Construction of bimodal silsesquioxane-based porous materials from triphenylphosphine or triphenylphosphine oxide and their size-selective absorption for dye molecules

Article abstract of DOI:10.1039/c6ra02963a

Two novel hybrid porous polymers were easily prepared by the Friedel-Crafts reaction of octavinylsilsesquioxane with triphenylphosphine and triphenylphosphine oxide, respectively. They possessed unique bimodal pores with uniform micropores and mesopores centered at 1.5 nm and 3.7 nm, respectively, high surface areas up to 1105 m² g^-1, high thermal stability and an excellent size-selective adsorption for dyes. These hybrid porous polymers are very promising in dye separation, water purification and treatment.

Full text of DOI:10.1039/c6ra02963a

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Construction of bimodal silsesquioxane-based
porous materials from triphenylphosphine or
triphenylphosphine oxide and their size-selective
absorption for dye molecules†
Cite this: RSC Adv., 2016, 6, 37731
a
ab
*
Rong Shen and Hongzhi Liu
Two novel hybrid porous polymers were easily prepared by the Friedel–Crafts reaction of
octavinylsilsesquioxane with triphenylphosphine and triphenylphosphine oxide, respectively. They
possessed unique bimodal pores with uniform micropores and mesopores centered at 1.5 nm and
Received 1st February 2016
Accepted 8th April 2016
3.7 nm, respectively, high surface areas up to 1105 m2 ꢀ1, high thermal stability and an excellent size-
g
DOI: 10.1039/c6ra02963a
selective adsorption for dyes. These hybrid porous polymers are very promising in dye separation, water
www.rsc.org/advances
purification and treatment.
triphenylphosphine oxide (denoted as TPPO), are usually rigid
trigonal pyramidal molecules, and possess different steric
Introduction
crowding around the phosphorus atom, tended to take a more
tetrahedral geometry (Scheme 1), which make them become two
ideal building blocks for constructing functional porous poly-
mers. Some phosphorous-containing porous polymers have
been prepared by different methods, such as the Friedel–Cras
reaction,41 the Yamamoto reaction,42 and the Sonogashira–
Hagihara coupling reaction.43 From a practical point of view, the
use of commercial TPP or TPPO is highly desirable to prepare
some novel cost-effective phosphorus-containing porous poly-
mers in a large-scale via the Friedel–Cras reaction.
In this paper, triphenylphosphine (TPP) and triphenylphos-
phine oxide (TPPO) were chosen to react with cubic octavi-
nylsilsesquioxane (OVS) to prepare two novel parallel series of
hybrid phosphorus-containing porous polymers (denoted as
HP-TPPs and HP-TPPOs) via the Friedel–Cras reaction,
respectively. These hybrid porous polymers possessed high
surface areas, unique bimodal pores with uniform micropores
and mesopores centered at 1.5 nm and 3.7 nm, respectively, and
an excellent size-selective adsorption for dyes. They displayed
an outstanding adsorption ability for rhodamine B (RB) with
maximum equilibrium adsorption capacities of 828.6 mg gꢀ1
Porous materials have attracted much attention during the last
few decades because they show great potential applications in
the elds of gas storage and separation,1–4 catalysis,5,6 opto-
electronics,7,8 chemosensors,9–11 drug delivery12–15 and environ-
ment.16–18 Recently, porous materials formed by covalent
bonded linkage are of great interest for their characteristic
advantages: large specic surface areas, low skeletal density,
high thermal and chemical stability, etc.19–21 Rational selection
of suitable rigid building blocks with different geometries and
advantageous functionalities will be helpful in the construction
of porous materials with novel topology structures and
properties.
Cubic octavinylsilsesquioxane (OVS) (Scheme 1), a versatile
precursor, has been extensively explored as a starting material
for nanohybrid synthesis.22–29 Recently, many hybrid porous
polymers were prepared via the topology combination from
cubic OVS with planar molecules,30 tetrahedral molecules,31,32
cubic molecules33–36 and polymer.37 By far, there was no report
on hybrid porous polymers by the combination of trigonal
pyramidal triphenylphosphine with cubic OVS.
Triphenylphosphine (denoted as TPP) is an important ligand
for noble metals, and widely used in the cross-coupling reac-
tions in modern synthesis chemistry.38–40 TPP and its derivative,
aKey Laboratory of Special Functional Aggregated Materials, Ministry of Education,
School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100,
P. R. China. E-mail: liuhongzhi@sdu.edu.cn; Fax: +86 531 88364691; Tel: +86 531
88364691
bState Key Laboratory of Molecular Engineering of Polymers, Fudan University,
Shanghai 200433, P. R. China
Scheme 1 Structure of octavinylsilsesquioxane (OVS), triphenylphos-
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra02963a
phine (TPP) and triphenylphosphine oxide (TPPO).
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 37731–37739 | 37731

View Article Online
RSC Advances
Paper
and could rapidly remove more than 90% RB within 3 minutes V1.04. Before measurement, the samples were degassed at 150
when the initial concentration of the RB solution was 50 ppm. ꢁC under vacuum for about 15 h. UV-vis absorption spectra of
organic dyes were collected on an a TU-1901 double beam UV-
vis spectrophotometer.
Experimental section
Materials
Synthesis of OVS
OVS was synthesized from the previous reports.44,45 675 mL of
acetone, 66.8 (0.45 mol) g of vinyltrimethoxysilane, 112.5 mL of
concentrated hydrochloric acid and 129.6 mL of deionized
water were charged into a 1 L ask equipped with a magnetic
stirrer, reuxed at 40 ꢁC for 48 h. A brown mixture solution was
obtained. The white power could be obtained by ltering,
washing with ethanol and recrystallizing from the mixed solu-
tions of dichloromethane and acetone to afford 11.9 g of OVS
with 33% yield. FTIR (KBr, cmꢀ1): 3043 (n C–H), 1605 (n C]C),
1410, 1276 (d C–H), 1112, 463 (n Si–O–Si), 584 (d Si–O–Si), 778
(n Si–C) (Fig. S1†); 1H NMR (CDCl3): d 5.89–6.16 (m, H2C]CH–,
24H) (Fig. S2†).
