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Arsenic adsorption by functionalized polystyrene microplastics: kinetics and mechanisms
Summary
This study investigated arsenic adsorption characteristics for As(III) and As(V) onto two functionalized 80–82 nm polystyrene microplastics—carboxyl-modified (PS-COOH) and amine-modified (PS-NH2). PS-COOH achieved higher maximum adsorption capacities of 0.57 mg/g for As(III) and 0.37 mg/g for As(V), with hydrogen bonding, hydroxyl complexation, and electrostatic forces identified as key mechanisms via pseudo-second-order kinetics and Langmuir isotherm modeling. Adsorption was significantly inhibited by increasing salinity and humic acid, confirming that microplastics can alter the environmental behavior of arsenic in aquatic ecosystems.
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-NH 2 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.