Mesoporous ZnO microcube derived from a metal-organic framework as photocatalyst for the degradation of organic dyes

Article abstract of DOI:10.1016/j.jssc.2017.09.002

A cube-like porous ZnO architecture was synthesized by direct two-step thermolysis of a zinc-based metal-organic framework [(CH₃)₂NH₂][Zn(HCOO)₃]. The obtained ZnO microcube was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption and desorption isotherms. The mesoporous ZnO microcube was comprised by many nanoparticles, and inherited the cube shape from [(CH₃)₂NH₂][Zn(HCOO)₃] precursor. With large surface area and mesoporous structure, the ZnO microcube exhibits excellent photocatalytic activities against methyl orange (MO) and rhodamine B (RhB) under UV irradiation, and the degradation rates reached 99.7% and 98.1% within 120 min, respectively.

Full text of DOI:10.1016/j.jssc.2017.09.002

Author’s Accepted Manuscript
Mesoporous ZnO microcube derived from a metal-
organic framework as photocatalyst for the
degradation of organic dyes
Jin-jin Ban, Guan-cheng Xu, Li Zhang, He Lin,
Zhi-peng Sun, Yan Lv, Dian-zeng Jia
www.elsevier.com/locate/yjssc
PII:
S0022-4596(17)30359-6
http://dx.doi.org/10.1016/j.jssc.2017.09.002
YJSSC19931
DOI:
Reference:
To appear in:
Journal of Solid State Chemistry
Received date: 4 August 2017
Revised date: 28 August 2017
Accepted date: 3 September 2017
Cite this article as: Jin-jin Ban, Guan-cheng Xu, Li Zhang, He Lin, Zhi-peng Sun,
Yan Lv and Dian-zeng Jia, Mesoporous ZnO microcube derived from a metal-
organic framework as photocatalyst for the degradation of organic dyes, Journal
of Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2017.09.002
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Mesoporous ZnO microcube derived from a metal-organic
framework as photocatalyst for the degradation of organic dyes
Jin-jin Ban, Guan-cheng Xu*, Li Zhang, He Lin, Zhi-peng Sun, Yan
Lv, Dian-zeng Jia*
Key Laboratory of Energy Materials Chemistry, Ministry of Education; Key
Laboratory of Advanced Functional Materials, Autonomous Region; Institute of
Applied Chemistry, Xinjiang University, Urumqi, 830046 Xinjiang, P. R. China.
* Corresponding author. E-mail: xuguanchengxju@163.com
Abstract
A cube-like porous ZnO architecture was synthesized by direct two-step thermolysis
of a zinc-based metal-organic framework [(CH3)2NH2][Zn(HCOO)3]. The obtained
ZnO microcube was characterized by powder X-ray diffraction, scanning electron
microscopy, transmission electron microscopy and nitrogen adsorption and desorption
isotherms. The mesoporous ZnO microcube was comprised by many nanoparticles,
and inherited the cube shape from [(CH3)2NH2][Zn(HCOO)3] precursor. With large
surface area and mesoporous structure, the ZnO microcube exhibits excellent
photocatalytic activities against methyl orange (MO) and rhodamine B (RhB) under
UV irradiation, and the degradation rates reached 99.7% and 98.1% within 120 min,
respectively.

Graphical Abstract
Mesoporous ZnO microcube was synthesized via two-step thermolysis of
metal-organic framework [(CH3)2NH2][Zn(HCOO)3], and exhibit excellent
photocatalytic activity towards MO and RhB.
Keyword:
Mesoporous ZnO microcube, Metal-organic framework, Photocatalyst, Organic dye
degradation
1. Introduction
Metal-organic frameworks (MOFs) are rapidly growing materials made up of
metals or metal clusters and organic bridging ligands [1]. By combining organic and
inorganic building blocks [2], MOFs have shown many attractive characteristics, such
as high surface area, large pore volume and good thermal stability [3]. These special

