Catalysis Communications
Preparation and photocatalytic performance of Bi nanoparticles by
microwave-assisted method using ascorbic acid as reducing agent
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Zhankui Cui , Yange Zhang, Senlin Li, Suxiang Ge
Key Laboratory of Micro-Nano Materials for Energy Storage and Conversion of Henan Province, Institute of Surface Micro and Nano Materials, Xuchang University, Xuchang 461000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 August 2015
Received in revised form 23 September 2015
Accepted 24 September 2015
Available online 28 September 2015
Bismuth nanoparticles (NPs) were prepared by using microwave (MW) as heating source and ascorbic acid as
reducing agent. Pure phase of Bi NPs was obtained and the size was uniform with the mean value of 70 nm.
The visible light absorption was good and the optical band gap was 1.77 eV. The photocatalytic efficiency was
2.7 times that of the sample by solvothermal method for degradation of methyl blue (MB) under visible light ir-
radiation. The hydroxyl radicals during photocatalysis were detected due to the transition of Bi from semimetal to
semiconductor. The small size effect was considered to contribute a lot to the efficient photocatalytic activity.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Bi NPs
Microwave assisted
Ascorbic acid
Photocatalysts
Hydroxyl radicals
1. Introduction
reducing agent and successfully prepared small size and uniform Bi
NPs by MW assisted method. The samples were characterized and the
Elemental Bi is a typical group V semimetal material and has inter-
esting electronic properties such as low carrier density, small effective
mass and long carrier mean free path [1–3]. When the size of Bi particles
is reduced to a critical value, the semimetal-to-semiconductor transition
becomes possible [4,5]. The bulk Bi has a very small band gap of about
38 meV while the value increases obviously for nanosized Bi [6,7]. Re-
cently, Bi nanoparticles (NPs) were found to have photocatalytic prop-
erties when used to decompose organic dyes and pollutant gases such
as Rhodamine B and NO [8–11]. Several routes were used to synthesize
Bi NPs, such as liquid phase method, hydrothermal or solvothermal
method [12,13]. Though much work has been done on the production
and characterization of Bi NPs, the reliable preparation of Bi NPs with
uniform size is still a great challenge and visible light driven high perfor-
mance Bi photocatalyst still needs to be developed.
Microwave (MW) assisted method has been widely used to produce
nanomaterials with uniform morphology since microwave fields can
quickly and uniformly heat a solution by directly coupling to molecules
within the solution through polarization or conduction [14–16]. As for
Bi powders, Bi spheres of micrometer by MW assisted method were re-
ported by Chen's group [6]. However, to the best of our knowledge, re-
ports are rare on the preparation of uniform nanosized Bi NPs by MW
assisted method and the use of Bi NPs as an efficient photocatalyst
through the transition from semimetal to semiconductor has not been
reported. Herein we optimized the procedure by using ascorbic acid as
photocatalytic activity was evaluated by photodegrading MB organic
dye under visible light irradiation. The measurement of hydroxyl radi-
cals generated during the photocatalytic process was conducted. Addi-
tionally, the photocatalytic mechanism of Bi NPs was also discussed.
2. Experimental
2.1. Synthesis of materials
All the reagents are of analytical grade and used as received without
further purification. In a typical procedure, 1.50 g Bi(NO3)3·5H2O was
dissolved in 20 ml ethylene glycol (EG) and 1.0 g ascorbic acid was
added into above solution. The solution was transferred to a 50 ml
three-neck round-bottom flask and was heated using a 700 W micro-
wave oven for 30 min. After that, the powders were collected using a
centrifuge, washed with ethanol and dried in a vacuum oven at 70 °C
for 6 h. Then the products were obtained for use. Additionally, Bi parti-
cles were also prepared by solvothermal method [17] for comparison
using the same recipe. The two kinds of Bi NPs were labeled MW-Bi
for MW-assisted method and SV-Bi for solvothermal method.
2.2. Characterization
The phase of the samples was studied using X-ray diffraction (XRD)
method on a BRUKER D8 advance diffractometer with Cu Kα radiation
(λ = 1.5406 Å). The morphology was observed using a Zeiss EVO LS15
SEM. The optical property measurements were conducted by a Cary
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Corresponding author.
1566-7367/© 2015 Elsevier B.V. All rights reserved.