New perspective of a nano-metal preparation pathway based on the hexahydro-closo-hexaborate anion

Article abstract of DOI:10.1039/d0ra05914e

Today, metal-based nanomaterials play an increasingly important role in the energy, environment, medical and health fields. In order to meet the needs of various fields, it is necessary to continuously develop advanced technologies for preparing metal-based materials. Inspired by previous research, the results of a proof-of-concept experiment show that the hexahydro-closo-hexaborate anion (closo-[B₆H₇]^?) in the borane cluster family has properties similar to NaBH₄.Closo-[B₆H₇]^?can not only convert common precious metal ions such as Au³⁺, Pd²⁺, Pt⁴⁺and Ag⁺to the corresponding zero-valence state, but also convert some non-precious metals such as Cu²⁺and Ni²⁺to the zero-valent or oxidation state.Closo-[B₆H₇]^?moderate reduction to cause rapid aggregation of metal-based materials is not easy compared with NaBH₄. Compared withcloso-[B₁2H₁₂]^2?,closo-[B₆H₇]^?achieves the conversion of Pt⁴⁺to Pt⁰under ambient conditions, and its reduction performance extends to non-precious metals. The excellent stability and easy modification characteristics determine the universality of thecloso-[B₆H₇]^?reduction strategy for metal ions.

Full text of DOI:10.1039/d0ra05914e

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New perspective of a nano-metal preparation
pathway based on the hexahydro-closo-
hexaborate anion
Cite this: RSC Adv., 2020, 10, 33444
Jun Liu, Xue Zhao* and Haibo Zhang *b
a
ab
Today, metal-based nanomaterials play an increasingly important role in the energy, environment, medical
and health fields. In order to meet the needs of various fields, it is necessary to continuously develop
advanced technologies for preparing metal-based materials. Inspired by previous research, the results of
À
a proof-of-concept experiment show that the hexahydro-closo-hexaborate anion (closo-[B
6
H
7
] ) in the
À
borane cluster family has properties similar to NaBH
. Closo-[B H
4 6 7
]
can not only convert common
3+
2+
4+
+
precious metal ions such as Au , Pd , Pt and Ag to the corresponding zero-valence state, but also
2+
2+
convert some non-precious metals such as Cu and Ni to the zero-valent or oxidation state. Closo-
À
[B
6
H ]
7
moderate reduction to cause rapid aggregation of metal-based materials is not easy compared
Received 7th July 2020
Accepted 28th August 2020
2À
À
4+
0
with NaBH
4
. Compared with closo-[B
1
2H12
]
, closo-[B H
6 7
]
achieves the conversion of Pt to Pt
under ambient conditions, and its reduction performance extends to non-precious metals. The excellent
DOI: 10.1039/d0ra05914e
À
stability and easy modification characteristics determine the universality of the closo-[B
H
6 7
]
reduction
rsc.li/rsc-advances
strategy for metal ions.
reduction potential, and the solution must not contain other
substances that are easily converted. On the other hand, because
Introduction
Bulk metals severely limit their surface exposure due to their low the reaction occurs on the electrode, this limits the possibility of
specic surface area, and the development of metal nanoparticles large-scale preparation of zero-valent nanometals, and the
has promoted rapid changes in the chemical world. Today, the nanometals obtained by electrodeposition can only be supported
excellent performance of nanometals is driving rapid progress in on specic electrode carriers. The mechanical grinding method
different elds such as molecular catalysis, biomedicine, energy is the most traditional way to crush a bulk metal body from top to
storage, optics, and magnetism, and researchers from various bottom to reach a specied size, and its realization is usually
10
regions are constantly exploring the multifunctional applications carried out in a ball mill or mortar. The mechanical grinding
1–4
of diverse nanometals. Traditional methods for preparing method can increase the specic surface area of the metal to
nanometals usually include thermal decomposition of metal a certain extent, but it is usually accompanied by uneven particle
ions, chemical reduction, electrodeposition, and mechanical size of the metal particles and air oxidation pollution caused by
grinding. The thermal decomposition of metal ions is usually long-term grinding. The chemical reduction method is the most
done in hydrothermal (or solvothermal) kettles and tube furnaces widely used method for preparing the corresponding zero-valent
(
or muffle furnaces), where the principle is that the chemical nanometals from metal ions, and is characterized by being fast,
reducing agent (such as ethylene glycol or H ) converts the metal simple and practical. In general, sodium borohydride (NaBH ) is
from the ionic state to the zero-valent state or oxide. The the most widely used chemical reducing agent, and can reduce
2
4
5–7
11
implementation of this method requires the support of special most metal ions due to its strong reducing ability. However, the
equipment, and is oen accompanied by potential safety hazards strong reducing power of NaBH results in the reaction being
4
and large energy consumption. Electrodeposition is a new way of completed instantaneously. The result is severe aggregation or
preparing zero-valent metals, which converts metal ions to a zero- large particle size distribution of the nanometals. Based on this,
valent state by applying a certain potential (depending on the it is of practical signicance to continue to develop new boro-
8,9
standard electrode potential of the metal ions). On the one hydrides with appropriate reducing power as chemical reducing
hand, the electrodeposition method needs to strictly control the agents for the preparation of nanometals.
