Influence of the Micro-Nanostructuring of Titanium Dioxide Films on the Photocatalytic Degradation of Formic Acid under UV Illumination

Abstract

Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO2 coatings during formic acid degradation under UV illumination. The micro-nanostructuring was performed using the UV illumination of microspheres deposited on a photopatternable sol-gel layer, leading to a hexagonal arrangement of micropillars after development. The structures and coatings were characterized using Raman spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy. When the sol-gel TiO2 films were unstructured and untreated at 500 °C, their effect on formic acid’s degradation under UV light was negligible. However, when the films were annealed at 500 °C, they crystallized in the anatase phase and affected the degradation of formic acid under UV light, also depending on the thickness of the layer. Finally, we demonstrated that surface micro-nanostructuring in the form of nanopillars can significantly increase the photocatalytic efficiency of a coating during the degradation of formic acid under UV light.

Micro-nanostructuring by optical lithography and nitridation of photo-patternable TiO2 sol-gel to obtain micro-nanostructured TiN

“…The thin film resulting from the nitration of a TiO2 sol-gel using RTN treatment, as seen in Figure 1, confirms the formation of a TiN layer through the presence of Raman bands characteristic of the TiN crystalline phase. This is consistent with previous studies [25][26][27][28][29][30][31][32][33][34][35][36][37] . The Raman spectrum of the TiO2 (Figure 1 in black) shows multiple peaks but no features of crystallized TiO2.…”

“…This can be attributed to residual porosity from the preparation method. However, as previously stated in our research [25][26][27][28][29][30][31][32][33][34][35][36][37] , these results indicate that the TiN layer, obtained through a simplified and cost-effective method, can still be potentially used as a plasmonic layer in the NIR range, despite some losses.…”

“…After nitridation, the thickness of the TiN film is estimated to be around 40 nm, as determined by profilometry. The real part of the refractive index slightly differs from the bulk value of TiN reported in literature 31 , which can be explained by porosity in the layer that slightly reduces it. The value of extinction coefficient k shows that the TiN thin layer absorbs in the infrared range (k = 3 for 1000 nm), whereas it is close to zero for the TiO2 thin layer in the visible and infrared ranges.…”

“…It involves TiO2 sol-gel film that can be first photo-patterned and converted into TiN using thermal nitridation in an ammonia atmosphere [22][23][24][25][26] . The main benefit of using a sol-gel based process is the ability to produce submicron structures with various reproducible shapes, such as gratings 22,27, or pillars [28][29][30][31] , on large surface areas 28 without shape restrictions 32,33 . Traditional nitridation processes for TiO2 films are typically done in ovens at high temperatures for processing time (more than 800°C for several hours) 34,35 , which limits their use for stable substrates at high temperatures and their industrial applicability.…”

Effect of Ethylene Glycol: Citric Acid Molar Ratio and pH on the Morphology, Vibrational, Optical and Electronic Properties of TiO2 and CuO Powders Synthesized by Pechini Method

“…An ongoing quest of the scientific community is discovering the ways in which the synthesis might influence the optical and electronic properties of these materials. Metal oxide-based semiconductor materials have been obtained using different methods, including chemical vapor synthesis [ 3 ], sol-gel [ 4 , 5 ], hydrothermal [ 6 ], controlled precipitation [ 7 ] and polymeric precursor [ 8 ]. The polymeric precursor method, commonly known as the Pechini method, is one of the most economical and easily implemented methods to produce metal complexes from concentrated solutions of polyfunctional organic acids, salts or oxides of the cations required for the formation of metal oxides [ 9 ]; it combines low-temperature processing and versatility in the proportions of citric acid and metal cations to control the stoichiometry and the morphology of the particles and/or agglomerates, obtain compositional homogeneity and ensure low toxicity to produce a single-phase nanometric powder [ 10 , 11 ].…”