Functional Hyper-Crosslinked Polypyrene for Reductive Decolorization of Industrial Dyes and Effective Mercury Removal from Aqueous Media

Article abstract of DOI:10.1002/cplu.201800494

A rigid and valuable hyper-crosslinked polymer (HCP) has been synthesized from the polycyclic aromatic hydrocarbon pyrene: hyper-crosslinked polypyrene (HCPPy). HCPPy was prepared through a simple one-step Friedel-Crafts alkylation reaction that involves ZnBr₂-catalyzed crosslinking in the presence of an external crosslinker, bromomethyl methyl ether (BME). Interestingly, the unreacted bromomethyl groups (?CH₂Br) on the surface of HCPPy could be quantified, which later aided in modification as per our requirement. We aimed at modifying with disulfide-containing cystamine dihydrochloride (Cys-HCPPy). Cys-HCPPy exhibited an extended π-conjugated system with uniform (～1 μm diameter) morphology and high porosity (specific surface area: 445 m² g^?1). As a fundamental application, the Cys-HCPPy composite was used as a sorbent to remove Hg²⁺ ions from aqueous media. Thus, at pH 6, the adsorption capacity for mercury ions reached 1124.82 mg g^?1 after 24 h. Furthermore, the immobilization of Ag nanoparticles on the surface of Cys-HCPPy (Ag@Cys-HCPPy) enhanced the catalytic properties, which allowed for the reductive decolorization of industrial dyes such as methylene blue, methyl orange, and Congo Red in the presence of NaBH₄ as a reducing agent.

Full text of DOI:10.1002/cplu.201800494

Accepted Article
Title: Functional Hyper-crosslinked Polypyrene for Reductive
Decolorization of Industrial dyes and Effective Mercury Removal
from Aqueous Media
Authors: Anuraj Varyambath, Wen Liang Song, and Il Kim
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemPlusChem 10.1002/cplu.201800494
Link to VoR: http://dx.doi.org/10.1002/cplu.201800494
A Journal of
www.chempluschem.org

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
Functional Hyper-Crosslinked Polypyrene for Reductive
Decolorization of Industrial dyes and Effective Mercury Removal
from Aqueous Media
Anuraj Varyambath, Wen Liang Song, and Il Kim*[a]
Abstract: A rigid and valuable hyper-crosslinked polymer (HCP) has
been synthesized using pyrene, a polycyclic aromatic hydrocarbon
(HCPPy). The HCPPy was prepared through a simple one-step
Friedel-Crafts alkylation reaction that involves ZnBr2-catalyzed
crosslinking in the presence of an external crosslinker, bromomethyl
methyl ether (BME). Interestingly, the unreacted bromomethyl groups
(−CH2Br) on the surface of HCPPy could be quantified, which later
aided in modification as per our requirement. We aimed at fabricating
with disulfide containing cystamine dihydrochloride (Cys-HCPPy).
The Cys-HCPPy exhibited an extended π-conjugated system with
uniform (~1 µm diameter) morphology and high porosity (specific
surface area: 445 m2/g). As a fundamental application, the Cys-
HCPPy composite was used as a sorbent to remove Hg2+ ions from
aqueous media. Thus, at pH 6, the adsorption capacity of mercury
ions reached 1124.82 mg g−1 after 24 h. Furthermore, the
immobilization of Ag nanoparticles on the surface of Cys-HCPPy
(Ag@Cys-HCPPy) enhanced the catalytic properties, which allowed
for the reductive decolorization of industrial dyes such as methylene
blue, methyl orange, and Congo Red in the presence of NaBH4 as a
reducing agent.
Photocatalysis involving the use of TiO2, a well-known
photocatalytic material, is the primarily used methodology for azo
dye degradation. However, photocatalysts can be activated only
in the presence of ultraviolet light, which limits their practical
application because the UV region constitutes only 4% of the
entire solar spectrum [5]. Consequently, the development of
simpler and effective methodologies for the efficient degradation
of azo dyes has gained much importance.
The most harmful contaminants of industrial wastewaters are
mercury and its derivatives, which result in health issues and
environmental pollution. Among the methods introduced for the
[6]
detection of mercury in aqueous solutions, the most effective
one is the use of adsorbents modified by incorporating sulfur-
based ligands such as thiol and thiourea groups [7]. In particular,
mesoporous silica is one of the most competent adsorbents for
trapping heavy metal ions because of its high specific surface
area, regular and tunable pore size, etc. [8]. However, the
exploration for more economically feasible and chemically stable
adsorbents with easy functionalization of organic ligands for more
efficient removal of Hg2+ and other heavy metals is underway.
Microporous materials have recently attracted considerable
attention owing to their distinctive properties such as large surface
area, small pore size, and low skeletal density [9]. These materials
also exhibit satisfactory chemical, thermal, and mechanical
stability for application to various fields such as gas sorption and
storage, heterogeneous catalysis, sensing and heavy metal
removal [10]. Hyper-crosslinked polymers (HCPs) are a new
subclass of porous materials synthesized from inexpensive
organic monomers, and they have satisfactory stability, tunable
porosity, and potential for synthetic modification. The porosity
remains permanent owing to the extensive crosslinking in HCPs,
which prevents the polymer chains from aggregating into a dense,
nonporous state [11]. HCPs can be produced using a formaldehyde
dimethyl ether crosslinker through a simple one-step Friedel–
Crafts reaction, so that this approach can be extended to the
synthesis of a diverse range of polymers derived from simple
aromatic monomers [12]. Surface areas, pore-size distributions,
and surface functionalities of HCPs are apparently tuned by
changing the aromatic monomer, the reaction stoichiometry, or
via the addition of functionalized aromatic comonomers.
Introduction
The substantial worldwide industrialization is one of the major
threats to the environment in this century. Various industries such
as textile industries, paper and pulp, plastics, cosmetics, and
leather industries annually utilize huge quantities of different dyes
and pigments [1], especially azo dyes. Azo dyes are common
synthetic colors that contain an azo group, in their structure.