2
À
Recently, our team has proved that closo-[B12
H
12
]
can
3
+
2+
4+
+
reduce Au , Pd , Pt and Ag noble metal ions to the zero
valence state, and except for Pt , which needs to be reduced at
80 C, the other reduction reactions can be successfully ach-
a
College of Chemistry and Materials Engineering, Hunan University of Arts and
4+
Science, Changde 415000, P. R. China. E-mail: xuezhao0208@gmail.com
ꢀ
b
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P. R.
12–20
ieved at room temperature.
The development of this
China. E-mail: haibozhang1980@gmail.com
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technology has opened up a brand-new route for the prepara- Then, 20.2 mL of HAuCl
4
(24.8 mM) solution was added to
tion of precious metal nanoparticles (including supported solution A and solution B, respectively. Aer ve minutes, the
nanometals), which benets from the excellent modication solid product was separated by high-speed centrifugation and
2
À
ꢀ
properties of the new closo-[B H ]
reducing agent. For dried at 60 C under vacuum for 6 h.
1
2
12
2
+
example, constructing a boron organic polymer or metal boron
Cs[B
] and 38.0 mg (1 mmol) NaBH
realize the pre-xation of the reducing agent in the frame, and ultra-pure water, respectively, to form solution A and solution B.
precious metal ions can be converted into the corresponding Then, 14.8 mL of Na PdCl (33.9 mM) solution was added to
solution A and solution B, respectively. Aer ve minutes, the
6
H
7
] and NaBH
4
reduce Pd . 204.8 mg (1 mmol) Cs
2
À
organic polymer frame material with closo-[B12
H
12
]
can [B
6
H
7
4
were dissolved in 5 mL
2
4
2
À
zero-valent metals in situ (by replacing the closo-[B12H ]
12
position). This is an innovative strategy for preparing metal- solid product was separated by high-speed centrifugation and
ꢀ
based catalysts. However, the properties of other closed boro- dried at 60 C under vacuum for 6 h.
2
À
4+
hydrides of the closo-[B H ] family have not been developed
Cs[B H ] and NaBH reduce Pt . 409.6 mg (2 mmol) Cs
6 7 4
n
n
and reported in this regard.
6 7 4
[B H ] and 76.0 mg (2 mmol) NaBH were dissolved in 5 mL
Here, we report a closed borohydride reductant with ultra-pure water, respectively, to form solution A and solution B.
2
À
a reduction capacity between NaBH and closo-[B12H ] , closo- Then, 25.0 mL of Na PtCl (20 mM) solution was added to
4 12 2 6
2
À
[
B
6
H
6
]
(except in strong alkali environments, where it exists in solution A and solution B, respectively. Aer ve minutes, the
À
the form of closo-[B
6
H
7
] ), which can not only reduce noble solid product was separated by high-speed centrifugation and
ꢀ
metal ions to the corresponding zero-valent metals, but also dried at 60 C under vacuum for 6 h.
+
reduce some non-noble metal ions. On the one hand, closo-
Cs[B H ] and NaBH reduce Ag . 204.8 mg (1 mmol) Cs
6 7 4
2
À
[
B H ]
has a moderate reduction capacity compared to [B H ] and 38.0 mg (1 mmol) NaBH were dissolved in 5 mL
6 7 4
6
6
NaBH
4
, which can avoid excessive violent reaction. On the other ultra-pure water, respectively, to form solution A and solution B.
2
À
hand, closo-[B has the same modiable characteristics as Then, 170.0 mg (1 mmol) AgNO
À
12
closo-[B12H ] , so it can be used in various elds, which will water) was added to solution A and solution B, respectively.
