Synthesis of an Ag@AgCl catalyst with amorphous copper as the support and its catalytic performance in the reduction of 4-nitrophenol

Article abstract of DOI:10.1177/1747519820942018

The support used in a composite catalyst has an important influence on the catalytic performance of the catalyst. Amorphous metals have good electron-transfer properties and the presence of defect structures on the surface will introduce additional active sites and should be excellent catalyst supports. In this study, an Ag@AgCl composite catalyst with amorphous Cu (a-Cu) as the support is prepared by a two-step precipitation method at room temperature and a light irradiation reduction method. Compared to the Ag@AgCl and a-Cu, the catalytic rate of the Ag@AgCl/a-Cu composite catalytic rate was 2.04 times and 6.69 times faster during the reduction of 4-NP in NaBH₄ aqueous solution. The high-performance catalytic efficiency and reusability of Ag@AgCl/a-Cu may be attributed to the synergistic effect between Ag@AgC and amorphous metal elements. This work may provide an effective reference for the synthesis of high activity catalysts using amorphous metals as supports.

Full text of DOI:10.1177/1747519820942018

942018CHL0010.1177/1747519820942018Journal of Chemical ResearchZhang et al.
research-article2020
Research Paper
Journal of Chemical Research
1–7
© The Author(s) 2020
Article reuse guidelines:
sagepub.com/journals-permissions
Synthesis of an Ag@AgCl catalyst with
amorphous copper as the support and its
catalytic performance in the reduction of
4-nitrophenol
https://doi.org/10.1177/1747519820942018
DOI: 10.1177/1747519820942018
journals.sagepub.com/home/chl
Jian Zhang, Chenchen Qin, Luying Liu, Hanfeng Dong,
Yujuan Wang, Lei Bao, Wei Gan, Xucheng Fu and Hequn Hao
Abstract
The support used in a composite catalyst has an important influence on the catalytic performance of the catalyst.
Amorphous metals have good electron-transfer properties and the presence of defect structures on the surface will
introduce additional active sites and should be excellent catalyst supports. In this study, an Ag@AgCl composite catalyst
with amorphous Cu (a-Cu) as the support is prepared by a two-step precipitation method at room temperature and
a light irradiation reduction method. Compared to the Ag@AgCl and a-Cu, the catalytic rate of the Ag@AgCl/a-Cu
composite catalytic rate was 2.04 times and 6.69 times faster during the reduction of 4-NP in NaBH4 aqueous solution.
The high-performance catalytic efficiency and reusability of Ag@AgCl/a-Cu may be attributed to the synergistic effect
between Ag@AgC and amorphous metal elements. This work may provide an effective reference for the synthesis of
high activity catalysts using amorphous metals as supports.
Keywords
4-nitrophenol reduction, Ag@AgCl, amorphous Cu, support, synergistic effect
Date received: 16 March 2020; accepted: 18 June 2020
solution. It was found that the catalytic performance of
Ag@AgCl in the reduction of 4-NP by NaBH4 was assisted
Introduction
4-Aminophenol (4-AP) is a valuable intermediate used to
synthesize various drugs and plastic products, and can be
obtained by reducing 4-nitrophenol (4-NP).1–7 Furthermore,
Anhui Provincial Laboratory of Biomimetic Sensor and Detecting
the conversion of 4-NP to 4-AP is a common probe reaction
to test the catalytic activity of some supported metal cata-
lysts. Based on a previous report,8 Ag@AgCl has bifunc-
tional catalytic properties, which not only promotes the
photo degradation of 4-NP under visible light but also
reduced 4-NP to 4-AP in the presence of NaBH4 in aqueous
Technology, West Anhui University, Lu’an, P.R. China
Corresponding author:
Hequn Hao, Anhui Provincial Key Laboratory of Biomimetic Sensor and
Detecting Technology, West Anhui University, Lu’an 237012, Anhui,
P.R. China.
Email: haohequn@163.com

