Electrospun flexible self-standing Cu-Al2O3 fibrous membranes as Fenton catalysts for bisphenol A degradation

Article abstract of DOI:10.1039/c7ta04386d

Novel flexible self-standing Cu-Al₂O₃ fibrous membranes have been successfully synthesized via electrospinning technique, and they exhibited high Fenton catalytic activities under neutral pH values. The copper species are distributed uniformly in the fibers in the form of Cu⁺ and Cu²⁺, which was responsible for the Fenton catalytic performance. Over 87% of BPA was degraded within 180 min in the membrane reactor using the 1 wt% Cu-Al₂O₃ membrane at neutral pH values with H₂O₂ addition. The membranes can continuously degrade BPA by batch in the membrane reactor without any additional separation process. The excellent catalytic performance, good flexibility of the membranes, and the facile preparation process make the membranes good candidates for novel heterogeneous Fenton catalysts.

Full text of DOI:10.1039/c7ta04386d

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PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
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Electrospun flexible self-standing Cu-Al2O3 fibrous membranes as
Fenton catalysts for bisphenol A degradation
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Yan Wanga, Jiang Lia, b, Jianyang Suna, Yanbin Wanga, Xu Zhao*a, c
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a, Key Laboratory of Drinking Water Science and Technology, Research Center for
EcoꢀEnvironmental Sciences, Chinese Academy of Sciences, Beijing 100085, P.R. China.
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b, School of Light Industry and Chemical Engineering, Dalian Polytechnic University, Dalian
116034, P. R. China
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c, University of Chinese Academy of Sciences, Beijing, P.R. China.
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Abstract: Novel flexible selfꢀstanding CuꢀAl2O3 fibrous membranes have been successfully
synthesized via electrospinning technique, which exhibited high Fenton catalytic activities under
neutral pH values. The copper species distribute uniformly in the fibers with the form of Cu+ and
Cu2+, which was responsible for the Fenton catalytic performance. Over 87% BPA was degraded
within 180 min in the membrane reactor using the 1 wt% CuꢀAl2O3 membrane in neutral pH values
with H2O2 addition. The membranes can continuously degrade BPA by batch in the membrane
reactor without any other extra separation process. The excellent catalytic performance, good
flexibility of the membranes, as well as the facile preparation process supposed the membranes to be
good candidates as novel heterogeneous Fenton catalysts.
Keywords: Electrospinning; CuꢀAl2O3 fibrous membranes; Fenton catalysts
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1. Introduction
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Recalcitrant organic pollutants are frequently detected in the water environment and being a
serious health hazard to mankind.1,2 Developing an effective and practical method to remove the
organic pollutants is of significance and becoming a research hotspot these years.3,4 Fenton processes
are efficient advanced oxidation processes (AOPs) to remove organic pollutants from water.5 In
Fenton reaction, highly aggressive free hydroxyl radicals (•OH) were generated via the reduction of
hydrogen peroxide (H2O2) with Fe2+ or other reducing transition metals.6 It is well known that there
are two main limitations for the homogeneous Fenton process, which includes the low pH value
range (3ꢀ5) required in the reaction as well as the iron containing sludge accumulation.7, 8, 9 As
alternatives, the heterogeneous Fenton catalysts could minimize the above disadvantages, and
various kinds of heterogeneous catalysts including supported gold nanoparticles,5 ironꢀcontaining
solids,9, 10, 11 and bimetallic composites,12 have been developed. However, mostly, the pH values of
the solution still need to be adjusted to 3~5, and more efforts are needed for exploring Fenton
catalysts with high catalytic performance at neutral pH values.
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Cuꢀbased materials exhibit a Fenton catalytic activity with a wide pH range from 3 to 7. Up to now,
various Cuꢀbased Fenton catalysts such as Cu doped mesoporous γꢀAl2O3 (γꢀCuꢀAl2O3),13 copper–
aluminum–silica nanospheres,14 and Cuꢀcontaining zeolites,15 have been developed. Nevertheless, up
to now, the Cuꢀbased heterogeneous Fenton catalysts are scattered forms in macrograph, which
usually disperse in water, and need filtration or centrifugation to separate them after use. Sometimes
the incomplete separation will lead to a possible catalyst lost and a second pollution to water.
Electrospun fibrous membranes are composed of nanofibers with small diameter, and many
interconnected open pores existing in the membranes. Thus the membranes possess good
permeability and are favored in many environmental remediation areas.16,17 Meanwhile,
electrospinning technique offers a simple and versatile way to fabricate nanofibers, membranes and
films from various materials.18,19,20 However, most inorganic membranes are fragile and transform to
scattered form during use. Up to now, only a few kinds of flexible inorganic membranes have been
developed via electrospinning method, such as SiO2–TiO2 composite membranes,17
silica/mesoporous alumina coreꢀshell fibrous membranes21 and γ–alumina fibrous membranes.22
Most of these membranes are limited to adsorption or filtration performance. The membranes with
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catalytic performance are still needed more efforts to study. Therefore, the research on fabricating
membranes with a high Fenton catalytic activity is desired.
