Facile synthesis of microcellular foam catalysts with adjustable hierarchical porous structure, acid-base strength and wettability for biomass energy conversion

Article abstract of DOI:10.1039/c5ta02239h

Herein we report a novel synthetic strategy for fabrication of microcellular foam catalysts (MFCs) with hydrophobic, acid-base, and hierarchical porous properties for conversion of one-pot cellulose to a key chemical platform (i.e. 5-hydroxymethylfurfural, HMF) for biofuels. The water-in-oil (W/O) Pickering high internal phase emulsions (HIPEs), stabilized by both amino-functionalized nanoparticles (namely, S-NH₂) and Span 80, were used as the template for simultaneous polymerization of oil phase containing 1-octene, divinylbenzene (DVB), and trihydroxymethylpropyl trimethylacrylate (TMPTMA). After subsequent sulfonation process, acid and base sites resulting from grafted -SO₃H group of polydivinylbenzene (PDVB) and S-NH₂ were both located on the surface of the MFCs. The resultant MFCs composite had a typical hierarchical porous structure, and the macropores with a well-defined open-cell and interconnecting pore throat structure could be controlled via the composition of the oil phase of emulsion, with the mesopore structure closely related to the degree of cross-linking of oil-soluble functional monomer. The representative catalyst MFCs-3 had a hierarchical porous structure (macropores ranging from 1.0 μm to 30 μm and uniform mesopores in 32.1 nm), hydrophobic surface (water contact angle of 125°), 0.735 mmol g^-1 of base, and 1.305 mmol g^-1 of acid. The HMF yield of 41% for cellulose conversion showed its excellent catalytic performance. This work opens up a route for simple and controlled fabrication of multifunctional polymeric catalysts for biomass energy conversion.

Full text of DOI:10.1039/c5ta02239h

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Journal of Materials Chemistry A
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DOI: 10.1039/C5TA02239H
Facile Synthesis of Microcellular Foam Catalysts with Adjustable Hierarchical Porous Structure, Acid-base
Strength and Wettability for Biomass Energy Conversation
Heping Gaoa,b, Jianming Pana∗, Donglai Hanc, Yunlei Zhanga, Weidong Shia, Jun Zengb, Yinxian Pengb∗,
Yongsheng Yana
a School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China
b School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology , Zhenjiang 212003, China
c Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Abstract
Herein we report a novel synthetic strategy for the fabrication of microcellular foam catalysts (MFCs) with
hydrophobic, acidꢀbase and hierarchical porous properties for conversion of oneꢀpot cellulose to a key chemical
platform (i.e. 5ꢀhydroxymethylfurfural, HMF) for biofuels. The waterꢀinꢀoil (W/O) Pickering high internal phase
emulsions (HIPEs), stabilized by both aminoꢀfunctionalized nanoparticles (namely, SꢀNH2) and Span 80, were used
as the template for simultaneous polymerization of oil phase containing 1ꢀoctene, divinylbenzene (DVB) and
trihydroxymethylpropyl trimethylacrylate (TMPTMA). After subsequent sulfonation process, acid and base sites
resulted from grafted ꢀSO3H group of polydivinylbenzene (PDVB) and SꢀNH2 were both located on the surface of
MFCs. The resultant MFCs composite possessed typical hierarchical porous structure, and the macropores with
wellꢀdefined openꢀcell and interconnecting pore throat structure could be controlled via the composition of the oil
phase of emulsion, as well as the mesopores structure was closely related with the degree of cross linking of
oilꢀsoluble functional monomer. The representative catalyst MFCsꢀ3 had hierarchical porous (macropores ranging
from 1.0 µm to 30 µm and uniform mesopores in 32.1 nm), hydrophobic surface (water contact angle of 125 o), 0.735
mmol gꢀ1 of base amount, 1.305 mmol gꢀ1 of acid amount, and its HMF yield of 41% for cellulose conversion showed
excellent catalytic performance. This work opens up a route for simple and controlled fabrication of multifunctional
polymeric catalysts for the biomass energy conversion.
Keywords: Hydrophobic; Acidꢀbase; Hierarchical Porous; PolyHIPEs; Cellulose to HMF; Emulsionꢀtemplating
1. Introduction
With increasing concern about the global warming and declining reserves for the easily accessible nonꢀrenewable
fossil fuel, developing the clean and sustainable resources such as chemical feedstock has grown to a considerable
extent. Abundant renewable biomass mainly derived from photosynthetic process of plants, producing both energy
and organic compounds with many applications, is the most potential and sustainable source to replace fossil fuels.1ꢀ3
Thus, effective conversion of cellulose, nonꢀedible components of biomass to high valueꢀadded chemicals has
become an attractive study area. As an important chemical platform derived from cellulosic biomass,
5ꢀhydroxymethylfurfural (HMF) has a potential leading role in the bioꢀbased energy, because HMF as intermediate
can be converted by effective methods into many versatile and multifunctional compounds such as
5ꢀhydroxyꢀ4ꢀketoꢀ2ꢀpentenoic acid,4 the promising fuel 2,5ꢀdimethylfuran,5ꢀ7 and other organic derivatives.8ꢀ10
Among many methods to produce HMF, acidꢀcatalyzed dehydration of C6ꢀbased carbohydrates especially cellulose to
HMF has the most broad application perspective in relieving the energy crisis. In the acid catalysts system, the
heterogeneous acid catalysts, owing to their advantages including low corrosion of equipment, high catalytic activity
and recyclability, simple handling requirements, and environmentꢀfriendly nature, have gradually replaced the
traditional corrosive and hazardous homogeneous acid catalysts, such as HCl, H2SO4, HClO4, and H3PO4.11ꢀ13
∗ Corresponding author. Tel.: +086 88791708; fax: +086 88791800.
Eꢀmail address: zhenjiangpjm@126.com (J.M. Pan)
1

