Functions of boric acid in fabricating TiO2 for photocatalytic degradation of organic contaminants and hydrogen evolution

Article abstract of DOI:10.1016/j.mcat.2019.110614

Boric acid-induced hydrolysis for fabricating TiO₂ photocatalyst for photodegradation of organic contaminants (such as phenol, methyl orange and methylene blue) and hydrogen evolution is developed. The water dehydrated from boric acid in absolu

Full text of DOI:10.1016/j.mcat.2019.110614

Molecular Catalysis 479 (2019) 110614
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Functions of boric acid in fabricating TiO for photocatalytic degradation of
2
organic contaminants and hydrogen evolution
⁎
⁎
Kaihong Xie, Hong Zhang, Sufang Sun , Yongjun Gao
Key Laboratory of Analytical Science and Technology of Hebei Province, College of Chemistry and Environmental Science, Hebei University, Baoding, 071002, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
2
Boric acid-induced hydrolysis for fabricating TiO photocatalyst for photodegradation of organic contaminants
Photocatalysis
Degradation
Hydrogen evolution
Organic contaminants
Boric acid
(such as phenol, methyl orange and methylene blue) and hydrogen evolution is developed. The water dehy-
drated from boric acid in absolute ethanol promote the slow hydrolysis of tetrabutyl titanate during the hy-
drothermal process so that the crystalline size of TiO
reagent for tetrabutyl titanate, but also as support for TiO
Moderate dosage of boric acid and calcinating temperature during the synthesis of TiO
2
is smaller. Boric acid not only function as hydrolytic
nanoparticles during the annealing procedure.
promote the exposure of
2
2
active (001) facets and large surface area, resulting to the excellent photocatalytic activity in the degradation of
organic contaminants and hydrogen evolution.
Introduction
[17–20]; ii) hydrogenating TiO
visible-light can be effectively absorbed [8,12,21]; iii) doping metal or
non-metal into TiO , which dopes hetero-orbit into band gap of TiO
decreasing actual band gap of TiO [22–25].
Among the three measures to enhance the photocatalytic perfor-
mance of TiO , introducing doping non-metal dopants into TiO is re-
2 2
to produce colorful TiO so that
With the rapid development of modern industry, environmental
pollution and energy crisis are becoming two major issues besetting us,
which urge scientists to find effective measures to ameliorate the si-
tuation [1,2]. Photocatalytic pollutant degradation and hydrogen pro-
duction, which can improve environment quality and provide clean fuel
respectively just under solar irradiation, are effective and promising
2
2
,
2
2
2
latively simple and promising method because it is conducive the
electron-hole separation and improves the visible-light absorption
way to solve these two problems [3–6]. In the past decades, TiO
2
has
2
property [22]. Boron-doped TiO has been researched in photo-
been thoroughly studied for the photocatalysis because of its non-
toxicity, low cost, high stability and excellent photocatalytic activity
degradation of various organic pollutants in recent years [26–29]. The
relationship between the content of boron dopants with photocatalytic
[
7–9]. The photogenerated hydroxyl radicals OH• resulting from the
interaction between photoholes with water and/or oxygen on the sur-
face of TiO , owing strong oxidizing ability (standard redox potential
2.8 V), can oxidized most of organic compounds to mineral end-
performance was also investigated [30]. With boric acid (H
boron resource and tetrabutyl titanate as precursor, a tiny amount of
water was usually introduced to hydrolyze tetrabutyl titanate to TiO
[28,29], which makes the process of hydrolysis quick and size of TiO
3 3
BO ) as
2
2
2
+
product, such as carbon dioxide and water [10]. On the other side, the
photogenerated electrons can reduce hydrogen ions in water to hy-
large that impacts photocatalytic performance. In this article, the
functions of H BO in fabricating TiO with excellent photocatalytic
3
3
2
drogen in the present of sacrifice agent [11]. Therefore, TiO
usually used to photodegrade organic pollutants or photocatalytic hy-
drogen generation [12–16]. However, its wider band gap (about 3.2 eV)
2
was
activity in the degradation of organic contaminants and the hydrogen
generation are extensively investigated. The excessive boric acid not
only induces the slow hydrolysis of tetrabutyl titanate, but also be ex-
pected to serve as hard template and boron resource during the hy-
drothermal process and annealing procedure, so that the products
possess high surface area and porous structure. It was found that the
amount of H BO and annealing temperature is relative to the factors
3 3
impacting photocatalytic activity such as crystallinity, surface area and
pore size. Therefore, this research is important to develop outstanding
illustrates that the light absorption of TiO
tensively hampering the utilization of solar irradiance [12]. To extend
the absorption region of TiO to visible region and improve the pho-
tocatalytic activity, three strategies as following are often adopted: i)
hybridizing TiO with other semiconductive materials, which can ef-
2
is in UV-light region, ex-
2
2
fectively decrease recombination of photo-hole and photo electron
⁎
Corresponding authors.
