**4. Sample preparation**

All chemicals were purchased from the Emsure, are of analytical purity and used without further purification. All experiments were carried out in atmospheric pressure.

### **4.1 Synthesis of ZnO nanoparticles**

Zinc Chloride is dissolved in 200ml deionised water in beaker of 250ml and placed on the magnetic stirrer and heated up to 70°C and at a speed rate of 450rpm as shown in **Figure 2**. Similarly, Polyvinyl alcohol is dissolved in 200ml deionised water in beaker of 250ml and placed on the magnetic stirrer and heated up to 70°C respectively. After this 180ml of Zinc Chloride solution is mixed with 180ml of Sodium Hydroxide solution [5] and to this mixture about 10ml of PVA solution is added in 500ml beaker, which is then placed on the magnetic stirrer and is heated upto 70°C for one hour. This solution is then kept inside a black box for one whole night for proper mixing and for cooling. After this solution is filtered using filter paper [6]. This will give a solution and powder of ZnO nanoparticles as shown in (**Figure 3**).

$$\text{ZnCl}\_2 + \text{Na}(\text{OH})\_2 \rightarrow \text{ZnO} + \text{NaCl}\_2 + \text{H}\_2\text{O} \tag{1}$$

**Figure 2.** *Zinc chloride solution is heated on a magnetic stirrer at speed 450 rpm upto 70°C.*

**Figure 3.** *Beaker containing ZnO solution.*