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Recently, various solid acid catalysts were produced and applied in catalyzing cellulose into HMF, for example,
Lanzafame et al. successfully synthesized sulphated zirconia solid acid catalyst supported over mesoporous silica
(SBAꢀ15) by hydrolysis method, and HMF were obtained by catalyzing cellulose to HMF at 190 oC in water
solution.14 In our previous work, we adopted waterꢀinꢀoil (W/O) Pickering high internal phase emulsions (HIPEs)
template to prepare macroporous polymerized solid acid with openꢀcell structure, interconnecting pores and strong
acidity, and then polymerized solid acid was used to convert cellulose into HMF. Meanwhile, the shortcoming of
mesoporous catalyst that large molecules (e.g. cellulose) were difficult to diffuse into the mesopores was also
overcame.15 We also applied precipitation polymerization and polymerization in Pickering emulsion combined with
sulfonation process to synthesize two kinds of polymeric solid acid for converting cellulose to HMF.16 Although the
present catalysts showed obvious availability in the oneꢀpot cellulose to HMF conversion, the main problem about
improving the HMF yield from cellulose still poses a serious challenge in this field.
In recent years, huge efforts have been focused on how to improve the HMF yield from C6ꢀbased carbohydrates.
Moreover, the concept for rational design and synthesis of the solid acid catalyst mainly came from below important
facts. Firstly, it is commonly accepted that most of the solid acid catalysts are deactivated or decomposed by the
water produced as a byproduct or added into the reaction system, because the water coꢀadsorbed on the surface of the
catalyst produces a more hydrophilic interface.17, 18 As a result, HMF was easy to degrade into other products in
hydrophilic acid system, resulting in the low HMF yield. Recently, Xiao’s group synthesized a series of acidic
mesoporous polymeric catalyst with excellent hydrophobicity by copolymerization of divinylbenzene and sodium
pꢀstyrene sulfonate, and a high HMF yield (>99.0 %) was gained by using the hydrophobic acid catalyst to catalyze
the fructose.19 Secondly, the possible mechanism of cellulose conversion to HMF involves three main reactions: (1)
cellulose to glucose depolymerization in the presence of acid catalyst, (2) glucose to fructose isomerization by using
base catalyst, and (3) fructose to HMF dehydration by acid catalyst. Therefore, Wu et al. successfully synthesized
acidꢀbase biꢀfunctionalized mesoporous silica nanoparticles for oneꢀpot conversion of cellulose to HMF in an ionic
liquid system, and it was found that acidꢀbase biꢀfunctionalized solid catalyst could significantly elevate the HMF
yield from cellulose.20 Thirdly, mesoporous catalyst exhibited the excellent catalytic activity in various kinds of
catalytic reaction due to their high specific surface area.21, 22 Meanwhile, the main shortcomings of mesoporous
catalyst, such as extra isolation steps for catalyst recycling and slow mass transfer to the active sites on the internal
surface, could be overcame by using hierarchical porous (i.e. mesoꢀ/macropores) polymeric catalysts.23, 24 To the best
of our knowledge, the catalysts possessed hydrophobic, acidꢀbase and hierarchical porous structure
(mesoꢀ/macropores) may be used to efficiently improve HMF yield from cellulose, but it is still a serious challenge to
fulfill the multifunctional polymeric solid catalyst.
In summary, a series of microcellular foam catalysts (MFCs) with hydrophobic, acidꢀbase and hierarchical porous
properties were successfully designed and synthesized by W/O Pickering HIPEs template method and subsequent
sulfonation process (Scheme1). Firstly, both asꢀprepared hydrophobic aminoꢀfunctionalized nanoparticles (namely,
SꢀNH2) and span 80 were used to stabilize W/O Pickering HIPEs with an internal phase volume ratio of 84.8%. Then,
Pickering HIPEs of external oil phase containing 1ꢀoctene, trihydroxymethylpropyl trimethylacrylate (TMPTMA)
and divinyl benzene (DVB) monomer, and internal phase comprising of K2SO4 aqueous solution were applied to
fabricated porous polymeric materials. After sulfonation in 98% H2SO4, MFCs were obtained via grafting ꢀSO3H
groups onto polydivinylbenzene (PDVB). Moreover, the amounts of base and acid were controlled by adjusting the
content of SꢀNH2 and DVB monomer, respectively, and variety of wettability of MFCs were further obtained via
changing the volume of 1ꢀoctene. Finally, obtained MFCs were characterized, and their catalytic activities were
explored in detail by optimizing the reaction time, temperature and catalysts loading amounts in catalyzing cellulose
into HMF.
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2. Material and Methods
2.1. Materials
All of the chemicals, 1ꢀethylꢀ3ꢀmethylꢀimidazolium chloride ([EMIM]ꢀCl), cellulose (powder, ca. 50 micron),
5ꢀhydroxymethylfurfural (HMF, >99%), trihydroxymethylpropyl trimethylacrylate (TMPTMA, 98%), styrene (St,
99.9%), divinylbenzene (DVB, 80%), glycidyl methacrylate (GMA, 97%), N,Nꢀdimethylformamide (DMF, 99.8%),
hexadecane (>99%) and tetrahydrofuran (THF, 99.9%) were supplied from Aladdin reagent CO., LTD (Shanghai,
China). Fluorescein isothiocyanate (FITC), 2,2′ꢀazobis (2ꢀmethylꢀpropionitrile) (AIBN, 99%), ethanol, methanol,
Span 80, K2SO4, potassium persulfate (KPS), NH3·H2O (25 wt%), and acetone were purchased from Sinopharm
Chemical Reagent Co., Ltd. (Shanghai, China). All other chemicals were purchased by local suppliers and used
without further purification.
2.2. Synthesis of S-NH2 as stabilizers
SꢀNH2 was synthesized via two steps according to slightly modified method.25 Firstly, a few epoxyꢀbearing
polymerized St nanoparticles (i.e. SꢀGMA) were prepared by surfactant free emulsion polymerization reaction. In a
typical run, 0.6 mL of GMA and 50 mL of deionized water were placed in a 250 mL three neck roundꢀbottom flask,
and deoxygenated by filling nitrogen gas into the solution for 10 min under stirring before 2.0 mL of St and 1.0 mL of
DVB were added into the flask. Then, the mixture was heated to 90 °C in an oil bath, and 80 mg of the initiator KPS
preꢀdissolved in 10 mL of deionized water was added into the flask. The solution was left to react for 3.0 h under
nitrogen protection. Subsequently, the reaction products were collected and washed by centrifugation for several
times with DMF, THF and ethanol, respectively. Finally, the uniformly sized SꢀGMA was obtained through drying for
24 h at 40 oC in vacuum drying oven.
Secondly, asꢀprepared SꢀGMA was further modified by NH3·H2O. As a typical run, SꢀGMA (0.5 g) and NH3·H2O
(10 mL) were mixed and stirred at 60 oC for 9.0 h in a 50 mL flask with reflux condenser. Subsequently, the reaction
products were separated and washed by centrifugation with ethanol several times. Finally, SꢀNH2 was gained through
drying for 12 h at 40 oC in vacuum drying oven.
2.3. Fabrication of MFCs
MFCs were prepared by polymerization reaction and subsequent sulfonation process. The first step was the
fabrication and polymerization of a stable W/O Pickering HIPEs, and the HIPEs recipes were listed in Table 1. Firstly,
the aqueous phase comprised of K2SO4 was dropped into the organic phase (which was formed by stirring the
mixture containing TMPTMA, 1ꢀoctene, DVB, AIBN, SꢀNH2 and Span80 in a 100 mL threeꢀneck flask) under a fast
and continuous mechanical stirring with digital display electric blender at 400 rpm for over 10 min, and a stable W/O
Pickering HIPEs was obtained. Secondly, the obtained Pickering HIPEs were transferred into a plastic centrifuge tube
and polymerized in a circulating air oven at 70 oC for 12 h. Then, asꢀprepared polymerized HIPEs monoliths were
washed with deionized water and acetone in turn by Soxhlet extraction, and further dried at 80 oC for 12 h in a
vacuum oven, until a constant weight was achieved.
The second step was to graft the above monoliths with ꢀSO3H groups by sulfonation process. Briefly, polymerized
HIPEs monoliths (1.0 g, column diameter was 2.6 cm) and 98% H2SO4 (30 mL) were mixed and continuous stirred at
room temperature for 12 h. Then, the products were filtered and washed to remove the excess of H2SO4 by using
amounts of deionized water. Finally, MFCs were gained after drying in vacuum at 80 oC for 3.0 h, and to adapt the
experimental condition, the big MFCs monoliths were further grinded to powder.
2.4. The conversion of cellulose to HMF and analysis of HMF
A typical procedure for the conversion of cellulose to HMF according to modified Huang’s method,26 which was
3

