Production of silver nanoparticles using spent coffee ground for antibacterial effect

Abstract

In the past few years, many efforts were put into developing new greener and cheaper methods for the synthesis of silver nanoparticles (AgNPs). This study opted two different types of spent coffee grounds (SCGs) extracts, obtained from pressed spent coffee grounds (Pr-SCGs) and simple boiled spent coffee grounds (SB-SCGs) for the biosynthesis of AgNPs. Several parameters affecting silver reduction, such as the volume ratio of SCG extracts, the concentration of silver nitrate, pH, temperature and reaction time were investigated to obtained optimal reaction conditions for the preparation of AgNPs. Successful synthesis of Pr-SCGs-AgNPs and SB-SCGs-AgNPs were confirmed via characterization analysis using UV-Vis spectrophotometer, FESEM (Field Emission Scanning Electron Microscopy), EDX (Energy Dispersive X-ray), FTIR (Fourier-transform infrared spectroscopy) and XRD (X-ray diffraction). Finally, Pr-SCGs-AgNPs and SB-SCGs-AgNPs were tested for their antibacterial activity against Escherichia coli and Staphylococcus aureus. Pr-SCGs-AgNPs and SB-SCG-AgNPs reduced the silver ions into AgNP within 90 min of heating the reaction mixture (90°C) as indicated by the developed dark brown and reddish-brown colours, respectively. The UV-Vis spectrum of AgNPs revealed a characteristic surface plasmon resonance (SPR) peak at 407 nm and 404 nm for Pr-SCGs-AgNPs and SB-SCGs-AgNPs, respectively. The morphology of both samples was identified in spherical shape with an average size of 19±6 nm and 16±1 nm. The FTIR spectroscopy confirmed the role of SCG as a reducing and capping agent of silver ions by revealing the presence of functional groups, such as carboxyl, hydroxyl, and amine groups, and the crystallinity of the nanoparticles confirmed by XRD is as face-centered cubic (FCC). Pr-SCGs-AgNPs and SB-SCGs-AgNPs showed effective antibacterial activity against the representative bacteria. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) results of Pr-SCGs-AgNPs and SB-SCGs-AgNPs for both E. coli and S. aureus were (5-18) mg/mL, and (3.4-16) mg/mL, respectively. The difference in the coffee brewing process contributed to the variation in the properties of the AgNPs. Overall, Pr-SCGs-AgNPs and SB-SCGs-AgNPs have proven their antimicrobial properties, showing their potential as antimicrobial products in the future.