Decorating of Ag and CuO on Cu Nanoparticles for Enhanced High Catalytic Activity to the Degradation of Organic Pollutants

Article abstract of DOI:10.1021/acs.langmuir.7b01540

Metal/semiconductor composites are promising catalysts with superior catalytic activity. In this work, a Cu/CuO-Ag composite with structure that consisted of Ag and CuO nanoparticles (NPs) decorated on the surface of Cu were fabricated via a facile in situ method. With characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and inductively coupled plasma atomic emission spectrometry (ICP-AES), the structure and components of the Cu/CuO-Ag composite were well-defined. The Cu/CuO-Ag composite exhibited superior catalytic activities for the reduction of 4-nitrophenol (4-NP) in the presence of NaBH₄ with just a trace amount of Ag NPs (1.28 wt %). The reduction reaction is completed in 75 s with an apparent rate constant k_app of 4.60 × 10^-2 s^-1. The Cu/CuO-Ag composite also showed excellent durable catalytic stability, as no significant activity loss was detected in the consecutive five reaction runs. With the aid of the Sabatier principle and volcano plot, the opportune chemical adsorption energy of the reagent 4-NP on the Cu/CuO-Ag composite was inferred to be the key to its high reaction rate. The CuO NPs as a semiconductor with narrow band gap also could help the Cu/CuO-Ag composite to capture the electrons/hydride ions and increase opportunities for 4-NP to be reduced. Furthermore, the Cu/CuO-Ag composite exhibited outstanding activity on the oxidative degradation of methylene blue (MB). This work enriched the bimetal/semiconductor catalyst system and supplied new insight into the catalysis mechanism.

Full text of DOI:10.1021/acs.langmuir.7b01540

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Article
Decorating of Ag and CuO on Cu nanoparticles for the Enhanced
High Catalytic Activity to the Degradation of Organic Pollutants
Yu Liang, Zhe Chen, Wen Yao, Pengyi Wang, Shujun Yu, and Xiangke Wang
Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01540 • Publication Date (Web): 19 Jul 2017
Downloaded from http://pubs.acs.org on July 23, 2017
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Decorating of Ag and CuO on Cu nanoparticles for the Enhanced High Catalytic
Activity to the Degradation of Organic Pollutants
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Yu Liang, Zhe Chen,* Wen Yao, Pengyi Wang, Shujun Yu, Xiangke Wang*
College of Environmental Science and Engineering, North China Electric Power
University, Beijing 102206, PR China.
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Eꢀmail: chenz@ncepu.edu.cn; xkwang@ncepu.edu.cn
ABSTRACT: The metal/semiconductor composites are promising catalysts with
superior catalytic activity. In this work, a Cu/CuOꢀAg composite with structure that
Ag and CuO nanoparticles (NPs) decorated on the surface of Cu were fabricated via a
facile inꢀsitu method. With the characterization by transmission electron microscopy
(TEM), Xꢀray diffraction (XRD), Xꢀray photoelectron spectroscopy (XPS), energy
dispersive Xꢀray spectroscopy (EDX) and inductively coupled plasma atomic
emission spectrometry (ICPꢀAES), the structure and structure and component of
Cu/CuOꢀAg composite were wellꢀdefined. The Cu/CuOꢀAg composite exhibited
superior catalytic activities for the reduction of 4ꢀnitrophenol (4ꢀNP) in the presence
of NaBH4 with just trace amount of Ag NPs (1.28 wt%). The reduction reaction is
completed in 75 s with apparent rate constant kapp of 4.60×10ꢀ2 sꢀ1. The Cu/CuOꢀAg
composite also showed excellent durable catalytic stability, as no significant activity
loss was detected in the consecutive five reaction runs. With the aid of Sabatier
principle and volcano plot, the opportune chemical adsorption energy of the reagent
4ꢀNP on Cu/CuOꢀAg composite was inferred to be the key to their high reaction rate.
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The CuO NPs as a semiconductor with narrow band gap also could help Cu/CuOꢀAg
composite to capture the electrons/hydride ions and increase opportunities for 4ꢀNP to
be reduced. What’s more, the Cu/CuOꢀAg composite exhibited outstanding activity
on the oxidative degradation of methylene blue (MB). This work enriched
bimetal/semiconductor catalyst system and supplied new insight on the catalysis
mechanism.
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1. INTRODUCTION
Over the years, transition metallic nanoparticles (NPs) have attracted much research
attention due to their wide range of application.1ꢀ9 Among them, silver is an excellent
catalyst, which has shown remarkable catalytic activity in hydrogenation,10 oxygen
reduction reaction,11 and hydrogen production reaction,12 etc. The catalytic properties
of the Ag NPs are highly dependent upon size, lattice plane and shape.13ꢀ15 Enormous
works have been reported on the controlled synthesis of Ag nanostructures including
nanosphere, nanowire, nanocube, triangular nanoplate, nanobelt, etc.16ꢀ18 However,
high price and harsh synthetic conditions have caused a bottleneck in industrial
application. Attributing to the synergistic effects between two metals, bimetallic
nanomaterials often exhibited superior physicochemical properties comparing to their
individual metals, such as high activity, functionality and stability.13 Cu nanomaterials
are particularly attractive for the synthesis of bimetallic nanomaterials on account of
copper’s low cost, high natural abundance and facile production.19 Many research
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have reported that Cu was coupled with noble metals to form bimetallic NPs for
improving the catalytic performance, such as CuꢀAu NPs promoting the reduction of
carbon dioxide,20 Cu–Ni NPs as the active catalyst for the synthesis of carbon
nanofibers,21 CuꢀPt NPs as catalyst for oxygen reduction reaction,22 and PdꢀCu NPs as
an excellent bimetallic catalyst for the Sonogashira reaction,23 etc. Thereby, Cuꢀbased
bimetallic NPs have been regarded as the preeminent alternative metal catalyst, which
could not only reduce the cost but also enhance the catalytic properties for the
nanocatalysts.
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On the other hand, the catalytic performance of metalꢀbased catalyst would also
be affected by the decorating of semiconductor metal oxide, such as SnO2, CuO and
TiO2. Zhou et al. found that mesoporous SnO2 coated Ag nanostructures display
interesting multifunctional activity on 4ꢀnitrophenol (4ꢀNP) reduction.24 Oldfield et al.
observed that the capacitance of Au NPs increased upon coating with SnO2, because
the SnO2 promoted the interactions as well as prolonged the lifetime of electrons.25
Sasmai et al. reported that the catalytic activity of ternary Cu2OꢀCuꢀCuO composite
was surprisingly higher than that of the metal Cu NPs for 4ꢀNP reduction, and they
maintained that the unusual activity came from the inꢀsitu generated ternary
Cu2OꢀCuꢀCuO nanocomposite.26 Therefore, the effect of the semiconductor on the
metal/semiconductor system to the catalytic activity was not fully defined and it is
worth to explore its influence on catalysis. Herein, we developed a facile inꢀsitu
reduction method to build Cu/CuOꢀAg composite with the structure that Ag and CuO
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