Elsevier

Sensors and Actuators B: Chemical

Volume 202, 31 October 2014, Pages 1070-1077
Sensors and Actuators B: Chemical

Silicate sol–gel stabilized silver nanoparticles for sensor applications toward mercuric ions, hydrogen peroxide and nitrobenzene

https://doi.org/10.1016/j.snb.2014.06.069Get rights and content

Highlights

Abstract

Here, we developed a silver nanoparticles (Ag NPs) based sensor for the detection of mercuric ions (Hg(II)), hydrogen peroxide (H2O2) and nitrobenzene. The silicate sol–gel (SSG) stabilized Ag NPs were synthesized via one-pot synthetic route using the mixture of hydrazine, ammonium chloride and nitric acid as reduction solution. The Ag NPs were further characterized by absorption spectra, XRD, SEM, TEM, EDX and SAED analyses. The spectral and colorimetric methods revealed the efficiency of Ag NPs to detect Hg(II) ions and the lowest detection limit was found to be 5 μM. Also, Ag NPs exhibited selectivity toward Hg(II) ions in the presence of other environmentally relevant heavy metal ions. For the detection of H2O2, an enzymeless electrochemical sensor was prepared by modifying glassy carbon electrode with SSG stabilized Ag NPs. Using the linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV) techniques, the lowest experimental detection limits for H2O2 sensing were found to be 0.5 and 0.1 μM, respectively. Similarly, the electrochemical sensing of nitrobenzene using the modified electrode was identified to have the lowest experimental detection limit of 1 μM by square wave voltammetry (SWV).

Introduction

Silver nanoparticles (Ag NPs) have received ever increasing attention owing to their great performance in a wide range of applications including sensing and catalysis [1], [2], [3], [4]. Solution-phase syntheses for the production of Ag nanostructures with different shapes have been reported earlier [5], [6], [7]. Synthesis of Ag NPs using a variety of stabilizing agents [1], [8], [9], [10], [11] and silicate sol–gel (SSG) stabilized Ag NPs [12] have been established and widely used. The three dimensional network provided by SSG matrix for the stabilization of Ag NPs is extremely beneficial in catalytic applications [3], [12]. Also, the Ag NPs modified electrodes have been used in electrocatalysis and electrochemical sensors [13], [14], [15], [16]. Considering the advantages and different modes of applications, our group has developed newer methodologies for the preparation of Ag NPs embedded with SSG matrix and evaluated their sensor and catalytic applications [3], [17], [18].

Heavy metal ions are potential environmental pollutants even at ppm level concentration, among which Hg(II) ions are of great concern because of their deleterious effects to human health and environment [19]. Therefore, sensing of Hg(II) ions using a cost effective method with rapid detection remains the prime area of research. Ag NPs based sensors have been successfully reported for Hg(II) ions sensing earlier [20], [21], [22], [23]. Among the various sensors, the optical sensor is highly attractive due to the easy detection of metal ions by using spectroscopic instrumentation technique. Hence, using metal NPs as optical sensors is recognized to be a promising approach for simple and cost effective protocols with high sensitivity and rapid detection of toxic metal ions in aqueous medium [24], [25].

H2O2 is a by-product in many oxidase catalyzed reactions and it has profound applications as an essential mediator in biological, clinical, industrial and environmental analyses. Hence, developing electrochemical sensors for the detection of H2O2 has gained more attention. It is in this stream, Ag NPs are highly preferred when compared to other noble metal NPs like gold (Au), platinum (Pt) or palladium (Pd) [26], [27] due to their low cost. Similarly, the high cost of enzyme and complicated immobilization process has led to the development of enzyme-free H2O2 sensor. Nitrobenzene, another environmental pollutant, is extensively used for the production of aniline dyes, explosives, pesticides and drugs, and has become a threat to human health and environment due to its carcinogenic nature [28]. Therefore, in recent years, nanomaterials based electrochemical sensors for the effective detection of nitrobenzene derivatives are reported [3], [29], [30], [31].

Herein, we report a facile one-pot synthesis of Ag NPs stabilized in silicate sol–gel matrix for the detection of Hg(II) ions, H2O2 and nitrobenzene. The synthesized Ag NPs were characterized by absorption spectra, XRD, SEM, TEM, EDX and SAED analyses. Sensing of Hg(II) ions was analyzed using spectral and colorimetric methods. The Ag NPs showed selectivity toward Hg(II) ions in the presence of other environmentally relevant heavy metal ions. The electrochemical sensor based on Ag NPs modified electrode was developed and used for the sensing of H2O2 and nitrobenzene.

Section snippets

Materials

N-[3-(trimethoxysilyl) propyl] diethylenetriamine (TPDT), silver nitrate (AgNO3) and mercury(II) chloride (HgCl2) were purchased from Sigma–Aldrich. Nitrobenzene, H2O2, PbCl2, CuCl2·2H2O, CoCl2·6H2O, CdCl2, CaCl2·2H2O, NiCl2·6H2O, ZnCl2, MnCl2·4H2O, FeCl2·6H2O, FeCl3·6H2O, hydrazine hydrate, ammonium chloride and nitric acid were received from Merck. All glassware was cleaned with aqua regia solution followed by rinsing with distilled water prior to use. (Precaution: Aqua regia is highly

Absorption, HRTEM and XRD studies of Ag NPs

The synthesized SSG stabilized Ag NPs were primarily confirmed by recording their absorption spectrum. The absorption spectrum of aqueous Ag NPs revealed a characteristic sharp and single SPR band at 406 nm (Fig. 1). Since the absorption band of Ag NPs is very sensitive to their size and shape [5] the obtained sharp and single absorption band suggests that the formed Ag NPs are uniform in shape and more naturally spherical. The measurements of the absorption spectrum showed that the synthesized

Conclusions

A facile synthetic method was developed for the preparation of silicate sol–gel stabilized Ag NPs and the Ag NPs were used for the optical and electrochemical detection of various analytes. The sensing of Hg(II) ions was performed by spectral and colorimetric methods. The Ag NPs showed selectivity toward Hg(II) ions in the presence of other environmentally relevant heavy metal ions and the lowest detection limit of 5 μM was achieved. The TPDT-Ag NPs modified electrode was used as an enzymeless

Acknowledgments

The financial support from the Science and Engineering Research Board (SERB) (Grant no: SB/S1/IC-03/2013), India, is gratefully acknowledged. PV is a recipient of UGC-BSR fellowship. The authors thank Dr. Anuradha M. Ashok, PSG Industrial Institute, Coimbatore, for the HRTEM analysis.

Perumal Rameshkumar obtained his M.Sc. chemistry (2009) from Madurai Kamaraj University. He joined as junior research fellow (2010) at the same University and subsequently promoted as senior research fellow (2012). His current research interests include preparation of metal nanoparticles embedded in polymer matrix, modified electrodes, optical sensors, electrocatalysis and electrochemical sensors.

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    Perumal Rameshkumar obtained his M.Sc. chemistry (2009) from Madurai Kamaraj University. He joined as junior research fellow (2010) at the same University and subsequently promoted as senior research fellow (2012). His current research interests include preparation of metal nanoparticles embedded in polymer matrix, modified electrodes, optical sensors, electrocatalysis and electrochemical sensors.

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