Elemental bismuth-graphene heterostructures for photocatalysis from ultraviolet to infrared light

Article abstract of DOI:10.1021/acscatal.7b02170

For an optimized use of solar energy, the fabrication of photocatalysts that are sufficiently stable and responsible for harvesting full-spectrum light from ultraviolet to infrared is required to solve environmental issues and the water shortage crisis but remains a great challenge so far. Here, we show that elemental bismuth-graphene heterostructures synthesized by a solvothermal method followed by calcination have high photocatalytic activity under not only ultraviolet but also visible and even infrared light. These heterostructures are very stable after many photocatalytic cycles, and no leaching of bismuth is observed. Analysis of the morphological structures indicates that the heterostructures remain unchanged after repeated cycling, while displaying no appreciable loss in activity. Furthermore, the experimental and theoretical results demonstrate that the heterostructures have the sufficient band gap energy for simultaneously absorbing across the whole solar spectrum and producing photogenerated electrons which can be shuttled across the elemental bismuth-graphene interface, ultimately turning out to be responsible for the degradation reaction. These findings may help the development of elemental photocatalysts with compatible activities from ultraviolet to infrared regions and hence enable solar energy conversion.

Full text of DOI:10.1021/acscatal.7b02170

Subscriber access provided by GRIFFITH UNIVERSITY
Article
Elemental bismuth-graphene heterostructures for
photocatalysis from ultraviolet to infrared light
Liang Yan, Zhanjun Gu, Xiaopeng Zheng, Chenyang Zhang, Xu Li, Lina Zhao, and Yuliang Zhao
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b02170 • Publication Date (Web): 07 Sep 2017
Downloaded from http://pubs.acs.org on September 7, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 9
ACS Catalysis
1
2
3
4
5
6
7
8
9
Elemental bismuth-graphene heterostructures for photocatalysis
from ultraviolet to infrared light
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Liang Yan†‡, Zhanjun Gu*†‡, Xiaopeng Zheng†, Chenyang Zhang†, Xu Li†, Lina Zhao†, Yuliang
Zhao*†‡
†
CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics,
Chinese Academy of Sciences, Beijing 100049, China, and CAS Center for Excellence in Nanosciences, National Cen-
ter for Nanosciences and Technology of China, Beijing 100190, China
‡
University of Chinese Academy of Sciences, Beijing 101408, China
ABSTRACT: For an optimized use of solar energy, the fabrication of photocatalysts that are sufficiently stable and respon-
sible for harvesting full-spectrum light from ultraviolet to infrared is required to solve environmental issue and water
shortage crisis, but remains a great challenge so far. Here, we show that elemental bismuth-graphene heterostructures
synthesized by solvothermal method followed by calcination have high photocatalytic activity under not only ultraviolet
but visible and even infrared light. These heterostructures are very stable after many photocatalytic cycles, and no leach-
ing of bismuth is observed. Analysis of the morphological structures indicates that the heterostructures remain un-
changed after repeated cycling, while displaying no appreciable loss in activity. Furthermore, the experimental and theo-
retical results demonstrate that the heterostructures have the sufficient band gap energy for simultaneously absorbing
across the whole solar spectrum and producing photogenerated electrons which can be shuttled across elemental bis-
muth-graphene interface, ultimately turning out to be responsible for the degradation reaction. These findings may help
the development of elemental photocatalysts with compatible activities from ultraviolet to infrared regions and hence
enable solar energy conversion.
semiconductor systems can efficiently facilitate the inter-
INTRODUCTION
facial electron transfer and tentatively extend photo-
response into infrared region.13-18 However, the photocata-
Motivated by the problem that is inadequate access to
safe water and sanitation, design and development of
suitable heterostructured materials for photocatalytic
solar-energy conversion systems has evoked great interest
in decontaminating water from source to point-of-use at
lower cost and with less energy.1-3 For full utilization of
solar energy, one key requirement is that nanomaterials
would combine an ability to efficiently degrade pollutants
in wastewater, having an optimal bandgap that absorbs
light in the wavelength region of not only ultraviolet
(<400 nm, ~5%), but visible (400-800 nm, ~45%) and
even infrared (>800 nm, ~50%), and to remain stable dur-
ing a long-term photocatalytic reaction (Figure S1). Over
the past decade, pioneer work has developed various pure
and modified inorganic semiconductors as the efficient
photocatalysts for water purification.4-9 For example, TiO2
and ZnO doping with metal impurities were proven to
show photodegradation capability under ultraviolet and
visible light.10,11 Nevertheless, the large-scale commercial
application still strongly suffers from the basic limita-
tions, including i) the bandgaps of oxide-based semicon-
ductors are typically too large for infrared and most of the
visible (>600 nm) light to be utilized, and ii) the defect-
sites can act as recombination centers and trap photocar-
riers before reaching to the reaction surface, thus decreas-
ing quantum yield.12 Indeed, the development of coupled
lytic activities of the as-made photocatalysts are not suffi-
cient due to the low photon energy and the strong ther-
moeffect. Moreover, most of them are incompatible to
harvest full-spectrum solar light.19 For these reasons, the
search for photocatalysts with compatible activity from
ultraviolet to infrared region and excellent stability at-
tracts significant attention and becomes an important
pursuit towards enabling a continual economy.