These dyes are an abundant source of colored organics
originating as unwanted substances from the industry dyeing
process. This widespread use of colored dyes is extremely
hazardous to the environment owing to the discharge of toxic and
potentially poisonous substances into aqueous systems. Color
removal using Fenton reagents results in heavy sludge deposition,
which also requires further separation and appropriate disposal [2]
.
[3]
[4]
In recent years, photocatalysis
and adsorption
have been
used for wastewater treatment to effectively remove colored
organics at ambient temperatures. The adsorption tactics causes
the gradual transfer of effluents from wastewater to solid wastes.
The flexible nature of HCPs may help in moderating the
environmental problems caused by poisonous heavy metals and
dye molecules. Significantly, HCPs are a less explored class of
porous materials for environmental pollutant removal [13]. To the
best of our knowledge, the duel application of HCPs for both dye
degradation and Hg2+ removal from an aqueous solution has not
yet been reported. Our strategy is to employ an HCP and its post-
modification with a disulfide-containing chelating agent for the
reductive decolorization of industrial dyes and the adsorption of
[a]
Anuraj Varyambath, Wen Liang Song and Prof. Il Kim*
BK21 PLUS Center for Advanced Chemical Technology,
Department of Polymer Science and Engineering,
Pusan National University, Busan 609-735, Republic of Korea
E-mail: ilkim@pusan.ac.kr
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
Hg2+ from aqueous solutions. The HCP is synthesized via a one-
pot Friedel–Crafts alkylation promoted by anhydrous ZnBr2, using
a low-cost pyrene monomer with an external crosslinking agent,
BME. Further, the unreacted bromomethyl groups on the surface
of HCPPy are simply substituted with cystamine. Furthermore,
this hybrid material i.e., Cys-HCPPy, is used for the removal of
Hg2+ from aqueous solutions, primarily owing to the presence of
disulfide-containing cystamine dihydrochloride, and for the
reductive degradation of MB, MO, and CR dyes by immobilizing
Ag nanoparticles (Ag NPs) on the surface of Cys-HCPPy.
contains an uncrosslinked portion that exists as bromomethylated
PPy. Hence, the entire bromomethylated polyaromatic networks
resembling the Merrifield resin (chloromethylated polystyrene)
can be widely used for the synthesis of various reactive and
functional polymers that are strong and insensitive to the solvent,
and the swelling problem seen for styrene-divinylbenzene resins
does not exist [15]. Consequently, we found that these polymeric
spherical networks serve as exceptional substrates for
functionalization via simple substitution reactions [16]. This paper
describes the functionalization of cystamine dihydrochloride on
polypyrene spherical networks, Cys-HCPPy, and further
stabilization of Ag NPs on the cystamine supported polypyrene,
Ag@Cys-HCPPy, via a simple chemical reduction without any
reducing agents. Previously reported synthetic methods by
assembling noble metal NPs on solid surfaces based on chemical
reduction have the difficulty in removing extra-reducing or
protecting agents, which further affect the catalytic activity of
NPs/polymer hybrid system. Interestingly, we have observed
amine group present in the Cys-HCPPy directly acts as a reducing
agent without applying any additional reductants or surfactants [17]
Our emphasis here is to simultaneously utilize the large surface
area and high electron density of PPy, flexible structure of the
cystamine moieties, and the catalytic activity of the Ag NPs,
toward the degradation of industrial organic dyes and adsorption
of Hg2+ ions. For a better understanding of the synthesis and
modification of HCPPy, we have schematically illustrated the
entire synthesis process in Scheme 1.
Results and Discussion
Synthesis and modification of HCPPy
Following our previous report [14], the HCP was obtained via
simple one-pot synthesis involving crosslinking of a pyrene-like
aromatic hydrocarbon in the presence of an external crosslinker.
In brief, the polymer networks were prepared via Friedel-Crafts
alkylation involving the condensation of BME and the pyrene
monomer in the presence of ZnBr2 as a Lewis acid catalyst.
Anhydrous ZnBr2 can induce the Friedel-Crafts crosslinking of the
polypyrene with BME to construct methylene bridges that are
essential for rigid aromatic network formation. The electrophilic
substitution reaction for methylene bridge formation
regioselectively occurred at the 1-, 3-, 6-, and 8-positions of the
pyrene ring, which are more electron-rich centers. The polymer
.
Scheme 1. Synthesis of HCPPy via polymerization of pyrene, subsequent modification with cystamine dihydrochloride using the unreacted bromomethyl groups on
the surface, and final immobilization of Ag NPs.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
Characterization of Cys-HCPPy and Ag@Cys-HCPPy hybrid
materials
at position of 163.6 eV was observed for S–S bond in the
cystamine (Figure 2(d)). Overall, the XPS data confirmed the
functionalization of cystamine on the HCPPy surface [21]. Figure
S3 in SI shows the wide-scan XPS spectrum of Ag@Cys-HCPPy
and its core-level XPS spectrum for Ag 3d. Two clear peaks can
be observed due to Ag 3d5/2 (368.8 eV) orbit and Ag 3d3/2 (374.9
eV) orbit, which is associated to the formation of Ag0.
The functionalization of HCPPy with cystamine moieties was
traced via a weight loss between 200 °C and 800 °C using TGA
thermograms (Figure 1). Both HCPPy and Cys-HCPPy samples
show minor weight losses around 100 °C owing to the loss of
moisture and adsorbed water molecules. The degradation of
amine groups and ethylene moieties covalently attached to the
surface of HCPPy are observed between 200-300 °C. A sharp
decrease in the temperature range between 350°C to 650 °C in
HCPPy and stepwise degradation with the loss of 25% in Cys-
HCPPy is due to the destruction polymer networks. Moreover, the
TGA thermogram of Ag@Cys-HCPPy (Figure S1 in Supporting
Information (SI)) shows the similar thermal degradation behavior
with the smallest weight loss at 650 °C.
