synthesis of ni doped invo4 for enhanced photocatalytic hydrogen evolution using glucose as electron...
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Synthesis of Ni Doped InVO4 for Enhanced PhotocatalyticHydrogen Evolution Using Glucose as Electron Donor
Xianghui Zhang
Received: 8 March 2014 / Accepted: 9 April 2014
� Springer Science+Business Media New York 2014
Abstract InVO4 and Ni–InVO4 were synthesized by a
solid-state reaction route. The products were characterized
by X-ray diffraction, UV–Vis diffusive reflectance spec-
troscopy and scanning electron microscope. Using glucose
as an electron donor, photocatalytic hydrogen generation
over InVO4 and Ni–InVO4 was investigated. The results
showed that glucose was degraded effectively with the
hydrogen generation. The photoactivity of InVO4 was
enhanced when Ni was doped into the crystal structure. The
effect of NaOH concentration on the hydrogen generation
rate was also studied. The results exhibited that the basic
condition is favorable for photocatalytic hydrogen gener-
ation, and there was an optimal NaOH concentration at
0.1 mol L-1.
Keywords BiVO4 � Hydrogen production � Glucose �Doping
1 Introduction
In 1972, Fujishima and Honda demonstrated the potential
of TiO2 semiconductor materials which can split water into
hydrogen and oxygen in a photoelectrochemical cell [1].
This work has triggered the development of semiconductor
photocatalysis in a wide range of environmental and energy
applications. Therefore, photocatalytic hydrogen evolution
over semiconductor materials has been considered as one
of the ultimate solutions for energy and environmental
issues because of its potential to use the abundance of solar
energy and water on the earth [2]. To produce hydrogen
effectively by water splitting, the band gap of photocatalyst
has to be larger than the theoretical dissociation energy of
water molecular (1.23 eV), where the band edge of con-
duction band should be more negative than the reduction
potential of water to form hydrogen while the valence band
level should be more positive than the oxidation potential
of water to form oxygen. Numerous semiconductor mate-
rials have been developed and used as effective photocat-
alysts for photocatalytic hydrogen evolution during the past
40 years [3].
During the photocatalytic reaction process, the effi-
ciency of hydrogen evolution usually becomes low because
of the recombination of photoinduced electrons and holes.
Researches show that appropriate addition of electron
donor as sacrificial agent to irreversibly deplete oxygen,
hole, or �OH radicals can inhibit the recombination and
improve the hydrogen evolution efficiency. From the
viewpoint of practical application, the electron donor for
the hydrogen evolution should be cheap and easy to obtain.
Many organic pollutants themselves are good electron
donors and have already been used for photocatalytic
hydrogen evolution, such as methanol [4], ethylene dia-
mine tetraacetic acid (EDTA) [5], triethanolamine [6], and
formic acid [7]. Biomass, such as glucose, the most ver-
satile renewable resource, can also be utilized for the
sustainable production of hydrogen. Li et al. [8, 9] have
reported that Pt/CdxZn1 - xS and Pt/ZnS–ZnIn2S4 can
generate hydrogen efficiently using biomass glucose as
electron donor over under visible light irradiation. Jing
et al. [10] have also investigated the photocatalytic
hydrogen evolution performance over BixY1 - xVO4 solid
solutions using glucose as electron donors. The photocat-
alytic hydrogen production system combined with control
of organic pollutants not only can greatly reduce hydrogen
X. Zhang (&)
College of Physics and Electronic Information, Luoyang Normal
University, Luoyang 471022, People’s Republic of China
e-mail: [email protected]
123
Catal Lett
DOI 10.1007/s10562-014-1258-9
production costs but also can degrade the organic pollu-
tants effectively, which achieves the dual purpose of
hydrogen evolution and pollution control. The activity of
hydrogen evolution can also be increased in the meantime.
As an important fundamental material, indium vanadate
(InVO4) has received considerable attention because of its
potential applications in various fields, such as gas-sensor
[11], photogegradation [12] and photoelectrchemistry [13].
Not only that, Ye et al. [14] has found that InVO4 is a good
photocatalyst for water splitting under visible light irradi-
ation. The photocatalytic properties have been attributed to
a small band gap and the open crystal structure of InVO4.
