Influence of Morphology and Crystallinity on Surface Reactivity of Nanosized Anatase TiO₂ Studied by Adsorption Techniques. 2. Solid–Liquid Interface

Abstract

The aim of this study was to provide new insight into the evaluation of the effect of the crystallinity, size, and morphology of TiO2-anatase nanoparticles on their acid–base properties at the solid–liquid interface. This was achieved through monitoring the evolution in the surface charge density with the solution acidity and point of zero net proton charge (PZNPC) for a set of anatase nanoparticles with a mean size in the 5–20 nm range and various shapes. Different anatase nanoparticles were obtained by a sol–gel synthesis approach using different precursors, pH conditions, and various inorganic or organic additives. The measured PZNPC values were found to vary more than one pH unit depending on the degree of crystallinity and presence of differently exposed surfaces. To discriminate slight differences in the surface reactivity at the solid–water interface, high-resolution titration curves of surface charge for each anatase sample were recorded, and a fine analysis by the titration derivative isotherm summation (TDIS) method and proton affinity distributions (PADs) was performed. They provided accurate data on the strength (pK position) of various local domains of proton adsorption with their relative surface contributions in relation with the particle morphology. The increase in the proportion of sites that are more present on the {101} faces or that of medium acid sites largely present on the {100} faces shifted the point of zero net proton charge to more acidic pH values for particles possessing a majority of such surfaces. In addition to these experiments, the relative acidity of the surface sites on the different surfaces of anatase was evaluated with the multisite complexation model (i.e., MUSIC model) applied to the theoretically optimized surfaces, and a comparison was drawn.

Morphological control of TiO2 anatase nanoparticles: What is the good surface property to obtain efficient photocatalysts?

“…In the present experimental conditions the titania surface charge is slightly positively charged as determined elsewhere on those samples. [61] In that pH range, RhB is also positively charged and electrostatic interactions are consequently excluded. However, both an adsorption of the RhB dye with the carboxylate group or with the lone pair of amino groups is possible.…”

An Experimental and Theoretical Approach to Understanding the Surface Properties of One-Dimensional TiO2 Nanomaterials

“…The shift to lower pH is attributed to the preferential adsorption of cations on the NWs or NTs surfaces previously reported results. 10,14,[65][66] The ionic strength has a significant effect on the lowering the pH of the NTs and NWs suspension. We believe that for the NWs the shift in pH iep and the electrolyte effect in the electrolyte titration are to some extent related to the Na + ion s association being much stronger than the NO 3 -ion association this is also something that emerges from the paper of Bourikas et al 65 The role of the cations has been shown in other TiO 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 systems, often by molecular dynamics simulations.…”

“…Acidbase behavior of NWs and NTs is a superposition of the contributions from the reaction sites of the different crystal planes. Ahmad et al14 emphasized the complex correlation of the acid-base surface properties with surface acidity and surface heterogeneity as well as crystallinity, surface area and crystal plane properties. To understand acid-base equilibria of the NWs and NTs we should take into account exposed crystal planes and their effects on the surface reactivity/acidity.…”

MUSIC Speciation of γ-Al2O3 at the Solid Liquid Interface: How DFT Calculations Can Help with Amorphous and Poorly Crystalline Materials

“…Measurements were carried out using homemade titration set-up composed of an auto-burette (ABU901) ionometer-pHmeter (PHM250) equipped with GK2401 pH electrode (all from Radiometer), these devices being controlled by the TestPoint procedure. The experimental procedure was adapted from Ali Ahmad et al 26 . Alumina (0.1 g of γ-Al 2 O 3 ) was first placed in contact with a 50 mL NaNO 3 background electrolyte.…”