Identification of thienopyridine carboxamides as selective binders of HIV-1: Trans Activation Response (TAR) and Rev Response Element (RRE) RNAs

Article abstract of DOI:10.1039/c8ob02753f

Small organic molecules that can selectively bind to RNA with specificity are relatively rare. Here we report the synthesis, biochemical and structural studies of thienopyridine carboxamide derivatives with the capacity of selectively recognizing and binding with HIV-1 TAR and RRE RNAs that are essential elements for viral replication.

Full text of DOI:10.1039/c8ob02753f

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PAPER
Fast adsorption of methylene blue, basic fuchsin,
and malachite green by a novel sulfonic-grafted
triptycene-based porous organic polymer†
Cite this: RSC Adv., 2018, 8, 41986
a
ab
a
a
Li Zhou,a Ting Xu,a Jun Hu,
Changjun Peng
*
*
Cheng Li, Yan He,
and Honglai Liua
In this study, a novel triptycene-based porous polymer grafted with sulfonic acid (TPP-SO3H) was
successfully synthesized by the post-synthetic modification of the non-functionalized polymer TPP. The
polymer TPP-SO3H was well-characterized and was found to be a fast and effective absorbent for the
cationic dyes methylene blue (MEB), basic fuchsin (BF), and malachite green (MG), with over 95%
removal being observed within 10 min from initial concentrations of 100 mg Lꢀ1, 100 mg Lꢀ1, and
300 mg Lꢀ1, respectively. The adsorption process for MEB, BF, and MG was pH-dependent. The
adsorption behaviours for MEB, BF, and MG follow pseudo-second-order kinetics and fit the Langmuir
model. Moreover, the maximum adsorption capacities of MEB, BF, and MG at room temperature were
981.8 mg gꢀ1, 586.2 mg gꢀ1, and 1942.5 mg gꢀ1, respectively. It is worth noting that the values of the
MEB, BF, and MG adsorption capacities on TPP-SO3H were 5.5, 3, and 1.8 times that of the non-
functionalized polymer TPP based on the same adsorbent weight. It is suggested that (i) there are strong
electrostatic attractions between the sulfonic groups of the TPP-SO3H and cationic dyes and (ii) the
higher surface area and good porosity may contribute to the high dye adsorption capacity. Furthermore,
TPP-SO3H exhibited good cyclic stability, which can be regenerated at least five times without
a significant loss of adsorption capacity. Therefore, the facile strategy synthesis, as well as the excellent
adsorption capacity and reusability, make polymer TPP-SO3H an attractive adsorbent for wastewater
treatment.
Received 31st October 2018
Accepted 4th December 2018
DOI: 10.1039/c8ra09012b
rsc.li/rsc-advances
activated carbon,6 zeolites,7 and oriented clay lms,8 have been
extensively studied. However, these materials have disadvan-
Introduction
tages of low adsorption capacities and long adsorption times.
To overcome these problems, exploring novel porous adsor-
bents for efficient adsorption and the removal of dyes is still of
great signicance and a technical challenge.
Triptycene and its derivatives with D3h symmetry and a three-
dimensional (3D) rigid structure are widely applied in supra-
molecular chemistry and materials science elds and are
already in use in the synthesis of porous organic polymers.9,10
Compared to conventional adsorbents, the obvious features of
triptycene-based porous materials are high surface areas, good
porosities, and high thermal stability. Thus, triptycene-based
With the development of industry, water pollution from organic
dyes has become a serious issue due to its potential toxicity to
humans and the natural environment.1,2 To reduce harm to the
ecological environment and human health, it is important to
search for an effective, convenient, and fast method to deal with
wastewater. Presently, there are a large number of technologies
that have been adopted for this purpose, including physical,
chemical, biological, and adsorption.3,4 Among these methods,
adsorption has attracted considerable attention owing to its
highly efficient, easy-operation, low-cost, and recyclability.5 The
key to adsorption technology is to choose efficient adsorbents.