Herein, a novel flexible selfꢀstanding CuꢀAl2O3 fibrous membrane was fabricated via
electrospinning technique. The CuꢀAl2O3 membrane was composed of randomly arranged nanofibers,
and the copper species distribute uniformly in the fibers. The high Fenton catalytic activities of the
membranes were exhibited, which suggested that the CuꢀAl2O3 fibrous membranes are good
candidates as Fenton catalysts.
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2. Experimental section
2.1 Preparation procedure
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All materials were analytical grade and commercially purchased without any further purification,
including HCOOH, CH3COOH, aluminum powder, polyethylene oxide (PEO, MW=500000),
polyvinylpyrrolidone (PVP, MW=1300000), CuSO4.
Preparation of alumina sol. The alumina sol was prepared according to our previous reports with
some modifications.22 In a typical synthesis, 30.16 mL HCOOH and 34.29 mL CH3COOH were
dissolved in 86.4 mL deionized water. Then, 5.4 g aluminum powder was added to the solution. The
mixture was stirred and refluxed at 60ꢀ80 oC until the aluminum powder had reacted completely. The
solution was filtered to remove a small amount of possible particulates to guarantee the clarity of the
solution. Finally, 125 mL colorless transparent alumina solution was obtained.
Preparation of copper-alumina electrospinning precursor.
10 mL of the alumina sol was taken in to a 25 mL beaker, then 0.035 g PEO and 0.035 g PVP were
added and the solution was stirred for 2 h. Then 0.0408 g CuSO4 was added and stirred for 1 h to
prepare the to prepare electrospinning precursor for the CuꢀAl2O3 fibrous membrane with 1wt%
copper content, which denoted as 1 wt% CuꢀAl2O3. Similarly, 0.1224, 0.204 and 0.2856 g CuSO4
were respectively added to the 10 mL solution to prepare electrospinning precursor for the 3 wt%, 5
wt%, 7 wt% CuꢀAl2O3 fibrous membrane.
Preparation of Cu-Al2O3 fibrous membrane
The electrospining process was performed on a SSꢀ2535H device (Ucalery Inc., Beijing, China.)
with the parameters as follows: The volume of the plastic syringe was 10.0 mL, the inner diameter of
the electrospinning metallic needle was 0.9 mm, the push speed was 2.0 mL/h, the distance between
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the needle and the collector was 25.0 cm, the applied voltage was 12 kV, and the humidity was below
10%. After electrospinning, the xerogel fibrous membranes are obtained.
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The xerogel fibrous membranes were calcined at high temperatures with 1 °C minꢀ1 heating rate
and kept at the target temperature for 2 h. and The membranes calcined at 600, 700 and 800 °C were
denoted as CuꢀAl2O3ꢀ600, CuꢀAl2O3ꢀ700 and CuꢀAl2O3ꢀ800, respectively.
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2.2 Characterization
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The morphology of the fibers was characterized on a field emission scanning electron microscope
(SEM, SUꢀ8020, Hitachi, Japan). Transmission electron microscopy (TEM) was performed by
H7500 microscope (Hitachi, Japan). Xꢀray diffraction (XRD) were measured on a X`pert PRO MPD
PC system using Cu Kα (λ=0.15 418 nm, 40 kV, 40 mA) as the Xꢀray source. Xꢀray photoelectron
spectroscopy (XPS) was performed on a Phi Quantern instrument. The binding energy (B. E.)
measurements were calibrated for charging effects with C 1s peak (284.8 eV) as the reference.
Thermoꢀgravimetric (TG) and differential scanning calorimetry (DSC) measurements were
characterized on a Mettler TGAꢀ1 thermogravimetric analyzer with a heating rate of 10 °C minꢀ1 and
up to 1000 °C in air atmosphere. The diffuse reflectance absorption spectra (DRS) were investigated
in the range from 200 to 800 nm on a MAYA 2000 PRO (OCEANOPTICS INC.) spectroscope. N2
adsorptionꢀdesorption isotherms were tested on a Quadrasorb SI apparatus. All the membranes were
degassed at 200 oC under a vacuum for 5 h before analysis.
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2.3 Fenton oxidation experiments
The Fenton catalytic performance of the CuꢀAl2O3 membranes was tested by fixing 10 mg
membrane in the membrane reactor. 10 mL BPA aqueous solution (20 mgLꢀ1) was added into the
reactor, and stirred to establish adsorption/desorption equilibrium. Then, 12 mM H2O2 was added
and the solution kept stirring unless otherwise specified. At appropriate time intervals, 0.50 mL
solution was collected and mixed with 500 ꢁL methanol to quench the residual •OH, and then
filtered through a Millipore filter (pore size 0.45 ꢁm) for HPLC analysis.
The samples were analyzed using a HPLC (LCꢀ20AT,Shimadzu) equipped with a C18
reversedꢀphase column (250 mm × 4.6 mm,5 µm, GL, Science Inc.) and a UV detector (λ = 280
nm). The mobile phase consisted of a 70/30 v/v mixture ofmethanol/water at a flow rate of 1 mL/min.
