Research on Heavy Metal Ion Adsorption Using Metal Organic

Frameworks (MOFs) Materials

Meng Xi

College of Environmental and Chemical Engineering, Nanchang Hangkong University, Nanchang, Jiangxi, China

Keywords: Metal-Organic Frameworks, Adsorption, Heavy Metal Contamination.

Abstract: Heavy metal contamination has led to significant environmental issues and poses risks to human health.

Among various methods for treating heavy metals, adsorption is particularly effective. Metal-organic

frameworks (MOFs), as a highly promising new class of adsorbents, excel in addressing complex heavy metal

pollution due to their superior adsorption capabilities. This paper aims to analyze the sources and hazards of

heavy metal pollution and to investigate the advantages of MOFs in the adsorption of heavy metals. In this

paper, it is concluded that MOFs materials are mainly categorized into six series such as ZIF and UiO.

Numerous MOFs have demonstrated remarkable adsorption efficiency for common heavy metals such as lead,

mercury, chromium, and arsenic. However, there are still challenges in the practical application of MOFs

materials such as enhancing the stability of the materials in the actual water body; making the materials take

into account a variety of excellent properties; and discovering cost-effective methods to prepare MOFs

materials. This paper can provide a feasible reference for heavy metal treatment.

1 INTRODUCTION

In recent years, increased industrial activity,

especially in sectors like metallurgy and battery

production, has released large amounts of heavy

metals, including mercury and lead, severely

impacting the environment. Smelting operations

alone contribute approximately 40-73% of human-

generated heavy metal emissions. Most heavy metals

are not biodegradable and are easily transferred and

enriched among organisms, eventually entering the

human body through the food chain (Zhang, 2022).

Excessive concentrations of heavy metals can cause

serious harm to the human respiratory and digestive

systems and may even be life-threatening. Therefore,

it is imperative to control heavy metal pollution.

Chemical precipitation, membrane filtration, and

ion exchange have been used to treat heavy metal

wastewater, but most of the methods are costly and

complicated to operate in the application process and

may cause secondary pollution. In recent years,

adsorption has become a powerful heavy metal

treatment method and has been widely used for the

efficient removal of heavy metals from water (Lin,

2023). Therefore, it has become a trend to prepare

https://orcid.org/0009-0008-8856-5730

new adsorbents that combine high adsorption

performance with green and non-polluting properties.

In recent decades, metal-organic frameworks (MOFs),

as new organic-inorganic hybrid materials, have

attracted much attention due to their ordered porosity,

large specific surface area, well-proportioned

structural cavities, and thermal and chemical stability.

Moreover, these properties have been demonstrated

in studies of the ZIF, MIL, and UiO series. This

means that organic ligands and various metals can be

combined as expected (Ru, 2021). The properties of

MOF can effectively promote the adsorption of

targets on the MOFs surface. MOFs materials are

more advantageous than conventional adsorbents in

heavy metal adsorption.

The purpose of this paper is to introduce the

application performance and potential of various

MOFs materials in heavy metal ion adsorption and to

predict and prospect the application prospect of

MOFs materials. This paper will discuss the sources

and hazards of heavy metals, the definition and

classification of MOFs materials, and the adsorption

performance of MOFs materials on heavy metals, and

analyze the application of MOF materials in heavy

metal adsorption.

254

Xi, M.

Research on Heavy Metal Ion Adsorption Using Metal Organic Frameworks (MOFs) Materials.

