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β-Cyclodextrin functionalized SBA-15 via amide linkage as a super adsorbent for rapid removal of methyl blue

https://doi.org/10.1016/j.jcis.2020.09.006Get rights and content

Highlights

  • SBA15-A-CD was facilely prepared via postsynthetic modification of SBA-15.

  • Multi-functionalization with β-CD and amine can enhance the methyl blue adsorption performance.

  • The maximum adsorption capacity of SBA15-A-CD2 for methyl blue was 1790.92 mg·g−1.

  • Adsorption mechanism was proposed through theoretical calculation and 2D NMR.

Abstract

To remove the bulky aqueous organic dye e.g. methyl blue (MB) from water, ordered mesoporous silica SBA-15 has been functionalized with β-cyclodextrin (β-CD) via amide linkage. The surface physical and chemical properties of the surface of the resulted β-CD-functionalized adsorbents (abbrev. SBA15-A-CD) were characterized systematically. The results indicate that the channels of SBA-15 were uniformly modified with amine groups and were further β-CD-terminated via amide linkages, without ruining its ordered mesoporous structure. The effects of contact time, pH, ionic strength, temperature and salt on the adsorption performance were explored. SBA15-A-CD showed maximum adsorption capacity for MB up to 1791 mg·g−1 combined with excellent recyclability. Besides, the adsorption behavior of MB onto SBA15-A-CD has been investigated by DFT calculation and two-dimensional NMR. Specifically, the enhanced adsorption capacity for MB stems from the tailored host–guest interaction between β-CD cavity and aromatic moiety of MB in combination with the electrostatic attraction between amine groups and sulfonated group of MB. These findings offer good opportunities for improving the ability of mesoporous silica in adsorption of bulky anion dyes in wastewater.

Introduction

Methyl blue (MB) is a typical bulky anionic dye, which consists of a triamino-triphenylmethane group and sodium aromatic sulfonate groups (Scheme 1a). Due to its xenobiotic and antiseptic properties, MB is widely used in a number of biological and industrial applications, such as microscopic staining, textile and leather production [1], [2]. The widespread use of MB inevitably leads to emission of wastewater containing MB, and the discharge of MB contained wastewater would be undoubtedly escalated worldwide especially in China while its economy has been experiencing rapid growth. MB present in the industrial effluent, like most other synthetic dyes, is hardly-biodegradable and recalcitrant, posing potential threat to human beings. Therefore, it is urgently needed to remove MB from the related wastewater.

In the last decade, several technologies have been used and evaluated for remediation of MB contaminated water, including chemical degradation,[3] photocatalytic degradation, [4] and adsorption [5], [6], [7]. Among them, adsorption treatment is of special concern due to the merits of high efficiency, simple operation and low cost, etc. There are many existing reports concerning removal of MB from aqueous solution with numerous adsorbents, such as graphene based sorbents, [8], [9], [10] modified clays, [11], [12] inorganic porous microspheres, [13], [14] magnetic particles, [15], [16] metal organic frameworks, [17], [18] and polymeric adsorbents [19], [20]. However, compared to their excellent ability for adsorbing the low-molecular-weight dyes, the above adsorbents mostly exhibited moderate adsorption properties to MB with the molecular weight of 799.8 g·mol−1. The current limitation observed in these most extensively studied microporous adsorbents for removal of common toxic dye can be assigned to a mass transport limitation that the small-sized pores are too narrow to accommodate the bulky MB molecules and thus prone to be completely blocked. Given active site accessibility and easy elution of MB during adsorption/desorption processes, it is desired to fabricate efficient adsorbent using ordered mesoporous materials as matrix.

