A green synthetic approach to synthesize silver nanoparticles (AgNPs) using the stem extract of Piper chaudocanum for highly sensitive colorimetric detection of Hg 2+ with a low limit of detection of 23 nM and easy colorimetric read-out has been reported. In addition, the biosynthesized AgNPs demonstrated efficient antibacterial activity against Escherichia coli , Pseudomonas aeruginosa and Staphylococcus aureus . The morphology and structure of the as-synthesized AgNPs were examined using SEM, TEM, EDX, XRD and FT-IR analyses. The XRD and TEM results confirm the formation of AgNPs with an average particle size of 8–12 nm. The TLC, CC and HPLC revealed that four main compounds, pentacosanoic acid ( 1 ), piperine ( 2 ), β -sitosterol ( 3 ), and campesterol glucoside ( 4 ), isolated from P. chaudocanum extract act as reducing and stabilizing agents for AgNP formation, and piperine plays a vital role in green synthesis. The chemical structures of these compounds were determined by ESI MS, FTIR, and one- and two-dimensional NMR spectroscopic data analysis. This approach is an efficient, green, cost-effective, eco-friendly and promising technique for synthesizing AgNPs with applications in the colorimetric detection of Hg 2+ and antibacterial activity.

In this study, Zinc oxide nanoparticles (ZnO NPs) were green synthesized using Piper chaudocanum L. (PC) leaf extract by sol-gel method and used as an adsorbent for the removal of Pb (II) ions from aqueous solution. The synthesized ZnO NPs were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Ultraviolet - visible spectroscopy (UV-Vis) and Brunauer - Emmet - Teller (BET). The results revealed high purity and wurtzite hexagonal structure of ZnO NPs in the size range of 28-37 nm. The morphology of the ZnO NPs varies in different polycrystalline aggregates depending on the amount of extract used, from nanorods to NPs clusters with a BET surface area of 8.56 m2g-1. Pb (II) ion adsorption was investigated at different pH, contact time, initial metal ion concentration, adsorbent dose and temperature. ZnO NPs were synthesized using 30 mL PC leaf extract (ZS30) is the best Pb (II) absorbent. The adsorption isotherm was well described by Langmuir (at low concentration of Pb (II)) and Freundlich isotherm model (at higher concentration of Pb (II)). The adsorption process follows pseudo-second-order reaction kinetic with a high regression coefficient. The calculated thermodynamic parameters, ΔGo (between - 8.699 and - 7.569 kJ/mol at 298 - 316 K), ∆Ho (-20.085 kJ/mol) showed that the adsorption of Pb (II) on ZS30 surface was feasible, spontaneous and exothermic, respectively. The first layer absorption is chemisorption while the next layers are physical adsorption.

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