Simultaneous Phase Transfer and Surface Modification of TiO₂ Nanoparticles Using Alkylphosphonic Acids: Optimization and Structure of the Organosols

Abstract

An original protocol of simultaneous surface modification and transfer from aqueous to organic phases of anatase TiO2 nanoparticles (NPs) using alkylphosphonic acids (PAs) is studied. The influence of the solvent, the nature and concentration of the PA, and the size, concentration, and aggregation state of the TiO2 NPs was investigated. Complete transfer was observed for linear alkyl chains (5, 8, 12, and 18 C atoms), even at very high sol concentrations. After transfer, the grafted NPs were characterized by (31)P solid-state MAS NMR. The dispersion state of NPs before and after phase transfer was monitored by dynamic light scattering (DLS). Small-angle neutron scattering (SANS) was used to characterize the structure of PA-grafted NPs in the organic solvent. Using a quantitative core-shell model cross-checked under different contrast conditions, it is found that the primary particles making up the NPs are homogeneously grafted with a solvated PA-layer. The nanometric thickness of the latter is shown to increase with the length of the linear carbon chain of the PA, independent of the size of the primary TiO2 NP. Interestingly, a reversible temperature-dependent aggregation was evidenced visually for C18PA, and confirmed by DLS and SANS: heating the sample induces the breakup of aggregates, which reassemble upon cooling. Finally, in the case of NPs agglomerated by playing with the pH or the salt concentration of the sols, the phase transfer with PA is capable of redispersing the agglomerates. This new and highly versatile method of NP surface modification with PAs and simultaneous transfer is thus well suited for obtaining well-dispersed grafted NPs.

Study of Perfluorophosphonic Acid Surface Modifications on Zinc Oxide Nanoparticles

“…The zeta potential of ZnO was −11.48 mV in THF, and became more negative following modification, with the most negative being −89.12 mV for ZnO nanoparticles that were modified with F 21 DDPA ( Table 3 ). The perfluorinated phosphonic acid modifications were negatively charged, imparting a negative charge to the dispersed nanoparticles, as previously reported [ 53 , 54 ]. This negative charge led to electrostatic repulsion between molecules, stabilizing the nanoparticles.…”

Selectivity in the Ligand Functionalization of Photocatalytic Metal Oxide Nanoparticles for Phase Transfer and Self‐Assembly Applications

“…The phase transfer process requires strong nanoparticle-ligand bonding in order for the nanoparticles to cross the interfacial barrier between the polar and the nonpolar phases. [35,36] Apparently, the amine-ZnO or À CuO and thiolÀ TiO 2 or À WO 3 interactions are too weak to permanently hydrophobize the nanoparticle surfaces for the interfacial transfer. The thiolÀ ZnO or CuO bond are strong, resulting in smooth phase transfer and very pronounced infrared absorption bands even after repeated washing steps.…”

A green, facile, and rapid method for microextraction and Raman detection of titanium dioxide nanoparticles from milk powder

“…In another study, alkylphosphonic acids and chloroform were used for simultaneous surface modication and phase transfer of TiO 2 NPs. 33 Although they claimed total transfer by eye observation, overnight evaporating was used to concentrate the transferred TiO 2 NPs, which is again time consuming. In contrast, our developed method is much 98.9 AE 3.5 faster (<1 h) and more convenient due to the fact that TiO 2 NPs were extracted and concentrated into an interlayer between aqueous phase and organic phase.…”