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: zxhlynu@163.com

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).

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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