The construction of accelerated catalytic Fenton reaction based on Pd/MIL-101(Cr) and H2

Article abstract of DOI:10.1039/c9nj00204a

A novel catalytic Fenton system based on H₂ and the solid catalyst Pd/MIL-101(Cr) (MHACF-MIL-101(Cr)) was developed at normal temperature and pressure. In this system, the reduction process of Fe^III back to Fe^II was accelerated significantly. Using only trace levels of Fe^II at the beginning of the reaction, MHACF-MIL-101(Cr) provided continuous production of hydroxyl radicals and rapid degradation of the model contaminant 4-chlorophenol (10 mg L^-1) under the initial conditions of pH 3, 25 μM Fe^II, 25 mM H₂O₂, 85 mL min^-1 H₂ and 2 g L^-1 Pd/MIL-101(Cr). The activity of the solid catalyst gradually decreased from 100% to about 70% after 6 consecutive degradation reaction cycles of 18 h. This may mainly be attributed to the structural damage and the surface area reduction of this catalyst.

Full text of DOI:10.1039/c9nj00204a

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: X. Liu, S. Gao, J.
Fan, X. li, H. Qin, X. Wang, S. Ma, Z. Liu and Y. Yu, New J. Chem., 2019, DOI: 10.1039/C9NJ00204A.
This is an Accepted Manuscript, which has been through the
Volume 40 Number
1 January 2016 Pages 1–846
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
Accepted Manuscripts are published online shortly after
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Page 1 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ00204A
The Construction of Accelerated Catalytic Fenton Reaction Based on
6
7
Pd/MIL-101(Cr) and H2
8
9
Xin Liuabc, Shi-Qian Gao*a, Jin-Hong Fanb, Xiao-Meng Li a, He-He Qinb, Jun-Xia
Wanga, San-Jian Ma a, Zhong-Xing Liu a, and Yang Yua
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Abstract: A novel catalytic Fenton system based on H2 and solid catalyst
Pd/MIL-101(Cr) (MHACF-MIL-101(Cr)) was developed at normal temperature and
pressure. In this system, the reduction process of FeIII back to FeII was accelerated
significantly. With using only trace level FeII at the beginning of the reaction, the
MHACF-MIL-101(Cr) provided continuously production of hydroxyl radicals and
rapidly degradation of the model contaminant 10mg·L-1 4-chlorophenol in the initial
condition of pH 3, 25μM FeII, 25mM H2O2, 85 mL·min-1 H2 and 2g·L-1
Pd/MIL-101(Cr). The activity of solid catalyst gradually decreased from 100% to
about 70% during the 6 consecutive degradation reaction cycles of 18h. That may
mainly attribute to the structural damage and the surface area reduction of this
catalyst.
1 Introduction
As the significant effectiveness on degradation of recalcitrant organic pollutants at
normal temperature and pressure conditions, the application of Fenton reaction has
aJiangsu Key Laboratory of Environmental Science and Engineering, School of Environmental
Science and Engineering, Suzhou University of Science and Technology, No.1, KeRui Road,
Suzhou New District, Suzhou, Jiangsu Province 215009, China. E-mail address:
gaoshiqian123@163.com
bNational Engineering Research Center for Urban Pollution Control, State Key Laboratory of
Pollution Control and Resources Reuse, College of Environmental Science and Engineering,
Tongji University, No.588, MiYun Road, Yangpu District, Shanghai 200092, China.
cSuzhou Mengli Environmental Technology Co., Ltd., No.58, Xiangjiang Road, Changshu
National New & Hi-tech Industrial Development Zone Suzhou, Jiangsu Province 215500, China.
*

New Journal of Chemistry
Page 2 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
received increasing attention.1-10 The hydroxyl radical (·OH), one of the most
powerful reactive oxygen species (E° =2.73 V, pH 3), produced by inexpensive FeII
and H2O2, is the key role of the Fenton reaction (Equ.(1)).6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
FeII+H2O2→·OH+OH-+FeIII
(k=63 M-1·S-1)
(1)
(2)
(3)
·
FeIII+ H2O2→FeII+ HO2 +H+
(k=0.002 M-1·S-1)
(k=3.2×108 M-1·S-1)
(k=3.3×107 M-1·S-1)
(k=7.8×105M-1·S-1)
(k=1.3×106M-1·S-1)
FeII+ ·OH→FeIII+ OH-
·
H2O2+·OH→HO2 + H2O
(4)
·
FeIII+ HO2 →FeII+ O2+H+
(5)
(6)
·
FeII+ HO2 +H+→FeIII+ H2O2
However, due to the much higher oxidation rate of FeII (Equ.(1), Equ.(3) and
Equ.(6)), more FeIII will be generated during the whole reaction process. In order to
maintain the production of ·OH, the FeII and H2O2 should be continuously added into
the reaction system. Therefore, a large number of iron sludge will be produced after
the reaction completed. The iron sludge, consisted of FeII and FeIII oxyhydroxides,
could not be incinerated. And the landfill of those iron sludge will take up a lot of
land. According to the practice of Fenton reaction in recent years, the application of
this process will be inhibited significantly by how to properly dispose the iron sludge
in future.
For the purpose of reducing the final disposal amount of iron sludge derived
from the Fenton reaction, the key core is to accelerate the reduction reaction process
from FeIII to FeII in Fenton reaction. In previous studies, ascorbate11 and
hydroxylamine12 could be used to significantly promote the reduction reaction of FeIII.

