C. Wang et al. / Journal of Alloys and Compounds 748 (2018) 314e322
315
charges [19]. On the other hand, the metal organic frameworks
(MOFs) material has been widely used in the photocatalytic process
because of its high specific surface area, adjustable aperture and
good stability [20e22]. In particular, UiO-66, a Zr-based MOF has
been extensively used for photocatalysis. UiO-66 not only exhibits
high structural stability [23], but maintains such stability after the
modification of active functional groups or the introduction of
missing joint defects [24]. These properties make UiO-66 a partic-
ularly prospective candidate for photocatalytic applications in
water treatment. This creates a motivation to exploit UiO-66 based
photocatalysts for water treatment. Hence, the UiO-66 with high
specific surface area was selected as the support to control the
growth of AgI.
In this article, AgI nanoparticles were grown in situ on the UiO-
66 framework. The phase structures, morphologies and optical
properties of the prepared catalysts were detected. Moreover, the
effects of water environmental factors (pH value, inorganic salt
ions, common anions and water matrix) on the degradation of SMZ
were discussed. In addition, the photocatalytic mechanism of SMZ
was also investigated, including active substances, oxidation
products and degradation pathways.
50ꢂ. The morphology features of as-prepared samples were
observed by transmission electron microscopy (TEM, FEI, TECNAI
G20). The optical properties of the samples were researched using
UVeVis diffuse reflectance spectroscopy (Shimadzu, UV3600).
2.4. Photocatalytic experiments
2.4.1. Photocatalytic degradation of SMZ
In this experiment, 25 mg of the as-prepared sample was added
to 50 mL of 5 mg/L SMZ aqueous solution and kept in dark condi-
tions for 1 h to achieve adsorption equilibrium. Then the mixture
solution was irradiated by a 300 W Xe lamp (Beijing Zhongjiaoji-
nyuan, CEL-HXF300) with a 400 nm cut-off glass filter. After the
start of the illumination, 1.5 mL of the solution was taken at regular
intervals and filtered with a 0.22 mm syringe filter to remove the
suspended solid particle before the detection of the concentration
of SMZ. The blank experiment of SMZ photolysis was the same as
above procedure except that no catalyst was added. The environ-
mental factor experiment was carried out by the similar procedure.
2.4.2. Trapping experiments of active species
The trapping experiments were carried out under the same
reaction conditions except that the capture agent was added into
2. Materials and methods
ꢁ
the photocatalytic reaction solution. The active species were OH,
2.1. Reagent
ꢁOꢀ2 and hþ which were captured by tert-butanol (5 mmol/L), p-
benzoquinone (1 mmol/L) and EDTA-2Na (5 mmol/L) respectively.
Zirconium tetrachloride, terephthalic acid, N, N-dimethyl
formamide, methanol, potassium iodide, argentum nitricum, hy-
drochloric acid (HCl), sodium hydroxide (NaOH), sodium chloride,
sodium sulfate, sodium bicarbonate, ferric chloride, calcium chlo-
ride, magnesium chloride and potassium chloride were purchased
from Sinopharm (China). SMZ was purchased from Aladdin
(America). Pure water was acquired from a purification system
(Millipore Milli-Q, USA). Acetonitrile and formic acid were supplied
by Tedia (America), and they were chromatographic pure reagents.
Other reagents were all analytical reagents.
2.5. Analysis methods
The concentration of SMZ was detected by high performance
liquid chromatography (HPLC, Waters e2695) with a UV detector at
270 nm. The chromatographic column was reversed phase C18
column (4.6 mm ꢃ 150 mm, 5
acetonitrile and 70% water (pH ¼ 3) adjusted with phosphoric acid
at a flow rate of 1 mL/min. The injection volume was 10 L and the
mm). The mobile phase was 30%
m
column temperature was maintained at room temperature during
injection analysis.
2.2. Preparation of material
The intermediates produced during the degradation of SMZ
were identified via liquid chromatography-triple quadrupole mass
spectrometry (LC-MS, Agilent, 6460 Triple Quad LC/MS series) with
2.2.1. Preparation of UiO-66
UiO-66 was synthesized by modified solvothermal method [25].
Zirconium tetrachloride (2.0 mmol) and terephthalic acid
(2.0 mmol) were successively dissolved in N, N-dimethyl form-
amide (100 mL) and the solution was transferred into a 200 mL of
stainless steel autoclave. The autoclave was sealed and heated in a
120 ꢂC oven for 24 h. After natural cooling, the precipitate was
centrifuged and immersed in methanol for three days. Methanol
was changed every 24 h. Finally, the white products were dried
under vacuum at 60 ꢂC.
a C18 column (2.1 mm ꢃ 50 mm, 1.8
conditions of the HPLC were shown as follows: the flow rate was
0.2 mL/min and the column temperature was 25 ꢂC with 5
L of the
mm). The chromatographic
m
injection volume. The mobile phase was aqueous solution A con-
taining 0.1% formic acid and acetonitrile B containing 0.1% formic
acid. The gradient elution program was presented as follows:
0e3 min, 10%e20% B, 3e8 min, 20%e35% B, 8e15 min, 35%e60% B,
then equilibrated for 6 min. An electrospray ionization source API-
ES was used for MS/MS measurements in the positive ion mode and
full spectrum scanning. The other parameters were set as follows:
the capillary voltage was 3000 V. The atomization pressure and the
drying gas temperature were 30 psi and 300 ꢂC, respectively, and
the flow rate of dry gas was 10 L/min.
2.2.2. Preparation of AgI/UiO-66
Potassium iodide (153 mg) was dissolved in 45.5 mL of pure
water. Then, UiO-66 (250 mg, structural formula noted as
Zr24O120C192H96 [26]) was added into the above solution under
vigorous stirring. After stirring for 1 h, 4.61 mL of 0.2 M AgNO3
aqueous solution was added into the above mixture solution and
kept stirring at room temperature for 12 h. Next, the products were
collected by centrifugation and washed thoroughly with pure water
for several times. Ultimately, the obtained samples were dried
under vacuum at 60 ꢂC.
3. Results and discussion
3.1. Characterization
In order to more clearly observe the appearance of the sample,
we conducted TEM and HRTEM characterization. It can be seen from
Fig. 1(a) that UiO-66 is a regular cube structure. In Fig. 1(b) and (c),
several nanometers to dozens of nanometers of small particles
adhere to the surface of UiO-66 and grow around UiO-66. In addi-
tion, Fig. 1(d) showed that 0.210 nm and 0.225 nm lattice edge
spacing correspond to 103 and 110 lattice planes of AgI nanocrystals.
2.3. Characterization
The X-ray diffraction patterns of the samples were analyzed by
Rigaku's SmartLab diffractometer in the range of 2q
between 5ꢂ and
Wang, Chao