6
2
H
6
]
3
(dissolved in 20 mL ultrapure
add a wide range of uses and lay a solid foundation for this new Aer ve minutes, the solid product was separated by high-
ꢀ
+
boron polyhedron-stabilized metal nanocatalyst.
speed centrifugation and dried at 60 C under vacuum for 6 h.
2
Cs[B H ] and NaBH reduce Ni . 819.6 mg (4 mmol) Cs
6
7
4
[
B H ] and 151.0 mg (4 mmol) NaBH were dissolved in 20 mL
6 7 4
Experimental
Chemicals and materials
ultra-pure water, respectively, to form solution A and solution B.
Then, 580.0 mg (2 mmol) Ni(NO $6H O (dissolved in 10 mL
ultrapure water) was added to solution A and solution B,
3
)
2
2
21
6 7
Cs[B H ] was synthesized according to the literature method,
and other chemical reagents were purchased from Aladdin respectively. Aer ve minutes, the solid product was separated
ꢀ
Chemical Reagent Co., Ltd. (Shanghai, China). Among them, by high-speed centrifugation and dried at 60 C under vacuum
NaBH , HAuCl , Na PdCl , H PtCl , AgNO , Ni(NO ) $6H O and for 6 h.
4
4
2
4
2
6
3
3 2
2
2
+
Cu(NO ) $3H O are all analytical grade. Except for HAuCl ,
Cs[B
] and 151.0 mg (4 mmol) NaBH
4
6
H
7
] and NaBH
4
reduce Cu . 819.6 mg (4 mmol) Cs
3
2
2
4
Na PdCl and H PtCl , which were formulated into a solution of [B
H
were dissolved in 20 mL
2
4
2
6
6
7
specied concentration, the other chemical reagents were used ultra-pure water, respectively, to form solution A and solution B.
À1
directly as they are. Milli-Q ultrapure water (18 MU cm ) was Then, 483.1 mg (2 mmol) Cu(NO
3
)
2
$3H
2
O (dissolved in 10 mL
used to prepare all solutions.
ultrapure water) was added to solution A and solution B,
respectively. Aer ve minutes, the solid product was separated
ꢀ
by high-speed centrifugation and dried at 60 C under vacuum
for 6 h.
Characterization method
In this study, X-ray photoelectron spectroscopy (XPS, ESCA-
LAB250Xi, USA) and powder X-ray diffraction (PXRD, Rigaku
Miniex600, Japan) were mainly used to identify the valence
state and crystal phase composition of the metal aer the
reaction. Field emission scanning electron microscopy (FE-
SEM, Zeiss SIGMA, UK) and transmission electron microscopy
Simulated preparation of commercial 20 wt% Pt/C. 25 mL of
H PtCl (20 mM) solution and 475.0 mg of graphite powder were
added to 100 mL of H O and then mixed ultrasonically. Then,
H ] (dissolved in 5 mL of ultrapure
6 7
water) was added under stirring. Aer stirring for 10 min, the
lter cake was collected by ltration and washed three times
with ultrapure water. The obtained solid was dried at 60
under vacuum for 6 h to obtain the simulation 20 wt% Pt/C.
2
6
2
409 mg (2 mmol) of Cs[B

(TEM, HITACHI H-7000FA, Japan) were used to observe the
ꢀ
C
À
micro morphology of Au, Pd, Pt and Ag driven by closo-[B H ] .
Among them, SEM adopted the InLens mode and the acceler-
ation voltage was 5 kV, and the voltage and current of TEM were
6
7
Electrocatalytic water decomposition to H . The electro-
2
chemical test was completed in a single-chamber electrolytic
cell containing a three-electrode system. Among them, the
working electrode is carbon paper containing a catalyst, the
counter electrode is a graphite rod (purity 99.999 wt%), the
75 kV and 4 A, respectively.
Experimental procedures
3
+
Cs[B H ] and NaBH reduce Au . 204.8 mg (1 mmol) Cs reference electrode is an Ag/AgCl electrode lled with saturated
6
7
4
[B
6
H
7
] and 38.0 mg (1 mmol) NaBH
4
were dissolved in 5 mL KCl solution, and the electrolyte is a 1 M KOH solution. The
ultra-pure water, respectively, to form solution A and solution B. working electrode was prepared as follows: 10 mg simulation
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2
1
0 wt% Pt/C was dispersed in 1 mL of isopropanol containing ions into the corresponding zero valence states in a mild
4
+
0
00 mL of 5 wt% Naon solution, and the suspension was manner, where only Pt to Pt requires an additional condition
ꢀ
sonicated for 30 min to form a uniform ink. Then, 20 mL of ink is of 80 C. This indicates that the closed borane anion cluster has
evenly coated on carbon paper (0.5 Â 0.5 cm), which is the properties similar to NaBH . However, apart from the reports of
4
working electrode aer natural air drying. Before each electro- our team, few other studies have been reported. In order to
À
chemical test, 10 cyclic voltammetric (CV) sweeps were per- explore the potential of closo-[B
6
H
7
]
in the preparation of
formed to activate the working electrode, and then a linear metal-based materials, we carried out a detailed exploration
sweep voltammetric (LSV) curve was recorded at a sweep rate of with NaBH
4
as a reference.
