Highly efficient and heterogeneous OMS-2 for the directly oxidative degradation of organic dyes under acidic condition

Article abstract of DOI:10.1016/j.inoche.2020.107969

Manganese oxide octahedral molecular sieves (OMS-2) are important environmental oxidants and catalysts in sewage treatment; however, most existing work has only focused on its catalytic activity. In this work, we first report the highly efficient and heterogeneous OMS-2 for the directly oxidative degradation of organic dyes (including reactive red 2, reactive blue 19, acid orange 7, rhodamine B and methylene blue), via a non-radicals process, under acidic condition. Then the effects of OMS-2 concentration, pH condition, reaction temperature and initial concentration of organic dye have been investigated for directly oxidative degradation. In addition, OMS-2 has been successfully recycled at least five times for directly oxidative degradation without any obviously decrease in activity. These findings provide general guidance for designing active OMS-2 for cost-effective water and wastewater treatment.

Full text of DOI:10.1016/j.inoche.2020.107969

Inorganic Chemistry Communications 117 (2020) 107969
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short communication
Highly efficient and heterogeneous OMS-2 for the directly oxidative
degradation of organic dyes under acidic condition
a
a
b,⁎
a,⁎
Shuhui Wang , Yu Huang , Xu Meng , Xiang Liu
a
College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, Material Analysis and Testing
Center, China Three Gorges University, Yichang, Hubei 443002, China
b
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of
Sciences, Lanzhou 730000, China
G R A P H I C A L A B S T R A C T
A R T I C L E I N F O
A B S T R A C T
Keywords:
Manganese oxide octahedral molecular sieves (OMS-2) are important environmental oxidants and catalysts in
sewage treatment; however, most existing work has only focused on its catalytic activity. In this work, we first
report the highly efficient and heterogeneous OMS-2 for the directly oxidative degradation of organic dyes
OMS-2
Oxidative degradation
Wastewater treatment
Organic dyes
(
including reactive red 2, reactive blue 19, acid orange 7, rhodamine B and methylene blue), via a non-radicals
process, under acidic condition. Then the effects of OMS-2 concentration, pH condition, reaction temperature
and initial concentration of organic dye have been investigated for directly oxidative degradation. In addition,
OMS-2 has been successfully recycled at least five times for directly oxidative degradation without any obviously
decrease in activity. These findings provide general guidance for designing active OMS-2 for cost-effective water
and wastewater treatment.
Heterogeneous
1
. Introduction
hazardous industrial wastewaters, containing a variety of organic pol-
lutants such as dyes, antibiotics and pesticides, have been produced by
As the development of modern society, the globally fresh water
a large number of plants (including leather, textiles, printing, food,
cosmetics, plastic and pharmaceutics) [2]. Among these organic pol-
lutants, organic dyes have raised considerable attention due to the high
crisis has become increasingly severe due to the indiscriminate dis-
charge of industrial and municipal wastewater [1]. In general,
⁎
Corresponding authors.
E-mail addresses: xumeng@licp.cas.cn (X. Meng), xiang.liu@ctgu.edu.cn (X. Liu).
https://doi.org/10.1016/j.inoche.2020.107969
Received 24 February 2020; Received in revised form 12 May 2020; Accepted 12 May 2020
Available online 15 May 2020
1387-7003/ © 2020 Elsevier B.V. All rights reserved.

