A detailed investigation of the microwave assisted phenylphosphonic acid modification of P25 TiO2

Abstract

The microwave assisted reaction between P25 titanium dioxide (TiO2) and phenylphosphonic acid (PPA) is explored thoroughly and the influence of the reaction conditions on the grafting mechanism and formed products is presented. While the surface grafting is observed at low temperatures and water free conditions, the formation of titaniumphosphonate is favored in water and high reaction temperatures. For the first time the correlation between the amorphous TiO2 phase and the formation of titaniumphenylphosphonate is reported. Materials are fully characterized by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), solid-state 31 P Nuclear Magnetic Resonance (31 P-NMR) spectroscopy, energy dispersive X-ray (EDX) spectroscopy and transmission electron microscopy (TEM).

Surface- and Structural-Dependent Reactivity of Titanium Oxide Nanostructures with 2-Chloroethyl Ethyl Sulfide under Ambient Conditions

“…Materials 2 and 3 clearly display C–H stretching bands from the alkylphosphonic acids within the 3000–2800 cm –1 spectral region. Additional peaks in a region of 1500–800 cm –1 are also indicative of C–H (1450 cm –1 ) and potential P–C (1460 cm –1 ) and Ti–O–P (∼1080, 1040, and 1020 cm –1 ) functionality, consistent with the XPS and EDS data in Figure and Figures S4 and S5, respectively. ,− Significant overlap within the 1500–800 cm –1 region limits the direct assignment of specific peaks relating to C–H and Ti–O–P bands in the spectra in Figure . While O–H stretching bands located at 3400–3360 cm –1 are visible in all the materials, they are the most prominent in material 4 and the commercial P25 TiO 2 .…”

“…Modification of metal oxides with alkylphosphonic acids usually leads to formation of self-assembled monolayers on the surface. − To compare the surface composition of the four materials, XPS analysis was carried out. Figure shows Ti2p, O1s, and P2p core-level spectra collected from materials 1 – 4 .…”

“…Another route for improving the reactivity of TiO 2 is through self-assembled monolayers (SAMs) of phosphonic acid (PA) molecules, which form stable covalent Ti–O–P bonds. − The formation of PA SAMs on TiO 2 has been shown to influence alcohol dehydration rates through active site blocking and transition state stabilization effects. , Active site blocking limits adjacent Lewis acid sites necessary for competitive dehydrogenation reactions, thus promoting alcohol dehydration. , Similarly, cyclohexene epoxidation reactions on a PA-modified SiO 2 -TiO 2 surface were also reduced due to blocking of the Lewis acid sites by surface-bound PA . With respect to photochemically driven reactions, TiO 2 modified with PAs has also been shown to influence band structures due to bond-induced dipoles. , Rivest et al demonstrated through density functional theory (DFT) calculations the tuning of Anatase TiO 2 band edge energies through the structure property relationship of functionalized phenylphosphonic acids.…”

Phosphonate‐Mediated Immobilization of Rhodium/Bipyridine Hydrogenation Catalysts

“…Grafting molecular catalysts onto surfacest of orm heterogeneous systems offerss everalp otential advantages, including easier product separation and catalyst recovery.C ommon routes for immobilizing molecular catalystsi nclude their incorporation into organic polymers [1] and their adsorptiono nto high surfacea rea inorganic frameworkss uch as zeolites and mesoporousm icelle-templated materials, silica, or otherm etal oxides. [2][3][4][5][6][7][8][9] Another strategy is derivatization of solid materials with molecular catalysts, which consists of grafting appropriate functional molecules onto the surface and provides improved control of the arrangemento ft he organic component at the surface.G rafting of organometallic catalysts in acontrolled and stablem anner requires the presence of functional groups that vary accordingt ot he chemical nature of the solid support to be modified.S ome of the most popular combinations are thiol/gold, [10] SiH 3 ,S i(OR) 3 ,o rS iCl 3 /silica or glass, [11][12][13] and P(O)(OR) 2 (R = Ho ra lkyl)/metal oxides [14][15][16][17][18][19][20][21][22][23][24][25] or any type of materialsc ontaining surface-exposed metal centers. [26] Immobilizedcatalysts usually mirrorthe behavior of their homogeneous counterparts, but the accessibility of the catalytic site can be altered by the orientationo ft he catalyst with respect to the surfaceo rb ya ggregation,w hich results in lower reactionr ates.…”

“…Grafting of organometallic catalysts in a controlled and stable manner requires the presence of functional groups that vary according to the chemical nature of the solid support to be modified. Some of the most popular combinations are thiol/gold, SiH 3 , Si(OR) 3 , or SiCl 3 /silica or glass, and P(O)(OR) 2 (R=H or alkyl)/metal oxides or any type of materials containing surface‐exposed metal centers …”