Competitive Adsorption of ZrO₂ Nanoparticle and Alkali Cations (Li⁺–Cs⁺) on Muscovite (001)

Abstract

We studied the adsorption behavior of ZrO nanoparticles on a muscovite (001) surface in the presence of cations from the alkali series (Li, Na, K, Rb, and Cs). The results of X-ray reflectivity, i.e., specular crystal truncation rod and resonant anomalous X-ray reflectivity in combination with AFM images, show that the sorption of ZrO nanoparticles is significantly affected by the binding mode of alkali ions on the muscovite (001) surface. From solutions containing alkali ions binding as outer sphere surface complexes (i.e., Li and Na), higher uptake of Zr is observed corresponding to the binding of larger nanoparticles, which relatively easily replace the loosely bound alkali ions. However, Zr uptake in solutions containing alkali ions binding as inner sphere surface complexes (i.e., K, Rb, and Cs) is significantly lower, and smaller nanoparticles are found at the interface. In addition, the uptake of Zr in the presence of inner sphere bound cations displays a strong linear relationship with the hydration energy of the coexisting alkali ion. The linear trend can be interpreted as competitive adsorption between ZrO nanoparticles and inner sphere bound alkali cations, which are replaced on the surface and undergo rehydration after release to the solution. The rehydration of alkali ions gives rise to a large energy gain, which dominates the reaction energy of the competitive adsorption process. The competitive adsorption mechanism of ZrO nanoparticles and alkali ions is discussed comprehensively to highlight the potential relationship between the hydration effect of alkali ions and the effect of charge density of the nanoparticles.

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“…Li et al [23] reported similar problems detecting UV-Vis signals at concentrations as low as 0.05 wt%. The observations made in the batch sorption experiments attribute temperature a minor effect in adsorption behaviour do not confirm the work presented by Pham and Nguyen [34]. There, an increased nanoparticle aggregation rate at elevated temperatures was attributed to the higher kinetic energy and more frequent particle collisions.…”

“…The work conducted by Pham and Nguyen [34] showed reduced adsorption in higher concentrations of nanofluid. They suggested surface modifications provide stability to the dispersion beyond a certain concentration threshold.…”

“…Hence, electrostatic stabilisation is expected to fail in these conditions since the energy barrier for particle agglomeration is lowered, and the kinetic energy increasingly dictates particle aggregation [33]. The compression of the EDL was also thought to be the primary influence of particle aggregation in the presence of NaCl in the work presented by Pham and Nguyen [34]. The observation of the highest absorption in FW and lowest in the alkali solution could also be explained with their respective pH.…”

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“…As an example, Fig. 16 shows representative data and the corresponding electron densities at the mica/water interface, after reacting muscovite with Zr for 24 h in two different background electrolytes (LiCl and CsCl) (Qiu et al, 2018). The CTR-derived electron density changes abruptly at the mica surface (0 Å , defined as the position of the top-most oxygen layer in the mica structure) from the crystalline structure left to the aqueous phase right.…”

“…(b) Representative RAXR data at two values of q (dots) and best fit models (lines). (c, d) CTR-derived total electron density distributions (drawn lines) and RAXR-derived interfacial Zr electron densities (filled areas) above the mica (001) basal plane for the two media (Qiu et al, 2018).…”