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detailed as follow: Firstly, cellulose (0.1 g) and [EMIM]Cl (2.0 g) were heated at 130 °C for 30 min under the stirring
until the formation of a clear solution to destroy the degree of crystallization and regularity of the cellulose (Fig. S1a).
Then, asꢀprepared representative catalyst MFCsꢀ3 powders (40 mg) were added into the mixed solution, and
continued to react at 130 oC for 20 min under continuous stirring (Fig. S1b). Next, the reaction products were
quenched immediately with cold water, and diluted for 5000 times with deionized water. Finally, liquid samples were
analyzed by a high performance liquid chromatography (HPLC) with Agilent 1200. HMF was detected with a
UVꢀVis detector at wavelength of 283 nm. The column used was Agilent TCꢀC18 Column (4.6 × 250 mm, 5.0 mm).
The mobile phase was the mixed water and methanol with the volume ratio of 30 : 70, and flow rate and column oven
were set to 0.7 mL minꢀ1 and 25 oC, respectively. Meanwhile, the HMF content was obtained according to the
standard curve method. In this work, the HMF yield was defined as the ratio of total moles number of carbon atoms
of HMF (n1) and total moles number of carbon atoms in initial cellulose loaded in the reactor (n0), which was
expressed in Eq. (1).
YHMF % =100× n / n
(1)
(
)
(
)
1
0
2.5. Instruments and characterization
A confocal laser scanning microscope (CLSM, Leica, TCSSP5II, Germany) was used for fluorescence testing. The
optical micrographs of Pickering HIPEs were collected by a DMMꢀ330C optical microscope equipped with a high
performance digital camera (CAIKON, China). The organic functional groups of MFCs were characterized with
solidꢀstate NMR spectroscopy (Bruker DSXꢀ400WBNMRspectrometer, NMR/Solid 400). The electrospray
ionization mass spectrometry (ESIꢀMS) was measured by liquid chromatgraphyꢀion trap mass spectrometry (Thermo
LXQ, U.S.A.). FTꢀIR spectra were measured by a Nicolet NEXUSꢀ470 FTIR apparatus (U.S.A.). The morphology of
the nanoparticles and MFCs were characterized by field emission scanning electron microscopy (SEM, JSMꢀ7100F).
XPS spectra were performed on a Thermo ESCALAB 250 with Al Kɑ radiation at y = 901 for the Xꢀray sources, the
binding energies were calibrated using the C1s peak at 284.9 eV. Elemental composition was recorded by the vario EL
III elemental analyzer (Elementar, Hanau, Germany). The acidic and basic features of samples were both measured
according to NH3 temperatureꢀprogrammed desorption (NH3ꢀTPD) and CO2 temperatureꢀprogrammed desorption
(CO2ꢀTPD) curves, which were recorded by thermal conductivity detector (TCD, DASꢀ7000, Beijing, China),
respectively. TGA of samples was performed for powder (near 10 mg) using a Diamond TG/DTA instruments
o
o
(PerkinꢀElmer, U.S.A.) under a nitrogen atmosphere up to 800 C with a heating rate of 5.0 C minꢀ1. The water
contact angles of samples were measured through the Optical Contact Angle Measuring Device (KSV CM200).
Detailed test procedure was described as follow. 2.0 µL of deionized water was injected on the sample surface
through the syringe pump, and then the images of the water droplet were obtained using the camera in measuring
device after the water droplet was formed on the sample surface about 30 s. Finally, these images were analyzed
using the supplied software to determine the contact angle of sample.
3. Results and discussion
3.1. Morphology of stable nano-particles and hierarchical porous structure of catalysts
Catalytic amination of the epoxy nanoꢀparticles was the main technique used to produce basic particles with the
ꢀNH2 functional groups. The SEM images of the SꢀGMA (a) and SꢀNH2 (b) samples are presented in Fig. 1. The
SꢀGMA nanoparticles (Fig. 1a) were clearly uniform with a size of 128 ± 2.0 nm. After amination, the size of the
SꢀNH2 (Fig. 1b) particles increased to 131 ± 2.0 nm, indirectly indicating successful grafting of the amino groups.
In general, particleꢀstabilized (surfactant free) HIPEs templates are termed Pickering HIPEs; Based on some
special cases, such as continuous phase of emulsion including unable polymerized monomer, open porous polymeric
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materials from Pickering HIPEs can be synthesized.27ꢀ30 However, in most cases, Pickering HIPEs were apt to
produce closedꢀcell macroporous polymers with large pores.31 In contrast, conventional polyHIPEs, synthesized from
surfactant stabilized HIPEs only, have poor mechanical properties and low permeabilities.32ꢀ35 Thus, novel polyHIPEs
having an open porous structure and greatly enhanced permeability have been synthesized by many researchers by
exploiting both particles and few polymeric surfactants stabilized HIPEs. The fabricated HIPEs systems employing
polymeric surfactants as well as particles were also termed Pickering HIPEs in previous studies.36 This may be
because the particles were the primary stabilizer of the HIPEs in the presence of few polymeric surfactant.36 In this
study, MFCs were synthesized by polymerizing the waterꢀinꢀoil (W/O) Pickering HIPEs stabilized by Span 80 in
combination with SꢀNH2 particles; SEM images of MFCsꢀ1 (c), MFCsꢀ2 (d), MFCsꢀ3 (e), and MFCsꢀ4 (f) are also
presented in Fig. 1. All MFCs possessed controllable macropores with wellꢀdefined, openꢀcell and interconnecting
pore throat structures, but the MFCs differed in terms of size and the detailed macroporous structure. MFCsꢀ1 had a
void size of 15 ± 5.0 ꢁm of the openꢀcell and a few interconnecting pore throats of 3.0 ± 2.0 ꢁm. The openꢀcell (15 ±
7.0 ꢁm) and a large number of small interconnecting pore throats (1.0 ± 0.5 ꢁm) were observed in the case of
MFCsꢀ2 (Fig. 1d). An openꢀcell structure (void size of 20 ± 10 ꢁm) with a large number of big interconnecting pore
throats with sizes in the range of 1.0ꢀ5.0 ꢁm were observed in the case of MFCsꢀ3 (Fig. 1e). Based on the slight
difference in the openꢀcell structure, it can be concluded that the poreꢀcell size of the MFCs could be also controlled
based on the composition of the oil phase, except for the inner volume fraction of the emulsions, and the emulsion
was extremely stable during the polymerization process. However, the sizes of the interconnecting pore throats were
obviously different; the differences in the mode of pore throat formation may arise as follows: (1) sufficiently thin
films formed at the gap between two waterꢀoil interfaces stabilized by the same surfactant (i.e. Span 80) to separate