Page 3 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
And humic acid13-14 and quinones15-18 could be used as redox mediators which create
an intermediate electron-shuttling cycle between FeIII (final electron acceptor) and
H2O2 (electron donor). However, the addition of these organic compounds may be
hard to precisely control in real time in practice. The residual of them in effluent is
extremely easy to lead to new organics pollution.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
H2 is an inorganic strong reductant. FeIII could be transferred to FeII by it at
normal temperature and pressure conditions (Equ.(7)).19 The byproduct of Equ.(7) is
only H2O. However, a large amount of H2 should be continuously supplied into
reaction system during the whole process because it is hard to be dissolved in water.
Most of H2 returned into the atmosphere from water immediately after it was supplied
into the reaction system. This will cause a lot of waste of H2.
[Fe(H2O)5(OH)]2++0.5H2→[Fe(H2O)6]2+
ΔRG0=-87kJ·mol-1 (pH around 3) (7)
H2 could be adsorbed on the surface of hydrogen storage materials. Noble metal
catalysts Pd0 could be used to adsorb and active H2 (Equ.(8-15)). An accelerated
catalytic Fenton reaction system, which Pd0 was introduced into it, was successfully
developed to degrade MTBE.19 The concentration of the FeII could be only 1 mg·L−1.
FeIII could be continuously reduced to FeII. The need for iron sludge disposal could be
eliminated.
2Pd+H2→2Pd-H
(8)
Pd-H+ FeIII→Pd +FeII+H+
(9)
Pd
H2O2
2·OH
(10)
(11)
Pd
H2+O2→H2O2

New Journal of Chemistry
Page 4 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
Pd
H2O2→H2O+0.5O2
(12)
(13)
(14)
(15)
Pd
H2O2+H2→2H2O
Pd
H2+0.5O2→H2O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Pd-H+·OH→Pd+H2O
The metal-organic frameworks materials (MOFs), with large pore size or volume,
high specific surface area and diversity open metal sites, are also a new type of
hydrogen storage materials that have been developed rapidly in recent years. They are
showing great application potential of energy storage,20-21 gas separation,22-24
sensing,25-26 catalysis,27-31 and medical treatment32-33 in recent years. The hybrid
architecture of this material is usually flexibility, and the pore size of it is tunable.
These properties facilitate the adsorption of H2 on the surface of it. If it was
introduced into the H2-Fenton reaction system, part of the dissipated H2 could be
adsorbed by it. To a certain extent, that may extend the retention time of hydrogen in
water. Furthermore, the H2O2 of Fenton reaction may also be decomposed to
produce ·OH by MOFs.34-38 That may increase the yield of ·OH and improve the
degradation effect of Fenton reaction.
In this work, both of the MIL-101(Cr) (Fig.1(a)) with the capability of hydrogen
storage39-41 and H2 with strong reduction, were introduced into Fenton reaction system
at normal temperature and pressure. Pd0 was loaded on the surface of MIL-101(Cr) by
reduction process. And trace concentration of FeII was used to catalyzed the
decomposition
of
H2O2.
It
was
called
MHACF-MIL-101(Cr)
(MIL-101(Cr))-H2-Accelerated Catalytic Fenton) system.

Page 5 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
The main objective was to investigate: 1) the variation of FeII and H2O2 in the
system; 2) the oxidation capacity of the MHACF-MIL-101(Cr) system; 3) the
durability of materials after several reactions.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2 Experimental Methods
2.1 Materials
All the chemicals, except for Pd/Al2O3 catalyst, were of analytical grade
(purity≥99.0%) and used without further purification. They were purchased from
China National Pharmaceutical Group Corporation. As Pd/Al2O3 catalyst, the sieve
fraction 80-150 μm of the crushed Pd on γ-Al2O3 egg-shell catalyst with (0.5 ± 0.02)
wt % Pd from Shaanxi Kaida Chemical Engineering Co, Ltd, China, was used. The
catalyst has a BET surface area of about 150 m2·g-1.
All aqueous solutions were prepared with ultra-pure water (Millipore Milli-Q
system, resistivity>18.2 MΩ). Fe2+, Fe3+ and benzoic acid (BA) solution was prepared
by dissolving FeSO4·7H2O, FeCl3 and BA in ultra-pure water respectively. The initial
pH was adjusted by H2SO4 and NaOH.
2.2 Synthetic procedures
MIL-101(Cr) was prepared via a modification of the procedure reported by
P.Rallapalli.42 In a typical synthesis process, Cr(NO3)3·9H2O (4 g), terephthalic acid
(1.54 g) and sodium acetate solution (50 mL, 0.05 M) was mixed added into
high-pressure reactor. The homogeneous solution was placed in a preheated oven at
220℃ for 12h. The reaction system was cooled to room temperature and was
alternately washed 3 times by using anhydrous ethanol and ultra-pure water. Then the