S. Wang, et al.
Inorganic Chemistry Communications 117 (2020) 107969
water solubility, toxicity, carcinogenicity and mutagenicity [3]. As a
result, it has become a serious threaten to human health and ecological
environment, even at very low concentration [4]. Therefore, it is an
obligatory step to degrade these polluting organic dyes from the ef-
fluents before their discharge [5]. Accordingly, a range of efficient and
eco-friendly methods and technologies, such as adsorption, oxidation/
reduction, advanced oxidation processes, biological degradation, or
combination of the above methods, have been developed to degrade
these organic dyes into simple compounds and organic acids/groups,
even mineralization to carbon dioxide and water [6].
Over the last couple of decades, heterogeneous catalysts based on
manganese oxide have been considered as the potential materials to
degrade organic dyes and purify water due to its high natural abun-
dance, green, low toxicity, environmental friendliness and clean de-
gradation process [7]. Among them, manganese oxide octahedral mo-
lecular sieves (OMS-2), with a 2 × 2 tunnel structure (constructed from
edge-shared double [MnO ] octahedral chains), have attracted a wide
6
range of interest due to their highly porous structure, various different
pore structures, open tunnels, and mild acid-base stability [8]. OMS-2
has been found applications in battery materials, gas sensing, separa-
tion, energy storage, sewage treatment and catalysis in oxidation, re-
duction, combustion, amination and hydrogenation [9]. Recently,
OMS-2 has gained great attention in sewage treatment. For example, in
2
015, Xu’s group first reported cryptomelane type manganese oxide
OMS-2 for heterogeneous activation of peroxymonosulfate (PMS) in the
degradation of acid orange 7 in aqueous solutions, via sulfate radical-
based advanced oxidation process. They also found that the OMS-2
catalyst is very active for the degradation of methyl orange, rhodamine
B, reactive brilliant blue KN-R, methylene blue and reactive brilliant
bed X-3B, and it has been successfully reused at least 5 times without
any decrease in activity. The XPS and ESR also illuminated that the
highly catalytic efficiency is attributed to the redox pair of Mn(IV)/Mn
Fig. 1. (a) The TEM of OMS-2, (b) The XRD of OMS-2.
(
III) (in OMS-2) in the activation of PMS to sulfate radicals [10]. In
019, Zhang’s group also studied the effects of different types of MnO
α-, β-, γ- and δ-MnO ) on activation of peroxymonosulfate for the
degradation of bisphenol A under acidic conditions [11]. In addition,
they found δ-MnO exhibited the highest catalytic activity in the di-
2
2
at 100 °C for 1d. Then the product is filtered, washed, and dried at
(
2
1
3
20 °C for 8 h. Finally, the dry OMS-2 is calcined in a muffle furnace at
50 °C for 2 h. Then, the black powder, OMS-2, was obtained.
2
rectly oxidative degradation of bisphenol A [12]. In fact, our groups
have long term interest in the synthesis of OMS-2 or modified OMS-2
and their applications in wastewater treatment and catalysis [13].
Hence, in this work, we first report the highly efficient and hetero-
geneous OMS-2 nanorods for the directly oxidative degradation of or-
ganic dyes (including reactive red 2, reactive blue 19, acid orange 7,
rhodamine B and methylene blue), via a non-radicals process, under
acidic condition. We have also investigated the effects of the OMS-2
concentration, organic dye concentration, reaction temperature and pH
condition for the degradation reaction. In addition, OMS-2 catalyst has
been successfully recycled at least five times for reactive red 2 de-
gradation without obviously decrease in activity.
2.3. Characterization
We have characterized all properties of OMS-2 in our previous paper
by Braunauer Emmett Teller analysis, transmission electron micro-
scopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction
(
XRD) [14]. So, we only characterized the re-synthesized OMS-2 by
BET, TEM and XRD in this work, XRD spectra were acquired from a
Rigaku Ultima IV (Rigaku, Japan) of Material Analysis and Testing
Center of China Three Gorges University, using Cu-Kα radiation at
4
0 kV and a 40 mA.
2.4. Oxidative degradation experiments
2
. Material and methods
First, the HCl (2 mol/L) was added into a round-bottom flask con-
2.1. Chemicals
taining RR2 solution (50 mL, 20 mg/L) to adjust the pH (pH = 1) of the
solution. Then, 12.5 mg of OMS-2 was added into this solution. The
3 mL of sample was taken from the reaction solution every minute, and
immediately detected by UV–vis. After the detection, the 3 mL of
sample was taken back to reaction solution immediately. Acid orange 7,
methylene blue, reactive blue 19 and rhodamine B are degradated using
the same method.
All commercial materials were used without further purification,
unless indicated. The deionized water was prepared in the laboratory.
The KMnO
4
, manganese sulfate monohydrate, HNO , reactive red 2,
3
reactive blue 19, acid orange 7, rhodamine B, methylene blue, HCl and
NaOH were purchased from Aladdin Reagent Co., Ltd. (Shanghai,
China, http://www.aladdin-e. com/).
3
. Results and discussion
2.2. The synthesis of OMS-2
3.1. The synthesis of OMS-2
Based on our previous work [14], first, 2.95 g of KMnO in 50 mL of
4
neat water is added into a solution of 15 mL of neat water containing
Based on our previous work [15], OMS-2 catalyst was synthesized
4
.4 g MnSO
4
and 1.5 mL of concentrated HNO
3
. The solution is refluxed
by the reaction of manganese(II) sulfate monohydrate, potassium
2

