Application of Different Analysis Methods Based on Metal-Organic
Frameworks for Different Heavy Metal Ions Detection
Lu Gong
*
Nanjing Foreign Language School, Nanjing 210000, China
Keywords: MOFs, Heavy Metal Ions, Detection, Sensing Methods.
Abstract: The heavy metal pollution is a huge problem to the world as it is extremely harmful to human health and
ecological balance. There are various kinds of heavy metal, like copper, lead and mercury which is widely
distributed on the earth. However, traditional analysis methods to detect heavy metal ions are quite time-
consuming and expensive. In order to achieve a higher level of detection, a new determining strategy is in
urgent need. Metal-organic frameworks (MOFs) is a relatively advanced group of materials for many purposes
including chemical sensing. As it has many comparative advantages, for example, high electrocatalytic
activity and large surface area, it shows great potential in this area. When MOFs-based functional materials
are combined with other distinct techniques, the “chemical nose” can even get more sensitive. For a specific
kind of heavy metal ions, a unique detection method should be prepared to detect them with high sensitivity
and selectivity. This research will introduce some advanced and up-dated heavy metal determining strategies
based on MOFs materials. The synthesis of some MOFs-based materials is also included in this research in
detail. It is quite meaningful to discover a new material and explore its potential application. As the technology
is developing so rapidly, MOFs materials will definitely dominate in the future.
1 INTRODUCTION
The word “heavy metal” means those elements
containing an atomic density above 5 g/cm
3
, which
must show metallic properties (Kim, 2019).
Typically, they occur in rater low concentration, but
they can be found all through the crust of the earth.
In common, heavy metal ions include transition
metals, post-transition metals, and lanthanides. Some
metals are essential to the entire human metabolism
and they possess the functions indispensable for
various biological process, like copper, zinc, or
selenium. However, due to anthropogenic activities,
heavy metal pollution has also become a global issue
and is widely discussed. Since industrial revolution,
the increasing demand for exploration of the natural
resources on the earth has exceeded people’s
expectations. In light of this, after heavy metals enter
the environment, it will cause serious environmental
pollution and destroy the natural ecosystem due to the
high toxicity of heavy metals and their migration and
transformation properties. The heavy metal pollution
can also be increased by some natural causes
including volcanic activities and soil erosion (Mishra
G. K, 2017).
Heavy metal plays an important role in human
body and environment. Some of the heavy metals
serve as microelements which can support
metabolism, speed up the enzyme production and
enhance the enzyme activity. However, the presence
of these heavy metal ions in an exceeding amount is
highly likely to cause irreversible problems to both
human health and the environmental protection. As
the development of industrialization is getting faster,
people should pay attention to these potential
hazards. For example, the overuse of pesticides
containing mercury in agriculture will cause mercury
pollution. The mercury is one of the most hazardous
and poisonous heavy metal because it will do harm to
the nerves and the brain. The damage to the nervous
system results in mental diseases like depression
which is a huge threat to human health. Also, the
mercury pollution is also destructive to the
environmental protection and ecological balance.
Due to the existence of biological magnification, it
will cause series of problems to the whole food chain
such as some fatal diseases. In addition, the
reproductive system may be destroyed since there
will be a significant decline in the quantity of
reproduction. In light of this, if human release too
106
Gong, L.
Application of Different Analysis Methods Based on Metal-Organic Frameworks for Different Heavy Metal Ions Detection.
DOI: 10.5220/0012003200003625
In Proceedings of the 1st International Conference on Food Science and Biotechnology (FSB 2022), pages 106-111
ISBN: 978-989-758-638-5
Copyright
c
 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

much mercury to the environment, people will suffer
from both health and environmental hazard. Besides
mercury, lead and chromium are other examples of
harmful heavy metals. When lead and lead containing
compounds enter the human body, it will
immediately do harm to various systems like
digestive system, endocrine system, nervous system
and cardiovascular system. Chromium and its
containing compounds are already classified as
cancerogens which may cause cancer. In addition,
since chromium ions are deadly to most aquatic
organisms, too much chromium will significantly do
harm to ecological balance as a result. Therefore, it is
quite meaningful and important for human to pay
attention to these threats. The toxicological homes of
metalloids are continuously delivered about by
means of way of their fashion to structure covalent
bonds, most important them to bind covalently with
herbal groups. In addition, given that metals can’t be
damaged down and are non-biodegradable, when the
heavy metals are absorbed by means of capacity of
human bodies, they bio-accumulate in our system.