properties have allowed MOFs to be applied in gas adsorption and storage [4],
catalysis [5], drug delivery [6], and sensing [7]. MOFs have recently been found to be
easily transformed into metal oxides [8], carbon materials [9] or carbon composite
materials [10] through simple calcination under different atmospheres and conditions.
Compared to other precursors [11], MOFs not only offer adjustable structure and size
but also have stable framework and porosity [12]. MOFs have been used as templates
to prepare different metal oxides [13]. Spindle-like MIL-88-Fe can be completely
transformed to mesoporous α-Fe2O3 with the retained morphology by the two-step
calcination [14]. The electrochemical performance of as-prepared α-Fe2O3 can be
improved significantly due to interconnected nanometer-sized subunits. By heat
treatment under mild conditions, porous CuO/Cu2O composites have been
successfully prepared from Cu-BTC MOFs (BTC: 1,3,5-benzenetricarboxylic acid).
The morphologies and sizes of Cu-BTC MOFs can be adjusted at controlled
temperatures for different times. The porous CuO/Cu2O materials inherit the different
shapes of Cu-BTC MOFs including cube, octahedron, rod and wire, and show
excellent CO oxidation performance [15,16]. Therefore, MOFs with controlled
features and porous structures are ideal candidates for precursors in solid state
calcination to obtain different metal oxides with novel structures and properties [17].
Among new series of MOFs, [AmineH][M(HCOO)3] with perovskite-like
structures templated by protonated amines have been synthesized recently [18].
Formate anion, HCOOˉ, is a suitable choice as a linker of MOFs, and it is the simplest
carboxylate with the fundamental properties of carboxylate [19]. AmineH+ cations are
located in the channel/cages of the 3D anionic [M(HCOO)3ˉ] frameworks [20]. The
crystal structures and morphologies of [AmineH][M(HCOO)3] can be modulated by
employing different ammonium cations [21]. Among them,
－
[(CH3)2NH2][Zn(HCOO)3] is crystallized in the space group R3c. The Zn2+ is
octahedrally coordinated by six bridging formate ligands in an anti-anti mode, and the
+
trigonal disordered (CH3)2NH2 cations are located in the 1D channel of the 3D

[Zn(HCOO)3ˉ] framework (Fig. S1) [22]. [(CH3)2NH2][Zn(HCOO)3] can be converted
into metal oxide through simple thermal treatment in air, and a porous structure can
be readily obtained due to the release of internally generated gas during calcination
[23].
On the other hand, ZnO is an environmental friendly oxide semiconductor with a
direct wide band gap (3.37 eV) and a high exciton-binding energy of 60 meV [24].
ZnO can function as a photocatalyst to degrade organic pollutants in water under UV
irradiation [25]. For photocatalytic degradation [26], MOF-derived ZnO shows
excellent activity during catalysis due to favorable surface area [27] and large pore
volume [28]. Recently, Li et al. have synthesized Zn-CPs (Zn-based coordination
polymers) via a convenient one-pot method, which could be converted into ZnO with
the retention of original morphology by simple thermal treatment [29]. The obtained
ZnO exhibits excellent activity in the photocatalysis under open air condition owing
to its large surface area and mesoporous structure. The ZnO sample can degrade
rhodamine B (RhB) completely in 2 h [30]. In a word, pyrolyzing the MOFs are
desirable alternatives for the porous zinc oxides to boost the photocatalysis processes.
Motivated by all these developments and to further contribute to the preparation
of metal oxides with novel structures and properties, we herein successfully
synthesized mesoporous ZnO microcube through two-step heat treatment of Zn-based
MOF [(CH3)2NH2][Zn(HCOO)3]. The obtained ZnO microcube, which was composed
of numerous nanoparticles, managed to photocatalytically degrade organic dyes
(methyl orange, MO and rhodamine B, RhB) effectively under UV light irradiation.
After irradiation for 120 min, the degradation rates of MO and RhB reached 99.7%
and 98.1% respectively.
2. Experimental
2.1. Materials