Of these adsorbents, many traditional porous materials, such as
polymers as adsorbents have
a distinct advantage in
adsorption-related elds, including the storage of hydrogen,
uptake and selectivity of CO2, and adsorption of organic
solvents and dyes.11–13 In addition, in our previous research, we
successfully synthesized an alkyl-substituted amino function-
alized triptycene-based 3D rigid polymer network via the post-
synthetic modication method. The resulting compound had
a high surface area and good CO2 adsorption capacity.14
Except for the amine group, some other active groups, such
as sulfonic, hydroxyl, and carboxyl groups, have been graed to
aKey Laboratory for Advanced Materials and Department of Chemistry, East China
University of Science and Technology, Shanghai 200237, China. E-mail: cjpeng@
ecust.edu.cn
bJiangxi Province Key Laboratory of Polymer Micro/Nano Manufacturing and Devices,
School of Chemistry, Biology and Materials Science, East China University of
Technology, Nanchang, 330013, People's Republic of China. E-mail: yanhe@ecit.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra09012b
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organic or inorganic porous solids by the post-synthetic modi-
cation method.15–17 Among these groups, sulfonic acid groups
have the following advantages: (1) they are hydrophilic, making
it easy to wet a solid surface with water,18 (2) they are sufficiently
easily ionized that the surface is negatively charged, facilitating
the adsorption of cations,19 and (3) the three oxygen atoms of
the sulfonic acid group are preferred hydrogen bond acceptors
and have a strong ability to form hydrogen bonds.20,21 All of
these advantages greatly enhance the adsorption of cationic
dyes. Recently, it has been reported that the graing of sulfonic
acid groups on the resin and MOF has been used for cationic
dye adsorption, but the adsorption capacities of BF, MEB, and
MG is only 127.0 mg gꢀ1, 351 mg gꢀ1, and 596 mg gꢀ1
,
respectively, and the adsorption time is long, owing to the low
surface area or low adsorption sites.22,23 Thus, a highly porous
polymer network with sulfonic acid functionality should be an
excellent adsorbent for scavenging and removing cationic dyes,
as it has a high surface area and a high density of dye adsorp-
tion active sites. However, the application of sulfonic acid
porous organic polymer for organic dye removal has rarely been
reported.
Fig. 1 Structures of the organic dyes MEB, BF and MG.
was further puried via Soxhlet extraction in methanol for 24 h.
Finally, the product was dried at 120 ꢁC under vacuum to yield
a yellow solid TPP with a good yield.
In this report, we describe the successful work of creating
a sulfonic functionalized triptycene-based porous polymer TPP-
SO3H as a new adsorbent for the fast adsorption of cationic
dyes, including MEB, BF, and MG. The adsorption kinetics,
adsorption isotherms, effect of pH and regeneration of the
adsorbent for the removal MEB, BF, and MG from an aqueous
solution of TPP-SO3H were studied in detail. In addition, the
interaction between TPP-SO3H and cationic dyes was analysed
by quantitative calculations and desorption experiments.
Synthesis of sulfonic-graed triptycene-based porous polymer
(TPP-SO3H)
As shown in Scheme 1b, chlorosulfonic acid (1.0 mL, 15 mmol)
was added dropwise to an ice-bath-cooled mixtures of TPP (125
mg) in dichloromethane (10 mL). The resulting solution was
stirred at room temperature for three days. Then, the solid was
collected aer the obtained mixtures were poured into ice.
Aerwards, the product was washed liberally with water and
dried to produce a brown TPP-SO3H powder.
Experimental
Reagents and materials
Instruments and characterization
The solid-state 13C NMR spectra were recorded on a Bruker
AVIII 500 MHz spectrometer. The morphology of the samples
All of the purchased chemicals were of at least reagent grade
and were used without further purication. Triptycene (98.0%),
anhydrous ferric chloride (FeCl3, $98.0%), 1,2-dichloroethane
(DCE, 99.8%), formaldehyde dimethyl acetal (FDA, $98.0%),
and chlorosulfonic acid (ClSO3H, 99%) were purchased from
Sigma-Aldrich. All of the other solvents were purchased from
TCI America. The methylene blue (MEB, 99%), basic fuchsin
(BF, 98%), and malachite green (MG, 98%), were purchased
from Macklin Biochemical Co. Ltd. (Shanghai, China), and the
above three dyes were used without further purication. Their
structures are shown in Fig. 1.