Total organic carbon (TOC) was determined by a Shimadzu TOCꢀVCPH analyzer. The leaching
copper and aluminum ions from the membranes after catalytic reaction were determined by ICPꢀOES
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(OPTIMA 2000, Perkin Elmer Co., U.S.A.). The electron spinꢀresonance (ESR) spectra were
recorded on a BrukerA 300ꢀ10/12 ESR spectrometer at room temperature and DMPO was used as
spin trap agents.
The intermediates of BPA degradation were identified by UPLCꢀQꢀTOFꢀMS (ACQUITY UPLC,
Quattro Premier XE, Waters, America) with a C18 column (2.1 mm×50 mm×1.7 ꢁm). The mobile
phase containing A (miliꢀQ water) and B (methanol) was delivered at 0.3 mL minꢀ1. The gradient
was 99% A for 15 min, then decreased to 80% for 10 min, then 50% for 10 min, and then increased
to 99% for 4 min. The mass spectrometer was operated in the m/z 50ꢀ800 range with negative
electrospray ionization.
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3. Results and discussion
3.1 Fabrication and morphology of Cu-Al2O3 membranes
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Fig. 1. Schematic illustration of the formation of CuꢀAl2O3 membrane.
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The formation of CuꢀAl2O3 fibrous membranes involves several processes. As shown in Fig. 1,
the alumina powder was reacted with carboxylic acid to acquire a stable homogeneous alumina
solution 22. Then a small amount of PVP and PEO were added to respectively adjust the spinnability
and viscosity of the alumina solution, and CuSO4 was dissolved in the solution. Hence, a light blue
transparent electrospinning precursor, which contains evenly distributed Cu2+ and Al3+ was formed.
During the electrospinning process, the solvent evaporate rapidly, leading to the immediately
formation of CuꢀAl2O3 nanofibers with high aspect ratio. The electrospinning method can avoid the
long time evaporation of solvent by the evaporationꢀinduced selfꢀassembly method that involves in
most literatures, and can directly obtain the membrane form catalysts. The details of the methods for
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preparing CuꢀAl2O3 catalysts are discussed in the supporting information. As shown in Fig. S1A,
SEM images indicate that the fibers are continuous with high aspect ratios. The average diameter is
ca. 500 nm. TGꢀDSC curves (Fig. S1B) of the xerogel membranes indicate that the mass loss
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(65.05%) mainly occurred before 500 C, which was caused by the decomposition of organics as
well as the removal of H2O. Correspondingly, three exothermic peaks in the range of 30~500 oC are
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observed in the DSC curves. Hence, the calcination temperatures were chosen above 500 C. After
calcinations, the flexible CuꢀAl2O3 membranes were formed, and ꢀAlꢀOꢀCuꢀ chemical bond was
supposed to formed in the fibers.
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Fig. 2 (A) SEM image, (B) STEM image and (C) TEM image of 5 wt% CuꢀAl2O3ꢀ600 membranes,
the insert in (A) is an optical image, and insert in (C) is the HRTEM image of the membranes.
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The morphology and microstructure of the CuꢀAl2O3ꢀ600 membranes were presented in Fig. 2.
The membranes could be bended many times and still keep integrated without any cracks,
demonstrating that the membranes possess excellent flexibility. The SEM image shows that the
membranes are uniformly and composed of randomly oriented nanofibers. There are many
interconnected open pores in the membranes, which is beneficial for the permeability of the
membranes. Fig. S2 presents the SEM images of the CuꢀAl2O3 membranes with various Cu content
and calcined at various temperatures. It can be seen that all the membranes are composed of
randomly arranged nanofibers. The average fiber diameters for the membranes calcined at 600 oC are
slightly decreased with the increasing of the Cu content, which are 390, 360, 340 and 320 nm for 1, 3,
5, 7 wt% CuꢀAl2O3 fibrous membranes, respectively (Table S1). Meanwhile, with the increasing
calcination temperatures, the average fiber diameters decreased obviously, which are 340, 270, and
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190 nm for 5 wt% CuꢀAl2O3 membranes calcined at 600, 700 and 800 C (Table S1). STEM images
(Fig. 2B) indicate that the fibers are homogeneous without any particles or other phases, indicating
that the copper species distribute homogeneously in the fibers instead of forming copper or copper
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oxide particles. The surfaces of the fibers are smooth without any cracks, which are beneficial for its
flexibility. TEM images (Fig. 2C) further demonstrate the homogeneous of the fibers.
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Fig. 3 EDS of a single fiber of 5 wt% CuꢀAl2O3ꢀ600.
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EDS analysis of a single fiber was carried out to identify the element distribution. In Fig. 3, three
elements including Al, O and Cu are observed and distributed uniformly. The copper wire mesh was
used for preparing the samples for analysis, thus some Cu elements are detected outside the fiber.
The homogeneous distribution of copper element is beneficial for its sufficient contact with the target
pollutants in water and thus in favor of the catalytic process. Moreover, the EDS spectrum of the
membrane was tested to give an overall analysis of of the elements in the fibers. As presented in Fig.
