Piezoelectric quartz crystal (PQC) with photochemically deposited nano-sized Ag particles for determining cyanide at trace levels in water

doi:10.1016/j.snb.2004.12.120

Sensors and Actuators B: Chemical

Volume 108, Issues 1–2, 22 July 2005, Pages 925-932

https://doi.org/10.1016/j.snb.2004.12.120 Get rights and content

Abstract

A sensitive and cost-effective cyanide sensor has been developed based on piezoelectric quartz crystal (PQC) for determining cyanide at trace levels in water. The sensing layers were fabricated by depositing photochemically generated nano-sized silver particles on titanium dioxide film at the electrode surface of PQC. The freshly produced metallic Ag interacts strongly with cyanide, leading to improved sensor performance (3 times higher sensitivity and 12 times lower detection limit as compared to the bulk Ag-coated PQC). The linear working range was over three orders of concentration from 0.1–10 μmol/L. Under the optimized conditions for photochemical deposition of nano-sized Ag with controlled TiO₂ film thickness and desired silver particles in nano-sized range, factors affecting its analytical application such as background buffer, solution pH and potential interferents were investigated. Satisfactory recovery at 98.8% and good repeatability (R.S.D. for n = 3) at 3.19% were obtained in spiked cyanide concentration from 0.013–0.233 mg/L. The procedure was shown able to provide a reliable method for quantitative determination of cyanide at more than 30 times lower than the World Health Organization (WHO) guideline value for drinking water.

Introduction

Cyanide has gained historical notoriety as a poison used with intent to cause fatality. The toxic effect is due to its reaction with the trivalent iron in the cytochrome oxidase to inhibit electron transport and thus preventing the cells from consuming oxygen, leading to a rapid impairment of the vital functions. The fatal oral dosage to human is only about 60–90 mg [1]. However, cyanide salts have found indispensable use in hydrometallurgy [2], electroplating and manufacture of Perspex and Nylon [3]. Thus, about 1.4 million tons of the very toxic hydrogen cyanide is produced annually world-wide by industry. This leads to periodical reports of cyanide poisoning for worker handling cyanide and accidental contamination of water bodies by leachate from metal extraction plants or other sources. Due to its extreme toxicity, the World Health Organization (WHO) has issued a guideline value of 0.07 mg/L for cyanide in drinking water in 1996 [4]. Other related guideline values for cyanide in drinking water are 0.2 mg/L (United States Environmental Protection Agency) [5], 0.05 mg/L (European Union) and 0.5 mg/L (World Bank) [2].

In order to meet the need for cyanide determination in emergency cases, a fast responding sensor capable of determining cyanide at trace levels is required. Thus, various methods have been developed to determine cyanide in water, either directly by spectrophotometry [6], titrimetry [7], voltammetry [8] and coulometry [9], or after separation such as by ion chromatography [10] and head-space gas chromatography [11]. However, the sensitivity of the direct analysis methods are insufficient to meet the requirement of the guideline values, thus the need of a lengthy pre-concentration step and a large sample size. Although the use of the separation methods can solve the matrix interference problem, the procedures are complicated and require a dedicated instrument. Due to its high sensitivity and simplicity in operation, the piezoelectric quartz crystal (PQC) sensor has been developed for cyanide detection [12], [13]. PQC with silver-plated electrodes has been shown to give detection limit down to 1 μmol/L or 0.026 mg/L for the detection of cyanide [14]. The detection limit is close to the WHO guideline value. For repeatable quantitation, the detection limit should be at least 10 times lower than the guideline value.

As freshly generated nano-sized silver particles are known to produce a much higher reactivity and shown to deposit by a simple and reliable procedure at electrode surface via photo-deposition on TiO₂ [15], [16]. Thus, this approach has been adopted in the present work to develop a more sensitive and cost-effective PQC sensor. Each step for the fabrication of the sensing layer by depositing nano-sized silver particles photochemically onto the TiO₂ film at the surface of PQC in AgNO₃ solution has been studied and factors, such as pH and organic additives, affecting the efficiency of silver photo-deposition in the photo-reaction systems have been investigated with an aim to obtain a well-dispersed silver deposition and to generate a reproducible coating surface. Using the optimized coatings developed, the analytical applicability of the PQC cyanide sensor are determined. The effect of pH, background buffer and potential interferents commonly found in environmental water samples on sensor performance will be discussed in light of the results obtained.