Synthesis of triptycene-based porous polymer (TPP)
TPP was synthesized according to previous work.11 As shown in
Scheme 1a, triptycene monomer (1.1054 g, 4.35 mmol) was
dissolved in 20 mL of anhydrous DCE. To this solution, form-
aldehyde dimethyl acetal (FDA, 17.4 mmol) and anhydrous
FeCl3 (17.4 mmol, 2.82 g) were added in a nitrogen environ-
ment. The reaction mixture was magnetically stirred and heated
to 80 ꢁC for 24 h. Aer cooling to room temperature, the crude
product was collected via ltration and repeatedly washed with
Scheme 1 (a) Simple synthesis of triptycene-based porous organic
polymer and (b) schematic representation of the synthesis of the
methanol until the ltrate was nearly colourless. The product sulfonic functionalized polymer TPP-SO3H.
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was characterized using a Nova NanoS 450 eld emission either 0.01 M HCl or 0.01 M NaOH solution. Then, 2.5 mg of the
scanning electron microscope (FE-SEM). High-resolution porous polymer TPP-SO3H were added tꢀo15 mL of 300 mg Lꢀ1
transmission electron microscope (HRTEM) images were MEB, 200 mg Lꢀ1 BF, and 800 mg L
recorded on a JEM-2100 transmission electron microscope. The different pH values at room temperature.
powder samples were treated in ethanol using ultrasound for
MG solutions with
20 min and then dropped and dried on carbon-coated copper
Desorption experiments and reusability of TPP-SO3H
grids. The powder X-ray diffraction (XRD) data were collected on
a D/Max2550 VB/PC diffractometer (40 kV, 200 mA) using a Cu
Ka as the radiation. The N2 adsorption–desorption isotherms
were measured at 77 K using a volumetric adsorption analyser
(Micromeritics ASAP 2020). Before taking the adsorption
The adsorption/desorption cycles were conducted as follows.
Each adsorption experiment consisted of 50 mg of TPP-SO3H
with 100 mL of 100 mg Lꢀ1 MEB, 100 mg Lꢀ1 BF, and
300 mg Lꢀ1 MG solutions for 12 h. Aer the adsorption exper-
iments, the regeneration adsorbent was then ltered and
separated from the solution and washed with 0.1 M HCl/ethanol
(10 : 90, v/v), and the regeneration adsorbent was dried at 80 ꢁC
under vacuum. This cycle was repeated ve times.
ꢁ
measurements, the samples were degassed at 100 C for 24 h.
The specic surface areas were calculated using the Brunauer–
Emmett–Teller (BET) and Langmuir methods. The total volume
was calculated at p/p0 ¼ 0.99. The micropore volume was
derived from the t-plot method. The UV-visible (UV-vis) spectra
of the dye solutions were recorded using a UV-2550 spectro-
photometer. The X-ray photoelectron spectroscopy (XPS)
spectra were obtained with a Thermo ESCALAB 250XI multi-
functional imaging electron spectrometer using 1486.6 eV Al-Ka
radiation. The thermogravimetric analysis (TGA) was performed
using a NetzschSta 449c thermal analyser system at a heating
Uptake calculations
(1) The calculation of the adsorption capacities and removal
percentages can be expressed as:25
ðC0 ꢀ CtÞ ꢂ V
ꢁ
qt ¼
(1)
(2)
(3)
rate of 10 C min in a N2 atmosphere. The Fourier Transform
m
Infrared (FTIR) spectra were determined using a Nicolet iS10
FTIR spectrometer using the KBr pellet technique.
À
Á
C0 ꢀ Ceq ꢂ V
qeq
¼
m
Adsorption test
Organic dyes adsorption24
ðC0 ꢀ CeÞ
R% ¼
ꢂ 100%
C0
where qt (mg gꢀ1), R, and qeq (mg gꢀ1) represent the uptake
amount at a time t (min), removal percentages of the dyes and
Three organic pollutants, MEB, BF, and MG, were used to study
the adsorption performance of TPP-SO3H. In a typical MEB
adsorption experiment, 2.5 mg of TPP-SO3H were added to 5 mL
of MEB aqueous solution while being mechanically shaken at
room temperature. Aer adsorption for 24 h, the mixture was
ltered with a 0.22 mm Millipore hydrophobic PTFE membrane,
and the ltrate was measured using UV-vis spectroscopy. The
best adsorption wavelengths of the MEB, BF, and MG are
664 nm, 543 nm, and 618 nm, respectively. The initial MEB
concentration varied from 10 to 1200 mg Lꢀ1. Adsorption of the
other two dyes on TPP-SO3H was performed using solution
concentrations of 10 to 2000 mg Lꢀ1 for BF, and 10 to
3000 mg Lꢀ1 for MG. The MEB, BF, and MG solution concen-
trations from 1 to 1000 mg Lꢀ1 were employed for the adsorp-
tion study on TPP.
the equilibrium state, respectively, C0, Ct, and Ceq (mg Lꢀ1
)
denote the concentrations of the dye solution at the initial, time
t (min) and equilibrium state, and V (L) and m (g) indicate the
volume of the dye solution and mass of the adsorbent.