Zinc nitrate hexahydrate (Zn(NO3)2∙6H2O), 40% aqueous dimethylamine solution
and formic acid (HCOOH) were purchased from Tianjing Fuchen chemical reagents
factory, polyvinylpyrrolidone K30 (PVP K30) was purchased from Tokyo Chemical
Industry Co., Ltd., ethanol (C2H5OH), edetate disodium (EDTA-2Na), benzoquinone
(BQ) and tert-Butyl alcohol (t-BuOH), MO and RhB were commercially available and
used as purchased without further purification.
2.2. Characterization
Powder X-ray diffraction (XRD) patterns were collected on a Bruker D8 advance
diffractometer with Cu-Kα radiation (λ = 1.54178 Ǻ) in the range of 10-80° at a scan
rate of 2°∙min-1. Morphological features were studied by field emission scanning
electron microscopy (FESEM, Hitachi S-4800 microscope). Internal structures of the
samples were observed by transmission electron microscopy (TEM, Hitachi H600
microscope) at an accelerating voltage of 200 kV. Thermogravimetric analysis (TGA)
was performed on a Netzsch SDT 449F3 thermal analyzer with a heating rate of 10
°C∙min-1. Nitrogen adsorption and desorption isotherms were obtained at the liquid
nitrogen temperature (77 K) using a Quantachrome (ASIQ) instrument. The specific
surface area and porous structural features of the samples were calculated by the
Brunauer-Emmett-Teller (BET) method and the Barrett-Joyner-Halenda (BJH)
method, respectively. Photocatalytic performances were investigated by a Model
XPA-7 photocatalytic reactor (Xujiang Electromechanical Plant, Nanjing, China).
UV-vis diffuse reflectance spectrum was recorded on a Hitachi 3900H
spectrophotometer. UV-vis absorption spectroscopy of clarified solution was
performed (UV Hitachi 3900H spectrophotometer) at room temperature at the
wavelength from 200 to 700 nm.
2.3. Preparation of [(CH3)2NH2][Zn(HCOO)3] and ZnO
An ethanol solution (25 mL) of HCOOH (8 mmol), PVP K30 (0.5 g) and
dimethylamine (8 mmol) was added to another ethanol solution of Zn(NO3)2∙6H2O (1

mmol) and PVP K30 (0.5 g) under vigorous stirring. Precipitate formed from the
transparent solution after 10 s, and the suspension was stirred for 1 h and incubated
for 4 h at room temperature. Tiny white block crystals were collected by
centrifugation and washed with ethanol three times. [(CH3)2NH2][Zn(HCOO)3]
precursor was obtained by drying in a vacuum oven at 60 °C for 4 h.
The precursor [(CH3)2NH2][Zn(HCOO)3] was transferred into a ceramic boat and
pyrolyzed by a two-step process in a temperature-programmed furnace as follows.
[(CH3)2NH2][Zn(HCOO)3] was heated to 125 °C at a ramp of 1 °C∙min-1 in air and
kept for 60 min. Then the intermediate was heated up to 225 °C with the same rate
and maintained for 60 min, giving mesoporous ZnO microcube.
2.4. Photocatalytic Experiments
A certain amount of ZnO sample (18 mg) was dispersed into 50 mL aqueous
solution of MO (50 mL, 10 mg·L-1) and RhB (50 mL, 10 mg·L-1) respectively. Before
UV irradiation, the suspensions were magnetically stirred in dark for 60 min to reach
adsorption-desorption equilibrium. Then, the suspension was exposed to a 300 W UV
light source. A small amount of solution (4 mL each) was collected at regular interval
of time (20 min), and centrifuged at 10000 rpm to separate the porous ZnO catalyst.
The clarified solution was measured with UV-vis absorption spectroscopy at the
wavelength from 200 nm to 700 nm.
3. Results and discussion
3.1. Preparation and characterization of [(CH3)2NH2][Zn(HCOO)3]
[(CH3)2NH2][Zn(HCOO)3] was prepared by a facile solution-precipitation
method. The XRD pattern of [(CH3)2NH2][Zn(HCOO)3] is shown in Fig. S2a. The
simulated XRD pattern was obtained from single-crystal structure using the program
Mercury. Clearly, all the diffraction peaks of the formed [(CH3)2NH2][Zn(HCOO)3]
match well with those of the simulated pattern in the 2θ range of 10-50°.