E-mail addresses: sunsufang@hbu.edu.cn (S. Sun), yjgao@hbu.edu.cn (Y. Gao).
https://doi.org/10.1016/j.mcat.2019.110614
Received 3 July 2019; Received in revised form 3 September 2019; Accepted 10 September 2019
2468-8231/ © 2019 Elsevier B.V. All rights reserved.

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
photocatalyst TiO
2
and demystify the function of boric acid in synthe-
temperature. For example, TiO
2
-5B-600 means that 5 g boric acid was
sizing TiO
2
with excellent photocatalytic activity.
used and the annealing temperature is 600 °C. As control experiment,
sample was not annealed at high temperature, just washed with boiled
water, it was termed as TiO
boric acid.
2
-xB, x still represents the gram number of
Experimental
Materials
Photodegradation of phenol and dyes
Butyl titanate (Kermel, 99.0%), ethanol absolute (Fangzheng, ana-
lytical reagent grade), boric acid (Fuchen, 99.5%), methanol (Concord,
The photodegradation of phenol is carried out on a photochemical
reactor (YM-GHX-V II, Yuming Instrument, Shanghai, China). The
Xenon lamp is used as the light source, and its power is 1000 W, the
99.90%), phenol (Fuchen, analytical reagent grade), Methyl Orange
(
Beijing, analytical reagent grade), Methylene Blue (Beijing, analytical
–2
luminous intensity is 170 mW cm . Typically, photocatalyst (50 mg)
reagent grade), Ethylene glycol (Fangzheng, analytical reagent grade),
Glycerol(Huadong, analytical reagent grade), P25 (Macklin,99.8%) are
all used as received.
−
1
and phenol aqueous solution (50 mL, 10 mg L ) are charged into a
quartz tube reactor in turn. Then, the tubes containing reactants are
placed around a Xenon lamp and magnetically stirred in dark for 0.5 h
before irradiation in order to achieve an adsorption and desorption
equilibrium between the photocatalyst and the phenol solution. The
Xenon lamp is placed in a quartz cold well cooled down by circulating
water at 10 °C so that the impact of infrared radiation on reaction can
be eliminated. The picture of photochemical reactor can be seen in Fig.
S1. During the irradiation, samples are taken at constant time intervals
Characterizations
Transmission electronic microscopy (TEM, Tecnai G2 F20 S-TWIN)
and scanning electronic microscopy (SEM, JSM-7500) are used to ob-
serve morphology of all samples. X-ray diffractometer (Bruker D8
α
ADVANCE, CuK (1.5418 Å), 40 kV, 40 mA) records the powder X-ray
(
once an hour), sampling 1 mL each time, and then analyze the contents
diffraction (XRD) patterns. The scanning speed is 4 degrees per minutes
from 2θ = 4° to 80°. Laser Confocal Micro-Raman Spectroscopy
of residual phenol and intermediates by high performance liquid
chromatograph (HPLC, LC-20A, Shimadzu) equipped with a C-18
column (4.6*250 mm, 5um). The UV detector (SPD-20A) is set to a
wavelength of 270 nm, and the mobile phase is water/acetonitrile (1:1
(
LabRAM HR800, Horiba Jobin Yvon, France) with 532 nm laser pre-
sents Raman spectra for all samples. X-ray photoelectron spectroscopy
XPS, Thermo ESCALAB 250XI) is utilized to analyze the elemental
(
(
v/v)) with flow rate of 0.8 mL/min.