À1
1
mV s . All reported potentials are relative to the reversible
Fig. 1 shows the PXRD of metal-based materials prepared
À
hydrogen electrode.
with closo-[B H ] and NaBH as reducing agents, respectively,
6
7
4
Reduction of 4-nitrophenol to 4-aminophenol. At room which can show the crystalline phase composition in the
temperature, 189.0 mg (5 mmol) NaBH was added to 20 mL (50 material. Among them, Fig. 1a–f are the results of a reducing
4
3
+
2+
4+
+
2+
2+
mM) of 4-NP aqueous solution. Aer mixing well, 10.0 mg of agent acting on Au , Pd , Pt , Ag , Ni and Cu ; closo-
À
copper powder prepared by Cs[B
6
H
7
] reduction was added to the [B
6
H
7
]
and NaBH
4
can reduce them to the zero valence state,
above mixed solution, and the reaction system was kept mixing and they present a face-centered cubic structure. In the case of
À
under magnetic stirring. Within the same time interval (2 min), closo-[B
6
H
7
]
and NaBH
4
as reducing agents, the PXRD results
1
00 mL of the sample was removed from the mixture and diluted of the metal-based materials obtained are almost consistent,
À
to 20 mL. Aer ltering to remove the catalyst, the changes in indicating that the mechanism of action of closo-[B H ] is
6
7
absorbance at 400 nm were recorded by an ultraviolet-visible consistent with that of NaBH . Although PXRD can judge the
4
spectrometer.
composition state of the material to a certain extent from the
crystal phase composition, some compositions exist in a disor-
dered state. In order to further understand the evolution of
Results and discussion
3+
2+
4+
+
2+
2+
Au , Pd , Pt , Ag , Ni and Cu under the action of closo-
À
[B
6
H
7
] , the valence state of the composition in the material
The scope of application of nanomaterials is constantly
expanding, and their preparation strategies are also being
constantly enriched. Previous studies have shown that closo-
3
+
was analyzed by XPS (Fig. 2). In the XPS aer Au evolution,
only two separate signal peaks appear, among which the two
peaks near the bond energy of 84.0 eV and 87.7 eV can be
2À
3+
2+
4+
+
[B
12
H
12
]
can transform Au , Pd , Pt and Ag noble metal
2
+
attributed to Au4f7/2 and Au4f5/2. In the evolution of Pd , there
6 7 6 7
Fig. 1 PXRD results of metal materials prepared with Cs[B H ] and Fig. 2 XPS results of metal materials prepared with Cs[B H ] and
3
+
2+
3+
2+
NaBH
4 4
as reducing agents. (a) Converted Au ; (b) converted Pd ; (c) NaBH as reducing agents. (a) Converted Au ; (b) converted Pd ; (c)
4+
+
2+
4+
+
2+
converted Pt ; (d) converted Ag ; (e) converted Ni ; and (f) con- converted Pt ; (d) converted Ag ; (e) converted Ni ; and (f) con-
2+
2+
verted Cu
.
verted Cu .
