**3. Results and discussion**

### **3.1 Preparation of CDs**

The microwave assisted synthesis of carbon dots is an effective method to prepare CDs. When a solution of BTCA in aqueous medium, is allowed to get exposure of microwaves for a definite time, there occurs uniform heating and finally the volume of the solution is almost reduced to one tenth of the original volume. Now, the residue is taken out and is diluted by the addition of distilled water. The CDs solution, so obtained is centrifuged under high resolution speed of 10000 rpm and the supernatant is collected. The passage of laser beam through the solution is preliminary indication of the formation of carbon dots. The overall synthetic procedure and passage of laser beam through the solution are shown in **Figure 1(a)** and **(b)** respectively.

#### **3.2 Size determination of carbon dots**

As per conventional definition, carbon nanoparticles with a diameter of less than 10 nm are called carbon dots [19, 20]. Such small carbon dots are required for for cell imaging and other related biomedical applications [21]. However, in the present work, CDs with relatively larger size were required so that they could be used as efficient crosslinker to control the permeation properties of the chitosan film. The results of TEM analysis are shown in **Figure 2**.

It can be seen that the particles are almost spherical and bear size in the range of 40 to 60 nm. The relatively bigger size range could be attributable to the fact that we did not use any stabilizer in the preparation of CDs and hence chances of formation of bigger carbon nanoparticles could not be ruled out. There are

**Figure 1.**

*(a) Scheme showing formation of carbon dots, (b) passage of laser beam through the pale yellow solution of CDs.*

several reports which describe formation of bigger carbon nanoparticles. For example, Smagulova et al. [22] have synthesized carbon dots from birch soot via hydrothermal approach and reported their size in the range of 10 to 60 nm with a maximum percent of particles with diameter of around 25 nm. Similarly, Hou et al. [23] synthesized carbon dots from human hair for detection of Hg (II) ions and reported their diameter in the range of 29 to 80 nm. Similarly, Runa et al. [24] reported synthesis of carbon dots from spider silk via hydrothermal approach and reported an average diameter of 178 nm. Therefore, it appears that it is possible

**101**

ated –NH3

+

*Wound Dressing Application of Ch/CD Nanocomposite Film*

to prepare carbon dots of different sizes, depending upon their applicability. For example, CDs mentioned in the aforesaid examples cannot be used for bio imaging

We also measured zeta potential of as –prepared carbon dots which was found to be −20.2 mV, thus indicating the negatively charged surface of carbon dots. This is simply attributable to the presence of carboxylate groups on the surface of carbon

A survey scan, ranging from 0 to 1200 eV is shown in **Figure 3(a)**. It is evident that two elements, namely C (286 eV) and O (543 eV) are present in the spectrum [25]. The detailed XPS spectra of C 1S and O 1S are shown in **Figure 3(b)** and **(c)**

The C 1S signal peak can be divided in to three peaks, located at 283.8, 284.83and 287.4 eV. These peaks correspond to C-C, C=C and C=O respectively [26]. Finally, in the XPS spectrum of O1S, the peak at 532.25 eV refers to oxygen singly bound to aliphatic carbon while the smaller or low intensity peak at 535.53 eV refers to COO<sup>−</sup> thus confirming the presence of carboxylate groups on the surface of carbon dots.

In this work, we prepared Ch/CD films by solvent evaporation method. When

was found to be 6.2. At this pH, -COOH groups present on the surface of the carbon

charges on the surface of CDs. These negative charges bind electrostatically to the protonated amino groups of chitosan chains and a crosslinked network is formed.

groups along the macromolecular chains. The final pH of the solution

groups, thus rendering negative

the film forming solution is placed in an oven (see experimental section), the solvent is evaporated and semi-transparent film with dark brown appearance is obtained. The crosslinking of chitosan chains by carbon dots may be described as follows: In the film forming solution, chitosan exists in dissolved state with proton-

*DOI: http://dx.doi.org/10.5772/intechopen.95107*

and intracellular sensing.

respectively.

**Figure 2.**

**3.3 XPS analysis of carbon dots**

*TEM image of CDs with 100 nm bar length.*

**3.4 Preparation of Ch/CD films**

dots, ionize to give negatively charged –COO−

dots, thus rendering them negatively charges surface.

*Wound Dressing Application of Ch/CD Nanocomposite Film DOI: http://dx.doi.org/10.5772/intechopen.95107*

#### **Figure 2.** *TEM image of CDs with 100 nm bar length.*

to prepare carbon dots of different sizes, depending upon their applicability. For example, CDs mentioned in the aforesaid examples cannot be used for bio imaging and intracellular sensing.

We also measured zeta potential of as –prepared carbon dots which was found to be −20.2 mV, thus indicating the negatively charged surface of carbon dots. This is simply attributable to the presence of carboxylate groups on the surface of carbon dots, thus rendering them negatively charges surface.