In addition to compound semiconductors, primary el-
ement-based nanomaterials such as silicon have emerged
as an interesting type of photocatalytic system for organic
contaminant degradation and hydrogen generation due to
their suitable band structures.20-22 For example, there was
report of red phosphorus for photocatalytic hydrogen
production from water under visible light irradiation.23
Alternatively, significant attempts have been focused on
understanding their unusual electronic properties and
designing bismuth photocatalysts capable of using the
less abundant but more energetic ultraviolet light.24,25 For
example, bismuth nanoparticles were found to be very
efficient in the degradation of dyes under ultraviolet26 and
visible irradiation27-30, but not under infrared light. Bene-
fitting from their size/shape dependent plasmonic ef-
fects31-33 (0.45-2.63 eV), we predict that the photocatalytic
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 9
response of elemental bismuth-based photocatalysts can Bi(CH3COO)3 (0.2000 g) was dispersed in 30 mL of
1
be extended to infrared region via enhancing the electri-
cal coupling between elemental bismuth and active mate-
rials, which should overcome the challenge in simultane-
ously achieving a) sufficient ultraviolet, visible and infra-
red-light response, b) suitable energy levels of conduction
and valence bands, and c) effective interfacial separation
of photogenerated electron. To demonstrate this, using
graphene as the active material, we fabricate the hetero-
structures of elemental bismuth and graphene, and then
explore their photocatalytic activity from ultraviolet to
infrared region for the degradation of pollutants (Scheme
1 and Supporting Information). First, elemental bismuth
nanoparticles were grown on the surface of graphene ox-
ide (GO, Figure S2) by solvothermal reduction of bismuth
acetate at 180 °C (named as BGHs). Subsequently, the
dried BGHs were calcined at 500 °C in argon to ensure
molecular-level mixing of graphene with elemental bis-
muth and then create the high-quality heterostructures
with intimate interfacial contact (named as c-BGHs). As a
comparison, pure bismuth nanoparticles were also syn-
thesized using the similar protocol except the absence of
GO (named as BNPs and c-BNPs for products before and
after calcination).
DMSO. After vigorous stirring, to the resulting solution
was added 0.5 mL of GO (~4 mg mL-1). According to the
electrostatic interactions, BiIII ions would deposit on the
surface of GO nanosheets during vigorously stirring at
room temperature. Then the mixture was transferred into
a 45-mL Teflon-lined stainless steel autoclave and heated
at 180 °C for 4 h. The obtained product (named as BGHs)
was collected by centrifugation, washed extensively with
ethanol and water several times, and dried in a freezer
dryer under vacuum. At last, the dried BGHs were cal-
cined at 500 °C for 2 h under an argon atmosphere to
form heterojunctions. For comparison, bismuth particles
without graphene were also received using the similar
protocol but without the addition of GO (named as BNPs
and c-BNPs for products before and after calcination) and
pure graphene nanosheets were synthesized in the ab-
sence of bismuth(III) acetate (named as rGO and c-GO
for products before and after calcination).
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Physical characterizations. Morphologies of samples
were characterized using electron microscopes with an
energy-dispersive X-ray (EDX) analyzer including filed-
emission scanning electron microscope (FE-SEM, S-4800,
an acceleration voltage of 10 kV, Hitachi High-
technologies, Japan) and transmission electron micro-
scope (TEM, Tecnai G2 20 S-TWIN, an acceleration volt-
age of 200 kV, FEI Company, USA). X-ray diffraction
(XRD) analysis was carried out on a Bruker D8 Advance
X-ray diffractometer (Bruker, USA) with Cu-Kα radiation
(λ=1.5406 Å) at a scanning rate of 5° min-1 and a scanning
range from 10° to 90°. X-ray photoelectron spectroscopy
(XPS) measurements and the element valence states were
performed with an ESCALab220i-XL spectrometer using a
twin-anode Al-Kα X-ray source (1486.6 eV). Micro-Raman
spectra were acquired with a Raman Spectroscope (Ren-
ishaw inVia plus, United Kingdom) under ambient condi-
tions with 514 nm excitation from an argon ion laser. Ul-
traviolet-visible (UV-vis) data were obtained with a U-
3900 spectrophotometer (Hitachi, Ltd., Japan). Diffuse
reflectance ultraviolet-visible-infrared (UV-vis-IR) spectra
in the reflectance mode were recorded using an Agilent
Cary 500 UV-vis-IR Spectrometer equipped with an inte-
grating sphere at room temperature using BaSO4 as a ref-
erence. Ultraviolet photoelectron spectroscopy (UPS)
measurements were performed with an unfiltered He I
gas discharge lamp (21.22 eV). Fourier transform infrared
(FT-IR) spectra were recorded on an infrared microscope
(iN10-IZ10, Thermo Fisher). Atomic force microscope
(AFM) measurements were conducted with a Bruker Mul-
timode 8 AFM (Bruker, USA) in ScanAnalyst mode with
cantilevers with spring constant of 0.35 N m-1 and a fre-
quency of 65 kHz. The photoluminescence properties
were studied using a Horiba Jobin Yvon FluoroLog3 spec-
trometer. The photocurrents were corrected on a Keithley
4200 station with the computer-controlled four-probe
technique.
Scheme 1. Process for preparation of c-BGHs through a
solvothermal route followed by further calcination at 500
°C for 2 h.