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À
6 7
are signal peaks that can be split further. The two narrower and [B H ] , due to the strong polarization of B, each H atom carries
21
prominent signal peaks around 335.0 eV and 340.3 eV were an excess of electrons (0.00345e), so it exhibits properties
attributed to the contribution of zero-valent Pd (Pd3d5/2 and similar to NaBH (the consistency from the PXRD results has
4
Pd3d3/2), while the two weaker wide peaks around 337.0 eV and been veried). The difference is that the reducing ability of
3
3 3 4
42.0 eV were attributed to PdO d5/2 and PdO d3/2, respectively. NaBH is too strong, and the metal ions that are instantly
4
+
In the XPS aer Pt evolution, only two independent signal converted (or reduced) tend to agglomerate, which seriously
peaks appear at 71.6 eV and 74.95 eV, corresponding to the hinders the uniformity and nanometerization of zero-valent
À
3+
binding energy of Pt4f7/2 and Pt4f5/2. Similarly, in the XPS aer metals. Closo-[B
6
H
7
]
has a mild reducing ability, and Au ,
Ag evolution, only two independent signal peaks appear at Pd , Pt , and Ag are converted into sols at room temperature
68.3 eV and 374.3 eV, corresponding to the contribution of (Fig. 3a–d). On the other hand, the color of these sols is lighter
+
2+
4+
+
3
2
+
Ag3d5/2 and Ag3d3/2. XPS shows that Ni evolved into two forms than that of NaBH , indicating better dispersibility and smaller
4
of Ni and NiO. The signal peak of 852.5 eV is the characteristic particle size (generally, the stronger the aggregation of nano-
binding energy of Ni2p3/2, and the signal peak of the corre- materials, the more the color they show tends to blue shi). FE-
3
+
2+
sponding salt appears at 861.3 eV. The XPS signal peak of NiO SEM and TEM can also show that Au (Fig. 3e and f), Pd
2
+
+
appears near 855.5 eV, and the signal peak of its corresponding (Fig. 3g and h), Pd (Fig. 3i and j) and Ag (Fig. 3k and l) evolved
À
salt appears near 880.0 eV. It is difficult to analyze the evolution into nano-scale particles under the action of closo-[B
2
O and to the chemical adsorption between Pt and closed cage borane,
CuO are similar (all around 932.5 eV), but combined with the so Pt nanoparticles appear to be encapsulated ). For non-noble
PXRD results, it can be well judged that Cu has evolved into metal ions Ni and Cu , the reduction ability of closo-[B H ]
zero-valent Cu and CuO. In summary, the analysis of the XPS is gentler, and the reduction reaction needs to reach about 60 C
results is: (1) Au , Pt and Ag are almost completely converted before it can start. As we all know, NaBH
to the zero-valent state (Au , Pt , Ag ); (2) the vast majority of preferentially reduces the metal ions that are arranged behind
Pd is converted to Pd , and a small part is in the state of PdO, the metal activity sequence. Therefore, when there are metal
some of which may come from the inevitable oxidation of the ions stronger than H , NaBH
is reductively similar to NaBH , it can almost
and a small part is in the zero valent state; (4) Cu is converted convert the noble metal ions Au , Pd , Pt and Ag into the
6
H
7
]
(due
2
+
of Cu in XPS, because the binding energies of Cu, Cu
20
2
+
2+
2+
À
7
6
ꢀ
3
+
4+
+
4
in aqueous solution
0
0
0
2
+
0
+
+
4
preferentially reduces H . Since
2
+
À
surface; (3) most of the Ni is converted into the form of NiO, closo-[B
6
H
7
]
4
2
+
3+
2+
4+
+
2
+
2+
into two forms of Cu and CuO.
corresponding zero-valent state. For Cu and Ni , one part
In NaBH , H exists in the form of À1 valence, so it has evolves into an oxide, and the other part is in a zero-valent state
4
2
+
a strong reducing ability for transition metal ions, and itself is (where only a small part of Ni is converted to a zero-valent
converted into sodium borate in aqueous solution. In closo- state). In order to compare the similarities and differences
3
+
2+
4+
+
3+
Fig. 3 The phenomenon when sodium borohydride and Cs[B
6
H
7
] act on Au , Pd , Pt , and Ag , respectively. (a) Converted Au ; (b) con-
verted Pd ; (c) converted Pt ; and (d) converted Ag . Among them, (i) and (ii) marked in red represent the situation when NaBH and Cs[B
] acting on Au , Pd , Pt and Ag are shown in (e, g, i and k), respectively. The TEM
] acting on Au , Pd , Pt and Ag are shown in (f, h, j and l), respectively.
