Enhanced UV Flexible Photodetectors and Photocatalysts Based on TiO2 Nanoplatforms

Abstract

In this study, titanium dioxide (TiO 2) nanostructured films were synthesized under microwave irradiation through low temperature synthesis (80 °C) and integrated in ultraviolet (UV) photodetectors and as photocatalysts. Bacterial nanocellulose (BNC), tracing paper, and polyester film were tested as substrates, since they are inexpensive, flexible, recyclable, lightweight, and when associated to low temperature synthesis and absence of a seed layer, they become suitable for several low-cost applications. The nanostructured TiO 2 films and substrates were structurally characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. The optical properties of all materials were investigated. The TiO 2 nanostructured films were implemented as a photoactive layer of UV photodetectors and demonstrated significant increase of conductance upon exposed to UV irradiation. The photodetection behaviour of each material was investigated by in-situ Kelvin probe force microscopy experiments, in which the contact potential difference varied under dark or UV irradiation conditions, demonstrating higher shift for the BNC-based UV photodetector. Photocatalytic activity of the films was assessed from rhodamine B degradation under solar radiation, and BNC based devices revealed to be the best photocatalyst. The structural characteristics of the TiO 2 films and substrates were correlated to the differences in the UV photodetection and photocatalytic performances.

Paper-Based Nanoplatforms for Multifunctional Applications

“…EDS point analyses were also performed to provide the relative quantities (at.%) of each element (Table S1). As previously observed in an analogous study, all the TiO 2 films were grown on both sides of the cellulose-based substrates [12].…”

“…Three different types of papers have been used, i.e., Whatman grade 2, office paper from INAPA Tecno SuperSpeed, and commercial hospital paper coming in a coach roll. For the uniform growth of ZnO nanostructures, a seed layer of ZnO had to be previously deposited on paper substrates [1], while for TiO 2 no previous treatment on the paper's surface has been carried out [12]. The ZnO seed layer was deposited by radio frequency (RF) sputtering with Argon (Ar), at room temperature [1].…”

“…where α is the linear absorption coefficient of the material, hv is the photon energy, A is a proportionality constant, and m is a constant exponent which determines the type of optical transitions (m = 2 is for direct allowed transition and m = 1/2 for indirect transitions) [12]. The bandgaps of the nanostructures on hospital and office papers were not presented due to the high influence (high reflectance peaks) coming from the paper substrates.…”

“…Titanium dioxide is also an n-type semiconductor like ZnO, and its field of application ranges from sensors to solar cells [12][13][14]. Presently, this material is largely used as a photocatalyst [15][16][17].…”

“…Among the substrates used, it has been previously reported that cellulose is compatible with wet-chemical synthesis routes [1,12]. Moreover, this material is known as being the most abundant biopolymer on Earth, flexible, inexpensive, and recyclable, among other advantages.…”