Table 5.
Parameters involved in the process of dye photodegradation by TiO2 and ZnO nanostructures synthesized by green routes. The dyes methylene blue, rhodamine B, malachite green, methyl orange, Congo red and crystal violet are indicated by the abbreviations MB, RhB, MG, MO, CR and CV, respectively.
| Morphology/Material Phase | Green Synthesis Method | Radiation | Dye | Dye Concentration | Catalyst Concentration | pH | Exposure Time (min) | Efficiency (%) | Reference |
|---|---|---|---|---|---|---|---|---|---|
| Nanorods/TiO2 anatase | Microwave | Artificial sunlight | RhB | 10−5 M (50 mL) | 50 mg/10 mL | dye pH | 120 | >98% | [182] |
| Spherical NPs/TiO2 anatase | Co-precipitation * | Solar light | Coralline red | 5 mg/100 mL | 10 mg/100 mL | 8 | 140 | 92.17% | [103] |
| Meso/macro-porous nanostructures | Precipitation * | Sunlight | MB | 20 mg/L | - | dye pH | 135 | >95% | [183] |
| Spherical NPs/TiO2 anatase | Continuous ultrasonic stimulation | UV light | MB | 10 ppm | 1 g/L | dye pH | 150 | 92.5% | [184] |
| Elliptical NPs/TiO2 anatase | Sol-gel * | Visible light | MB, fuchsine, CV, and Rhodamine 6G | 10 mg/L (100 mL) | 0.1 g | dye pH | 180 | 88–99% | [185] |
| Dandelion-like structures/TiO2 anatase-rutile | Hydrothermal | UV light | MB | 10 mg/L (40 mL) | 20 mg–40 mL | dye pH | 650 | >97% | [132] |
| Spherical NPs/TiO2 rutile | Microwave * | Sunlight | MB, MO, CV, and alizarin red | 1 mg/100 mL | 10 mg/50 mL | dye pH | 360 | 77.3–92.5% | [186] |
| Spherical NPs/TiO2 anatase | Co-precipitation * | UV light | Reactive Green-19 | 6.7 mM | 0.030 g/100 mL | 3.5, 10.5 | 120 | 98.88% | [94] |
| Non-spherical NPs/TiO2 anatase | Sol-gel | UV light | MO | 20 ppm (100 mL) | 0.1 g | dye pH | 150 | 94% | [187] |
| Spherical structures/TiO2 anatase | Precipitation | Sunlight | MB | 6–40 ppm (200 mL) | 0.05–0.40 g | dye pH | 120 | 100% | [110] |
| Nanoflowers/ZnO wurtzite | Co-precipitation * | UV light | MB, MG, CR, and Eosin Y | 15 mg/L | 5 mg/L | dye pH | 90 | 100% | [188] |
| Spherical and hexagonal prismatic NPs and nanosheets/ZnO wurtzite | Co-precipitation | Visible light | RhB | 5 × 10−6 M (2 mL) | 1 mg/2 mL | dye pH | 120 | 75–84% | [125] |
| Leaf-like structures/ZnO wurtzite | Co-precipitation * | Dark condition | MG | 10 mg/L (90 mL) | 5 mg/90 mL | dye pH | 240 | ~80% | [124] |
| Hollow microspheres/ZnO wurtzite | Hydrothermal * | UV light | MG | 10 mg/L (200 mL) | 1 g/L | 5 | 60 | ~90% | [189] |
| Nanosheets/ZnO wurtzite | Hydrothermal | UV light | MB | 1 × 10−5 M (200 mL) | 0.05 g/200 mL | dye pH | 50 | 99.2% | [190] |
| Flower-like nanostructures/ZnO wurtzite | Co-precipitation * | UV light | MB | 50 µM | 0.5–1.0 g/ml | dye pH | 30 | 97.5% | [116] |
| Quasi-hexagonal NPs/ZnO wurtzite | Microwave * | UV light | MB | 5 mg/L (100 mL) | 30 mg (100 mL) | 3–11 | 40 | 70–100% | [191] |
| Spherical NPs/ZnO wurtzite | Mechanically assisted metathesis reaction | UV light | MB | 10 mg/L (100 mL) | 10 mg/100 mL | dye pH | 120 | 78% | [192] |