S3, five elements including Al, O, Cu, S and Au are observed. Among them, Al, O, and Cu are the
main elements of the CuꢀAl2O3 membranes, Au is derived from the Au spraying pretreatment, which
could enhance the conductivity of the CuꢀAl2O3 membrane to get a high quality of SEM image. A
small amount of S element is also observed between 2ꢀ3 kV, and it is due to the incomplete removal
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of SO4 that introduced by CuSO4. According to previous reports, H2SO4 is often used as common
acidꢀbase regulators to control the pH of the solution, because SO42ꢀ rarely affects the degradations.23
Hence, the small amount of residual SO42ꢀ in the fibers is considered to have negligible effect on the
catalytic performance of the CuꢀAl2O3 membranes. Moreover, the concentration of Cu element in the
fiber is 6.59 wt% (Table S2), similar but not the same with the calculated concentration (5 wt%) due
to the semiꢀquantitative analysis of the EDS analysis.
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Fig. 4 (A) XRD patterns the 5 wt% CuꢀAl2O3 membranes calcined at various temperatures and (B)
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UVꢀVis DRS of individual Al2O3 and 5 wt% CuꢀAl2O3 membranes.
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XRD (Fig. 4A) analysis was performed to identify the crystal phase of the membranes. As for the
xerogel fibrous membranes and the membranes calcined at 600 oC, no peaks but humps are observed
in the XRD patterns, indicating that the phase are amorphous. While the peaks of γꢀalumina (PDF
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card number: 50ꢀ0741) appear when the membranes calcined at 700 C, and the crystallinity
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becomes better when the calcination temperature increased to 800 C. In addition, it is worth noting
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that no copper and copperꢀrelated diffraction peaks appeared for all the samples, indicating that the
copper species with the individual crystal phase were not formed. In the UVꢀVis spectra (Fig. 4B), no
obvious absorptions are observed for individual Al2O3 membranes. While for CuꢀAl2O3 membranes
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calcined at 600 and 800 C, the absorption peaks at 750 nm were observed and attributed to the
electron transitions in Cu2+ in alumina lattice,24 which confirmed that the copper species mostly
incorporated in alumina matrix.
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Fig. 5 XPS analysis of the 5 wt% CuꢀAl2O3ꢀ600 membrane, (A) XPS survey (B) Cu 2p and
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(C) Al 2p spectra.
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The complete information of the surface of the CuꢀAl2O3 membranes were identified by the XPS
survey spectrum. As shown in Fig. 5A, the peaks of Al, O, Cu, S and C in the XPS survey spectrum
of the 5 wt% CuꢀAl2O3ꢀ600 membrane are observed. Among them, Al, O, and Cu are the main
elements of the membranes; The S element is derived from the residual SO42ꢀ in the membrane, and
this is consistent with the EDS analysis (Fig. S3); The peak of C element is appeared unavoidably
due to the adsorbed CO2 from air. In addition, the peaks of S element are absence in the XPS survey
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spectrum of the 5 wt% CuꢀAl2O3ꢀ800 membrane (Fig. S4), indicating that SO4 is totally removed
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when the membrane calcined at 800 oC.
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The specific chemical environments and oxidation states of the Cu and Al elements were analysed
by Cu 2p and Al 2p XPS spectra (Fig. 5B and Fig. 5C). In Cu 2p spectra, the peaks centred at 933.1
eV was corresponding to the reduction state of copper species. The auger kinetic energy at 914.6 eV
based on AES measurements confirmed the reduction state of copper was Cu+. The peaks assigned to
the oxidation state of copper was observed at 935.1 eV, and the shakeup satellite line at 942.8 eV also
appeared, confirming the Cu2+ existing. The atomic ratio of Cu+ to Cu2+ was calculated to be 1.63.
These results indicate that the copper species were well doped on the surface of the fibers in the form
of Cu+ and Cu2+. The XPS spectra of Al 2p was fitted to two peaks centered at 74.2 and 75.3 eV,
respectively ascribing to Al−O−Al and Al−O−Cu. Moreover, the concentration of copper species on
the fiber’ surface was 4.64 wt% based on XPS analysis, a little lower than that theoretically
calculated (5.0 wt%), indicating that the copper species were well dispersed in the bulk matrix.25
According to previous reports,26 the dispersed copper species in the bulk alumina matrix can
introduce oxygen vacancies (VO) and other intrinsic defects, which may result in the excess electrons
caused by charge compensation. The excess electrons could stimulate the reducing transformation
from Cu2+ to Cu+, and stable the Cu+ by avoiding its oxidization. Moreover, it is worth nothing that,
the surface copper concentration increased to 7.69 wt% when the calcination temperature increased
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to 800 C (Fig. S4), suggesting that some copper species migrated to the fibers’ surface due to the
rearrangement of Al, O and Cu atoms during crystallization.
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Fig. 6 N2 adsorptionꢀdesorption isotherms of (A) CuꢀAl2O3ꢀ600 membranes with various copper
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content, (B) 5 wt% CuꢀAl2O3 membranes calcined at various temperatures.