Unless otherwise noted, all reagents were obtained from
commercial suppliers and used without further purication.
Octavinylsilsesquioxane (OVS) was synthesized from the
previous reports.44,45 Triphenylphosphine oxide (TPPO) was
prepared according to the previous report.46 1,2-Dichloroethane
was dried by distillation over calcium hydride under reux prior
to use.
Methods
FTIR spectra were measured within a 4000 cmꢀ1 to 400 cmꢀ1
regions on a Bruker TENSOR-27 infrared spectrophotometer
(KBr pellet). Solution-state 1H NMR spectra were measured with
a Bruker Avance 300 spectrometer in CDCl3 with tetrame-
thylsilane as the internal standard. Solid-state 13C cross polar-
Synthesis of TPPO
ization (CP) magic angle spinning (MAS) NMR, 29Si MAS NMR TPPO was prepared according to the previous report.46 2.65 g
and 31P high power decoupling (HPDEC) MAS NMR spectra (10.1 mmol) triphenylphosphine (TPP), 50 mL tetrahydrofuran
were carried out on a Bruker Avance-500 NMR spectrometer (THF) and 30% hydrogen peroxide (30 mL) were charged into
operating under a magnetic eld strength of 9.4 T. A chem- a 150 mL ask with a magnetic stirrer and stirred over night at
agnetics of 5 mm triple-resonance MAS probe was used to room temperature. The mixture was evaporated and puried to
acquire 13C, 29Si and 31P NMR spectra. 29Si MAS NMR spectra give a white solid (2.75 g). Yield: 98%. FTIR (KBr, cmꢀ1): 3070,
with high power proton decoupling were recorded using a p/2 3027 (n C–H), 1581 (n C]C), 1438, 1263 (d C–H), 1189, 1116
pulse length of 5 ms, a recycle delay of 120 s and a spinning rate (n P–O), 724 (n P–C) (Fig. S3†); 1H NMR (CDCl3): d 7.70–7.64 (m,
of 5 kHz. The 13C chemical shis were referenced externally via 6H), 7.58–7.52 (m, 3H), 7.49–7.43 (m, 6H) (Fig. S4†).
the resonance of tetramethylsilane (TMS) of 0 ppm. The 31P
chemical shis were referenced externally via the resonance of
NH4H2PO4 at an isotropic chemical shi of 1.058 ppm.
Elemental analysis was performed by using an Elementarvario
EL III elemental analyzer. Nitrogen sorption isotherm
measurements were performed by using a Micro Meritics
surface area and pore size analyzer. The samples were degassed
for 12 h at 150 ꢁC prior to measurement. A sample of ca. 100 mg
and a UHP-grade nitrogen (99.999%) gas source were chosen in
the nitrogen sorption measurements at 77 K and collected on
a Quantachrome Quadrasorb apparatus. BET surface areas were
evaluated over a P/P0 range from 0.02 to 0.20. Nonlocal density
functional theory (NL-DFT) pore size distributions were
conrmed using the carbon/slit-cylindrical pore mode of the
Quadrawin soware. Thermal gravimetric analysis (TGA) was
conducted on a Mettler-Toledo TGA/DSC system under a N2
atmosphere at a heating rate of 10 ꢁC minꢀ1 from room
temperature to 800 ꢁC. Powder X-ray diffraction (PXRD) were
measured with a Rigaku D/MAX 2550 diffractometer with Cu-Ka
radiation, 40 kV, 200 mA with a 2q range of 5–80ꢁ (scanning rate
Synthesis of hybrid porous polymers
A typical procedure for HP-TPP-1 was given in detail as follows.
OVS (0.95 g, 1.5 mmol), TPP (0.35 g, 1.3 mmol), anhydrous
aluminum chloride (0.40 g, 3.0 mmol) and 1,2-dichloroethane
(40 mL) were charged in an oven-dried ask. The mixture was
stirred at room temperature for 0.5 h and then under reux for
24 h. Aer cooling to room temperature, the mixture was
ltered and washed with THF, methanol, acetone, chloroform,
sequentially, in order to remove any unreacted monomers or
residuary catalyst. The product was further puried under the
Soxhlet extractor with THF for 24 h and methanol for 24 h,
respectively, and then dried in vacuum at 70 ꢁC for 48 h to
obtain a yellow power (0.89 g, 69%). HP-TPP-2, HP-TPP-3, HP-
TPPO-1, HP-TPPO-2 and HP-TPPO-3 were synthesized as same
as the procedure of HP-TPP-1. Elemental analysis of HP-TPPs
and HP-TPPOs were shown in Table S1.†
Dye adsorption experiments
of 10ꢁ minꢀ1) at room temperature. The eld-emission scan- The batch mode adsorption studies were done by taking dye
ning electron microscopy (FE-SEM) experiments were recorded molecules as probes, including rhodamine B (RB), methylene
by using a HITACHI S4800 spectrometer. The high-resolution blue (MB), and methyl orange (MO) (Scheme 2). Dye solutions
transmission electron microscopy (HR-TEM) experiments were were prepared by deionized water with known amounts of RB,
characterized by using a JEM 2100 electron microscope (JEOL, MB and MO. The adsorption isotherm was obtained by the
Japan) with an acceleration voltage of 200 kV. CO2 adsorption addition of 10 mg HP-TPP-3 or HP-TPPO-3 into 30 mL dye
capacity was measured at 273.0 K at 1.0 bar with a TriStar II 3020 solutions of different initial concentrations. The mixture was
37732 | RSC Adv., 2016, 6, 37731–37739
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Scheme 2 Structure of rhodamine B (RB), methylene blue (MB),
methyl orange (MO).
stirred for several hours (typically 24 h) at room temperature to
reach adsorption equilibrium. Subsequently, the adsorbents
were removed by ltering. And the collected solutions were
reserved to be analyzed by UV-vis spectrophotometer. The
wavelengths for the detection are 554, 665, and 466 nm for RB,
MB, and MO, respectively.
