Morphology and photoluminescence study of titania nanoparticles

Abstract

Titania nanoparticles are prepared by sol-gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)-block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol-gel components-hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer-are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol-gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13-20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies.

Scheme 1

Variation of the sol–gel components

Fig. 1

SFM height (1), phase (2), and SEM (3) images of as-prepared samples: 2% TTIP (a), 2% polymer (b), 1% HCl (c), 2% HCl (d), and 3% HCl (e). Height scales are 60 nm (a1), 50 nm (b1), 30 nm (c1), 50 nm (d1), 40 nm (e1) with phase scales 40° (a2), 20° (b2), 3° (c2), 8° (d2), and 7° (e2). Scale bars correspond to 1 μm

Fig. 2

SEM images of plasma-treated and annealed at 450 °C samples, 1% HCl (a), 2% HCl (b), 1% HCl (c), 2% TTIP (d), and 2% polymer (e). Scale bars correspond to 200 nm

Fig. 3

SEM images of plasma treated and annealed at 1,000 °C samples for 1% HCl (a), 2%HCl (b), 3%HCl (c), 2% TTIP (d), and 2% polymer composition (e). Scale bars correspond to 200 nm. Arrows point the representative primary titania structures (L1) in all images, and the cluster size (L2) is depicted with a line in (a)

Fig. 4

Double-logarithmic plots of the out-of-plane cuts of the 2D intensity as a function of the q _y component of the scattering vector. For clarity, the curves are shifted along the intensity axis. The dashed line indicates the resolution limit of the μGISAXS experiment. Colored lines are the fits, from unified fit model, for determining the prominent in-plane length scales, corresponding to the scattering data in black below them. From bottom to top, the curves correspond to samples from 2% TTIP (cyan), 2% BCP (polymer, green), 1% HCl (purple), 2% HCl (blue), and 3%HCl (red) concentration compositions in each graph. Upper graph (a) is for as-prepared, middle (b) is for heated at 450 °C, bottom graph (c) is for heated at 1,000 °C samples

Fig. 5

XRD diffractograms of as-prepared (a), heated at 450 °C (b), and heated at 1,000 °C (c) 1%HCl samples (standard sol–gel). Typical anatase titania peaks [6] are shown at the bottom

Fig. 6

Photoluminescence spectra of as-prepared (solid points) and heated at 450 °C (open points) samples