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HNTs–PSt–PDVB(II). To the end, theꢀproducts were ltrated and
washed with water and dried at 60 C, respectively. The ultima
catalysts named as HNTs–PSt–PDVB–SO3H(I) and HNTs–PSt–
PDVB–SO3H(II), respectively.
2.2. Preparation of vinyl-modied HNTs
2.0 g of treated HNTs were dispersed into 100 mL of dry toluene
by ultrasonic vibration, and then 4.0 mL of TMSPMA was slowly
injected into the mixture under nitrogen at 90 ꢀC, and the
reaction were then proceeded for 24 h under the mechanical
stirring. Aer cooling, the resulting products were collected and
washed with fresh toluene for several times, and then dried in
2.6. Characterization of HNTs–PSt–PDVB–SO3H(I) and
HNTs–PSt–PDVB–SO3H(II)
ꢀ
vacuum at 60 C overnight. The nal products were named as
The morphology of HNTs–PSt–PDVB–SO3H(I) and HNTs–PSt–
PDVB–SO3H(II) were observed by scanning electron microscope
(SEM, S-4800). TGA of samples were performed for powder
samples (about 10 mg) using a Diamond TG/DTA instruments
(Perkin-Elmer, U.S.A.) under a nitrogen atmosphere up to
800 ꢀC with a heating rate of 5.0 ꢀC minꢁ1. XPS spectra were
performed on a Thermo ESCALAB 250 with Al Ka radiation at y
¼ 901 for the X-ray sources, the binding energies were cali-
brated using the C1s peak at 284.9 eV. The acidic features
including the strength of the acid center from 30 ꢀC to 700 ꢀC of
HNTs–PSt–PDVB–SO3H(I) and HNTs–PSt–PDVB–SO3H(II) solid
acid catalysts were determined by means of temperature pro-
grammed desorption (NH3-TPD) using a TP 5000-II multiple
adsorption apparatus (Tianjin Xianquan Corporation of Scien-
tic Instruments, China) in which taking chromatographic
thermal conductivity detector, NH3 as the adsorbate, He as the
carrier gas. FTIR spectra were obtained using the KBr pressed
pellet method with a Bruker VERTEX 70 Fourier transform
infrared spectrometer. The KBr pellets were prepared by
pressing mixtures of catalysts to KBr at the mass ratio of 1 : 100.
All spectra were collected at room temperature using 64 scans in
the range of 4000–400 cmꢁ1 with a resolution of 4 cmꢁ1. The
morphology of the synthesized by Pickering emulsion poly-
merization dried particles was observed by a type of BM-59XCC
optical microscope (BMCO., LTD, China).
vinyl-modied (V-HNTs).
2.3. Synthesis of HNTs–PSt–PDVB(I) by precipitation
polymerization
Synthesis of HNTs–PSt–PDVB(I) by precipitation polymeriza-
tions was implemented by following steps mentioned in the
previous literature with a slight modication,39 where St was
adopted as the functional monomer, TRIM and DVB as the
cross-linker and the AIBN as the initiator, respectively. As a
typical run of preparing HNTs–PSt–PDVB(I), 0.5 g of V-HNTs was
added to 250 mL three-necked ask, and then the dispersing
solution St (79.6 mmol), cross-linker (TRIM, 8.0 mmol and DVB,
8.0 mmol), initiator (AIBN, 0.6 mmol), and dispersing medium
(water, 80 mL) were adequately mixed and dispersed by vigorous
agitation (600 rpm), bubbled with a nitrogen stream throuꢀghout
the procedure. The polymerization was completed at 70 C for
24 h. The resulting HNTs–PSt–PDVB(I) were separated from the
mixed solution with the help of ltration, and were then washed
with toluene and methanol several times. Finally, the products
ꢀ
HNTs–PSt–PDVB(I) were dried in vacuum at 60 C overnight to
get powders.
2.4. Synthesis of HNTs–PSt–PDVB(II) by Pickering emulsion
polymerization
HNTs–PSt–PDVB(II) was synthesized by Pickering emulsion
polymerization. A typical procedure was detailed as follows:
aqueous phase were formed by adding 0.572 g of NaCL, 0.3 g of
treated HNTs to 25 mL of water, and oil phase were contained
toluene (0.14 mL), St (2.0 mL) and DVB (2.0 mL). Followed by
emulsication of the mixture of aqueous phase and oil-phase by
an ultrasonic processor for 10 min and under nitrogen stream
for 20 min to form a stable o/w Pickering emulsion. The
obtained emulsion was subsequently polymerized at 65 ꢀC in
the presence of 0.12 mL of dimethyl 2,20-azobis(2-methyl-
propionate) for 12 h. The obtained composites HNTs–PSt–
PDVB(II) were ltrated and washed with toluene and methanol
2.7. Catalytic reactions
2.7.1 Typical procedures for cellulose hydrolysis using
HNTs–PSt–PDVB–SO3H(I) and HNTs–PSt–PDVB–SO3H(II) as
catalysts in ionic liquids. Experiments were carried out in 25 mL
graduated pyrex glass tube immersed in an oil bath preheated at
the required temperature using a hot plat with a digital
magnetic stirrer. The cellulosic conversion included two steps
of pre-treatment and reaction. In a typical experiment for pre-
treatment, cellulose (0.1 g) was added into 2.0 g of [EMIM]-Cl,
ꢀ
and the whole mixture was heated at 120 C and stirred at 800
rpm for 0.5 h for dissolution of cellulose. For the typical reac-
tion step, catalyst (0.1 g) was added into the cellulose/[EMIM]-Cl
solution while keeping heating and stirred at 800 rpm at the
optimized conditions. All reaction steps were repeated three
times.
ꢀ
respectively, followed by being dried in vacuum at 25 C.
2.5. Sulfonation of as-prepared HNTs–PSt–PDVB(I) and
HNTs–PSt–PDVB(II)
To obtain the solid acid catalysts, the as-prepared HNTs–PSt–
PDVB(I) and HNTs–PSt–PDVB(II) were sulfonated by 98% H2SO4.
In a typically run, HNTs–PSt–PDVB(I) was added to the 98%
H2SO4 at the ratio of 30 mL per gram. To ensure homogeneous
dispersion of HNTs–PSt–PDVB(I), the reaction was carried out in
Cellulose conversion was obtained by the change of cellulose
weight before and aer the reaction. The yield of products were
calculated from the equation:
Weight of products
Yield ð%Þ ¼
ꢂ 100%
Weight of cellulose put into the reactor
ꢀ
a oil bath oscillator with a rate of 800 rpm under 70 C. Same
procedure was taken out for the sulfonation of as-prepared
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 23797–23806 | 23799
Zhang, Yunlei
