Cu(OH)2 nanorods undergo sulfidation in water: in situ formation of CuO nanorods as intermediates and enhanced toxicity to Escherichia coli

Fate and risk of nanomaterials in the environment have attracted wide attention over the years. Copper hydroxide (Cu(OH)2) nanorods have been used as antibacterial nanomaterials in agricultural products, leading to their release into the environment. Yet, knowledge about the transformation of Cu(OH)2 nanorods is currently scarce, representing a potential for the environment. Here we investigated the sulfidation process of Cu(OH)2 nanorods by dissolved sulfide (Na2S) in aqueous solutions with varied molar ratios of Cu(OH)2 nanorods versus Na2S. The solid products were characterized with focus on the roles of dissolved oxygen (DO) and dissolved sulfide on CuS formation. The impact of sulfidation on the toxicity of Cu(OH)2 nanorods for Escherichia coli was also investigated. Copper oxide (CuO) nanorods with comparable morphology to Cu(OH)2 nanorods were identified as the intermediate of Cu(OH)2 nanorods sulfidation. We proposed that in situ formation of self-assembly CuS nanorods was achieved through an anion-exchange reaction between O2− of CuO and S2− of Na2S. We found that sulfidation enhanced the toxicity of Cu(OH)2 nanorods to E. coli: the inhibition of E. coli growth increased from 1.2 to 22.6% with increasing sulfidation due to an increase of dissolved Cu concentration.