Adsorption of III/v ions (In(III), Ga(III) and As(v)) onto SiO₂, CeO₂ and Al₂O₃ nanoparticles used in the semiconductor industry

The semiconductor industry annually uses thousands of tons of nanoparticles (NPs) in chemical mechanical polishing (CMP) processes. When iii/v materials are processed with CMP, the NPs and In(iii), Ga(iii) and As(v) ions (i.e., iii/v ions) coincide and end up in wastewater from electronics fabrication lines. CMP NPs (colloidal SiO₂ (C-SiO₂), fumed SiO₂ (F-SiO₂), CeO₂ and Al₂O₃) may interact with iii/v ions (e.g. In(iii), Ga(iii) and As(v)) and facilitate their transport in aquatic systems. Across a range of pH levels, we found that appreciable adsorptions of In(iii) ions onto CeO₂ or Al₂O₃ NPs, Ga(iii) ions onto C-SiO₂, F-SiO₂, CeO₂ or Al₂O₃ NPs, and As(v) ions onto CeO₂ or Al₂O₃ NPs occur. We determined the intrinsic surface complexation constant (K_C,intr) between the ions and NPs by fitting the experimental data with a surface complexation model (SCM). We then extended the SCM to calculate adsorption as a function of NP size. As size increases, surface site density (SSD) increases, whereas specific surface area (SSA) decreases; both eventually reach a plateau where the bulk material stands. Nonetheless, mass site density (MSD), i.e. the site number per mass, increases with size reduction, indicating that smaller particles give higher adsorption capacity based on the same mass. Upon a 1 nm size reduction of C-SiO₂ NPs, the model predicts that the MSD increases <1% for sizes >100 nm and >10% for sizes <10 nm. For C-SiO₂ NPs adsorbing Ga(iii) ions, the model predicts that decreasing the NP size enhances the adsorption efficiency the most in the pH ranges of 2.5-3 and 8.5-11. This work represents the first SCM capable of incorporating size-dependent NP properties to predict adsorption of environmentally relevant ions.