Section snippets

Material and standards

All chemicals are A.R. grade unless otherwise stated. Titanium dioxide (TiO₂) was purchased from Degussa (P25, ca. 80% anatase and 20% rutile) with surface area of about 50 cm² g⁻¹ and density of 3.8 g/cm³. The working solution for photo-reduction of nano-sized silver was made up to 10⁻⁴ mol/L AgNO₃ by a suitable dilution using an aqueous methanol solution (10% (v/v) methanol in water). The high purity water used in the experiments was doubly quartz-distilled prior to demineralization using the

Results and discussion

Two procedures are used in the preparation of PQC sensor with nano-sized silver coatings. The first procedure is the preparation of TiO₂ coating on PQC electrode surface and the second procedure is the photo-deposition of nano-sized silver on TiO₂ coated PQC electrode surface. As the first procedure is well documented [19], [20], the current work is thus focused on the optimization of the working conditions for photo-deposition of nano-sized silver on TiO₂ coated PQC electrode surface,

Conclusions

A procedure for photo-deposition of Ag nano-particles on TiO₂-coated PQC surface has been developed in the present work to produce highly reactive nano-Ag particles for trace cyanide determination in water. The procedure is shown to generate an excess amount of Ag sufficient for operation over a month, capable of regeneration of the spent electrode by UV-irradiation, and produce a reproducible coating surface with satisfactory analytical performance. Under the optimized conditions to generate

Acknowledgements

We would like to acknowledge the financial supports from the Seed Fund for Basic Research of the Hong Kong University Research Grants Committee, the Competitive Research Grant (HKU 7043/03P) from the Hong Kong Research Grants Council, and the Innovation and Technology Fund (ITS/125/01) of the Hong Kong SAR Government.

Ms. H. Sun had received a Bachelor degree in environmental science from Wuhan University in 1994, and a Master degree in analytical chemistry from Nankai University in 2002. Currently, she is taking a PhD programme at the University of Hong Kong. Her research is focused on developing sensor for monitoring environmental pollutants.

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Ms. Y.Y. Zhang is an associate professor in the Chemical Research Institute, Hunan Normal University. She had received her MSc degree from Hunan Normal University, China. She is a doctoral student at the State Key Laboratory of Chemo/Biological Sensing and Chemometrics, Hunan University. Her research is focused on chemical and biological sensing. Her current research includes piezoelectric quartz crystal sensor and electrochemical sensor.

Professor S.H. Si had received his PhD degree from Hunan University, and undertaken collaboration research work at the University of Hong Kong from 1997 to present. He is currently a professor in the Department of Chemistry, Central South University, PR China. His research interests include photoelectrochemistry of semiconductor nanoparticles, improvement of chemo/biosensors using nanoporous films, piezoelectric crystal biosensors, adsorption and binding of proteins, enzymes and DNA on chemically modified surface.

Dr. D.R. Zhu had received his PhD degree from the University of Hong Kong in 2002. He is currently a research associate in the Department of Chemistry, the University of Hong Kong. His research interests include room temperature molten electrochemistry, electrophoretic deposition of nanopolymeric particles and improvement of chemo/biosensors with nanoporous films.

Professor Y.S. Fung received his PhD degree from the Imperial College of Science, Technology and Medicine, University of London, UK in 1980. He has been appointed as guest professors at the Changchun Institute of Applied Chemistry, Jilin University and Dongguan Institute of Technology in China, as well as academic advisors for various industrial and environmental groups and associations in Hong Kong. He is currently an associate professor in the Department of Chemistry, the University of Hong Kong. His research interests include the development and application of the following methodologies: (1) chemical sensor and biosensor for pollutants and bacteria based on quartz piezoelectric crystal microbalance methodology, (2) capillary electrophoresis (CE) and microchip CE for environmental, food and clinical investigation; (3) chemometric method integrated with chemical analysis for apportionment of pollution sources and quality assessment of herbal Chinese Medicine, and (4) nanotechnology for advanced lithium battery application, nano-particle characterization and fabrication of industrial products.

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Piezoelectric quartz crystal (PQC) with photochemically deposited nano-sized Ag particles for determining cyanide at trace levels in water

Abstract

Introduction

Section snippets

Material and standards

Results and discussion

Conclusions

Acknowledgements

Miner. Eng.

Anal. Chim. Acta

Anal. Chim. Acta

Anal. Chim. Acta

Trac-Trend Anal. Chem.

Sens. Actuators B

Sens. Actuators B

Appl. Catal. B: Environ.

Chem. Phys. Lett.

Thin Solid Films

J. Photochem. Photobiol. A: Chem.

J. Mol. Catal. A: Chem.

Toxicological Chemistry