Effect of Variations of Washing Solution Chemistry on Nanomaterial Physicochemical Changes in the Laundry Cycle

Engineered nanoparticle (ENP) life cycles are strongly dependent on the life-cycle of the nanoenhanced products in which they are incorporated. An important phase for ENP associated with textiles is washing. Using a set of liquid and powdered commercially available detergents that span a wide range of different chemistries, washing studies were performed with one "standard" nanoparticle suspended in wash solution to systematically investigate (changes to) particle size distribution, dissolution, reprecipitation (i.e., "new" particle formation), and complexation to particulate matter. Au ENPs were used as a "tracer" through the system. TEM and EDX analysis were performed to observe morphological and chemical changes to the particles, and single-particle ICP-MS was used to build a size distribution of particles in solution. Varying the washing solution chemistry was found to dictate the extent and rate of dissolution, particle destruction, surface chemistry change(s), and new particle formation. Detergent chemistry, dominated by oxidizing agents, was a major factor. The detergent form (i.e., powder vs liquid) was the other decisive factor, with powder forms providing available surfaces for precipitation and sorption reactions. Control experiments with AgNO3 indicated metallic Ag particles formed during the washing process from dissolved Ag, implying not all Ag-NPs observed in a textile washing study are indicative of released Ag-ENPs but can also be the result of sequential dissolution/reduction reactions.