Elsevier

Talanta

Volume 204, 1 November 2019, Pages 224-228
Talanta

Fabrication of a covalent organic framework and its gold nanoparticle hybrids as stable mimetic peroxidase for sensitive and selective colorimetric detection of mercury in water samples

https://doi.org/10.1016/j.talanta.2019.05.086Get rights and content

Highlights

  • A novel composite COF-AuNPs was fabricated.

  • COF-AuNPs show high stability as mimetic peroxidase in the presence of Hg2+.

  • A sensitive and selective method was developed for the determination of Hg2+.

Abstract

Gold nanoparticles (AuNPs) without surface capping agents are easily aggregated owing to their high surface energy, leading to an unexpected decrease of their catalytic activity. Herein, we report gold nanoparticles decorated covalent organic framework (COF) as mimetic peroxidase for colorimetric detection of mercury. 1,3,5-Tris-(4-formyl-phenyl)triazine (PT) and 4, 4′-azodianiline (Azo) was employed as the monomers to prepare a novel imine based COF PTAzo under solvothermal conditions. AuNPs are further decorated into the PTAzo to form COF-AuNPs hybrid via a citrate reducing method. The COF-AuNPs show high stability, and exhibits enhanced peroxidase mimetic activity in the presence of Hg2+. The Hg2+ concentration dependent peroxidase mimetic activity of COF-AuNPs enables the development of a sensitive and selective method for detection of Hg2+ in aqueous solution. The developed method gives good linearity in the range of 5–300 nM with the limit of detection of 0.75 nM. The results show that Hg2+-enhanced peroxidase mimetic activity of COF-AuNPs offers great potential for the detection of Hg2+ in real samples.

Graphical abstract

A novel imine based covalent organic framework and gold nanoparticle composite COF-AuNPs was fabricated as stable mimetic peroxidase for sensitive and selective colorimetric detection of mercury.

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Introduction

Gold nanoparticles (AuNPs) have attracted immense interest due to their excellent catalytic activity [[1], [2], [3]]. The catalytic performance of AuNPs highly depends on their dispersibility and accessibility [4]. However, AuNPs without surface capping agents are easily aggregated owing to their high surface energy, leading to an unexpected decrease of their catalytic activity [5,6]. Therefore, a method that prevents AuNPs from aggregation while keeps their intrinsic catalytic activity is highly desirable.

Covalent organic frameworks (COFs) are porous crystalline materials orderly linked by organic monomers [[7], [8], [9]]. Owing to their unique properties and structures, such as large surface area, predicable structures and low density, COFs have shown high potential for applications in diverse fields such as sensing [[10], [11], [12]], catalysis [13,14] and separation [15]. Mercury ion (Hg2+) is a toxic heavy-metal pollutant in the environment. It can cause serious damage to humans and animals even at ppm levels of mercury accumulation [16]. To date, COFs-based approach has been developed for the detection of Hg2+ [11]. However, the selectivity and sensitivity of the aforementioned approach was limited due to the lack of specific recognition group and turn-off detection. Thus, a sensitive and selective COFs-based sensor for detection of Hg2+ is highly desired.

Integrating COFs with functional nanoparticles is an attractive way to enhance their performance such as solubility and broaden their applications [[17], [18], [19], [20], [21], [22]]. COFs provide rich metal binding sites due to the large surface area and the pre-designable pore size to allow rapid diffusion of substrate molecules [23]. The π electronic architecture is helpful to the absorption of substrate molecules [24,25]. Moreover, COFs can improve the thermal and chemical stability of AuNPs [17].

Herein, we report a one-step reducing method to prepare a highly stable COF supported AuNPs hybrids (COF-AuNPs) for colorimetric detection of Hg2+. A stable, crystalline and porous imine based COF PTAzo was synthesized from monomers 1,3,5-tris-(4-formyl-phenyl)triazine (PT) and 4, 4′-azodianiline (Azo) as an example. The COF-AuNPs show higher stable peroxidase mimetic activity than bare AuNPs. Hg2+-enhanced peroxidase mimetic activity of COF-AuNPs enables efficient oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 for sensitive and selective detection of Hg2+.

Section snippets

Reagents

All chemicals and reagents used are at least of analytical grade. Ultrapure water was purchased from Wahaha Foods Co. (Hangzhou, China). Azo, TMB, Hg(NO3)2, KNO3, Mg(NO3)2, HAuCl4 and sodium citrate were obtained from Sigma-Aldrich Co. LLC (St. Louis, MO, USA). 1,3,5-tris-(4-formyl-phenyl)triazine (PT) was obtained from Chengdu Tongchuangyuan Pharmaceutical Technology Co. (Chengdu, China). o-Dichlorobenzene (o-DCB), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and dichloromethane

Preparation and characterization of PTAzo

PTAzo was prepared from PT and Azo in a mixture of o-DCB and DMAc under solvothermal conditions (Fig. 1a). The monomer PT possesses planar structure that guarantees high crystalline stability and easy synthesis of PTAzo [26]. PTAzo contains triazine and N element to facilitate the formation of AuNPs. Such structures and properties make PTAzo an ideal platform for loading AuNPs.

PXRD pattern shows several peaks at 2.27°, 4.25°, 5.87° and 25.71°, being consistent with the simulated pattern for

Conclusions

In summary, we have reported a novel imine COF PTAzo and its AuNPs hybrid (COF-AuNPs) via one-step reducing method. The COF enhanced the stability while kept intrinsic catalytic activity of AuNPs. Based on Hg2+-enhanced peroxidase mimetic activity, COF-AuNPs show promising application in sensitive and selective detection of Hg2+ in real samples.

Notes

The authors declare no competing financial interest.

Acknowledgements

This work was supported by National Natural Science Foundation of China (Grant 21775056), the China Postdoctoral Science Foundation (Grants 2018M630511, 2018M630510), the National First-class Discipline Program of Food Science and Technology (Grant JUFSTR20180301), and the Fundamental Research Funds for the Central Universities (Grant JUSRP51714B).

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