Water adsorbents 10 and environmental protection 11 due

Water is an important and
essential component of this universe and plays a vital role in the proper
functioning of the Earth’s ecosystems. In spite of this, safe drinking water is
not available in some parts of the world. More than seven hundred organic and
inorganic pollutants have been reported in water along with microbial
populations. Among these, certain Azo dyes are dangerous because of their
highly toxic and carcinogenic
effects. Other classes of synthetic dyes are also known to be carcinogenic,
causing diseases such as kidney, bladder and liver cancer1, 2.

 Dyes are widely used in many
fields as textiles, papers, plastics, and leather, therefore; more attention
has been gained for the recovery of these dyes from aqueous solutions due to
their toxic, mutagenic and carcinogenic effect. There are many processes for
separation of dyes from aqueous solutions, such as coagulation and
flocculation, membrane separation, oxidation or ozonation, electrocoagulation
and adsorption 3-6.
The most suitable method among all these methods is adsorption due to low cost,
simply operating and high efficiency. Recently biosorbents such as lignin7 and
Chitosan(CS), the linear cationic amino polysaccharide composed of  ?-D-glucosamine, 6 attracted strong interest due to environmental and cost-effective.
CS is extensively used in many fields such as biomedicals 8, drug delivery 9, adsorbents 10 and environmental protection 11 due to its hydrophilic, anti-bacterial activity, biocompatibility
and non-toxicity properties. However, the solubility of CS in acidic media
limited some applications. To avoid this limitation, crosslinking of CS was
made between the functional groups and different kinds of crosslinking such as
epichlorohydrin 12, vanillin13, gluteraldhyde 14 and tripolyphosphate 15, however this crosslinking leads to decrease the efficiency of CS
as adsorbent due to the consumption of functional groups in crosslinking 16, 17 Conducting polymer hydrogels consisting of polypyrrole (PPY) and
CS was prepared by polymerization of pyrrole using methyl orange as dopant and
ferric sulphate as the oxidant in CS solution 18. This hydrogel exhibits good electrical conductivity, excellent
swelling/de-swelling behaviors due to the participation of one dimensional PPY
blocks in the hydrogel network 14. Recently, polypyrrole chitosan composite 15 was prepared by using potentiostat at a constant voltage. In
PPY/CS composite hydrogel 19, the participation of one dimensional PPY blocks in the formation
of the hydrogel network avoids a possible migration of PPY from the hydrogel,
this pH-sensitive composite showed good water absorbencies in distilled water
and saline solution.

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Graphene nanosheets, two-dimensional carbon nanomaterials, have
received significant attention due to the unique electronic, mechanical
properties, large surface areas 18 (theoretical value of 2600 m2/g) 20, excellent electronic conductivity, high chemical stability
and low manufacturing cost 21. Graphene displays high ?-conjugation and hydrophilic properties
however the functionalization of graphene is a requirement to improve the
chemical affinity for specific guest molecules and facilitate the dispersion in
aqueous media 22. Graphene oxide (GO)  has gained considerable attention as a
significant biosorbent (which is similar to carbon nanotube) due to presence of
plenty oxygen atom on the backbone in the form of epoxy, carboxyl and hydroxyl
groups protruding from its layers that can bind to dyes through electrostatic
interaction in addition to the high surface area 19. However, the surface of GO sheets are highly negatively charged
when dispersed in water due to the ionization of carboxylic acid and hydroxyl
groups on the GO sheets. This negative charge limits their application on the
adsorption of negatively charged dyes. Graphene oxide, glutaraldehyde,
crosslinked chitosan and CS/GO showed enhanced adsorption capacity for Au(??)
and Pd(?), 23. A
three-dimensional Chitosan/vacuum-stripped (VSG) grapheme/polypyrrole interface
was fabricated for dopamine detection. The sensor exhibits good selectivity,
high sensitivity, low detection limit and good sensing performance in human
serum samples 23, 24. A hierarchical
porous CS/VSG/PPY scaffold was prepared via a two-step strategy involving
freeze-casting and electrochemical polymerization techniques. To the best of
our knowledge, there is no reported study on the synthesis of PPC/GO
nanocomposite by a chemical method, the performance of the nanocomposite still
not reported as an adsorbent. With the purpose of developing low cost, with
high-quality composite pushing us in the present work to synthesize PPC/GO
nanocomposite via in-situ polymerization of PY in CS/GO dispersion.
Characterization of the composite has been carried out using Fourier
transformed infrared spectra (FTIR), scanning electron microscope (SEM),
transmission electron microscope (TEM) and X-ray diffraction pattern techniques
(XRD). The adsorption of ponceau 4R (as a model) into the nanocomposite was
studied. The kinetics and isotherm of the adsorption have been discussed. The
difference between CS/GO, GO and the PPC/GO nanocomposite toward the adsorption
of ponceau 4R was considered. Various parameters such as initial concentration
of dye, amount of adsorbent, contact time, temperature, pH, adsorption
isotherms, and kinetics were studied, Also desorption process was tested to
study the reusability of sorbents.