EXPERIMENTAL SECTION
Reagents and Chemicals. Graphite (99%), bismuth(III)
acetate (Bi(CH3COO)3, 99%), dimethyl sulfoxide (C2H4OS,
DMSO, 99.9%), methyl orange (C14H14N3NaO3S, MO), 1,5-
diphenylcarbazide (C13H14N4O, >97%), titanium(IV) oxide
(TiO2, P25, 99.9%), and potassium dichromate (K2Cr2O7,
99%) were purchased from Alfa Aesar. Concentrated sul-
furic acid (H2SO4, 98%), potassium permanganate
(KMnO4), hydrochloric acid (HCl, 37% w/w aq.), hydro-
gen peroxide (H2O2, 35% w/w aq.), sodium hydrosulfite
(Na2S2O8), sodium oxalate (Na2C2O4), 2-propanol, and
ethanol were obtained from Beijing Chemical Reagent Co.
Ultra-high purity argon (>99.999%) was supplied by Bei-
wen Special Gases Factory. All the chemicals were used as
received without further purification and all experiments
were performed at room temperature unless otherwise
indicated. Furthermore, fresh deionized (DI) water (ari-
um® Lab Water Systems, 18.2 MΩ cm) was required for the
whole experiment.
Fabrication of elemental bismuth-graphene hetero-
structures. Elemental bismuth-graphene nanostructures
were prepared via a general two-step method. Typically,
Experimental set up for photodegradation of MO
under direct sunshine. The photocatalytic activity of c-
BGHs was further evaluated by the degradation of MO
ACS Paragon Plus Environment

Page 3 of 9
ACS Catalysis
under direct sunshine. The experiments were carried out
on the sunny day (14th Feb 2015) at Beijing city between 12
1
2
3
4
5
6
7
8
p.m. and 2 p.m. where the intensity fluctuation of sun-
shine was minimal (outside temperature 2-5 °C). The so-
lar power density (as well as other light sources) was
measured at 0.039-0.048 W cm-2 by an Optical Power Me-
ter (PM100D, Thorlabs Inc., USA). In such case, 15 mg of
c-BGHs was dispersed in 15 mL of acidic aqueous solution
of MO (pH 2.00, 60 μg mL-1). After the adsorp-
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2-
tion/desorption equilibrium was reached, 30 mL of C2O4
solution was added to the above suspension. Finally, the
samples were analyzed by UV-vis spectrophotometer after
centrifugation. Similarly, the control experiments were
also conducted under solar light with P25 to compare the
photocatalytic activity of each other and without catalyst
to measure any possible direct photolysis of the dyes.
Calculation of highest occupied molecular orbitals
and lowest unoccupied molecular orbitals. In this
work, the Gaussian 03 program was applied to perform
the computations in the gas phase. B3LYP and MP2 ap-
proaches were used to calculate the frontier molecular
orbitals of MO molecules, including highest occupied
molecular orbitals (HOMOs) and lowest unoccupied mo-
lecular orbitals (LUMOs).
Figure 1. (a) SEM image of c-BGHs. (b) High-resolution
TEM image of c-BGHs. Inset: EDS analysis of the corre-
sponding bismuth nanoparticle. (c) Comparison between
the XRD data of BGHs and c-BGHs. (d,e) XPS core-level
spectra and deconvolution into Bi4f (d) and O1s. (e) Con-
tributions for c-BGHs. (f) Schematic structure of c-BGHs.
RESULTS AND DISCUSSION
Characterization of c-BGHs by SEM shows that bismuth
nanoparticles retain their size at the nanoscale (~300 nm)
after calcination and are wrapped intimately by graphene
nanosheets (Figure 1a and Figure S3). Compared with
BGHs, there are inappreciable changes in size and mor-
phology of bismuth nanoparticles except the creation of
more nanoscale wrinkles in graphene. This is in contrast
to the morphology of c-BNPs (Figure S4) and suggests the
presence of strong interfacial interaction of bismuth na-
noparticles with graphene sheets (Figure S5).34 A high-
resolution TEM image indicates that the surface of bis-
muth nanoparticles is covered by a layer of ~4 nm in
thickness (Figure 1b). Together with the result from ener-
gy dispersive X-ray spectroscopy (Figure 1d, inset), we
infer that this layer is most like an oxide of bismuth.
Further insights into the structural information were
obtained by XRD analysis. XRD patterns before and after
calcination exhibit similar diffraction peaks. The distinct
reflections typically associate with the rhombohedral
bismuth crystals (JCPDS no. 44-1246),35 in accordance
with the result from TEM measurement (Figure 1c and
Figure S6a). The absence of the stacking-related (002)
diffraction peak (at ~26° for graphite and ~13° for graphite
oxide) indicates that the dispersion of graphene is proba-
bly close to the single-sheet level.34 Remarkably, the weak
peak at ~27.92° which is assigned to diffraction from the
(201) plane of bismuth oxide (Bi2O3, JCPDS no. 27-0050)
can be found in c-BNPs (Figure S6b).36 This is not surpris-
ing because bismuth is easily oxidized under oxygen at-
mosphere.26 However, this peak shifts to 28.08° after cal-
cination, in accordance with the (101) plane of bismuth
suboxide (BiO, JCPDS no. 27-0054).37 This indicates that
the additional structures are developed during calcination
with the assistance of graphene. The change in the chem-
ical states is further demonstrated by XPS (Figure S7,8).