Fig. 1 FTIR spectra of HP-TPPOs, TPPO and OVS.
The RB adsorption rate test was done by adding 10 mg HP-
TPP-3 or HP-TPPO-3 into 15 mL aqueous RB solution of same
initial concentration (50 ppm). The mixture was stirred and
remained in different time at room temperature. The next
procedure was the same as the batch mode.
vibration for OVS at ca. 1111 cmꢀ1 (Fig. 1), those for the porous
networks became broader, indicating the presence of cross-
linking networks in the hybrid porous polymers.30,32,33 The
symmetric stretching vibrations of P]O at 1187 cmꢀ1 (Fig. 1)
was not observed in HP-TPPOs, which could be attributed to the
overlap of P]O and Si–O–Si. The FTIR spectra of HP-TPPs were
shown in Fig. S5.†
Results and discussion
Synthesis and characterization of hybrid porous polymers
Solid-state 13C CP/MAS, 29Si MAS and 31P HPDEC/MAS NMR
were also used to further conrm the structures of these hybrid
crosslinked porous polymers. Considering their similar spectra,
HP-TPPO-3 was selected as a representative sample to analyze in
HP-TPPO series. As shown in Fig. 2, the signals of the carbon
atoms of the bridging phenyl units and of the unreacted double
bonds from TPPO and OVS were observed in the range of 127–
151 ppm. The resonance peaks at 19.6 ppm and 23.4 ppm were
mainly ascribed to the methylene carbon atoms (Si–CH2–CH2–
Ar–P]O and Si–CH2–CH2–Ar–P]O), which conrmed the
formation of single C–C bonds derived from the vinyl units aer
the Friedel–Cras reaction.30,32 The signal at d ¼ 46 ppm might
be assigned to the carbon atom from methanol. Similar result
was also observed in the solid-state 13C CP/MAS NMR spectrum
of HP-TPP-3 (Fig. S6†).
Octavinylsilsesquioxane (OVS) reacted with TPP and TPPO to
prepare two novel parallel series of hybrid porous polymers, i.e.
HP-TPPs and HP-TPPOs, respectively, as shown in Scheme 3.
The resulting products were yellow powders, had a low density,
and were not soluble in any common organic solvents. These
hybrid porous polymers were rst characterized by FTIR spec-
troscopy. We took HP-TPPOs as samples to conrm the success
of the Friedel–Cras reaction. Compared with the FTIR pattern
of OVS, the intensities of the peaks at about 3023, 1609, 1412,
and 1277 cmꢀ1 decreased to different degrees (Fig. 1), which
indicated that the cross-linking reaction occurred in varying
degrees in HP-TPPOs. The decrease of C]C (1609 cmꢀ1
)
vibrations and unsaturation C–H (3023 cmꢀ1) vibrations of the
OVS demonstrated the successful synthesis of the hybrid porous
polymers. And the band of approximate 2963 cmꢀ1 conrmed
the presence of methylene groups (Si–CH2–) in HP-TPPOs,
which also indicated that the Friedel–Cras reaction was
successful. Compared with the typical Si–O–Si stretching
Scheme 3 Synthesis of hybrid porous polymers.
Fig. 2 Solid-state 13C CP/MAS NMR spectrum of HP-TPPO-3.
RSC Adv., 2016, 6, 37731–37739 | 37733
This journal is © The Royal Society of Chemistry 2016

View Article Online
RSC Advances
Paper
Fig. 3 showed the solid-state 29Si MAS NMR spectrum of HP- shape of nitrogen adsorption isotherms (Fig. S9†), a sharp
TPPO-3. There were two main signals at ca. ꢀ68.4 and ꢀ80.2 uptake at low relative pressures and a gradually increasing
ppm in Fig. 3, which could be assigned to the silicon atoms of uptake at higher relative pressures with a hysteresis, indicating
the T3 units (Tn: CSi(OSi)n(OH)3ꢀn) from the Si–CH2–CH2– units that the synthesized hybrid porous polymers contained both
formed aer the Friedel–Cras reaction and the unreacted micropores and mesopores.32,33 The detailed porosity data of
Si–CH]CH2 units, respectively. The signal of Si–CH2–CH2– these hybrid porous polymers were compiled in Table 1. The
units further conrmed the success of the Friedel–Cras reac- SBET of HP-TPP-1, HP-TPP-2, HP-TPP-3, HP-TPPO-1, HP-TPPO-2
tion. Similar phenomenon was also observed in the solid-state and HP-TPPO-3 was calculated as 966, 1018, 1105, 887, 920 and
29Si MAS NMR spectrum of HP-TPP-3 (Fig. S7†).
976 m2 gꢀ1, respectively. The respective micropore surface area
Fig. 4 showed the solid-state 31P HPDEC/MAS NMR spectrum (Smicro) was calculated to be 375, 277, 260, 189, 172 and 78 m2
of HP-TPPO-3. A single broad peak in the range of 50–100 ppm gꢀ1 by using the t-plot method. With the increasing mole ratio
was assigned to phosphorus in phosphine oxide units in HP- of OVS to TPP or TPPO, the SBET of the hybrid porous polymers
TPPO-3. The solid-state 31P HPDEC/MAS NMR spectrum of increased and approached a maximum SBET of 1015 and 976 m2
HP-TPP-3 (Fig. S8†) exhibited two main signals. The signal at gꢀ1 when the molar ratio was 1.5 : 0.8 (i.e. HP-TPP-3 and HP-
22.6 ppm corresponded to phosphorus in triphenylphosphine TPPO-3), respectively; however, the Smicro of the hybrid poly-
units in HP-TPP-3; another signal at 65.1 ppm was assigned to mers decreased.
