Screen-printed electrochemical Cr(VI) sensing electrodes for - - PowerPoint PPT Presentation

Eurosensors 2012-XXVI - Kraków-Cracow 1

Thomas Maeder1, Silvia Miscoria2, Caroline Jacq1, Peter Ryser1 and Martín Negri2

1) LPM, EPFL, Lausanne, Switzerland
 2) INQUIMAE, UBA - University of Buenos Aires, Argentina thomas.maeder@epfl.ch
 http://lpm.epfl.ch/tf

Screen-printed electrochemical Cr(VI) sensing electrodes for effluent bioremediation monitoring

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Cr(VI) in industrial effluents

Use of Cr(VI) in industry

• Leather tanning
• Electroplating & anticorrosion coatings

Problems

• Good solubility of many chromates
• Cr(VI) genotoxic & carcinogenic

Remediation and monitoring

• Chemical reduction
• Bioremediation, e.g. with acidophilic bacteria
• Monitoring (process & environment): sensors

Bioreactor & sensors for Cr(VI) reduction developed at UBA Electronic nose integrated in reactor for gaseous phase monitoring

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Toxicity of hexavalent chromium

Cr(VI) species

• Acid pH, dil.: HCrO4
• (hydrogenochromate)
• Acid pH, conc.: Cr2O7

2-

(dichromate)

• Basic pH: CrO42- (chromate)

Health risk

• Cr(VI) enters cell & reacts with

DNA

• Genotoxic, carcinogenic
• Cr(III) has low toxicity (vital

trace element), stays outside.

Interactions of Cr species with cells

2009 Vacek thesis Brno (CZ)

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Thick-film sensors

§ Wide range of applications

§ High-reliability ceramic § Low-cost polymer

§ Simple processing

§ Additive process § Screen-printing § (+ dispensing, etc.)

§ Many materials

§ Substrates, dielectrics § Conductors / electrodes § Resistors § PTC / NTC / piezoresistors § Solders, adhesives, etc.

Force & pressure piezoresistive sensors Fluidics devices

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Thick-film sensors

§ Wide range of applications

§ High-reliability ceramic § Low-cost polymer

§ Simple processing

§ Additive process § Screen-printing § (+ dispensing, etc.)

§ Many materials

§ Substrates, dielectrics § Conductors / electrodes § Resistors § PTC / NTC / piezoresistors § Solders, adhesives, etc.

Force & pressure distribution sensor - piezoresistive elastomer Force-sensing beams – PCB & carbon- polymer piezoresistors

2005 Fahrny 2012 Canavese

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Thick-film sensors

§ Wide range of applications

§ High-reliability ceramic § Low-cost polymer

§ Simple processing

§ Additive process § Screen-printing § (+ dispensing, etc.)

§ Many materials

§ Substrates, dielectrics § Conductors / electrodes § Resistors § PTC / NTC / piezoresistors § Solders, adhesives, etc.

Screen printer Ink deposition process Paste on screen Mesh & mask

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Thick-film sensors

§ Wide range of applications

§ High-reliability ceramic § Low-cost polymer

§ Simple processing

§ Additive process § Screen-printing § (+ dispensing, etc.)

§ Many materials

§ Substrates, dielectrics § Conductors / electrodes § Resistors § PTC / NTC / piezoresistors § Solders, adhesives, etc.

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Carbon "paste" (resin) electrode

Active electrode

§ Porous (low binder) § Permeable to water § Conductive (percolation) § Doped with ionophore

Passive conductor

§ Dense (high-binder) § Barrier to water § Conductive (percolation) § Undoped

Graphite Ag bottom conductor (optional) Resin

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Which resin to use?

Ethylcellulose (EC)

§ Standard thick-film binder § Ethyl substitution ≈2.5 (of 3) § Acid-sensitive glycoside bond

Polyvinyl butyral (PVB)

§ Acid-stable polyolefin backbone § ≈78% butyral + 20% alc. + 2% ac.

Epoxy resins (EP)

§ Standard, high stability § Fully reactive, no solvent needed § Limited shelf / pot life

(Epoxy with amine hardener)

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Sensor structure & fabrication (1/2)

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Sensor structure & fabrication (2/2)

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Sensor structure

• Ag insulated from solution by dense

PVB-graphite layer

• Ionophore = DTPA

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Results – complete scans

PVB system

• K2Cr2O7 – H2SO4

(pH=1)

• Reference electrode

= Ag‑AgCl‑KCl

• Scan rate: 50 mV/s

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Results – Cr(VI) vs. Cr(III)

PVB system

• K2Cr2O7/CrCl3 – H2SO4

(pH=1) [Cr3+/6+] = 2mM

• Reference electrode =

Ag‑AgCl‑KCl

• Scan rate: 50 mV/s

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Results – reduction peak currents

PVB system

• K2Cr2O7 – H2SO4

(pH=1)

§ Voltammetric cycles § Good sensitivity, < 100 µM § No degradation observed (PVB or EP)

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Results – amperometric measurements

PVB system K2Cr2O7 – H2SO4 (pH=1) U = 150 mV

§ Successive additions of 5 (AB) & 10 µM (CD) Cr(VI) as K2Cr2O7 § Steps of 5 µM resolvable § Resolution ≈ 90 µA/ mM at low [Cr]

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Conclusions & outlook

Promising sensor sytem § Simple materials, PVB- or epoxy-based

§ 1) dense conductor, 2) porous electrode, 3) insulating dielectric

§ Integration of counter-electrode (dense conductor) § No degradation observed Outlook § Importance & optimisation of carbon & ionophore § Long-term tests § Possible perturbations from other ions § Total integration, including Ag-AgCl-KCl reference electrode

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• Thank you !

Thomas Maeder EPFL-LPM, BM1.136, station 17 CH-1015 Lausanne, Switzerland +41 21 693 58 23 thomas.maeder@epfl.ch http://lpm.epfl.ch/tf

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Results – linearity at large concentration

PVB system K2Cr2O7 – H2SO4 (pH=1) U = 150 mV

§ Sensitivity somewhat reduced at high concentrations