Plasmonic silver nanoparticle, AgNPs (~14.1 nm) having an absorption peak at 421 nm was fabricated via a biogenic, rapid, and costless technique using Banana Waste Peduncles (BWP) as new disposals instead of plant extracts. According to HPLC analysis, BWP included gallic acid, catechin, chlorogenic acid, caffeic acid, etc. Degussa (P25) has been in-situ added in one-step to AgNPs using the microwave synthesis to produce nanocomposite sensitive to solar-light irradiation. Transmission electron microscope (TEM) images showed incorporation of P25 over plasmonic AgNPs grown by spherical shape. Based on the photocatalytic process, methylene blue (MB) was fully degraded, and 16 min was sufficient for chromium (IV) reduction. AgNPs/Degussa nanocomposite is photochemical stable even after eight cycles. Besides, the antimicrobial activity indicated the capability of the nanocomposite, as an efficient antimicrobial agent for killing and prevent the diffusion of the nominated microbes; Staphylococcus aureus, Escherichia coli, Candida albicans, and Aspergillus niger due to the synergistic effect of AgNPs. The cell viability showed up to 94.85% reliable cell migration, particularly at higher concentrations. The significant improvement of photoactivity and stability of the as-synthesized photocatalysts might be relevant for their reusability in practical applications.