Experiments on the Adsorption of Pharmaceuticals and Personal Care Products (PPCPs) to Nano-Scale Oxides
Jeffrey Wilcox, Hope College
Dr. Michael Seymour, Hope College
Dr. Jonathan Peterson, Hope College
Pharmaceuticals and personal care products (PPCPs) have been detected in sediment-freshwater systems, where nanometer-size (10-9 m) oxides are important in contaminant transport. To investigate interactions between PPCPs and oxide nanoparticles (NPs), experiments were performed using six NPs (TiO2, Fe2O3, MgO, SiO2, Al2O3, and CaO) and seven PPCPs: salicylic acid, propanolol, carbamazepine, bisphenol-a, diclofenac, caffeine, and ibuprofen. Composite PPCP solutions (1-10ppm) were batched with 50 mg of each NP. Aqueous concentrations were determined by LC/MS after mixing, and sorption was quantified by comparison to control samples.
Results illustrate how sorption can be controlled by the surface charge of the NP and the overall charge on the PPCPs. Over the pH range investigated (~6-8), PPCPs are either cationic, neutral, or anionic, and the net surface charge of NPs depends on their PZC (point of zero charge; the pH value below which the NP has a net positive surface charge). For example, sorption of anionic ibuprofen and diclofenac to negatively-charged SiO2 (PZC=2) was negligible (Kd<0.1 L/kg), while sorption coefficients for these compounds to positively-charged MgO (PZC=12) were 43±8 L/kg and 394±66 L/kg, respectively.
Results also demonstrate that compound charge and NP PZC are not the only parameters controlling sorption. For example, the cationic propanolol was the only compound with significant sorption to SiO2 (Kd=10±6 L/kg), but its sorption to positively-charged MgO was greater (67±33 L/kg). Diclofenac was highly sorbed to Fe2O3 (PZC=~7; Kd=361±80 L/kg) and MgO (PZC=12; Kd=394±66 L/kg) compared to TiO2 (PZC=7.2; Kd=4.4±0.7 L/kg), CaO (PZC=~8; Kd=9.5±1.0), and Al2O3 (PZC= 9.1; Kd=9.6±0.9). Bisphenol-A exhibited greater sorption to MgO (Kd=119±9 L/kg) than the other five NP (1.6 to 11 L/kg). Sorption coefficients for carbamazepine (<0.1 to 6.0 L/kg) and caffeine (0.6 to 2.9 L/kg) were consistent for all six NP. Future work will investigate nonlinear or competitive sorption, PPCP complexation, and NP aggregation.
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