Table 1. Elemental composition of Cys-HCPPy
Cys-HCPPy
XPS data report
EA data report
C (wt %)
93.53
H (wt %)
N (wt %)
3.11
S (wt %)
3.08
-
90.21
4.65
2.95
2.55
The covalent links between cystamine and HCPPy were
verified via FT-IR spectroscopy (Figure 1(a)). The remaining
uncrosslinked bromomethylated groups in the HCPPy provided
more domains for Cys-HCPPy and were distinctly detectable from
the IR spectra. The characteristic band of HCPPy was observed
at 574 cm−1 (C−Br stretching vibration of the CH2Br group). For
Cys-HCPPy, the C-Br peak disappeared and a new peak at 1247
cm−1 (C–N stretching vibrations) appeared. Furthermore, the
[18]
spectrum exhibited the vibration band of N−H at 1630 cm−1
.
FTIR spectrum of Ag@Cys-HCPPy shown in the Figure S2 in SI.
Figure 2. Wide-scan XPS spectrum of Cys-HCPPy (a); core-level spectra of
C1s (b), N1s (c), and S2p (d).
Figure 1. FTIR spectra (a) and TGA profiles (b) of HCPPy and Cys-HCPPy.
For the structural morphology analysis of polymeric system,
as-synthesized samples were subjected to FE-SEM and TEM
characterization. From the FE-SEM images (Figure 3), spherically
self-assembled HCPPy could be observed, which was
interestingly obtained within 30 min of polymerization. Uniform
microspheres with a particle size of approximately 1 µm could be
intrinsically fabricated without using any templates. Post-
modification with cystamine on HCPPy did not lead to any
morphological variation (Figure 3(b)). Figures 3(c) and (d)
demonstrate the formation of Ag NPs on the Cys-HCPPy
microsphere surface after modification with silver nitrate solution.
The TEM images of Ag@Cys-HCPPy (Figures 3(g) and (h))
indicated that Ag NPs are immobilized on the surface of Cys-
HCPPy, revealing the formation of the Ag@Cys-HCPPy
composite. The existence of Ag NPs on the surface of the Cys-
HCPPy was also confirmed using an EDS detector coupled to
SEM system, which demonstrated the presence of C, O, and Ag
in Figure 4 (d). The sample was coated with Au before the
For further confirmation of the surface functionalization of
HCPPy with cystamine, we carried out XPS and EA of the as-
synthesized Cys-HCPPy. The weight percentages of different
elements are shown in Table 1. The presence of nitrogen and
sulfur was attributed to the functionalization of cystamine. More
information was obtained by observing the high-resolution spectra
of C1s, N1s, and S2p (Figure 2(a)). The XPS spectrum of HCPPy
shows the Br3d at 72.5 eV that is considerably reduced after the
functionalization. The C1s spectrum of Cys-HCPPy could be
deconvoluted into two peaks centered at 284.4, and 285.5 eV,
which corresponded to sp2 C and C–N bonds, respectively
[19]
(Figure 2(b)). As seen in Figure 2(c), the N1s peak could be fitted
into two curves with binding energies of 399.4 and 401.8 eV,
which attributed to the formation of a primary amine (–CH2–NH2)
and a secondary amine (–NH–CH2–) [20]. The lower energy peak
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
analysis, so the presence of this element was also indicated in the
EDS mapping.
The surface porosity parameters of HCPPy and Cys-HCPPy
were investigated via nitrogen adsorption analysis at 77.3 K. As
shown in the Figure 4(a), the isotherm of the polymer exhibits a
type I character, with a sharp nitrogen gas uptake at low P/P0 with
polymer networks.[23] The BET surface area calculated for HCPPy
is 520 m2 g−1 at a low relative pressure (P/P0 < 0.001), whereas
the calculated surface area of Cys-HCPPy is 445 m2 g−1. The
slight decrease in the surface area is due to the functionalization
by Cys. Based on pore size distribution analysis (Figure 4(b)), as
determined by NLDFT, micropores with width of ca. 0.86 nm and
minor mesopores peaked around 2.08 nm are confirmed for
HCPPy. The micropore volume and total pore volume are 0.6841
cm3/g and 0.9528 cm3/g, respectively, where the micropore
volume was determined using the t-method. After the
functionalization, mesopore peak decreases gradually and a
minor peak appears around 2.2 nm.
a large microporous structure; the significance of
broad
hysteresis in the HCPPy isotherm suggests the presence of
mesopores [22]. After the functionalization, the hysteresis loop was
decreased as shown in the isotherm of Cys-HCPPy. The
broadness between the desorption and adsorption branches at
low relative pressures might be due to the swelling of the porous
Figure 3. FE-SEM [(a)–(d)] and TEM [(e)–(h)] images of HCPPy (a), Cys-HCPPy (b, e and f), and Ag@Cys-HCPPy (c, d, g and h) under low- and high-magnifications.
Figure 4 (c) shows the XRD patterns of the pure HCPPy, Cys-
HCPPy, and corresponding nanocomposites with Ag NPs. The
representative Bragg diffraction peaks for Ag at 2θ = 37.88o,
44.19o, 64.14o, and 77.28o were observed in the XRD pattern of
Ag@Cys-HCPPy, which corresponded to the face-centered cubic
[24]
(fcc) phase of Ag (111), (200), (220), and (311), respectively
.
The sharp diffraction peaks distinctly indicated the existence of
Ag NPs on the polymer surfaces. Moreover, a broad band
centered at 2θ = 22.71o was present, which was characteristic of
the amorphous nature of the polymer networks.