In Figure 1d, the two peaks of c-BGHs located at 156.8 and
162.1 eV, respectively, attributed to the binding energies of
Bi4f7/2 and Bi4f5/2 in metallic bismuth, are nearly identi-
cal to those of BGHs; however, other doublet shift down
to 158.6 and 163.9 eV, respectively, corresponding to a 1.8
eV shift relative to the peaks of metallic bismuth. This
chemical shift is less than that obtained for BiIII, evidenc-
ing the formation of suboxide species on the surface of
ACS Paragon Plus Environment

ACS Catalysis
bismuth nanoparticles.38,39 Most interestingly, in compari-
Page 4 of 9
1
2
3
4
5
6
7
8
son of the evolution of O1s spectra, O=C-O peak shifts
towards higher binding energy after calcination due to
the decrease of the total charge density (Figure 1e). Cou-
pled with the result of density functional calculations
(Figure S9), it is indicative of O=C-O groups bonding with
BiII at the hetero-interface, forming thermodynamically
stable four-membered-ring.40 This is also confirmed by
the results of Fourier transform infrared and Raman spec-
troscopy (Figure S10,11). Ideally, the ring structure can
serve as a “bridge” which makes bismuth nanoparticles
and graphene cross-linked but not physical mixed nor
isolated (Figure 1f), permitting the interaction between
electronic states at the graphene-bismuth interface and
thus leading to extend the absorption into infrared region
and promote interfacial charge transfer.41,42
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Then, we performed the photocatalytic experiments
with c-BGHs under visible, infrared, ultraviolet light as
well as full-spectrum light (Figure 2,3, Figure S12, Table S1,
and Supporting Information). Their photocatalytic activi-
ties were evaluated by investigating the degradation rates
of methyl orange (MO, an azo dye) and chromium (VI)
(CrVI, a heavy metal ion) in acidic water (pH<3.00). As
expected, c-BGHs show a high photocatalytic activity un-
der visible and infrared light, far higher than that of
commercial TiO2 (P25): we obtained more than 95% (un-
der visible light) and 60% (under infrared light) photo-
degradation of MO after a 40-min irradiation, while no
degradation was obtained with P25 (Figure 2a,b). In par-
ticular, to identify the infrared photocatalytic activity, we
conducted the photodegradation test under monochro-
matic light of wavelength of 808 nm. They achieved a
degradation rate of 95% within 40 min, demonstrating
that their photocatalytic activity indeed originated from
infrared light (Figure S13). Besides, c-BGHs display good
photocatalytic activity under ultraviolet light: an 85%
degradation rate of MO was reached in 40 min irradiation
(Figure 2c). Similar trends are observed for the photocata-
lytic degradation of CrVI: c-BGHs produced degradation
rates of 80% and 60% after 40-min irradiation by visible
and infrared light, respectively, but no reaction was ob-
served with P25 control (Figure 3a,b). The degradation
rate under ultraviolet light was 80%, which was somewhat
lower than that of P25 (Figure 3c).
Figure 2. (a-d) Photocatalytic degradation of MO under
visible (a), infrared (b), ultraviolet (c) and full-spectrum
(d) light irradiation. (e) Illustration of the time evolution
of MO photodegradation using c-BGHs under infrared
light.
Figure 3. (a-d) Photocatalytic degradation of CrVI under
visible (a), infrared (b), ultraviolet (c) and full-spectrum
(d) light irradiation. The concentration of various photo-
catalysts in acidic water was 1 mg mL-1.
To further attest the correlation between photocatalyt-
ic degradation and heterostructures, we carried out pollu-
tant degradation experiments in the presence of BNPs, c-
BNPs and a mixture of calcined graphene oxide (c-GO)
and c-BNPs (Figure 2,3 and Figure S14). We found that
BNPs displayed rather limited photocatalytic activity un-
der visible, infrared and ultraviolet irradiation (Table S2),
and almost no pollutant degradation was obtained with c-
BNPs. Even the mixture of c-GO and c-BNPs showed only
a slight decomposition of pollutants under the same con-
ditions. We also measured the kinetic rate constants for
each of the above photocatalytic events using pseudo-
first-order kinetic model (i.e. Langmuir-Hinshelwood
model, Supporting Information),43,44
ACS Paragon Plus Environment

Page 5 of 9
ACS Catalysis
tion band energy level for c-BGHs is located above the top
ꢃꢄ
ꢀꢁ ꢂ ꢆ ꢇ ꢈꢉꢊꢊ ꢋ ꢌ
(1)
ꢃꢅ
1
of the lowest unoccupied molecular orbital (LUMO) level
for MO+ and the reduction level for CrVI, which permits
transfer of electrons. These results indicate that c-BGHs
are capable of degrading MO+ and CrVI under visible, in-
frared and ultraviolet light via reduction process (Figure
4d). Moreover, based on the results of electrospray ioniza-
tion mass spectrometry (Figure S18), the possible pathway
of reduction is further proposed in Figure S19.
where ꢍꢎ and ꢍꢏ are the concentrations of pollutant in
2
solution at time and , respectively, and ꢈꢉꢊꢊ is the ap-
0
ꢌ
3
4
5
6
7
8
9
parent rate constant. Especially, for MO degradation by c-
BGHs, the rate of adsorption equilibrium is comparable to
that of degradation reaction. Therefore, the Langmuir-
Hinshelwood model is no longer applicable. To extract
the degradation rates of MO, we fitted these data to the
following formula, which assumed the light absorbance
proportional to the concentrations of MO both in solu-
tion and on the surface of c-BGHs,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ꢒ
ꢖ
ꢒ
ꢖ
ꢐ ꢇ ꢑ exp ꢓꢈꢔꢕꢌ ꢗ ꢘ exp ꢓꢈꢙꢌ
(2)
where ꢔꢕ is the desorption rate constant and ꢈꢙ is the
ꢈ
rate constant. Good fits were obtained for the above mod-
el, confirming that the light absorbance was assuredly
proportional to the total MO concentration in the solu-
tion (Figure S15). The estimates of kinetic rate constants
from above models are summarized in Table S3,4. To-
gether with the process efficiency and catalytic efficiency
(Table S5-8), these calculations give the values to quantify
the photocatalytic activity and consistently suggest that
the heterostructures have the fastest reaction rates.
