Monitoring Bisphosphonate Surface Functionalization and Acid Stability of Hierarchically Porous Titanium Zirconium Oxides

Abstract

To take advantage of the full potential of functionalized transition metal oxides, a well-understood nonsilane based grafting technique is required. The functionalization of mixed titanium zirconium oxides was studied in detail using a bisphosphonic acid, featuring two phosphonic acid groups with high surface affinity. The bisphosphonic acid employed was coupled to a UV active benzamide moiety in order to track the progress of the surface functionalization in situ. Using different material compositions, altering the pH environment, and looking at various annealing conditions, key features of the functionalization process were identified that consequently will allow for intelligent material design. Loading with bisphosphonic acid was highest on supports calcined at 650 °C compared to lower calcination temperatures: A maximum capacity of 0.13 mmol g(-1) was obtained and the adsorption process could be modeled with a pseudo-second-order rate relationship. Heating at 650 °C resulted in a phase transition of the mixed binary oxide to a ternary oxide, titanium zirconium oxide in the srilankite phase. This phase transition was crucial in order to achieve high loading of the bisphosphonic acid and enhanced chemical stability in highly acidic solutions. Due to the inert nature of phosphorus-oxygen-metal bonds, materials functionalized by bisphosphonic acids showed increased chemical stability compared to their nonfunctionalized counterparts in harshly acidic solutions. Leaching studies showed that the acid stability of the functionalized material was improved with a partially crystalline srilankite phase. The materials were characterized using nitrogen sorption, X-ray powder diffraction, and UV-vis spectroscopy; X-ray photoelectron spectroscopy was used to study surface coverage with the bisphosphonic acid molecules.

Host-Guest Interactions on Electrode Surfaces for Immobilization of Molecular Catalysts

“…42,43 Furthermore, the relatively low surface area and high background activities of gold for many catalytic processes make the analysis of catalytically active adsorbates very difficult. 44 To address these issues and to compliment the array of available analytical techniques to study the surface- To transfer the HGC chemistry from the gold to the MO substrates, two strategies were employed: direct introduction of multiple suitable binding groups, geminal bisphosphonates (BP), 46 to the host scaffold (host 5, see Figure 1) or pre-functionalization of the MO substrates with propiolic acid and subsequent thiol-yne click chemistry on the surface. 47 Both strategies are schematically shown in Figure S15.…”

Host-Guest Interactions on Electrode Surfaces for Immobilization of Molecular Catalysts

“…Furthermore, by preparing mesoporous layers of the MOs, higher surface areas are easily accessible, allowing for the use of further spectroscopic methods and simplifying the analysis of electrochemical data. To transfer the HGC chemistry from the gold to the MO substrates, two strategies were employed: direct introduction of multiple suitable binding groups, geminal bisphosphonates (BP), 44 to the host scaffold (host 5)…”

Actinide and Lanthanide Adsorption onto Hierarchically Porous Carbons Beads: A High Surface Affinity for Pu

“…We have shown that such materials display enhanced mass transport properties while at the same time retaining the high surface areas and uniform pores in the micro- and mesoporous range [32,33]. Both crystallization and surface capping with bisphosphonates produce highly acid-resistant materials [34]. We have also shown that pores at the higher end of the mesopore regime give enhanced diffusion kinetics [33,35].…”