Nickel foam decorated with ZnO nanocrystals using mesoporous silica templates for ultrasensitive electrogenerated chemiluminescence determination of diazinon
Introduction
Due to increase population in the world, need to agricultural products have constantly increased and thus the consumption of pesticides has dramatically increased. To manage pesticide usage, the Environmental Protection Agency (EPA) has controlled pesticides at different concentration levels. This variety of analysis for measuring different environmental and food samples has created a large potential for making different sensors [1]. Organophosphate pesticides (Ops) are a large group of pesticides that cause disease and death in humans. These problems are caused by various direct and indirect exposures of human with these pesticides. Therefore, developing a highly sensitive method for rapid and accurate determination of Ops is urgent [2]. Diazinon (Scheme 1) belongs to the organophosphate pesticide that is a subfamily of phosphorothioic acid and has a nonsystemic effect. Also, diazinon is a very effective pesticide and could control almost any insect [3]. The main application of diazinon is for rice, fruit trees, vineyards, cane, corn, cotton, tobacco, and potato [4]. So far, many effective methods have been used to determine low concentration levels of diazinon, including high performance liquid chromatography [5, 6], gas chromatography (GC) [7, 8], gas chromatography-mass spectrometry (GC–MS) [9], voltammetry [10], photocatalytic degradation [11] and a chemiluminescence methods [12]. However, these methods are expensive, and the duration of the tests are also long due to complicated pretreatment steps. Also, the detection limit of voltammetric techniques alone for determination of diazinon is not desirable. Electrogenerated chemiluminescence (ECL) method with its promising properties is a good choice and can meet necessary demands for a simple on-site analytical tool [13]. The ECL method can be performed by variety of luminophore compounds like luminol [14], ruthenium complexes [15, 16] and quantum dots [17]. This method with having high sensitivity and low background uses the high sensitivity of electrochemistry and wide linear range of chemiluminescence and therefore it is applied for clinical and environmental analysis such as glucose [18], biotoxin [19] and pesticide sensor [20, 21].
Zinc oxide (ZnO) is a nontoxic semiconductor and a member of the Wurtzite family which has a wide band gap (3.37 eV) II–VI with unique properties as high thermal resistance, high mechanical stability, superior piezoelectric and pyroelectric properties [22]. It can be synthesized by electrochemical and hydrothermal methods [23].This is an important material in electronic devices [24] in the last decade. Also, ZnO is one of the cheapest and richest nanostructures in the nanoscale which have a high-mobility semiconductor properties [25] and strong luminescence [26] at room temperature. That's why it's an ideal choice for a variety of sensors [27, 28], solar cells [29], transistors and photodetectors [30]. Also, according to the unique features of ZnO, photoluminescence (PL) [31], and ECL [32] properties of ZnO in nano scale have been investigated.
Metal foam as nickel foam is a new category of three-dimensional material. Due to its large active surface area, high charge storage capacity, high electrical and thermal conductivity and also unique electrocatalytic properties and a much higher loading amount of active materials per unit electrode area [33], it has been used in the construction of batteries [34], fuel cells [35], supercapacitors [36] and sensors [37]. In this study, the nickel foam electrode was modified with ZnO nanocrystals using the silica templates. The mesoporous silica was formed by electrochemically-assisted self-assembly (EASA) method on the three-dimensional Ni-foam electrode, and then ZnO nanocrystals were successfully electrodeposited on the Ni foam. After removing the silica templates, the fabricated modified electrode (ZnO/Ni-foam) was truly applied for determination of diazinon at low concentration levels by ECL method. To the best of our knowledge, this study is the first report on the ECL determination of diazinon.
Section snippets
Materials and apparatus
Diazinon (O, O-Diethyl O-[4-methyl-6-(propan-2-yl) pyrimidin-2-yl] phosphorothioate) was purchased from Sigma-Aldrich. Cetyltrimethylammonium bromide (CTAB, 99%), sodium nitrate, ethanol (95–96%) and HCl (37%) were purchased from Merck. zinc (II) nitrate (hexahydrate), and potassium chloride were purchased from the Fluka Company. All reagents were of analytical grade and were used as received without further purification. A commercial Ni foam (Liyuan Co from Changsha, China, 100 µm pore size,
Study of physical morphology of the modified electrode
To study of the electron transfer processes between the electrolyte and the electrode surface, the electrochemical impedance spectroscopy was performed in the frequency range of 100 kHz to 100 mHz. Fig 1A and the inset plot in Fig 1A show the Nyquist plots and the equivalent circuit model of the bare Ni-foam and ZnO/Ni-foam electrodes. The semicircular part of the Nyquist plot at high frequencies is related to the charge transfer impedance (Rct) appointed to combination of faradic charge
Conclusion
In summary, a novel ultrasensitive cathodic ECL pesticide sensor based on ZnO/Ni-foam electrode was firstly fabricated for determination of diazinon. Modification of the Ni-foam electrode with the ZnO nanocrystals was performed using the silica templates which uniformly covered on the surface of the nickel foam. Investigation results indicated that diazinon had a good enhancing effect on the ZnO/Ni-foam cathodic ECL owing to its coordinative interaction with ZnO and improving the radical
Declaration of competing interest
The authors whose names are listed immediately below certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in
Acknowledgments
The authors express their deepest appreciation to the Research Council of the University of Zanjan for support of this work.
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