New Journal of Chemistry
Page 6 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
solid was transferred into the reactor equipped with 80mL anhydrous ethanol and
purified at 90℃ for 6h in the preheated oven. The final solid as the major product was
dried in a vacuum drying oven overnight at 100°C. Before it was used to synthesize
the Pd/MIL-101(Cr) material or in Fenton reaction, it would be activated in the
vacuum drying oven 2.5h at 100℃.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Pd/MIL-101(Cr) was prepared via a modification of the procedure reported by
J.Chen.43 Polyvinyl alcohol (18.8 mg) was dissolved in ultra-pure water. Then the
solution was transferred into a two-necked flask containing PdCl2 solution (43.8 mL,
200 mg·L-1). The mixture was stirred under vigorous agitation at 0℃ for 1 hour.
Freshly prepared NaBH4 solution (2.4 mL, 37.83 g·L-1) was added into the mixture to
produce Pd0. The hydrochloric acid was used to adjust the pH 7-8. Then the activated
MIL-101(Cr) (1g) was added into the solid-liquid mixture under vigorous agitation
for 4h at 0℃. That was the preparation of Pd/MIL-101(Cr) (Pd 0.523 wt % based on
ICP-OES). Finally, the final solid as the major product was collected and dried in a
vacuum drying oven overnight at 100°C. Before it was used in Fenton reaction, it
would be activated in the vacuum drying oven 2.5h at 100 °C.
2.3 Characterization of MIL-101(Cr) and Pd/ MIL-101(Cr)
The Brunauer-Emmett-Teller (BET) surface area of the samples were measured
with N2 adsorption-desorption isotherms at 77 K using a Autosorb IQ3 (Quantachrome,
USA). Samples were degassed under vacuum at 473K for 24h prior to data collection.
Fourier transform infrared (FT-IR) spectra were collected at room temperature
using a 670-IR + 610-IR spectrometer (Varian, USA) with a resolution of 0.1 cm-1.

Page 7 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
The binding energies of C, O, Cr and Pd of the composite microspheres were
detected on an ESCALAB250Xi X-ray photoelectron spectroscopy (XPS) (Thermo
Fisher, USA) using an Al-KX-ray source.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The crystalline phases of the materials were characterized by D8 Advance X-ray
diffraction (Bruker, Germany) with Cu Ka radiation emission, 40kV/40mA current
and 3°·min-1 scanning rate.
Surface morphologies of the materials were observed using a S4800 scanning
electron microscope (Hitachi, Japan) equipped with energy-dispersive X-ray analysis
(Thermo Fisher, USA).
Transmission electron microscopy (TEM) and elemental mapping analysis were
collected using a Tecnai G2 F30 S-TWIN high-resolution transmission electron
microscope (FEI, USA) equipped with energy-dispersive X-ray analysis (EDXA,
USA).
2.4 MHACF-MIL-101(Cr) Reaction System
The reaction experiments were conducted in a series of 200 mL two-necked flat
bottom flask equipped with HJ-6 magnetic stirrer at room temperature (20 ± 2°C).
The outer wall of the flask was covered with aluminum foil to protect it from light.
The high purity H2 (purity≥99.999%) was generated by TH-500 hydrogen generator
(Beijing BCHP Analytical Technology Institute, China). Before the starts of
experiment, the H2 was continuously supplied into solution 5min in order to eliminate
dissolved oxygen. The experiment started after the H2O2 was added into the flask
finally.

New Journal of Chemistry
Page 8 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
During the robustness process of MHACF-MIL-101(Cr) reaction system, each
reaction cycle was set at 180 min. At the end of each reaction cycle after the samples
had been taken out, 4-CP and H2O2 was added into the system immediately to
maintain the initial 4-CP and H2O2 in the next reaction cycle at about 10 mg·L-1 and
25 mM, respectively.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
At the given reaction time intervals, samples was taken out and filtered using
0.45μm hydrophilic polyethersulfone (PES) syringe filters. The filtrate was then
withdrawn for the assay of p-HBA, H2O2, Fe2+, Total Cr (Cr3+ and Cr6+, abbreviated
as TCr), Total Pd(abbreviated as TPd) and 4-chlorophenol (4-CP).
2.5 Methods of analysis
Quantitative analysis of p-Hydroxybenzoic acid (p-HBA) was performed with
LC-20AT high performance liquid chromatography (Shimadzu, Japan) equipped with
a reversed phase Agilent ZORBAX Eclipse XDB-C18 column (4.6 mm×150 mm,
5μm). A SPD-M20A detector was used for the analysis. The quantitative analysis
method of p-HBA was from S.Pang.44 And the quantitative analysis method of 4-CP
and its intermediate degradation products was from X.Liu.6
The quantitative analysis method of H2O2 was from R.Nogueira.45 The
concentration of Fe2+ was measured spectrophotometrically by the
1,10-phenanthroline.6 The concentration of TCr and TPd was measured by
ICP-OES(Agilent 720ES, USA). pH was determined by pHSJ-3F pH meter (Shanghai
Precision & Scientific Instrument Co. Ltd, CHN).
Error bars in all figures represent the standard deviation among triplicate