Considering the simulated polymerization method can be
tailored to mimic complicated polymerization systems
accompanied by crosslinking in multistep processes,
a
computational methodology for structure generation of HCPPy
polymers was studied, consisting of a crosslinking simulation
script using Forcite – an atomistic molecular dynamics module
[25]
within BIOVIA’s Materials Studio
. For the simulation,
amorphous cell is constructed by a random packing of repeat
units into a box under periodic boundary conditions at an initial
density, 0.8 g/cm3. The chemical structures of the repeat units are
defined as shown in Figure 5(a) and 100 units of 1-
(bromomethyl)pyrene, 67 units of 1,6-bis(bromomethyl)pyrene
and 22 units of 1,3,6-tris(bromomethyl)pyrene are packed in a unit
cell as illustrated in Figure 5(b). Then, a polymerization step is
performed so that close contacts between the pair of reactive
atoms (R1 and R2 in Figure 5(a)) that meets all bonding criteria
Figure 4. Nitrogen adsorption/desorption isotherm of HCPPy and Cys-HCPPy
(brown filled symbols for adsorption branch and green filled symbols for
desorption branch) (a); pore size distribution curves calculated via NL-DFT (b);
XRD patterns of HCPPy, Cys-HCPPy, and Ag@Cys-HCPPy (c); and SEM-EDS
spectrum of Ag NPs. The peak at 3 keV confirms the presence of Ag (d).
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
can be selected. After a new bond is formed between predefined
R1 and R2, and side product, HBr, is removed from the box, an
energy minimization is performed to relax the newly formed bond.
If no pair meeting all bonding criteria is found, a molecular
dynamics simulation is performed and a polymerization step is
attempted again. This is repeated until the targeted conversion is
achieved. As shown in Figure 5(b), a segment of a line of the
At low degree of conversion, crosslinked networks would not
be formed and the polymers are essentially nonporous, since the
flexible and mobile nature of growing polymer chains prevents
pores from forming. As the degree of conversion increases to a
specific degree inducing gelation, expected micropores are
formed. Figure 5(b) display the variation of pore volumes as
[26]
defined by the solvent-accessible surface
with respect to the
periodic box bearing 200 monomers is 47.13
Å
before
degree of conversion from X=0.0% to 100%. A solvent-accessible
surface area (SASA) was calculated for each cell with a solvent
diameter set to 3.681 Å (the kinetic diameter of nitrogen). The
amorphous cells for the 200-unit cluster with solvent-accessible
surfaces (in blue) are shown in Figure 5(b). The surface area is
calculated from the center of the probe molecule for the
accessible surface and the accessible solvent-accessible surface
polymerization. However, it sharply decreases to 41.64 Å even at
very low conversion (X) of 4.8%, then, it decreases monotonously
according to X value to yield 40.04 Å at X = 100%. The degree of
conversion are easily identified by the decrease of the number of
red balls representing bromine atoms.
Figure 5. Bromomethylated PPy monomers to build networks and simplified flow chart to obtain HCPPy network (a), and snapshots of molecular simulation boxes
of HCPPy networks taken at various degrees of conversion showing the solvent-accessible surface areas (blue areas). For amorphous cells construction, 200 units
of monomer consisting of 100 units of M1, 67 units of M2 and 33 units of M3 were used. Dark blue areas represent the micropore surface, grey balls and sticks
represent newly formed crosslink sites, and red balls represent unreacted bromine groups (b).
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
area describes the surface area of pore structures more
accurately in terms of real physical sorbent-sorbate interactions
presence of the catalyst using NaBH4. In the absence of the
catalyst, the degree of degradation only reached 17.6% in 150
min (Figure 6(g)).
and is also related to the entropy of the adsorbed molecules [25]
.
At low degree of conversion, X=4.8% to 38.7%, the solvent
accessible area is around 50 m2/g, which is variable upon
simulation conditions, since the growing polymer chains are
flexible and movable until gelation occurs. The SASA sharply
increases to 245.2 m2/g at X=52.0%, demonstrating the formation
of micropores by the primary gelation; however, it decreases to
28.6 m2/g at X=88.6%, most probably due to the secondary
gelation inside of crosslinking networks. The SASA value
increases to 480.8 m2/g at X=92.2%. Even though the simulated
geometric and BET surface areas are fundamentally different and
should be compared with care, and strict trend of the variation of
SASA according to the degree of crosslinking is not observed,
considering the experimental BET surface area of HCPPy is 520
m2/g, the calculated solvent-accessible surface areas show
reasonable agreement with the experimental BET value as
measured by N2 sorption. The origination of discrepancies
between BET surface area and SASA have been well described
As shown in Figure 6(e), CR (0.143 mol L−1) exhibited the
typical absorption peak at 494 nm and degradation as a function
of reaction time. After 40 min, the color of the CR solution
disappeared, indicating degradation resulting from the cleavage
of azo bonds of this dye, similar to MO. It was observed that
98.1% of CR was degraded, but this required a longer time than
of MO (Figure 6(f)), this might be due to the presence of two azo
groups in CR. The degree of degradation only reached 14.5% in
150 min in the absence of the catalyst (Figure 6(g)). Generally,
the reductive decolorization of industrial dyes on a metal surface
is catalyzed via the formation of a metal hydride on the catalyst
surface after the adsorption of NaBH4. Subsequently, desorption
results in the formation of a vacant space for further dye
adsorption, so that the reduction continues [28]
.
In the reductive dye-decolorization study, we found that the
large redox potential barrier between donor (BH4-) and acceptor
(dyes) hinders rapid degradation. However, in the presence of the
catalyst, the high surface area and the interconnected large pores
within the frameworks of Ag@Cys-HCPPy hybrid significantly
favor double electron transfer to adsorb the dyestuffs owing to the
electrostatic force of attraction, and the required reactions are
terminated within a short time [29]. Excess NaBH4 (reaction
equivalent) does not affect the reduction rate; thus, the reaction is
considered to follow pseudo-first-order kinetics based on the
straight line obtained in the (Figure 6(h)) plot of ln(At/A0) verses
time.