phosphorus in phosphine oxide units in HP-TPP-3, which
originated from aerobic oxidation of PIII.41,47
Pore-size distributions (PSD) of the hybrid porous polymers
were evaluated from the nonlocal density functional theory (NL-
The Brunauer–Emmet–Teller (BET) specic surface area DFT). The results were in accordance with the patterns of the N2
(SBET) and pore structures of hybrid porous polymers were sorption isotherms and suggested the presence of micropores
characterized by nitrogen adsorption and desorption isotherms and mesopores within the hybrid porous polymers. As shown in
experiments at 77 K. All of the samples showed the type IV Fig. 5, the polymers showed similar PSD curves with unique
bimodal pores, which indicated the uniformity of micro-
mesopores in the networks. All the samples showed uniform
micropores with an average diameter located at around 1.5 nm
and uniform mesopores with an average diameter centered at
about 3.7 nm. And the ratio of the micropore volume (Vmicro) to
Vtotal for HP-TPP-1 to HP-TPPO-3 was 0.28, 0.16, 0.13, 0.14, 0.11
and 0.03, respectively (Table 1). According to the IUPAC classi-
cation, these hybrid porous polymers could be regarded as
mesoporous polymers because of the low Vmicro/Vtotal ratio.
It was interesting that SBET and Vtotal of the hybrid porous
polymers increased monotonically with the increasing molar
ratio of OVS to TPP or TPPO; while Smicro, Vmicro and Vmicro/Vtotal
decreased. The increasing molar ratio of OVS to TPP or TPPO
meant the increasing reactive sites of the phenyl groups in the
TPP or TPPO and the increasing locally crosslinked density,
which favored mesopores.32 Different from previous
phosphorus-containing microporous polymers,42,43 two kind of
novel hybrid polymers with unique bimodal pores, i.e. uniform
micropores and mesopores centered at 1.5 nm and 3.7 nm,
Fig. 3 Solid-state 29Si MAS NMR spectrum of HP-TPPO-3 (‘*’ meant
satellite peaks).
respectively, were easily prepared through the topology combi-
nation of TPP or TPPO with OVS via the Friedel–Cras reaction.
Thermal stability and morphology
TGA was used to evaluate the thermal stability of the hybrid
porous polymers. These porous polymers possessed good
thermal stability and exhibited high thermal decomposition
temperature. The decomposition temperatures (Td at 5 wt%) of
HP-TPPOs and HP-TPPs were above 500 ꢁC (Fig. 6), which were
signicantly higher than those of OVS, TPP and TPPO. This
result could be predominantly ascribed to the formation of
highly crosslinked network aer the Friedel–Cras reaction;30,33
in addition, the inorganic silica-like cages and phosphorus
elements containing in the hybrid polymers also contributed to
Fig. 4 Solid-state 31P HPDEC/MAS NMR spectrum of HP-TPPO-3.
37734 | RSC Adv., 2016, 6, 37731–37739
the thermal staibility.32,37,48 The crystallographic order of these
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Table 1 Porosity data of HP-TPPs and HP-TPPOs
Sample
Molar ratio of OVS to TPP/TPPO
SBET/m2 gꢀ1
Smicro/m2 gꢀ1
Vtotal/cm3 gꢀ1
Vmicro/cm3 gꢀ1
Vmicro/Vtotal
HP-TPP-1
HP-TPP-2
HP-TPP-3
HP-TPPO-1
HP-TPPO-2
HP-TPPO-3
1.5 : 1.3
1.5 : 1.0
1.5 : 0.8
1.5 : 1.3
1.5 : 1.0
1.5 : 0.8
966
1018
1105
887
920
976
375
277
260
189
172
78
0.67
0.75
0.82
0.58
0.66
0.72
0.18
0.12
0.11
0.08
0.07
0.02
0.28
0.16
0.13
0.14
0.11
0.03
from 500 nm to several micrometers.30,32,33 The worm-like
texture showed in translucent HR-TEM images (Fig. S12†)
indicated a porous and not dense structure of the materials with
relatively uniform pore diameters but no evidence of long-range
ordering. The results were consistent with other OVS-based
porous materials.30–33
CO2 storage of HP-TPP-3 and HP-TPPO-3
Gas storage is one of the most important potential applications
for porous materials,49,50 especially in storing CO2. HP-TPP-3
and HP-TPPO-3 possessed the same molar content of phos-
phorus and the highest SBET in HP-TPPs and HP-TPPOs,
respectively; therefore, they were selected to compare their
CO2 capture properties. The CO2 capture capacities for HP-TPP-
3 and HP-TPPO-3 were 3.97 wt% (0.90 mmol gꢀ1) and 4.63 wt%
(1.05 mmol gꢀ1) at 273.0 K/101 kPa, respectively (Fig. 7). The
result showed that the introduction of P]O bond into hybrid
network indeed improved CO2 adsorption, agreeing with
previous reports.42,43
Dye adsorption of HP-TPP-3 and HP-TPPO-3
Fig. 5 NL-DFT pore-size distributions of HP-TPPs and HP-TPPOs.
Water contamination remains a serious environmental and
public problem, especially by toxic organic dyes. Rapid and
convenient removal of organic dyes from wastewater by various
techniques has been studied in the past, among which
adsorption is the simplest and widely adopted technology.51,52
The same reason with CO2 capture, HP-TPP-3 and HP-TPPO-3
Fig. 6 (a) TGA curves of HP-TPPs, OVS and TPP in N2; (b) TGA curves
of HP-TPPOs, OVS and TPPO in N2.