| Hollow nanospheres/ZnO wurtzite | Hydrothermal | UV and visible light | CR | 20 ppm (50 mL) | 25 mg/50 mL | 5–9 | 90 | 99% | [193] |
| Spongy cave-like structures/ZnO wurtzite | Solution combustion * | UV and sun light | MB | 5 ppm (100 mL) | 50 mg/100 mL | 2–12 | 90 | ~18–100% | [194] |
| Mysorepak-like, canine teeth, hollow pyramid, and aggregated hexagonal/ZnO wurtzite | Combustion * | UV light | MB | 5–20 ppm (100 mL) | 50–200 mg/100 mL | 2–12 | 150 | 85–100% | [195] |
| Quasi-spherical NPs/ZnO wurtzite | Co-precipitation * | Sunlight | MB | 1 × 10−5 M (100 mL) | 100 mg/100 mL | dye pH | 90 | 100% | [113] |
| Spherical NPs/ZnO wurtzite | Sol-gel | Visible light | Direct blue 129 | 20 mg/L (50 mL) | 30–60 mg/50 mL | dye pH | 105 | ~60–95% | [196] |
| Spherical NPs/ZnO wurtzite | Hydrothermal * | UV light | MB and MO | 10 mg/L (50 mL) | 1–30 mg/50 mL | dye pH | 50–60 | 96.6–98.2% | [197] |
| Spherical and rod-like NPs/ZnO wurtzite | Co-precipitation * | Visible light | RhB | 10 mg/L | 1 g | dye pH | 180 | 88–92% | [117] |
| Sponge-like structures/ZnO wurtzite | Combustion * | UV and sun light | MB and MG | 5–25 ppm (100 mL) | 50–200 mg/100 mL | 2–12 | 120–150 | ~10–100% | [198] |
| NPs/ZnO wurtzite | Combustion * | UV light | Rose Bengal | 2–40 ppm (250 mL) | 20–80 mg/250 mL | 6–10 | 90 | ~70–90% | [199] |
| Porous NPs/ZnO wurtzite | Solution combustion * | UV e sun light | MB | 5–20 ppm (100 mL) | 50–200 mg/100 mL | 2–12 | 120 | ~3–99% | [50] |
| Spherical NPs/ZnO wurtzite | Combustion * | UV light | CR | 10–40 ppm (250 mL) | 20–80 mg/250 mL | 6–10 | 60 | 70–90% | [200] |
| Hexagonal NPs/ZnO wurtzite | Solution combustion * | UV and sun light | MB | 5–20 ppm (100 mL) | 100 mg/100 mL | 3–12 | 40–50 | 90–100% | [201] |
| Nanoflowers/ZnO wurtzite | Co-precipitation * | Sunlight | RhB | 10 µM (100 mL) | 20 mg/100 mL | dye pH | 200 | 98% | [201] |
| Sphere-like nanostructures | Co-precipitation * | UV light | MB | 50 µM | 50 mg | dye pH | 210 | 98.6% | [119] |
| Spherical NPs/ZnO wurtzite | Hydrothermal * | UV light | MB and MO | 10 mg/L (50mL) | 5–30 mg/50 mL | dye pH | 50 | 96.6–98.2% | [202] |
| Spherical NPs/ZnO wurtzite | Sol-gel * | UV light | MB, MO, and Methyl red | 5–25 ppm (50 mL) | 50 mg/50 mL | dye pH | 35 | 60–100% | [197] |
| Spherical morphology/ZnO wurtzite | Solvothermal * | Visible light | MB | 20 mg/L (100 mL) | 100 mg/100 mL | 4.0–9.8 | 30 | 7.6–96.8% | [203] |
| Nanoflowers/ZnO wurtzite | Co-precipitation | Sunlight | Indigo carmine | - | 50 mg | dye pH | 120 | 83% | [204] |
| Quasi-spherical NPs/ZnO wurtzite | Combustion * | UV light | MB | 5 × 10−5 M (30 mL) | 20 mg/30 mL | 5–12 | 120 | 40–96% | [115] |
| Plates, bullets, flower, prismatic tip, and closed pinecone nanostructures/ZnO wurtzite | Solution combustion * | UV and sun light | MB | 10 ppm (250 mL) | 60 mg/250 mL | dye pH | 60 | 85–92% | [205] |
The * in the second column indicates that the green syntheses were aided by plant extracts.