltration
[3], ion exchange [4], and absorption process [5].
Among these approaches, the absorption method is
more cost-effective, efficient, and easy-to-absorb,
and extensive studies on the absorption of arsenic
by adsorption processes have been reported [7-5].
However, researches are looking for adsorbents
with a higher absorption rate, the identification of
an ideal adsorbent for the maximum absorption
of arsenic has not yet been suggested clearly.
Activated carbon has been used with the proper
properties as an efficient absorbent in treatment of
industrial wastewater for a Long time, especially
in the absorption of metal ions. In the meantime,
various technologies, including nanotechnology,
have increased the capacity of adsorbents used
to absorb more pollutants, including arsenic,
so that a new view has been opened in the field
of wastewater treatment. For example, carbon
nanotubes [8], graphene [9], graphene-oxide
[10], various graphene base materials, including
graphene hybrids [11] and graphene/metal oxide
nanocomposites [12], including nano-absorbents
which have been used in extensive researches,
and by using them, the best results have been
obtained. Moreover, no information is available
to use the adsorption of graphene/activated carbon
for removing arsenic from wastewaters. Graphene
oxide has shown good results in the removal of
some heavy metals from the effluent, which, in
its structure, oxygen acts as an absorption agent
for metal ions [13]. In graphene/activated carbon
composite, each of graphene and activated carbon
structures exhibits distinct effects on each other’s
performance. For example by considering the
effect of activated carbon on graphene behavior, it
can be admitted that the layer of graphene plate is
rolled onto activated carbon that not only prevents
the graphene from sticking together, but also
increases the porosity of the composite structure.
Consequently, it increases the specific surface of
adsorbents, which it is ideal target for sorbents.
On the other hand, graphene sheets, due to their
very small structures, act as a filler among the
active carbon structures and due to its conductive
behavior, and thereby, the absorption path in the
new structure of activated carbon is shortened.
It also facilitates the transfer of free electrons in
the composite structure and lowers its resistance.
This phenomenon is also the ideal goal of an
ideal adsorbent in sorption of ions [14]. In this
research, the graphene/activated carbon composite
synthesized as a porous adsorbent with a high
specific surface area is used for absorbing arsenic
from industrial effluent.
2. Experimental
2.1. Synthesis of Activated carbon/gra phene composite
absorbent
At First, graphene oxide has been obtained by
Hammers method with the mechanism of opening
of graphite layer sheets. After that, a double layer
dish with dilute sulfuric acid is washed, and while
the solution of sulfuric acid including graphite is
stirred, the temperature of the solution is reached to
0 °C using liquid cooling circulator. The amount of
2300 ml of sulfuric acid (98%) has been poured into
the reactor and mixed with 100 g of pure graphite
powder into the container, and the mixing operation
has been carried out for 30 minutes. Afterwards, the
amount of 300 g of solid potassium permanganate
powder is slowly added to the mixture during
6 hours, and the mixture is stirred for one hour
after completion. Then the temperature circulator
is increased to 40 °C, and after stabilizing the
temperature, the mixing operation continuous for
about three hours. For dilution, 500 ml of distilled
water is added with caution to the reactor, and the
circulator bleach and 3.5 liters of distilled water
are poured into a larger container, and then the
contents of the reactor are slowly transferred to a
larger container. Afterwards, the mixing operation
is carried out for one hour. The amount of 300 ml
hydrogen peroxide 30% has been slowly added to
the container, then mixing condition has continued
for 2 hours. Then 3 liters of chloride acid have
been added to 3 liters of distilled water separately.