Amino acids adsorption in differently aged and concentrated aqueous suspensions of ZnO and TiO2 nanoparticles

Abstract

Amino acids may be effectively used for preventing aggregation of engineered nanoparticles (NPs) in aqueous suspensions. This paper is primarily focused on the influence of exposure duration and particles content on adsorption coefficient (Ads) for ZnO and TiO2 nanoparticles with an average size of 40-60 nm exposed to 2M aqueous solutions of glycine and L-glutamic acid. The value of Ads was estimated from surfactant concentration related to the intensity of infrared peak spectroscopy at 1300-1400 cm−1. It has been shown that in more concentrated suspensions (0.08-0.12 g/mL) Ads has ±5% fluctuation in measurement error’ interval, whereas in less concentrated systems (0.02-0.04 g/mL) 3…20 h exposure of NPs may result in slight desorption of surfactant as shown for ZnO NPs or total desorption of surfactant as shown for TiO2 NPs in glycine solutions. Six times decrease of 0.02 g/mL NPs concentration leads to Ads augmentation by 3-4 and 1.5-6 times, respectively, on ZnO and TiO2 nanoparticles. From a methodological view point, it has been concluded that in order to provide effective comparative study of NPs adsorption properties it is not reasonable to concentrate the NPs suspension more than 0.04 g/mL and it is better to expose them during 3 h in order to avoid surfactant desorption.