Table 1.
The chemical reduction synthesis methods, properties and photocatalytic applications of representative black TiO2 materials.
| Materials | Applications | References | ||
|---|---|---|---|---|
| Synthesis | Characterization | Experimental | Photocatalysis efficiency | |
| NaBH4 reduction | ||||
|
TiO2 sol-gel synthesis: Solution A: 5 mL tetrabutyl titanate and 25 mL EtOH. Solution B: 4 mL HNO3 (0.6 M) and 5 mL EtOH NaBH4 reduction: NaBH4 add in the sol 0.025, 0.05, 0.1, 0.3 and 0.4 g |
Phase: anatase, D= 9…35 nm Band-gap energy: 2.87 eV BET surface area: 18…27 m2/g for black TiO2 (priscine: 2 m2/g) | Rhodamine B 10 mg/L Catalyst 1g/L Light source: 500 W tungsten halogen lamp, filter (λ > 420 nm), 300 W high-pressure Hg lamp, filter (λ <365 nm) | Degradation efficiency: 100% after 5 h (sample 0.1-TiO2). The degradation rate increase 9 time after washing with HCl. | Fang et al., 2014 |
| TiO2 synthesis: anodic oxidation of titanium foils, annealed NaBH4 reduction: nanotube arrays were dipped in 0.1 M NaBH4 for different times at room temperature | Phase: anatase, rutile and brookite Morphology: nanotube ~7 mm, pore diameter ~ 100 nm Band gap energy: 2.46 eV, (pristine 3.09 eV) | TiO2 (working electrodes), Pt (counter-electrode), Ag/AgCl (reference electrode). Light source: 300 W Xe lamp, UV cut-off filter of 420 nm, light intensity 0.37 W cm−2 | H2 production rate: 1.31% at 0.40 VRHE after 40 min (pristine 0.32% at 0.48 VRHE) | Kang et al., 2013 |
| TiO2@TiO2−x synthesis: 4.0 g of Degussa TiO2 powder, 1.5 g of NaBH4, heated to 300–400°C, Ar, 5–60 min, dark blue TiO2 300°C/50 min | Phase: Anatase, rutile Morphology: core-shell Band-gap energy: 1.1…2.1 eV (priscine 3.1 eV) BET surface area: 43…50 m2/g for black TiO2 (priscine: 45 m2/g) | Methyl orange 20 ppm (V=50 mL, pH=1), Catalyst 1 g/L | Degradation efficiency: 90% after 10 min (Pristine 75%) | Tan et al., 2014 |
| Methanol (120 mL, 25%), Catalyst 50 mg/1 wt%Pt Light source: 300 W Xe lamp, UV cut-off filter of 400 nm | H2 production rate: 6.5 mmol·h−1·g−1 (7.2 times better than pristine) | |||
| TiO2 synthesis: hydrothermal TiCl4, ethylene glycol, heated at 150°C/6 h Defective TiO2−x synthesis: dual-zone tube furnace, Ar, 500°C/1h, TiO2:NaBH4 mass ratio of 1 to 4 | Phase: low crystallinity | Methanol (30 mL, 10%) Catalyst 0.03 g/0.03 wt% Rh Light source: 500 W mid-pressure Hg lamp and a 420 nm cut-off filter | H2 production rate: 580 mmol· h−1· g−1 | Xu et al., 2019 |
| Metal reduction | ||||
| Reduced TiO2−x synthesis: Aluminum reduction into two zones tube furnace, p <0.5 Pa, Al heated at 800°C, and TiO2 heated at 300… 600°C, 6 h and 20 h Anneling: 500….900°C, 12h, Ar | Phase: anatase, rutile, highly crystalline Morphology: core-shell,~25 nm in diameter Band gap energy: ~3.2 eV similar to pristine BET surface area: 42 m2/g (priscine: 43 m2/g) | Methyl orange 0.1 M (100 mL) Phenol 0.3 M Catalyst 1 g/L | Degradation efficiecy: 52% MO (4% pristine) after 6 h 78% Phenol (82% pristine) after 3.5 | Wang et al., 2013 |
| Methanol 25% (120 mL) Catalyst (0.5 wt% Pt) 0.8 g/L Light source: UV irradiation: 300 W Hg lamp | H2 production rate: H2 6.4 mmol h−1 g−1 (8.5 times higher than that of pristine TiO2 (0.75 mmol h−1 g−1) | |||
| TiO2 hallow sphere synthesis: 1 mmol tetrabutyl titanate, 0.5 g carbon spheres, stirred for 6 h, washed and dried at 90°C for 6 h. Annealing: 400–500°C, 4 h. Black TiO2: Aluminum two-zones tube furnace, TiO2 500°C zone, Al 800°C zone. Annealing: 6 h | Phase: high crystalline, D~8 nm anatase, rutile (>500°C) Morphology: Hollow sphere Band gap energy: BET surface area: 168.8 m2 g−1 | Methanol 10% (100 mL) Catalyst: 0.2 g/L Light source: 300 W Xe-lamp band-pass filter (λ = 365 nm) | H2 production rate: 56.7 mmol·h−1·g−1, 2.5 times higher than pristine | Song et al., 2017 |
| Reduced TiOx (x <2) nanoparticles (white, gray, blue, and black) were prepared by reducing P25 TiO2 (400 mg) with Mg (60…400 mg). Annealing: 600°C, 4 h, Ar. | Phase: TiO0.89, TiO2 anatase TiO2 rutile, D ≈24 nm (as pristine) Morphology: core-shell | Light source: solar-simulated light irradiance at an intensity of 1000 W m−2 (1 Sun). | Solar thermal conversion efficiency: Black TiOx: 50% | Ye et al., 2017 |
| Organic molecules reduction | ||||
| TiO2−x hydrothermal synthesis: L-ascorbic acid (0, 0.3 g and 0.7 g), 70 mL DI water, 3.1 mL of TiCl3, NaOH solution (1 mol/L) to pH=4. The mixture was transferred to a 100 mL Teflon- lined stainless steel autoclave and heated at 180°C for 12 h. | Phase: Anatase D=10…50 nm Morphology: core 10…50 nm Band gap energy: 1.0 eV BET surface area: 64.56 (white), 188.75 (brown), 263.95 m2 g−1 (black), respectively | Methylene blue (MB) 20 mg/L (V=40 mL) Phenol 10 mg/L Photocatalyst 0.5 g/L Light source: 300 W Xenon lamp, UV cut-off filter (λ > 420 nm) | Degradation efficiecy: MB 90% (black TiO2−x), 70% (brown TiO2−x), 50% (white TiO2−x), 5% (pristine), after 100 min Phenol 100% (black TiO2−x), after 80 min | Wajid Shah et al., 2015 |