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N2 adsorptionꢀdesorption isotherms of the membranes were analyzed to shed some light on the
BET surface area of the membranes. In Fig. 6A, All the CuꢀAl2O3ꢀ600 membranes with various
copper content exhibit the typeꢀⅢ like adsorption isotherms, which corresponds to the adsorption of
N2 on nonporous materials.21 As shown in Table S3, the BET surface areas were 12.33, 9.26, 10.10
and 8.11 m2 gꢀ1 for the 1 wt%, 3 wt%, 5 wt% and 7 wt% CuꢀAl2O3ꢀ600 membranes, respectively.
These results indicate that the effect of copper content on the surface area of the CuꢀAl2O3
membranes is very small. The surface areas of 5 wt% CuꢀAl2O3 membranes calcined at various
temperatures were also tested. As shown in Fig. 6B, when the calcination temperature increased to
700 and 800 oC, the membranes exhibit typeꢀⅣ like adsorption branches, indicating the existence of
mesopores in the fibers.22, 27 The BET surface areas were 10.10, 40.56, 38.63 m2 gꢀ1 for the 5 wt%
CuꢀAl2O3 membranes calcined at 600, 700 and 800 oC, respectively. The BET surface area increased
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when the calcination temperature increased from 600 to 700 C, and then changed very little form
700 to 800 oC. The higher surface area could provide more active sites, and increase the contact area
of the active sites and the pollutants, hence improve the degradation rate.
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3.2 Catalytic performance of Cu-Al2O3 membranes
The Fentonꢀlike catalytic performance of the CuꢀAl2O3 membranes was evaluated by using
bisphenol A (BPA) as the target pollutant, which is a representative endocrine disrupter. Especially, a
membrane reactor (Fig. 7) was used for the Fenton reactions. The membranes were cut into the round
shape to match the reactor, and then fixed in the bottom of the reactor. Prior to the main experiments,
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the reaction was optimized by varying the H2O2 dosage due to it is a a key factor that influence the
Fenton reaction.13 The detailed analysis is shown Fig. S5 and discussed in the supporting information.
The results indicate that 12 mM was the optimal H2O2 dosage in this reaction, and 12 mM H2O2 was
used in all experiments unless otherwise specified. Fig. 8 presents the results of the Fenton catalytic
performance toward BPA degradation under various conditions. In Fig. 8A, nearly no removal of
BPA was observed with individual H2O2 addition. Meanwhile, ~3% BPA was removed due to the
adsorption by the individual membranes, and the adsorption equilibrium established within 30 min.
Notably, 82% BPA was removed for 5 wt% CuꢀAl2O3ꢀ600 membranes using the membrane reactor
with the addition of H2O2, while under the same condition, ~84% BPA was removed by stirring the
membranes in a beaker and forming the conventional suspension. The difference on the removal
ability of the membrane reaction and the suspension form is slight, suggesting that the molecular
mass transfer rate in the membrane reactor is still fast and nearly not affect the catalytic process.
Moreover, the effects of initial pH on Fenton catalytic performance were investigated. The initial pH
values were adjusted by 0.1 M H2SO4. As shown in Fig. 8B, ~86% BPA was removed within 180
min at pH 3, 5 and 7. The neutral pH values are favorable in practical applications, because there is
no need to adjust the pH value. Therefore, the pH value of 7 was chosen as the optimal conditions for
further investigations.
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Fig. 7 (A) Illustration of the membrane reactor, (B) Picture of a 5 wt% CuꢀAl2O3ꢀ600 membrane.
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Fig. 8 (A) Removal efficiency of BPA with initial pH 7.0 and (B) the influence of initial pH on the
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performance of 5 wt% CuꢀAl2O3ꢀ600 membranes. Conditions: [BPA] = 20 mg/L, [H2O2] = 12 mM.
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Fig. 9A presents the catalytic performance of CuꢀAl2O3ꢀ600 membranes with various Cu content.
It can been seen that ~15% BPA was removed for the individual Al2O3ꢀ600 membrane, while 87%,
82%, 84% and 93% BPA were removed respectively for 1, 3, 5 and 7 wt% CuꢀAl2O3ꢀ600 membranes.
The degradation ability of the membranes with 1~7 wt% Cu content are all satisfying.
Correspondingly, the TOC removal percentages were 59.8%, 52.1%, 57.8% and 63.20% for 1, 3, 5
and 7 wt% CuꢀAl2O3ꢀ600 membranes, respectively. These TOC removal percentages were much
higher than that in previous reports (10~30%) under similar conditions for Fenton catalytic oxidation
of BPA.28, 29 Fig. 9B presents the catalytic performance of 5 wt% CuꢀAl2O3 membranes calcined at
different temperatures. The BPA removal percentages within 3 h were ~82%, ~100% and ~100% for
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the membranes calcined at 600, 700 and 800 C, respectively. The catalytic activities of the
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membranes calcined at 700 and 800 C increased obviously compared to 600 C, which was due to
the higher BET surface areas (Fig. 6) and higher surface copper concentration (Fig. S4) at high
calcination temperatures.
