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tent was determined on a 2400 Series II CHNS/O elemental ana-
lyzer (PerkinElmer). XPS was conducted on a Thermo VG scientific
ESCA MultiLab-2000 spectrometer with a monochromatized AlKa
source (1486.6 eV) at a constant analyzer pass energy of 25 eV. The
binding energy was estimated to be accurate within 0.2 eV. All
binding energies were corrected by being referenced to the C 1s
(284.6 eV) peak of the contamination carbon as an internal stan-
dard.
fields, such as acid-catalyzed biomass conversion and organic
reactions. The integrated utilization of a biorenewable feed-
stock, catalyst, and solvent is a typical example of an ideal
green chemical process to produce potential liquid fuels.
Experimental Section
Materials and methods
FeSO4·7H2O (99.5%), FeCl3·6H2O (99.5%), aqueous NH3 (28 wt%),
chlorosulfonic acid, ethanol (99.5%), and TEOS (99.5%) were pur-
chased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, P.R.
China). Inulin and sucrose were purchased from the J&K Chemical
Co. Ltd., (Beijing, P.R. China). HMF (98%) was purchased from Bei-
jing Chemical Co. Ltd. (Beijing, P.R. China). EMF (98%) was pur-
chased from Hangzhou Imaginechem Co., Ltd. (Zhejiang, P.R.
China). Fructose was purchased from Sanland-Chem International
Inc. (Xiamen, P.R. China). Acetonitrile (HPLC grade) was purchased
from Tedia Co. (Fairfield, USA). All other reagents were provided by
local suppliers (Wuhan, P.R. China) and used without further purifi-
cation.
Titration of solid
The amount of H+ in Fe3O4@SiO2ꢀSO3H was determined by acid–
base titration. Liberated H3O+ was titrated by means of a standard
NaOH titration.
Synthesis of EMF from HMF
Typically, HMF (126 mg, 1 mmol), Fe3O4@SiO2ꢀSO3H (100 mg), and
ethanol (5 mL) were charged in a 15 mL flask coupled with a reflux
condenser, and the condenser was sealed with a balloon charged
with nitrogen to avoid the release of ethanol during the reaction.
The reactor was placed into a preheated oil bath kept at 1008C
and stirred magnetically at 600 rpm for a given reaction time.
Small aliquots were withdrawn from the reaction mixture at
a given reaction time, and diluted with deionized water to a certain
concentration for HPLC detection.
Preparation of the catalyst[27]
A mixture of FeCl2·4H2O (368 mg, 1.85 mmol) and FeCl3·6H2O (1 g,
3.7 mmol) was dissolved in deionized water (30 mL) under a nitro-
gen atmosphere at room temperature, then a 25% solution of
NH4OH (10 mL) was added to the resulting solution with vigorous
mechanical stirring (700 rpm) at a rate of 1 mLminꢀ1. A black pre-
cipitate of Fe3O4 NPs was produced instantly. After 30 min, Fe3O4
was collected by means of an external magnet and the superna-
tant was decanted. Finally, the black precipitate was washed twice
with ethanol. The obtained Fe3O4 particles were dried in vacuum at
708C overnight.
Synthesis of HMF from fructose-based carbohydrates
Typically, fructose (1 mmol, 180 mg) and Fe3O4@SiO2ꢀSO3H
(200 mg) were added to ethanol (5 mL) and the reaction was per-
formed at 1008C. Other steps were the same as those for the syn-
thesis of EMF from HMF.
Fe3O4 magnetic NPs (2.0 g) were dispersed in a mixture of ethanol
(70 mL) and H2O (10 mL) by sonication for 15 min. NH3·H2O (5 mL)
and TEOS (5.0 mL) were then added successively. The mixture was
stirred vigorously for 24 h under a nitrogen atmosphere. The
Fe3O4@SiO2 precipitate was collected by means of a permanent
magnet and rinsed repeatedly with deionized water until the fil-
trate was neutral. The sample was washed three times with etha-
nol. Finally, the product was dried at 708C in vacuum overnight.
Analytic methods for the detection of products and byprod-
ucts
HMF and EMF were quantified by the external standard calibration
curve method, which was conducted on a ProStar 210 HPLC
system coupled with a UV detector. Samples were separated by
means of a reversed-phase C18 column (200ꢁ4.6 mm) at 258C
with a detection wavelength of l=280 nm. The samples were
eluted at 1.0 mLminꢀ1 with acetonitrile and a 0.1 wt% aqueous so-
lution of acetic acid (15:85 v/v). The content of HMF and EMF in
samples were obtained directly by interpolation from calibration
curves, with a coefficient of 0.999.
Fe3O4@SiO2 (2 g) was charged into a suction flask, which was
equipped with a constant-pressure dropping funnel and a gas inlet
tube for conducting HCl gas over an adsorbing solution of NaOH
was used. Chlorosulfonic acid (0.7757 gmol) was then added drop-
wise at room temperature. HCl gas immediately evolved from the
reaction vessel. After the addition was completed, the mixture was
shaken for 30 min. A brown solid of magnetic sulfonic acid (2.5 g)
was obtained.
The content of fructose and sucrose was analyzed by an aminex
column HPX-87 column and Refractive Index detector. If using
HMF as a starting material, the EMF yield and HMF conversion
were obtained by using Equations (1) and (2):
Catalyst characterization
TEM images were obtained by using an FEI Tecnai G2--20 instru-
ment. The sample powders were first dispersed in ethanol and
dropped onto copper grids for observation. FTIR measurements
were recorded on a Nicolet NEXUS-6700 FTIR spectrometer with
a spectral resolution of 4 cmꢀ1 in the wavenumber range of n˜ =
500–4000 cmꢀ1. Powder XRD patterns of samples were determined
with a Bruker advanced D8 powder diffractometer (CuKa). The scan
ranges were 10–808 with 0.0168 steps, respectively. The sulfur con-
moles of HMF
moles of starting HMF
ð1Þ
ð2Þ
HMF conversion ¼
ꢂ 100 %
moles of EMF
moles of starting HMF
EMF yield ¼
ꢂ 100 %
If using fructose as starting material, product yields and fructose
conversion were obtained by using Equations (3) and (4):
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ChemPlusChem 2014, 79, 233 – 240 239