Integrated polyaniline with graphene oxide-iron tungsten nitride nanoflakes as ultrasensitive electrochemical sensor for precise detection of 4-nitrophenol within aquatic media

https://doi.org/10.1016/j.jelechem.2020.114406Get rights and content

Highlights

  • Graphene oxide was synthesized and decorated with iron tungsten nitride

  • Polyaniline was reinforced with as prepared hybrid 2D nanoflakes

  • Developed nanocomposite was used for modification of glassy carbon electrode

  • Fabricated sensor detected the 4-Nitrophenol (4-NP) till nano molar level

  • Developed sensor proved to be highly sensitive and accurate toward detection of 4-NP

Abstract

Extensive release of highly toxic pollutants within the ecosystem resulting from industrial/human activities has adversely affected the life of living species and raised the requirement for development of sensitive/accurate detection systems for monitoring the level of hazardous pollutants within the ecosystem. Among these toxic pollutants, 4-nitrophenol (4-NP) and its derived compounds applied serious damages to the nature that require practical protocols to remove them from the environment. To address this demand, we boosted the polymeric structure and sensitivity of polyaniline (PANi) through its reinforcement with decorated graphene oxide (GO) nanoflakes with interconnected, porous and highly dense pattern of iron tungsten nitride (GO-ITN) toward modification of glassy carbon electrode (GCE) for precise and real-time detection of 4-NP within the aqueous media. The developed nanocomposite showed superior sensitivity along with improved protonation that exhibited detection limit/quantification limit/sensitivity of 5.2 nM/18.2 nM/253.08 μA.μM.cm−2 and 2.4 nM/7.1 nM/354.92 μA.μM.cm−2 for oxidation and reduction peak currents, respectively. The developed sensor also showed superior sensitivity toward detection of 4-NP within real samples which highlighting the capability and functionality of the developed sensor toward the real-time detection of 4-NP within different aqueous media.

Introduction

Nowadays, wide distribution of toxic substrates within the ecosystem and their resulting adverse consequences, raised a global requirement for finding practical approaches for their accurate determination and rapid removal from the nature. Among these toxic pollutants, 4-nitrophenol (4-NP) (i.e., 4-hydroxynitrobenzene or p-nitrophenol) as a highly toxic organic chemical compound with chemical formula of C6H5NO3 found to be highly problematic for life of living species due to its mutagenic, phyto- and cyto-toxic effects which known as a precursor for fabrication of pharmaceutical, dyes, papers, insecticides, herbicides and pesticides [[1], [2], [3]]. 4-NP exist in two polymorphs including alpha and beta, where the alpha type is colorless and stable under sunlight but unstable at room temperature (RT), while the beta form is yellow colored, stable at RT and unstable under sunlight [4].

Human being can be adversely affected by 4-NP through several pathways, including inhalation, ingestion and skin conduct. When this compound polluting the food chain, it could deteriorate the performance of liver and kidney, cause cancer in diverse parts of the body, and negatively affect the function of nervous system [5]. Moreover, 4-NP can lead to inflammation/irritation in eyes repiratory tract and nose. It also interact with the blood and generate methaemoglobin which is responsible for the methaemoglobinemia that lead to cyanosis unconsciousness and confusion [6]. Short term exposure to 4-NP may cause various kinds of health problems among which headaches, nausea, cyanosis and drowsiness can be mentioned [7]. Thus, due to these harmful effects, the U.S Environmental agencies considered the 4-NP as one of the most toxic pollutants for the life of living species and ecosystem, while 20 ppb (i.e., 0.14 μM) considered as the maximum permissible limit of this toxic compound within the aquatic environment [5,8].

So far, various methods have been utilized for precise detection of 4-NP within aqueous media, including UV–vis spectroscopy [9], liquid chromatography [10], fluorescence spectroscopy [11], capillary electrophoresis [12], gas chromatography [13], indirect enzymatic immunosorbent assay [14] and chemiluminescence [15]. Despite the fact that these methods can detect the 4-NP with high accuracy and ideal resolution, however, time consuming approach, expensive equipment, requirement of pretreatment, complicity of the method, tedious procedure, high amount of solvent consumption and restriction of the real-time detection narrowed down the applicability of such approaches and raised the requirement for a rapid, economic, real-time and precise method for detection of 4-NP within aquatic media [2,8].

