Ultralong Ag_1.92Mo₃O₁₀·H₂O nanowires have been serendipitously obtained due to selective etching of ammonium phosphomolybdate (APM) only by Ag⁺ ions in water under stirring conditions. The spherical yellow APM particle upon etching by Ag+ ions generates a hollow sphere, and PO₄ ³⁻ ions are expelled as a consequence of etching. The etching and hollowing disrupt the APM structure. Concentration of the etching agent and reaction time are crucial for the formation of Ag_1.92Mo₃O10·H₂O nanowire. The growth of nanowires occurs probably due to etching followed by Ostwald ripening, oriented attachment, and splitting process. Finally, the as-synthesized nanowire exhibits a high capacity to adsorb cationic dyes on its surface. It shows superb adsorption properties, with maximum adsorption capacity of 110 mg g⁻¹, 175 mg g⁻¹, 160 mg g⁻¹ for Methylene Blue, Methyl Green, Crystal Violet, respectively. Moreover, the adsorption process of Methylene Blue on the nanomaterial was investigated taking it as a representative adsorbate. The selective adsorption capability of the nanomaterial toward cationic dye molecules makes it a competent candidate for water purification.