The rate constant (k) for the reaction is calculated using
ln(At/A0) = –kt, where k is the pseudo first order rate constant; At
and A0 are the absorbance for the initial concentration of the dye
and that at a specific time, respectively. The kinetic constants A0,
At, and k for MB, MO, and CR degradation were obtained via
exponential regression from the experimental data. The k value
for MB is 0.0491 min–1 and that for MO with one azo group is
0.4788 min–1. Because CR has two azo groups, the k value is
much smaller, 0.0227 min–1, under similar conditions. After the
catalytic reactions under the NaBH4 environment, the Ag@Cys-
HCPPy material characterized using SEM, confirming that Ag
NPs are bound on the surface of polymer networks and no
significant changes are observed (Figure S4 in SI). Based on the
experimental results of catalytic reduction of MB, MO and CR
displayed in the Figure 6 and associated schemes given in the
Figure S5 in SI, a possible mechanism for reductive decolorization
in the literature [27]
.
Catalytic reduction of MB, MO, and CR
To explore the promising competency of Ag@Cys-HCPPy to
remove impurities from wastewater, the catalytic activity of Ag NP-
immobilized polymer microstructures was evaluated with respect
to the reduction of MB, MO, and CR in the presence of NaBH4 as
a reducing agent. Experiments were conducted in both the
presence and absence of the catalyst. The reduction of MB
solution (0.313 mol L−1) catalyzed by Ag@Cys-HCPPy (1 mg) was
conducted in the UV cuvette and monitored via time-varied
absorbance spectral changes at 664 nm with the addition of
freshly prepared 50 µL of 0.1 M NaBH4.
As shown in Figure 6(a), the absorption spectra evidently
demonstrated a continuous decrease in the absorption intensity
of the blue colored MB solution, indicating the reduction of MB.
The absorption intensity was unaffected in the absence of the
catalyst or NaBH4 even after 150 min. Figure 6(b) shows the
degree of degradation of MB versus reaction time for Ag@Cys-
HCPPy. The degree of degradation was calculated using the
expression (I0 − I)/I0×100. The degree of degradation increased
linearly with time and reached 90.7% after 40 min in the presence
of the catalyst and NaBH4. In the absence of the catalyst, the
degree of degradation only reached up to 15% in 150 min (Figure
6(g)).
The decolorization experiments were also conducted on other
azo dyes such as MO and CR, which contain diazo chromophores. of dye molecules can be described. Ag NPs stabilized on the Cys-
The Ag@Cys-HCPPy (1 mg) was used to treat MO solution (0.305
mol L−1) with the addition of 50 µL freshly prepared 0.1 M NaBH4.
The degradation was monitored in situ by UV/Vis spectroscopy.
Fig. 6(c) shows the variation in the UV/Vis absorbance spectra as
a function of time; the prime absorption peak for MO appears at
467 nm, which decreases and flattens after 12 min. The degree
of degradation reached 99.9% after 12 min (Figure 6(d)) in the
HCPPy help the electron relay from the donor species to the
acceptor substrate. Then, a redox mechanism occurs where the
Ag NPs catalyze the transfer of electrons from donor BH4¯ ions to
the acceptor dye molecule. This type of electron conducting
phenomenon is called as “electron relay effect” in which metal
NPs perform as a redox catalysts [30]
.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
Figure 6. UV–visible spectra recorded during MB (a), MO (c), and CR (e) degradation over Ag@Cys-HCPPy, degree of degradation versus time profiles of MB (b),
MO (d), and CR (f), degree of degradation versus time profiles (g) in the absence of any catalysts, and pseudo-first-order kinetic plots (h) for the degradation of MB,
MO and CR using Ag@Cys-HCPPy.
Adsorption of Hg2+ from aqueous solution
aliquots was obtained by ICP-OES analysis. After treatment with
the metal ion-containing aqueous solution using HCPPy and Cys-
HCPPy, the initial concentration of Hg2+ in the solution reduced to
1059.89 ppm and 169.52 ppm. The adsorption capacity of the
adsorbent for divalent mercury per gram (qe, in mg g–1) was
determined. In the presence of unmodified HCPPy, very less
adsorption capacity for the Hg2+ species (234 mg g–1) was
observed in 24 h, which might be due to the presence of surface
porosity. Simultaneously, Cys-HCPPy exhibited significant
adsorption capacity of 1124.82 mg g–1. This observation is
After identifying the structural stability, porosity, and sulfur content
of the chelating groups of Cys-HCPPy, we studied their capability
to adsorb Hg2+ from aqueous solutions. To measure the overall
ability of Cys-HCPPy for Hg2+ adsorption, the equilibrium data
were collected after effective treatment of Hg2+ aqueous solutions
with initial concentrations of 1294.34 ppm at pH 6. As previously
reported, metal hydrolysis might occur above pH 6 and the
resultant Hg(OH)2 slightly inhibits the adsorption capacity of the
adsorbent [31]. The metal ion concentration of all post-filtered
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
certainly favored with respect to the coordination reaction
between Hg and disulfide-containing cystamine ligands.
The Hg2+ adsorption capacity of Cys-HCPPy, in comparison with
that of other micro- and mesoporous materials, is shown in Table
2. Compared with thiol-functionalized non-silicate adsorbents, the
catalysis. In the preliminary study, Cys-HCPPy was used as the
potential adsorbent for the removal of Hg2+ from aqueous
solutions. The ligand nature of the Cys-HCPPy surface
significantly enhanced the Hg2+ adsorption capacity. Furthermore,
we demonstrated the reductive degradation of MB, MO, and CR
dyes after immobilization of Ag NPs on the surface of Cys-HCPPy.
The findings of this study indicate that these types of rigid and
cost-effective post-modified microporous polymers will propel
research in the area of environmental remediation.
Table 1. Systematic literature survey of materials used for Hg2+ adsorption
[a]
Supporting
material
qe
Entry
1
Adsorbent
Ligands
Ref.