In this matter, electrochemical-based methods found to be desirable alternative instead of aforementioned protocols due to their superior accuracy, ideal sensitivity, cost affordability, simplicity, real-time viability and rapid measurement/response that can easily identify the analyst within real samples [[16], [17], [18], [19], [20], [21]]. However, development of a highly accurate and sensitive electrochemical sensor with ideal electroanalytical performance is still a required demand [22]. Additionally, the catalytic reduction is a much more supportable method for conversion of 4-NP into 4-aminophenol due to the importance of this compound for fabrication of pigments, pharmaceutical and agrochemicals [23].

In addition, various kinds of nano-based electrocatalysts have been developed for modification of electrodes for precise electrochemical detection of phenol-based compounds, such as carbonaceous materials (e.g., graphene and its by-products including carbon nanotube (CNT) and mesoporous carbon) [[24], [25], [26]], conductive polymers (e.g., polypyrrole and polyaniline) [27,28], metal oxides (e.g., Fe3O4, ZnO and MnO2) [[29], [30], [31]] and noble metals (e.g., Pd, Au and Ag nanoparticles) [7,32,33]. In this matter, carbonaceous materials found to be ideal alternative as support for other metallic or non-metallic materials due to their superior specific surface area, porous structure, hierarchically and multifunctionality that make them fantastic electrocatalysts. Usage of graphene by-products as an active electrode in electrochemical-based sensors/biosensors, could enhance the redox current of the final platform and decrease the final detection limit along with improving the linear detection range. Graphene can considerably improve the current response, while its modification with metallic-complexes can inhibit their aggregation and improve their electrocatalysis performance. Their usage also lead to intense analytical signals owing to their ideal conductivity and high specific surface area [34,35].

Among conductive and electroactive polymers, polyaniline (PANi) considered as ideal candidate for modification of electrodes due to its simple preparation method, high electrical conductivity and ideal stability that make it fantastic alternative for development of precise sensors and electronic devices [36]. In this case, PANi was applied for detection of 4-NP owing to its superior environmental stability, tunable electrical conductivity and facile doping process [37,38]. What is more, doped PANi with practical materials could improve the sensitivity and enhance the dynamic factor of the electrochemical reaction [39], while the modified PANi with metallic complexes showed significantly better sensing, electrical and catalytic responses compared with the pure PANi [40]. Furthermore, integration of PANi with graphene by-products can improve their catalytic performance and modify/control their morphology [41].

Herein, well-exfoliated GO nanoflakes were decorated with interconnected, porous, highly dense and sensitive pathway of iron tungsten nitride and thence the protonated polymeric structure of PANi was reinforced/modified with different weight percentages of iron tungsten nitride toward improving its sensitivity for accurate detection of 4-NP within aquatic media. Thereafter, the electrode was modified using as prepared nanocomposite consisted of polyaniline-GO‑iron tungsten nitride and then applied for accurate detection of 4-NP in the aqueous samples through a real-time and repeatable approach. Outcome of performed evaluations exhibited the superior sensitivity and very low detection limit of the developed sensor till the nano molar level.

Section snippets

Characterization of developed nanomaterials

In this part, developed nanomaterials were subjected to diverse analyses to confirm their successful synthesis and modification. In Fig. 1 (a), outcome of XRD analysis for developed GO nanoflakes can be seen. As shown, GO nanoflakes exhibited 2θ peak of about 23.06 that attributed to the (002) plane of heterocyclic graphene. Likewise, Fig. 1 (b) illustrated the outcome of micro Raman spectroscopy for graphene nanoflakes that showed well-resolved D, G and D + G bands at 1366.25, 1627.42 and

Conclusions

The uprising level of 4-NP consumption in diverse industries and its careless disposal in the ecosystem highlighted an urgent requirement for developing an accurate method for its determination and removal from the aquatic ecosystem. Herein, we addressed this requirement through reinforcement of PANi with interconnected, porous and highly sensitive hybrid GO-ITN nanoflakes toward real-time and accurate detection of 4-NP within aqueous media. In this matter, the surface of GCE electrode was

Acknowledgement

Full details of experimental section including used chemical reagents, procedures, characterization techniques and details of electrochemical setup can be seen within the supporting information.

Declaration of Competing Interest

None.

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