(2) Isotherm calculations.
The adsorption isotherms were tted using the Langmuir
and Freundlich models, respectively. The linear form of the
Langmuir isotherm and Freundlich isotherm models can be
expressed as:26,27
Ceq
qeq
1
Ceq
¼
þ
(4)
KLqmax qmax
1
ln qeq ¼ ln KF þ ln Ceq
(5)
Organic dye adsorption kinetics. A volume of 2.5 mg of
porous polymer TPP-SO3H was added to 5 mL of MEB, BF, and
nF
where qeq (mg gꢀ1) is the equilibrium adsorption capacity, Ceq
(mg Lꢀ1) is the equilibrium dye concentration, qmax (mg gꢀ1) is
maximum adsorption capacity, and KL is the Langmuir
constant. Therefore, the maximum adsorption amount qmax can
MG solution with initial concentrations of 100 mg Lꢀ1
,
100 mg Lꢀ1, and 300 mg Lꢀ1 under mechanical shaking at room
temperature. Aer adsorption for a predetermined time (from
1 min to 540 min), the mixture was ltered with a 0.22 mm
Millipore hydrophobic PTFE membrane, and the ltrate was
measured using UV-vis spectroscopy.
be obtained from the reciprocal of the slope of the plot of Ceq
/
qeq versus Ceq. In addition, KF is the Freundlich constant (mg
gꢀ1) and 1/nF is the heterogeneity factor.
(3) Calculation of the adsorption kinetics.
The kinetic parameters were t using the pseudo-rst-order
pH effect
The effect of pH on pollutant extraction was studied using and pseudo-second-order models, which can be described
different pH conditions, where the pH was adjusted by adding as:28,29
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the results conrmed the amorphous nature of TPP-SO3H.
Thermal gravimetric analysis (TGA) shows that the TPP-SO3H
was relatively stable (Fig. S2, ESI†). The initial small weight loss
below 100 ꢁC was mainly caused by the release of entrapped
solvent or some small gaseous molecules in the micropores.
The polymer TPP-SO3H was stable to approximately 160 ꢁC due
to the decomposition of the functionalization sulfonic acid
group. All of the obtained polymer TPP-SO3H was insoluble in
dilute solutions of NaOH and HCl, as well as common organic
solvents, such as dichloromethane, acetone, methanol, THF
and DMF, indicating the good chemical stability of the polymer.
We note that the high physicochemical stability of the polymer
is good enough for potential applications in organic dyes
capture.
Nitrogen adsorption–desorption isotherms of the TPP
(Fig. 2c) and TPP-SO3H (Fig. 2d) were collected at 77 K. Notably,
the polymer TPP-SO3H exhibited almost ideal type-I isotherms
and a large desorption hysteresis disappeared aer the modi-
cation of the TPP. The Brunauer–Emmett–Teller (BET) surface
areas obtained from the experimental data were 1220.1 m2 gꢀ1
and 573.3 m2 gꢀ1 for TPP and TPP-SO3H, respectively. As ex-
pected, the surface area decreased upon functionalization
modication. The pore size distributions (PSD) of the TPP (the
inset of Fig. 2c) and TPP-SO3H (the inset of Fig. 2d) were derived
using the entire range of the N2 adsorption isotherms measured
at 77 K. Along with the decrease in surface area, the pore size
became progressively smaller with aromatic sulfonation. The
detailed porous properties of the polymers are summarized in
Table S1.†
ln(qmax ꢀ qt) ¼ ln qeq + K1t
(6)
(7)
t
1
t
¼
þ
2
qt
K2qeq
qeq
where K1 and K2 are the specic rate constants for the pseudo-
rst-order kinetic and pseudo-second-order kinetic models,
respectively. For the rst-order kinetic model, k1 can be calcu-
lated from the intercept, and qeq could be calculated from the
slope. For the second-order kinetic model, the equilibrium
adsorption amount could be calculated from the slope, and k2
could be calculated from the intercept and qeq
.
