Detection of thiourea from electrorefining baths using silver nanoparticles-based sensors

• A method for the determination of thiourea based on Ag nanoparticles is presented.
• The method coincides with thiourea concentration range in electrorefining baths.
• The developed method is highly selective in the presence of other additives.
• Inexpensive silver nanoparticles screen printing sensors are employed.
• This system is useful to monitor and further recondition thiourea solutions.

A novel and easy-to-use colorimetric thiourea (TU) sensor based on immobilized polyvinylpyrrolidone-stabilized silver nanoparticles (PVP-AgNPs) is reported. The new sensor is aimed for its direct application in copper electrorefinery baths. Quantitative analysis was carried out by adding different thiourea amounts into a synthetic bath and monitoring the absorption changes of the surface plasmon resonance band (SPRB) by UV–Vis spectrophotometry. A linear correlation between the absorbance change and thiourea concentration was obtained, ranging from 0.125 mg/L to 1 mg/L. Our technique has the advantage of working in acidic and high ionic concentrated solutions as those used in electrorefinery baths. The influence of the nanoparticles synthesis conditions on the thiourea sensing was analyzed; particularly, the effect of using different silver concentrations and the same amount of borohydride ions as reducing agent ([Ag+]/[BH4−] ratios of 2:1, 8:1, 10:1 and 20:1 during the synthesis). The proposed system provides a simple, economical, easy-to-handle and rapid measurement tool for monitoring hydrometallurgical processes for optimizing the reconditioning of thiourea solutions, reducing its environmental impact.