Reduced recombination and enhanced UV-assisted photocatalysis by highly anisotropic titanates from electrospun TiO2–SiO2 nanostructures

Abstract

The surface areas of electrospun fibers/rice grain-shaped nanostructures of TiO 2 -SiO 2 composites were further enhanced after transforming them into thorn or sponge shaped titanates via selective leaching of SiO 2 , which was reported by our group previously [RSC Adv., 2012, 2, 992]. In this study, we report on their application in photocatalytic activity (PCA) when juxtaposed with photoluminescence (PL). Two defect related bands are observed in PL and their origin is discussed in relation to calcination, crystallization and nucleation effects. The relative PL intensity for sponge shapes was the lowest and hence had the lowest radiative recombination, which suggests carrier trapping at defect centers. This enables the charge carriers to migrate to the surface and participate in the PCA. The results of PCA suggested that the sponge-shaped titanate exhibits the highest degradation rate among all samples. A plausible mechanism for the differences in PCA is proposed based on the variation in the defect-densities.

Optoelectronic Properties of Layered Titanate Nanostructure and Polyaniline Impregnated Devices

“…Essentially the present nanostructure is a layered titanate . Previous investigation suggested a predominant Na 2‐x H x Ti 2 O 4 (OH) 2 phase which is believed to be the case here as well …”

“…Going into the specifics the distance between two adjacent O atoms is 0.3 nm which are located at the topmost corners of the octahedra sharing the edges (zigzag structure). In the process of synthesis TiO 2 ‐SiO 2 ‐polyvinyl acetate nanofibers were calcined followed by a treatment with NaOH solution . The alkali treatment etched away the SiO 2 and facilitated the structural rearrangement of titanate.…”

“…To detect the presence of intrinsic (radiative) defect states, PL studies were performed on titanate sample with different illumination wavelengths (λ ex1‐6 =325, 330, 350, 397, 450 and 540 nm), see Figure a. The PL spectrum from similar nanostructures was reported earlier however not extensively discussed . The first three (λ ex1 through λ ex3 ) wavelengths correspond to super‐gap excitations and the latter three (λ ex4 through λ ex6 ) were chosen to be less than that of band gap energy of titanate.…”

Photo-Catalytic Properties of TiO2 Supported on MWCNTs, SBA-15 and Silica-Coated MWCNTs Nanocomposites

“…All of the materials had intense absorptions in the UV-vis range, with a noticeable red shift with the ordered mesoporous titania samples. The band gap can be estimated from the plots of ( αhν ) 2 vs. hν [ 18 , 50 , 58 , 59 ], and the estimated band gap energies were 3.18, 3.34 and 3.42 eV for mesoporous the mesoporous titania, P25 sample and the titania supported on SBA-15, respectively. The titania supported on CNTs and SBA-CNT nanocomposites had an extended absorption feature well into the visible end of the spectrum and the corresponding plots of (αhν) 2 vs. hν had a continuous energy feature which may indicate excitations at low band gap energies.…”

Excitation dependent recombination studies on SnO2/TiO2electrospun nanofibers

“…Ariga et.al., 21 demonstrated that the photo-oxidation of format on the TiO 2 (001) surface has a threshold energy between 2.1 and 2.3 eV (539−590 nm), apparently much lower than that of the bandgap energy (3.0−3.2 eV). The two defect related bands were observed in titanate nanostructures (at 463 and 533 nm) 22 and assigned to carrier trapping at defect centers. On the other hand, the optical properties of SnO 2 are of great importance because of the even parity symmetry which precludes from the bandedge radiation transition 23 .…”