DOI: 10.5220/0013327000004558

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Modern Logistics and Supply Chain Management (MLSCM 2024), pages 254-258

ISBN: 978-989-758-738-2

2 SOURCES AND HAZARDS OF

HEAVY METAL IONS

In terms of environmental pollution, heavy metals are

chromium, mercury, lead, arsenic, and other biotoxic

heavy metals and metalloids. The five most toxic to

humans are arsenic, chromium, lead, mercury and

cadmium. Industrial pollution is the main source of

heavy metals, most of which are discharged into the

environment through industrial wastewater and waste

residues, and subsequently enriched in the human

body, animals, and plants, thus jeopardizing the

environment and human health. Heavy metal

pollution is mainly reflected in water pollution but

also exists in the atmosphere and solid waste. Unlike

organic pollutants, heavy metals are difficult to

degrade through physical, chemical, or biological

processes in nature and are easily enriched in the

environment and living organisms. Heavy metals

cannot be broken down when they enter a body of

water and can combine with other toxins in the water

to form more toxic substances (Lei, 2023). They

interact firmly with enzymes and proteins in the body,

which leads to the inactivation of biomolecules,

resulting in chronic or acute poisoning that poses a

serious threat to human health.

3 DEFINITION AND

CLASSIFICATION OF MOFS

The treatment of heavy metal pollution is urgent.

MOFs, as new adsorbents in the adsorption method,

have great potential in heavy metal adsorption. This

paper will center on four types of MOFs to understand

their characteristics and differences.

MOFs are crystalline porous materials formed by

linking inorganic metal nodes with organic ligands,

creating a periodic network structure (Chen, 2023). In

general, MOFs consist of two components, the

organic ligand and the metal center, which play the

roles of pillars and nodes, respectively (Kaur, 2023).

Representative classical MOF materials are IRMOFs,

ZIFs, MIL, and UiO series.

Isoreticular MOFs (IRMOFs) series of materials

are formed by the coordination of Zn2+ with the

oxygen in the terephthalic acid root, and the pore

sizes and porosities of the materials are different

depending on the length of the organic ligands and the

substituents on the benzene rings of the ligands

(Eddaoudi, 2002). However, because of the similar

synthesis methods, the materials have the same

topology and are thermally and chemically stable.

Zeolitic Imidazolate Frameworks (ZIFs) are

constituted by the coordination of metal ions with

tetrahedral coordination ability, such as Zn2+ and

Co2+, with nitrogen atoms in the imidazole moiety

(Cravillon, 2009). Because of the topological

similarity to zeolite, the ZIFs series are also known as

zeolite imidazolium ester backbone materials. The

ZIFs series are well-stabilized with good thermal (up

to 550°C), aqueous, and solution stability (alkaline

solutions, organic reagents), and can be used for

contaminant removal from water.

Material Institute Lavoisier (MIL) series materials

are constituted by coordination of metal ions such as

Fe3+, Cr3+, and Al3+with oxygen in dicarboxylic

acid ligands, and generally have good solvent and

thermal stability (Horcajada, 2010). The skeletons of

these materials are flexible and can undergo large

reversible deformation under external stimuli.

The University of Oslo (UiO) series of

isostructured MOFs, composed of Zr4+ ions bonded

to organic ligands, exhibit high stability (Cavka,

2008). UiO-66, the most representative structure,

features Zr6O4(OH)4 as the secondary building unit.

This unit consists of a Zr6 octahedral core

coordinated with 12 terephthalic acid ligands,

resulting in a highly symmetric structure. The strong

interaction between the Zr6 core and the carboxyl

groups of the ligands contributes to the excellent

water and thermal stability of the Zr6 octahedron.

The above four MOFs materials and their

derivatives have already shown excellent

performance in heavy metal adsorption treatment,

proving the potential of MOFs materials.

4 ADSORPTION PROPERTIES

OF MOFS ON HEAVY METAL

IONS

4.1 Plumbum (Pb)

Pb is a polluting heavy metal with a relative atomic

mass of 207. 2. Pb has a significant effect on human

health, and the damage to the bone marrow

hematopoietic system and the nervous system is very

serious. Roy et al. constructed ZIF-8 and used it for

adsorption of Pb(Ⅱ) by solvent-thermal method (Roy,

2021), and the results of their study show that the

adsorption of Pb(Ⅱ) by ZIF-8 is best when the

solution is weakly acid to neutral; in alkaline

environment Pb(Ⅱ) mainly remains in the form of

precipitation and gel such as Pb(OH)2, at this time the

adsorption turns to physical adsorption.