To understand the origin of photocatalytic activities of
c-BGHs under ultraviolet, visible and infrared light, we
then investigated their electronic band structures. As
shown in Figure 4a, DRS results suggest that the optical
absorption edge of c-BGHs is extended to infrared region
over both BNPs and BGHs due to the strong interfacial
interaction between graphene and bismuth nanoparticles
(Supporting Information).45 The optical energy bandgap
Figure 4. (a) Diffuse reflectance absorption spectrum of
BNPs, BGHs and c-BGHs. “I”, “II” and “III” represent ul-
traviolet region, visible and infrared region, respectively.
Inset: Photograph of c-BGHs. (b) A plot transformed ac-
cording to the Kubelka-Munk function versus energy of
light. The dashed line is the tangent of the curve. Inset:
the Kubelka-Munk transformed spectra of BNPs and
BGHs. (c) UPS spectrum of c-BGHs. The dashed red line
marks the base line and the tangents of the curve. Inset:
UPS spectrum of c-BGHs at high kinetic energy region.
(d) Possible photocatalysis mechanism with charge sepa-
ration in c-BGHs, with electron directly reducing pollu-
tants (MO and CrVI) in acidic water and hole oxidizing
water.
(ꢚꢛ) of c-BGHs is determined to be 1.38 eV from the ex-
trapolation of the Tauc plot (Figure 4b), suggesting that
c-BGHs can be activated by light from ultraviolet to infra-
red region. This is mainly due to the hybrid surface layer
consisting of bismuth suboxide and graphene, whose ab-
sorption is superimposed to a “background” absorption
from the bismuth core of the heterostructure. For charac-
terizing the energy levels of conduction and valence
bands, UPS was used to determine the ionization poten-
Chemically, pollutants except metal ions (including
CrVI) are eliminated via oxidation process, in which the
photoexcited carriers migrate to the surface and react
with oxygen or water to form radical oxygen species, fi-
nally degrading and mineralizing organic pollutants
(Supporting Information),46,47
tial (equivalent to the valence band energy, ꢚꢜꢝ) of c-
BGHs. The ꢚꢜꢝ is determined to be 1.65 eV by subtracting
the width of the He I UPS spectrum form the excitation
energy and then converting to electrochemical energy
potential in Volts (vs. reversible hydrogen electrode
(RHE)) (Figure 4c). The conduction band energy ꢚꢃꢝ is
thus estimated at 0.47 eV (vs. RHE) from ꢚꢜꢝ ꢓ ꢚꢛ. The
Fermi level is given (1.34 eV vs. RHE) by the formula for
ꢚꢜꢝ ꢓ ∆ꢚꢜꢝ, where ∆ꢚꢜꢝ is the energy position of the va-
lence band with respect to the Fermi level (Figure S16).
Furthermore, the bandgap of MO in neutral (MO0) and
acidic (MO+) conditions were evaluated by Guassian pro-
gram (Supporting Information). Depending on the align-
ment of the energy levels, the Fermi level for c-BGHs is
well positioned in the middle of the bandgap of MO0 and
MO+ after adsorption equilibrium. This ascertains that
the degradation of MO and CrVI is energetically possible
under acidic condition (mostly industrial wastewater),
but not under neutral condition (Figure S17). The conduc-
Oꢙ ꢗ ꢞꢃꢔꢝ → O∙ꢙꢔ
(3)
(4)
ꢠ
⋅
ꢔ ꢒ
ꢖ
ꢟꢜꢝ ꢗ OH or water → HO
where ꢞꢃꢔꢝ is conduction band electrons and ꢟꢜꢠꢝ is valence
band holes. However, unlike the above processes, in c-
BGHs the energy levels make reduction reaction thermo-
dynamically favorable, that is, directly transferring ꢞꢃꢔꢝ to
pollutants,
Dye ꢗ ꢞꢃꢔꢝ → Dyeꢡꢢꢣ
(5)
where subscript “Red” represents the reduced form of dye.
Remarkably, the advantage of reduction process is that no
apparent demand of intermediate states is listed in path
and the classic problem caused by low molecular oxygen
concentration is avoided.
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 9
The photogenerated electrons mobility in c-BGHs was radation rate of P25 (Figure 6 and Figure S22-24). This
1
2
3
4
5
6
7
8
further studied under visible, infrared and ultraviolet light
to explore the behavior of excess charge carriers (Figure
5a and Figure S20). We observe the consistent photocur-
rent responses for each switch-on and -off event, provid-
ing evidence that graphene acts as electron sinks, favoring
the separation of the photocarriers via the heterostruc-
tures while reducing thermoeffect, specially under infra-
red light irradiation.48 Similar conclusion is also obtained
from photoluminescence spectra (Figure S21). The effect
of scavengers on the degradation of MO was then exam-
ined to confirm the role of the photogenerated electrons
(Figure 5b). Trapping experiments were performed upon
introduction of SꢙOꢙꢤꢔ scavengers which reacted with elec-
trons to yield SOꢙꢥꢔ ions.49 This reaction competes with
reaction (5) and causes the decrease in electrons, which in
turn slows down the photodegradation kinetics compared
to the control under infrared light irradiation (Table S9).
result indicates that the efficient solar photocatalytic ac-
tivity of c-BGHs is robust for potential application in wa-
ter purification and wastewater treatment under natural
sunlight.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. Photographs of the photodegradation of MO by
2-
c-BGHs in the presence of C2O4 before (a) and after (b)
sunlight irradiation.