The degradation efficiencies of BPA by various Cuꢀbased catalysts are compared (Table S4).
Under the similar conditions, the BPA removal percentages were 98.3%, 100%, 90.4%, 87%, and 85%
by the copper–aluminum–silica nanospheres,14 Mesoporous γꢀCu−Al2O3 powders,13 Mesoporous
Cu/TUDꢀ1 powders,30 1 wt% Cuꢀ Al2O3ꢀ600 membranes, and 5 wt% Cuꢀ Al2O3ꢀ800 membranes,
respectively. The BPA degradation efficiencies by the CuꢀAl2O3 membrane catalysts are comparable
to those by the Cuꢀbased powder catalysts. Advantageously, the membrane form CuꢀAl2O3 catalysts
need no extra separation after use, and the degradation can continuously proceed in the membrane
reactor. Whereas, the powder form CuꢀAl2O3 catalysts usually disperse in water, and need filtration
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or centrifugation to separate them after use. Hence, the flexible CuꢀAl2O3 fibrous membranes have
an improvement over the stateꢀofꢀtheꢀart compared to the existing Fentonꢀlike catalysts, and show
great potentials in waste water remediation area.
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Fig. 9 The influence of (A) Cu content on the BPA removal performance and (B) calcination
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temperatures. Conditions: [BPA] = 20 mg/L, [H2O2] = 12 mM, initial pH = 7.
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The continuous batchꢀtype degradation of BPA in the membrane reactor was evaluated.
Specifically, 10 mL BPA solution was added to the membrane reactor with the addition of 12 mM
H2O2. After more than 5 h, the solution was pulled out from the outlet, labeled as No. 1. Then,
another 10 mL BPA solution with 12 mM H2O2 was added to the solution, and after more than 5 h,
the solution was pulled out from the outlet, labeled as No. 2, and so on. The removal percentages of
the BPA solution were presented in Fig. 10. Compared to the 87% removal percentage of No. 1
solution, the removal percentages were decreased but still kept at ~67% for the degradations toward
No. 2 ~ No. 7 solutions. The decrease of the catalytic activity was mainly occurred after the first time
use. According to the ICPꢀOES analysis, 0.151 mg Lꢀ1 copper was leached during the first time use,
which reduced the copper active sites in the fibers, and it is considered to be the main reason for the
decrease of the catalytic activity. Notably, the leaching amount of Cu decreased to less than 0.01 mg
Lꢀ1 over the third batchꢀtype degradation. Hence the catalytic activity hardly changed for the second
to the seventh batchꢀtype use, and the continuous treatment of bisphenol A could last at least 7 times.
Furthermore, the DMPO spinꢀtrapping ESR results (Fig. 10B) confirmed the generation of •OH in
the presence of CuꢀAl2O3 membranes with H2O2, demonstrating the Fenton catalytic activity of
CuꢀAl2O3 membranes. These results suggested that the CuꢀAl2O3 membranes are effective catalysts
for heterogeneous Fenton reactions, and can be used for continuous degradation of pollutant without
any extra separation or reclaim steps.
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Fig. 10 (A) Continuous batchꢀtype degradation of BPA in the membrane reactor, (B) DMPO
spinꢀtrapping ESR spectra recorded at ambient temperature for 1 wt% CuꢀAl2O3ꢀ600 fibrous
membranes.
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To check the stability of the CuꢀAl2O3 membranes, the leaching of Cu and Al after 3 h reactions,
as well as the SEM and XPS of the membranes after use were tested. According to ICPꢀOES analysis,
the Cu leaching amounts were respectively 0.151, 0.172, 0.308, and 0.517 mg Lꢀ1 for 1 wt%, 3 wt%,
5 wt% and 7 wt% CuꢀAl2O3ꢀ600 membranes, while the Al leaching amounts were remained ~0.18
mg Lꢀ1 for all these membranes. Correspondingly, the Cu leaching percentages in the membranes are
respectively 1.51%, 0.43%, 0.64%, 0.61% for 1, 3, 5, 7 wt% CuꢀAl2O3 membranes, and the Al
leaching percentages are all remained 0.02% (the detailed computation process is in the supporting
information). The leaching percentages of Cu and Al are small, indicating that the CuꢀAl2O3
membranes are relatively stable during use. Moreover, Both of Cu and Al leaching meet the standard
of drinking water, which regulate the limit of Cu is <1.0 mg Lꢀ1, and the limit of Al is <0.2 mg Lꢀ1
(GB 5750ꢀ85, China). Hence, there is negligible secondary pollution of the CuꢀAl2O3 membranes.
From the SEM images (Fig. S6), it can be seen that the membranes are still integrate without any
cracks after use. The XPS results of the membrane after use (Fig. S7 and the discussion in the
supporting information) are almost the same with that before use, except two small differences. One
difference is the disappear of SO42ꢀ in the XPS survey spectrum, which is due to the dissolving of the
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residual SO4 on the surface of the fibers. The other difference is the peak of Cu2+ (935.1 eV)
becomes more evident, which is due to the Cu2+/Cu+ cycles during reaction. These results prove that
the membranes are generally stable during use.