components. The nitrogen adsorption-desorption experiments are per-
formed on an automatic specific surface and porosity analyzer (V-sorb-
In photocatalytic degradation methyl orange (MO) and methylene
blue (MB), the whole experimental procedure is essentially the same as
the photocatalytic degradation of phenol except that the initial con-
2
800, Gold APP Instruments, Beijing). The sample was firstly degassed
in vacuum at 120 °C for 4 h before analysis. The surface area is calcu-
lated based on the adsorption data with a relative pressure (P/P
−
1
centration of MO and MB solution is controlled at 5 mg L . The re-
sidual concentration of MO is detected by HPLC, the wavelength of UV
detector is 460 nm, the mobile phase is water/acetonitrile (3:7 (v / v))
with a flow rate of 1 mL / min. The residual concentration of MB is
measured by a UV/Vis spectrophotometer at 660 nm (Beijing P&S
General T6 New Century).
0
)
ranging from 0.05 to 0.35 according to Brunauer-Emmett-Teller (BET)
theory. The total pore volume of each sample is calculated by using
single point adsorption data at P / P = 0.9970. Diffuse reflectance
0
UV–vis spectroscopy was conducted on a spectrophotometer (Shimadzu
UV-3600) equipped with an integrating sphere. Optical band gaps are
determined from Tauc plots for an indirect band gap material, F(R)=
2
1/2
Photocatalytic hydrogen production
(
1 − R)
×
hυ
using the Kubelka-Munk formalism, where R corre-
(
2R
)
sponds to the reflectivity (%R / 100) and the band gap is obtained from
Photocatalytic hydrogen production is carried out in a custom top-
irradiation quartz reactor with gas sampling hole. The photocatalyst is
dispersed in a methanol solution (50 mL, 20 vol %), and bubbled with
the intersection of the tangent to the energy axis of the function. The
surface acidity of the TiO
TPD experiments, using chemisorption instrument (VDSorb-91i, Vodo
instrument, Quzhou, China). The detailed procedure for NH -TPD is as
follow: 0.05 g of TiO -xB-600 was placed inside the U-type quartz qube
2 3
-xB-600 samples were determined by NH -
2
N under stirring for 30 min so that the air in the reactor can be suffi-
3
ciently discharged. Then the quartz reactor is sealed and irradiated
under Xenon lamp. Its power is 300 W and the wavelength distribution
is 350–780 nm. The output light intensity was controlled at 200 mW
2
and pretreated in helium atmosphere at 150 °C for 1 h. Subsequently the
sample was cooled down to room temperature and titrated with pure
NH . Afterwards, the physically-absorbed NH was removed by helium
3 3
gas for 0.5 h. The desorption process was performed from 30 to 500 °C
with a ramp of 10 °C /min and recorded by a thermal conductivity
detector (TCD).
–
2
cm . The reactor is cooled by running water at room temperature. The
picture of instrument for photocatalytic hydrogen generation is shown
in Fig. S2. The evolved gas is analyzed by gas chromatography (CHU-
ANHAO GC-7890, Shanghai, China) equipped with a thermal con-
ductive detector (TCD) and a 5A molecular sieve column. Nitrogen gas
is used as carrier gas. The temperature of column oven, inlet and TCD is
set to 50, 50 and 150 degrees, respectively.
