Elsevier

Carbohydrate Polymers

Volume 252, 15 January 2021, 117163
Carbohydrate Polymers

Enhancing the removal of organic and inorganic selenium ions using an exfoliated kaolinite/cellulose fibres nanocomposite

https://doi.org/10.1016/j.carbpol.2020.117163Get rights and content

Highlights

  • Exfoliated kaolinite/cellulose fibers was used in the uptake of different Se ions.

  • The qmax of Se (VI), Se(IV), and SeMt are 137, 161, and 95 mg/g, respectively.

  • The uptake behavior of the Se ions follow Langmuir and Pseudo-First order models.

  • The uptake energies of the Se ions (<8 kJ/mol) suggesting physisorption reactions.

  • The uptake of the three Se ions occurred by exothermic and spontaneous reactions.

Abstract

Exfoliated kaolinite sheets/cellulose fibres nanocomposite (EXK/CF) was synthesised as a novel hybrid of materials of enhanced surface area and adsorption capacities for inorganic—selenate [Se(VI)] and selenite [Se(IV)]—and organic selenium pollutants—selenomethionine (SeMt). The adsorption reactions of the addressed selenium forms followed pseudo-first-order as a kinetic model and Langmuir as an isotherm model. The fitting results and the calculated Gaussian energies—Se (VI) at 2.0 KJ/mol, Se (IV) at 2.2 KJ/mol, and SeMt at 1.7 KJ/mol—suggested physisorption uptake in a monolayer and homogeneous form. The theoretical maximum selenium uptake capacity (qmax) for Se (VI), Se (IV), and SeMt was 137.5 mg/g, 161.4 mg/g, and 95.4 mg/g, respectively. The thermodynamic investigation verified spontaneous and exothermic properties of the selenium uptake reactions by the EXK/CF composite.

Introduction

Groundwater is the main freshwater supply and essential strategic reserve for several countries throughout the world (Zeeshan, Khan, Shafiq, & Sabir, 2020). The contamination of groundwater by leached elements from natural mineral, rock, and soil components during mining and agricultural activities create the primary challenge to keep water supplies at the required levels for purity and safety (Abukhadra, Bakry, Adlii, Yakout, & El-Zaidy, 2019; Abukhadra, Refay, El-Sherbeeny, Mostafa, & Elmeligy, 2019). Selenium (Se) is a commonly detected element in groundwater. Generally, it is a vital element that positively affects human and animal health when present at its recommended level. Additionally, Se is a significant industrial element in the production of particular drugs, photosensitive materials, and semiconductor products (Lounsbury et al., 2019). Notably, selenium at specific concentrations possesses toxic and carcinogenic properties (Xu et al., 2020; Zeeshan et al., 2020).

Selenium is a metalloid component and exists in four oxidation states: selenite, or Se(IV); selenate, or Se(VI); selenide, or Se(-II); and native selenium element, or Se(0), species (Cui, Li, Wang, Zheng, & Zhang, 2018; Xu et al., 2020). Selenite and selenate are the principal species in the aquatic system with toxic properties if they exist at a concentration of 50 μg/L (Xu & Huang, 2019). Such species have dangerous health effects, including (a) the irritation of eyes and skin, (b) gastrointestinal disorders, (c) the loss of nails and hair, (d) neurological damage, and (e) monstrous deformities (He, Su, Chen, & Hu, 2020).

The adsorption decontamination of Se (IV) has been endorsed as an effective technique to achieve successful removal results; however, it has been reported as an inferior technique during the decontamination of Se (VI) ions (Xu et al., 2020). Moreover, selenium as a water pollutant has been detected in organic forms as selenocysteine (C3H7NO2Se) and selenomethionine (C5H11NO2Se), relating to the metabolic activities of some microorganisms. Furthermore, organic forms of selenium as water pollutants have been categorised as toxic and dangerous compounds as compared to inorganic forms because of the high solubility properties of organic forms in lipids and their high diffusion rates during the penetration of the cell membranes that cause rapid damage to or failure of the organs (Santra & Sen, 2019).

Therefore, numerous experimental and theoretical studies have been completed to develop advanced types of simple adsorbent products that are of better affinity for the existing selenium species in both inorganic and organic forms. The commonly studied adsorbents for this target have included polyamine/magnetic graphene oxide composite (Lu, Yu, Zeng, & Liu, 2017), Ca − Al − Cl LDH (Xu, Dong, Guo, Wen, & Jie, 2019), Fe-Al-Cl-LDH/ZVI (Xu & Huang, 2019); MgO nanosheets (Cui et al., 2018), chitosan/clay composite (Bleiman & Mishael, 2010); apatite (Moore, Rigali, & Brady, 2016), iron oxy-hydroxides (Kalaitzidou, Nikoletopoulos, Tsiftsakis, Pinakidou, & Mitrakas, 2019); Fe-impregnated biochar (Hong et al., 2020); hematite (Ma, Shan, Liang, & Tong, 2018), and Mg–FeCO3 LDH/cellulose fibres (Chen & An, 2012).

