Waste from Argentometric Determination of Chloride as a Source of Silver in the Synthesis of <i>p</i>-Hydroxybenzoic Acid Capped Silver Nanoparticles

This paper describes the utilization of waste from the argentometric determination of chloride in a chemistry teaching laboratory as a source of silver for the synthesis of p-hydroxybenzoic acid capped silver nanoparticles (AgNPs). All white and red-brick precipitates in the waste were first separated from the liquid and converted to silver chloride precipitate by washing the precipitates using hydrochloride acid 0.1 M. The silver chloride precipitate was then converted to diammineargentate complex ion by dissolving it into an ammonia solution. The conversion was successfully conducted by using 50 moles of ammonia for every mole of silver chloride. The formation of AgNPs was optimum by applying diammineargentate complex ion and p-hydroxybenzoic acid solutions at a molar ratio of 1 : 10. The formed AgNPs showed a yellow color and absorption peak at around 420 nm with an average particle size of 26.4 nm. The as-synthesized AgNPs were stable at least 16 weeks of storage, indicating that p-hydroxybenzoic acid did not only act as a reducing agent but also play a role as a capping agent.