<p>This paper describes a general approach for the biogenic synthesis of silver, platinum, and their bimetallic nanoparticles by the green chemical reduction method in the presence of poly(vinylpyrrolidone) (PVP) as capping agent. The platinum salt was reduced to the solid surface of metallic silver (Ag⁰) by replacing the silver ions into the solution via the galvanic replacement reaction and generating nanoscale hollow structures. The resulting sols of Ag⁰, Pt⁰, Ag⁰/Pt⁰, and Pt⁰@Ag⁰ are stable and can be isolated without precipitation or decomposition. The Pt⁰@Ag⁰ have been characterized by EDX, TEM, SEM, XRD, and FTIR techniques. The Pt⁰@Ag⁰ was used as adsorbent for the removal of xylenol orange (XO). The dye removal was optimized as 98.2% at adsorbent dose (0.03&#xa0;mg/L), XO (67.26&#xa0;ppm), pH (2.0), time (50&#xa0;min), and temperature (298&#xa0;K). The isotherm data fit the Freundlich model with intensity of adsorption (<i>n</i> = 2.3), and regression coefficient (R² = 0.993), while kinetic data follow the intraparticle diffusion model with thickness of the surface layer (I = 11.90&#xa0;mg/g), and rate of diffusion = 7.62&#xa0;g/mg.min^−0.5. The adsorption of XO on the adsorbent occurred through a combination of electrostatic interactions, hydrogen bonding, hydrophilic interactions, and van der Waals forces. Bimetallic Pt⁰@Ag⁰ is a promising adsorbent owing to its simple preparation, excellent stability, high adsorption capacity, and efficient XO removal from wastewater. The Ag⁰ nanoparticles were employed as a colorimetric sensor for the detection of platinum (II) ions (Pt²⁺) in solution. The orange colored aqueous sols of Ag⁰ became colorless with the addition of PtCl₄²⁻ ions. The silver nanoparticles can be applied to the detection of Pt²⁺ ions for real-field applications.</p>