Competitive adsorption of lead and cadmium onto nanoplastics with different charges: Two-dimensional correlation spectroscopy study

The competitive adsorption ability and mechanisms of lead (Pb2+) and cadmium (Cd2+) by nanoplastics (NPs) with positive charges (PS-NH2) and negative charges (PS-SO3H) were investigated by using batch adsorption experiments coupled with the two-dimensional correlation spectroscopy (2D-COS) method. The adsorption isotherm results showed that PS-SO3H exhibited a higher adsorption capacity for Pb2+ or Cd2+ compared to PS-NH2. The adsorption affinity of NPs for Pb2+ was higher than that of Cd2+. The competitive adsorption results showed that Pb2+ had a more pronounced negative effect on the adsorption of Cd2+. The adsorption capacities of NPs were affected by the surface charge and solution pH. Electrostatic force was the main factor influencing PS-SO3H to capture Pb2+ and Cd2+, while chelation was the main mechanism between PS-NH2 and metals. The functional groups of NPs played significant roles in the sorption of Pb2+ or Cd2+ according to the FTIR spectra and 2D-COS analysis. This study provided new insights into the impact of NPs on the transport of other pollutants.