Morphological Modification of TiO2 films by Polyethyleneglycol (PEG) and Their Photoelectrochemical Performance in the Presence of Glycerol as a Hole Scavenger

摘要

PEG-modified TiO2 films (xPEG-TiO2, x is the concentration of PEG 200 in the precursor solution in g/L) were successfully synthesised by a simple, versatile, and low-cost spray pyrolysis deposition method. The effects of PEG 200 as a surface modifier on the relevant properties of TiO2 films were investigated by means of SEM (surface morphology), XRD (crystallography), stylus profiler (thickness), UV-Vis absorbance spectroscopy (optical responses and band gap), and photoelectrochemical measurements (photoelectrolytic performance as photoanodes). The pure TiO2 films show regular, dense and compact nanoparticle network with relatively large grain size (mostly above 500 nm), well-defined grain boundaries, and a film thickness of ca. 1090 nm. Adding an amount of 10 g/L of PEG 200 into the precursor spraying solution results in smaller grain size (mostly below 400 nm) and thinner film (860 nm). Increasing the concentration of PEG 200 in the solution further decreases the grain size and film thickness, yet increase the roughness of the films (Figure 1a-e). The decrease of film thickness upon PEG addition may be attributed to the viscosity increase of the solution due to PEG introduction, which, at the same operating nozzle pressure, leads to lower spraying flow rates. XRD measurements of the pure TiO2 film indicate that the TiO2 crystal phase is of anatase with an observed characteristic peak at the 2θ of 25.3o which corresponds to (1 0 1) plane. This characteristic peak gradually disappears upon increasing the concentration of PEG 200. UV-vis absorbance measurements reveal that the band gap of pure TiO2 film is typically 3.19 eV and slightly increase to 3.20, 3.25, 3.28, and 3.30 eV for the case of 10PEG-TiO2, 20PEG-TiO2, 30PEG-TiO2, and 40PEG-TiO2, respectively.