Surface speciation of myo-inositol hexakisphosphate adsorbed on TiO₂ nanoparticles and its impact on their colloidal stability in aqueous suspension: A comparative study with orthophosphate

Despite extensive research demonstrating the influence of organic matter and inorganic phosphate on the stability of TiO₂ nanoparticles (NPs), far less research has assessed the impact of myo-inositol hexakisphosphate (IHP), a common organic phosphate widely present in the environment. In this study, the adsorption of IHP on TiO₂ NPs and its impact on their colloidal stability were investigated using batch experiments, dynamic light scattering (DLS) techniques, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and solid-state ³¹P nuclear magnetic resonance (NMR) spectroscopy. Inorganic orthophosphate (P_i) adsorption was run for comparison. The ratio of the P_i/IHP adsorption density (1.528: 0.453) at pH 5.0 suggested that IHP may complex on the TiO₂ surface through three of its six phosphate groups. Zeta potential measurements, ATR-FTIR and NMR spectra indicated that IHP/P_i adsorbed onto TiO₂ NPs by forming inner-sphere complexes and modified the surface charge of these NPs, which exerted a great impact on their colloidal stability. Interactions between NPs measured by sedimentation and aggregation size highly depended on the pH, surface phosphorus coverage, and surface phosphorus species. The impact of IHP on the aggregation and dispersion of TiO₂ NPs was significantly larger than that of P_i, in agreement with the calculation from the DLVO theory. This study highlighted the impact of IHP relative to P_i on the colloidal stability of TiO₂ NPs in phosphorus-enriched environments. - Highlights: • IHP/P_i plays a significant role in the colloidal stability of TiO₂ NPs. • The effect of IHP is much greater than P_i. • TiO₂ surface charge is modified by the formed inner-sphere P complexes. • IHP binds on TiO₂ by 3 of its 6 P groups leaving the other 3 dissociated and ionized. • Interaction between NPs depends on pH, surface P coverage, and surface P species.