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Potential of biocompatible calcium-based metal-organic frameworks for the removal of endocrine-disrupting compounds in aqueous environments


Rapid urbanization, industrialization and population growth have accelerated the amount and variety of emerging contaminants being released into the aqueous environment, including endocrine-disrupting compounds (EDCs). The introduction of these compounds constitutes a threat to human health and the environment, even at trace levels. Hence, new water treatment technologies are urgently required to effectively remove EDCs from water. The currently available technologies used in water remediation processes are expensive and ineffective, and some produce harmful by-products. Calcium-based metal-organic frameworks (Ca-MOFs) are porous synthetic materials that can potentially be applied as adsorbents. These MOFs are hydrolytically stable, biocompatible and low-cost compared with conventional porous materials. The structure of Ca-MOFs is maintained even though calcium metal centers in the structure can easily coordinate with water. Ca-MOFs and their composite derivatives have the potential for use in water purification because these biocompatible adsorbents have been shown to selectively extract a significant quantity of contaminants. This review highlights the potential of Ca-MOFs to adsorb EDCs from aqueous environments and discusses adsorbent preparation methods, adsorption mechanisms, removal capacity, water stability and recyclability. This review will support future efforts in synthesizing new biocompatible MOFs as an environmental treatment technology that can effectively remove EDCs from water, thereby improving environmental and human health.


1. Introduction

As the world population increases, water has become a crucial resource for domestic, commercial and industrial uses. These activities can lead to increased levels of contaminants being discharged. Various types of contaminants are found in water bodies, including endocrine-disrupting compounds (EDCs) (Schuwirth et al., 2018). Most EDCs originate from consumer products such as pesticides, personal care products, plastics and detergents (Liu et al., 2019aLiu et al., 2019bLiu et al., 2019c). These compounds are chemically active and can harm humans and animals by impacting the central nervous system and reproductive system (Wee and Aris, 2017). Even at trace levels, EDCs have a strong effect on the endocrine system and can bioaccumulate in the body (Ismail et al., 2017Jun et al., 2019Puma et al., 2010). EDCs constitute a wide range of both natural (e.g., hormones) and synthetic (e.g., industrial by-products) exogenous and emerging chemicals (Wee and Aris, 2017). EDCs are released into the environment through sewage systems and can then be taken up by organisms (Ismail et al., 2017). Fig. 1 depicts the sources and transport of EDCs through the environment before being taken up by humans. Numerous types of EDCs (Table 1) have been detected in wastewater treatment plant discharge and water bodies, such as pharmaceuticals and medical drugs (e.g. propranolol, ibuprofen and diclofenac), steroid hormones (e.g. testosterone, progesterone, 17β-estradiol and 17α-ethynylestradiol), polyhalogenated compounds (e.g. perfluorooctanoic acid and perfluorooctanesulfonic acid) and phenolic compounds (e.g. bisphenol A, bisphenol S and bisphenol F). These compounds are difficult to remove due to their hydrophobic characteristic and resistance to biodegradation (Jun et al., 2019Joseph et al., 2019Aris et al., 2014Zuo et al., 2013).


Water treatment plants play a vital role in controlling the fate and transport of EDCs in the aquatic environment. These compounds can easily flow through the treatment system and are discharged into the environment without being removed by the treatment process (Can et al., 2014). Therefore, it is urgent to monitor the concentration of EDCs in the water system. Analytical instrumentation is often applied to detect EDCs present in water samples upon discharge (Kasonga et al., 2021Basile et al., 2011), and treatment plants can remove a substantial amount of EDCs. However, treatment processes are unable to eliminate low concentrations of EDCs in water (Gadupudi et al., 2019). To remove EDCs from the water system, several types of treatment methods have been considered, for example, advanced oxidationozonationelectrochemical oxidation and photocatalytic decomposition (Jun et al., 2019). Bertanza et al. (2010) applied an advanced oxidation process of UV/H2O2 and ozonation to treat effluent and eliminated several phenolic compounds; however, the process showed only approximately 70% removal. These methods are not amenable for treating industrial wastewater, as the high concentrations of contaminants would lead to high costs and consume a large amount of energy.

These advanced methods are too expensive because of high operational and capital costs (Guerra et al., 2015). As an alternative, adsorption-based treatment has been reported as the most suitable method for EDC removal, as this method is inexpensive and more efficient (Fig. 2) (Lim and Aris, 2014). Moreover, adsorption materials have been widely used in water and wastewater treatment due to their strong interactions with hydrophobic organic contaminants such as EDCs (Joseph et al., 2019). Adsorbents used in adsorption treatment can be either natural organic, natural inorganic, or synthetic materials (Ndimele et al., 2018). Metal-organic frameworks (MOFs) are synthetic materials that have received considerable attention due to their useful characteristics such as diverse geometries, high porosity, thermal stability, selectivity and recyclability (Sun et al., 2019Kadhom and Deng, 2018Li et al., 2018a, ; Aris et al., 2020Jun et al., 2019). MOFs are metal–ligand coordination polymers constructed by a covalent bond between metals clusters and organic ligands, forming various porous frameworks such as one-dimensional (1D) chains, two-dimensional (2D) interpenetrating layers and three-dimensional (3D) materials (Alhamami et al., 2014He et al., 2010). A range of structural, magnetic, electrical, optical and catalytic properties can be incorporated through the choice of metal cluster and organic linker (Razavi and Morsali, 2019). Unlike other porous materials, a typical crystalline MOF structure has a porosity of over 50%, and the surface areas of MOFs range between 1000 and 10,000 m2/g. These values are larger than those of typical porous materials such as carbons and zeolites (Furukawa et al., 2013). Thus, MOFs can be used in specific applications, especially for gas capture, drug delivery, as catalysts and sensors, in separation/purification and as electrical conductors (Sun et al., 2020Dhakshinamoorthy et al., 2011Lazaro and Forgan, 2019Mahata et al., 2017Pi et al., 2018Sun et al., 2016). Many studies have exploited the ability of MOFs to adsorb contaminants in aqueous media. A material that is workable in an aqueous medium should ideally meet the following seven criteria: (i) high adsorption capacity; (ii) high selectivity; (iii) fast adsorption kinetics; (iv) regeneration ability; (v) long-term stability; (vi) tolerance to the other compounds; and (vii) low production cost (Abdelnaby et al., 2018).




Fahren Fazzer Sukatis, Sze Yee Wee & Ahmad Zaharin Aris 

Department of Environment, Faculty of Forestry and Environment, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

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Date of Input: 05/08/2022 | Updated: 05/08/2022 | lanjoy2006@g.mail.com


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