As one of the most prominent mesoporous silicas, hexagonally ordered silica SBA-15 exhibits many advantages in adsorption-related applications (especially for the large-molecule involved processes).[21] The highly ordered mesoporous structure with uniform pore size distribution facilitates the transfer of bulky molecules from the surface of SBA-15 into the pores, making high occupation of the pore.[22] Thus, SBA-15 has become a promising candidate for the fabrication of high-performance adsorbents. To improve the adsorption capacity of SBA-15, surface modifications have been used successfully in tailoring the surface chemistry. Many organic-functional groups have been applied to improve the adsorption capacity of SBA-15 for organic molecules [23], [24], [25], [26], [27]. Typically, a SBA-15/polyamidoamine dendrimer hybrid which was terminated with amine groups has been used for adsorption of anionic dyes [28]. However, to our best knowledge, few SBA-15 based adsorbent has been applied for MB adsorption.

It is well known that β-cyclodextrin (β-CD), a cyclic oligosaccharide with hydrophobic interior cavity, possesses remarkable ability to form inclusion complexes with a wide range of organic dyes (including MB) through host–guest interaction [29], [30], [31]. In particular, owing to the distinctive advantages such as low cost, easy access and abundance of hydroxyl groups on the external rim, β-CD has been widely explored to synthesize high-performance adsorbents. There have been numerous reports to immobilize β-CD on the matrix of various supports with differing strategies [32], [33]. For example, Kim et al. fabricated a hierarchically porous composite scaffold composed of SBA-15 and reduced graphene oxide functionalized with β-CD to remove bisphenol A from wastewater [34]. However, the tedious fabrication procedure in the above study decreased the synthetic efficiency to some extent. Hence, it is desirable to develop a simple and straightforward approach for constructing β-CD functionalized SBA-15 adsorbent.

Herein, β-CD functionalized SBA-15 via amide linkage (hereafter abbreviated as SBA15-A-CD) comprising multiple functional components was synthesized for MB removal from water according to Scheme 1, including: (1) SBA15: the ordered channels of mesoporous silica matrix that allows post-synthetic functionalization by amino-terminated silane coupling agent and accommodates adsorbate molecules; (2) A: the primary amine functions which were uniformly distributed in the channels of SBA-15 and partially transformed into amide groups in further amination; (3) CD: the pendent β-CD moieties which were chemically tethered to the amino-terminal by amidation. Clearly, SBA15-A-CD can be obtained by a facile, two-step and post-functionalization approach using SBA-15 as the matrix. Specifically, the channel of SBA-15 was amino-terminated through coupling reaction with 3-aminopropyltriethoxysilane, followed by amidation between the amine functions with the carboxyl groups of carboxymethyl-β-CD (CM-β-CD), affording the hybrid composites adsorbent SBA15-A-CD. To verify the successful functionalization of SBA-15 through the post-modification process, these samples were thoroughly characterized by various methods. Besides, in order to confirm the potential applications of the as-prepared hybrid, a series of adsorption experiments were conducted systematically. The adsorption enhancement mechanisms of SBA15-A-CD for removal of MB were also probed through theoretical calculation and 2D NMR technique. Our experiments show that SBA15-A-CD has excellent adsorption ability toward MB and other analogues of the bulky anion dye.

Section snippets

Chemicals

Pluronic P123 (EO20PO70EO20) triblock copolymer and methyl blue (MB) were provided by Sigma-Aldrich Reagent Co., USA. N-(3-Dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC⋅HCl, 97%), 4-dimethyl aminopyridine (DMAP, 99%), β-cyclodextrin (β-CD, >99%), Congo red (CR, 98%) and Rhodamine B (RB, 98%) were purchased from Adamas-beta Chemical Reagent Co., China. (3-Aminopropyl) triethoxysilane (APTES, 99%) was obtained from Macklin Chemical Reagent Co., China. Tetraethyl orthosilicate

Surface chemical properties

Firstly, the amination of SBA-15 and the subsequent immobilization of β-CD through amidation was monitored by FTIR. As shown in Fig. 1a, the stretching and bending vibration bands of Si-O-Si appear at 1086 and 799 cm−1, indicating the existence of Si-O-Si framework in the as-synthesized materials.[21] The spectrum on SBA15-A also registers the aliphatic Csingle bondH stretching vibration (2932 cm−1) and the bending vibration of Nsingle bondH (1547 cm−1). Moreover, compared with SBA-15, the apparent weakening of the

