The Influence of Calcination Temperature on Photocatalytic Activity of TiO2-Acetylacetone Charge Transfer Complex towards Degradation of NOx under Visible Light

Abstract

The improvement of photocatalytic activity of TiO2-based nanomaterials is widely investigated due to the tentative of their industrialization as environmental photocatalysts and their inherently low solar spectrum sensitivity and rapid recombination of charge carriers. Coupling of oxygen-based bidentate diketone to nanocrystalline TiO2 represents a potential alternative for improving the holdbacks. Formation of TiO2-acetylacetone charge transfer complex (CTC) by sol-gel route results in a hybrid semiconductor material with photodegradation activity against toxic NOx gas. In this research, the influence of the chelating agent acetylacetone (ACAC) content on the CTC photocatalytic efficiency under visible light was evaluated. A high content of ACAC in the CTC is not a decisive factor for efficiency of photocatalytic reactions. In fact, the highest efficiency for NOx degradation (close to 100%, during 1 h of visible light exposure) was reported for the material calcined in air at 300 °C with the content of strongly bonded acetylacetone not higher than 3 wt.%. Higher calcination temperature (400 °C) left TiO2 almost completely depleted in ACAC, while at the highest applied temperature (550 °C) a portion of anatase was transformed into rutile and the sample is free of ACAC. The analyses pointed out that superoxide anion radical (O2−) plays an active role in photo-oxidation of NOx. Our findings indicate that this CTC has both high visible light spectral sensitivity and photocatalytic efficiency.

TiO2-Acetylacetone as an Efficient Source of Superoxide Radicals under Reduced Power Visible Light: Photocatalytic Degradation of Chlorophenol and Tetracycline

“…Other LMCT complexes of TiO 2 and bidentate ligands, such as glucose [22] and alizarin [23], showed ~100% photocatalytic reduction of Cr (VI) during 1 h under visible light irradiation (Xenon lamp 300 W). Furthermore, the nanocrystalline charge transfer complex (CTC) between TiO 2 and acetylacetone (bidentate) calcinated at 300 • C in air revealed ~100% NOx gas photodegradation for 2 h under visible light irradiation (24 W) [16]. Another study on the amorphous TiO 2 -Acetylacetone complex revealed ~90% degradation of 2,4-dichlorophenol after 24 h in the absence of irradiation in the presence of high catalyst concentration (1 g•L −1 ) [24].…”

“…This maximization occurs through the increase in the formation of e − /h + pairs and, consequently, their interaction with the O 2 and H 2 O molecules to generate • O 2 − and •OH, respectively. Thus, the visible light sensitization mechanism denominated as the ligand-to-metal charge transfer (LMCT) has gained recognition in the development of TiO 2 -based nanomaterials [15], although the effect of point defects should also be considered [16][17][18]. The LMCT mechanism promotes, in theory, the efficient photogeneration of superoxide radicals under visible light [16] and consists of the direct injection of e − from the highest occupied molecular orbital (HOMO) of a chelating ligand into the conduction band (CB) of a semiconductor, such as TiO 2 [19].…”

“…Thus, the visible light sensitization mechanism denominated as the ligand-to-metal charge transfer (LMCT) has gained recognition in the development of TiO 2 -based nanomaterials [15], although the effect of point defects should also be considered [16][17][18]. The LMCT mechanism promotes, in theory, the efficient photogeneration of superoxide radicals under visible light [16] and consists of the direct injection of e − from the highest occupied molecular orbital (HOMO) of a chelating ligand into the conduction band (CB) of a semiconductor, such as TiO 2 [19]. The LMCT mechanism occurs via bonds formed between the chelating ligands (small organic molecules) and the TiO 2 surface [15,16,19].…”

“…The LMCT mechanism promotes, in theory, the efficient photogeneration of superoxide radicals under visible light [16] and consists of the direct injection of e − from the highest occupied molecular orbital (HOMO) of a chelating ligand into the conduction band (CB) of a semiconductor, such as TiO 2 [19]. The LMCT mechanism occurs via bonds formed between the chelating ligands (small organic molecules) and the TiO 2 surface [15,16,19].…”

Comparison Study of Metal Oxides (CeO2, CuO, SnO2, CdO, ZnO and TiO2) Decked Few Layered Graphene Nanocomposites for Dye-Sensitized Solar Cells

“…To avoid moisture, it was filtered and cleaned multiple times with distilled water before being dried in a hot air oven at 90 • C for 5 h. Consequently, the FLG/MOs nanocomposites were calcined in a muffle furnace. Those temperatures were FLG/CeO 2 at 600 • C for 4 h [17], FLG/CuO at 600 • C for 4 h [18], FLG/SnO 2 at 600 • C for 4 h [19], FLG/CdO at 400 • C for 4 h [20], FLG/ZnO at 400 • C for 12 h [21], and FLG/TiO 2 at 400 • C for 2 h [22]. For comparison, pure metal oxide (MOs; CeO 2 , CuO, SnO 2 , CdO, ZnO, and TiO 2 ) NPs were also produced by the same technique without GO and followed by different calcination temperatures.…”