2
Journal of Chemical Research 00(0)
no diffraction peaks. The diffraction peaks at 27.8°, 32.3°,
46.2°, 54.8°, 57.5°, 67.5°, 74.5°, and 76.7° corresponded to
the (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), and (4 0 0) planes
of crystalline AgCl (JCPDS:31-1238), and the weak dif-
fraction peak at 38.1° corresponded to the (1 1 1) plane of
Ag0 crystal (JCPDS: 04-0783) in the Ag@AgCl/a-Cu com-
posite.18,19 It indicated that a small amount of AgCl was
reduced to Ag0, and the addition of a-Cu during the prepa-
ration process had no significant effect on the formation of
AgCl crystals and Ag0. Except for the crystalline peaks of
AgCl and Ag, no other diffraction peak existed, which also
revealed that the elemental copper still was present in the
amorphous state in the Ag@AgCl/a-Cu composite.
The morphology of Ag@AgCl/a-Cu was investigated
with TEM. The TEM image of a-Cu is shown in Figure 2(a).
The amorphous copper was mainly composed of irregular
particles or fragments. Among them, the difference in bright-
ness evident in Figure 2(a) may be caused by copper parti-
cles with different stacking thickness. In order to confirm the
structure of amorphous copper, a high-resolution transmis-
sion electron microscope (HRTEM) and selective area elec-
tron diffraction (SAED) studies were applied (Figure 2(b)
and (c)). No obvious lattice fringe was displayed in the
HRTEM, and no diffraction ring or diffraction spots were
observed in the SAED, which confirmed that the metallic
copper was obtained as an amorphous structure. This result
was also consistent with the XRD results. In the TEM of the
Ag@AgCl/a-Cu composite, uniformly sized spherical dark
areas and sharp borders were evident in Figure 2(d), which
indicated that the particles may contain different substances
and should have anAg@AgCl structure. These black spheres
were about 20nm in diameter and were more evenly distrib-
uted in lighter shades (a-Cu) with traces of encapsulation.
This indicated that the Ag@AgCl structure was not simply
loaded in the aggregates of a-Cu, but may contain someAg@
AgCl covered by a-Cu, which is beneficial to improve the
stability of Ag@AgCl/a-Cu composites. To further deter-
mine the composition, HRTEM and SAED were also applied
and the results are shown in Figure 2(e)–(g). In the HRTEM
image (Figure 2(g)), the lattice fringe spacings of 0.23 and
0.28nm were consistent with cubic Ag (1 1 1) lattice plane
spacing and cubic AgCl (200) lattice plane spacing, respec-
tively.20 In addition, the image also showed the tight interface
between Ag and AgCl in the prepared sample and the forma-
tion of a heterojunction. This was also consistent with the
results of the XRD pattern, which further confirmed that Ag0
was formed on the surface of the AgCl particle.
Figure 1. X-ray diffraction patterns of the different catalysts.
by the catalyst through the transfer of electrons and hydro-
gen atoms on BH4− to organic compounds, as reported pre-
viously.9,10 In order to further improve the Ag@AgCl
catalytic performance, a standard method is to combine
Ag@ AgCl with a support material to form a composite
catalyst.11–15
As an amorphous material is in a metastable state, there
are numerous active sites formed by defects on its surface,
and many “dangling bonds” are present to increase the
adsorption with the target, hence such materials are more
efficient than the crystalline catalysts. Amorphous metal
nanoparticles such as Au and Cu have been used in the
16
17
reduction of N2 and CO2 and show excellent catalytic
ability. Due to its important physical and chemical proper-
ties, non-noble amorphous Cu was the selected support for
the composite catalysts, which should improve the cata-
lytic performance of the composite material. However, as
far as we know, there are very few reports in this research
field.
In this study, an Ag@AgCl composite catalyst with
amorphous Cu as the support is prepared by a two-step pre-
cipitation method at room temperature and a light irradia-
tion reduction method. The structure, morphology, and
chemical element states of the composite catalyst were
characterized by X-ray diffraction, transmission electron
microscopy, and X-ray photoelectron spectroscopy, which
confirmed the successful synthesis of the composite cata-
lyst. The catalytic reduction performance of the catalyst
was studied with 4-NP as the reduction target, and the
results showed that Ag@AgCl/a-Cu demonstrated high-
performance catalytic efficiency and reusability.
X-ray photoelectron spectroscopy was applied to ana-
lyze the chemical states of the elements contained in the
Ag@AgCl/a-Cu composite, and the energy spectrum was
calibrated by the C1s peak (284.8eV). From the analysis of
the XPS spectrum (Figure 3(a)), the Ag@AgCl/a-Cu com-
posites were mainly composed of three elements: Ag, Cl,
and Cu. The C1s and O1s peaks may originate from ethanol
Results and discussion
Characterization of the composite catalyst
The phase structure and diffraction pattern of a-Cu and or TA molecules adsorbed on the surface of the sample.
Ag@AgCl/a-Cu were studied by powder X-ray diffraction From the high-resolution core-level XPS spectrum for Cl2p
(XRD). Figure 1 shows the typical powder XRD pattern of (Figure 3(b)), the Cl2p peak was composed of two peaks,
a-Cu and Ag@AgCl/a-Cu. CuCl2 can be reduced to a-Cu 197.8eV (Cl2p3/2) and 199.3eV (Cl2p1/2), respectively,
with the assistance of tannic acid (TA), a mild reducing which indicated that the chlorine is in the Cl−1 state. In
agent, and a-Cu displayed the typical amorphous state with Figure 3(c), two double isolated peaks at ~368 and ~374eV