Afterwards, other researches have also demonstrated that
InVO4 could catalyze water to hydrogen under visible light
irradiation [15, 16]. The InVO4 possesses a narrow band
gap due to its electron orbits of transition metal V (3d-
metal). This fact suggests InVO4 is efficient in photocata-
lytic hydrogen evolution by water splitting.
Many studies reveal that doping foreign element into
active photocatalysts with a wider band gap is an effective
way to narrow the band gap. Then, the activity of photo-
catalyst will be improved due to its better ability to utilize
solar light as much as possible [17–19].
Therefore, InVO4 and Ni doped InVO4 (Ni–InVO4)
were synthesized and characterized by XRD, UV–Vis and
SEM techniques in this paper. The photocatalytic hydrogen
evolution using biomass glucose as electron donor over
InVO4 and Ni–InVO4 has been investigated. Ni–InVO4
shows a better activity for hydrogen evolution than pure
InVO4. Glucose can notably improve the activity of
hydrogen evolution. The effect of initial concentration of
NaOH was investigated.
2 Experimental
2.1 Preparation of Photocatalysts
All chemicals are analytical grade and used as received
without further purification. The preparation of InVO4
photocatalysts were accomplished by solid-state reaction
method, which uses In(NO3)3 and NH4VO3 as starting
materials. 3.32 g of In(NO3)3 and 1.02 g of NH4VO3 were
mixed and ground in an agate mortar, and calcinated in a
crucible at 850 �C for 12 h. In order to obtain high pho-
tocatalytic activity, Ni (0.1 wt%) as a dopant was doped
into InVO4. 3.32 g of In(NO3)3, 1.02 g of NH4VO3 and
0.68 mL of Ni(NO3)2 solution (0.1 mol L-1) were added
into 5 mL of deionized water. The mixture was dispersed
by a magnetic stirrer for 1 h, and then it was dried at 80 �C.
After drying, the mixture was transferred into a crucible
and calcinated at 850 �C for 12 h.
2.2 Characterization
X-ray diffraction (XRD) patterns of prepared photocata-
lysts were recorded in a wide angle range (2h = 10-80�)
by a Bruker D8 Advance X-ray diffractometer using Cu Kairradiation (k = 1.5406 A). An accelerating voltage of
40 kV and emission current of 40 mA conditions were
adopted in the measurements. Diffuse reflectance spectra
were measured on a Hitachi U-4100 UV–Vis-near-IR
instrument employed with a lab-sphere diffuse reflectance
accessory. The spectra were collected in the 300–760 nm
range at room temperature using BaSO4 as a reference. The
morphology of the photocatalysts was observed by SHI-
MADZU SSX-550 scanning electron microscope (SEM).
The Brunner–Emmet–Teller (BET) surface areas of the
photocatalysts were determined by physical adsorption of
liquid nitrogen at -196 �C in a Micromeritics ASAP 2020
nitrogen adsorption apparatus. Before the experiments,
samples were previously degassed under vacuum at 150 �C
for 3 h.
2.3 Photocatalytic Reactions
The photocatalytic reaction was carried out in an inner
irradiation type reactor. A 300 W high pressure Hg lamp
was used as the light source. Typically, 0.3 g of photo-
catalyst powder was dispersed by a magnetic stirrer in
400 mL aqueous solution containing 0.1 mol L-1 of glu-
cose as the electron donor and 0.1 mol L-1 of NaOH as the
pH regulator. Before the irradiation, the reactor was
deaerated with nitrogen for about 20 min. The gas evolved
was gathered and analysed by online thermal conductivity
detector (TCD) gas chromatography using a NaX zeolite
column and nitrogen as the carrier gas. During the entire
experiment, the reaction temperature was kept at
35 ± 0.1 �C by the thermostatic circulating water in the
water jacket of the reactor.
3 Results and Discussion
3.1 Crystal Structure
Figure 1 shows the XRD patterns of InVO4 and Ni–InVO4.
