Green synthesis of bimetallic Ag/Cu nanoparticle system using aqueous extracts of carica papaya and the investigation of water purification activity of the nanometals

Nanoparticles, known for their unusual properties and remarkable applications in different fields, are usually synthesized through chemical methods. However, due to its various limitations, green route for nanoparticle synthesis is highly sought. This study aims to use aqueous leaf extracts of Carica papaya to synthesize Ag, Cu and bimetallic Ag/Cu nanoparticles. In this study, the synthesis of monometallic Ag & Cu nanoparticles was optimized first by varying time and temperature conditions. The color changes of each solution was monitored and nanoparticle formation was confirmed by the appearance of the AgNP surface plasmon resonance (SPR) in UV-Vis Spectroscopy. Optimization revealed that synthesis at 90°C for 2hrs generated higher yield, and this condition was used in the synthesis of bimetallic Ag/Cu nanoparticles. SEM characterization revealed the presence of aggregates and particles that are mutually varied in size. EDX analysis showed the presence of C, N, O, Ag & Cu in the sample. Among the synthesized bimetallic nanoparticles, only the Ag/Cu prepared from coreduction displayed a unique star-shaped structure with the observed average hydrodynamic particle size of 420.7 nm (DLS) and TEM size of ~30 nm. XRD patterns of Ag/Cu NPs displayed crystallinity with observed peaks corresponding to Ag, Ag2O and CuO. The synthesized AgNP & bimetallic Ag/Cu NPs were then utilized for degradation activity of the pesticide chlorpyrifos (CP) in water. The NPs were shown to effectively degrade CP affording less toxic degradation products as characterized by UV-Vis Spectroscopy and Liquid Chromatography-Mass Spectrometry. It is recommended that bimetallic Ag/Cu NPs be mapped with a high resolution microscopy and spectroscopy to determine its detailed structure. It is further recommended that the degradation activities of core-shell (Ag-Cu, Cu-Ag) NPs and physically mixed Ag & Cu NPs (Ag + Cu) be investigated for catalytic activities and for other applications

Green preparation and characterization of tentacle-like silver/copper nanoparticles for catalytic degradation of toxic chlorpyrifos in water

The synthesis of bimetallic nanoparticles is gaining attention due to a number of interesting and striking new properties that can be derived from the combination of two metals. In this study, bimetallic silver/copper (Ag/Cu) nanoparticles were prepared by co-reduction method using aqueous leaf extracts of Carica papaya as reducing agent. The synthesized nanoparticles showed a single UV-vis peak with a maximum absorption at 776 nm. The SEM and TEM images of bimetallic Ag/Cu nanoparticles displayed, among others, a unique star-like structure. HR-TEM mapping revealed uniform distribution of Ag & Cu forming a bimetallic nanoparticle. The bimetallic Ag/Cu has an average hydrodynamic particle size of 420.7 nm (DLS) and TEM size of ∼150 nm. The presence of elemental Ag, Cu, C, N and O was confirmed in EDX spectra suggesting nitrogen containing metabolites capping the bimetallic Ag/Cu nanoparticles. The XRD patterns of bimetallic Ag/Cu nanoparticles displayed crystallinity with observed diffraction peaks corresponding to Ag, Ag2O and CuO. The synthesized bimetallic nanoparticles were then utilized for water purification application using the toxic pollutant, chlorpyrifos pesticide, as a model. Results showed that bimetallic Ag/Cu nanoparticles are efficient agents to promote degradation of chlorpyrifos in water, indicating the high potential of green synthesized nanometals for purifying water from pesticide contamination. © 2017 Elsevier Ltd. All rights reserved