Quantum calculations
All of the molecules were fully optimized using the B3LYP30,31
method combined with the 6-311G(d)32 basis set for all the
atoms involved. During the calculations, the same theoretical
method and basis set were used for the frequency analysis to
conrm that all the structures are real minimums on the
potential energy surface. In addition, no symmetry constraint
was performed. To simplify the complicated calculation
process, we only selected a part of the TPP-SO3H for calculation.
All the calculations were performed with the Gaussian 09 (ref.
33) soware. Additionally, the electrostatic potential surface
(ESP) and non-covalent interaction (NCI) analysis were per-
formed by the Multiwfn programme and visualized using the
VMD soware.
Results and discussion
The functional groups on the surface of TPP-SO3H were
studied using FTIR spectrophotometry over a range from range
of 4000 to 500 cmꢀ1 (Fig. S3, ESI†). The FTIR spectra of the
polymer TPP underwent signicant changes aer sulfonation
modication. The characteristic absorption peaks of the
sulfonic acid groups appeared at 1032 cmꢀ1, which are assigned
to the symmetric stretching of the S]O bond as a result of
inducing the SO3H groups into the TPP and an absorption at
610 cmꢀ1, which is due to the bending vibrations of OH groups
hydrogen bonded to SO3H groups.34 In addition, an XPS survey
spectrum of the TPP-SO3H was performed (Fig. S4a, ESI†),
which shows peaks corresponding to C, O, and S. This is
different from the XPS survey spectrum of the TPP, where only
peaks assignable to C and O are observed, suggesting that the
sulfur containing groups were introduced into the TPP through
the sulfonation modication. The presence of sulfur in the TPP-
SO3H could be further demonstrated by the high-resolution S 2p
spectrum (Fig. S4b, ESI†), which exhibits a single peak at
168.3 eV, indicating that the sulfur is in the form of sulfonic
acid.35,36 These results clearly demonstrate that the sulfonic acid
group was successfully modied on the surface of the TPP.
The molecular structure of the TPP-SO3H was further inves-
tigated by 13C NMR (Fig. S5, ESI†). The peaks at 90–120 ppm are
assigned to the carbon atoms in the aromatic systems. The peak
at 134 ppm corresponds to the carbon atoms of the substituted
aromatic ring. Additionally, the peak at 33.84 ppm indicates the
methylene carbon formed by the Friedele–Cras alkylation
reaction. The presences of –OCH2 (49.98 ppm) resonances
Characterization of TPP-SO3H
The morphology and crystalline nature of the synthesized TPP-
SO3H were investigated by FE-SEM, HRTEM, and XRD. As
shown in Fig. 2a, the TPP-SO3H exhibits a cluster morphology of
the submicrometer particles, which is not clearly changed
compared with the morphology of pristine polymer TPP.11 The
HRTEM image (Fig. 2b) shows that the TPP-SO3H possesses
a large amount of amorphous microporosity. In addition, with
a broad band from 10ꢁ to 80ꢁ in the XRD pattern (Fig. S1, ESI†),
Fig. 2 (a) HR-TEM of TPP-SO3H, (b) SEM of TPP-SO3H, (c and d) N2
adsorption–desorption isotherms and pore size distributions (the inset
of (c and d)) of TPP and TPP-SO3H at 77 K.
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indicate secondary reaction channels involving FDA during the –SO3H is strongly acid group with a large degree of ionization
polymerization.37
and is hardly unaffected by changes in the pH of the solution.40
It could be claimed that only negatively charged adsorbent
species exist in the whole examined pH solution range of 2–9 is
Adsorption kinetics of MEB,BF, and MG on TPP-SO3H
ꢀ
stated with a predominant role of SO3 groups. The surface of
The time-dependent adsorption of MEB, MG, and BF on TPP-
SO3H was investigated at initial concentrations of
100 mg Lꢀ1, 100 mg Lꢀ1, and 300 mg Lꢀ1. Fig. 3a shows the
adsorption kinetics curves for the three dyes. The removal
rates were all very rapid during the initial stages of the
adsorption process. Aer a very rapid adsorption, the uptake
rates slowly declined with time and reached equilibrium
values at approximately 10 min for all the three dyes, which
was faster than for some other materials.38,39 The equilibrium
adsorption rates constant(K2) of the MEB, BF, and MG were
0.0026, 0.0149 and 0.0093 g mgꢀ1 minꢀ1, respectively, those
K2 value were larger than those previously reported porous
adsorbents for the three dyes are listed in Table S2.† The high
initial uptake rate and the short adsorption equilibrium time
demonstrated that the surfaces of the polymer TPP-SO3H had
a high density of active sites for dyes adsorption. Hence,
a practical advantage of using the sulfonic acid polymer TPP-
SO3H as an adsorbent would be its ability to remove more
dyes in a considerably shorter adsorption time. However, to
analyse the adsorption kinetics of TPP-SO3H, the adsorption
data were analysed using pseudo-rst-order (Fig. S6, ESI†)
and pseudo-second-order kinetic models (Fig. 3b). The
correlation coefficients obtained by tting the pseudo-rst-
order and pseudo-second-order kinetic models are listed in
Table S3.† From the gures and the table, an extremely high
correlation coefficient (R2 > 0.997) was obtained for the
pseudo-second-order kinetic model, and the calculated dyes
adsorption capacity and experimental values are very close.