Zhang et al.
3
Figure 2. TEM, HRTEM, and SAED of a-Cu and Ag@AgCl/a-Cu. (a)–(c) are the TEM, HRTEM, and SAED of a-Cu support, (c) and
(d) are the TEM images of Ag@AgCl/a-Cu, the SAED pattern is shown in (e) as an illustration, and (f) and (g) are HRTEM images at
different magnifications.
for Ag3d with a ca. 6eV interval distance in the spectrum of metallic silver.8 However, in the case of Cu, it was found
can be assigned to each Ag3d5/2 and Ag3d3/2 binding mostly in the metallic state Cu0 (Figure 3(d)). Two major
energy.21,22 The peaks of Ag3d5/2 and Ag3d3/2 can be fur- peaks located at binding energies of 932.3 and 952.1eV
ther divided into different peaks at 367.45 and 368.25eV, corresponded to Cu 2p3/2 and Cu 2p1/2, respectively, typi-
373.45 and 374.15eV. The peaks of 367.45 and 373.45eV cally due to zero-valent Cu.17,23 In addition, the shake-up
can be attributed to the Ag3d peaks of AgCl, and the peaks satellite peaks located at 941.2 and 944.1eV were ascribed
at 368.25 and 374.15eV can be attributed to theAg3d peaks to the open 3d9 shell of Cu2+, which meant that a small

4
Journal of Chemical Research 00(0)
Figure 3. (a) The X-ray full-scan spectrum of Ag@AgCl/a-Cu. (b–d) The narrow scan spectra of the Cl 2p, Ag 3d, and Cu 2p
peaks.
amount of unreduced Cu2+ was co-present in the amor-
phous copper.24 Overall, XPS analysis confirmed the pres-
ence of metallic Ag, AgCl, and amorphous metallic Cu in
the Ag@AgCl/a-Cu composite.
Catalytic studies
The catalytic activity of theAg@AgCl/a-Cu composite was
evaluated by reducing 4-NP using NaBH4 as the reducing
agent. After NaBH4 had been added, the maximum absorp-
tion peak of 4-NP shifted from 317 to 400nm, and the color
of the solution changed from colorless to pale yellow due to
the formation of 4-nitrophenolate ions under alkaline con-
ditions. With the assistance of the Ag@AgCl/a-Cu compos-
ite catalyst, the solution became colorless within 120s, and
the peak at 400nm disappeared, accompanied by a new
Figure 4. UV-Vis absorption spectra of 4-nitrophenol,
4-nitrophenolate ion, and 4-aminophenol.
peak at 300nm, indicating that 4-NP had been reduced to
4-AP (Figure 4).
The changes in UV-Vis absorption values in relation to
time during the reduction of 4-NP to 4-AP with the assis-
tance of a-Cu, Ag@AgCl, and Ag@AgCl/a-Cu composites
are displayed in Figure 5, where Ct and C0 are the concen-