the droplets in the HIPEs may be easily broken to form interconnecting pore throats of the MFCs during the
polymerization process.37 (2) Generally, with the use of less TMPTMA crossꢀlinker and DVB, less volume
contraction occurs on conversion of the monomer to the polymer. Thus, the lower degree of crossꢀlinking between
TMPTMA and DVB in MFCsꢀ3 led to a looser polymer structure, and window formation occurred due to volume
contraction upon conversion of the monomer to the polymer, which was favourable for formation of bigger
interconnecting pore throats (1.0–5.0 ꢁm) during copolymerization.38 (3) The excess 1ꢀoctene in the case of MFCsꢀ3,
derived from the low conversion rate of polymerization, may function as a poreꢀforming reagent. The spatial effect
of the long chain of these molecules and the low degree of cross linking between TMPTMA and DVB in MFCsꢀ3
limited selfꢀpolymerization to form a polymerꢀnetwork, and simultaneous removal of low molecular weight 1ꢀoctene
by Soxhlet extraction was relatively facile; thus, the poreꢀforming reagent derived from the functional monomer may
facilitate formation of large interconnecting pore throats. Additionally, in order to estimate the effect of Span 80 and
SꢀNH2 on the structure of the catalyst, MFCsꢀ4 with many broken openꢀcells (20 ± 5.0 ꢁm) and interconnecting pore
throats (5.0 ± 2.0 ꢁm) was produced by polymerization of the surfactantꢀstabilized HIPEs, and the loose nature of
MFCsꢀ4 corroborates the affirmation that the poor mechanical properties of the conventional W/O HIPEꢀtemplating
porous polymers is due to the presence of a large amount of nonꢀionic surfactant during the emulsifying process.39
Although the nonꢀionic surfactant Span 80, which is known to be a suitable stabilizer for high internal phase
emulsions, was employed for preparation of the HIPEs, and the MFCsꢀ4 sample demonstrate that the HIPEs can be
stabilized solely by Span 80, in our previous study,40 it was demonstrated that the particles (SꢀNH2) acted as the
primary stabilizer of the Pickering HIPEs in the presence of this surfactant. Furthermore, the functionalized SꢀNH2
particles generated polymerization “nodes”, thereby increasing the crossꢀlinking of the polymeric scaffold, and
offered more active sites to form the tight structure of the catalyst during polymerization. Thus, the firm mechanical
properties of MFCsꢀ1, 2, and 3 are attributed to the presence of a large amount of functionalized SꢀNH2 particles
compared to MFCsꢀ4.
Mesopores in the structure have
a
remarkable effect on the catalytic efficacy.41 The nitrogen
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adsorptionꢀdesorption isotherms and the size distribution curves of MFCsꢀ1 (a), MFCsꢀ2 (b), MFCsꢀ3 (c), and
MFCsꢀ4 (d) are displayed in Fig. 2. Typical typeꢀΙV isotherms with step capillary condensation in the relative
pressure range of 0.1ꢀ0.9 were obtained for all samples, and this type of isotherm confirms the existence of
mesopores. The porous parameters of MFCsꢀ1, MFCsꢀ2, MFCsꢀ3, and MFCsꢀ4 are listed in Table 2. The
BrunauerꢀEmmettꢀTeller (BET) surface area (183.6 m2 gꢀ1) and pore volume (0.32 cm3 gꢀ1) of MFCsꢀ1 were
obviously higher than those of MFCsꢀ2 (108.4 m2 gꢀ1, 0.24 cm3 gꢀ1), MFCsꢀ3 (14.6 m2 gꢀ1, 0.05 cm3 gꢀ1), and MFCsꢀ4
(3.5 m2 gꢀ1, 0.01 cm3 gꢀ1). However, the BarrettꢀJoynerꢀHalenda (BJH) mean pore diameter (8.8 nm) of MFCsꢀ1 was
lower than that of MFCsꢀ2 (10.7 nm), MFCsꢀ3 (32.1 nm), and MFCsꢀ4 (47.3 nm). Interestingly, the highly permeable
MFCs were characterized by a lower surface area and pore volume, a larger BJH mean pore diameter, and a wider
size distribution range. This is attributed to the fact that the low degree of cross linking could decrease the tightness
of the network with consequent formation of a mesoporous structure. In short, the typical hierarchical porous
structure of the microcellular polymer foams was confirmed from the SEM and nitrogen adsorptionꢀdesorption
isotherm analyses and the size distribution curves of the MFCs. Furthermore, it is confirmed that the MFCs possessed
a wide size distribution from the nm level to the ꢁm level. According to previous research, only the mesopores larger
than 20 nm in the catalyst act as conductive zones for cellulose conversion.42ꢀ44 Thus, the asꢀprepared MFC catalysts
that possess a microcellular structure and hierarchical porous character were very suitable for conversion of cellulose
to HMF. Herein, a high HMF yield could be obtained by catalyzing the dehydration of cellulose to HMF over the
MFCs (vide infra).
The typical process for fabrication of MFCsꢀ3 is shown in Fig. 3. Firstly, in order to estimate the mean droplet
size, a drop of the resulting Pickering HIPEs was placed on a microscope slide and viewed using an optical
microscope. From Fig. 3a, it was evident that the droplets possessed typical HIPE morphology with spherical and
polydisperse characteristics. Furthermore, a CLSM was employed to determine the type of emulsion. FITC, a
fluorescent substance, was dissolved in the oil phase prior to formation of the emulsion. It could be deduced that the
obtained emulsions were W/O Pickering HIPEs (Fig. S2). Moreover, the droplet size (about 20 ꢁm) was close to that
of the openꢀcell of MFCsꢀ3 (Fig. 3a and Fig. S2), where the openꢀcell of MFCsꢀ3 originated from the void left by
removal of the inner salt water droplet, which suggests that the cell formed in the polymerization process was very
stable. After sulfonation, light red monoliths (density: 0.158 g cmꢀ3, Fig. 3c) were obtained from the white
polymerized HIPEs monoliths (density: 0.148 g cmꢀ3, Fig. 3b). The results suggest that MFCsꢀ3 had the advantages of
a low density, stable structure, and ꢀSO3H groups could be successfully grafted onto the polymerized HIPE monoliths
based on analysis of the density and colour of the monoliths.
3.2. Wettability properties of the stable particles and the catalysts
To understand the wettability properties of the stable particles and the catalysts, water contact angle images were
acquired as shown in Fig. 4a. The water contact angles of SꢀGMA and SꢀNH2 were about 140 ° and 121 °,
respectively, suggesting that amino groups were successfully grafted onto the surface of SꢀGMA via ring opening of
the epoxy group. The water contact angle of 121 ° perfectly satisfies the requirements for stabilizing the W/O
Pickering HIPEs.45 Moreover, the wettability differed for the various MFCs (i.e., water contact angle = 20 ° for
MFCsꢀ1, 103 ° for MFCsꢀ2, 125 ° for MFCsꢀ3, and 98 ° for MFCsꢀ4), where the wettability could be effectively