Research on Heavy Metal Ion Adsorption Using Metal Organic Frameworks (MOFs) Materials

255

The carboxylation modification can lower the

isoelectric point of the MOFs, thus allowing them to

adsorb Pb(II) efficiently even at lower pH. Zhao et al.

constructed UiO-66-(COOH)2 using homophthalic

acid, which is a MOFs with extreme acid-resistant

stability, and which maintains an adsorption capacity

of more than 200 mg/g of Pb(II), even at a pH of 2

(Zhao, 2019). The carboxylation modification also

enhanced the recycling performance of UiO-66-

(COOH)2, which could still recover about 85% of its

adsorption performance after four adsorption-

desorption cycles. At lower pH, Pb(II) mainly

remains in the form of hydrated ions with larger

particle sizes. In order to further enhance the

adsorption performance of MOFs for Pb(II) at lower

pH, Li et al. used tartaric acid to post-synthesize the

modification of UiO-66-NH2, and the results showed

that the exchange of tartaric acid for 2-amino

terephthalic acid disrupted the microporous

framework of UiO-66-NH2, and on the MOFs

mesopores ranging from 26 to 50 nm and macropores

ranging from 50 to 120 nm appeared, and the

oversized pore structure not only promoted the

diffusion of Pb(II) inside the MOFs, but also elevated

the rigidity of the MOFs, which exhibited the

maximum saturation adsorption of Pb(II) at 186. 14

mg/g (Li, 2020).

4.2 Mercury (Hg)

Hg belongs to the typical heavy metal atoms with a

relative atomic mass of 200. 6. Hg readily binds to

proteins and enzymes, inhibiting their biological

activities and possibly inactivating them. Hasankola

et al. constructed carboxylate-rich Zr-TCPP using

5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin and

Zr(IV) (Hasankola, 2020). The results show that

when the pH is low, the adsorption of Hg(II) on Zr-

TCPP mainly relies on cation-π electron cloud

interactions and ion exchange, and the interactions

are gradually transformed into electrostatic

interactions and ligand interactions with the increase

of pH, and the adsorption is transformed into the

deposition and filling of Hg(OH)2 in the pores of Zr-

TCPP when the pH exceeds the precipitation value of

Hg(II)

Altering the porous nature of MOFs is beneficial

in enhancing the interaction with Hg(II). Alshorifi et

al. introduced Co(II) with different coordination

numbers during the construction of MIL-101(Fe).

The porosity and specific surface area of MOFs

reached the maximum when the molar ratio of Co(II)

to Fe(III) was 1:1. At this time, the carboxyl group

exposed in MOFs was also the highest, and the Hg(II)

adsorption up to 312. 97 mg/g (Alshorifi, 2022). Ji et

al. prepared MOF-808-SH by post-synthetic

modification via ligand-exchange method using α-

mercaptoacetic acid to exchange formic acid in the

structure of MOF-808. The reactive carboxyl groups

on the MOF-808-SH could sequester Hg2+ at lower

pH, while the sulfhydryl group could to form stable

uncharged complexes with Hg(OH)+ and Hg(OH)2 at

higher pH (Ji, 2022).

4.3 Chromium (Cr)

Cr is one of the essential micronutrients for plants and

animals, with a relative atomic mass of 52. 01, but

excess Cr has a strong biotoxicity, in which Cr(VI) is

about one hundred times more toxic than Cr(III). The

distribution pattern of Cr(VI) in the water body is

related to the pH and concentration, and Noraee et al.

found that UiO-66 has a stronger adsorption capacity

for low concentrations of HCrO

under weakly acidic

conditions, when UiO-66 showed a stronger positive

charge (Noraee, 2019). Since UiO-66 has denser

pores, HCrO

is converted to H

CrO

when the pH is

about 2, when the physical adsorption of H

CrO

the appearance of MOFs mainly occurs. To enhance

the adsorption performance of Cr(Ⅵ) at low pH,

Rego et al. constructed a Ce(Ⅲ)-doped UiO-66, and

the difference in the coordination number caused a

certain amount of mesopores to appear in the

microporous structure of UiO-66, and the generation

of mesoporous structure with larger pore size allowed

CrO

to be still deposited in the pore space of Ce-

UiO-66 in acidic conditions, which showed an

excellent adsorption capacity for Cr(Ⅵ)(Rego, 2021).