Conclusion

SBA15-A-CD was obtained by a facile two-step procedure involving amino-functionalization of SBA-15, followed by the amidation of CM-β-CD with amine functions. The as-synthesized hybrid adsorbents preserved the ordered mesoscopic structure after sequential modifications including the amine coupling procedure and further immobilization of β-CD, as confirmed by the characterization results. Systematical investigation on the adsorption properties of SBA15-A-CD2 toward MB was conducted. These

CRediT authorship contribution statement

Dongli Li: Investigation, Formal analysis, Writing - review & editing. Kungang Chai: Conceptualization, Supervision, Funding acquisition, Writing - review & editing. Xingdong Yao: Writing - review & editing. Liqin Zhou: Software. Kongyou Wu: Formal analysis. Zhenghui Huang: Investigation. Juntao Yan: Investigation. Xingzhen Qin: Formal analysis. Wei Wei: Formal analysis. Hongbing Ji: Conceptualization, Supervision, Funding acquisition, Writing - review & editing.

Declaration of Competing Interest

The authors declared that there is no conflict of interest.

Acknowledgments

This work was supported by National Natural Science Foundations of China (21868002 and 21961160741), the Natural Science Foundation of Guangxi Province (No. 2018GXNSFAA281206), Specific research project of Guangxi for research bases and talents (AD18126005), and special funding for ‘Guangxi Bagui Scholars’. Theoretical calculations were done using the computing facilities of the High-Performance Computing Center in Guangxi University.

References (47)

  • Q. Gao et al.

    Ultrafast and high-capacity adsorption of Gd(III) onto inorganic phosphorous acid modified mesoporous SBA-15

    Chem. Eng. J.

    (2017)
  • X.D. Sun et al.

    New sucker-type precise capturer of tobacco specific nitrosamines derived from the SBA-15 in situ modified with polyaniline

    Chem. Eng. J.

    (2018)
  • H. Wu et al.

    Functionalization of SBA-15 mesoporous materials with 2-acetylthiophene for adsorption of Cr(III) ions

    Microporous Mesoporous Mater.

    (2020)
  • Y. Zhou et al.

    A novel amphoteric β-cyclodextrin-based adsorbent for simultaneous removal of cationic/anionic dyes and bisphenol A

    Chem. Eng. J.

    (2018)
  • H. Zheng et al.

    Investigation of the adsorption mechanisms of Pb(II) and 1-naphthol by beta-cyclodextrin modified graphene oxide nanosheets from aqueous solution

    J. Colloid Interface Sci.

    (2018)
  • A.Z. Badruddoza et al.

    Carboxymethyl-β-cyclodextrin conjugated magnetic nanoparticles as nano-adsorbents for removal of copper ions: synthesis and adsorption studies

    J. Hazard. Mater.

    (2011)
  • W. Humphrey et al.

    VMD: visual molecular dynamics

    J. Mol. Graphics

    (1996)
  • H. Li et al.

    Hyper-crosslinked beta-cyclodextrin porous polymer: an adsorption-facilitated molecular catalyst support for transformation of water-soluble aromatic molecules

    Chem. Sci.

    (2016)
  • N. Liu et al.

    Synthesis a graphene-like magnetic biochar by potassium ferrate for 17beta-estradiol removal: Effects of Al2O3 nanoparticles and microplastics

    Sci. Total Environ.

    (2020)
  • R. Lin et al.

    Selective adsorption of organic pigments on inorganically modified mesoporous biochar and its mechanism based on molecular structure

    J. Colloid Interface Sci.

    (2020)
  • V. Vimonses et al.

    Kinetic study and equilibrium isotherm analysis of Congo Red adsorption by clay materials

    Chem. Eng. J.

    (2009)
  • K. Chai et al.

    Dual functional adsorption of benzoic acid from wastewater by biological-based chitosan grafted β-cyclodextrin

    Chem. Eng. J.

    (2012)
  • Q. Huang et al.

    A phenyl-rich β-cyclodextrin porous crosslinked polymer for efficient removal of aromatic pollutants: Insight into adsorption performance and mechanism

    Chem. Eng. J.

    (2020)
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