S. Wang, et al.
Inorganic Chemistry Communications 117 (2020) 107969
Fig. 2. (a) UV–vis spectra of the degradation of RR2. Conditions: 40 mg/L of RR2, 0.25 g/L of OMS-2, pH = 1, 30 °C; (b) Influence of different initial pH condition.
Conditions: 40 mg/L of RR2, 0.25 g/L of OMS-2, 30 °C; (c) Influence of initial RR2 concentration. Conditions: 0.25 g/L of OMS-2, pH = 1, 30 °C; (d) Influence of
OMS-2 concentration on RR2 degradation. Conditions: 40 mg/L of RR2, pH = 1, 30 °C; (e) RR2 degradation at various temperatures. Conditions: 40 mg/L of RR2,
0
.25 g/L of OMS-2, pH = 1; (f) The degradation of AO7, MB, RR2, RB19 and RhB. Conditions: 20 mg/L of organic dyes, 0.25 g/L of OMS-2, pH = 1, 30 °C; C is the
0
initial concentration, and C
t
is the concentration at the time t (min).
permanganate and HNO
3
, followed by filtration, washing, drying and
(4 1 1), (6 0 0), (5 2 1), (0 0 2), (5 4 1) and (3 1 2) lattice planes of OMS-
calcination. First, the surface area, pore volume and pore size of OMS-2
2 (NO. JCPDS 29–1020), respectively (Fig. 1b).
have been examined by nitrogen adsorption/desorption analysis. N
2
sorption isotherms are shown in Fig. S1, We found the surface area,
3.2. Activity of OMS-2 in organic dyes degradation
2
2
pore volume and pore size is 59.1 m /g, 0.14 cm /g and 9.4 nm, re-
spectively. Then, the structure of OMS-2 has been characterized by
TEM. As shown in Fig. 1a, The TEM image exhibits that OMS-2 is
composed of structurally short nanorods, In addition, The XRD shows
these peaks at 12.8°, 18.3°, 28.8°, 37.7°, 41.9°, 50.0°, 56.6°, 60.2°, 65.3°,
The performance of OMS-2 has been studied for the degradation of
reactive red 2 (RR2) under acidic condition (Fig. 2a). The RR2 de-
gradation has been carried out in the presence of 40 mg/L of RR2,
0
.25 g/L of OMS-2 and pH = 1 at 30 °C. At the beginning, there are
6
9.9°, 73.1° are belonged to (1 1 0), (2 0 0), (3 1 0), (2 1 1), (3 0 1),
three main characteristic absorption peaks of 285, 330, and 538 nm in
3