There is no doubt that the photocatalytic activity of c-
BGHs essentially originates from the narrow bandgap of
elemental bismuth favoring efficient utilization of low-
energy photons. On one hand, graphene as a mechanical
clamping layer can dramatically inhibit the agglomeration
of bismuth nanoparticles during the calcination process,
thus maintaining their intrinsic electronic structures that
are unavailable in c-BNPs. On the other hand, when cou-
pling with graphene, in addition to the individual proper-
ties of each component, the formed heterostructures fa-
cilitate the avoidance of thermoeffect induced by infrared
light via promoting the charge separation, while generat-
ing the proper energy levels that enable the highly effec-
tive electron transfer at graphene/bismuth interfaces.51-53
Moreover, plenty of active sites for photodegradation are
provided due to the enough room originated from gra-
phene for electron extraction by pollutants. Figure 5c
summarizes the light absorption by the bismuth core with
very small bandgap (few tenths of eV) followed by elec-
tron transfer to the surface region, resulting in the en-
richment of charge carriers on the surface of graphene
under irradiation and then direct transfer to adsorbed
MO+ or CrVI under acidic condition, turning out to be
responsible for the degradation of pollutants.
Figure 5. (a) Photoresponse characteristics of c-BGHs
under ultraviolet, visible, infrared and full-spectrum light.
After as many as eight cycles, the behavior of c-BGHs re-
mains unchanged. (b) Effects of different scavengers on
the degradation of MO in the presence of c-BGHs under
infrared light irradiation. (c) Schematic of electron trans-
fer during photocatalytic process.
To further evaluate the role of oxygen, MO photodeg-
radation tests were performed under anoxic conditions in
which O∙ꢙꢔ radical generation was inhibited completely.
The result in Figure 4b shows almost no change in the
degradation kinetics, confirming the insignificant role of
O∙ꢙꢔ in the photocatalytic process, in agreement with the
analysis of the conduction band energy level. Neverthe-
less, when adding external hole scavengers (CꢙOꢙꢥꢔ) into
the above system we find that the decomposition kinetics
are drastically accelerated. This can be attributed to the
fact that the introduction of CꢙOꢙꢥꢔcan suppress the elec-
Another important aspect was the stability and recy-
clability of the photocatalyst, we found that the degrada-
tion rates remained almost unchanged even after five cy-
cles and no bismuth ions were released into the solution,
suggesting that c-BGHs could be efficiently reused for
repeated cycles without appreciable loss of activity and
mass (Figure 7a and Figure S25-27). Furthermore, no dis-
tinct difference was found, either in the morphology of c-
BGHs or in their chemical structures after photocatalytic
reactions, as attested by TEM, XRD and Raman character-
izations (Figure 7b-d).
tron-hole recombination via the reaction of ꢟꢜꢠꢝ with
50
.
CꢙOꢙꢥꢔ
These results undoubtedly demonstrate that the
degradation process is occurred through the direct trans-
fer of ꢞꢃꢔꢝ to the absorbed MO in which CꢙOꢥꢙꢔ as the sacri-
ficial donor that can increase electron transfer efficiency.
The photocatalytic degradation of MO was further carried
out under sunshine in the presence of CꢙOꢙꢥꢔ. Interesting-
ly, we found that c-BGHs produce a decomposition rate of
MO nearly 100% after 25 min compared to 5% photodeg-
ACS Paragon Plus Environment

Page 7 of 9
ACS Catalysis
Author Contributions
1
2
3
4
All authors have given approval to the final version of the
manuscript.
Notes
The authors declare no competing financial interest
5
6
ACKNOWLEDGMENT
7
8
9
10
11
12
13
14
15
This work was supported by the National Natural Science
Foundation of China (11621505, 21320102003, and 11435002)
and Innovation Program of the Chinese Academy of Sciences
(QYZDJ-SSW-SLH022). We thank Zhengwei Li at Institute of
High Energy Physics for assistance in data fitting; Chen Liu
and Jia-ou Wang in Beijing Synchrotron Radiation Facility
(BSRF) for their assistance in data collection during the UPS
measurement. We gratefully acknowledge the support from
BSRF at the Institute of High Energy Physics for UPS meas-
urement.
Figure 7. (a) Photocatalytic degradation of MO and CrVI
in the presence of c-BGHs after up to five cycles measured
after visible and infrared light irradiation of duration 10
min. (b) TEM image of c-BGHs after photodegradation of
MO under infrared light. Inset: EDX analysis of c-BGHs.
(c,d) Raman spectra (c) and XRD patterns (d) of c-BGHs
after photodegradation of MO under ultraviolet, visible,
infrared and full-spectrum light irradiation.
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
REFERENCES
1.
adis, J. G.; Marinas, B. J.; Mayes, A. M. Nature 2008, 452, 301-310.
2. Likodimos, V.; Dionysiou, D. D.; Falaras, P. Rev. Envi-
ron. Sci. Biotechnol. 2010, 9, 87-94.
Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgi-
3.
Keane, D. A.; McGuigan, K. G.; Ibanez, P. F.; Polo-
Lopez, M. I.; Byrne, J. A.; Dunlop, P. S. M.; O'Shea, K.; Dionysiou,
D. D.; Pillai, S. C. Catal. Sci. Technol. 2014, 4, 1211-1226.
CONCLUSIONS
4.