Page 9 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ00204A
measurements.
6
7
3 Results and discussion
8
9
3.1 Characterization of the MIL-101(Cr) and Pd/MIL-101(Cr)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.1 showed the basic structure of MIL-101(Cr), the appearance and FT-IR
spectrum of synthesized MIL-101(Cr), respectively. As shown in Fig.1(b), the
synthesized MIL-101(Cr) is green powder. According to the FT-IR spectrum of the
synthesized MIL-101(Cr) depicted in Fig.1(c), the vibrational band around 3429 cm-1
indicated the O-H band due to stretching modes of water molecules. And the band at
1404 cm−1 was assigned to O-C-O symmetrical stretching vibration. The bands
between 1600 and 600 cm−1 could be confirmed the presence of benzene ring which
included C=C stretching vibration at 1508 cm−1 and C-H deformation vibrations at
750, 883, 1018 and 1110 cm−1, respectively.46
The N2 adsorption-desorption isotherms and the pore size distribution curves of
synthesized MIL-101(Cr) and Pd/MIL-101(Cr) were shown in Fig.2. As seen in
Fig.2(a), the synthesized MIL-101(Cr) exhibit the typical type I isotherms. The pore
size distribution curves, displayed in Fig.2(b), shows the presence of two different
pore sizes with values of 1.5 nm and 2.1 nm, confirming the formation of micropores
of MIL-101(Cr). The surface area of synthesized MIL-101(Cr) was 2457.57m2·g-1
measured by BET test. It is similar with that reported by X.Xia47 and S.Zhao48.

New Journal of Chemistry
Page 10 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.1 (a) The basic structure of MIL-101(Cr); (b) The appearance of synthesized MIL-101(Cr); (c)
FT-IR spectra of synthesized MIL-101(Cr) in the wavenumber range from 4000 to 500 cm−1.
Fig.2 (a) N2 adsorption-desorption isotherms of synthesized MIL-101(Cr) and Pd/MIL-101(Cr) at
77 K; (b) The pore size distribution curves of synthesized MIL-101(Cr) and Pd/MIL-101(Cr). (Pd

Page 11 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
0.523 wt%).
5
6
7
8
The SEM of synthesized MIL-101(Cr) was shown in Fig.3(a) and Fig.3(b). Single
MIL-101(Cr) particle, of which the average diameter was about 450nm, exhibited the
pyramidal polygonal structure. According to the TEM images of synthesized
MIL-101(Cr), shown in Fig.3(c) to Fig.3(f), the edges of a single MIL-101(Cr)
particle could be clearly observed. It was exhibited a recognized classic regular
octahedral shape.39, 42, 49 It was in consistent with the SEM results. According to the
EDX and XPS spectrums of synthesized MIL-101(Cr), shown in Fig.3(g) and Fig.5, it
was demonstrated that the elements of C, O and Cr were distributed in the material.
As shown in Fig.4, the XRD pattern of the synthesized MIL-101(Cr) matched
well with the theoretical one of MIL-101(Cr) produced by using Diamond software
with versatile Crystallographic Information Framework (CIF) file given by
Crystallography Open Database.50
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

New Journal of Chemistry
Page 12 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.3 Characterization of the MIL-101(Cr): (a and b) The SEM photograph of MIL-101(Cr); (c-f)
The TEM photograph of MIL-101(Cr); (g) The EDX photograph of MIL-101(Cr).

Page 13 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.4 (a) The simulated Ref. XRD pattern of MIL-101(Cr); (b) The XRD pattern of synthesized
MIL-101(Cr); (c) The XRD pattern of synthesized Pd/MIL-101(Cr); (d) The XRD pattern of
residual Pd/MIL-101(Cr) after 6 consecutive reaction cycles.
All the results mentioned above indicated that MIL-101(Cr) was successfully
synthesized.
Compared with the synthesized MIL-101(Cr), the appearance of the synthesized
Pd/MIL-101(Cr) is a little dark green powder, as shown in Fig.5(f). The SEM of
Pd/MIL-101(Cr), exhibited in Fig.6(a) and Fig.6(b), was similar with that of
MIL-101(Cr). The EDX spectrum shown in Fig.5(e) and the element mappings
images of Pd/MIL-101(Cr) shown in Fig.6(g), demonstrated that the elements of C, O,
Cr and Pd were distributed in the Pd/MIL-101(Cr). The XPS, shown in Fig.5(a) to
Fig.5(d), was used to study the chemical state of Pd during the preparation of
Pd/MIL-101(Cr). The photoelectron peaks of main elements on the surface of
Pd/MIL-101(Cr) appeared at the binding energies of 284.78 eV (C 1s), 531.88 eV (O
1s), 586.68 eV and 577.08 eV (Cr 2p), and 335.78 eV (Pd 3d) , respectively. It was