(mg g–1)/h
Extracellular
biopolymer
γ-Glutamic
[32]
γ-PGA
96.8
acid
Experimental Section
Thiol-
CNT/Fe3
O4
MWCNT/
Fe3O4
[33]
2
Thiol
65.5
[b]
Materials
[34]
[35]
3
4
SH-HMS
COF-
LZU8
Silica
Thiol
Thiol
140.1/12
236
The aromatic monomer, pyrene (98%), and cystamine dihydrochloride
(96%, Sigma-Aldrich) were used without further purification. Other
chemicals, including the bromomethyl methyl ether (BME) crosslinker
(95%, TCI, Japan), ZnBr2 (98%, TCI, Japan), silver nitrate (AgNO3, ACS
reagent, ≥99.0%, Sigma-Aldrich), and mercury (II) nitrate hydrate,
(Hg(NO3)2·H2O, ACS, 98.0%, Alfa Aesar) were also used as received.
Congo Red (CR), methylene blue (MB), methyl orange (MO), 1,2-
dichloroethane (DCE), and dichloromethane (DCM) were procured from
Daejung Chemical Co. (Korea). DCE and DCM were distilled before use.
COF[c]
SH-SBA-
15
[36]
[37]
[38]
5
6
7
Silica
POP[d]
POP
Thiol
Thiol
EDA
429
PAF-1
CBAP-1
(EDA)
CBAP-1
(AET)
Cys-
1000/8
181/1
[38]
8
9
POP
HCP
AET
232/1
This
work
Cystamine
1124.8/24
HCPPy
Instrumentation
[a] Adsorption capacity/time. [b] Multiwall carbon nanotube/magnetite
nanocomposites. [c] Covalent organic framework. [d] Porous organic
polymer.
The functional groups of the polymers were analyzed using a Fourier
transform infrared (FT-IR) spectrometer (Nicolet iS5, Thermo Scientific)
and a PHI 5400 X-ray photoelectron spectroscope (XPS, Physical
Electronics, Mg Kα source). The surface morphologies of the samples
were investigated using a field emission scanning electron microscope
(FESEM, ZEISS Supra 40VP SEM) and transmission electron microscope
(TEM). The surface areas were analyzed using a NOVA 3200e surface
area and pore size analyzer. The Brunaeur-Emmett-Teller (BET) surface
areas were determined using the BET theory. The total pore volumes (Vt),
estimated from the amount of nitrogen adsorbed at a relative pressure
(P/P0) of ∼0.997 at 77 K, were measured using a Nova 3200e system
(Quantachrome Instruments, USA). Pore size distribution was analyzed
using the nonlocal density functional theory (NLDFT) method combined
disulfide-containing
material demonstrated significantly higher adsorption capability
for Hg2+ ions. The qe value was higher than those of g-glutamic
cystamine-functionalized
Cys-HCPPy
acid-functionalized
biopolymers
and
thiol-functionalized
CNT/Fe3O4, as well as those of thiol-functionalized mesoporous
silica and microporous COF-LZU8, as described in the literature.
Generally, the high adsorption capacity of mesoporous materials
is attributed to the unimpeded and easy diffusion of Hg2+ ions to
the adsorption sites (Entries 5 and 6). Recently, ethylenediamine
(EDA)- and 2-aminoethanethiol (AET)-functionalized microporous
polymers were used as adsorbents with excellent adsorption
capacity (Entries 7 and 8). Thus, we expect that the synergetic
effect of the micro- and mesoporous nature of HCP might
enhance the adsorption capacity for Hg2+ in aqueous solutions.
with
nonnegative
regularization
and
medium
smoothing.
Thermogravimetric analysis (TGA) was performed using a TGA N-1000
(Scinco, Korea) instrument. X-ray diffraction (XRD) analysis was
performed using an automatic Philips powder diffractometer with nickel-
filtered Cu Kα radiation. The diffraction patterns were collected in the 2θ
range of 0–80° in steps of 0.02° and at counting times of 2 s step−1
.
Elemental analysis was conducted on a GmbH elemental analyzer and
Energy-dispersive X-ray spectroscopy (EDS) coupled with SEM. The Hg2+
concentrations were measured by inductively coupled plasma-optical
emission spectroscopy (ICP-OES, ACTIVA, JY HORIVA).
Conclusions
Synthesis of HCPPy
In summary, we have developed a HCP using pyrene monomer
through a simple one-step Friedel-Crafts alkylation involving
ZnBr2-catalyzed crosslinking in the presence of BME. Further
chemical modification of the -CH2Br moiety on the periphery of
HCPPy via cystamine dihydrochloride was successfully achieved,
and the resulting material was well characterized. As discussed
in the results, Cys-HCPPy has a reasonably large specific surface
area, extended π-conjugated system, and microporous structure,
which make it an effective material for use in adsorption and
BME (0.60 g, 4.8 mmol) was added dropwise to the DCE (15 mL) solution
containing ZnBr2 (0.54 g, 2.4 mmol) and pyrene (0.50 g, 2.4 mmol) under
nitrogen atmosphere, and subsequently, the mixture was stirred for 12 h
at 40 °C. The resulting precipitate was thoroughly washed with water and
methanol until the filtrate became clear. After Soxhlet extraction with
methanol for 24 h, the spherical HCPPy was collected (60% yield) and
dried overnight in a vacuum oven at 110 °C. The concentration of
unreacted −CH2Br was assayed via colorimetric estimation [16]. The
bromine content of HCPPy was 4.7 mmol g−1
.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
Functionalization of HCPPy with cystamine dihydrochloride
Default user parameters were used to run the script. Close contact
exclusion rules were applied during the condensation polymerization.
HCPPy (0.1 g) was dissolved in CH2Cl2 (15 mL) in a 25 mL flask, and
cystamine dihydrochloride 0.47 mmol (0.074 g) was added slowly at room
temperature (r.t.). The mixture was stirred for 12 h at r.t. The resulting
cystamine-functionalized polymer (Cys-HCPPy) was centrifuged, washed
with CH2Cl2 (10 mL), and dried at 80 °C for 4 h.