controlled by varying the amounts of DVB and 1ꢀoctene. The lower the content of DVB utilized, the more
hydrophobic the surface of the MFCs, which indicates that a higher content of DVB monomers produced more
hydrophilic ꢀSO3H groups during the sulfonation process. Increasing the content of the 1ꢀoctene monomer was
beneficial for increasing the hydrophobicity of the catalyst. Thus, adjusting the volume of DVB and 1ꢀoctene is an
effective and simple approach for manipulating the wettability of the catalyst.
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3.3. Chemical composition of the catalysts
The chemical composition of the stable particles and the catalysts was further analysed based on elemental, 13C
CP/MAS NMR, FTꢀIR, Xꢀray photoelectron spectroscopy (XPS) analyses, and thermogravimetric
analysisꢀdifferential scanning calorimetry (TGꢀDSC). The elemental compositions of the samples are shown in Fig.
4b. N was present in SꢀNH2, MFCsꢀ1, MFCsꢀ2, and MFCsꢀ3, and the mass percent of N and S in MFCs (5.8% S for
MFCsꢀ1, 6.1% S for MFCsꢀ2, 6.77% S for MFCsꢀ3, and 6.2% S for MFCsꢀ4; 1.3% N for MFCsꢀ1, 1.22% N for
MFCsꢀ2, and 1.03% N for MFCsꢀ3) were slightly different. It was possibly because the uneven distribution of SꢀNH2
in MFCs and the different sulfonation content of DVB to graft the ꢀSO3H groups onto the surface of MFCs. Moreover,
the N was not detected in SꢀGMA and MFCsꢀ4, suggesting that N was derived from the amination reaction of
SꢀGMA with the epoxy groups, and the stable particles of SꢀNH2 were retained in the MFCs after polymerization and
sulfonation. In addition, the condensed structural formulas of SꢀNH2 and MFCsꢀ3 (Fig. 5a) were decided according to
the 13C CP/MAS NMR spectrum measurements, meanwhile, the presence of S and N in the MFCs confirmed the
success of the sulfonation and amination processes, respectively, and the signal was both detected at d = 45.4 ppm
assigned to the carbon atoms bonded to amine groups (Fig. 5b, 5c) in the 13C CP/MAS NMR spectrum of MFCsꢀ3
and SꢀNH2.46 Furthermore, the another signal was also at d=137.3 ppm assigned to the carbon atoms of benzene ring
bonded to ꢀSO3H groups in the 13C CP/MAS NMR spectrum of MFCsꢀ3. This observation confirms the presence of
amine and sulfonic acid groups.
Figure S3 shows the FTꢀIR spectra of MFCsꢀ3 (a), MFCsꢀ1 (b), MFCsꢀ4 (c), MFCsꢀ2 (d), SꢀGMA (e), and SꢀNH2
(f). Peaks at 1456 cmꢀ1 associated with the benzene ring could be clearly observed for all samples,47 indicating the
presence of the PDVB component. Additionally, peaks around 1033 cmꢀ1, attributed to the CꢀS bond, and at 1162
cmꢀ1 (assigned to the ꢀSO3H group) were also clearly observed for the MFCs, indicating that the ꢀSO3H groups were
successfully grafted onto the benzene rings of the PDVB component. Moreover, a peak at 1630 cmꢀ1 assigned to
ꢀNH2 groups was observed for all samples except for MFCsꢀ4 and SꢀGMA, and peaks around 907 cmꢀ1, attributed to
the epoxy groups, were apparent in the spectrum of all samples, which indicates that ꢀNH2 groups was successfully
grafted, and stable particles of SꢀNH2 with a small number of epoxy groups were retained in the MFCs after
polymerization, owing to the incomplete amination for SꢀGMA.
Figure 6 shows the XPS data for MFCsꢀ3 and MFCsꢀ4. Signals of S, C, and O were clearly observed for MFCsꢀ3
and MFCsꢀ4 (Fig. 6a), indicating the presence of ꢀSO3H groups in the MFCs. Correspondingly, a peak around 284.3
eV, associated with the CꢀS bonds, was apparent in the C1s XPS spectrum of these catalysts (Fig. 6b). This result
further proved the successful introduction of ꢀSO3H into the network of these samples, where the ꢀSO3H groups
should increase the acid strength of these solid acids.48 Moreover, the N1s peak at 427.2 eV could only be observed
for MFCsꢀ3 (Fig. 6c), demonstrating that the SꢀNH2 particles provided basic sites in the catalyst.
Figure 7 shows the TGꢀDSC curves of SꢀGMA (a), SꢀNH2 (b), MFCsꢀ1 (c), MFCsꢀ2 (d), MFCsꢀ3 (e), and MFCsꢀ4
(f). The TG profiles of all samples showed two distinct mass loss steps, and the corresponding DSC curves indicated
endothermic or exothermic reactions based on the peak temperature (Tp). The initial weight losses of SꢀGMA
(10.49%) and SꢀNH2 (44.23%) were observed in the region of 25 oC to 250 oC due to the dehydration process, and the
DSC curves also showed an endothermic peak in the case of SꢀGMA (Tp= 99.8 oC) and SꢀNH2 (Tp= 79.1 oC) in the
same temperature range, suggesting that the hydrophilic ꢀNH2 groups were successfully grafted onto SꢀGMA and
more water was captured by SꢀNH2. The second major mass loss was observed between 250 oC and 750 oC for
SꢀGMA (88.83%) and SꢀNH2 (52.31%). The DSC curve of SꢀGMA showed two endothermic peaks (Tp= 269.6 oC
and 437.4 oC), and the DSC curve of SꢀNH2 showed one endothermic peak (Tp= 405.2 oC) that could be attributed to
decomposition of the polymer network. The final residue from thermal decomposition of SꢀGMA and SꢀNH2 may be
litter carbon from calcination of the polymers, where the residue constituted about 0.68% and 3.46% of the respective
initial masses. A peak indicative of slight weight loss and only one endothermic peak were observed for MFCsꢀ1
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(16.56%, Tp= 57.9 oC), MFCsꢀ2 (17.73%, Tp = 60.6 oC), MFCsꢀ3 (13.90%, Tp = 57.8 oC), and MFCsꢀ4 (18.36%, Tp =
o
o
63.4 oC) within the initial temperature range (<250 C for MFCsꢀ2, MFCsꢀ3 and MFCsꢀ4, <300 C for MFCsꢀ1),
which may also be derived from loss of H2O from these samples.49 Increasing the temperature to 800 oC resulted in
significant weight loss and an exothermic peak was observed in the profile of MFCsꢀ2 (66.57%, Tp = 508.7 oC),
o
o
MFCsꢀ3 (57.28%, Tp = 505.7 C), and MFCsꢀ4 (72.66%, Tp = 508.4 C); significant weight loss and a large
endothermic peak due to the oxidation of the organic matter (pyrolysis) and decomposition of the ꢀSO3H groups50 was
also observed for MFCsꢀ1 (55.76%, Tp = 463.4 oC). Furthermore, the TGꢀDSC curves of MFCsꢀ2, MFCsꢀ3, and
MFCsꢀ4 were similar, suggesting that the chemical composition and chemical structure of these species were similar.
However, the TGꢀDSC curve of MFCsꢀ1 was distinctly different from those of the other MFCs. Notably, sharp
weight loss and a large endothermic peak were observed at about 463.4 oC in the case of MFCsꢀ1. The difference in
the TGꢀDSC curves may arise from the fact that MFCsꢀ1 possessed less oxygen than the other MFCs that contained