Schneider, J.; Matsuoka, M.; Takeuchi, M.; Zhang, J.;
In summary, we present here the heterostructures of ele-
mental bismuth and graphene as an efficient and stable
photocatalyst that is able to degrade pollutants in acidic
environment under visible, infrared and ultraviolet light.
The emerging understanding of the mechanism indicates
that these heterostructures can take advantage of the
unique catalytic and electronic properties of individual
component of the system and extend the photocatalytic
activity towards infrared region. The present discovery
provides new insights into generalizing the concept of
elemental bismuth-graphene heterostructures to other
elemental photocatalysts to develop solar-light-efficient
photocatalytic applications. Moreover, this work adds to
the growing potential of bismuth-based photocatalysts,54
and is expected to accelerate the pace of the development
of new generation photocatalysts with ultrahigh efficacy
under full-spectrum solar light.
Horiuchi, Y.; Anpo, M.; Bahnemann, D. W. Chem. Rev. 2014, 114,
9919-9986.
5.
Jing, L.; Zhou, W.; Tian, G.; Fu, H. Chem. Soc. Rev.
2013, 42, 9509-9549.
6.
Fan, Y.; Ma, W.; Han, D.; Gan, S.; Dong, X.; Niu, L. Adv.
Mater. 2015, 27, 3767-3773.
7.
Yang, W.; Zhang, L.; Hu, Y.; Zhong, Y.; Wu, H. B.; Lou,
X. W. Angew. Chem. Int. Ed. 2012, 51, 11501-11504.
8.
Wu, J. C. S.; Wang, X. Nat. Commun. 2015, 6, 8340.
9. Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y.
Science 2001, 293, 269-271.
Zhou, Y.; Zhang, Y.; Lin, M.; Long, J.; Zhang, Z.; Lin, H.;
10.
Gaya, U. I.; Abdullah, A. H. J. Photochem. Photobio. C-
Photochem. Rev. 2008, 9, 1-12.
11.
Samadi, M.; Zirak, M.; Naseri, A.; Khorashadizade, E.;
Moshfegh, A. Z. Thin Solid Films 2016, 605, 2-19.
12.
Sang, Y.; Zhao, Z.; Zhao, M.; Hao, P.; Leng, Y.; Liu, H.
Adv. Mater. 2015, 27, 363-369.
ASSOCIATED CONTENT
13.
Tian, J.; Sang, Y.; Yu, G.; Jiang, H.; Mu, X.; Liu, H. Adv.
Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
Additional information about synthesis of GO nanosheets,
photocatalytic activity measurements, kinetic modelling of
photodecomposition and desorption, calculation of process
efficiency and catalytic efficiency, calculation of optical ener-
gy bandgap, and physical characterizations, as well as sup-
plementary figures and tables.
Mater. 2013, 25, 5075-5080.
14.
Wang, W.; Huang, W.; Ni, Y.; Lu, C.; Xu, Z. ACS Appl.
Mater. Interfaces 2014, 6, 340-348.
15.
Jiang, W.; Wu, Z.; Yue, X.; Yuan, S.; Lu, H.; Liang, B.
RSC Adv. 2015, 5, 24064-24071.
16.
Wang, H.; Li, S.; Liu, Y.; Ding, J.; Lin, Y.-H.; Xu, H.; Xu,
B.; Nan, C.-W. Sci. Rep. 2016, 6, 24620.
17.
Zhuang, T.-T.; Liu, Y.; Li, Y.; Zhao, Y.; Wu, L.; Jiang, J.;
Yu, S.-H. Angew. Chem. Int. Ed. 2016, 55, 6396-6400.
AUTHOR INFORMATION
18.
Low, J.; Yu, J.; Jaroniec, M.; Wageh, S.; Al-Ghamdi, A.
A. Adv. Mater. 2017, 29, DOI: 10.1002/adma.201601694.
Corresponding Author
*zjgu@ihep.ac.cn and zhaoyl@nanoctr.cn
ACS Paragon Plus Environment

ACS Catalysis
Page 8 of 9
19.
Ghosh, S.; Kouamé, N. A.; Ramos, L.; Remita, S.; Dazzi,
36.
Chen, J.; Wang, R. Appl. Surf. Sci. 2013, 282, 538-543.
37. Leontie, L.; Caraman, M.; Alexe, M.; Harnagea, C. Surf.
Sci. 2002, 507–510, 480-485.
38. Dharmadhikari, V. S.; Sainkar, S. R.; Badrinarayan, S.;
Yang, X.; Lian, X.; Liu, S.; Jiang, C.; Tian, J.; Wang, G.;
1
2
3
4
A.; Deniset-Besseau, A.; Beaunier, P.; Goubard, F.; Aubert, P.-H.;
Remita, H. Nat. Mater. 2015, 14, 505-511.
20.
Ansari, S. A.; Ansari, M. S.; Cho, M. H. Phys. Chem.
Chem. Phys. 2016, 18, 3921-3928.
5
21.
Shen, Z.; Yu, J. C., in Nanostructured Photocatalysts:
Goswami, A. J. Electron Spectrosc. Relat. Phenom. 1982, 25, 181-
Advanced Functional Materials (eds Yamashita, H. & Li, H.) 295-
312 (Springer International Publishing, 2016).
189.
6
7
39.
Kim, T. W.; Ping, Y.; Galli, G. A.; Choi, K.-S. Nat.
8
9
22.
Zhu, X.; Zhang, T.; Sun, Z.; Chen, H.; Guan, J.; Chen,
Commun. 2015, 6, 8769.
