Highly Porous SnO2/TiO2 Heterojunction Thin-Film Photocatalyst Using Gas-Flow Thermal Evaporation and Atomic Layer Deposition

Abstract

Highly porous heterojunction films of SnO2/TiO2 were prepared using gas-flow thermal evaporation followed by atomic layer deposition (ALD). Highly porous SnO2 was fabricated by introducing an inert gas, Ar, during thermal evaporation. To build heterogeneous structures, the TiO2 layers were conformally deposited on porous SnO2 with a range of 10 to 100 cycles by means of ALD. The photocatalytic properties for different TiO2 thicknesses on the porous SnO2were compared using the degradation of methylene blue (MB) under UV irradiation. The comparisons showed that the SnO2/TiO2-50 heterostructures had the highest photocatalytic efficiency. It removed 99% of the MB concentration, and the decomposition rate constant (K) was 0.013 min−1, which was approximately ten times that of the porous SnO2. On the other hand, SnO2/TiO2-100 exhibited a lower photocatalytic efficiency despite having a TiO2 layer thicker than SnO2/TiO2-50. After 100 cycles of TiO2 ALD deposition, the structure was transferred from the heterojunction to the core–sell structure covered with TiO2 on the porous SnO2, which was confirmed by TEM analysis. Since the electrons photogenerated by light irradiation were separated into SnO2 and produced reactive oxygen, O2−, the heterojunction structure, in which SnO2 was exposed to the surface, contributed to the high performance of the photocatalyst.

Photocatalytic Activity in the In-Flow Degradation of NO on Porous TiO2–Coated Glasses from Hybrid Inorganic–Organic Thin Films Prepared by a Combined ALD/MLD Deposition Strategy

“…Previously, the glasses were washed with water and soap and dried on an absorbent paper. The SiO 2 coating plays a multifaceted role, as it inhibits the diffusion of alkaline ions from the glass substrate to the photocatalytic coating during the annealing process [45,52], provides thermal stability to the supported TiO 2 via the formation of covalent Ti-O-Si bonds [22], while it prevents agglomeration, phase transformation and assist the adsorption process, increasing optical path length [53].…”

“…The activity of TiO 2 -materials deposited by MLD has been investigated employing benchmark test reactions such as the photodegradation of methylene blue [43][44][45], Azure B [46] or porphyrin [39]. However, to the best of our knowledge, in contrast with TiO 2 coatings deposited by other techniques [47], the photodegradation of nitrogen oxides remains unexplored for TiO 2 films generated by MLD processes.…”

One-Step Synthesis of TiO2/SiO2-np Nanocomposite Photocatalytic Multilayer Films: Effect of Incorporation Time Sequences of SiO2 Nanoparticles during the TiO2 Film Growth

“…Many deposition methods for synthesizing TiO 2 thin films with different morphologies have also been studied by varying some parameters, such as, for sol-gel and CVD technique, the effect of the annealing temperature [ 11 , 12 , 13 , 14 ]; for spray pyrolysis technique, the film morphology has been evaluated by changing the synthesis temperature [ 15 , 16 ]; for PVD techniques, studies have been carried out on film morphology by changing the working pressure, oxygen partial pressure, sputtering time, and DC power [ 17 , 18 , 19 ]. The TiO 2 film morphology can also be altered by doping [ 20 , 21 , 22 ] or by incorporating nanoparticles to create nanocomposite films [ 23 , 24 , 25 , 26 , 27 , 28 ]. However, both methods, usually not only change the morphological characteristics of the film, but also affect other properties of TiO 2 , i.e., optical [ 22 , 23 , 24 , 25 ], photocatalytic [ 20 , 21 , 22 , 23 , 24 , 25 ], and surface energy properties [ 26 , 27 , 28 ].…”

Removal of Paracetamol from Aqueous Solutions by Photocatalytic Ozonation over TiO2-MexOy Thin Films

“…Well-known for its catalytic properties and chemical stability, TiO 2 represents a very good candidate for the development of new nanosystems with an environmental application, however, its photocatalytic applications are limited, as a consequence of the large band gap (~3.2 eV) and fast recombination of the exciton of TiO 2 . This drawback can be overcome by the use of heterostructures of TiO 2 and metal oxides with lower valence bands (i.e., SnO 2 ), which hinders charge recombination, thus obtaining efficient photo-catalysis [45]. In an attempt to overcome another drawback in applying photo-catalysis to the treatment of polluted water (the recovery of the powder catalyst), TiO 2 -based thin films, immobilized on different supports (aerogels, polymers, glass, etc.)…”