hybrid porous polymers was investigated by powder X-ray
diffraction (PXRD) analysis. Although OVS, TPP and TPPO
were highly crystalline, the resulted hybrid porous polymers HP-
TPP-3 and HP-TPPO-3 were amorphous and showed a broad
diffraction peak at 2q z 22ꢁ (Fig. S10†), which were evidently
associated with the Si–O–Si linkages.32,33 The particle size and
morphology could be observed by FE-SEM (Fig. S11†). HP-TPPO-
3 was selected as a representative sample to analyze. The sample
aggregated into interlinking irregular shapes looked like cloud
Fig. 7 CO2 adsorption isotherms of HP-TPP-3 and HP-TPPO-3 at
with nanostructure appearance and a wide range of diameters 273 K.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 37731–37739 | 37735

View Article Online
RSC Advances
Paper
were also selected to compare their adsorption efficiency of equilibrium within 30 minutes. It was interesting that MO
different kinds of dyes. A UV-vis spectrophotometer was showed lower adsorption capacity compared to MB although
employed to trace the adsorption behaviors of HP-TPP-3 and they both possessed smaller sizes. This was probably related
HP-TPPO-3 according to changes in the intensities of the with the nature of porous materials and dyes. As we know, these
maximum absorption wavelengths of rhodamine B (RB), hybrid porous materials were prepared from cubic silsesquiox-
methylene blue (MB), and methyl orange (MO) at 554, 665, and ane and triphenylphosphine or triphenylphosphine oxide;
466 nm, respectively.
therefore, the content of O and P were higher, which possessed
The specic amount adsorbed onto adsorbents was calcu- partially negative charges. MB was a kind of cationic dye, which
lated based on the following formula:53
had stronger electrostatic attraction interactions with the
hybrid porous polymers. However, MO was a kind of anionic
dye, which had electrostatic repulsion interactions with the
hybrid porous polymers. So the adsorption capacity of MO was
lower than that of MB.
ðC0 ꢀ CeÞ ꢂ V
Qe ¼
(1)
M
where Qe (mg gꢀ1) is the equilibrium adsorption capacities, C0
(mg Lꢀ1) is the initial concentration, Ce (mg Lꢀ1) is the equi-
librium concentration, V (L) is the volume of the aqueous
solution and M (g) is the mass of the adsorbent used.
In view of the maximum Qe of RB, we further investigate its
adsorption behaviors. Three well-known isotherm equations,
Langmuir isotherm,55–58 Freundlich isotherm58–60 and Dubinin–
Radushkevich isotherm,61,62 were applied to evaluate the data of
RB adsorption (the three isotherm equations see ESI†).
The adsorption isotherms of RB (Fig. 8) demonstrated
a positive relationship between the adsorption capacity of the
hybrid porous polymers and the equilibrium concentration.
The detailed tting isotherm parameters were listed in Table 3.
For HP-TPP-3, the correlation coefficient (RL2, 0.9909) of the
linearized Langmuir equation was higher than those of
Freundlich equation (RF2, 0.9267) and Dubinin–Radushkevich
equation (RD2, 0.8955), indicated that the adsorption behaviors
of RB onto HP-TPP-3 could better t to Langmuir model.
The molecular size of RB, MB and MO molecule, estimated
by Newtonian ball and spring model, was in the order of RB >
MB > MO, listed in Table 2.53 It was interesting to observe that
they showed distinctly different equilibrium adsorption capac-
ities (Qe) for three dye molecules; RB possessed the maximum
Qe of 828.6 mg gꢀ1 and MO possessed the minimum Qe of 25.9
mg gꢀ1. This result suggested that these porous polymers
possessed an excellent size-selective adsorption for dyes. As
mentioned above, the hybrid porous polymers showed unique
bimodal pores with micropores centered at around 1.5 nm and
mesopores centered at about 3.7 nm, respectively. Adsorption is
a complex process. Adsorption capacity of dyes in porous
materials is a comprehensive result of various factors, among
which pore structure plays an important role in the adsorption
process. For these hybrid materials in this work, most pores
should be open and interconnecting; and micropore sizes
centered at 1.5 nm, which was larger than that of MB and MO.
Although mass transfer of MB and MO was more efficient in the
porous materials, they could rapidly enter into pores; at the
same time, they also easily leave from pores and led to low
adsorption capacities in the porous polymers because of small
spatial hindrance. However, the diameter of RB was larger than
1.5 nm, the mass transportation in the small-size pores was
seriously inhibited; thus, vast RB molecules could block the
orice of micropores or bind in the mesopores.53,54 Therefore,
the adsorption capacities of RB was much larger than those of
MB and MO. This unique bimodal pores structure made these
porous polymers prefer to absorb bulky dye molecules. This was
supported by the adsorption equilibrium experiment, which
showed that the adsorption equilibrium time of MB and MO
nearly needed 24 hours; however, RB almost achieve adsorption
Fig. 8 Rhodamine B adsorption isotherms of HP-TPP-3 and HP-
TPPO-3. The inset shows the low-limit of detection with a linear fit in
the linear concentration range.
Table 2 Adsorption capacities for three dye molecules onto adsorbents
Qe (mg gꢀ1
)
Dye
Molecular size (nm)
Molecular weight (g molꢀ1
)
HP-TPP-3
HP-TPPO-3
Rhodamine B (RB)
Methylene blue (MB)
Methyl orange (MO)
1.59 ꢂ 1.18 ꢂ 0.56
1.26 ꢂ 0.77 ꢂ 0.65
1.31 ꢂ 0.55 ꢂ 0.18
478
320
327
674.6
154.0
25.9
828.6
145.0
64.6
37736 | RSC Adv., 2016, 6, 37731–37739
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Table 3 Parameters of isotherms for rhodamine B adsorption onto
adsorbents
observed that the characteristic bands of RB became increas-
ingly weaker with the increasing treatment time, and both of the
bands were completely removed aer being treated for 3 h;
more than 90% of the dyes were rapidly removed by HP-TPP-3
within 6 minutes and by HP-TPPO-3 within 3 minutes, respec-
tively. The inset gures showed the corresponding camera
images of the dye solutions over time. The colors of the dyes
became increasingly lighter and nally faded aer 3 h.
In order to further examine the adsorption process of RB,
pseudo-rst-order (eqn (2)),64 pseudo-second-order (eqn (3))65
and intraparticle diffusion (eqn (4))66 models were used to test
the experimental data.