This indicates that the rate of adsorption of the TPP-SO3H
adsorbent for the organic dyes MEB, BF, and MG depends on
the available adsorption sites.
TPP-SO3H is negatively charged whereas the dye molecules are
positively charged. Thus, as it was expected taking into account
possibility of electrostatic interactions between the cationic
dyes and the sulfonic groups, the adsorption of MEB, BF, and
MG on TPP-SO3H is pH independent. As seen in Fig. 4, the
removal efficiency of the dye does not obviously change with the
pH range 2.0 to 9.0, and most of the dye wastewater is in this
range. In fact, the acidic dyes wastewater is pre-treated with
alkali before treatment. In addition, literature data report that
pH does not inuence on the dyes adsorption on the strongly
acid cation exchanger.22
Although ion exchange is the most signicant mechanism in
MEB, BF, and MG removal via TPP-SO3H, some extent of pure
physical adsorption may also occur. For example, p–p stacking
interactions between the aromatic rings of the cationic dye and
the aromatics rings of TPP-SO3H can play a role in the adsorp-
tion of MEB, BF and MG. Furthermore, the high affinity of the
dye for the TPP-SO3H may also result from the formation of H-
bonds.
To gain a deeper understanding of the adsorption mecha-
nism of the MEB, BF, and MG dyes on TPP-SO3H, we employed
theoretical quantum calculations to analyse the interactions
between the TPP-SO3H and cationic dyes. The ESP surfaces
(isosurfaces with an electron density ¼ 0.001 au) with the most
negative surface ESPs (Vs,min) or the most positive surface ESPs
(Vs,max) are depicted in Fig. S7.† The ESP surfaces for the MEB,
BF, and MG are shown in blue and have a Vs,max of
83.25 kcal molꢀ1, 96.48 kcal molꢀ1, and 74.08 kcal molꢀ1
,
respectively. In contrast, the ESP of the TPP-SO3H is negative
and shown in red, with a Vs,min of ꢀ37.35 kcal molꢀ1, suggesting
that it is easy to adsorb cations. The ESP analysis conrms that
TPP-SO3H will favourably adsorb MEB, BF, and MG via elec-
trostatic interactions.
Effect of pH on the adsorption of MEB, BF, and MG on TPP-
SO3H
The adsorption of MEB, BF, and MG dyes from aqueous solu-
tion on TPP-SO3H is primarily inuenced by the surface charge
of the adsorbent and the degree of ionization of the adsorptive
sites. The effect of the pH on the adsorption of MEB, BF, and
MG was studied in the pH range of 2.0 to 9.0. As is well-known,
Fig. 3 (a) MEB, BF, and MG adsorption on the polymer TPP-SO3H at Fig. 4 Effect of pH on the adsorption of MEB (black), BF (red), and MG
different times. (b) Plots of the pseudo-second-order kinetics for the (blue) (concentration MEB: 300 mg Lꢀ1, BF concentration: 200 mg Lꢀ1
,
adsorption of MEB, BF and MG (MEB and BF almost coincide).
and MG concentration: 800 mg Lꢀ1).
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The optimized structures of the complexes are shown in
RSC Advances
(Fig. S8, ESI†). It is known that if the distance between two
atoms is less than the sum of the van der Waals radii of them
˚
˚
(H: 1.2 A, O: 1.52 A), then the two atoms are bonded to each
˚
other. We show all the O–H bonds (less than 2.72 A) with red
dashed lines. These O/H–C bonds conform to the character-
istics of hydrogen bonding. In addition, we further conrmed
the existence of hydrogen bonds by NCI, where blue represents
a strong attraction interaction, green represents a weak inter-
action, and red represents a repulsive interaction. As shown in
Fig. 5, there is a distinct dark green isosurface between the O
and H atoms (indicated by the red circle). Thus, there is a typical
hydrogen bond between the polymer and the dye, which
enhances the interaction between the polymer and the dye.