To check the thermal stability of the precursor, simultaneous TGA-DTA curves
were plotted (Fig. S2b). TGA shows that the first weight loss starts at 120 °C and
ends at 200 °C with the mass loss of 37.4%, and one endotherm peak is also observed
in the DTA trace. It corresponds to the departure of a dimethylammonium cation and
formate anion per chemical formula unit, and the observed mass loss is in good
agreement with the calculated value (calcd. 37.2%). By heating, the second stage
occurs in the temperature range of 230 °C - 300 °C, corresponding to the
decomposition of formate ligands, and the observed mass loss (30.3%) is consistent
with the theoretical value (30.7%). The final residue, estimated as ZnO, has the
observed mass of 32.3%, being in good agreement with the calculated value (32.1%).
In short, ZnO was obtained by pyrolyzing the [(CH3)2NH2][Zn(HCOO)3] precursor.
Furthermore, the typical size and morphology of the as-synthesized
[(CH3)2NH2][Zn(HCOO)3] were observed by FESEM. As shown in Fig. 1a, the
precursor has a double-edge solid cube morphology, with a highly uniform size of ca.
4 µm. As evidenced the corresponding magnified sample in Fig. 1b, the microcubes
have smooth surfaces.
3.2. Structural and morphology characterization of ZnO microcube
ZnO microcube was obtained by calcining the [(CH3)2NH2][Zn(HCOO)3]
precursor in air with a two-step temperature program (Scheme 1). The
crystallographic structure and phase purity of the calcined product ZnO were analyzed
by XRD (Fig. 2a). The as-synthesized porous ZnO corresponds well to the
hexahedron wurtzite structure of pure ZnO (PDF#36-1451), without any impurity
phases like Zn or Zn(OH)2. The typical morphology of microcube is shown in Fig. 1e
and 1f. Obviously, ZnO inherits the cube-shape of the [(CH3)2NH2][Zn(HCOO)3]
precursor. In comparison to the precursor, the ZnO cube constructions are little shrunk
and the sizes of the cubes are ca. 3.5 μm. Interestingly, the ZnO microcube comprises
numerous tiny particles with an average diameter of ca. 100 nm. As presented in inset
of Fig. 1f, ZnO is a visible porous structure inside but not a solid box. During the

transformation from [(CH3)2NH2][Zn(HCOO)3] to ZnO upon thermal decomposition,
the cube shape remains basically unchanged, except the double edges disappear (Fig.
1f).
In this study, uniform ZnO microcubes were obtained by pyrolyzing MOF
precursor in air by a two-step process. [(CH3)2NH2][Zn(HCOO)3] was firstly
pyrolyzed at 125 °C for 60 min. The second step was to further raise the temperature
up to 225 °C that was kept for 60 min. In order to verify this pyrolysis process, the
morphology of intermediate was observed (Fig. 1c and 1d). The intermediate has
similar size and double-edge shape to those of the precursor. According to TGA, the
intermediate is Zn(HCOO)2. There are many holes on the surface of the intermediate
(Fig. 1d) owing to partial removal of dimethylammonium cation and formate anion.
By heating, the residual formate ligands were removed and porous ZnO microcube
was produced. In order to explore the calcining condition, we tried to synthesize the
ZnO microcube with a one-step pyrolyzation, and [(CH3)2NH2][Zn(HCOO)3] was
directly pyrolyzed at 225 °C for 60 min. Aggregated ZnO particles were obtained
instead of well-defined mesoporous ZnO microcubes (Fig. S3), which may be caused
by the quick release of the gas. Therefore, the two-step pyrolysis was favorable to
keep the cubic shape and form the porous structure.
In order to characterize the porous structure, we analyzed the nitrogen
adsorption-desorption isotherms and BJH pore size distribution (Fig. 2b). The
obtained ZnO microcube displays a typical IV-type adsorption isotherm with a
distinct hysteresis loop in the range of ca. 0.4-1.0 P/P0. The pore size distribution
(inset of Fig. 2b) reveals the presence of mesoporous structure. As suggested by
several sharp peaks at about 2.2 nm, 3.5 nm and 5.7 nm, the pore sizes of ZnO
microcube are not uniform due to the arrangement of solid ZnO particles. The BET
surface area is 19.82 m2∙g−1. Collectively, the ZnO microcube has a developed porous
structure containing interconnected mesopores.
3.3. Photocatalytic performace

