Photocatalytic, antioxidant and antibacterial potential of bio-synthesized ZnO nanoparticles derived from espresso spent coffee grounds: optimization by central composite design

This article presents a rapid, costless, and environment-friendly technique for the biosynthesis of ultra-small ZnO nanoparticles (NPs), which were synthesized using espresso spent coffee grounds (SCG). The synthesized ZnO NPs were determined by Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR). The photocatalytic activity of the ZnO NPs was evaluated for photodegradation of tartrazine (Tz) dye under UV light. The response surface method (RSM) in a central composite rotatable design (CCRD) was used to design the experiments. The parameters affecting the efficiency of the degradation were evaluated and optimized. The ZnO NPs were assessed for antimicrobial and antioxidant activities. The results showed that XRD, FESEM, and FT-IR confirmed the formation of ZnO NPs. At optimized values, high removal efficiencies (92.5%) were found. Significant antioxidant activity of the NPs was demonstrated using a DPPH (2, 2-diphenyl-1-picrylhydrazyl) free radical assay with the IC₅₀ value of 0.9586 mg/mL.