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

Screen-printed electrochemical Cr(VI) sensing electrodes for effluent bioremediation monitoring � Thomas Maeder 1 , Silvia Miscoria 2 , Caroline Jacq 1 , Peter Ryser 1 and Martín Negri 2 � 1) LPM, EPFL, Lausanne, Switzerland 
 2) INQUIMAE, UBA - University of Buenos Aires, Argentina � thomas.maeder@epfl.ch 
 http://lpm.epfl.ch/tf � Eurosensors 2012-XXVI - Kraków-Cracow 1 �

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 � Bioreactor & sensors Electronic nose for Cr(VI) reduction integrated in reactor Remediation and monitoring � developed at UBA � for gaseous phase monitoring � • Chemical reduction � • Bioremediation, e.g. with acidophilic bacteria � • Monitoring (process & environment): sensors � Eurosensors 2012-XXVI - Kraków-Cracow 2 �

Toxicity of hexavalent chromium � Cr(VI) species � - • Acid pH, dil.: HCrO 4 Interactions of Cr species with cells � (hydrogenochromate) � 2- • Acid pH, conc.: Cr 2 O 7 (dichromate) � • Basic pH: CrO4 2- (chromate) � Health risk � • Cr(VI) enters cell & reacts with DNA � • Genotoxic, carcinogenic � • Cr(III) has low toxicity (vital 2009 Vacek thesis Brno (CZ) � trace element), stays outside. � Eurosensors 2012-XXVI - Kraków-Cracow 3 �

Thick-film sensors � § Wide range of applications � § High-reliability ceramic � § Low-cost polymer � § Simple processing � § Additive process � Force & pressure § Screen-printing � piezoresistive sensors � § (+ dispensing, etc.) � § Many materials � § Substrates, dielectrics � § Conductors / electrodes � Fluidics § Resistors � devices � § PTC / NTC / piezoresistors � § Solders, adhesives, etc. � Eurosensors 2012-XXVI - Kraków-Cracow 4 �

Thick-film sensors � § Wide range of applications � § High-reliability ceramic � Force & pressure distribution § Low-cost polymer � sensor - piezoresistive § Simple processing � elastomer � 2012 Canavese � § Additive process � § Screen-printing � § (+ dispensing, etc.) � § Many materials � § Substrates, dielectrics � Force-sensing beams – PCB § Conductors / electrodes � & carbon- polymer § Resistors � piezoresistors � § PTC / NTC / piezoresistors � 2005 Fahrny � § Solders, adhesives, etc. � Eurosensors 2012-XXVI - Kraków-Cracow 5 �

Thick-film sensors � § Wide range of applications � § High-reliability ceramic � § Low-cost polymer � § Simple processing � § Additive process � Paste on screen � Screen printer � § Screen-printing � § (+ dispensing, etc.) � Ink deposition process � § Many materials � § Substrates, dielectrics � § Conductors / electrodes � Mesh & § Resistors � mask � § PTC / NTC / piezoresistors � § Solders, adhesives, etc. � Eurosensors 2012-XXVI - Kraków-Cracow 6 �

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. � Eurosensors 2012-XXVI - Kraków-Cracow 7 �

Carbon "paste" (resin) electrode � Active electrode � § Porous (low binder) � § Permeable to water � § Conductive (percolation) � § Doped with ionophore � Graphite � Passive conductor � Resin � § Dense (high-binder) � § Barrier to water � § Conductive (percolation) � § Undoped � Ag bottom conductor (optional) � Eurosensors 2012-XXVI - Kraków-Cracow 8 �

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) � § (Epoxy with Standard, high stability � amine § hardener) � Fully reactive, no solvent needed � § Limited shelf / pot life � Eurosensors 2012-XXVI - Kraków-Cracow 9 �

Sensor structure & fabrication (1/2) � Eurosensors 2012-XXVI - Kraków-Cracow 10 �

Sensor structure & fabrication (2/2) � Eurosensors 2012-XXVI - Kraków-Cracow 11 �

Sensor structure � • Ag insulated from solution by dense PVB-graphite layer � • Ionophore = DTPA � Eurosensors 2012-XXVI - Kraków-Cracow 12 �

Results – complete scans � PVB system � � K 2 Cr 2 O 7 – H 2 SO 4 (pH=1) � � Reference electrode = Ag ‑ AgCl ‑ KCl � � Scan rate: 50 mV/s � Eurosensors 2012-XXVI - Kraków-Cracow 13 �

Results – Cr(VI) vs. Cr(III) � PVB system � � K 2 Cr 2 O 7 /CrCl 3 – H 2 SO 4 (pH=1) � [Cr 3+/6+ ] = 2mM � � Reference electrode = Ag ‑ AgCl ‑ KCl � � Scan rate: 50 mV/s � Eurosensors 2012-XXVI - Kraków-Cracow 14 �

Results – reduction peak currents � § Voltammetric cycles � PVB system � � § Good sensitivity, < 100 µM � K 2 Cr 2 O 7 – H 2 SO 4 (pH=1) � § No degradation observed (PVB or EP) � Eurosensors 2012-XXVI - Kraków-Cracow 15 �

Results – amperometric measurements � PVB system � K 2 Cr 2 O 7 – H 2 SO 4 (pH=1) � U = 150 mV � § Successive additions of 5 (AB) & 10 µM (CD) Cr(VI) as K 2 Cr 2 O 7 � § Steps of 5 µM resolvable � § Resolution ≈ 90 µA/ mM at low [Cr] � Eurosensors 2012-XXVI - Kraków-Cracow 16 �

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 � Eurosensors 2012-XXVI - Kraków-Cracow 17 �

� 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 � Eurosensors 2012-XXVI - Kraków-Cracow 18 �

Results – linearity at large concentration � PVB system � K 2 Cr 2 O 7 – H 2 SO 4 (pH=1) � U = 150 mV � § Sensitivity somewhat reduced at high concentrations � Eurosensors 2012-XXVI - Kraków-Cracow 19 