4.4 Arsenic (As)

As belongs to the class of heavy metals, has the nature

of amphoteric elements, the relative atomic mass is

74. 92, As will inhibit the biological activity of

enzymes and cause metabolic hindrance. The

existence of As in the water body is mainly in the

form of As(Ⅲ) and As(Ⅴ). The morphology of As(Ⅲ)

is related to pH, and the As(Ⅲ) mainly remains in the

form of H

AsO

when the pH is less than 9. 1. Pervez

et al. found that under weakly alkaline conditions

AsO

is more easily exchanged with MOF-808 in

ligands, and its adsorption performance is enhanced

with the increase of surface carboxyl group content;

at pH greater than 9. 1, the As(Ⅲ) mainly remains in

the form of H

AsO

. Alkaline conditions H

AsO

more susceptible to ligand exchange with MOF-808,

and its adsorption performance is enhanced with the

elevation of the carboxyl group content on the surface;

MLSCM 2024 - International Conference on Modern Logistics and Supply Chain Management

256

at pH greater than 9. 1, As(Ⅲ) then exists in the form

of H

AsO

, which can be adsorbed onto MOFs

through electrostatic interactions and interactions

between anionic-π electron clouds, but there is a high

requirement for alkali resistance of MOFs (Pervez,

2022). Highly oxidizing functional groups or metal

ions can also be present in MOFs, e.g., MOFs

containing Mn(Ⅳ) can oxidize the more reducing

As(Ⅲ) to As(Ⅴ) under acidic conditions, but this

redox reaction causes irreversible defects in the

framework of MOFs.

Amination modification can enhance the positive

electronegativity of MOFs, thus enhancing their

adsorption performance for As(V). Yin et al. showed

that MIL-101(Fe/Al)-NH2 could adsorb more than 90%

of As(V) efficiently in the pH range of 3-11. Under

acidic conditions, this adsorption is mainly dependent

on the electrostatic interaction of protonated amino

groups with As(V) (Yin, 2022). If the MOFs are

simultaneously modified by carboxylation and

amination, the carboxyl and amino groups can also

form a stable hydrogen-bonding network and

synergistically adsorb As(V), which effectively

weakens the conformational distortion of the organic

ligand, enhance the rigidity of the MOFs, and

improve the water stability of the MOFs.

5 CHALLENGE

Among the many properties of MOFs, porousness,

surface activity, and framework flexibility are the

core properties of MOFs as adsorbents. The water

stability, scalability, biotoxicity, and recyclability of

MOFs are the key to their use as adsorbents in high-

performance water treatment fields. A breakthrough

in certain properties of MOFs can be realized by

modulating metal ions, organic ligands, and synthesis

methods. Although some progress has been made in

the preparation methods, performance studies, and

multidimensional applications of MOFs in recent

years, the practical application of MOFs for the

adsorptive removal of heavy metal ions still faces

many challenges.

(1) Although MOFs show some stability in neutral,

acidic, and alkaline solutions, in the actual water body,

which contains more strongly liganded organic matter

and metal ions, this ligand or metal ion exchange can

destroy the structure of MOFs. Meanwhile, in order

to increase the adsorption capacity of MOFs, the

synthesis conditions or functionalization

modification are usually changed to expose more

active functional groups, but such MOFs with higher

adsorption capacity often have more obvious

structural defects, and MOFs with structural defects

often imply the loss of water stability and

recyclability, so there is still a need for in-depth study

of the equilibrium between the adsorption

performance and the water stability of MOFs.

