Fabrication of CeVO4 as nanozyme for facile colorimetric discrimination of hydroquinone from resorcinol and catechol

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Highlights

  • As the chromogenic catalyst, CeVO4 exhibits high catalytic activity, stability, low cost, ease of preparation, and excellent reproducibility.

  • CeVO4 was demonstrated to exhibit dual enzyme activities for the first time.

  • A colorimetric method for the discrimination of hydroquinone from resorcinol and catechol was developed based on the mimic oxidase activity of CeVO4.

  • The proposed colorimetric sensing method has a good selectivity.

Abstract

A simple method was proposed for the preparation of CeVO4. The as-synthesized CeVO4 was, for the first time, demonstrated to exhibit both peroxidase-like and oxidase-like activity, which catalyzes the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) to form a typical blue solution in the presence or absence of H2O2. Moreover, the mechanism of its dual-enzyme activity was investigated in detail. The Michaelis constant (Km) value for CeVO4 (0.136 mM) was lower than that of horseradish peroxidase (0.424 mM) with TMB as the substrate. Interestingly, hydroquinone (H2Q), dihydroxybenzene isomer, undergoes reduction accompanying the oxidation of TMB by the CeVO4 oxidase mimic along with a visible color change, while the other two dihydroxybenzene isomers, i.e., resorcinol (RC) and catechol (CC), do not. Based on these findings, a colorimetric platform was developed to discriminate H2Q from RC and CC. Under optimal conditions, a linear relationship between the H2Q concentration and absorbance was observed from 0.05 to 8 μM, and a limit of detection of 0.04 μM was achieved. Moreover, this colorimetric platform can selectively reveal H2Q concentrations in the presence of other dihydroxybenzene isomers.

Introduction

Discriminating isomers of organic compounds is an important challenge in analytical and organic chemistry owing to their similar physiochemical properties [1], [2]. Hydroquinone (H2Q), resorcinol (RC), and catechol (CC) are three isomers of dihydroxybenzene, are often present as contaminants in food, medical, and environmental samples [2]. They are regard as second kind of environmental contaminants because of their low degradability and toxicity to humans [3], [4]. H2Q is an important intermediate in the production of mono- and dialkyl ethers, and is used as a photographic developer, a paint stabilizer, and an excellent de-pigmenting agent. However, in addition to these beneficial aspects, it also harm to humans [5]. Therefore, the discrimination of H2Q from RC and CC is highly important to guarantee human health.

A number of methods are currently used for the determination of H2Q, such as liquid chromatography [6], flow-injection chemiluminescence [7], gas chromatography/mass spectrometry [8], electrochemical methods [9], pH-based-flow injection analysis [10], and fluorescence methods [11]. These methods exhibit good sensitivity and specificity; however, they also present several disadvantages, including high operational costs, the need for complicated sample pretreatments, and long analysis times, all of which limit their application. Colorimetric analysis may represent a favorable means of H2Q detection owing to its simplicity, rapidity, and low cost. Moreover, it can be used for field analysis by the naked eye [2], [12].

In recent years, a number of nanozyme-based sensors have emerged as important colorimetric tools owing to their inherent advantages of low cost, excellent stability, and ease of preparation over natural enzymes. A number of nanozymes have been widely used in the detection of species such as H2O2, glucose, ascorbic acid, biothiols, dopamine, melamine, sulfite, metal ions, and immunological agents [13]. However, the application of nanozymes to the colorimetric organic isomers is limited. Very recently, Zhao et al. [14] reported that Fe3O4/nitrogen-doped graphene quantum dot hybrids exhibit peroxidase-like activity, and used them for discriminating the isomers of organic compounds by means of color changes. This was the first report that nanoenymes could be used for the discrimination of organic isomers based on their catalytic activity. Thus, the use of nanozymes for colorimetric discrimination of organic isomers is a promising technique and requires further investigation.