Nevertheless, little research has focused on the experimental efficiency of known or new clay mineral-based adsorbents in the effective removal of selenium, especially in their advanced modified forms. Clay minerals refer to broad groups of layered silicate natural materials that exhibit noticeable ion exchange properties, significant surface areas, and valuable adsorption capacities. Moreover, such minerals are naturally available and widely distributed (Abukhadra, Bakry et al., 2019; Abukhadra, Refay et al., 2019; Dardir, Mohamed, Abukhadra, Ahmed, & Soliman, 2018). From these clay minerals, kaolinite, which has a 1:1 layered structure and a hydrous aluminium silicate composition, has been used extensively in numerous environmental and industrial applications (Shaban, Sayed, Shahien, Abukhadra, & Ahmed, 2018). The organic and inorganic modification of kaolinite shows promise in prompting the surface reactivity of its sheets as well as its surface area and directing its adsorption affinity for specific ions that support its technical value in the decontamination of different species of water pollutants (Shaban et al., 2018; Tan, Yuan, Annabi-Bergaya, Liu, & He, 2014).

Recently, exfoliation of the layered structure of common clay minerals into single sheets has been recommended as a promising modification technique, resulting in the significant enhancement of surface reactivity, surface area, and adsorption capacities of clay minerals (Abukhadra, Bakry et al., 2019; Abukhadra, Refay et al., 2019; Ma et al., 2016). While several studies have focused on the environmental and technical qualifications of exfoliated montmorillonite, unfortunately, little research has focused on the production of exfoliated kaolinite sheets. Moreover, no previous studies have demonstrated its application as an advanced adsorbent.

Notably, the combination of exfoliated kaolinite sheets and cellulose fibres as natural biopolymers of excellent technical properties are expected to result in a novel composite of promising adsorption capacity of these metal ions with enhanced affinity for both organic and inorganic forms (Abukhadra, Bakry et al., 2019; Abukhadra, Refay et al., 2019). Cellulose is a known natural biopolymer that is classified as polysaccharide polymer and plays a vital role in numerous industrial, medical, and environmental applications (Putro, Santoso, Ismadji, & Ju, 2017). Structurally, cellulose polymer chains are composed of two essential anhydroglucose rings that bind to each other by b-1,4 glycoside bonds. Additionally, these cellulose-based materials are safe, non-toxic, and highly reactive products that possess excellent adsorption properties and significant surface area (Fakhri, Tahami, & Nejad, 2017; Pooresmaeil, Javanbakht, Nia, & Namazi, 2020).

Based on these considerations, the presented manuscript involved the synthesis of exfoliated kaolinite sheets/cellulose fibres composite (EXK/CF) as a novel composite with an enhanced adsorption affinity for toxic species selenium pollutants selenite: Se (IV), Se (VI), and SeMt (C5H11NO2Se). The study involved the detection of their adsorption behaviours and optimisation for the best removal factors as well as equilibrium and thermodynamic properties.

Section snippets

Materials

The raw kaolinite was obtained from Central Metallurgical Research & Development Institute in Egypt. Cetyltrimethylammonium bromide (CTAB), high purity methanol, and analytical-grade dimethyl sulfoxide (DMSO) to be used as exfoliation reagents were obtained from Sigma-Aldrich, Egypt. Crystalline cellulose fibres were used in the preparation of the composite of exfoliated kaolinite. Sodium selenite (Na2SeO3), sodium selenate (Na2SeO4), and selenomethionine (C5H11NO2Se) were used as sources for

X-ray powder diffraction (XRD) analysis

As a raw material, kaolinite is distinguished by its essential peaks at 12.3º, 20.8°, 24.9º, and 26.6° relating to high-crystalline kaolinite of a triclinic system and corresponding to its (001), (-110), (002), and (111) crystallographic planes, showing the d-spacing value of 0.7 nm (Fig. 1A). The XRD pattern of DMSO-intercalated kaolinite reflected a reduction of several kaolinite-related peaks with a noticeable detection for two peaks only, (001) and (002), which were observed as deviated

Conclusion

The integration between the kaolinite as exfoliated sheets and the cellulose fibres resulted in an advanced hybrid structure of an enhanced surface area, surface reactivity, and multifunctional active groups. Considering the previous enhancement in the physicochemical properties of the EXK/CF composite, the hybrid structure was applied for the effective decontamination of different species of selenium as water pollutants: Se (VI), Se (IV), and SeMt. Moreover, the EXK/CF composite showed changes

CRediT authorship contribution statement

Mostafa R. Abukhadra: Conceptualization, Project administration, Visualization, Formal analysis, Writing - original draft, Writing - review & editing. Ali AlHammadi: Data curation, Formal analysis, Software, Writing - review & editing, Writing - original draft. Ahmed M. El-Sherbeeny: Project administration, Funding acquisition, Writing - review & editing, Funding acquisition, Investigation. Mohamed Abdel Salam: Conceptualization, Writing - original draft, Writing - review & editing. Mohammed A.

Acknowledgment

The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group number (RG-1440-047).

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