In situ Functionalized Mesoporous Silicas for Sustainable Remediation Strategies in Removal of Inorganic Pollutants from Contaminated Environmental Water

Natalia G Kobylinska; Vadim G Kessler; Gulaim A Seisenbaeva; Oksana A Dudarko

doi:10.1021/acsomega.2c02151

In situ Functionalized Mesoporous Silicas for Sustainable Remediation Strategies in Removal of Inorganic Pollutants from Contaminated Environmental Water

ACS Omega. 2022 Jul 1;7(27):23576-23590. doi: 10.1021/acsomega.2c02151. eCollection 2022 Jul 12.

Authors

Natalia G Kobylinska¹, Vadim G Kessler², Gulaim A Seisenbaeva², Oksana A Dudarko³

Affiliations

¹ A.V. Dumansky Institute of Colloid and Water Chemistry, NAS of Ukraine, blvd. Akad. Vernads'koho, 42, Kyiv 03680, Ukraine.
² Department of Molecular Sciences, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden.
³ Chuiko Institute of Surface Chemistry of NAS of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine.

Abstract

Low-cost mesoporous silicas of the SBA-15 family were prepared, aimed for removal of a broad spectrum of both cationic and anionic forms of hazardous metal pollutants (Cr(III, VI), Mn(II, VII), Pb(II), Cd(II), and Cu(II)) from environmental water. Series of mono- and bifunctional materials with immobilized ethylenediaminetriacetic acid (EDTA), primary amine (NH₂), and quaternary ammonium (QAS) groups were prepared in a cost-efficient one-step synthesis using two silica sources, low-cost sodium metasilicate (Na₂SiO₃ 9H₂O) and the conventional source-tetraethylorthosilicate (TEOS). The functionalized SBA-15 samples obtained from both silica sources were highly ordered, as evidenced by TEM and SAXS data. All obtained materials were mesoporous with high surface area values of up to 745 m²/g, pore volumes from 0.99 to 1.44 cm³/g, and narrow pore distributions near 7 nm. The adsorption affinity of the EDTA-functionalized samples followed the common order Pb(II)> Cd(II)> Cu(II)> Cr(III)> Mn(II), which could be explained based on the Pearson theory. The highest adsorption capacities were observed for samples functionalized by EDTA groups using TEOS for synthesis (TEOS/EDTA): 195.6 mg/g for Pb(II), 111.2 mg/g for Cd(II), 58.7 mg/g for Cu(II), 57.7 mg/g for Cr(III), and 49.4 mg/g for Mn(II). Moreover, organic matter (humic acid up to 10 mg/L) and inorganic (Na(I), K(I), Mg(II), Ca(II), etc) macrocomponents present in environmental water had almost negligible effect on the removal of these cations. The NaSi/EDTA/NH₂ sample revealed a better selectivity compared to the NaSi_/NH₂ sample towards such species as Cr(III), Mn(II), Cd(II), and Cu(II). The chromate-ions uptake at pH 7.5 by the TEOS/QAS sample turned practically unaffected by the presence of doubly charged anions (CO₃ ^2-, SO₄ ^2-). The content of functional groups on the surface of MS decreased only slightly (∼1-5%) after several regeneration cycles. The complete desorption of all heavy metal ions can be achieved using 1 mol/L EDTA solution. Reusability tests demonstrated the complete stability of the adsorbent for at least five to six consecutive adsorption/desorption cycles with no decrease in its adsorption characteristics compared to those obtained by 0.05 mol/L HNO₃ treatments. The synthesized mesoporous materials were evaluated for removal of the heavy metal ions from drinking and different natural water samples, proving their potential as sustainable, effective, and cost-efficient adsorbents.