the polyꢀTMPTMA component. Normally, when less oxygen is involved in the pyrolysis process, less energy is
released during oxidation of the organic matter to gas. Nevertheless, the rapid decomposition of ꢀSO3H around 463.4
oC required a significant amount of energy, resulting in the large endothermic peak and sharp weight loss of MFCsꢀ1
at about 463.4 oC. The remaining mass of the catalysts at 800 oC may be residual carbon generated by calcination of
the polymers.51 Overall, it was found that the MFCs had high thermal stability, and the chemical composition and
chemical structure of MFCsꢀ1 were different from those of the other MFCs.
3.4. Acidic and basic properties of the catalysts
The approach presented herein is an effective way to synthesize acidꢀbase biꢀfunctionalized catalysts, where the
acidic and basic properties can be easily adjusted by controlling the content of DVB and SꢀNH2. The ꢀSO3H groups
grafted onto the benzene ring of DVB offered acidity, whereas the SꢀNH2 particles served the multifunctional roles of
stabilizing the emulsion and providing the basic sites. The acid and base strengths of the MFCs were measured and
classified based on CO2ꢀTPD and NH3ꢀTPD data (Fig. 8). These results provide reliable data based on the
measurement principle even if the MFCs are degraded at high temperature. Using this technique, the test gas (CO2
and NH3) adsorbed on the active site of the MFCs can be totally desorbed at a high temperature followed by analysis
of the desorbed gas; moreover, no test gas (NH3) was generated during degradation of the MFCs. Although it is likely
that an acrylic polymer release CO2 when it decomposes, the content of acrylic group in MFCs is very low.
Furthermore, the content of CO2 released from the acrylic group would be lower because it is impossible that the
acrylic group only release CO2 when it decomposes based on the TPD measures under He environment. In brief, as
shown in Fig. 8, the MFCs all had different active site types with strong, middle, or weak strength;52 the number of
acidic and basic sites was further calculated as summarized in Table 3. Moreover, the total amount of acid and base
were closely related to the content of S (0.755 mmol gꢀ1 for MFCsꢀ1, 1.658 mmol gꢀ1 for MFCsꢀ2, 1.32 mmol gꢀ1 for
MFCsꢀ3, and 1.293 mmol gꢀ1 for MFCsꢀ4) and N (0.480 mmol gꢀ1 for MFCsꢀ1, 0.662 mmol gꢀ1 for MFCsꢀ2, 0.735
mmol gꢀ1 for MFCsꢀ3, and 0 mmol gꢀ1 for MFCsꢀ4) in the MFCs (Table S1), where these elements are derived from
the volume of DVB and the amount of SꢀNH2, respectively. Although MFCsꢀ1 had the largest volume of DVB (2.0
mL) and the highest BET specific surface area (183.6 m2 gꢀ1), the acid amount (0.769 mmol gꢀ1) was lower than that
of the other catalysts (MFCsꢀ2 with 1.732 mmol gꢀ1, MFCsꢀ3 with 1.305 mmol gꢀ1, MFCsꢀ4 with1.332 mmol gꢀ1).
This may be because the dense polymer network resulting from the highly crossꢀlinked structure of TMPTMA and
DVB53 in MFCsꢀ1, which hindered grafting of the ꢀSO3H groups to the benzene ring of DVB during the sulfonation
process. Furthermore, the total base content of MFCsꢀ1 (0.48 mmol gꢀ1), MFCsꢀ2 (0.62 mmol gꢀ1), and MFCsꢀ3
(0.735 mmol gꢀ1) were different. Kovačič group found that stabilized nanoparticles were randomly embedded within
the surface of macroporous polymers derived from Pickering HIPEs.54 In this work, although the same amount of
SꢀNH2 was used to stabilize the emulsion, a possible reason for the difference to base content of MFCs is that distinct
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amounts of SꢀNH2 were distributed into the catalysts per unit mass. Furthermore, there was only N in the unsulfonated
MFCsꢀ3 (0.894 mmol gꢀ1 of N and 0.873 mmol gꢀ1 of basicity, Table S1, Fig. S4), which further demonstrated that
sulfonation process have no effect on the base amount of catalyst. And the fact that S was introduced into MFCs by
sulfonation process. Thus, the acidꢀbase properties of the MFCs could be easily adjusted by controlling the volume of
DVB and the amount of SꢀNH2, thereby offering a simple method for judicious manipulation of the acidꢀbase
strength of polymeric catalysts.
3.5. Conversion of cellulose to HMF
In general, thermal stability of catalysts is very important for their practical application in catalytic reactions.
Although TG analysis of the MFCs indirectly indicated strong thermal stability of the catalysts, it is still necessary to
further confirm whether the thermal stability of the MFCs meets the requirements for conversion of cellulose to HMF.
Thus, MFCsꢀ3 was further treated for 5.0 h at 200 oC, which exceeds the highest reaction temperature of 150 oC. SEM
image in Fig. S5 demonstrated that heatꢀtreated MFCsꢀ3 possessed stable macropores with a wellꢀdefined, openꢀcell
and interconnected pore throat structure, which was similar to that of asꢀproduced MFCsꢀ3. Furthermore, ESIꢀMS
spectra (Fig. S6) and FTꢀIR spectra (Fig. S7) of the solution were largely similar before and after solution treatment
when MFCsꢀ3 powder (50 mg) was added to hexadecane (2.0 g) or [EMIM]ꢀCl (2.0 g) at 150 oC for 5.0 h under
stirring, suggesting that MFCsꢀ3 had high thermal stability and there was no leaching of the acidic and basic groups
of MFCsꢀ3 in the reaction medium. The practical use of the MFCs for catalytic conversion of cellulose to HMF was
investigated. To ensure the use of optimal reaction conditions, MFCsꢀ3 was used as a representative MFC catalyst.
The influence of the catalyst loading on the catalytic activity is summarized in Fig. 9a. Increasing the catalyst loading
from 20 mg to 40 mg induced a gradual increase of the HMF yield to reach a maximum of 41% at a loading of 40 mg.
A further increase in the catalyst loading decreased the yield, indicating that the decomposition side reaction or
polymerization of HMF was enhanced with high catalyst loading.55 Using the optimized catalyst loading of 40 mg,
the effects of the reaction temperature and time on the conversion of cellulose into HMF were evaluated as shown in
Fig. 9b. The HMF yield increased rapidly in the initial period and then decreased with progress of the reaction time.
Moreover, an appropriate combination of reaction temperature and reaction time was beneficial for obtaining the
maximum HMF yield (i.e., 110 oC and 180 min for 35.5%, 120 oC and 60 min for 41.0%, 130 oC and 20 min for
42.2%, 140 oC and 20 min for 30.1%). It is possible that elevation of the reaction temperature reduced the viscosity of
the ionic liquids thereby enhancing the catalyst activity; this could accelerate the degradation of cellulose to HMF, but
