Investigation on the Modification of Physicochemical Properties of Cerium Oxide Nanoparticles through Adsorption of Cd and As(III)/As(V)
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Copyright 2018 American Chemical Society. Previous studies have demonstrated that engineered nanoparticles (ENPs) and metal(loid)s mutually affect their accumulation in plant tissues. Adsorption of metal(loid)s on ENPs is deemed as an important mechanism for their interactions. However, quantitative information on the extent of adsorption in environmentally relevant conditions is lacking. Information is also lacking on how the adsorption of metal(loid)s on ENPs may change the physicochemical properties of ENPs such as their size and zeta potential and consequently their plant uptake. This study measured the adsorption isotherms of Cd and As(III)/As(V) onto 100 mg L-1 cerium oxide nanoparticles (CeO2NPs) in both the presence and absence of synthetic root exudates (SRE) in batch reactors. The adsorption study was allowed to proceed for 48 h to ensure equilibrium. Addition of SRE lowered the pH of the mixture from around 5.9 to 2.3. Both As and Cd displayed strong adsorption on CeO2NPs at pH 5.9. The adsorption was drastically reduced at pH 2.3 without SRE. The presence of SRE mitigated the pH effect, but the adsorption of As and Cd was invariably lower at pH 2.3 than at pH 5.9, irrespective of the SRE. The interactions of metal(loid)s with CeO2NPs significantly increased the hydrodynamic size of some CeO2NPs to micrometer and significantly changed the zeta potential of these nanoparticles to the range of -10 to +10 mV. Different effects on CeO2NPs properties were noticed for Cd and As at different oxidation states. The results shed new lights on the reciprocal effect of CeO2NPs and these two metal(loid)s on their plant uptake and accumulation and demonstrated for the first time that coexisting heavy metal(loid)s may significantly alter the fate and accumulation of ENPs in plants.
