SILVER NANOPARTICLES FROM ORANGE PEEL EXTRACT AS SELECTIVE SENSOR FOR LEAD IONS IN AQUEOUS SOLUTIONS

Orange peels represent one of the precious waste materials that is composed mainly of cellulose, pectin, hemicellulose, lignin, flavonoids, chlorophyll pigments and other low molecular weight hydrocarbons containing various functional groups, such as carboxyl and hydroxyl. In addition, flavonoid compounds are interesting for their antioxidant properties that can be applied in the reduction of metal ions into nanoparticles. Silver nanoparticles (AgNPs) can be used as a surface plasmon resonance (SPR) colorimetric sensor; the correlation between the SPR phenomenon and the aggregation state of nanoparticle allows the real-time detection of a target molecule. Surface functionalization of NPs with proper molecular baits is often performed to establish the selectivity of the sensor. Orange Peel Water Extract (OPE) was prepared by adding ultrapure water to orange peel and stirring at 40°C, filtering, and cooling. The freshly obtained OPE was used immediately after filtration or frozen until use. This study exploits the synthesis of green silver nanoparticles (AgNPs) by using orange peel extract as reducing and functionalizing agents. The AgNPs were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analyzers (EDX), DLS and infrared spectroscopy. These nanoparticles have been demonstrated to be spherical, with a maximum diameter size around 25 nm, and were shown to associate into larger clusters in the presence of divalent cations dependind on type and concentration. Specifically, these AgNPs were successfully used as selective sensor to detect micromolar levels of Pb2+ at concentration below 6.6 x 10-5 M. In this concentration range, the aggregation process led to a major change in optical properties of the AgNPs suspension, consisting of a red shift of the SPR band at 405 nm with a progressive linear decrease in the intensity as function of the concentration.