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3.3 Proposed mechanisms
Herein, the •OH generation mechanism via the CuꢀAl2O3 membrane catalysts as well as the
mechanistic pathway of bisphenol A in this system were proposed. The •OH generation mechanism
via the CuꢀAl2O3 membrane catalysts is shown in Fig. 11. Based on the XPS analysis, the AlꢀOꢀCu is
existed in the fibers, and the chemical states of copper are Cu+ and Cu2+. As shown in Fig. 11, the
action mechanism could be generally divided into three steps: In step ①, Cu+ reacts with H2O2 to
generate •OH, and along with the oxidization of Cu+ to Cu2+;13 In step ②, BPA and Cu2+ in the
CuꢀAl2O3 membrane form the σꢀCu2+ꢀligands complexes via σꢀbonding of Cu2+ with the lone pairs of
the oxygen atom in the phenolic OH group.13, 31 In the σꢀCu2+ꢀligands complexes, π→Cu2+ electron
transfer occurs, which could on one hand reduce the Cu2+ to Cu+, on the other hand increase the
electronic polarizability of the aromatic ring.13, 31 In step ③, H2O2 reacts with the aromatic ring that
chelated to Cu2+, and form the substituted aromatic species, which is a key intermediates.32, 33 The
H2O2 interacted with the aromatic ring could on one hand discharge an electron to Cu2+ via the
σꢀCu2+ꢀligands complexes, contributing to the reduction of Cu2+ to Cu+, on the other hand form the
•OH radicals. These three steps possess synergistic effect. Therefore, the Cu2+/Cu+ cycles are
succeeded on the surface of the CuꢀAl2O3 fibers, and •OH free radicals are well generated in this
catalytic system.
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Fig. 11 The •OH generation mechanism via the CuꢀAl2O3 membrane catalysts.
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Hydroxyl radical (•OH) is an extraordinarily reactive species; it possesses strong oxidation
ability with high oxidation potential (E0=2.8 V ), and can attack most organic molecules and
mineralize them to nontoxic carbon dioxide and water.34, 35 Herein, the intermediates in the reaction
were identified (Table. S5 and the analysis in supporting information), and the mechanistic pathway
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of bisphenol A was proposed. As presented in Fig. 12, the reaction pathway was generally divided
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into three steps. In step ①, BPA was hydroxylated, or only one ring was occurred ringꢀopening
reactions by the •OH attack and form the oneꢀring aromatic compounds, or decomposed into
oneꢀring aromatic due to the cleavage of isopropylidene bridge by the •OH attack. In step ②, the
aromatic ring was further cleavaged by the attack of •OH, leading to the formation of aliphatic acids.
Finally, in step ③, all the organic intermediates were further oxidized and mineralized to CO2 and
H2O by the further attack of •OH. As a consequence, BPA was oxidized to CO2 and H2O by the •OH
attack in this reaction.
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Fig. 12 A proposed degradation pathway of BPA in the reaction.
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4. Conclusions
In summary, a novel CuꢀAl2O3 heterogeneous Fenton catalyst in the form of selfꢀstanding
membrane has been successfully synthesized via electrospinning technique. The flexibility of the
membrane is good and favorable for its practical applications. The copper exists in the form of Cu+
and Cu2+ in bulk alumina matrix with high evenly dispersion, providing much active sites in the
fibrous membranes. Over 87% BPA was degraded within 180 min in the membrane reactor using the
1 wt% CuꢀAl2O3 membrane in neutral pH values with H2O2 addition. This work opens up new
avenues for the preparation and application of membranes with Fenton catalytic activities.
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Acknowledgements
This work was financially supported by projects of the National Key Research and Development
Program of China (No. 2016YFA0203101) and Beijing Natural Science Foundation (No. 8174076).
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References
[1] G. Zhao, L. Jiang, Y. He, J. Li, H. Dong, X. Wang, W. Hu, Adv.Mater. 2011, 23, 3959ꢀ3963.
[2] N. Wang, L. Zhu, M. Lei, Y. She, M. Cao, H. Tang, ACS Catal. 2011, 1, 1193ꢀ1202.
[3] N.N. Tušar, D. Maučec, M. Rangus, I. Arčon, M. Mazaj, M. Cotman, A. Pintar, V. Kaučič, Adv.
Funct. Mater. 2012, 22, 820ꢀ826.
3
4
5
6
[4] C.ꢀC. Wang, J.ꢀR. Li, X.ꢀL. Lv, Y.ꢀQ. Zhang, G. Guo, Energy Environ. Sci. 2014, 7, 2831ꢀ2867.
[5] S. Navalon, R. Martin, M. Alvaro, H. Garcia, Angew. Chem. Int. Edit. 2010, 49, 8403ꢀ8407.
[6] S. Navalon, M. de Miguel, R. Martin, M. Alvaro, H. Garcia, J. Am. Chem. Soc. 2011, 133,
2218ꢀ2226.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
[7] M. Hermanek, R. Zboril, I. Medrik, J. Pechousek, C. Gregor, J. Am. Chem. Soc. 2007, 129,
10929ꢀ10936.