Acknowledgements
The Basic Science Research Program through the National
Research Foundation of Korea (2015R1D1A1A09057372)
supported this work. The authors also thank to BK21 PLUS
Program for partial financial support.
Fabrication of Ag NPs on Cys-HCPPy (Ag@ Cys-HCPPy)
Cys-HCPPy (50 mg) was dispersed in de-ionized water upon sonication in
a 100 mL two-neck round bottom flask. To the solution, 10 mL of 0.01 M
AgNO3 solution was added dropwise, and the mixture was stirred for 5 h.
The obtained light pink colored solution was filtered, washed thrice with
water, and dried under vacuum to yield Ag@Cys-HCPPy.
Keywords: dye degradation • hyper-crosslinked polymers •
mercury absorption • polypyrene • silver nanoparticles.
[1]
a) U. Akpan, B. Hameed, J. Hazard Mater. 2009, 170, 520-529; b) G.
Mezohegyi, A. Fabregat, J. Font, C. Bengoa, F. Stuber, A. Fortuny, Ind.
Eng. Chem. Res. 2009, 48, 7054-7059; c) H. Pinheiro, E. Touraud, O.
Thomas, Dye Pigment 2004, 61, 121-139.
Dye degradation study
For dye degradation study, a stock solution of 100 mg L−1 of the industrial
dyes (MB, MO, and CR) were prepared in milli Q water. For each
decolorization study, 1 mL of stock solution was treated with 50 µL of 0.1
M NaBH4 and 1 mg of catalyst inside the UV cuvette. The decrease in
absorbance of the supernatant solution was frequently monitored via
spectrophotometric measurements at 664 nm, 467 nm, and 494 nm on a
UV-1650PC spectrophotometer (Shimadzu, Kyoto, Japan). The degree of
degradation of the samples was determined using the relation (I0 − I) ×100
/ I0, where I0 is the initial absorbance of the sample and I is the absorbance
at time t.
[2]
[3]
M. S. Lucas, J. A. Peres, Dye Pigment 2006, 71, 236-244.
a) J. Lee, H. S. Shim, M. Lee, J. K. Song, D. Lee, J. Phy. Chem. Lett.
2011, 2, 2840-2845; b) M. Yan, Y. Wu, Y. Yan, X. Yan, F. Zhu, Y. Hua,
W. Shi, ACS Sustain. Chem. Eng. 2016, 4, 757-766.
[4]
A. K. Sarkar, A. Saha, A. Tarafder, A. B. Panda, S. Pal, ACS Sustain.
Chem. Eng. 2016, 4, 1679-1688.
[5]
[6]
J. Zhang, Z. Xiong, X. Zhao, J. Mater. Chem. 2011, 21, 3634-3640.
a) M. M. Matlock, B. S. Howerton, D. A. Atwood, J. Hazard Mater. 2001,
84, 73-82; b) D. M. Findlay, R. A. McLean, Environ. Sci. Technol. 1981,
15, 1388-1390.
Hg2+ adsorption using Cys-HCPPy adsorbents
[7]
a) X. Feng, G. Fryxell, L.-Q. Wang, A. Y. Kim, J. Liu, K. Kemner, Science
1997, 276, 923-926; b) D. Esquivel, J. Ouwehand, M. Meledina, S.
Turner, G. Van Tendeloo, F. J. Romero-Salguero, J. De Clercq, P. Van
Der Voort, J. Hazard Mater. 2017, 339, 368-377.
The conventional method was employed to study the adsorption of Hg2+
from aqueous solutions onto the unmodified and modified HCPPy. The
adsorbent (10 mg) was suspended in 10 mL of aqueous solution
containing Hg(NO3)2·H2O at pH 6, and the mixture was stirred for 24 h at
r.t. The initial concentration of mercury in the adsorption mixture was 3.7
mmol (1294.34 mg L−1). The solid was separated via filtration using a 0.45
µm PTFE syringe filter. The quantity of residual Hg2+ ions in the solution
was measured via ICP-OES [36]. The amount of divalent mercury species
per gram of adsorbent was calculated based on the difference between
the initial and final concentrations of the solution. The adsorption capacity
(qe, in mg g−1) of the metal ions onto Cys-HCPPy was calculated based on
the following mass balance equation: qe = [(C0 − Ce)/m] × V, where C0 is
the initial concentration of metal ions in solution, Ce is the concentration at
equilibrium after adsorption (mg L−1), m is the mass (g) of adsorbent, and
V is the initial volume of the solution (L).
[8]
[9]
Z. Wu, D. Zhao, Chem. Commun. 2011, 47, 3332-3338.
Z. Jia, K. Wang, T. Li, B. Tan, Y. Gu, Catal. Sci. Technol. 2016.
[10] a) J. Jiang, Y. Zhao, O. M. Yaghi, J. Am. Chem. Soc. 2016, 138, 3255-
3265; b) A. Thomas, Angew. Chem. Int. Ed. 2010, 49, 8328-8344; c) N.
B. McKeown, P. M. Budd, Macromolecules 2010, 43, 5163-5176; d) R.
Dawson, E. Stöckel, J. R. Holst, D. J. Adams, A. I. Cooper, Energy
Environ. Sci. 2011, 4, 4239-4245; e) Q. Sun, B. Aguila, J. Perman, L. D.
Earl, C. W. Abney, Y. Cheng, H. Wei, N. Nguyen, L. Wojtas, S. Ma, J.
Am. Chem. Soc. 2017, 139, 2786-2793; f) B. Aguila, Q. Sun, J. A.
Perman, L. D. Earl, C. W. Abney, R. Elzein, R. Schlaf, S. Ma, Adv. Mater.
2017, 29, 1700665.
[11] J.-S. M. Lee, M. E. Briggs, T. Hasell, A. I. Cooper, Adv. Mater. 2016, 28,
9804-9810.
[12] B. Li, R. Gong, W. Wang, X. Huang, W. Zhang, H. Li, C. Hu, B. Tan,
Macromolecules 2011, 44, 2410-2414.
