Quantitative Determination and Comparison of the Surface Binding of Phosphonic Acid, Carboxylic Acid, and Catechol Ligands on TiO₂ Nanoparticles

Abstract

The adsorption, desorption, co-adsorption, and exchange behavior of phosphonic acid, carboxylic acid, and catechol derivatives on the surface of titanium oxide (anatase) nanoparticles are investigated. Thermogravimetric analysis provides a facile and fast-track quantitative determination of the wet-chemical monolayer adsorption constants and grafting densities of ten adsorbates, all under neutral pH conditions. This characterization protocol allows straightforward quantification of the relevant thermodynamic data of ligand adsorption and a comparison of ligand adsorption strengths. The reported procedure is proposed as a universal tool and it should be applicable to many other colloidal metal oxide materials. Moreover, the determined values for the adsorption constants and the monolayer grafting densities provide a toolbox for the assessment of the adsorbates' behavior in desorption, exchange, and co-adsorption equilibria. This versatile evaluation procedure will help to identify optimal monolayer-surface combinations and to evaluate critical parameters, such as monolayer robustness, ligand exchange rates, or targeted mixed assembly of functionalities.

Manufacturing Nanoparticles with Orthogonally Adjustable Dispersibility in Hydrocarbons, Fluorocarbons, and Water

“…To study this hydrophobic interaction driven self‐assembly with nonionic surfactants, we synthesized a simple model amphiphile HC‐PEG 4 to investigate its ability to increase the dispersibility of metal oxide nanoparticles coated with alkyl‐phosphonic acid [MO x ‐ 1 ]. The amphiphile HC‐PEG 4 used in this study was synthesized through the esterification of lauric acid chloride 7 with triethylene glycol according to a modified literature procedure (Figure ) . Compound 4 exhibits an alkyl moiety covalently linked to a glycol moiety and, thus, represents a simple nonionic hydrocarbon–water surfactant.…”

“…Ac ovalents urface modification of metal oxide nanoparticles with phosphonic acidd erivatives has been provent op rovide denselyp acked self-assembled monolayers on the nanoparticle surfaced isplaying remarkable chemical stability. [19][20][21] As metal oxides, we used the commercially availables tarting materials TiO 2 nanoparticles and superparamagnetic Fe 3 O 4 nanoparticles. The average diameter sizes were 34 and 15 nm, respectively.…”

“…The amphiphile HC-PEG 4 used in this study was synthesized through the esterification of lauric acid chloride 7 with triethylene glycol according to am odifiedl iterature procedure ( Figure 2). [19] Compound 4 exhibits an alkyl moiety covalently linked to ag lycol moiety and, thus, represents as imple nonionic hydrocarbonwater surfactant. We also sought to investigate whether this hydrophobic interaction driven self-assembly was transferrable to other particle-capping ligandsa sw ell as other solvente nvironments.T herefore, we synthesized amphiphiles HC-FC 5 and FC-PEG 6,b oth consistingo faperfluorinated alkyl moietyc ovalentlyl inked to either ah ydrocarbon or at riethylene glycol moiety ( Figure 2).…”

“…The metal oxide nanoparticles were functionalized in a wet‐chemical functionalization process in 0.15 wt % dispersions in isopropanol. To ensure full coverage, the particles were exposed to 5.0 mm solutions of phosphonic acids 1–3 . The particles were functionalized in a volume of 25 mL, corresponding to approximately 30 mg nanoparticles.…”

“…To ensure full coverage, the particles were exposed to 5.0 mm solutions of phosphonic acids 1-3. [19] The particles were functionalized in av olume of 25 mL, corresponding to approximately 30 mg nanoparticles. After adding the phosphonic acid, the dispersions were sonicated for 30 min.…”