Catalyst preparation
In general, tetrabutyl titanate (10 mL), ethanol absolute (10 mL) and
boric acid were added into a Teflon-lined stainless steel autoclave in
turn. The mixture was stirred with a glass rod before seal up and then
hydrothermal treated at 180 °C in oven for 24 h. The product was
Results and discussions
Photodegradation of phenol and dyes
named as O-TiO
in oven at 80 °C overnight and annealed at high temperature
400–800 °C) in muffle furnace for two hours. Then the annealed
powder was boiled up in a large amount of water for one hour and
thermally filtered so that boric acid or boron oxide in sample can be
removed. The product was dried in oven at 100 °C for two hours and
2
(original TiO
2
). After filtration, the product was dried
Phenol is one of the most common organic pollutants in surface
water sources and is widely found in industrial waste water, which is
harmful to all living organisms [31,32]. Photocatalytic degradation of
phenol in wastewater is an effective measure to improve the quality of
(
2
water [32]. To evaluate the photocatalytic activity of TiO samples
hydrolyzed by boric acid and calcinated at different temperature, we
firstly conduct photodegradation of phenol with these samples as cat-
alyst in water.
named as TiO
2
-xB-y, in which x represents the gram number of boric
acid used in hydrothermal process and y indicates the annealing
2

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
2
Fig. 1. Photocatalytic performance of TiO samples in photodegradation of phenol.
Table 1
2
Structure characteristics and photoactivity of TiO -xB-y samples.
Apparent rate constants for photodegradation of phenol Ka(×10 2, h−1
)
−
sample
Relative crystallinity
crystallite size(nm)
XRD(001/101)
Raman(514/144)
TiO
TiO
TiO
TiO
TiO
TiO
2
-5B-500
2
-5B-600
2
-5B-700
2
-5B-800
2
-1B-600
2
-10B-600
0.642
1
2.653
3.413
1.052
1.480
103
168
521
> 1000
184
0.185
0.204
0.188
0.197
0.169
0.206
0.069
0.106
0.059
0.060
0.070
0.088
19.55
35.64
19.49
5.45
14.52
65.18
279
3

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
As shown in Fig. 1a, phenol shows a stable existence under Xe lamp
irradiation in the absence of catalyst, whereas degradation occurs if
TiO catalysts exist in the system. TiO -5B and commercial P25 exhibit
similar photocatalytic performance, which cannot effectively photo-
degrade phenol even in nine hours. When TiO -5B is calcinated at
higher temperature, the photocatalytic activity increased. Compered to
TiO -5B-500, TiO -5B-700 and TiO -5B-800, TiO -5B-600 shows ex-
cellent photocatalytic performance, which is even higher than the
performance of commercial P25. If the calcination temperature is
higher than 600, the photocatalytic performance decrease, maybe re-
sulting from the increase of crystallite size and the decrease of surface
Characterizations of TiO
2
-xB-y
2
2
To explore the specific functions of boric acid in fabricating TiO
samples with different photocatalytic performance, series of char-
acterizations are conducted to probe the microstructure of all samples.
2
2
In the hydrothermal process for synthesizing TiO
containing boric acid, no extra water was introduced into the system
and tetrabutyl titanate yet was hydrolyzed to TiO . In control experi-
ment, TiO powder cannot be achieved if boric acid is absent in the
2
in absolute alcohol
2
2
2
2
2
2
system under same hydrothermal conditions. XRD pattern of the solid
product achieved after hydrothermal process presents obvious char-
area. The linear transforms of ln(C
that the photocatalytic degradation of phenol is first-order reaction.
The apparent rate constant of TiO -5B-600 is larger than TiO -5B-500,
TiO -5B-700 and TiO -5B-800 according the slope values of lines
Table 1). As control experiment, TiO -600, produced through water-
0
/C) ∼ t shown in Fig. 1b illustrate
2
acteristic diffraction of anatase TiO and boron oxide (Fig. 3a), con-
firming that the water promoting the hydrolysis of tetrabutyl titanate
generated from the dehydration of boric acid at hydrothermal condition
and boric acid became into boron oxide. Furthermore, due to the poor
solubility of boric acid or boron oxide in absolute ethanol, the solid
boric acid or boron oxide can serve as support to load the generated
2
2
2
2
(
2
induced hydrolysis of tetrabutyl titanate, show poor photocatalytic
activity (Fig. 1c). This result illustrates that boric acid play positive
TiO
small TiO
boron oxide (Fig. 3b). In the following annealing process, boron oxide
can also function as hard template to generate TiO with large surface
area and pore structure. After boron oxide is washed in boiling water,
TiO -xB-y can be achieved. The SEM image of TiO -5B-600 shown in
Fig. 3c indicates that TiO -5B-600 is composed of assembled TiO na-
noparticles. The TEM image of TiO -5B-600 further points out that the
size TiO nanoparticles in TiO -5B-600 are about 25∼50 nm (Fig. 3d).