(2) Although MOFs possess excellent porosity,

framework flexibility, scalability, surface activity,

water stability, recyclability, and low biotoxicity, it is

difficult for MOFs applied to water treatment to have

almost all of the above properties at the same time,

such as scalability and surface activity, water stability

and surface activity, framework flexibility and water

stability, framework flexibility and recyclability, and

biotoxicity and porosity. It is difficult to have all of

these properties at the same time, so how to balance

the bond between the various advantages of MOFs

and prepare high-performance adsorbents for water

treatment still needs to be further researched.

(3) Currently, MOFs applied to heavy metal

adsorption are mostly tiny powder particles, and the

adsorption of heavy metal ions is still at the stage of

laboratory exploration, and the studies on the

biotoxicity and scalability of MOFs are still immature,

so it is still necessary to analyze the mechanism of

their environmental effects such as migration, cycling,

and enrichment in ecological environments, as well

as the preparation of wholesale MOFs with low-cost

and high efficiency.

6 CONCLUSION

This paper discusses the sources and hazards of heavy

metal pollution, the definition and classification of

MOFs, with the adsorption of heavy metals by MOFs

as the main line. Heavy metals refer to metals and

metalloids that are significantly biotoxic and

originate from industrial pollution, transportation

pollution and domestic waste pollution. In nature

heavy metals are difficult to degrade by physical,

chemical or biological processes and are easily

enriched in the environment and in living organisms.

Heavy metals entering water bodies may combine

with other toxins in the water to form more toxic

substances, which can interact strongly with enzymes

and proteins in the human body and pose a serious

threat to human health. The definition and

classification section of MOFs introduces four

representative classes of classical MOFs materials,

namely, IRMOFs, ZIFs, MIL, and UiO. From the

perspective of the adsorption of four major heavy

metals, namely, Pb, Hg, Cr, and As, by MOF

materials and their derivatives, the adsorption

performances and related adsorption mechanisms that

Research on Heavy Metal Ion Adsorption Using Metal Organic Frameworks (MOFs) Materials

257

have been reported to have been demonstrated by

MOFs and their derivatives materials in the

application of treatment of these four heavy metal

pollutions are discussed. The future development of

MOF materials in the field of heavy metal adsorption

is still challenging in terms of the improvement of

adsorption performance and actual water stability, the

balance between various excellent properties, and the

balance between cost and benefit. The aim of this

paper is to provide referable solutions for the

application of MOFs in the field of heavy metal

adsorption.

REFERENCES

Alshorifi, F. T., El Dafrawy, S. M., & Ahmed, A. I. 2022.

Fe/Co-MOF nanocatalysts: greener chemistry approach

for the removal of toxic metals and catalytic

applications. ACS omega, 7(27), 23421-23444.

Cavka, J. H., Jakobsen, S., Olsbye, U., Guillou, N.,

Lamberti, C., Bordiga, S., & Lillerud, K. P. 2008. A

new zirconium inorganic building brick forming metal-

organic frameworks with exceptional stability. Journal

of the American Chemical Society, 130(42), 13850-

13851.

Chen, Y., Ma, J., Yang, H., Ji, H., Li, W., Pi, Y., & Pang,

H. 2023. Application of modified metal-organic

frameworks in water treatment. Materials Today

Chemistry, 30, 101577.

Cravillon, J., Müntzer, S., Lohmeier, S. J., Feldhoff, A.,

Huber, K., & Wiebcke, M. 2009. Rapid room-

temperature synthesis and characterization of

nanocrystals of a prototypical zeolitic imidazolate

framework. Chemistry of Materials, 21(8), 1410-1412.

Eddaoudi, M., Kim, J., Rosi, N., Vodak, D., Wachter, J., O’

Keeffe, M., & Yaghi, O. M. 2002. Systematic design of

pore size and functionality in isoreticular MOFs and

their application in methane storage. Science,

295(5554), 469-472.

Hasankola, Z. S., Rahimi, R., Shayegan, H., Moradi, E., &

Safarifard, V. 2020. Removal of Hg2+ heavy metal ion

using a highly stable mesoporous porphyrinic

zirconium metal-organic framework. Inorganica

Chimica Acta, 501, 119264.