2+
4+
+
4
6 7
H ]
3+
2+
4+
+
6 7
are used as reducing agents. The FE-SEM images of Cs[B H
3+
2+
4+
+
6 7
images of Cs[B H
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6 7
Fig. 4 (a) FT-IR results. The black line is the FT-IR signal of Cs[B H ],
3+
6 7
the red line is the FT-IR signal after Cs[B H ] acts on Au , and the blue
3
+
À
line is the FT-IR signal after NaBH
4
acts on Au . (b) Closo-[B
6
H ] and
7
À
BH
4
have similar conversion paths when reducing metal ions.
between Cs[B H ] and NaBH reducing metal ions, we have
6
7
4
performed the following experiments. The feed ratio between
3
+
the metal ions (Au ) and Cs[B
0 : 1 to consume all Cs[B ] (or NaBH
tant aer the reaction was collected and the solvent was
6
H
7
] (or NaBH
4
) was increased to
1
6
H
7
4
). Then, the superna-
Fig. 5 LSV curves (a) and corresponding Tafel slopes (b) when
distilled off under reduced pressure, and the Fourier transform commercial 20 wt% Pt/C and simulated 20 wt% Pt/C are used as the
infrared spectroscopy (FT-IR, Fig. 4a) signal of the solid was working electrodes, respectively. (c and d) UV-vis spectra and kinetic
fitting results of the conversion of 4-nitrophenol to 4-aminophenol
collected. The results showed that aer Cs[B H ] and NaBH
6
7
4
6 7
catalyzed by Cu-based materials prepared by Cs[B H ].
reduced metal ions, the FT-IR signals of the products were
2
À
almost the same (BO species were generated), indicating that
Cs[B ] and NaBH
had the same conversion pathway aer pseudo-rst-order kinetic equations shown in the inset were
reducing metal ions (Fig. 4b). In addition, the B–H stretching further obtained (Fig. 5d). Under the same conditions, the S.
and the cage-effect signal at 1000– Sun team's report needs about 90 min to complete. These
300 cm disappeared, which proved that the cage structure of results indicate the superiority of the metal-based materials
6
H
7
4
À1
22
vibration at 2480 cm
À1
1
Cs[B
À
6
H
7
] was dissolved and the B–H bond became a B–O bond. prepared with closo-[B
6
H
7
]
as a reducing agent.
In order to evaluate the pros and cons of metal-based
À
materials obtained by the closo-[B H ] reduction method in
6
7
Conclusions
catalytic reactions, Pt and Cu were elected as representatives of
precious metals and non-precious metals, respectively, to In summary, this research revealed for the rst time the
À
explore their catalytic properties. In the electrochemical potential of closo-[B
H
6
]
in the closed borane family in the
7
hydrogen evolution reaction (E-HER) of water, simulation preparation of metal-based materials, and developed
2
0 wt% Pt/C showed excellent performance. Compared to a completely new route for the preparation of metal-based
À
commercial 20 wt% Pt/C, simulation 20 wt% Pt/C only needs to catalysts. Closo-[B
6
H
7
]
has a milder reduction capacity than
apply an overpotential of 71 mV to achieve a current density of NaBH
4
, which can effectively avoid the aggregation (or evolution
À2
1
0 mA cm (Fig. 5a), and the corresponding Tafel slope is as into bulk) of metal-based materials. Compared with closo-
À1
2À
À
4+
low as 43 mV dec (Fig. 5b). Then, the catalytic performance of [B12
H
12
]
, closo-[B
6
H
7
] not only realizes the conversion of Pt
À
0
Cu NPs obtained by closo-[B
6
H
7
]
was tested by the model to Pt at room temperature, but also expands the reduction
reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), which range of the closed borane family from noble metals to non-
is usually catalyzed by metal nanomaterials. Initially, in the UV- noble metals. In the E-HER of water and reduction reaction of
vis spectrum of the mixed aqueous solution of 4-NP and NaBH
4
,
4-nitrophenol, the Pt-based materials and Cu-based materials
a strong absorption peak at 400 nm was shown and attributed to prepared by this strategy showed excellent performance. With
the formation of 4-nitrophenolate anions. Even aer a long the continuous upgrading of catalyst preparation technology,
period of time, this peak remained unchanged, indicating that this research provides researchers with an alternative way to
the reduction reaction did not occur in the absence of catalyst. choose a suitable preparation strategy, which is of great
Once the Cu-based nanomaterials were added into the system, signicance for the development of nanomaterials.
the reduction reaction proceeded immediately, accompanied by
a distinct color change from dark to yellow to colorless in
a short time. The reaction progress was monitored through
Conflicts of interest
time-dependent UV-vis spectroscopy (Fig. 5c), which showed There are no conicts to declare.
a rapid decrease of the absorbance value at 400 nm with time.
The corresponding conversion over time was obtained and
presented in Fig. 5c. It clearly showed that Cu-based materials
Acknowledgements
This work was nancially supported by the Fundamental
can completely convert 4-NP to 4-AP in less than 10 min. The
Research Funds for the Central Universities (no. 2042016
33448 | RSC Adv., 2020, 10, 33444–33449
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