Its microstructure illustrates that the sample are not completely crys-
talline and a layer of amorphous state around TiO nanoparticles
2
. From the SEM image of O-TiO2, it can be clearly observed that
function to improve the photocatalytic activity of TiO
further investigate the function of boric acid, TiO catalysts with dif-
ferent dosages of boric acid during the hydrothermal step are prepared
under same conditions, that is, TiO -1B-600 and Ti-10B-600. As was
expected, TiO -10B-600 exhibits the highest photocatalytic perfor-
mance than other all samples because almost 100% degradation of
phenol in only five hours. Linear transforms of ln(C /C) ∼ t indicates
that TiO -10B-600 possess the largest apparent rate constant (Fig. 1d).
Furthermore, we also investigate the degradation of phenol and inter-
mediates distribution along with the reaction time with TiO -10B-600
2
-5B-600. To
2
nanoparticles load on the surface of laminated boric acid/
2
2
2
2
2
2
2
2
0
2
2
2
2
2
2
as photocatalyst (Fig. 1e). During this photodegradation, small amount
of intermediates such as hydroquinone, catechol and benzoquinone are
also detected and finally degraded, which is similar to the other report
showing lattice fringe can be clearly observed (Fig. 3d). We also use
XRD characterizations to research the impact of the calcination tem-
perature and the dosage of boric acid on the microstructure of TiO
2
-xB-
[
6
33]. More importantly, the photocatalytic performance of TiO
00 for phenol degradation still highly remains even after four ex-
perimental cycles, suggesting it possesses a stable degradation ability
Fig. 1f). TiO -10B-600 exhibits different photocatalytic activities under
2
-10B-
y (Fig. 4a and b). In order to study the crystallinity of TiO -xB-y, TiO -
2
2
5B-600 is selected as the reference sample so that its relative crystal-
linity is set as 1. The relative crystallinity of the remaining samples can
be estimated according to the ratio of (101) diffraction intensity of
(
2
different pH conditions (Fig. 1g and h). The results indicate that the
2 2
TiO -xB-y to that of TiO -5B-600 (Table 1). It can be clearly observed
photodegradation of phenol is more favorable in near-neutral solution
or acid solution than in alkaline solution, suggesting that TiO -10B-600
2
has broad applicability in practical application for photodegradation of
phenol.
that the crystallinity of the sample is better as the annealing tempera-
ture is increased. At the same time, the dosage of boric acid used during
the synthesis is also considered to be a factor affecting the crystallinity.
The larger dosage of boric acid leads to the higher crystallinity of the
sample. In addition, according to the line width analysis of anatase
(101) diffraction peak based on Scherrer formula calculation, the
The photocatalytic degradation of MO and MB by TiO
2
-10B-600 is
also investigated (Fig. 2). The results suggest that TiO -10B-600 has
2
photodegradation ability to both anionic dye MO and cationic dye MB.
When the irradiation time is 7 h, 80% of MO and almost 100% of MB
crystallite size of TiO
temperature (Table 1). In the pattern of TiO
2
increase along with the raise of calcination
-5B-800, the characteristic
2
were degraded (Fig. 2a). The linear transforms of ln(C
indicate that the photodegradation of MO and MB is also first-order
reaction. It is proved that TiO -10B-600 has general applicability in
photocatalytic degradation of organic contaminations.
0
/C)∼t in Fig. 2b
diffraction peaks of rutile can be obvious observed. Moreover, it is well
established that (001) face of anatase phase is more active in photo-
catalysis because photogenerated electrons favor to assemble on low-
energy (101) face while photogenerated holes migrate to high-energy
2
(
[
001) faces, making for the separation between electrons with holes
34]. The more exposure of (001) faces in anatase TiO is, the higher
photocatalytic activity of TiO possesses. After careful analysis of XRD
2
2
Fig. 2. Photocatalytic performance of TiO
2
-10B-600 in photodegradation of MO and MB.