New Journal of Chemistry
Page 14 of 34
1
2
3
View Article Online
similar with the previous research results.51-55 That indicated the existenceDOoIf: 10P.1d0309,/C9NJ00204A
reduced by sodium borohydride, on the surface of Pd/MIL-101(Cr).45 Notably, the
XPS signal of Pd was weak compared with those of C, O, Cr. It indicated very low
levels of Pd within the XPS analysis depth of a few nm and no surface aggregation.
That may attributed to the low load content of Pd0 (only 0.523 wt %) on the surface of
MIL-101(Cr). According to the TEM images of the Pd/MIL-101(Cr) shown in Fig.6(c)
to Fig.6(f), the Pd0, with the particle sizes of about 6.5 nm, was uniformly dispersed
within MIL-101(Cr) abundant cavities.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

Page 15 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.5 (a-d) XPS spectras of MIL-101(Cr), Pd/MIL-101(Cr) and residual Pd/MIL-101(Cr) after 6

New Journal of Chemistry
Page 16 of 34
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ00204A
consecutive reaction; (e) The EDX photograph of Pd/MIL-101(Cr); (f) The appearance of
Pd/MIL-101(Cr).
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.6 Characterization of the Pd/MIL-101(Cr): (a and b) The SEM photograph of Pd/MIL-101(Cr);
(c-f) The TEM photograph of Pd/MIL-101(Cr); (g) Element mappings images of Pd/MIL-101(Cr).

Page 17 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ00204A
As seen in Fig.2(a), the synthesized Pd/MIL-101(Cr) also exhibit the type I
isotherms. The pore size distribution curves, displayed in Fig.2(b), shows the presence
of two different pore sizes with values of 1.5 nm and 2.0 nm, confirming the
formation of micropores of Pd/MIL-101(Cr). The surface area of synthesized
MIL-101(Cr) was 1900.596m2·g-1 measured by BET test. It is similar with that
reported by D.Yin.56 That may attribute to of the occupation of cavities or block of
outer surfaces of MIL-101(Cr) with Pd0 particle.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The XRD of the synthesized Pd/MIL-101(Cr) was depicted in Fig.4. It was well
matched with the simulated XRD pattern, presenting the characteristic diffraction
peaks at 2θ 2.79°, 3.29°, 3.96°, 5.17°, 5.9°, 9.64°, which confirmed the successful
construction of MOF supported for the loading of Pd0.
All the results mentioned above indicated that the Pd/MIL-101(Cr) was
successfully synthesized.
3.2 FeII/FeIII redox cycle in MHACF-MIL-101(Cr) system
The reduction of FeIII in H2-Pd/MIL-101(Cr) reaction system, H2-MIL-101(Cr)
reaction system, and only H2 without MOFs addition reaction system was studied,
respectively. As seen in Fig.7(a), the concentration of Fe2+ increased from 0 to 24.45
μM in H2-Pd/MIL-101(Cr) reaction system, while it increased from 0 to about 2.3 μM
in H2-MIL-101(Cr) reaction system. That means the Fe3+ could be reduced to Fe2+ by
H2 at normal temperature and pressure. The reduction of FeIII was significantly
enhanced by the introduction of Pd0. That may attribute to the activation of H2 by Pd0
(Equ. (8) and Equ. (9)).19 The concentration of Fe2+ could not be detected without the

New Journal of Chemistry
Page 18 of 34
1
2
3
View Article Online
addition of MOFs material. As known, H2 is hardly soluble in water. ThereforDeO, It:h10e.1039/C9NJ00204A
contact between H2 and Fe3+ was limited. Furthermore, the production of Fe2+ could
also be oxidized by the trace dissolved oxygen derived from the operation of agitating.
Both of them may result the low production of Fe2+. On the other hand, it indicated
that the retention time of hydrogen was extended in solution based on MIL-101(Cr)
porosity and H2 storage,20, 21, 39 which promoted the reduction efficiency of Fe3+ by H2.
Overall, the reduction of Fe3+ by H2 could be significantly improved by using Pd0 and
MIL-101(Cr) at normal temperature and pressure.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.7 (a) Variation profiles of Fe2+ in Fe3+-H2-Pd/MIL-101(Cr) reaction system,
Fe3+-H2-MIL-101(Cr) reaction system, and Fe3+-H2, respectively (initial pH 2.5). (b) Variation
profiles of Fe2+ and pH in MHACF-MIL-101(Cr) system, and variation profile of Fe2+ in classic
Fenton reaction system (without the addition of MOFs material and using H2). Except for the
parameters investigated, other initial parameters was Fe3+ 25μM, Pd/MIL-101(Cr) 2g·L-1,
MIL-101(Cr) 2g·L-1, H2 85mL·min-1, Fe2+ 25μM, H2O2 25mM and initial pH 3.
The variation profiles of Fe2+ and pH in MHACF-MIL-101(Cr) were depicted in
Fig.7(b). The pH of the solution was stable at 3-3.11. According to Equ.(8) and Equ.
(9), the activation of H2 by Pd0 may result in the decreasing of solution pH by the

