Designing bimetallic zeolitic imidazolate
frameworks (ZIFs) for aqueous catalysis: Co/Zn-
ZIF-8 as a cyclic-durable catalyst for hydrogen
peroxide oxidative decomposition of organic dyes
in water
Osama Abuzalat,
*
a
Hesham Tantawy,
a
Mustafa Basuni,
b
Mohamed H. Alkordi
b
and Ahmad Baraka
a
ZIF-8 is well known hybrid material that is self-assembled from inorganic and organic moieties. It has several
potential applications due to its unique structure. One of these potential applications is in advanced
oxidation processes (AOP) via a heterogeneous catalysis system. The use of modified ZIF-8/H
2
O
2
for the
destruction of the azo dye methyl orange (MO) is presented in this work to explore its efficacy. This work
presents the bimetallic Co/Zn-ZIF-8 as an efficient catalyst to promote H
2
O
2
oxidation of the MO dye.
Co/Zn-ZIF-8 was synthesized through a hydrothermal process, and the pristine structure was confirmed
using XRD, FTIR, and XPS. The Co/Zn-ZIF-8/H
2
O
2
system successfully decolorized MO at the selected
pH 6.5. It was found that more than 90% of MO (10 ppm) was degraded within only about 50 minutes.
Proposed radical and redox mechanisms are presented for H
2
O
2
decomposition where the redox
mechanism is suggested to predominate via a Co(II)/Co(III) redox consecutive cyclic process.
1. Introduction
Zeolitic imidazolate frameworks (ZIFs) represent a particular
class of coordination polymers that are built from metal ion
nodes and methyl-imidazolate (MIM) linkers. ZIFs are crystal-
line solids possessing structures analogous to aluminosilicate
zeolites with an intrinsic permanent porosity and considerable
thermal and chemical stability.
1,2
Due to the many desirable
characteristics of this class of microporous solids, ZIFs were
heavily explored within the last decade for applications such as
gas separation, adsorption (gas and liquid phases), sensing
3
electronic devices, drug delivery, and catalysis.
4,5
Indeed, applying ZIFs for heterogeneous catalysis has been
systematically investigated and has covered several approaches
such as degradation of some dyes/organics (e.g., methylene blue
and indigo carmine) via photocatalysis
6
catalytic synthesis of
some organic derivatives (styrene carbonates),
7
hydrogen
generation,
8
CO
2
conversion,
9
Knoevenagel condensation,
10
Friedel–Cras acylation,
11
trans-esterication,
12
and mono-
glyceride synthesis.
13
Although reductive catalytic degradation
of some dyes was previously investigated by the ZIF-8/NaBH
4
catalysis system,
14
or adsorption by ZSM-5 zeolite
15
utilization of
ZIFs for the counter-redox direction, the oxidative catalytic
degradation of organic contaminants (heterogeneous catalysis
employing the oxidant H
2
O
2
), to best of our knowledge has not
previously been reported. This scarcity of in-depth investiga-
tions into the catalytic activity of ZIFs for oxidative degradation
of organic dyes did not allow for critical evaluation of ZIFs in
many environmental applications, one of which is the efficient
oxidative remediation of wastewater.
In this work, the known bimetallic Co/Zn-ZIF-8 has been
selected for oxidative catalysis degradation primarily due to its
signicant hydrolytic stability in aqueous solutions, a decisive
factor for any material to utilize in aqua-degradation systems.
6
Synthesis and characterization of Co/Zn-ZIF-8 are presented,
especially detailed XPS analysis. The rate and kinetic-modelling
of oxidative catalytic degradation of the stable dye methyl
orange by Co/Zn-ZIF-8/H
2
O
2
system are presented as well. To
the best of our knowledge, this is the rst report presenting the
activity of a bimetallic ZIF-8 for degrading a synthetic dye via
catalytic H
2
O
2
decomposition.
2. Experimental
2.1 Materials
All chemicals were of analytical grade and have been used
without further purication: 2-methylimidazole (2-MIM, 99%,
Sigma-Aldrich), triethylamine (TEA, 99%, Alfa Aesar), zinc
acetate dihydrate (Zn(CH
3
CO
2
)
2
$2H
2
O, 98%, Sigma Aldrich),
a
Department of Chemical Engineering, Military Technical College, Cairo, Egypt.
E-mail: osama.abuzalat@mtc.edu.eg
b
Center for Materials Science, Zewail City of Science and Technology, Giza 12578,
Egypt
Cite this: RSC Adv. , 2022, 12, 6025
Received 12th January 2022
Accepted 11th February 2022
DOI: 10.1039/d2ra00218c
rsc.li/rsc-advances
© 2022 The Author(s). Published by the Royal Society of Chemistry RSC Adv., 2022, 12, 6025–6036 | 6025
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