RESULTS AND DISCUSSION Characterization of pure CaO and Zr-TiO 2 /CaO nanocomposite

Transcription

1 RESULTS AND DISCUSSION 4.1. Characterization of pure CaO and Zr-TiO 2 /CaO nanocomposite Scanning electron microscopy analysis (SEM) SEM images of prepared CaO are shown in Fig. 4.1 (a and b). CaO surface had porous nature to enhance the adsorption of Zr-TiO 2 on to the surface molecules. a b Fig. 4.1 ( a and b): SEM images of CaO at different magnifications

2 Fig. 4.2 ( a and b) shows the surface morphology of Zr-TiO 2 /CaO at different magnification. The surface of Zr-TiO 2 /CaO nanoparticles was unevenly distributed on the surface of CaO. Incorporation of Zr-TiO 2 onto CaO surface resulted in less porosity of composite. a b Fig. 4.2 (a and b): SEM images of Zr-TiO 2 /CaO nanocomposite at different magnifications

3 Energy Dispersive X-ray analysis (EDX) EDX pattern of CaO is shown in Fig indicated that elements Ca, O and C were present in CaO. Higher was the peak in a spectrum, more was the concentration of elements in the specimen. In the EDX pattern of CaO, Ca element showed the higher peaks than C and O elements. Fig. 4.3: EDX pattern of CaO Fig. 4.4: EDX pattern of Zr-TiO 2 /CaO nanocomposite Fig exhibited EDX pattern of Zr-TiO 2 /CaO nanocomposite. Ca, O, Ti and Zr are the main elements present in Zr-TiO 2 /CaO. EXD analysis confirms the successful preparation of Zr- TiO 2 /CaO.

4 Transmission electron microscopy analysis (TEM) TEM images of Zr-TiO 2 /CaO nanocomposite are shown in Fig. 4.. The Zr-TiO 2 /CaO nanocomposite consisted of sphere like structures. Fig. 4.: TEM images of Zr-TiO 2 /CaO nanocomposite TEM images of Zr-TiO 2 /CaO indicated that particles were of spherical shape having size varied from nm to 1 nm. The dark surface in the given images indicated the attachment of Zr-TiO 2 onto CaO surface.

5 X-ray diffraction analysis (XRD) XRD diffraction graph for calcium oxide (CaO) is shown in Fig Diffraction peaks at the position of 34.78, , 4.31 and corresponded to (111), (2), (22) and (311) planes shown in Table 1, which were in good agreement with the standard JCPDS file (JCPDS ) for CaO (Balazsi et al., 27). XRD pattern showed that it was semi-crystalline in structure. The crystallite size of CaO lies in range between 1 nm to 3 nm. Table 1: d-spacing for various planes of CaO 2θ angle Diffraction peaks for CaO d-spacing (Å) (111) (2) (22) (311) A Lin (Counts) Theta - Scale A - File: A.raw - Type: 2Th/Th locked - Start:. - End: 1. - Step:.19 - Step time: 38.4 s - Temp.: 2 C (Room) - Time Started: 12 s - 2-Theta:. - Theta: 2. - Chi:. - Phi:. Operations: Import Fig. 4.6: XRD pattern of CaO XRD for synthesized Zr-TiO 2 /CaO nanocomposite is shown in Fig Diffraction peaks at the position of 2.472, 29.9, 34.21, 37.96, ,.981, 4.488, and corresponded to (11), (111), (2), (111), (2), (22), (211), (222) and (116) planes shown in

6 Iobs [cts] Table 2. The results of the data matched well with the standard JCPDS file (JCPDS--189) (Vijaya et al., 213) and (JCPDS ) (Mu et al., 211).The shift in few diffraction peaks of plane may be due to the bonding between CaO and Zr/TiO 2. XRD pattern indicated composite as a whole exhibits semi-crystalline structure. Table 2: d-spacing for various planes of Zr-TiO 2 /CaO nanocomposite 2θ angle Diffraction peaks for Zr- TiO 2 /CaO nanocomposite d-spacing (Å) (11) (Ti) (111) (Zr) (2) (Ca/Zr) (111) (Ti) (2) (Ti/Ca) (22) (Zr) (211) (Ti/Ca) (222) (CaO-Zr/TiO 2 ) (116) (Ti) Pos. [ 2Th.] Fig. 4.7: XRD pattern of Zr-TiO 2 /CaO nanocomposite

7 4.1.. Fourier transform infrared spectroscopy analysis (FTIR) FTIR spectrum of CaO particles is shown in Fig The peak at 712 cm -1 corresponded to Ca-O bond. Peaks at 1417 cm -1 and 866 cm -1 were ascribed to C-O bond. The absorption peak at 342 cm -1 is due to O-H bond (Roy and Bhattacharya, 211). The peaks at 2982 cm -1, 287 cm -1, 216 cm -1 and 1798 cm -1 were due to amines and amides present in eggshell membrane (Tsai et al., 26) , ,42 287,41 216, %T ,23 712, , , cm-1 Fig. 4.8: FTIR spectra of CaO