Ct
ln
= −kt
C0
trations of 4-nitrophenol at time t and 0, respectively. where k represents the rate constant (s−1). Figure 5(d) shows
Compared with a-Cu and Ag@AgCl, the Ag@AgCl/a-Cu the 4-NP reduction rate constants for α-Cu, Ag@AgCl, and
composite exhibited the best catalytic activity.
the Ag@AgCl/a-Cu composite. The results indicated that
NaBH4 was present in a large excess compared to 4-NP, 4-NP reduction follows the pseudo-first-order model,
so the NaBH4 concentration can be assumed as constant, which is consistent with previously reported works.25–28
and the reduction of 4-NP favors pseudo-first-order kinet- The Ag@AgCl/a-Cu composite sample has the highest
ics. The reduction rates of 4-NP by the as-prepared cata- reduction rate constant of 2.81×10−2 s−1, which is 2.04
lysts were calculated using the following pseudo-first-order times that of Ag @ AgCl (1.38×10−2 s−1) and 6.69 times
kinetic equation
that of a-Cu (3.31×10−3 s−1). As previously reported by

Zhang et al.
5
Figure 5. Time-dependent UV-Vis absorption spectra for the reduction of 4-NP to 4-AP with (a) a-Cu, (b) Ag@AgCl, and (c)
Ag@AgCl/a-Cu as the catalyst. The plot of (d) Ct/C0 and (e) –ln(Ct/C0) versus the reaction time for the different catalysts. (f) The
recyclability of the Ag@AgCl/a-Cu composite catalyst for the reduction of 4-NP in NaBH4 solution.
ability.8,16 In this study, the prepared Ag@AgCl/a-Cu com-
posite exhibited excellent catalytic reduction properties for
4-NP, which may be due to the good synergistic effect
between the two catalytic materials. In addition, Table 1
gives a detailed comparison of the analytical parameters
between the proposed system and other recently reported
catalysts. Compared with other catalysts, Ag@AgCl/a-Cu
has higher catalytic activity.
For practical catalysts, especially those containing noble
metal elements, recyclability is a very important issue. The
catalyst was tested for its stability and reusability by recy-
cling experiments. The results of five cycles are displayed
in Figure 5(f), indicating that the catalytic efficiency
decreases slightly based on the number of cycles. On the
fifth reuse, the catalytic reduction efficiency was 84.7%.
Table 1. Comparison of Ag@AgCl/a-Cu with other recently
reported catalysts for the reduction of 4-NP.
Catalyst
ks−1
References
Ag
Au
Cu
5.9×10−4
9.8×10−4
1.6×10−3
1.17×10−2
2.0×10−3
1.17×10−2
3.831.6×10−4
Esumi et al.29
Wang et al.30
Deka et al.31
Wu et al.32
Zhang et al.33
Yang et al.34
Ayodhya and
Veerabhadram2
This work
Cu/Ag
Pt@Pd
Cu@CNT
CuS/g-C3N4
Ag@AgCl/a-Cu
2.81×10−2
Wang et al.,8 the catalytic property of the AgCl@Ag com-
posite for the reduction of 4-NP by NaBH4 is due to the
-
donation of an electron or hydrogen atom from BH4 to
Conclusion
organic compounds. As an amorphous Cu, it not only
retains the good electron conductivity of the metal but also
has many structural defects and dangling bonds distributed
on the surface, which results in it having a good catalytic
In conclusion, an Ag@AgCl/a-Cu composite catalyst has
been prepared by a two-step precipitation method at room
temperature followed by a light irradiation reduction