Page 19 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
production of H+. In addition, the hydrolysis of Fe3+ produced in Fenton reaction may
also decrease the solution pH.57 Both of them would neutralize the increasing trend of
solution pH (Equ.(1) -Equ.(6)). The concentration of Fe2+ in MHACF-MIL-101(Cr)
system gradually decreased from 25.1 μM to 15.1 μM during the whole 180min
reaction time, while it rapidly decreased from 24.92 μM to 5.62 μM in 5 min, and then
gradually decreased to 4.96 μM in the next 175 min in classic Fenton reaction system.
That may attribute to the H2 enhanced reduction of FeIII in MHACF-MIL-101(Cr)
system (Equ.(1), Equ.(3) and Equ.(6)). Therefore, the whole oxidizing ability could be
improved due to the significantly extended retention time of Fe2+ in this novel
reaction system.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3.3 Decomposition of H2O2 and existence of ·OH in MHACF-MIL-101(Cr) system
As shown in Fig.8(a), the concentration of H2O2 in MHACF-MIL-101(Cr)
system rapidly decreased from 25 mM to about 2 mM in 5 min, and then gradually
decreased to 1.5 mM in the next 175 min. According to J. A. Dean,58 with the
increasing of the pH, the stability of H2O2 will reduce. As seen in Fig.7(b), the pH of
the MHACF-MIL-101(Cr) system was stable at 3-3.1. At this pH condition, the H2O2
will not be spontaneously decomposed to O2 and H2O. That may attribute to the rapid
generation of ·OH and its precursor (Equ.(1), Equ.(2) and Equ.(10)).

New Journal of Chemistry
Page 20 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.8 (a) Variation profile of H2O2 in MHACF-MIL-101(Cr) system. (b) The addition of BA(1.8
g·L-1) as ·OH scavenger and the detection of p-HBA in MHACF-MIL-101(Cr) system (The pH of
the solution would not be adjusted to 3 until the 1.8g·L-1 BA completely dissolved). Except for the
parameters investigated, other initial parameters was Fe2+ 25μM, H2O2 25mM, Pd/MIL-101(Cr)
2g·L-1, H2 85mL·min-1and pH 3.
The BA could be used as the scavenger of ·OH. The product of the reaction
between ·OH and BA is p-HBA.6, 44 As seen in Fig.8(b), the concentration of p-HBA
rapidly increased from 0 to 788.43 μM in 5 min, and then gradually increased to
907.83 μM in the next 175 min. Therefore, it could be verified the existence of ·OH in
the MHACF-MIL-101(Cr) system.
3.4 The robustness of MHACF-MIL-101(Cr) system
4-CP was chosen as the model contaminant because it is widely used as
disinfectants, paints, leather preservatives and insecticides in China.59, 60 And as one
of a particular group of priority toxic pollutants, it is also respectively in the Clean
Water Act by US EPA and the European Decision 2455/2001/EC.61, 62 According to
the previous research results,6, 61, 62 4-CP could be oxidized by ·OH in solution at

Page 21 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
normal temperature and pressure. The stripping operation and the direct oxidaDtiOoI:n10o.1f039/C9NJ00204A
O2, and the coagulation sedimentation of Fe3+ and Fe2+ was found to be negligible
during the removal of 4-CP.6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
As shown in Fig.9(a), 4-CP could be degraded in 2h in the first reaction cycle of
classic Fenton system. However, the degradation efficiency of 4-CP in the second
reaction cycle rapidly decreased from 100% to about 8.5%. And it continued to
decrease in the next 4 reaction cycles. At the end of the sixth reaction cycle, the
degradation efficiency of 4-CP was less than 1%. As known, it is the ·OH produced
by the reaction between FeII and H2O2 that is the key factor to degraded organic
pollutants in Fenton reaction. Although the H2O2 was added into the classic Fenton
system at the beginning of each reaction cycle, the ·OH was still insufficient in each
reaction cycle except the first reaction cycle because of the faster consumption rate of
FeII according to Equ.(1)- Equ.(6).

New Journal of Chemistry
Page 22 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.9 (a) 4-CP degradation efficiency of MHACF-MIL-101(Cr) system, classic Fenton system and
Pd/Al2O3+H2O2 system during 6 consecutive reaction cycles, respectively. Variation profile of pH
in MHACF-MIL-101(Cr) during 6 consecutive reaction cycles. (b) the degradation control test of
4-CP. (c) Variation profiles of TCr in MHACF-MIL-101(Cr) system (without the addition of 4-CP)
and sulfuric acid solution (without the addition of H2, 4-CP, Fe2+ and H2O2), respectively. The
parameter was Fe2+ 25μM, H2O2 25mM, Pd/MIL-101(Cr) 2g·L-1, Pd/Al2O3 2g·L-1, MIL-101(Cr)
2g·L-1, H2 85mL·min-1and initial pH 3.
Both of the degradation of 4-CP in MHACF-MIL-101(Cr) system and Pd/Al2O3
+ H2O2 system were significantly higher than that in classic Fenton system. It could
also be degraded in 2h in the first reaction cycle of MHACF-MIL-101(Cr) system
while it could be maintained at least more than 68% degradation efficiency
corresponding to each reaction cycle of Fenton system. That may be attributed to the
sufficient ·OH production in each reaction cycle because of the faster production rate
of FeII accelerated by the introduction of H2 and Pd/MIL-101(Cr) according to
Equ.(8)- Equ.(15). The pH of MHACF-MIL-101(Cr) system decreased gradually
from initial 3 to 2.79 at the end of the sixth reaction cycle. That may be attributed to
the rapid generation of ·OH and its precursor (Equ.(1), Equ.(2) and Equ.(10)). In first

