Self-Assembled Monolayers Supported on TiO₂:  Comparison of C₁₈H₃₇SiX₃ (X = H, Cl, OCH₃), C₁₈H₃₇Si(CH₃)₂Cl, and C₁₈H₃₇PO(OH)₂

Abstract

The solution-phase reactions of octadecylsilanes with different headgroups (C18H37SiH3, C18H37Si(OCH3)3, C18H37SiCl3, and C18H37Si(CH3)2Cl) and of octadecylphosphonic acid (C18H37PO3H2) with titanium dioxide (anatase) were investigated. Chemical analysis and FTIR suggested that all the reactions, with the exception of that of C18H37Si(CH3)2Cl, yielded closely packed self-assembled monolayers (SAMs). SAMs were characterized with high grafting density (∼4.3-4.8 octadecyl groups/nm 2 ) and with high degree of ordering of alkyl chains. Reaction of C18H37Si(CH3)2Cl yielded less ordered surfaces with grafting density ∼1.5 group/nm 2 . The kinetics plots were similar for all the reactions and illustrated two distinct regions, a rapid attachment followed by a slow growth of the grafting density. The uptake curves were adequately described by the first-order kinetics with two rate constants that differed from each other by 1-2 orders of magnitude. According to the rate constants, the following range of reactivity was established: C18H37SiCl3 . C18H37-PO(OH)2 > C18H37Si(CH3)2Cl > C18H37Si(OCH3)3 > C18H37SiH3. Two distinct types of the SAM growth, uniform and islandlike ones, were proposed on the basis of the FTIR study of the SAMs at submonolayer coverage. Silanes capable of cross-linking (C18H37SiX3, X ) H, Cl, OCH3) gave SAMs with a high degree of ordering at relatively low surface coverage, suggesting nonuniform (islandlike) film growth. For SAMs of C18H37Si(CH3)2Cl and C18H37PO(OH)2, the order gradually improved with coverage and highly ordered SAMs were obtained only for high surface coverage, arguing for the uniform mechanism of the film growth. The thermal stability of the supported monolayers was characterized by TGA. All the SAMs showed good thermal and oxidative stability, and no mass loss was observed below ∼200 °C in air. The temperatures of the maximum mass loss rate were close for all SAMs (∼300 °C).

Self‐assembled Monolayers of Alkylphosphonic Acids on Aluminum Oxide Surfaces – A Theoretical Study

“…nm -2 for closely packed monolayers of APAs, which has been estimated by the cross-section area of the phosphonic acid head group (σ = 0.23 nm 2 ) [17] . This result also agrees with experimental surface coverages reported in the literature for ODPA on mica [18] , TiO 2 [19] , ZrO 2 [19] and Si/SiO 2 [20] . In the tridentate models we had to remove a proton from the adjacent adsorption site for each APA molecule in order to balance the positive charge which is implicated in this coordination mode (see Figure 2d) [10] .…”

Enhanced photocatalytic reduction of Hg(II) in aqueous medium by 2-aminothiazole-modified TiO2 particles

“…The asymmetric and symmetric stretch of -CH 2 groups characteristic of a chloropropyl agent are visible in the TiSA and TiAT spectra at 2961 and 2935cm -1 , respectively. 18 Other modes at 1338, 1386, and 1471 cm -1 can be attributed to the deformation mode δ(CH 2 ) of the propyl bridging group. 19 The small absorption band observed at 2858 cm -1 is due to the -CH stretching of aromatic olefins, confirming the anchorage of the 2-aminothiazole group.…”

Development and characterization of polymer-grafted ceramic membranes for solvent nanofiltration

“…These represent the best grafted layer. Different studies with octadecylphosphonic acid (OPDA) [176][177][178] on metal oxide supports showed the formation of well-ordered monolayers with high grafting densities of about 4 groups/nm -2 . Self-assembly monolayers, comprising the molecules of three phosphonic acids, namely CF 3 (CF 2 ) 7 (CH 2 ) 11 PO 3 H 2 , n-C 16 H 33 PO 3 H 2 and n-C 22 H 45 PO 3 H 2 , on the surface of aluminium metal covered with a native oxide film were studied [179].…”