Adsorbent
Model
Parameters
HP-TPP-3
HP-TPPO-3
Langmuir
isotherm
Qmax (mg gꢀ1
)
847.46
0.111
0.9909
2.191
133.903
0.9267
3.141 ꢂ 10ꢀ6
0.399
0.8955
590.41
1627.34
0.065
0.8099
2.331
196.549
0.7354
3.629 ꢂ 10ꢀ6
0.371
0.9803
758.26
KL (L mgꢀ1
)
2
RL
n
Freundlich
isotherm
KF (mg1ꢀ1/n L1/n gꢀ1
)
2
RF
Dubinin–
Radushkevich
isotherm
KD (mol2 Jꢀ2
)
E (kJ molꢀ1
)
2
RD
kf
Qmax (mg gꢀ1
)
logðQe ꢀ QtÞ ¼ log Qe ꢀ
ꢂ t
(2)
(3)
2:303
t
1
1
¼
þ
ꢂ t
2
Qt
ks ꢂ Qe
Qe
However, the adsorption behaviors of RB onto HP-TPPO-3 fol-
lowed Dubinin–Radushkevich isotherm more satisfactorily
than other two isotherms. From the Langmuir plot (Fig. S18†),
Qmax for HP-TPP-3 was calculated to be 847.46 mg gꢀ1 and
higher than the experimental Qe of 674.6 mg gꢀ1, probably due
to the adsorption of solvent onto adsorbents. From the Dubi-
nin–Radushkevich plot (Fig. S20†), Qmax for HP-TPPO-3 was
calculated to be 758.26 mg gꢀ1, and lower than the experimental
Qe of 828.6 mg gꢀ1. This experimental Qe was signicantly
higher than those for other porous materials, such as active
carbon,63 mesoporous carbons,53 et al. (Table S2†). And the E
values of RB adsorption onto HP-TPPO-3 or HP-TPP-3 were
lower 8 kJ molꢀ1; thus, the adsorption behavior of RB belonged
to physical adsorption.58
Qt ¼ ki ꢂ t0.5
(4)
where Qt (mg gꢀ1) and Qe (mg gꢀ1) are amount of dye adsorbed
at each time and equilibrium, respectively. And kf (minꢀ1), ks (g
mgꢀ1 minꢀ1), and ki (mg gꢀ1 minꢀ0.5) are the rate constants of
pseudo-rst-order, pseudo-second-order, and intraparticle
diffusion models, respectively. The tting results of RB onto
adsorbents HP-TPP-3 and HP-TPPO-3 were exhibited in
Fig. S22–S24.† It could be easily observed that linear relation of
pseudo-second-order kinetic tting curve was much better than
those of pseudo-rst-order kinetic tting curve and intraparticle
diffusion kinetic tting curve. The kinetic parameters were all
listed in Table 4. It suggested that pseudo-second-order model
was more suitable in explaining this adsorption process. In
addition, the values of Qe calculated by pseudo-rst-order
kinetic model largely deviated the experimental values, which
further indicated that pseudo-second-order model was the
optimal candidate in explaining RB onto adsorbents HP-TPP-3
and HP-TPPO-3.
As shown in Fig. 9, it showed the absorption spectra at
different time intervals of RB aqueous solutions aer they were
treated with HP-TPP-3 and HP-TPPO-3, respectively. It could be
It was interesting that the equilibrium adsorption capacities
and adsorption rates for RB onto HP-TPPO-3 were higher than
those for RB onto HP-TPP-3 by the introduction of the P]O
bond (Fig. 8 and 9). As we all know, the cubic OVS and trigonal
pyramidal TPP molecule are nonpolar compounds,67–69 which
Table
4 Kinetic parameters for the adsorption of rhodamine B
adsorption on adsorbents
Adsorbent
HP-TPP-3
Model
Parameters
HP-TPPO-3
Pseudo-rst-order
Qe,exp (mg gꢀ1
)
79.29
94.37
kf (minꢀ1
)
0.1243
0.9753
15.30
0.0242
79.55
0.1402
0.5982
12.85
0.0542
94.43
Rf2
Qe,cal (mg gꢀ1
)
Fig. 9 Dye adsorption properties of HP-TPP-3 and HP-TPPO-3. (a
and c) UV-vis adsorption spectra of the RB solutions after being treated
with HP-TPP-3 and HP-TPPO-3 at different time intervals. The initial
concentration of the RB solution is 50 ppm; (b and d) the RB
adsorption rate of HP-TPP-3 and HP-TPPO-3. The insets show the
corresponding camera images.
Pseudo-second-order
ks (g mgꢀ1 minꢀ1
)
Qe,cal (mg gꢀ1
)
2
Rs
1.0000
0.1955
1.0000
0.1165
Intraparticle diffusion
RI2
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 37731–37739 | 37737

View Article Online
RSC Advances
Paper
make the HP-TPP-3 hydrophobic. However, the introduction of
P]O bond caused HP-TPPO-3 to possess certain hydrophilicity
compared with HP-TPP-3. What's more, P]O bond is a kind of
hydrogen bond acceptor,70 making the interaction force
between HP-TPPO-3 and water molecules stronger. This two
factors mentioned above, make HP-TPPO-3 easier to form
a uniform dispersion in RB aqueous solution. Thus, the RB in
water could fully contact with the hybrid porous polymers and
easily enter into the pores of the hybrid polymers. In addition,
5 J. S. Seo, D. Whang, H. Lee, S. Im Jun, J. Oh, Y. J. Jeon and
K. Kim, Nature, 2000, 404, 982–986.
6 C. H. Christensen, K. Johannsen, I. Schmidt and
C. H. Christensen, J. Am. Chem. Soc., 2003, 125, 13370–13371.
7 A. Patra and U. Scherf, Chem.–Eur. J., 2012, 18, 10074–10080.
8 V. S.-Y. Lin, K. Motesharei, K.-P. S. Dancil, M. J. Sailor and
M. R. Ghadiri, Science, 1997, 278, 840–843.
9 P. Wu, J. Wang, Y. Li, C. He, Z. Xie and C. Duan, Adv. Funct.
Mater., 2011, 21, 2788–2794.