6
Journal of Chemical Research 00(0)
method. The reduction-catalytic activity of the Ag@AgCl/ ESCALAB 250 spectrometer with monochromatic Al Kα as
a-Cu composites was studied in the reduction of 4-NP in the excitation source. The UV-Vis spectra were recorded on
aqueous NaBH4 solution, and 95.1% of 4-NP was reduced a UH4150 (Hitachi) UV-Vis spectrophotometer.
to 4-AP in 120s by fresh Ag@AgCl/a-Cu composite cata-
lyst. The high-performance catalytic efficiency and reusa-
bility of Ag@AgCl/a-Cu can be attributed to the synergistic
Reduction of 4-NP
effect between Ag@AgC and amorphous metal elements.
This research may provide an effective reference for the
preparation of high-performance composite catalysts using
amorphous metals as supports.
The reduction of 4-NP was performed in a glass flask in the
presence of the different catalysts (a-Cu, Ag@AgCl, and
Ag@AgCl/a-Cu) and aqueous NaBH4 solution under con-
stant stirring. In a typical procedure, first, 4-NP (20mL,
0.10mM) aqueous solution was purged with N2 to remove
dissolved oxygen in the aqueous solution, and then freshly
prepared NaBH4 (5mL, 20mM) were added. At this time,
the colorless and transparent aqueous solution turned pale
yellow. So, 4-NP showed a characteristic absorption peak at
317nm in a neutral or acidic medium but after adding
NaBH4, the 4-nitrophenolate ion was formed, and the
absorption peak shifted to 400nm. After the addition of the
catalyst, the characteristic peak at 400nm decreased with
time and a new peak appeared at 300nm. The solution was
stirred during the reaction, and the supernatant was trans-
ferred to a quartz cuvette for UV-Vis spectrum measure-
ments. The decrease in the 400nm characteristic absorption
peak indicated a decrease in the amount of 4-NP.
Experimental section
Materials and reagents
Copper chloride dehydrate (CuCl2·2H2O, AR, 99%), tan-
nic acid (TA, 99%), sodium hydroxide (NaOH, AR, 96%),
sodium borohydride (NaBH4, AR, 99%), silver nitrate
(AgNO3, AR, 99%), and 4-nitrophenol (4-NP, AR, 99%)
were purchased from Sinopharm Chemical Reagent Co.,
LTD. All reagents were used without further purification
and distilled water with a resistance of 18.2MΩ was used
throughout the experiments.
Synthesis of amorphous Cu (a-Cu) support
Declaration of conflicting interests
CuCl2·2H2O (0.2g) and TA (0.08g) were added to deion-
ized water (38mL) and were completely dissolved by ultra-
sonic treatment and stirring. Next of NaOH (2.0mL, 1M)
was added dropwise to the above solution during stirring
for 10min, and the solution was then stirred for a further
15min again. The product was collected by centrifugation,
washed with water and ethanol several times, and then
dried under vacuum overnight. All the operations described
above were performed at room temperature.
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article:
This work was financially supported by West Anhui University
(WGKQ201702022, WXBSH2019004, 201910376003), Anhui
Provincial Education Department (gxgnfx2019029), and Anhui
Provincial Natural Science Foundation (1808085QH233, 18080
85QB33).
Synthesis of the composite catalyst
CuCl2·2H2O (0.2g) and TA (0.08g) were added to deion-
ized water (38mL), and were completely dissolved by soni-
cation and stirring. Next, during stirring, NaOH (2.0mL,
1M) was added dropwise to the above solution for 10min,
and after stirring the solution for 15min, AgNO3 (0.2g) was
added, and stirring was continued for 30min. The product
was collected by centrifugation, washed several times with
water and ethanol, and then dried under vacuum overnight.
The resulting powder was irradiated under an ultraviolet
lamp for 60min to ensure that Ag+ was partly reduced to
Ag0 to give Ag@AgCl/a-Cu composite catalyst as a gray
powder. The Ag@AgCl composite catalyst was synthe-
sized by a similar method.
ORCID iD
Hequn Hao
https://orcid.org/0000-0002-9758-4115
References
1. Afedz TW, Kwon E, Tuan DD, et al. Sci Total Environ 2020;
703: 134781.
2. Ayodhya D and Veerabhadram G. Flat Chem 2019; 14:
100088.
3. Kang X, Teng D, Wu S, et al. J Colloid Interf Sci 2020; 566:
265.
4. Sun X, He P, Gao Z, et al. J Colloid Interf Sci 2019; 553: 1.
5. He L, Tong Z, Wang Z, et al. J Colloid Interf Sci 2018; 509:
448.
6. Peng X, Cao J, Xie B, et al. Ecotox Environ Safe 2020; 188:
109869.
Characterization
7. Karaoğlan GK, Gümrükçü G, Koca A, et al. Dyes Pigm
2011; 90: 11.
The XRD patterns were recorded on the D8 advance
Diffractometer(Bruker)equippedwithCuKα(λ=1.54056Å)
radiation (40kV, 40mA). TEM analysis was carried out by
transmission electron microscopy (2010-Plus, JEOL) at an
accelerating voltage of 200kV. X-ray photoelectron spec-
troscopy (XPS) was carried out using a ThermoScientific
8. Zheng Y, Shu J and Wang Z. Mater Lett 2015; 158: 339.
9. Sun L, He J, An S, et al. Chinese J Catal 2013; 34: 1378.
10. Lin FH and Doong RA. J Phys Chem C 2011; 115: 6591.
11. Zou Y, Huang H, Li S, et al. J Photoch Photobio A 2019;
376: 43.

