Adsorption of Cetylpyridinium Chloride at Silica Nanoparticle/Water Interfaces (I): Dependence of Adsorption Equilibrium on Particle Size

Abstract

In the current work, a size-effect model was developed to describe the particle size-dependence of adsorption at solid/liquid interfaces. A parameter, ΔQ ad, was introduced, defined as the change of the product of the solid/liquid interfacial tension and the molar volume of solid surface components caused by adsorption. The model predicts that with a decrease in particle radius (r), the saturation adsorption amount per unit area (Γm, mol/m2) decreases, while the change of the adsorption equilibrium constant (K ad) is determined by the ΔQ ad, namely, it decreases if ΔQ ad > 0 but increases if ΔQ ad < 0. There exists a critical r at which the saturation adsorption amount per unit mass (Γm g, mol/g) attains a maximum. In addition, the adsorption of cetylpyridinium chloride (CPyCl), a cationic surfactant, on silica nanoparticles with different r (ca. 6–61 nm) values was determined at 298 K and pH 9, showing an obvious size-dependence. With a decrease in r, K ad and Γm decrease, indicating a decrease in the affinity of silica particles toward CPyCl. The size-dependent adsorption data can be well described using our model. Adsorption can affect the molar volume of the solid surface phase, which plays an important role in the size-dependence of adsorption. This work provides a better understanding of the size-dependent adsorption phenomenon at solid/liquid interfaces.

Adsorption of Cetylpyridinium Chloride at Silica Nanoparticle/Water Interfaces (II): Dependence of Surface Aggregation on Particle Size

“…Four silica samples, with average radii (r) of ∼6, 10, 24, and 61 nm (denoted as S6, S10, S24, and S61, respectively), were synthesized using the Stober method. 35 The specific surface areas (A s ) of samples S6, S10, S24, and S61 were calculated from the r values and the bulk density of silica (2.2 g/cm 3 ) to be 227, 136, 58, and 23 m 2 /g, respectively. 35 All other reagents used in this work were analytical grade.…”

“…22−28 A possible reason is that adsorption may affect the molar volume of the solid surface phase (V ̃sp ), which was ignored in the existing models. In our previous work, 35 a size-effect model was developed by taking into account the change in V ̃sp caused by adsorption. The validity of our model was confirmed by the Langmuir-type adsorption data of cetylpyridinium chloride (CPyCl), a cationic surfactant, on silica nanoparticles with different radii (r, ca.…”

“…6−61 nm) at 298 K and pH 9 and by the literature-reported data of surfactants, proteins, and heavy metal ions on different solid nanoparticles. 35 In fact, adsorption at solid/liquid interfaces is a complex interfacial phenomenon, especially for the adsorption of surfactants that is considered here. Similar to the case in bulk solution, the surfactant molecules adsorbed at solid/liquid interfaces can aggregate with each other, forming surface micelles (hemimicelles or admicelles).…”

The Adsorption Characteristics of Uranium(VI) from Aqueous Solution on Leonardite and Leonardite-Derived Humic Acid: A Comparative Study

“…This has often been used for quantifying adsorption capacity, which assumes monolayer adsorption on the adsorbent site surface. According to this model, once a site is occupied, it cannot be replaced by another adsorbate molecule until a saturation state is reached with the maximum adsorption capacity. , It is depicted according to eq below …”

“…According to this model, once a site is occupied, it cannot be replaced by another adsorbate molecule until a saturation state is reached with the maximum adsorption capacity. 28,29 It is depicted according to eq 5 below…”