From the figure, it can be found that the XRD patterns of
the products present similar profiles and can be well-
indexed as an orthorhombic (Cmcm) phase of InVO4 with
lattice constants a = 5.753 A, b = 8.520 A, c = 6.587 A,
which can be in good agreement with the standard card
(JCPDS PDF 48-0898). The peaks are sharp and narrow,
indicating the high crystallization of the products. No
impurity peaks are observed in the patterns, indicating that
the products are absolutely orthorhombic phase and the
X. Zhang
123
transition metal ion Ni2? is successfully doped into the
InVO4 structure.
The average crystallite sizes can be roughly calculated
by the full width at half-maximum of XRD peak around
28� using the Scherrer formula. The calculation results
show that the crystallite size were about 65.3 and 59.8 nm
for InVO4 and Ni–InVO4, respectively. The crystal size of
Ni–InVO4 was smaller than that of nondoped InVO4. The
reason for the decrease in crystal size is that when Ni ions
were doped into InVO4, the defects would appear on the
surface of photocatalyst, which could inhibit the growth of
the crystal and therefore decrease the crystal size. The
crystal size influences the distance that photogenerated
electrons and holes have to migrate in the bulk of the
photocatalyst particle to reach the active sites. It is very
important to suppress the recombination of electrons with
holes to achieve high photocatalytic activity for water
splitting. Therefore, in the present Ni–InVO4, a decrease in
the crystallite size is an important factor. Because the
crystallite size is decreased, the probability of the surface
reaction of electrons and holes with water molecules is
increased in comparison with the recombination in the
bulk, leading to an increase in the photocatalytic activity
for water splitting. Therefore, the high crystallinity and
fineness of photocatalyst particles obtained by Ni doping
probably cause the high activity of Ni–InVO4.
3.2 Optical Properties
Seeing that the energy band gap plays a key role in
determining the photocatalytic activity of semiconductors,
the UV–Vis diffused reflection spectra studies were per-
formed. As presented in Fig. 2, the UV–Vis spectra of
InVO4 and Ni–InVO4 show a broad absorbance in the
visible region. This allows the as-prepared products
respond to a wide range of solar spectrum and utilize vis-
ible light for photocatalysis. In addition, it can be seen that
10 20 30 40 50 60 70 80
Ni-InVO4Inte
nsi
ty (
a.u
.)
2θ ( ° )
InVO4
Fig. 1 X-ray diffraction patterns of InVO4 and Ni–InVO4
300 400 500 600 7000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Ab
s(a.
u.)
Wavelength(nm)
InV04
Ni-InVO4
Fig. 2 UV–Vis diffused reflection spectra of InVO4 and Ni–InVO4
Fig. 3 a SEM image of InVO4 b SEM image of Ni–InVO4
Synthesis of Ni Doped InVO4
123
the Ni–InVO4 exhibits more absorbance than InVO4 in the
visible light region. The band gap energy (Eg) of the
photocatalyst can be estimated by using the equation:
Eg = 1,240/kg, where kg is the absorption edge of photo-
catalyst. The absorption edge of the as-prepared InVO4 and
Ni–InVO4 photocatalyst is 550 and 590 nm, respectively,
so the band gap energy was estimated to be 2.3 and 2.1 eV,
respectively. Based on the density function theory calcu-
lations and optical properties for InVO4 and Ni–InVO4
[20], the valence band of InVO4 is spanned dominantly by
O 2p orbital, the V 4d orbital contribute to the conduction
band levels of InVO4. For the Ni-doped sample [21],
orbital-splitting from discrete Ni 3d level will form above
the edge of valence band of InVO4 by doping Ni2? into
InVO4. The Ni 3d level works as the donor level for
photoexcitation. Because of it, a smaller value of the
energy band gap for Ni–InVO4 samples compared to that
for the undoped samples was observed. A narrower band
gap of Ni–InVO4 is beneficial to absorb visible light as
well as ultraviolet light for the excitation of electrons from
the valence band to the conduction band. Therefore, the
Ni–InVO4 product can utilize the solar energy more
effectively.
3.3 Morphology
Figure 3 shows the SEM images of InVO4 and Ni–InVO4.
From the SEM images, well-crystallized particles with
particle sizes of several micrometers were observed, and
the shape of both powders is irregular.