Zhang et al.
7
12. Shen H, Wei H, Pan Z, et al. Appl Surf Sci 2017; 423: 403.
13. Jiao Z, Zhang J, Liu Z, et al. J Photoch Photobio A 2019;
371: 67.
14. Cai A, Guo A, Du L, et al. Mater Res Bull 2018; 103: 225–
233.
24. Anandan S, Lee GJ and Wu JJ. Ultrason Sonochem 2012; 19:
682.
25. Rostami-Vartooni A, Nasrollahzadeh M and Alizadeh M. J
Alloy Compd 2016; 680: 309.
26. Jiang X, An QD, Xia ZY, et al. J Phys Chem Solids 2020;
138: 109250.
15. Li X, Wu D, Luo Q, et al. J Alloy Compd 2017; 702: 585.
16. Li SJ, Bao D, Shi MM, et al. Adv Mater 2017; 29: 1700001. 27. Sahu K, Satpati B, Singhal R, et al. J Phys Chem Solids
17. Duan YX, Meng FL, Liu KH, et al. Adv Mater 2018; 30:
2020; 136: 109143.
1706194.
28. Zeynizadeh B and Karami S. Polyhedron 2019; 166: 196.
18. Gan W, Fu X and Zhang J. Mat Sci Eng B- Adv 2018; 229: 29. Esumi K, Isono R and Yoshimura T. Langmuir 2004; 20:
44–52.
237.
19. Ai C, Yang S, Zhang F, et al. Adv Powder Technol 2019; 30: 30. Wang X, Long Y, Wang Q, et al. Carbon 2013; 64: 499–
3193–3202.
506.
20. Zhang S, Gao H, Li J, et al. J Hazard Mater 2017; 321: 92– 31. Deka P, Deka RC and Bharali P. New J Chem 2014; 38:
102.
1789.
21. Liu L, Deng J, Niu T, et al. J Colloid Interf Sci 2017; 493: 32. Wu W, Lei M, Yang S, et al. J MaterChem A 2015; 3:
281.
3450.
22. Xia D, An T, Li G, et al. Water Res 2016; 99: 149.
23. Diyarbakir S, Can H and Metin Ö. ACS Appl Mater Inter
2015; 7: 3199.
33. Zhang J, Gan W, Fu XC, et al. Mater Res Express 2017;4:
10.
34. Yang T, Tang Y, Liu L, et al. Chem Phys 2020; 533: 110738.