Page 23 of 34
New Journal of Chemistry
1
2
3
View Article Online
reaction cycle of MHACF-MIL-101(Cr) system, about 0.6 mg·L-1 maleic acidDaOnI:d100.10.539/C9NJ00204A
mg·L-1 4-chlorocatechol were detected at 120 min. And about 0.4 mg·L-1 maleic acid
was detected at 180 min. The hydroquinone and p-benzoquinone were not detected
during the whole reaction cycle. The result was similar with that reported by T.Zhou63
and X.Liu.6 Therefore, the accumulation of intermediate degradation products may
also decrease the solution pH.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Compared with the degradation of 4-CP in MHACF-MIL-101(Cr) system, the
degradation of 4-CP in Pd/Al2O3 + H2O2 system could also be completed in 2h in the
first reaction cycle. According to Equ.(10) and Equ.(11), ·OH and its precursor could
also be generated by Pd and H2O2. It decreased gradually to about 50% degradation
efficiency after the next 5 reaction cycles. During the whole reaction process, the
Pd/Al2O3 catalyst was gradually broken into powder under stirring condition. The Pd0
loaded on the Al2O3 would be peeled off. And they would be agglomerated in the
solution. This will reduce the effective contact area of Pd0. Therefore, the introduction
of MIL-101(Cr) is conducive to the fixation of Pd0.
As seen in Fig.9(a) and Fig.9(b), 4-CP could only be removed less than 30% in
3h in the MIL-101(Cr) system. Phenols could be adsorbed on the surface of
MIL-101(Cr).64 As mentioned above, MIL-101 (Cr) contained 2457.57 m2·g-1 huge
specific surface area measured by BET test. 4-CP could be adsorbed into the surface
of MOFs material in MIL-101(Cr) system. However, the removal process of 4-CP in
MIL-101(Cr) + H2O2 system was similar with that in MIL-101(Cr) system. The
production of ·OH in MIL-101(Cr) + H2O2 system was weak compared with classic

New Journal of Chemistry
Page 24 of 34
1
2
3
4
5
6
7
8
9
View Article Online
Fenton system. The MIL-101(Cr) may play a role as a carrier of Pd0 and the hDyOdIr:o10g.1e0n39/C9NJ00204A
storage material in this work. The Fe-based MOFs may improve the production
of ·OH by heterogeneous Fenton-like reaction.34, 37, 65, 66
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Also as shown in Fig.9(a), the 4-CP degradation efficiency of each reaction cycle
in MHACF-MIL-101(Cr) system successively decreased from 100% (1st cycle),
94.52% (2nd cycle), 86.35% (3rd cycle), 81.36% (4th cycle), 74.91% (5th cycle), to
68.68% (6th cycle). As mentioned above, the ·OH is the key factor to degraded
organic pollutants in MHACF-MIL-101(Cr) system. The downward trend
performance exhibited in it may be attributed to the net reduction of ·OH
corresponding to per unit concentration 4-CP, while H2O2 was added into the system
immediately at the end of each reaction cycle after the samples had been taken out in
order to maintain the sufficient concentration of H2O2 in the next reaction cycle. The
accumulation of intermediate degradation products in each reaction cycle mentioned
above may be one of the factors affecting the degradation efficiency of 4-CP in the
next reaction cycle.
The concentration of TCr in MHACF-MIL-101(Cr) system could be detected in
solution without the addition of 4-CP. As seen in Fig.9(c), it increased gradually
during the 3h reaction from 0 to about 0.14 mg·L-1. It could be completely
precipitated after adjusting the final solution pH to 7.5. The Pd was not detected in the
solution. The variation of TCr in Pd/MIL-101(Cr) and in sulfuric acid solution was
similar with that of MHACF-MIL-101(Cr) system. Therefore, the structure of this
material would be damaged gradually after it was used in MHACF-MIL-101(Cr)

Page 25 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
system for a long time. That may be attributed to the general instability of theDMOIO: 10F.1s039/C9NJ00204A
6
7
in acidic solutions.36, 37
8
9
Furthermore, the morphology changing of Pd/MIL-101(Cr), exhibited in Fig.10,
provided direct evidence for it. As shown in Fig.10(i), the residue collected after the 6
consecutive reaction cycles (without the addition of 4-CP) was yellow green powder.
The EDX spectrum shown in Fig.10(h), the element mappings images of the residue
shown in Fig.10(g) and the C, O and Cr XPS signal intensive of the residue shown in
Fig.3, were demonstrated that the elements of C, O, Cr and Pd were still distributed in
it.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

New Journal of Chemistry
Page 26 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