3.4 Specific Surface Area
The specific surface area of InVO4 and Ni–InVO4 powders
were measured from BET analysis. The results show that
the Ni–InVO4 sample possesses a surface area of
1.63 m2 g-1, while the nondoped InVO4 sample possesses
a surface area of 1.58 m2 g-1. The higher specific surface
area of Ni–InVO4 can be attributed to its reduced crystal
size. The surface area affects the number of active sites,
thus more active sites can be supplied during photocatalytic
reaction over Ni–InVO4 photocatalyst, resulting in its
higher activity [22].
3.5 Photocatalytic Properties
Figure 4 displays the photocatalytic hydrogen production
performance from aqueous solution containing
0.1 mol L-1 glucose and 0.1 mol L-1 NaOH under UV
light irradiation over InVO4 and Ni–InVO4 with various
Ni2? doping. Here, glucose was used as electron donor and
NaOH was used as pH regulator. Control experiment
showed no hydrogen evolution either in the dark or without
photocatalyst, indicating that the hydrogen evolution pro-
ceeds in a photocatalytic way. Not only nondoped InVO4
but also Ni–InVO4 were active and stable in hydrogen
production. As the amount of doped Ni was increased, the
photocatalytic activity of Ni–InVO4 was increased. The
highest activity was obtained when 0.1 wt% of Ni was
doped. The phenomenon indicated that the Ni doping plays
a key role in determining photocatalytic hydrogen evolu-
tion rate. After Ni as a dopant was doped into InVO4, the
light absorption band of Ni–InVO4 grew, which allowed
maximum utilization of incident light; the crystallite size
became smaller, which facilitated faster transportation of
photogenerated electrons from bulk to surface, and the
specific surface area became larger, which provided more
active sites. These factors together gave Ni–InVO4 higher
activity. However, when the concentration of Ni doped was
above 0.1 wt%, the activity was decreased. Several other
researches had reported the similar dependence of photo-
catalytic H2 evolution upon the amount of dopant [23, 24].
The inactivation of InVO4 doped with excessive Ni could
attribute to the excessive Ni, which might work as
recombination sites between photogenerated electrons and
holes. Therefore, the photocatalyst activity of hydrogen
production decreased [18].
For further investigation, the time courses of photocat-
alytic hydrogen production over the optimized Ni (0.1
wt%)–InVO4 at various NaOH concentrations were recor-
ded, as shown in Fig. 5. Again, control experiment con-
firmed no hydrogen production in the absence of light
irradiation or photocatalyst. From Fig. 5, it could be found
that the NaOH concentration strongly affected the hydro-
gen production performance. The amount of hydrogen
production increases at first with the growth of the NaOH
0 1 2 3 4 5 6 7 8 9 10 110
5
10
15
20
25
30
35
40
Am
ount
of
H2
Pro
duct
ion
(µ m
ol)
Reaction Time (h)
0.0 wt% 0.05 wt% 0.1 wt% 0.2 wt%
Fig. 4 Photocatalytic hydrogen production performance from aque-
ous glucose solution under UV light irradiation over InVO4 and Ni–
InVO4 with various Ni2? doping
X. Zhang
123
concentration, reaches the peak at 0.1 mol L-1, and then
decreases with further growth of the NaOH concentration.
The relation between solution pH value and hydrogen
production performance is considered to be quite compli-
cated, relating to the changes of the chemical state of
glucose and redox potential of H?/H2. The acid dissocia-
tion constant pKa of glucose is about 12.3 [25]. The glucose
in the solution is mainly in molecular form when the
pH \ pKa, and otherwise glucose can dissociate into H?
and C6H11O6-, which has been suggested to capture holes
more efficiently than the molecular form [26]. Under our
basic solution experimental condition, the dissociated
C6H11O6- can act as a hole scavenger to facilitate hydro-
gen production. The concentration of C6H11O6- increases
with NaOH concentration grew, leading to the improve-
ment of the hydrogen production activity. However, with
the growth of the NaOH concentration, the redox potential
of H?/H2 will become more negative, which is unfavorable
to efficient hydrogen production. Therefore, there is a
maximum hydrogen production activity when NaOH at its
optimal concentration of 0.1 mol L-1.