This is categorized as unsafe due to the fact the bio-
accumulation reasons natural and physiological
complications. For some heavy metals, they are
essential to useful resource existence and are
commonly required for some physiological
functions. Nevertheless, these heavy metals can
moreover be toxic if they current in massive amounts.
Thus, the detection of heavy steel ions is pretty
massive to human health and the environmental
protection (Ding, 2021).
A traditional way to detect heavy metal ions is the
atomic absorption spectrometry. The principle is that
all atoms can absorb light with specific wavelengths.
However, this kind of technique hold the
disadvantage of high instrument complexity and
instrument cost. Another way to detect heavy metal
ions is to use electrochemical aptasensor-based
technology. Nevertheless, the reproducibility and
balance of electrochemical sensors want greater
improvement. For different detection methods,
enzyme evaluation for example, even though it has
excessive sensitivity, it is challenging to discover a
single heavy metallic ion and it is solely successful
for water samples. For immunoassay, it is genuine
that the detection can be extraordinarily quickly and
it can acquire an excessive selectivity, however the
practice of metallic ion monoclonal antibodies is very
tough and polyclonal antibodies are challenging to
meet the precise necessities for steel ions. Thus, a
miniaturized heavy metal ion detector with excellent
sensitivity, selectivity and stability is demanded. In
fact, luminescent MOF based detectors show great
potential in the field of heavy metal protection (Chen,
2021). This material can be combined with other
analytical methods for better application. As a result,
this research mainly introduces different sensing
methods based on MOFs materials and used to detect
heavy metal ions, including mercury ions (Hg
2+
), lead
ions (Pb
2+
) and cadmium ions (Cr
3+
).
The aim of this article is to explore the potential
of various techniques based on MOFs materials for
detection of different heavy metal ions. The MOFs
materials have lots of advantages in this field such as
higher selectivity and greater sensitivity. In modern
society, the demand for hazards detectors with such
quality is getting increasingly urgent. For instance, it
is necessary for households to pay attention to the
potential risk of mercury poisoning. Also, for
environmental protection sectors, they have suffered
from various pollutions like heavy metal pollution for
a long time. However, all current detectors have some
limitations like high maintaining cost. Therefore,
with the help of MOFs materials, all of these
concerns will be eliminated. It is extremely certain
that the detectors based on MOFs will dominate the
field of heavy metal ions detection and other sensing
fields.
2 DETECTION OF HG
2+
The detection of Hg
2+
is quite significant because it
is highly likely to cause digestive and neurological
diseases for human due to its toxicity, non-
degradability and water stability. In addition, because
Hg
2+
is the most stable form that mercury can exist, it
will cause serious consequences like environmental
pollution even at low concentrations. However,
although traditional detection methods may be
efficient in Hg
2+
detection, they are extremely
expensive and they take large amount of time, like
gas chromatography and anodic stripping
voltammetry. Therefore, developing new methods
are in urgent need for detection of Hg
2+
.
Application of Different Analysis Methods Based on Metal-Organic Frameworks for Different Heavy Metal Ions Detection
107

Figure 1: Change of the fluorescence intensity of the used MOFs materials in the presence of different concentrations of Hg
2+
(Samanta, 2018).
MOFs-based functional materials have been
widely used to construct different sensing methods
and have recently been used to achieve the goal. Most
MOFs-based Hg
2+
sensors are based on chemosensors
and they can be identified in to two sets. The first
group of MOFs-based sensors have nitrogen or amine
groups at center, which are able to coordinate to Hg
2+
.
Another group of sensors have sulfur-rich probes,
which allows Hg
2+
to bind with the sulfur center.
Nevertheless, such probes have some limitations.
First of all, amines and sulfides will inevitably be
oxidized by the air during long-period storage.
Therefore, the results of detection will be negatively
affected. In addition, the sulfur-based probes cannot
offer a proper signal in an environment that is full of
sulfur if there’s too much mercury presented. In order
to solve these problems, scientists have carried out a
lot of progress. Instead of the use of any amine or
sulfur to function, chemodosimeter-based method is
employed. With the assist of chemodosimeter, the
purpose analyte can react with dosimeter molecules
to furnish everlasting signals. It is well-known that
the Hg
2+
ions react with alkyne organizations by way
of ability of viable of oxymercuration response in the
presence of water. Therefore, the new sensing method
based on MOFs can be fabricated to detect the
presence of Hg
2+
in water sources.
