Hierarchical TiO₂ Nanoflower Photocatalysts with Remarkable Activity for Aqueous Methylene Blue Photo-Oxidation

Abstract

This study systematically evaluates the performance of a series of TiO 2 nanoflower (TNF) photocatalysts for aqueous methylene blue photo-oxidation under UV irradiation. TNF nanoflowers were synthesized from Ti(IV) butoxide by a hydrothermal method and then calcined at different temperatures ( T = 400–800 °C) for specific periods of time ( t = 1–5 h). By varying the calcination conditions, TNF-T-t photocatalysts with diverse physicochemical properties and anatase/rutile ratios were obtained. Many of the TNF-T-1 photocatalysts demonstrated remarkable activity for aqueous methylene blue photo-oxidation at pH 6 under UV excitation (365 nm), with activities following the order TNF-700-1 > TNF-600-1 > TNF-500-1 > TNF-400-1 ∼ P25 TiO 2 ≫ TNF-800-1. The activity of the TNF-700-1 photocatalyst (99% anatase, 1% rutile) was 2.3 times that of P25 TiO 2 at pH 6 and 14.4 times that of P25 TiO 2 at pH 4. Prolonged calcination of the TNFs at 700 °C proved detrimental to dye degradation performance due to excessive rutile formation, which reduced the photocatalyst surface area and suppressed OH • generation. The outstanding activities of TNF-700-1 and TNF-600-1 are attributed to their hierarchical nanoflower morphology which benefitted UV absorption, a near-ideal anatase crystallite size for efficient charge separation, and their unusually low isoelectric point (IEP = 4.3–4.5).

Methylthionine chloride degradation on pilot UV-C reactors: Kinetics of photolytic and heterogeneous photocatalytic reactions

“…Photocatalysis experiments in the absence of H 2 O 2 did not yield good degradation results: higher degradation was 4%, reached at 7.2 pH. This shows that, in heterogeneous photocatalysis, e − /h + generation, which takes place when radiation under 380 nm reaches TiO 2 surface (Calzada et al, 2019;Schneider et al, 2019;Harris et al, 2020), is not the main mechanism for MTC degradation. A possible explanation could be the adsorption of dye on the fiber, saturating the zones where oxidation of MTC in e − /h + could take place.…”

“…As MTC is a cationic molecule (Houas et al, 2001;Nuñez et al, 2015), better results from photocatalysis experiments were expected from basic pH, at which TiO 2 is negatively charged (Calzada et al, 2019;Schneider et al, 2019;Harris et al, 2020), and electrostatic interactions play a role in photocatalysis experiments (Núñez-Núñez et al, 2018). Instead, such electrostatic attraction was detrimental for degradation: as the electron/hole is not the main mechanism for degradation, the mesh color saturation took place faster in basic pH than in acidic conditions, where TiO 2 surface is positively charged.…”

Effects of Reaction Temperature on the Photocatalytic Activity of TiO2 with Pd and Cu Cocatalysts

“…The summary of the pseudo-first-order kinetics of the as-prepared samples under UV light irradiation is shown in Table 2. From Figure 7b, it is plausible to suggest that the photocatalytic degradation reactions of methylene blue on the catalyst followed the pseudo-first-order reaction according to the Langmuir-Hinshelwood (LH) model and may be expressed as [17,19,26,28,44,45]:…”

Synthesis of Anatase/Brookite Mixed Phase TiO2 Nanostructures and its Photocatalytic Performance Study

“…[14][15][16][17][18][19][20] Over the past twothree decades, the use of nanostructured semiconductor materials, especially TiO 2 , ZnO, SnO 2 , ZnS, SnS 2 , MoS 2 , CdS, CeO 2 , Fe 2 O 3 , Ta 2 O 5 , WO 3 , Nb 2 O 5 , SrTiO 3 and many more, has been utilized as potential photocatalysts. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Amongst the reported semiconductor oxides and sulfides, TiO 2 is the most studied photocatalyst due to its chemical and biologically stable nature, cost effective, having optimum band gap and band positions with stronger reducing and oxidizing electronsholes respectively. Additionally, titanium dioxide (TiO 2 ) is a semiconductor oxide exists in three crystalline phases i. e. anatase, rutile, and brookite with an excellent photocatalytic property having direct band gap of 3.2, 3.0 and 3.4 eV respectively.…”