ZnO is a well-known effective semiconductor photocatalyst used frequently to
solve environmental pollution. In this study, the UV-vis diffuse reflectance spectrum
of ZnO microcube was recorded by UV-vis spectrophotometer in the range from 250
to 800 nm (Fig. 3). It can be clearly seen that the basal absorption of the ZnO
microcube occurs near wavelength of 400 nm. The band gap energies (Eg) can be
estimated by Kubelka-Munk transformation. The Eg of ZnO microcube is calculated
to be 3.2, and the ZnO microcube exhibits absorption in the UV region (insets of Fig.
3). MO and RhB were often chosen as the typical organic dyes to examine the
photocatalytic activities of photocatalysts. The photocatalytic performance of the
mesoporous ZnO microcube was evaluated by MO and RhB, respectively.
To reach adsorption-desorption equilibrium, the dye suspensions including ZnO
catalyst were stirred in dark for 60 min. The adsorption capacity of ZnO toward RhB
is slightly higher than that of MO (Fig. 4), and it also gives the absorption spectra of
RhB and MO solutions with increasing degradation time using ZnO as the catalyst.
Initially, MO and RhB show maximum absorption intensities at about 545 nm and
460 nm, respectively. With increasing UV irradiation time, the absorption intensities
of dyes decrease remarkably, indicating reduction in their concentrations. The colors
of the dyes also become lighter (insets of Fig. 4a, b). During the whole reaction
process, no other peaks appear in the absorption spectra, suggesting that the dyes had
been completely degraded in the presence of ZnO photocatalyst. The UV-visible
spectra shown in Figure 4b reveal a progressive hypsochromic shift of the main
absorption which can be attributed the removal one by one of the ethyl group [31].
Obviously, the concentrations of the two dye solutions decrease gradually. Fig. 5a
shows the calibration curves for the degradation rates of two dyes with or without
porous ZnO photocatalyst under UV irradiation within 120 min. The photocatalytic
degradation percentage of MO/RhB was calculated by the following equation: Deg%
= (A0-A)/A0×100%, where A0 and A are the absorbances of MO/RhB at time 0 and
time t, respectively. The MO degradation percentage for ZnO reached 99.7% in 120

min under UV irradiation, and that of RhB also approached 98.1% after the same
irradiation time. For comparison, the degradation rates of two dyes under UV light
irradiation without photocatalyst were also tested (Fig. 5a). Without ZnO
photocatalyst, the dyes hardly degraded under UV light irradiation. Only RhB
underwent mild self-degradation. We chose commercial ZnO as bare ZnO to compare
the photocatalytic performance of the mesoporous ZnO microcube. At the same
conditions, the photocatalytic degradation percentage of bare ZnO is more lower than
mesoporous ZnO microcube (Fig. 5a). The MO degradation rate for bare ZnO was
76.2% in 120 min under UV irradiation, and that of RhB approached 80.5% after the
same irradiation time. At the same time, the photocatalytic activity of the mesoporous
ZnO microcube was also compared to various ZnO samples in the other literature. All
the comparative data are sorted in Table S1. With the equivalent conditions, the
mesoporous ZnO microcube has an upper level for photocatalytic performance under
UV to degrade MO and RhB.
Moreover, the dynamic photocatalytic degradation of organic dye can be
described using the Langmuir-Hinshelwood mechanism, lnC0/Ct = kt (Fig. 5b). The
determined slopes provide quantitative estimation for the photocatalytic activity of the
sample. The photodegradation rate of the dyes follows the pseudo first-order kinetics,
and the determined reaction constant k of MO is much higher than that of RhB (inset
of Fig. 5b).
The photocatalytic stability is also key for the applications of a photocatalytic
material. The recycled performance of ZnO microcube is also evaluated in Fig. 6, and
the irradiation time for each test was 120 min. The photocatalytic efficiency of ZnO
microcube just decrease a little for two dyes (1% for MO, 3% for RhB) after three
recycles, which caused by the mass reduction of the catalyst during the recovery
process. Therefore, ZnO microcube exhibits excellent photocatalytic performance and
stability for the catalytic reduction of MO and RhB.

As mentioned above, the high photocatalytic activity of ZnO can mainly be
attributed to the structure of the mesoporous ZnO microcube. In fact, the
photocatalysis includes two steps. The first step is absorption during which dye
molecules are absorbed on the surface of the ZnO. Secondly, the electron-hole (e− -
h+) pairs inside the ZnO matrix degrade the dye molecules to CO2 or H2O. The higher
adsorption capacity is in accordance with the higher photocatalytic activity of
photocatalyst samples. The larger surface area of ZnO facilitates photocatalytic
reaction, and the special structure of ZnO matrix provides more surface active sites
for the photocatalytic reaction. Meanwhile, the efficiency of electron-hole separation
is improved. The separation of electrons (e−) from holes (h+) prevents charge
recombination, thereby augmenting the photocatalytic activity of ZnO. Taken
together, the geometric configurations of the mesoporous ZnO microcube from MOFs
may contribute to the outstanding photocatalytic performance.
The active species were also investigated to discuss the photocatalytic mechanism
-
under two organic dyes in Fig. 7. The holes (h+), superoxide radical anion (∙O2 ) and
hydroxyl radicals (∙OH) are the probable active species taking part in organic dyes
photodegradation. In this study, the edetate disodium (EDTA-2Na), benzoquinone
-
(BQ) and tert-Butyl alcohol (t-BuOH) are often adopted as the traps for h+, ∙O2 and
∙OH in photodegradation reaction, respectively. It is clearly seen the maximum
photocatalytic degradation were took place without any scavenger (Fig. 7). As the
addition of the scavengers, the photocatalytic reaction was seriously suppressed in
-
two dyes. Moreover, h+ and ∙O2 are the main active species in the photodegradation
process because the photodegradation efficiencies of two dyes decrease more quickly
when EDTA-2Na and BQ are individually added.
The photocatalytic mechanisms could be explained as follow: When the
photocatalyst is irradiated under UV light, photogenerated electrons (e−) in the
valence band of ZnO are excited to the conduction band, leaving holes (h+) (Fig. 8).
The activated electron (e−) migrates to the surface, and catches oxygen to produce