Since in large amount of cases, the sensing and
determining of the focused analytes has been
obtained, the water balance is the most good-sized
standards for sensible functions. A crew of MOFs
named UiO sequence MOFs possess excessive
chemical steadiness supported by way of its
secondary constructing unit. For example, Samanta et
al. prepared a new functionalized MOF (UiO-
66@Butyne) and then deigned a new sensing method
to detect Hg
2+
in water (Samanta, 2018). Water-stable
zirconium-based MOFs have been synthesized
bearing butyne agencies as vigorous websites to cease
up conscious of mercury ion. As UiO-66 is
extraordinarily chemically stable, the butyne-
functionalized UiO-66@Butyne is a practicable Hg
2+
sensor due to the fact it can use an irreversible
oxymercuration response to produce signal. With the
assist of butyne functionality, the sensor can obtain
excessive selectivity and sensitivity. As shown in Fig.
1, based on the different fluorescence intensity
changes caused by different mercury ion
concentrations, the detection limit of the constructed
sensing method can reach 10.9 nM, showing the
outstanding sensitivity. Although a sensor with
mechanism based on reactions has failed to be
mentioned up to now in the MOF database, this MOF-
based sensor indicates tremendous doable in this
field.
Razavi et al. used the tetrazine-modified
MOF to develop a dual solvent detection method
for detection of mercury ion (
Razavi, 2017) . The
prepared MOFs material has good luminescence
properties and high stability. When it was used to
construct a mercury ion detection method, the method
showed great advantages, such as fast response time,
high sensitivity, and good selection. In this work, the
response time and sensitivity can reach 15 s and
1.8×10
-6
M, respectively. And the developed sensing
method based on MOFs shows a high selectivity, as
shown in Fig. 2.
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108

Figure 2: The selective analysis of the developed sensing
method (
Razavi, 2017).
3 DETECTION OF PB
2+
Heavy metallic ions are extremely harmful and
dangerous pollutants since they will do harm to
humans as well as atmosphere as a whole. Among all
the harmful heavy metal ions, Pb
2+
ions have been
paid lots of attention because it can be released from
various sources, such as smoking and industries. As
lead accumulate over time, it will substitute some
elements and tissues heading in the bone, leading to
diseases like cancer and causing damage. In some
extreme cases, the high amount consumption of lead
may even result in death. As a result, in order to
preserve human health and ecological sustainability,
the detection of lead ions is necessary. Different types
of lead ion detection methods have been developed,
such as electrochemical sensing methods,
colorimetric sensing methods, fluorescence sensing
methods, etc. However, these methods more or less
have their own drawbacks. The introduction of new
functional materials and the development of new lead
ion detection methods have received more and more
attention. Scientists have done some researches to
explore potential materials that are suitable for the
determination of heavy metal ions, such as noble
metal nanomaterials and graphene materials.
However, the challenge is that the sensitivity and
selectivity can’t achieve a high level. Among these
various materials, MOFs shows great adaptability
because MOFs materials have high crystallinity and
considerable porosity. As a result, a new detection
method based on MOFs materials has been developed
and used to realize the detection of lead ions.
Wang et al. used the prepared MOFs to develop a
new electrochemical detection method for lead ions
detection (Wang, 2013). The prepared MOFs material
(MOF-5) was modified on the carbon paste electrode,
which can be then used to adsorb lead ions in the
solution, resulting in the change of the induction
signal. The electrodes constructed with this material
exhibited good electrochemical response behaviour
and improved detection limit up to 4.9×10
-9
M. in
addition, as shown in Fig. 3, when using the prepared
MOFs material to modify the functional electrode, the
electrode can be used continuously for at least 50
times, showing excellent stability. Ding et al. used the
MOFs material (UIO-66) to design an
electrochemical sensing method for simultaneous
detection of cadmium ions and lead ions (Ding, Wei,
2021). The synthesized MOFs material (UIO-66) was
carbonized and then used to modify the electrode,
thereby constructing a highly sensitive
electrochemical detection method. The results show
that the limit of detection for the developed
electrochemical sensing method is 1.16 μg/L and 1.14
μg/L for cadmium ions and lead ions, respectively.
