**2.7 Green synthesis**

Green synthesis is a simple and ecofriendly method used for the preparation of nanomaterials. Abisharani et al. [58] synthesized TiO2 NPs from titanium trychloride using Cucurbita pepo seeds extract. FTIR results showed that the existence of different functional biomolecules acted as a reducing factor for conversion of TiO4 into TiO2 NPs.

Isnaeni et al. [59] prepared TiO2 NPs by green method including TiCl3 hydrolysis with mango-peel extract. They revealed that the used method could be employed as an alternative to prepare phase pure anatase and rutile. Helmy et al. [60] synthesized S doped TiO2 NPs by a novel green synthesis using Malva parviflora plant extract. They also studied their photocatalytic, antimicrobial, and antioxidant activities. The results showed that the samples exhibited good antibacterial and photocatalytic activities.

In addition, Samhitha et al. [61] studied the TiO2 NPs prepared by various green synthesis methods for anticancer applications. Shen et al. [62] prepared Ce doped TiO2 NPs supported on porous glass. **Figure 12** shows TEM image of TiO2 NPs. The mean diameter was about 5 nm. This study concludes that the green method makes Ce doped TiO2 NPs immobilized on porous glass.

Additionally, TiO2 NPs were synthesized through green method from *Demostachaya bipinnata* extract [63]. It has been shown that the prepared TiO2 NPs are a good candidate for controlling mosquito vectors and agricultural pest management. Nabi et al. [64] prepared TiO2 NPs, with mean crystallite size in the range of 80–100 nm, by green method using citrus limetta extract (as presented in **Figure 13**). The results showed that the degradation activity was more than 90% within 80 min. This excellent photocatalytic activity confirms that TiO2 NPs are ecofriendly and have powerful applications in purification of water.

**Figure 12.** *TEM image of TiO2 NPs prepared by green method [62].*

### **Figure 13.**

*Schematic diagram of the synthesis of TiO2 NPs by green method [64].*