the oxygen-rich units (TPPO) make HP-TPPO-3 possess partially 10 P. Wu, J. Wang, C. He, X. Zhang, Y. Wang, T. Liu and
negative charges, which allow additionally strong electrostatic C. Duan, Adv. Funct. Mater., 2012, 22, 1698–1703.
interactions with cationic dye molecules (RB).71,72 This also 11 T. Fei, K. Jiang, S. Liu and T. Zhang, RSC Adv., 2014, 4,
explained the adsorption behaviors of HP-TPPO-3 could better 21429–21434.
t Dubinin–Radushkevich model. The last but not least, the 12 D. A. Edwards, J. Hanes, G. Caponetti, J. Hrkach, A. Ben-
adsorption amount of bulky dye molecules (such as RB) onto
porous materials increased with the increasing mesopore
Jebria, M. L. Eskew, J. Mintzes, D. Deaver, N. Lotan and
R. Langer, Science, 1997, 276, 1868–1872.
volumes.73,74 Although SBET of HP-TPP-3 was higher than that of 13 C.-Y. Lai, B. G. Trewyn, D. M. Jeinija, K. Jeinija, S. Xu,
HP-TPPO-3, HP-TPPO-3 had more mesopores than HP-TPP-3,
which made the Qe of HP-TPPO-3 larger than HP-TPP-3.
S. Jeinija and V. S.-Y. Lin, J. Am. Chem. Soc., 2003, 125,
4451–4459.
´
Aer these porous materials adsorbed dyes, they could be 14 P. Horcajada, C. Serre, M. Vallet-Regı, M. Sebban, F. Taulelle
´
regenerated by Soxhlet extraction with methanol and used and G. Ferey, Angew. Chem., 2006, 118, 6120–6124.
again. In addition, dye molecules could also be recycled aer 15 P. Horcajada, T. Chalati, C. Serre, B. Gillet, C. Sebrie,
methanol was removed by vacuum.
T. Baati, J. F. Eubank, D. Heurtaux, P. Clayette and
C. Kreuz, Nat. Mater., 2010, 9, 172–178.
16 M. Hartmann, S. Kullmann and H. Keller, J. Mater. Chem.,
2010, 20, 9002–9017.
Conclusions
Phosphorus-centered trigonal pyramidal molecule triphenyl- 17 Q. Liu, L. Wang, A. Xiao, J. Gao, W. Ding, H. Yu, J. Huo and
phosphine and triphenylphosphine oxide, and cubic octavi- M. Ericson, J. Hazard. Mater., 2010, 181, 586–592.
nylsilsesquioxane, were simultaneously used as building blocks 18 F.-H. Wang, W. Jiang, Y. Fang and C.-W. Cheng, Chem. Eng.
to easily synthesize two novel parallel series of hybrid porous J., 2015, 259, 827–836.
polymers via the Friedel–Cras reaction. The resulting mate- 19 D. Wu, F. Xu, B. Sun, R. Fu, H. He and K. Matyjaszewski,
rials possessed unique bimodal pores with uniform micropore Chem. Rev., 2012, 112, 3959–4015.
centered at 1.5 nm and mesopore centered at 3.7 nm, high 20 A. Thomas, Angew. Chem., Int. Ed., 2010, 49, 8328–8344.
surface areas up to 1105 m2 gꢀ1, and high thermal stability. 21 A. I. Cooper, Adv. Mater., 2009, 21, 1291–1295.
More importantly, they possessed an excellent size-selective 22 G. Cheng, N. R. Vautravers, R. E. Morris and D. J. Cole-
adsorption performance for different molecular size dyes and
could rapidly remove bulky rhodamine B. Simple synthetic 23 A. Sellinger and R. M. Laine, Chem. Mater., 1996, 8, 1592–
procedure, commercial raw materials, and inexpensive catalyst 1593.
make these hybrid porous polymers very promising to be 24 M. Asuncion and R. M. Laine, J. Am. Chem. Soc., 2010, 132,
Hamilton, Org. Biomol. Chem., 2008, 6, 4662–4667.
industrialized and be of great use in the eld of dyes separation
3723–3736.
and wastewater treatment.
25 H. Liu, M. Puchberger and U. Schubert, Chem.–Eur. J., 2011,
17, 5019–5023.
26 M. F. Roll, J. W. Kampf and R. M. Laine, Macromolecules,
2011, 44, 3425–3435.
Acknowledgements
This research was supported by the National Natural Science 27 J. C. Furgal, J. H. Jung, T. Goodson III and R. M. Laine, J. Am.
Foundation of China (NSFC) (grant number 21274081 and
21574075).
Chem. Soc., 2013, 135, 12259–12269.
28 L. Li and H. Liu, RSC Adv., 2014, 4, 46710–46717.
29 Y. Liu, W. Yang and H. Liu, Chem.–Eur. J., 2015, 21, 4731–
4738.
30 Y. Wu, D. Wang, L. Li, W. Yang, S. Feng and H. Liu, J. Mater.
Chem. A, 2014, 2, 2160–2167.
31 D. Wang, W. Yang, L. Li, X. Zhao, S. Feng and H. Liu, J. Mater.
Chem. A, 2013, 1, 13549–13558.
32 W. Yang, D. Wang, L. Li and H. Liu, Eur. J. Inorg. Chem., 2014,
2014, 2976–2982.
References
1 R. J. White, V. Budarin, R. Luque, J. H. Clark and
D. J. Macquarrie, Chem. Soc. Rev., 2009, 38, 3401–3418.
2 J. Germain, J. M. Frechet and F. Svec, Small, 2009, 5, 1098–
1111.
3 H. Furukawa and O. M. Yaghi, J. Am. Chem. Soc., 2009, 131,
8875–8883.
33 D. Wang, L. Xue, L. Li, B. Deng, S. Feng, H. Liu and X. Zhao,
Macromol. Rapid Commun., 2013, 34, 861–866.