Figure 3: Cycle times of electrodes modified with the
prepared MOFs materials (Wang, 2013).
4 DETECTION OF CR
3+
The detection of Cr
2+
is quite significant because it is
highly likely to cause digestive and neurological
diseases. In addition, chromium(III) can bind with
deoxyribonucleic acid in body, major to mutations or
malignant cells and chromium(VI) is successful to
cause genetic mutations in body. Therefore, once
chromium ions exist in the air in large quantities, they
are classified as serious air pollution with the resource
of the American environmental security agency.
Therefore, selective and touchy detection of
chromium ion is quite significant. Also, it is in
actuality really helpful for every human health and
environmental protection. However, the ordinary
Application of Different Analysis Methods Based on Metal-Organic Frameworks for Different Heavy Metal Ions Detection
109

detection strategies are commonly elaborate and
high-priced for the dedication of Cr
3+
. Nowadays,
using the detection methods for the detection of Cr
3+
with high selectivity has attracted a lot attention. In
moderate of this, fluorescence-based MOFs for
sensing Cr
3+
are increased effective and perfect in
distinction with these ordinary methods (Lv, 2016).
Because they are accessible to use and they are no
longer that expensive, they are higher cost-effective.
Figure 4: Change of the fluorescence intensity of NH
2
-Zn-
MOF in the presence of different concentrations of target
metal ions (Lv, 2016).
Zn(NO
3
)
2
·6H
2
O, TPOM, NH
2
-BDC, dimethyl-
formamide and H
2
O have been sealed into a stainless
steel vessel. Then, the combination will be heated.
Colourless rhombus crystals then would be acquired
by way of filtration and washed. The suspension will
be used for luminescent measurements. Since MOF
have d10 metallic ions and fragrant natural ligands,
they possess luminescent characteristics. In mild of
this, DMF can be an applicable dispersion medium.
The luminescent spectra of NH
2
-Zn-MOF separated
in DMF have been confirmed in room temperature.
The results show that NH
2
-Zn-MOF separated in
MOF suggests a launch at 420 nm. The robust
fluorescence emission of this type of MOF fabric is
critical for its utility in heavy metallic detection. The
fluorescence intensity of the NH
2
-Zn-MOF can be
changed by adding of the different concentrations of
the target metal ions (see Fig. 4).
To find out the possible capability of the
selectivity of the detection by using NH
2
-Zn-MOF for
chromium ions combined with different specific
heavy metal ions such as iron ion. They choose Fe
3+
as opposition ions which have the absolute fine
quenching efficiency. By way of potential of
examining the fluorescence spectra, scientists
Figure 5: Schematic diagram of the mechanism of
fluorescence detection of heavy metals based on MOFs
materials (Xiao, 2018).
conclude that the fluorescence depth is lowering
when they added iron ion into the solution. However,
the widespread trend of luminescence intensity shows
continuously greater desirable due to the addition of
chromium ions. The effects factor out that the greater
stage of selectivity is completed thru this type of
MOF. The developed amino-decorated MOF which
refers to NH
2
-Zn-MOF indicates immoderate
sensitivity towards chromium ions. As shown in Fig.
5, it is precisely because of the high sensitivity
exhibited by different detection methods constructed
based on MOFs-based functional materials, where
MOFs materials have been widely used (Xiao, 2018).
5 CONCLUSION
As the heavy metal pollution is getting worse
nowadays, it is necessary for scientists to explore a
new detection strategy. The detection with high
selectivity and sensitivity of chromium ion, mercury
ion and lead ion can be achieved by MOFs-based
functional materials. Chemodosimeter-based
approach shows great potential in the field of mercury
ion detection. MOF-5 is used to determine the
presence of lead ion. For the detection of chromium
ion, NH
2
-Zn-MOF based technique shows greater
advantage compared with other traditional methods
because of its luminescent properties. Although the
MOFs-based functional material is not that widely
used in the contraction with other materials, it will
FSB 2022 - The International Conference on Food Science and Biotechnology
110

definitely get increasingly popular and advanced with
further research and exploration. With the help of
MOFs-based functional materials to construct heavy
metal detectors with high selectivity and sensitivity,
people can get huge benefit from it in the field of
health and environmental protection.
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