4 Conclusions
In summary, InVO4 and Ni–InVO4 with orthorhombic
crystal phase were synthesized by a solid-state reaction
method. Using glucose as electron donor, photocatalytic
hydrogen production is promoted greatly over InVO4 and
Ni–InVO4 with simultaneous degradation of glucose. The
prepared Ni–InVO4 photocatalyst exhibits better activity
for hydrogen production than pure InVO4, which can be
attributed to the fact that the doped Ni broadens the
response range, decreases the crystallite size and enlarges
the surface area. The activity of hydrogen production from
glucose is strongly dependent on the initial pH of the
solution. The amount of hydrogen production increases
with the growth of NaOH concentration and reaches a
maximum when NaOH concentration is 0.1 mol L-1.
Acknowledgments The author gratefully acknowledges the finan-
cial support of the Natural Science Foundation of Henan Department
of Science and Technology (Contracted No. 132300410318) and the
Natural Science Foundation of Luoyang Normal University (Con-
tracted No. 10001421).
References
1. Fujishima A, Honda K (1972) Nature 238:37
2. Kudo A, Miseki Y (2009) Chem Soc Rev 38:253
3. Chen X, Shen S, Guo L, Mao SS (2010) Chem Rev 110:6503
4. Yu H, Yan S, Li Z, Yu T, Zou Z (2012) Int J Hydrogen Energy
37:12120
5. Matos J, Marino T, Molinari R, Garcıa H (2012) Appl Catal
417–418:263
6. Xu Z, Li Y, Peng S, Lu G, Li S (2011) Crys Eng Comm 13:4770
7. Li Y, Hu Y, Peng S, Lu G, Li S (2009) J Phys Chem C 113:9352
8. Peng S, Peng Y, Li Y, Lu G, Li S (2009) Res Chem Intermed
35:739
9. Li Y, Wang J, Peng S, Lu G, Li S (2010) Int J Hydrogen Energy
35:7116
10. Jing D, Liu M, Shi J, Tang W, Guo L (2010) Catal Commun
12:264
11. Chen L, Liu Y, Lu Z, Zeng D (2006) J Colloids Interface Sci
295:440
12. Wang Y, Dai H, Deng J, Liu Y, Zhao Z, Li X, Arandiyan H
(2013) Chem Eng J 226:87
13. Wang Y, Cao G (2007) J Mater Chem 17:894
14. Ye J, Zou Z, Oshikiri M, Matsushita A, Shimoda M, Imai M,
Shishido T (2002) Chem Phys Lett 356:221
15. Lin HY, Chen YF, Chen YW (2007) Int J Hydrogen Energy
32:86
16. Yan Y, Cai F, Song Y, Shi W (2013) Chem Eng J 233:1
17. Jing D, Liu M, Guo L (2010) Catal Lett 140:167
18. Zhang X, Jing D, Liu M, Guo L (2008) Catal Commun 9:1720
19. Zhang A, Zhang J (2010) J Hazard Mater 173:265
20. Ye J, Zou Z, Arakawa H, Oshikiri M, Shimoda M, Matsushita A,
Shishido T (2002) J Photochem Photobiol A 148:79
21. Cheng KW, Huang CM, Yu YC, Li CT, Shu CK, Liu WL (2011)
Sol Energy Mater Sol Cells 95:1940
22. Yu J, Yu JC, Ho W, Jiang Z (2002) New J Chem 26:607
23. Tsuji I, Kudo A (2003) J Photochem Photobiol A 156:249
24. Shen S, Zhao L, Zhou Z, Guo L (2008) J Phys Chem C
112:16148
25. Bunton CA, Savelli G, Sepulveda L (1978) J Org Chem 43:1925
26. Du M, Feng J, Zhang S (2007) Phys Rev Lett 98:066102
0 1 2 3 4 5 6 7 8 9 10 110
5
10
15
20
25
30
35
40A
mou
nt o
f H
2 P
rodu
ctio
n (µ
mol
)
Reaction Time (h)
0 mol L-1
0.05 mol L-1
0.1 mol L-1
0.2 mol L-1
Fig. 5 The time courses of photocatalytic hydrogen production over
Ni–InVO4 at various NaOH concentrations
Synthesis of Ni Doped InVO4
123