Table 2 Some doped-elements, preparation methods, and the doping effects of doped titania nanotubes as based on the classification of metal-doping, non-metal doping, and co-doping

Metal doping

K₃Fe(CN)₆

One-step anodizing

60 V 6 h at 25 °C

Fe

Band gap: 2.85/2.65/2.10/2.03 eV (undoped: 3.18 eV) photocurrent density: 930/1320/675/590 μA cm⁻²

(undoped: < 240 μA cm^− 2) at 1.5 V under visible light more stable and high photoresponse to visible light

Cu(NO₃)₂·3H₂O

One-step anodizing

20 V 1 h at room temperature

Cu

Band gap: 2.65 eV (undoped: 3.20 eV) total amount of H₂ evolved: 29 μL cm⁻² 2 h (undoped: 7.6 μL cm^− 2 2 h) higher decomposition rate of methylene blue higher stability after multiple reuses

K₂CrO₄

One-step anodizing

60 V 6 h

at 25 °C

Cr

Band gap: 2.82/2.71/2.30 eV (undoped: 3.20 eV) photocurrent density: 360/280/190 μA cm⁻²

(undoped: < 39 μA cm^− 2) at 1.0 V under visible light total amount of H₂ evolved: 37/28/12 μL cm^− 2 4 h (undoped: ≈ 0 μL cm⁻²) higher stability after multiple reuses

Zr(NO₃)₄

Two-step anodizing

3/7/10/15 V 1 h

Zr

Higher photocatalytic activities than that of pure TiO₂ nanotube arrays good photocatalytic stability and could be reused

ZnF₂

One-step anodizing 30 V 15 h

at 25 °C

Zn

Band gap: 2.86/2.84 eV (undoped: 3.00 eV) degeneration rate of methylene blue under visible light for 10 h:88/66% (undoped: ≈ 62%)

V₂O₅

One-pot hydrothermal method at 130 °C 3 h

V

Band gap: 2.91 eV (undoped: 3.18 eV) increased photocurrent density reaction rate (K_app)of rhodamine B: 3 ~ 9 fold as compared to undoped one under UV and visible light

Non-metal doping

NH₃

Annealing a flow rate of 400 mL min⁻¹ at 500 °C 3 h

N

Band gap: 2.8 eV (undoped: 3.1 eV) Table2: Some doped-elements, preparation methods, and the doping effects of doped titania nanotubes as a based on the classification of metal-doping, non-metal doping, and co-doping. Table 2: Some doped-elements, preparation methods, and the doping effects of doped titania nanotubes as a based on the classification of metal-doping, non-metal doping, and co-doping. Photocurrent density: 1.4 mA cm⁻² (undoped: 1.6 mA cm^− 2) at 0.9 V under UV-enhanced PEC activities under visible light and decreased UV light absorption

H₂TiF₆

Spray pyrolysis

F

Enhancement of surface acidity and creation of oxygen vacancies, increase of active sites

H₃BO₃

Anodizing 1.8 V

15-60 min

B

Band gap: 2.91 eV (undoped: 3.20 eV), photocurrent density: 311 μA cm⁻² (undoped: 41.7 μA cm⁻²) at − 0.6 ~ 0.9 V under UV

CH₄

Calcination at 820 °C 18 min in natural gas flame

C

Band gap: 2.84 eV (undoped: 2.92 eV) an additional intragap band: 1.30 eV increased lifetime of photogenerated carriers in the UV

K₂S₂O₅

One-step anodizing 20 V 1 h at 25 °C

S

Band gap: 2.61 eV (undoped: 3.20 eV) high stability after multiple reuses photocurrent density: > 1.22 mA cm⁻² (undoped:< 0.19 mA cm⁻²) at 1.50 V under visible light total amount of H₂ evolved: 41 μL cm⁻² 4 h (undoped: ≈ 0 μL cm⁻²)

KI、HIO₄

Two-step anodizing 1.5 V 15 min

at 23 ± 1 °C

I

Band gap: 2.95/3.0 eV (undoped: 3.07 eV) enhanced photocurrent density under both visible and UV illumination degeneration rate of methylene blue under visible light for 2 h: 71/65% (undoped: ≈ 31%)

Co-doping

NH₃

TaCl₅

Drop-casting method

at 450 °C 30 min

N-Ta

Band gap: 2.5 eV (undoped: 3.1 eV) photocurrent density: 2.5 mA cm⁻² (undoped: 1.6 mA cm⁻²) at 0.9 V under UV-enhanced PEC activities under both visible and UV illumination

NH₃

(NH₄)₅[(NbOF₄)(NbF₇)₂]

Anodizing 45 V at 25 ± 1 °C annealing a flow rate of 100cm³ min⁻¹ at 550 °C 2 h

N-Nb

Strongly enhanced PEC activities for water splitting under both visible light and UV light

K₂[Ni(CN)₄]

Anodizing 40 V 2 h at room temperature

Ni-N-C

Band gap: 2.588 ~ 2.972 eV (undoped: 3.062 eV) photocurrent density: 10 times greater than that of undoped one under visible light