X.; Ji, H.; Du, P.; Yang, S. Adv. Mater. 2017, 29,
DOI:10.1002/adma.201605776.
40.
Corneille, J. S.; He, J.-W.; Goodman, D. W. Surf. Sci.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1994, 306, 269-278.
23.
Liu, G.; Niu, P.; Yin, L.; Cheng, H.-M. J. Am. Chem. Soc.
41.
Dutta, S. K.; Mehetor, S. K.; Pradhan, N. J. Phys. Chem.
2012, 134, 9070-9073.
Lett. 2015, 6, 936-944.
24.
Wang, Z.; Jiang, C.; Huang, R.; Peng, H.; Tang, X. J.
42.
Png, R.-Q.; Chia, P.-J.; Tang, J.-C.; Liu, B.; Sivarama-
Phys. Chem. C 2014, 118, 1155-1160.
krishnan, S.; Zhou, M.; Khong, S.-H.; Chan, H. S. O.; Burroughes,
J. H.; Chua, L.-L.; Friend, R. H.; Ho, P. K. H. Nat. Mater. 2010, 9,
152-158.
25.
Qin, F.; Wang, R.; Li, G.; Tian, F.; Zhao, H.; Chen, R.
Catal. Commun. B, 2013, 42, 14-19.
26.
Dong, F.; Xiong, T.; Sun, Y.; Zhao, Z.; Zhou, Y.; Feng,
43.
44.
Turchi, C. S.; Ollis, D. F. J. Catal. 1990, 122, 178-192.
Manna, G.; Bose, R.; Pradhan, N. Angew. Chem. 2014,
X.; Wu, Z. Chem. Commun. 2014, 50, 10386-10389.
27.
Lee, S. C. ACS Sust. Chem. Eng. 2016, 4, 6912-6920.
28. Jiang, G.; Li, X.; Lan, M.; Shen, T.; Lv, X.; Dong, F.;
Zhang, S. Appl. Catal. B-Environ. 2017, 205, 532-540.
29. Dong, F.; Li, Q.; Sun, Y.; Ho, W.-K. ACS Catal. 2014, 4,
4341-4350.
Gao, Y.; Huang, Y.; Li, Y.; Zhang, Q.; Cao, J.-j.; Ho, W.;
126, 6861-6864.
45.
Xu, L.; Huang, W.-Q.; Wang, L.-L.; Huang, G.-F. ACS
Appl. Mater. Interfaces 2014, 6, 20350-20357.
46.
95, 735-758.
Linsebigler, A. L.; Lu, G.; Yates, J. T. Chem. Rev. 1995,
47.
Xie, X.; Kretschmer, K.; Wang, G. Nanoscale 2015, 7,
30.
Kouame, N. A.; Alaoui, O. T.; Herissan, A.; Larios, E.;
13278-13292.
Jose-Yacaman, M.; Etcheberry, A.; Colbeau-Justin, C.; Remita, H.
New J. Chem. 2015, 39, 2316-2322.
48.
782-796.
Xiang, Q.; Yu, J.; Jaroniec, M. Chem. Soc. Rev. 2012, 41,
31.
McMahon, J. M.; Schatz, G. C.; Gray, S. K. Phys. Chem.
49.
Syoufian, A.; Nakashima, K. J. Colloid Interface Sci.
Chem. Phys. 2013, 15, 5415-5423.
2008, 317, 507-512.
32.
Toudert, J.; Serna, R.; Jiménez de Castro, M. J. Phys.
50.
Calza, P.; Minero, C.; Ezio Pelizzetti, A. J. Chem. Soc.,
Chem. C 2012, 116, 20530-20539.
Faraday Trans. 1997, 93, 3765-3771.
33.
Gellini, C.; Deepak, F. L.; Muniz-Miranda, M.; Caporali,
51.
Deng, D.; Novoselov, K. S.; Fu, Q.; Zheng, N.; Tian, Z.;
S.; Muniz-Miranda, F.; Pedone, A.; Innocenti, C.; Sangregorio, C.
J. Phys. Chem. C 2017, 121, 3597-3606.
Bao, X. Nat. Nanotechnol. 2016, 11, 218-230.
52.
Liu, J.; Wang, X. Chem. Soc. Rev. 2014, 43, 5234-5244.
53. Bai, S.; Ge, J.; Wang, L.; Gong, M.; Deng, M.; Kong, Q.;
Song, L.; Jiang, J.; Zhang, Q.; Luo, Y.; Xie, Y.; Xiong, Y. Adv. Ma-
ter. 2014, 26, 5689-5695.
Wang, H.; Zhang, L.; Chen, Z.; Hu, J.; Li, S.; Wang, Z.;
34.
RamanathanT; Abdala, A. A.; StankovichS; Dikin, D.
A.; Herrera Alonso, M.; Piner, R. D.; Adamson, D. H.; Schniepp,
H. C.; ChenX; Ruoff, R. S.; Nguyen, S. T.; Aksay, I. A.; Pru-
d'Homme, R. K.; Brinson, L. C. Nat. Nanotechnol. 2008, 3, 327-
331.
54.
Ye, L.; Su, Y.; Jin, X.; Xie, H.; Zhang, C. Environ. Sci-
35.
Zhang, Q.; Zhou, Y.; Wang, F.; Dong, F.; Li, W.; Li, H.;
Nano 2014, 1, 90-112.
Patzke, G. R. J. Mater. Chem. A 2014, 2, 11065-11072.
ACS Paragon Plus Environment

Page 9 of 9
ACS Catalysis
TOC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
9
ACS Paragon Plus Environment