Yoshiyuki Sugahara

Single- and double-layered organically modified nanosheets by selective interlayer grafting and exfoliation of layered potassium hexaniobate.

Organically modified niobate nanosheets are promising building blocks for the design of advanced hybrid materials. Nanosheets with controlled thickness and surface composition are important for precise structural design of the nanosheet-based materials. In this work, single-layered and double-layered niobate nanosheets functionalized by phenylphosphonate moieties were selectively prepared by interlayer grafting of A-type and B-type intercalation derivatives of potassium hexaniobate (K4Nb6O17·3H2O) with phenylphosphonic acid (PPA), followed by exfoliation by ultrasonication in acetonitrile. The interlayer grafting of PPA was monitored using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and solid-state NMR spectroscopy, and the thicknesses of the exfoliated nanosheets were measured by atomic force microscopy (AFM). Transparent hybrid films were obtained by incorporating the single- and double-layered nanosheets into an epoxy matrix.

Preparation of water-dispersible TiO2 nanoparticles from titanium tetrachloride using urea hydrogen peroxide as an oxygen donor

TiO2 nanoparticles were prepared from titanium tetrachloride (TiCl4) in CH2Cl2 at 80 °C for 30 h, 42 h and 70 h using urea hydrogen peroxide (UHP) as an oxygen donor with a TiCl4u2006:u2006UHP molar ratio of 1u2006:u20062. The XRD patterns and Raman spectroscopy results showed that the products consisted of anatase TiO2. IR and solid-state 13C NMR with cross polarization and magic angle spinning techniques revealed the presence of urea. TEM observation revealed that the products prepared by the reactions for 30 and 42 h consisted of water-dispersible spheroid nanoparticles with a long axis of ~5 nm, while an aggregation of nanoparticles was evident upon reaction for 70 h. Thermogravimetry, inductively-coupled plasma emission spectrometry and CHN analysis showed that the amount of urea increases in the following order: TiO2_42h, TiO2_70h, TiO2_30h. The photocatalytic activity of the products dispersible in water (TiO2_30h and TiO2_42h) was estimated based on the degradation behaviour of methylene blue, and TiO2_42h showed higher photocatalytic activity than TiO2_30h. It is proposed that TiCl4 was directly oxidized by UHP to form anatase TiO2 in the early stage of the process.

Layered perovskite nanosheets bearing fluoroalkoxy groups: their preparation and application in epoxy-based hybrids

Nanosheets bearing CF3(CF2)7C2H4O groups on their surface were prepared from a CF3(CF2)7C2H4O derivative of ion-exchangeable layered perovskite HLaNb2O7·xH2O (HLaNb) via exfoliation, and were further utilized to prepare epoxy-based hybrids. The CF3(CF2)7C2H4O derivative of HLaNb (C10F_HLaNb) was prepared by reacting the n-decoxy derivative of HLaNb with 1H,1H,2H,2H-perfluorodecanol, CF3(CF2)7C2H4OH. TEM and AFM observations revealed that the C10F_HLaNb was exfoliated into individual nanosheets bearing surfaces covered with CF3(CF2)7C2H4O groups after ultrasonication in acetonitrile. The nanosheet dispersion in acetonitrile was employed to prepare epoxy-based hybrids, and the FE-TEM image of the epoxy-based hybrid with 5 mass% of the nanosheets (C10F_HLaNb/epoxy_5) showed that the nanosheets were dispersed in the epoxy matrix. Thermogravimetry of C10F_HLaNb/epoxy_5 and neat epoxy resin indicated that the initial mass loss due to water decreased and the thermal decomposition retarded by introducing C10F_HLaNb nanosheets. Dynamic mechanical thermal analysis revealed that the glass transition temperature of C10F_HLaNb/epoxy_5 (161 °C) was higher than that of neat epoxy resin (110 °C). These results clearly exhibit that thermal properties were improved by incorporating nanosheets bearing hydrophobic CF3(CF2)7C2H4O groups in the epoxy resin most likely due to a decrease in water content. A water uptake test demonstrated that the water uptake rate of C10F_HLaNb/epoxy_5 was lower than that of the neat epoxy.

Preparation of epoxy-based hybrid films from an aqueous TiO2 dispersion via solvent exchange and surface modification with n-octylphosphonic acid

Transparent TiO2/epoxy hybrid films with high refractive indices have been prepared from a 9-mass% aqueous TiO2 (rutile form) dispersion by a combination of dispersion medium exchange and surface modification with n-octylphosphonic acid (OPA). The dispersion medium was exchanged from H2O to N-methylformamide (NMF) by distilling off H2O after the addition of NMF. The TiO2 surface was then modified with OPA by heating at 80u2009°C for 24u2009h. IR and NMR spectra of the OPA-modified TiO2 nanoparticles (NPs) revealed that the OPA moiety was grafted onto the surface of the TiO2 NPs through Ti–O–P bonds. The resulting OPA-modified TiO2 NPs were employed to prepare epoxy-based hybrid films possessing excellent transparency. The transmittance in the entire visible range (400–800u2009nm) of the hybrid film containing 66.3u2009mass% TiO2 was above 94%. This hybrid film also exhibited the highest refractive index (nu2009=u20091.74), which represented a remarkable increase from that of the pure epoxy resin film (nu2009=u20091.51).

Modification of TiO2 Nanoparticles with Oleyl Phosphate via Phase Transfer in the Toluene-Water System and Application of Modified Nanoparticles to Cyclo-Olefin-Polymer-Based Organic-Inorganic Hybrid Films Exhibiting High Refractive Indices

Oleyl-phosphate-modified TiO2 nanoparticles (OP_TiO2) were prepared via phase transfer from an aqueous phase containing dispersed TiO2 nanoparticles to a toluene phase containing oleyl phosphate (OP, a mixture of monoester and diester), and employed for the preparation of OP_TiO2/cyclo-olefin polymer (COP) hybrid films with high-refractive indices. The modification of TiO2 by OP was essentially completed by reaction at room temperature for 8 h, and essentially all the TiO2 nanoparticles in the aqueous phase were transferred to the toluene phase. The infrared and solid-state 13C cross-polarization and magic-angle spinning (CP/MAS) NMR spectrum of OP_TiO2 showed the presence of oleyl groups originating from oleyl phosphate. The solid-state 31P MAS NMR spectrum of OP_TiO2 exhibited new signals at -1.4, 2.1, and 4.8 ppm, indicating the formation of Ti-O-P bonds. CHN and inductively coupled plasma analyses revealed that the major species bound to the TiO2 surface was tridentate CH3(CH2)7CH═CH(CH2)8P(OTi)3. These results clearly indicate that the surfaces of the TiO2 nanoparticles were modified by OP moieties via phase transfer. OP_TiO2/COP hybrid films exhibited excellent optical transparency up to 19.1 vol % TiO2 loading, and the light transmittance of the hybrid films with 19.1 vol % TiO2 loading was 99.8% at 633 nm. The refractive index of these hybrid films rose to 1.83.