Phosphate Adsorption on γ-Alumina: A Surface Complex Model Based on Surface Characterization and Zeta Potential Measurements

Abstract

An innovative approach using solid/liquid interface characterization (zetametry measurements, ATR-IR), coupled with ex situ FTIR has been used to build a phosphate complexation model at the alumina surface via the PHREEQC software. According to the phosphorus coverage impregnated on the alumina surface, two mechanisms of adsorption have been identified: a specific surface complex adsorbed on the predominant alumina facet and a surface precipitation process. At low phosphorus coverage (P coverage<1.2 at/nm²), the adsorption proceeds mainly through a monodentate complex adsorbed on µ 1 -Al IV -OH sites located on the (110) facet, a bidentate involving µ 1 -Al V -OH (110) is also discussed. However, the surface concentration of these particular sites is limited. Thus, above the threshold of 1.2 at/nm², a surface precipitation occurs with the formation of an amorphous AlPO 4 phase, experimentally observed by FTIR and zetametry measurements.

Enhanced phosphate removal with fine activated alumina synthesized from a sodium aluminate solution: performance and mechanism

“…8(a) . 44 The results in Fig. 9(b) and Table 3 show that the AlO 6 peak area increased by 15% while the AlO 4 peak area decreased by 15% after adsorption, which is consistent with the FTIR results in Fig.…”

Structural Characterization of Phosphate Species Adsorbed on γ-Alumina by Combining DNP Surface Enhanced NMR Spectroscopy and DFT Calculations

“…First, the increase of P surface concentration reduces the surface coverage in water during phosphate deposition, which hampers the available “active” sites of surface hydrolysis of oligomers originating from the solution, thus preserving covalently bonded oligomers of ν xy type (with x, y > 0). The decrease of hydroxyl coverage during phosphate exchange is also reported by various infrared spectroscopy studies. ,, …”

“…Several analytical approaches, such as spatially resolved Raman and UV–vis–NIR spectroscopy, X-ray absorption spectroscopy, , or Raman imaging techniques, have been applied in order to describe the phosphate species adsorbed onto alumina and elucidate their role in the different stages of catalyst preparation. Infrared (IR) spectroscopy on samples, either dried or in solution, has also been used to investigate the adsorption of phosphates onto γ-alumina and successfully demonstrated the presence of interactions between γ-Al 2 O 3 carriers and phosphate anions. − IR also revealed the evolution of the vibrational frequency of alumina OH groups as a function of phosphate concentration and provided interesting insights into the nature of OH groups involved in the exchange mechanisms in various conditions. ,,, However, an unambiguous identification of the adsorption mode of phosphates by IR spectroscopy remains difficult, as the vibrational frequencies of adsorbed phosphates cannot be easily deconvoluted . Hence, direct insight into the local P environment at the atomic scale required the use of an alternative approach.…”

The Journal of Physical Chemistry C Virtual Special Issue on Advanced Characterization by Solid-State NMR and In Situ Technology and in Recognition of Michael Hunger’s 65th Birthday

“…Artiglia and coworkers detected the size influence of ceria particles on the surface hydroxylation and hydroxyl stability by in situ XPS . The Lefèvre group built two phosphate complexation models at the alumina surface using in situ attenuated total reflection (ATR) measurements …”

“…43 The Lefevre group built two phosphate complexation models at the alumina surface using in situ attenuated total reflection (ATR) measurements. 44 The articles in this VSI show that solid-state NMR and in situ technologies enable a number of important studies in materials science. Michael Hunger played an important role in the development of this field, and this VSI has been organized in part to recognize Prof.…”