[8] H. Lim, J. Lee, S. Jin, J. Kim, J. Yoon, T. Hyeon, Chem.Commun. 2006 463ꢀ465.
[9] X.J. Yang, X.M. Xu, J. Xu, Y.F. Han, J. Am. Chem. Soc. 2013, 135, 16058ꢀ16061.
[10]R. GonzalezꢀOlmos, M.J. Martin, A. Georgi, F.ꢀD. Kopinke, I. Oller, S. Malato, Appl. Catal.
B-Environ. 2012, 125, 51ꢀ58.
[11] G. Zhang, Y. Gao, Y. Zhang, Y. Guo, Environ.Sci.Technol. 2010, 44, 6384ꢀ6389.
[12] Y. Wang, H. Zhao, G. Zhao, Appl. Catal. B-Environ. 2015, 164, 396ꢀ406.
[13] L. Lyu, L. Zhang, Q. Wang, Y. Nie, C. Hu, Environ.Sci.Technol. 2015, 49, 8639ꢀ8647.
[14] L. Lyu, L. Zhang, C. Hu, M. Yang, J. Mater. Chem. A 2016, 4, 8610ꢀ8619.
[15] M. Dükkancı, G. Gündüz, S. Yılmaz, R.V. Prihod’ko, J.Hazard.Mater. 2010, 181, 343ꢀ350.
[16] R. Gopal, S. Kaur, Z. Ma, C. Chan, S. Ramakrishna, T. Matsuura, J. Membrane. Sci. 2006, 281,
581ꢀ586.
[17] Q. Wen, J. Di, Y. Zhao, Y. Wang, L. Jiang, J. Yu, Chem. Sci. 2013, 4, 4378ꢀ4382.
[18] C.L. Zhang, S.H. Yu, Chem. Soc. Rev. 2014, 43, 4423ꢀ4448.
[19] R. Sridhar, R. Lakshminarayanan, K. Madhaiyan, V. Amutha Barathi, K.H. Lim, S.
Ramakrishna, Chem. Soc. Rev. 2015, 44, 790ꢀ814.
[20] P.S. Kumar, J. Sundaramurthy, S. Sundarrajan, V.J. Babu, G. Singh, S.I. Allakhverdiev, S.
Ramakrishna, Energy Environ. Sci. 2014, 7, 3192ꢀ3222.
[21] Y. Wang, W. Ding, X. Jiao, D. Chen, RSC Adv. 2014, 4, 30790ꢀ30797.
[22] Y. Wang, W. Li, Y. Xia, X. Jiao, D. Chen, J. Mater. Chem. A 2014, 2, 15124ꢀ15131.
17

Journal of Materials Chemistry A
Page 18 of 19
View Article Online
DOI: 10.1039/C7TA04386D
1
2
[23] Y. Lei, C. S. Chen, Y. J. Tu, Y. H. Huang and H. Zhang, Environ. Sci. Technol., 2015, 49,
6838ꢀ6845.
3
[24] K.ꢀi. Shimizu, H. Kawabata, H. Maeshima, A. Satsuma, T. Hattori, J. Phys. Chem. B 2000, 104,
2885ꢀ2893.
4
5
[25] L. Yang, C. Hu, Y. Nie, J. Qu, Environ. Sci. Technol. 2009, 43, 2525ꢀ2529.
[26] L. Fu, X. Li, M. Liu, H. Yang, J. Mater. Chem. A 2013, 1, 14592ꢀ14605.
[27]M. Kruk and M. Jaroniec, Chem. Mater., 2001, 13, 3169ꢀ3183.
[28] R.A. Torres, F. Abdelmalek, E. Combet, C. Petrier, C. Pulgarin, J. Hazard. Mater. 2007, 146,
546ꢀ551.
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
[29] R. Huang, Z. Fang, X. Yan, W. Cheng, Chem. Eng. J. 2012, 197, 242ꢀ249.
[30] M. P. Pachamuthu, S. Karthikeyan, R. Maheswari, A. F. Lee and A. Ramanathan, Appl. Surf. Sci.
2017, 393, 67ꢀ73.
[31]A. Lagutschenkov, R. K. Sinha, P. Maitre and O. Dopfer, J. Phys. Chem. A, 2010, 114,
11053ꢀ11059.
[32]S. Goldstein, G. Czapski and J. Rabani, J. Phys. Chem., 1994, 98, 6586ꢀ6591.
[33]C. Walling, D. M. Camaioni and S. S. Kim, J. Am. Chem. Soc., 1978, 100, 4814ꢀ4818.
[34] F. Ghanbari and M. Moradi, Chem. Eng. J., 2017, 310, Part 1, 41ꢀ62.
[35] R. A. Torres, J. I. Nieto, E. Combet, C. Pétrier and C. Pulgarin, Appl. Catal. B-Environ., 2008,
80, 168ꢀ175.
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Graphical abstract
Flexible Cu-Al2O3 membranes with high Fenton catalytic performance have been fabricated via
electrospinning technique.
1