Cerium vanadate (CeVO4) is an important semiconductor with a wide band gap (3.1–4.2 eV), and has attracted wide interest due to the suitability of its catalytic and electronic properties for application in electrochromic materials and gas sensors [15]. Very recently, Han et al. [16] reported that EDTA-assisted CeVO4 nanorods exhibited peroxidase-like activity, and used them for H2O2 detection. These CeVO4 nanorods presented several advantages, such as environmental benignity, nanostructure stability, desirable catalytic activity, and ease of separation and recycling. However, the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by the CeVO4 nanorods required the addition of an unstable H2O2-oxidation agent. Recently, a number of ceria-TMB systems were found to use for various colorimetric sensing based on their peroxidase-like activity or oxidase-like activity. These ceria-TMB systems only exhibit peroxidase-like activity or oxidase-like activity, which will limit their a wide of application [17]. Therefore, further research into the mimicking enzyme catalytic activity of CeVO4 is required. To the best of our knowledge, there have been no reports of the dual-enzyme activity of CeVO4 being used for colorimetric discrimination of the isomers of dihydroxybenzene.

In this paper, CeVO4 is reported to possess dual-enzyme-mimic activity for the first time. A facile and simple hydrothermal method was applied for CeVO4 synthesis. CeVO4 catalyzes the oxidation of TMB to generate a typical blue color. However, H2Q inhibits the generation of the blue color owing to its reducibility (Scheme 1). Based on these findings, a fast and facile colorimetric method was developed for the discrimination of H2Q from RC and CC.

Section snippets

Materials

O-phenylenediamine (OPD), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), and TMB were purchased from TCI (Shanghai, China). Acetic acid (HAc), H2O2 (30 wt%), and sodium acetate (NaAc) were purchased from Shantou Xilong Chemical Co., Ltd. (Guangdong, China). Tert-butyl alcohol, CC, RC, hydroethidine (HE), H2Q, cerium nitrate hexahydrate (Ce(NO3)3·6H2O), and ammonium metavanadate (NH4VO3) were obtained from Aladdin Chemistry Co., Ltd. (Shanghai, China). 3,3′-diaminobenzidine (DAB),

Characterization of CeVO4

XRD patterns of CeVO4 are shown in Fig. 1a. The diffraction peaks correspond to tetragonal CeVO4 (JCPDS card No. 12-0757, Cell = 7.399 × 6.496, α = 90°, β = 90°, γ = 120°). No impurity peaks are observed, which demonstrates that the as-synthesized CeVO4 is highly crystalline and good pure. Moreover, the structure of CeVO4 remains intact after the catalytic reaction and four H2Q detection experiments. The structure of CeVO4 was further analyzed by Raman spectroscopy (Fig. 1b). The peaks at 773 and 841 cm−1

Conclusions

In summary, a simple and environmentally benign method was developed to fabricate the CeVO4, which exhibits both peroxidase and oxidase-like activity, which were both investigated. The peroxidase-like catalytic activity of CeVO4 stemmed from the production of radical dotOH radicals upon H2O2 decomposition, while the oxidase-like catalytic activity of CeVO4 originated from the generation of ROSs. CeVO4 catalyzes oxidation of TMB to generate a blue color without adding H2O2, and H2Q inhibits oxidation of

Acknowledgements

The financial support from the National Natural Science Foundation of China (21365005), Guangxi Natural Science Foundation of China (2014GXNSFGA118002) and Guangxi Pharmaceutical Industry Talent Highland Project (1414) is gratefully acknowledged.

Haiguan Yang is currently a M.S. candidate in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. Her current interests are nanozymes.

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  • Cited by (0)

    Haiguan Yang is currently a M.S. candidate in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. Her current interests are nanozymes.

    Junqi Zha is currently a B.S. candidate in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. His current research topic is colorimetric sensors

    Peng Zhang is currently a M.S. candidate in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. Her current interests are monolithic stationary phase.

    Yuemei Qin is currently a M.S. candidate in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. Her current interests are nanozymes.

    Tao Chen is currently a M.S. candidate in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. His current interests are sample pretreatment

    Fanggui Ye is a professor in the College of Chemistry and Pharmaceutical Science of Guangxi Normal University. His main research interests are focused on nanozymes, chromatography and sample pretreatment.

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