Horcajada, P., Chalati, T., Serre, C., Gillet, B., Sebrie, C.,

Baati, T., . . . & Gref, R. 2010. Porous metal–organic-

framework nanoscale carriers as a potential platform for

drug delivery and imaging. Nature materials, 9(2), 172-

178.

Ji, C., Ren, Y., Yu, H., Hua, M., Lv, L., & Zhang, W. 2022.

Highly efficient and selective Hg (II) removal from

water by thiol-functionalized MOF-808: Kinetic and

mechanism study. Chemical Engineering Journal, 430,

132960.

Kaur, M., Kumar, S., Yusuf, M., Lee, J., Malik, A. K.,

Ahmadi, Y., & Kim, K. H. 2023. Schiff base-

functionalized metal-organic frameworks as an

efficient adsorbent for the decontamination of heavy

metal ions in water. Environmental Research, 116811.

Lei, Y., Xie, J., Quan, W., Chen, Q., Long, X., & Wang, A.

2023. Advances in the adsorption of heavy metal ions

in water by UiO-66 composites. Frontiers in Chemistry,

11, 1211989.

Li, L., Xu, Y., Zhong, D., & Zhong, N. 2020. CTAB-

surface-functionalized magnetic MOF@ MOF

composite adsorbent for Cr (VI) efficient removal from

aqueous solution. Colloids and Surfaces A:

Physicochemical and Engineering Aspects, 586,

124255.

Lin, G., Zeng, B., Li, J., Wang, Z., Wang, S., Hu, T., &

Zhang, L. 2023. A systematic review of metal organic

frameworks materials for heavy metal removal:

Synthesis, applications and mechanism. Chemical

Engineering Journal, 460, 141710.

Noraee, Z., Jafari, A., Ghaderpoori, M., Kamarehie, B., &

Ghaderpoury, A. 2019. Use of metal-organic

framework to remove chromium (VI) from aqueous

solutions. Journal of Environmental Health Science and

Engineering, 17, 701-709.

Pervez, M. N., Chen, C., Li, Z., Naddeo, V., & Zhao, Y.

2022. Tuning the structure of cerium-based metal-

organic frameworks for efficient removal of arsenic

species: The role of organic ligands. Chemosphere, 303,

134934.

Rego, R. M., Sriram, G., Ajeya, K. V., Jung, H. Y., Kurkuri,

M. D., & Kigga, M. 2021. Cerium based UiO-66 MOF

as a multipollutant adsorbent for universal water

purification. Journal of Hazardous Materials, 416,

125941.

Roy, D., Neogi, S., & De, S. 2021. Adsorptive removal of

heavy metals from battery industry effluent using MOF

incorporated polymeric beads: A combined

experimental and modeling approach. Journal of

Hazardous Materials, 403, 123624.

Ru, J., Wang, X., Wang, F., Cui, X., Du, X., & Lu, X. 2021.

UiO series of metal-organic frameworks composites as

advanced sorbents for the removal of heavy metal ions:

Synthesis, applications and adsorption mechanism.

Ecotoxicology and Environmental Safety, 208, 111577.

Yin, C., Li, S., Liu, L., Huang, Q., Zhu, G., Yang, X., &

Wang, S. 2022. Structure-tunable trivalent Fe-Al-based

bimetallic organic frameworks for arsenic removal

from contaminated water. Journal of Molecular Liquids,

346, 117101.

Zhang, H., Hu, X., Li, T., Zhang, Y., Xu, H., Sun, Y., . . .

& Gao, B. 2022. MIL series of metal organic

frameworks (MOFs) as novel adsorbents for heavy

metals in water: A review. Journal of hazardous

materials, 429, 128271.

Zhao, X., Wang, Y., Li, Y., Xue, W., Li, J., Wu, H., . . . &

Huang, H. 2019. Synergy effect of pore structure and

amount of carboxyl site for effective removal of Pb2+

in metal–organic frameworks. Journal of Chemical &

Engineering Data, 64(6), 2728-2735.

MLSCM 2024 - International Conference on Modern Logistics and Supply Chain Management

258