4

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
2 2 2 2
Fig. 3. a) XRD patterns of O-TiO and standard diffractions of anatase and boric acid; b) SEM image of O-TiO ; c) SEM image of TiO -5B-600; d) TEM image of TiO -
5B-600.
2 2 2 2
Fig. 4. a) XRD patterns of TiO -5B-y; b) XRD patterns of TiO -xB-600; c) Raman spectra of TiO -5B-y; d) Raman spectra of TiO -xB-600.
5

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
1
/2
Fig. 5. a) Nitrogen isotherms of TiO
2
-5B-y; b) porous width distribution of TiO
2
-5b-y samples; c) The plots of transformed KM function [αhv]
vs. hv based on
1
/2
diffuse reflectance spectra of TiO
2
-5B-y; d) The plots of transformed KM function [αhv]
vs. hv based on diffuse reflectance spectra of TiO -xB-600.
2
patterns, it is found that the (001)/(101) ratios of TiO
TiO -10B-600 are higher than other samples (Table 1). Because active
photogenerated hydroxyl radicals OH• possess standard redox potential
of +2.8 V, which can decompose organic to end-products [10], TiO
B-600 and TiO -10B-600 exhibit excellent photocatalytic activity in
2
-5B-600 and
decreases, the Raman peaks become broad and systematic frequency
shifts [37]. Compared to the sample TiO -5B-700 and TiO -5B-800, the
peaks of Eg mode (144 cm ) in the spectra of TiO -5B-500 and TiO
5B-600 are broad and exhibit a slightly red shift, suggesting that the
particle sizes of anatase in TiO -5B-500 and TiO -5B-600 are smaller
[34]. In addition, the intensity ratio of A1g (514 cm ) / E
represents the percentage of exposed [001] facets of TiO2. After careful
2
2
2
−
1
2
2
-
2
-
5
2
2
2
−
1
−1
photodegrade phenol. If only 1 g of boric acid is used in the hydro-
thermal process, the (001)/(101) ratio is only 0.17, which is sig-
g
(144 cm
)
−1
nificantly lower than TiO
So, we conclude that boric acid is favor to fabricate TiO
001)/(101) ratio, resulting to the final TiO product possess excellent
photodegradation activity.
We also use Raman spectra to investigate the impact of annealing
temperature on microstructure of TiO . As shown in Fig. 4c and d, the
characteristic Raman bands of anatase locating at 144 cm
2
-5B-600 (0.204) and TiO
2
-10B-600 (0.206).
analysis, it is found that the intensity ratio of A1g (514 cm ) / E
g
−
1
2
with high
(144 cm ) for TiO
2
-5B-500, TiO
2
-5B-600, TiO
2
-5B-700 and TiO
2
-5B-
(
2
800 are 0.07, 0.11, 0.06, and 0.06, respectively, illustrating that TiO
2
-
5B-600 possess more photocatalytic active sites. In comparison, the
−1
−1
intensity ratio of A1g (514 cm ) / E
only 0.07, which is lower than the corresponding values of TiO
and TiO -10B-600. (0.11 and 0.09 respectively) further indicating boric
g
(144 cm ) for TiO
2
-1B-600 is
2
2
-5B-600
−
1
(Eg),
(B1 g)
2
−1
−1
−1
−1
197 cm
(Eg), 399 cm
(B1 g), 513 cm
(A1 g), 519 cm
2
acid is make for active TiO photocatalyst. This result is in accordance
−
1
and 639 cm (Eg) can be observed for all samples [35,36]. For TiO
2
-
with the XRD analysis.