S. Wang, et al.
Inorganic Chemistry Communications 117 (2020) 107969
obviously that the rate of degradation increases gradually with the in-
crement of temperatures.
The activity of the OMS-2 for directly oxidative degradation of other
organic dyes with various chemical structures including the azo acid
orange 7 (AO7), quinone imine methylene blue (MB), the disodium salt
reactive blue 19 (RB19) and the xanthene dye rhodamine B (RhB), has
been tested under acidic conditions. As shown in Fig. 2f, these results
exhibit that all the organic dyes have also been directly oxidative de-
graded efficiently, indicating that OMS-2 is an very efficient material
for sewage treatment.
We also compared the performance activity of OMS-2 with recently
published literature examples. The RR2 degradation reaction conditions
and degradation time are listed in Table S1, it is clear that advanced
oxidation processes is more effective for the RR2 degradation reaction,
via a radical process. Anyway, we first report the highly efficient and
heterogeneous OMS-2 for the directly oxidative degradation of organic
dyes, via a non-radicals process, under acidic condition. It is a totally
different mechanism.
3.3. Recyclability and stability of OMS-2
The reusability and stability of OMS-2 has also been studied for the
directly oxidative degradation of RR2 under acidic conditions. The
OMS-2 is regained by the simple filtration, water-washing and drying
after each reaction. The degradation reaction has been re-initiated by
the addition of a fresh solution of RR2. Then the pH is accurately ad-
justed by adding HCl. Fig. 3a indicates the OMS-2 has been successfully
recycled at least five times for directly oxidative degradation of RR2
th
without any obviously decrease in activity. Then the obtained 5 re-
used OMS-2 has been further tested by using XRD (Fig. 3b). The the
th
structure of 5 reused OMS-2 remains unchanged as the fresh catalyst.
In addition, the K and Mn concentration in the solution, after comple-
tion of oxidative degradation of RR2, is 2.406 ppm and 9.671 ppm upon
by ICP-MS, respectively, confirming that OMS-2 is very recyclable and
stable in the directly oxidative degradation of RR2.
Fig. 3. (a) Degradation of RR2 using the recycled catalyst OMS-2. Conditions:
4
0 mg/L of RR2, 0.25 g/L of OMS-2, pH = 1, 30 °C; (b) XRD of the recycled
4
. Conclusion
catalyst OMS-2.
In summary, the highly efficient and heterogeneous OMS-2 catalyst
the UV/vis spectrum of RR2. The UV-band of 285 and 330 nm are
belonged to two adjacent rings, whereas the visible band of 538 nm is
characteristic of the long conjugated π system that is linked by two azo
groups [16]. It can been seen in Fig. 2a, the peaks at 285 nm and
for the directly oxidative degradation of organic dyes (including re-
active red 2, reactive blue 19, acid orange 7, rhodamine B and me-
thylene blue) under acidic condition has been developed for the first
time. In contrast to advanced oxidation processes [18], this directly
oxidative degradation is a non-radical mechanism. These effects of
OMS-2 concentration, pH condition and initial concentration of organic
dye have been investigated for directly oxidative degradation. Then we
found the activation energy (Ea) is 28.9 KJ/mol for OMS-2 based on the
Arrhenius equation. In addition, OMS-2 has been successfully recycled
at least five times for directly oxidative degradation without any ob-
viously decrease in activity. This work provides general guidance for
designing and developing active OMS-2 for cost-effective water and
sewage treatment.
3
30 nm declines very slowly, whereas the visible band at 538 nm de-
creases extremely rapidly. It suggests azo groups (N = N bonds) are
attacked by OMS-2 at under acidic condition. Then, RR2 is directly
oxidatively degraded to sodium 3,5-diamino-4-hydroxynaphthalene-
2
3
,7-disulfonate, 2,4-dichloro-1,3,5-triazine and aniline. Immediately
,5-diamino- 4-hydroxynaphthalene-2,7-disulfonate is oxidatively de-
graded to carboxylic acids upon hydroxylation and ring opening [17].
Finally, OMS-2 is found to show high efficiency for the directly oxida-
tive degradation of RR2 with a removal of 99% after 20 mins under the
condition of pH = 1. Then the RR2 degradation has been carried out at
different pH conditions, as shown in Fig. 2b. The result exhibits that the
removal efficiency of RR2 decreased as the increase of pH value, due to
the stronger oxidizing capacity of OMS-2 under the stronger acidic
condition. As shown in Fig. 2c, the high efficiency of OMS-2 has been
illuminated by the experiment carried out under different initial con-
centration of RR2 (from 20 to 500 mg/L). Various concentrations of
OMS-2 have been investigated for the degradation of RR2 (Fig. 2d). We
found that no degradation of RR2 without OMS-2. It has been observed
that the rate of RR2 degradation increases gradually by increasing the
OMS-2 concentrations from 0.064 to 0.5 g/L. Finally, the efficiency of
RR2 degradation in the presence of 0.25 g/L of OMS-2 at different re-
action temperatures from 0 to 50 °C is illustrated in Fig. 2e, it is
Author contributions
Shuhui Wang collected the experimental data, performed data
analysis; Yu Huang performed a part of data analysis; Xu Meng and
Xiang Liu wrote the manuscript and oversaw the project and performed
the overall editing of the manuscript.
Declaration of Competing Interest
The authors declare no competing financial interest.
4

S. Wang, et al.
Inorganic Chemistry Communications 117 (2020) 107969
Acknowledgment
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Financial support from the National Natural Science Foundation of
China (No. 21805166), the 111 Project (No. D20015), the Youth
Innovation Promotion Association CAS (2018456) and China Three
Gorges University is gratefully acknowledged.
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