4 S.-Y. Ding and W. Wang, Chem. Soc. Rev., 2013, 42, 548–568.
37738 | RSC Adv., 2016, 6, 37731–37739
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
34 I. Nischang, O. Bruggemann and I. Teasdale, Angew. Chem., 53 X. Zhuang, Y. Wan, C. Feng, Y. Shen and D. Zhao, Chem.
Int. Ed., 2011, 50, 4592–4596. Mater., 2009, 21, 706–716.
35 C. Zhang, F. Babonneau, C. Bonhomme, R. M. Laine, 54 C. Zhang, P.-C. Zhu, L. Tan, J.-M. Liu, B. Tan, X.-L. Yang and
C. L. Soles, H. A. Hristov and A. F. Yee, J. Am. Chem. Soc.,
1998, 120, 8380–8391.
H.-B. Xu, Macromolecules, 2015, 48, 8509–8514.
55 I. Langmuir, J. Am. Chem. Soc., 1918, 40, 1361–1403.
36 W. Chaikittisilp, M. Kubo, T. Moteki, A. Sugawara-Narutaki, 56 W. Shi, S. Tao, Y. Yu, Y. Wang and W. Ma, J. Mater. Chem.,
A. Shimojima and T. Okubo, J. Am. Chem. Soc., 2011, 133,
13832–13835.
37 Y. Wu, L. Li, W. Yang, S. Feng and H. Liu, RSC Adv., 2015, 5,
12987–12993.
38 S. U. Son, Y. Jang, K. Y. Yoon, E. Kang and T. Hyeon, Nano
Lett., 2004, 4, 1147–1151.
39 V. Farina and B. Krishnan, J. Am. Chem. Soc., 1991, 113,
9585–9595.
2011, 21, 15567–15574.
57 L. Zhou, C. Gao and W. Xu, ACS Appl. Mater. Interfaces, 2010,
2, 1483–1491.
58 A. M. Isloor, S. S. Shenvi, A. F. Ismail, S. J. Shilton and
D. A. Al-Ahmad, Ind. Eng. Chem. Res., 2015, 54, 4965–4975.
59 M. D. LeVan and T. Vermeulen, J. Phys. Chem., 1981, 85,
3247–3250.
60 S. Tao, C. Wang, W. Ma, S. Wu and C. Meng, Microporous
Mesoporous Mater., 2012, 147, 295–301.
40 T. Ishiyama, M. Murata and N. Miyaura, J. Org. Chem., 1995,
60, 7508–7510.
61 A. Gil and P. Grange, Colloids Surf., A, 1996, 113, 39–50.
41 B. Li, Z. Guan, W. Wang, X. Yang, J. Hu, B. Tan and T. Li, Adv. 62 C. Nguyen and D. Do, Carbon, 2001, 39, 1327–1336.
Mater., 2012, 24, 3390–3395.
42 Q. Zhang, Y. Yang and S. Zhang, Chem.–Eur. J., 2013, 19,
10024–10029.
63 K. Kadirvelu, C. Karthika, N. Vennilamani and S. Pattabhi,
Chemosphere, 2005, 60, 1009–1017.
64 Y. S. Ho and G. McKay, Water Res., 1999, 33, 578–584.
43 S. Qiao, W. Huang, Z. Du, X. Chen, F.-K. Shieh and R. Yang, 65 Y. S. Ho and G. Mckay, Trans. Inst. Chem. Eng., 1998, 76, 313–
New J. Chem., 2015, 39, 136–141. 318.
44 J. F. Brown, L. H. Vogt and P. I. Prescott, J. Am. Chem. Soc., 66 W. J. Weber and J. C. Morris, J. Sanit. Eng. Div., Am. Soc. Civ.
1964, 86, 1120–1125. Eng., 1963, 89, 31–60.
45 D. Chen, S. Yi, W. Wu, Y. Zhong, J. Liao, C. Huang and 67 I. Nischang, O. Bruggemann and I. Teasdale, Angew. Chem.,
W. Shi, Polymer, 2010, 51, 3867–3878. Int. Ed., 2011, 50, 4592–4596.
46 C. Liu, Y. Li, Y. Li, C. Yang, H. Wu, J. Qin and Y. Cao, Chem. 68 K. Tanaka and Y. Chujo, J. Mater. Chem., 2012, 22, 1733–
¨
Mater., 2013, 25, 3320–3327.
1746.
47 W. He, F. Zhang and H. Li, Chem. Sci., 2011, 2, 961–966.
69 I. Romm, E. Guryanova, N. Rozanelskya and K. Kocheskov,
Tetrahedron Lett., 1977, 18, 33–36.
¨
¨
48 K. C. Hogstrom, H. Lundgren, S. Wilken, T. G. Zavalis,
¨
M. Behm, K. Edstrom, P. Jacobsson, P. Johansson and 70 C. M. Whitaker, K. L. Kott and R. J. McMahon, J. Org. Chem.,
G. Lindbergh, J. Power Sources, 2014, 256, 430–439. 1995, 60, 3499–3508.
49 F. Vilela, K. Zhang and M. Antonietti, Energy Environ. Sci., 71 C. e. N. e. R. Rao, A. e. K. Sood, K. e. S. Subrahmanyam and
2012, 5, 7819–7832. A. Govindaraj, Angew. Chem., Int. Ed., 2009, 48, 7752–7777.
50 X. Zou, H. Ren and G. Zhu, Chem. Commun., 2013, 49, 3925– 72 X. Huang, Z. Yin, S. Wu, X. Qi, Q. He, Q. Zhang, Q. Yan,
3936. F. Boey and H. Zhang, Small, 2011, 7, 1876–1902.
51 C. Namasivayam and D. Sangeetha, J. Hazard. Mater., 2006, 73 C.-T. Hsieh and H. Teng, Carbon, 2000, 38, 863–869.
135, 449–452.
74 G. Walker and L. Weatherley, Chem. Eng. J., 2001, 83, 201–
52 A. Walcarius and L. Mercier, J. Mater. Chem., 2010, 20, 4478–
206.
4511.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 37731–37739 | 37739