Molecular simulations of condensation polymerization of pyrene
[13] P. Samanta, P. Chandra, A. V. Desai, S. K. Ghosh, Mater. Chem. Front.
2017, 1, 1384-1388.
Molecular models for the crosslinked polymer networks of pyrene
polymerization were generated using the BIOVIA Materials Studio 5.0
software package (Dassault Systemes, BIOVIA Corp., San Diego, CA)
with the polymer consistent force field (COMPASS II) [39]. Molecular
simulations were performed with the Forcite module, using a time step of
1 fs, the Nosé-Hoover thermostat with a Q ratio of 0.01, and the Andersen
barostat with a time constant of 1 ps. Pre-defined monomers are packed
into a periodic cell using Amorphous Cell module in Materials Studio. The
enclosed script implemented for a crosslinking simulation using Forcite
was adapted to join monomer units via a condensation polymerization
based on a set of predetermined connectivity rule with the removal of
generated simple molecules by condensation (see Fig. 5). Packing
monomers and defining their reactive atoms and crosslinking sites, the
crosslinked structure can be generated with any degree of crosslinking.
[14] X. Huang, S. Kim, M. S. Heo, J. E. Kim, H. Suh, I. Kim, Langmuir 2013,
29, 12266-12274.
[15] E. Coulon, J. Pinson, J.-D. Bourzat, A. Commerçon, J.-P. Pulicani, J. Org.
Chem. 2002, 67, 8513-8518.
[16] A. Varyambath, C. H. Tran, W. L. Song, I. Kim, ACS Omega 2017, 2,
7506-7514.
[17] M. Yamamoto, Y. Kashiwagi, M. Nakamoto, Langmuir 2006, 22, 8581-
8586.
[18] H. Li, X. Ye, X. Guo, Z. Geng, G. Wang, J. Hazard Mater. 2016, 314,
188-196.
[19] B. Xue, J. Zhu, N. Liu, Y. Li, Catal. Commun. 2015, 64, 105-109.
[20] P.-C. Ma, S.-Y. Mo, B.-Z. Tang, J.-K. Kim, Carbon 2010, 48, 1824-1834.
[21] V. Krylova, M. Andrulevičius, Int. J. Photoenergy 2009, 2009.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
[22] S. Wang, C. Zhang, Y. Shu, S. Jiang, Q. Xia, L. Chen, S. Jin, I. Hussain,
A. I. Cooper, B. Tan, Sci. Adv. 2017, 3, e1602610.
[23] J. Weber, M. Antonietti, A. Thomas, Macromolecules 2008, 41, 2880-
2885.
[24] C. Chen, L. Wang, G. Jiang, J. Zhou, X. Chen, H. Yu, Q. Yang,
Nanotechnology 2006, 17, 3933.
[25] A. Trewin, D. J. Willock, A. I. Cooper, J. Phys. Chem. C 2008, 112,
20549-20559.
[26] T. Düren, F. Millange, G. Férey, K. S. Walton, R. Q. Snurr, J. Phys. Chem.
C 2007, 111, 15350-15356.
[27] K. E. Hart, L. J. Abbott, C. M. Colina, Mol. Simulat. 2013, 39, 397-404.
[28] Z.-J. Jiang, C.-Y. Liu, L.-W. Sun, J. Phys. Chem. B 2005, 109, 1730-1735.
[29] U. P. Azad, V. Ganesan, M. Pal, J. Nanopart. Res. 2011, 13, 3951-3959.
[30] N. Gupta, H. P. Singh, R. K. Sharma, J. Mole. Catal. A: Chem. 2011,
335, 248-252.
[31] X. Luo, T. Shen, L. Ding, W. Zhong, J. Luo, S. Luo, J. Hazard Mater.
2016, 306, 313-322.
[32] B. S. Inbaraj, J. Wang, J. Lu, F. Siao, B. Chen, Bioresour. Technol. 2009,
100, 200-207.
[33] C. Zhang, J. Sui, J. Li, Y. Tang, W. Cai, Chem. Eng. J. 2012, 210, 45-52.
[34] W. Shi, S. Tao, Y. Yu, Y. Wang, W. Ma, J. Mater. Chem. 2011, 21, 15567-
15574.
[35] S.-Y. Ding, M. Dong, Y.-W. Wang, Y.-T. Chen, H.-Z. Wang, C.-Y. Su, W.
Wang, J. Am. Chem. Soc. 2016, 138, 3031-3037.
[36] Q. Li, Z. Wang, D.-M. Fang, H.-y. Qu, Y. Zhu, H.-j. Zou, Y.-r. Chen, Y.-P.
Du, H.-l. Hu, New J. Chem. 2014, 38, 248-254.
[37] B. Li, Y. Zhang, D. Ma, Z. Shi, S. Ma, Nat. Commun. 2014, 5, 5537.
[38] S. Ravi, P. Puthiaraj, K. H. Row, D.-W. Park, W.-S. Ahn, Ind. Eng. Chem.
Res. 2017, 56, 10174-10182.
[39] A. E. Bennett, C. M. Rienstra, M. Auger, K. Lakshmi, R. G. Griffin, J.
Chem. Phys. 1995, 103, 6951-6958.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201800494
ChemPlusChem
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Hyper-crosslinked
polypyrenes synthesized by Friedel-
Crafts alkylation of pyrene are
and
porous
Anuraj Varyambath, Wen Liang Song,
and Il Kim*[a]
effectively
functionalized
with
Page No. – Page No.
cystamine and allow to immobilize Ag
nanoparticles. The highly uniform
spherical materials are useful for the
absorption of Hg2+ ions from aqueous
media as well as for the reductive
decolorization of industrial dyes.
Functional Hyper-Crosslinked
Polypyrene for Reductive
Decolorization of Industrial dyes
and Effective Mercury Removal from
Aqueous Media
This article is protected by copyright. All rights reserved.