-
peroxide radicals (∙O2 ). The remaining hole reacts with water (H2O) or hydroxyl ions
(OH-) to produce active species, such as hydroxyl radicals (∙OH). With the strong
-
oxidation of OH∙ and ∙O2 , organic dye can mostly be oxidized to the final products
carbon dioxide (CO2) and water (H2O).
The possible reactions for organic dye degradation are listed in Eqs:
ZnO + hυ →e- +h+
-
e- +O2 → ∙O2
h+ + H2O → OH∙
-
∙O2 + OH∙ + dye → H2O
4. Conclusion
In summary, cube-shaped mesoporous ZnO was successfully synthesized by
thermolysis of [(CH3)2NH2][Zn(HCOO)3] precursor with a two-step process at
moderate temperature. Composed of many nanoparticles, the ZnO microcube has a
porous structure. The ZnO microcube exhibits excellent photocatalytic performance
for the catalytic reduction of MO and RhB, with the degradation rates reaching 99.7%
and 98.1% respectively within 120 min under UV light. The porous ZnO microcube
efficiently photocatalyzed the degradation of the two dyes. We rationalized that the
unique porous structure of ZnO microcube played an important role in the satisfactory
photocatalytic performance. This study may provide a promising way for fabricating
porous ZnO for photocatalysis, which may also be applicable to the preparation of
other transition metal oxides.

Acknowledgements
This work was financially supported by National Natural Science Foundation of
China (Nos., 21471127, 21361025, 21661029, 21663029), Natural Science Fund for
Distinguished Young Scholars of Xinjiang Uygur Autonomous Region (No.
2013711008).
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Scheme 1. Schematic illustration for the synthesis of mesoporous ZnO microcube.
Fig. 1 SEM images of [(CH3)2NH2][Zn(HCOO)3] precursor (a, b), intermediate (c, d)
and ZnO microcube (e, f). TEM images of ZnO microcube (insets of e, f).
Fig. 2 XRD pattern of ZnO microcube (a); N2 adsorption-desorption isotherms of
ZnO microcube; inset: pore size distribution (b).
Fig. 3 UV-vis diffuse reflectance spectrum of ZnO microcube (inset shows the energy
band gap).
Fig. 4 Variation of the absorption spectra for MO (a) and RhB (b) in the presence of
mesoporous ZnO microcubes under UV irradiation at different time intervals.
Fig. 5 Photocatalytic degradations of MO and RhB with mesoporous ZnO microcube
and bare ZnO catalysts under UV irradiation (a); Fitting of kinetic data using the first
order model (b).
Fig. 6 The reuse activity of mesoporous ZnO microcube for photodegradation of MO
and RhB.
Fig. 7 Effect of scavengers on the photodegradation of MO (a) and RhB (b) with the
mesoporous ZnO microcube catalysts.
Fig. 8 Scheme for the photocatalysis using ZnO microcube catalyst under UV
irradiation. CB: conduction band; VB: valence band.

Scheme 1.
Fig. 1

Fig. 2
Fig. 3

Fig. 4
Fig. 5

Fig. 6
Fig. 7

Fig. 8
Highlights:
1 Cubic MOF [(CH3)2NH2][Zn(HCOO)3] was prepared by
solution-precipitation method.
2 Mesoporous ZnO microcube was obtained by a two-step calcination of
MOF precursor.
3 ZnO microcube shows photocatalytic activity to MO and RhB under
UV irradiation.
-
4 The h+ and ∙O2 are main active species during the photodegradation
process.