simultaneously increased the formation of byꢀproducts, including unidentified soluble polymers and insoluble
compounds that covered the active sites of the catalysts. Zakrzewska also reported similar results where HMF was
decomposed into unidentified products at high temperature.56 Overall, the optimal yield of HMF was obtained with
MFCsꢀ3 (41%) at a catalyst loading of 40 mg at a reaction time of 60 min at a temperature of 120 oC.
The influence of wettability, acidꢀbase strength, and the hierarchical porous properties of the MFCs on the HMF
yield were further studied. Under the optimal reaction conditions determined above using MFCsꢀ3, the yields of HMF
obtained with MFCsꢀ1, MFCsꢀ2, MFCsꢀ3, and MFCsꢀ4 were 27.1, 30.1, 41, and 33.5%, respectively (Fig. 10). The
yield of HMF obtained with MFCsꢀ4 was lower than that obtained with MFCsꢀ3 owing to the lack of basic sites.
However, hydrophobic MFCsꢀ4 with a low BET specific surface area still gave rise to higher yield of HMF than
obtained with hydrophilic MFCsꢀ1 with a high BET specific surface area and basic sites. Additionally, the more
hydrophobic MFCsꢀ3 also gave rise to a higher yield of HMF than obtained with MFCsꢀ2 with a higher BET specific
surface area and acidꢀbase strength. Thus, it could be concluded that the hydrophobic surface and the basic sites
contributed to the excellent performance of the MFCs rather than the proper BET specific surface area and acid
strength.57 Moreover, the HMF yield was affected by these factors in the following order: surface hydrophobicity >
acidꢀbase biꢀfunctionailty > acid strength > hierarchical porous structure > mesoporous structure. This order can be
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explained as follows. First, the basic sites promote the isomerization of glucose to fructose. Secondly, a hydrophobic
surface is more conducive for curtailing the side reaction of HMF that generates other byꢀproducts. Thirdly, a higher
yield of HMF (33.5%) was obtained with MFCsꢀ4 having a hierarchical porous structure than obtained (10%) with
acidic silica nanoparticles with a strictly mesoporous structure,58 suggesting that the hierarchical porous structure was
advantageous for the conversion of cellulose to HMF. In order to discuss the effect of adsorption of a certain amount
of water and/or solvents by the polymeric foams prior to the catalytic experiments on the catalytic reaction, a small
amount of additional water was introduced into the reaction medium during the catalytic reaction under the same
reaction conditions employed for MFCsꢀ3. Interestingly, although this additional water was most probably released
into the reaction medium during catalysis, the HMF yield (41.3%) was similar to that obtained with MFCsꢀ3 (41%)
without addition of water, suggesting that a little adsorbed water in the catalyst had no influence on the HMF yield.
3.6. Reusability and characterization of reused MFCs-3
The reusability of the catalyst is very important for practical production of HMF in accord with the demand for
green and sustainable chemistry. Regeneration tests were conducted under the optimized reaction conditions, and the
HMF yield after four reaction cycles (41.3% ± 2.1, 40.1% ± 2.0, 38.4% ± 1.98, and 35.2% ± 1.76 for successive
cycles) is shown in Fig. 11a. MFCsꢀ3 was readily recovered by simply filtering the mixture at the end of the first
reaction cycle, washing copiously with a mixture of nꢀhexane and methanol, and drying at 30 oC for 24 h in a vacuum
oven. The pH of the transparent filtrate was near neutral, indirectly suggesting that there was no leaching of the acidic
and basic groups into the reaction medium during catalysis. The recovered MFCsꢀ3 was used to catalyze the
conversion of cellulose to HMF over four successive cycles, and MFCsꢀ3 recovered after the fourth cycle was again
characterized by elemental analysis, NH3ꢀTPD, CO2ꢀTPD, XPS, and SEM. The total amount of acid and base (1.2
mmol gꢀ1 of acid, 0.64 mmol gꢀ1 of base) and the elemental composition of S and N (2.77% and 1.179 mmol gꢀ1of S,
0.63% and 0.582 mmol gꢀ1of N) (Fig. 11b, Table S1) declined only slightly compared with the corresponding values
for asꢀprepared MFCsꢀ3 (1.305 mmol gꢀ1 of acid, 0.735 mmol gꢀ1 of base, 6.77% and 1.32 mmol gꢀ1of S, 1.22% and
0.782 mmol gꢀ1 of N), suggesting only a slight loss of the acid and base sites of the catalysts after repeated catalytic
cycles. Furthermore, the MFCsꢀ3 catalyst still retained excellent activity after four reaction cycles. Moreover, N and
S peaks were still detected in the XPS spectra of MFCsꢀ3 recovered after the fourth cycle (Fig. 11c), and the rigid
porous structure could also be observed from the SEM image (Fig. 11d), indicating that MFCsꢀ3 possessed superior
recyclability and reusability with high mechanical stability of the polymer network, as well as excellent chemical
stability of the acidic and basic sites. These results suggest that the heterogeneous MFCsꢀ3 catalyst has the potential
for application in practical production of HMF.
4. Conclusion
In summary, we prepared a series of adjustable hydrophobic, acidꢀbase and hierarchical porous microcellular
foams catalysts by Pickering HIPEs template method. The wettability, acidꢀbase and hierarchical porous of MFCs
could be adjusted via easily changing contents of DVB, TMPTMA, 1ꢀoctene monomer and SꢀNH2 nanoparticles,
respectively. The high HMF yield (41%) was achieved by oneꢀpot catalyze conversion of cellulose to HMF with
MFCsꢀ3, and it was confirmed that the hydrophobic surface had more advantageous influence than BET specific
surface area, acidꢀbase and hierarchical porous structure for the conversion of cellulose to HMF. This work opens up
a route to produce multifunctional polymeric catalysts for efficient oneꢀpot conversion of cellulose to HMF.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (no. 21107037, no.
21176107, no. 21306013, no. 21407064，no. 21203079, no. 21407064, no. 21203079), Natural Science Foundation of
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Jiangsu Province (no.BK20131223), National Postdoctoral Science Foundation (no. 2013M530240), Special National
Postdoctoral Science Foundation (no. 2014T70480), Postdoctoral Science Foundation of Jiangsu Province (no.
1202002B), Doctoral Innovation Fund of Jiangsu University of Science and Technology ( no. 635211202) and
Programs of Senior Talent Foundation of Jiangsu University (no. 12JDG090).
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12