Page 27 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ00204A
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.10 Characterization of the residual Pd/MIL-101(Cr) after 6 consecutive reaction cycles
(without the addition of 4-CP): (a and b) The SEM photograph of residue; (c-f) The TEM
photograph of residue; (g) Element mappings images of residue; (h) The EDX photograph of
residue; (i) The appearance of residue. Each reaction cycle was set at 180 min. At the end of each
reaction cycle, H2O2 was added into the system immediately to maintain the initial H2O2 in the
next reaction cycle at about 25mM.The parameter was Fe2+ 25μM, H2O2 25mM, Pd/MIL-101(Cr)
2g·L-1, H2 85mL·min-1and initial pH 3.
However, the morphologies of residue, exhibited in Fig.10(a) and Fig.10(b),
were changed compared with that of synthesized Pd/MIL-101(Cr) shown in Fig.6.
The single particle, of which the average diameter was less than 400nm, exhibited the
irregular structure. According to the TEM images of the residue shown in Fig.10(c) to
Fig.10(f), the representative octahedral structure of MIL-101(Cr) were no longer
clearly presented. The edges of the particle were flattened. The XRD pattern of the
residue, depicted in Fig.4(d), was matched with the XRD pattern of Pd/MIL-101(Cr)
though the intensive of the detection signal, especially presenting the characteristic
diffraction peaks at 2θ 16.5° and 17.4°, was significantly weakened.
The Pd XPS signal intensive of the residue, shown in Fig.5(d), increased
significantly. As shown in Fig.10(c) to Fig.10(f), the Pd0 with the particle sizes of
about 7.8nm, was sparsely and non-uniformly dispersed within the residue compared
with that of Pd/MIL-101(Cr) before the reaction. That means Pd0 of the residue was

New Journal of Chemistry
Page 28 of 34
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ00204A
more gathered during the reaction cycles than that of Pd/MIL-101(Cr).
6
7
8
9
The surface area of the residue was 1119.183 m2·g-1 compared with the 1900.596
m2·g-1 Pd/MIL-101(Cr) before reaction.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Therefore, it indicated the structure of Pd/MIL-101(Cr) was changed after the 6
consecutive reaction cycles. The load of Pd0 was reduced within this material because
of the structural damage and the reduction of surface area. And then the retention time
of H2 and the reduction of FeIII would be decreased. Finally, the production of ·OH
and the degradation efficiency of 4-CP would also be weaken.
4 Conclusions
The MHACF-MIL-101(Cr) system exhibited significantly higher reactivity than
classic Fenton system at normal temperature and pressure by using trace amounts of
FeII. It was achieved by introducing H2, recyclable solid Pd0 catalyst and MIL-101(Cr)
for accelerating the reduction of FeIII which is the rate-limiting step in Fenton reaction.
And it could reduce the final disposal amount of iron sludge derived from the Fenton
reaction. Therefore, the MHACF-MIL-101(Cr) system presented in this study offers
potential for the development of significantly improved the application of Fenton
reaction though the structure of MIL-101(Cr), as the load of Pd0, would be damaged
gradually.
Acknowledgments
This study has been financially supported by Natural Science Foundation of
Jiangsu Province (NO. BK20160359), State Key Laboratory of Pollution Control and
Resource Reuse Foundation (NO. PCRRF16027) and Science and Technology

Page 29 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ00204A
Innovation and Entrepreneurship Leadership Talent Program of Changshu (NO.
6
7
CSRC1708).
8
9
Conflict of Interest
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The authors declare no conflict of interest.
References
1 C.Dong, J.Ji, B.Shen, M.Xing and J.Zhang, Environ. Sci. Technol., 2018, 52,
11297-11308.
2 J.Liu, C.Dong, Y.Deng, J.Ji, S.Bao, C.Chen, B.Shen, J.Zhang and M.Xing, Water
Res., 2018, 145,312-320.
3 H.Lu, H.Chen, C.Kao, I.Chao and H.Chen, Phys. Chem. Chem. Phys., 2018, 35,
22890-22901.
4 W.Chen, A.Zhang, Z.Gu and Q.Li, Chem. Eng. J., 2018,354, 680-691.
5 A.Sharma, J.Ahmad and S. Flora, Environ. Res., 2018, 167, 223-233.
6 X.Liu, J.Fan and L. Ma, Chem. Eng. J., 2014, 236, 274-284.
7 J.Bolobajev, E.Kattel, M.Viisimaa, A.Goi, M.Trapido, T.Tenno and N.Dulova,
Chem. Eng. J., 2014, 255, 8-13.
8 S.Pouran, A.Raman and W. Daud, J. Clean Prod., 2014, 64, 24-35.
9 S.Guo, N.Yuan, G.Zhang and C.Yu, Micropor.Mesopor.Mat., 2017, 238, 62-68.
10 H.Zhang, J.Liu, C.Ou, J.Shen, H.Yu, Z.Jiao, W.Han, X.Sun, J.Li and L.Wang, J.
Environ. Sci., 2017, 53, 1-8.
11 X.Huang, X.Hou, F.Jia, F.Song, J.Zhao and L.Zhang, ACS Appl. Mater. Inter.,
2017, 9, 8751-8758.