Arsenic adsorption by carboxylate and amino modified polystyrene micro- and nanoplastics: kinetics and mechanisms

Abstract We investigate adsorption characteristics of As(III) and As(V) onto two different functionalized polystyrene (PS) microplastics (MPs). Our results show that there is the potential for PS MPs to adsorb both As(III) and As(V). Using a particle size of 80–82 nm, maximum As(III) and As(V) adsorption capacities of 0.57 mg/g and 0.37 mg/g were obtained by PS-COOH MPs. These capacities were markedly higher than those for PS-NH2 MPs, which were 0.409 mg/g and 0.27 mg/g, respectively. The pseudo-second-order adsorption kinetics and Langmuir isotherm model indicates that hydrogen binding, hydroxyl complexation and electrostatic forces are the key mechanisms controlling adsorption. Adsorption capacity markedly decreases with increasing salinity or presence of humic acid (HA), suggesting an inhibiting effect of salinity and HA through outer-sphere complexation. These findings confirm that microplastics have great potential to adsorb As and hence are ultimately highly likely to affect the environmental behavior of As in an ecosystem.