Fig. 6 (a and b) TPP-SO3H adsorption isotherms for the adsorption of
MEB, BF and MG and the corresponding Langmuir; (c and d) TPP
adsorption isotherms for the adsorption of MEB, BF and MG and the
corresponding Langmuir.
Adsorption isotherms of the MEB, BF and MG on TPP and
TPP-SO3H
Fig. 6a and c show plots of C0 versus qeq for dye adsorption at
room temperature. The adsorption amounts of MEB, BF, and
MG initially increase sharply with the dye concentration and
begin to stabilize at high dye concentrations. The adsorption
capacities of TPP-SO3H are obviously higher than pristine TPP,
showing that the sulfonic acid group has a positive effect on the
adsorption isotherm. To quantitatively analyse the adsorption
isotherm data, the Langmuir and Freundlich isotherm models
((eqn (4) and (5)) were used to describe the adsorption progress
and to investigate the mechanisms of adsorption. The inspec-
tion of the linear Langmuir(Fig. 6b and d) and Freundlich
isotherm plots (Fig. S9, ESI†) suggests that the Langmuir model
allows a much better analysis of data than the Freundlich
model. The Langmuir parameters, as well as the regression
coefficients (R2) are listed in Table S4.† The high correlation
coefficients (R2) indicate that the Langmuir isotherm can
explain the adsorption process. The maximum adsorption
capacities of the MEB, BF and MG calculated by the Langmuir
could be desorbed. Considering that the dye binding with the
TPP-SO3H may not be only via electrostatic interaction but also
by other binding forces, such as hydrogen bonding, ethanol was
also chosen for breaking these nonspecic binding interac-
tions. Regeneration of the MEB, BF and MG-loaded TPP-SO3H
by ethanol is completely unaffected, conrming that the strong
electrostatic attraction between the dyes and the TPP-SO3H is
the predominant mechanism of adsorption. However, using an
ethanol-water mixture with 0.1 M HCl shows a signicant
improvement in dye desorption performance, indicating that
the dye is bound to the TPP-SO3H through more than one
binding force, which has been proved by theoretical quantum
calculations, the previous literature49 also demonstrated the
existence of hydrogen bonds by similar desorption experiments.
As shown in Fig. 7, when using 0.1 M HCl/ethanol (10 : 90, v/v)
as the eluent, the adsorption capacity of the TPP-SO3H adsor-
bent does not signicantly change aer ve times reuse for the
MEB, BF and MG. The results indicate that the TPP-SO3H has
a remarkable potential for dye removal aer ve adsorption–
desorption cycles.
model were 983.4 mg gꢀ1, 588.2 mg gꢀ1, and 1947.0 mg gꢀ1
,
respectively. The adsorption capacities of the TPP-SO3H with
the previously reported porous adsorbents for the three dyes are
listed in Table 1. The TPP-SO3H exhibits a competitive adsorp-
tion capacity with respect to the other reported porous
adsorbents.
Table 1 Comparison of MEB, BF and MG adsorption among different
adsorbents
Desorption and regeneration of TPP-SO3H
qmax(mg gꢀ1) of different dyes
The regeneration and reuse of adsorbents is an important factor
in commercial viability. First, the most common methods for
the dye desorption, i.e., solutions of 0.1 M HCl and 0.1 M NaOH,
were used as the desorption solution. Unfortunately, no dyes
Adsorbents
MEB
BF
MG
Ref.
MOF-235
187
—
—
41
MOF-10-SO3H
MIL-100(Fe)
Modied biomass
Breadnut core
CEN
Magnetic NH2-MIL-101
Fe3O4/PCC MNPs
AGS
351
—
548.1
369
110.8
—
—
—
594
—
—
—
—
—
596
485
—
—
77.6
274
66.84
—
23
42
43
44
45
46
47
48
60.06
212
TPP
TPP-SO3H
175.50
981.81
188.34
586.86
1095.29
1942.50
This work
This work
Fig. 5 NCI isosurfaces of the three complexes.
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