5
B-800, even though the rutile crystal phase was observed in XRD, no
Nitrogen adsorption-desorption experiments point out that all the
samples are mesoporous properties (Fig. 5a). As the calcination tem-
perature increases, the BET specific surface area and pore diameter
gradually decrease (Fig. 5b). Large surface area and mesoporous
structure make the sample own more active sites and can easily interact
rutile signal was detected in the Raman spectrum because the amount
of the rutile crystal phase was very small. It has been established that
the full width at half maximum (FWHM) and frequency of Raman peaks
2 2 2
of TiO are related to crystallite size of TiO . If the particle size of TiO
6

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
2 2 2 2
Fig. 6. a) XPS full spectra of TiO -5B-y samples; b) XPS full spectra of TiO -xB-600 samples; c) XPS Ti2p spectra of TiO -xB-y samples; d) XPS O1s spectra of TiO -xB-
y samples.
2 2
Fig. 7. a) Photocatalytic performance of TiO -5B-y in hydrogen evolution; b) Photocatalytic performance of TiO -xB-500 in hydrogen evolution.
with substrates so that TiO
catalytic performance.
2
-5B-500 may exhibit excellent photo-
The UV–vis diffuse reflection shows that as the calcination tem-
perature increases (from 500 to 800), the optical band gap of the
sample gradually decreases (3.08-2.96) so that the absorption wave-
length shifts to the visible region. However, the photocatalytic activity
of TiO
there is also no obvious relationship between the dosage of boric acid
with band gap for these TiO -xB-y samples, which is same to the pre-
2
-5B-y is not correlated to the change of band gap. In addition,
2
vious reports that boron dopant cannot impact the band. These results
illustrate that the photodegradation of organic contaminants is not
sensitive to visible light but ultraviolet light. The key factor for the
photocatalytic degradation of organic contaminants is crystallite size
and surface area.
Although a large amount of boric acid is used during the synthesis of
TiO -xB-y samples, boron element is not detected according to XPS
2
analysis, suggesting boron atom is not doped into the samples. So, we
conclude that the boric acid just impacts the crystallite size and crys-
tallinity so that promote the photocatalytic activity in the photo-
gradation of organic contaminants. The XPS Ti2p spectra and O1s
spectra point out the existence of Ti(IV), illustrating the generation of
Fig. 8. Photocatalytic hydrogen evolution properties of TiO
different sacrificial agents.
2
-10B-500 with
7

K. Xie, et al.
Molecular Catalysis 479 (2019) 110614
TiO
2
during the synthesis. (Fig. 6). Although there are slight shifts in
performance of TiO
2
samples because higher annealing temperature
Ti2p spectra and O1s spectra between different samples, there is not
obvious correlation between the photocatalytic activities and the shift
of bonding energy. So, we attribute the slight shift of bonding energy to
obviously influences the surface area of sample Moderate annealing
temperature and dosage of boric acid contribute to the anatase owning
more active sites for photocatalysis.
the measurement error for different samples. We also use NH
experiment to determine the surface acidity of as prepared TiO
3
-TPD
sam-
2
Acknowledgments
ples and hope to find out the relationship between the catalytic per-
formance and surface acidity. Unfortunately, the experiment results
We thank for the financial support of the following funders:
National Natural Science Foundation of China (No. 21773053), Natural
Science Foundation of Hebei Province (No. B2017201084), the Hebei
provincial Technology Foundation for High-Level Talents (No.
CL201601), the One Hundred Talent Project of Hebei Province (No.
E2016100015), Advanced Talents Incubation Program of Hebei
University (No. 801260201019).
indicate that there is almost no difference between TiO
ples and the surface acid sites on these catalysts are negligible (Fig. S3).
So, we conclude that the surface acid of as-prepared TiO do not affect
2
-xB-600 sam-
2
the photocatalytic performance in the photodegradation of organic
contaminants. This result further illustrates that boron element is not
doped into TiO
preparation of TiO
acidity of final products.
2
-xB-600 samples and the dosage of boric acid during the
2
-xB-600 samples do not determine the surface
Appendix A. Supplementary data
Photocatalytic H
2
evolution
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.110614.
We also evaluate the photocatalytic activity of TiO
2
catalysts for
photocatalytic hydrogen evolution (Fig. 7). Firstly, commercial P25
almost has no photocatalytic activity for the hydrogenation evolution,
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