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Scheme1. The synthesis of MFCs and the conversion of cellulose into HMF in [Emim]Cl under atmospheric
pressure.

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Fig. 1 SEM images of S-GMA (a), S-NH2 (b), MFCs-1 (c), MFCs-2 (d),
MFCs-3 (e), and MFCs-4 (f)

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Fig. 2 Nitrogen adsorption-desorption isotherms of MFCs-1 (inset: pore distribution) (a), MFCs-2 (inset: pore
distribution) (b), MFCs-3 (inset: pore distribution) (c), and MFCs-4 (inset: pore distribution) (d)

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Fig. 3 Photos of Pickering HIPEs (a), polymerized HIPEs monoliths (b), and monoliths (c) of MFCs-3

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Fig. 4 Water contact angle measurements (a), Element contents (b) of the stable nanoparticles and the catalysts

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Fig. 5 The condensed structural formulas of S-NH2 and MFCs-3(a)，and 13C cross-polarization magicangle
spinning (CP/MAS) NMR spectrum of S-NH2 (b), and MFCs-3(c).

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Fig. 6 X-ray photoelectron spectroscopy (XPS) measurements of survey (a), N1s (b), and S2p (c) of MFCs-3 and
MFCs-4

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Fig. 7 TG-DSC curves of S-GMA (a), S-NH2 (b), MFCs-1 (c), MFCs-2 (d), MFCs-3 (e), and MFCs-4 (f)

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Fig. 8 NH3-TPD curves of MFCs-1 (a), MFCs-2 (b), MFCs-3 (c), MFCs-4 (d), and CO2-TPD curves of MFCs-1
(e), MFCs-2 (f), MFCs-3 (g)

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Fig. 9 Effect of catalyst loading (a) with reaction conditions: 130 oC, 20 min, 100 mg cellulose, 2.0 g [BMIM]Cl,
and the effects of reaction temperature and time (b) with reaction conditions: 40 mg MFCs-3, 100 mg cellulose,
2.0 g [BMIM]Cl on the conversion of cellulose into HMF by MFCs-3 as catalyst, respectively.

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Fig. 10 Dehydration of cellulose by different catalysts reaction conditions: 40 mg catalysts, 120 oC, 60 min, 100
mg cellulose, and 2.0 g [BMIM]Cl,

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Fig. 11 Reusability of MFCs-3 catalyst in the dehydration of cellulose into HMF in [EMIM]Cl under the optimized
conditions: 120 °C, 40 mg of catalyst based on 0.10g of cellulose, 60 min,2.0 g [EMIM]Cl (a), Element contents
(inset: contents of acid-base) (b), XPS measurements of survey (c), and SEM image (d) of MFCs-3 recovered after
the fourth cycle

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Table 1 Recipes of W/O Pickering HIPEs.
External organic phase
Internal aqueous phase
Samples
MFCs-1
MFCs-2
MFCs-3
MFCs-4
TMPTMA 1-Octene DVB AIBN S-NH2 Span80
Water
(mL)
16.8
16.8
16.8
16.8
K2SO4
(g)
0.08
0.08
0.08
0.08
(mL)
(mL)
(mL)
(g)
(g)
0.3
0.3
0.3
0
(mL)
0. 3
0. 3
0. 3
0. 3
0
1.0
2.0
2.0
2.0
2.0
0.5
0.2
0.2
0.05
0.05
0.05
0.05
0.5
0.8
0.8

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Table 2 The porosity properties of the catalysts.
Vt[a] (cm3 g-1)
DBJH[b] (nm)
8.8
SBET[c] (m2 g-1)
183.6
Samples
MFCs-1
MFCs-2
MFCs-3
MFCs-4
0.32
0.24
10.7
108.4
0.05
32.1
14.6
0.01
47.3
3.5
[a] Vt is the total pore volume determined at the relative pressure of 0.99.
[b] DBJH is BJH mean pore diameter calculated by the desorption branches of the nitrogen sorption isotherms.
[c] SBET is the BET specific surface area.

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Table 3 The acidic and basic properties of the MFCs.
Acid
strength
(ºC)
Acid
Total
acidity
Base
strength
(ºC)
Base
Total
Samples
MFCs-1
MFCs-2
MFCs-3
MFCs-4
amounts
amounts
basicity
(mmol g-1)
(mmol g-1)
(mmol g-1)
(mmol g-1)
168
528
694
0.119
0.376
0.274
297
426
567
0.094
0.096
0.290
0.769
1.732
1.305
1.332
0.480
0.662
0.735
0
168
450
566
335
412
463
309
412
450
0.058
0.380
1.294
0.740
0.330
0.235
0.370
0.504
0.458
311
420
528
309
425
579
0.196
0.248
0.218
0.291
0.302
0.142
0
0

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555x361mm (96 x 96 DPI)