8 FTIR spectrum of Zr-TiO 2 /CaO powder is shown in Fig The band at 448 cm -1 was ascribed to the stretching vibrations of Ti-O (Mu et al., 211). The absorption peak at 47 cm -1 existed for Ti-O-Zr. The peak at 66 cm -1 was due to the stretching vibrations of Zr-O (Vijaya et al., 213). There existed a band at 1489 cm -1 that arises from the stretching vibrations of C-O. The bands at 2923 cm -1 and 3399 cm -1 were assigned to the amines and amides present in egg shell. The band at 3642 cm -1 was assigned to O-H vibration. RC SAIF PU, Chandigarh ,2 2923,6 17,6 416, ,44 3 %T , ,31 47,32 448, , cm-1 Ajay S Shoolini-1.sp - 4/23/214 - Composite Fig. 4.9: FTIR spectra of Zr-TiO 2 /CaO nanocomposite

9 Log Absorbance 4.2. Solar degradation of methylene blue dye using Zr-TiO 2 /CaO nanocomposite During photodegradation of methylene blue dye the absorbance decreased with increase in reaction time, no significant changes had been observed in dark. The plot of log absorbance versus time follows pseudo first order kinetics with correlation co-efficient of.988, rate constant of min -1 and half life time of 23.8 min (Fig. 4.1) Time (min) y = -.12x -.29 R² = Fig. 4.1: Effect of contact time: Pseudo first order kinetics [MB] = M, [catalyst dose] = mg/ ml, ph = Effect of methylene blue dye concentration The probability of OH radicals formation on the catalyst surface and the probability of OH radicals reacting with the MB molecules represented the rate of degradation. The initial concentration of MB had been varied from M to M. The rate constant increased from min -1 to min -1 with the increase in the methylene blue concentration from M to 1-4 M. Thereafter, rate constant decreased from min -1 to min -1 with the increase in MB concentration from 1-4 M to M. The rate constant was maximal at 1-4 M of MB concentration. The results were presented in Table 3 and Fig This trend was attributed to the availability of more methylene blue molecules on

10 k 1-2 (min -1 ) t 1/2 1-2 (sec) photoactive volumes for the photodegradation process. It was observed that above optimal value the rate constant decreased with the increase in the concentration of MB and the decrease is attributed to the fact that the MB itself will start acting as filter for incident radiation and reducing the photoactive volume. Excessive adsorption of MB molecules on the catalyst surface Zr-TiO 2 /CaO hindered the competitive adsorption of OH ions and lowers the rate of formation of OH. Table 3: Effect of methylene blue dye concentration: [Catalyst dose] = mg/ ml, ph =, reaction time = 3 min [MB] 1-4 M t 1/2 k 1-2 min -1 min Dye concentration (1-4 M) Fig. 4.11: Effect of methylene blue concentration: [Catalyst dose] = mg/ ml, ph =, reaction time = 3 min

11 Effect of catalyst loading In present work, the amount of Zr-TiO 2 /CaO nanocomposites was varied from mg/ ml to 2 mg/ ml in reaction solution to explore the effect of catalyst dose for methylene blue degradation. Rate constant increased from min -2 to min -1 with the increase in Zr-TiO 2 /CaO loading from mg/ ml to 1 mg/ ml. The rate constant was maximal at 1 mg/ ml of photocatalyst loading. The results are represented in Table 4 and Fig The increase in the amount of catalyst resulted in the dye adsorption over the catalyst surface. It can be explained in the terms of availability of active sites on Zr-TiO 2 /CaO surface and the light penetration of visible light into the suspension. The actual degradation of methylene blue dye was caused by increased number of the available sites on the surface of catalyst due to increased photocatalyst loading and more penetration of solar light into the suspension. All these factors suggested that optimum amount of Zr-TiO 2 /CaO had to be added in order to avoid unnecessary excess of catalyst also to assure total adsorption of light photons for efficient photodegradation of MB. Table 4: Effect of catalyst loading: [MB] = M, ph =, reaction time = 3 min Zr-TiO 2 CaO (mg) k 1-2 (min -1 ) t 1/2 (min)

12 k 1-2 (min -1 ) t 1/2 1-2 (min) catalyst dose (mg ) Fig. 4.12: Effect of catalyst loading: [MB] = M, ph =, reaction time = 3 min Effect of ph With the increase in ph from 1 to, the value of rate constant increased from min -1 to min -1 and the effect is shown in Table and Fig Methylene blue dye is a cationic dye in aqueous solution and it can keep its cationic configuration in the ph range At ph basic, electrostatic interactions between the negative catalyst surface and cationic dye leads to strong adsorption of latter on the metal oxide support. The photocatalytic efficiency decreased with decreasing ph due to the electrostatic repulsion between the dye species and the surface of the catalyst as a result of which the photocatalytic degradation percentage was found to be minimum at strong acidic condition. These factors were responsible for optimal value of photodegradation of MB. Further increase in ph resulted in reduction in rate constant. The rate constant was maximal at ph after this it started decreasing.

13 k 1-2 (min -1 ) t 1/2 1-2 (min) Table : Effect of ph: [MB] = 1 1-4, [Catalyst dose] = mg/ ml, reaction time = 3 min ph k 1-2 (min -1 ) t 1/2 (min) ph Fig. 4.13: Effect of ph: [MB] = M, [Catalyst dose] = mg/ ml, reaction time = 3 min