Structural, Morphological Studies and Photocatalytic Activity of CdZns Nanoparticles Fused with Ocimum Tenuiflorum Leaf Extract

Synthesis of Nanoparticles

CdZnS nanoparticles mixed with Ocimum Tenuiflorum were synthesized by the chemical precipitation method. Following chemicals were used for the synthesis. Cadmium acetate (Cd(CH3COO)2.H2O), Zinc acetate (Zn(CH3COO)2.H2O), thiourea (NH2)2.CN), ammonia (NH3OH), triethanolamine, TEA (N(CH2CH2OH3 A specific amount of zinc acetate and cadmium acetate was added to water and mixed for 10 minutes using a magnetic stirrer. After stirring some triethanolamine was added to the solution and stirred for 10 minutes. Then ammonia was added to the solution and stirred well for 20 minutes, thiourea was added to the solution and it was colourless. The desired amount of Ocimum Tenuiflorum extract was added and stirred well. The solution was then placed in a constant temperature bath of 80oC for 1 hour to avoid any temperature gradient. And obtain a greenish- yellow coloured precipitated solution. The precipitate obtained is CdZnS nanoparticles mixed with Ocimum Tenuiflorum extract. The obtained precipitated solution was then centrifuged and washed with deionised water and dried in hot air at 70oC for 1.5 hours, a greenish-yellow powder was obtained. This powder was finely powdered with the help of Agate mortar for ½ an hour.

Preparation of Extract

Ocimum Tenuiflorum extract was prepared as follows, Ocimum Tenuiflorum leaves were collected, washed thoroughly with water and then with deionised water. The water content was dried and then crushed using a mortar. The crushed leaves were then squeezed to get the extract.

Characterization

The prepared sample was subjected to XRD characterization using a Bruker d2 Phaser X-ray diffractometer. The data were recorded over a range (2q) from 0o to 80o with a step size of 0.02o and of wavelength 1.50460 Å. The surface morphology of the nanoparticles was determined using Carel Zeiss, EV018 scanning electron microscope. Optical absorption spectra of the synthesized CdZnS nanoparticles were recorded on the Perkin Elmer UV- visible spectrometer, model- Lambda35 in the wavelength range 190nm to 1100nm. Elemental analysis of the prepared sample was done using TESCAN VEGA3 SBH, a versatile tungsten thermionic emission SEM system intended for both high- and low-vacuum operations.

Its resolution is 2 nm and the magnification ranges up to 1,50,000. Particle size analysis is used to interpret the size distribution of particles in a given sample. The analysis was done using the Micromeritics Model: Nano Plus The instrument can measure (Dilution Method) the particle size of samples suspended in liquids in the range of 0.1 nm to 12.3 µm with sample suspension concentrations from 0.00001% to 40%, and sensitivity for molecular weight to as low as 250 Da.

Structural Studies

The XRD patterns of pure CdZnS NPs and CdZnS with Ocimum Tenuiflorum extract are indicated in (Figure 1). All the peaks in the X-Ray diffraction patterns of NPs show a cubic- zinc blende phase structure of CdS. It was observed that the three diffraction peaks correspond to the lattice planes of (111), (220) and (311), respectively, suggesting that the contents of Ocimum Tenuiflorum have been incorporated into the CdZnS lattice. The XRD patterns demonstrate that the full width at half height maximum (FWHM) of the diffraction peaks increases with the concentration of extract added which results in the degradation and change in the crystalline size. Based on the FWHM, the average particle sizes of pure CdZnS nanoparticles and Ocimum Tenuiflorum added CdZnS NPs, were calculated using the Debye-Scherrer equation, D=0.9λ/(βcosθ); where λ=0.15418 nm, is the x-ray wavelength provided from a Cu (α) radiation, β is the FWHM in radians and θ is the Bragg’s angle, are 1.3 nm and 1.46 nm respectively.

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Particle Size Distribution-Dynamic Light Scattering Method

Dynamic light scattering is a well established technique for calibrating the average size and size distribution of particles in a suspension. The technique has the advantage of being fast and non-invasive, but it does require low particle con- centrations. As well, dynamic light scattering results are often lead to misjudgement if one is uninformed of the state of the sample and the method of data analysis. It measures time- dependent fluctuations in the scattering intensity arising from particles executing random Brownian motion. By analysing these fluctuations pieces of information regarding diffusion coefficient and particle size can be obtained. The fluctuation depends on the diffusion rate, smaller the particle rapid fluctuations take place. The time-dependent fluctuations in the intensity of scattered light were analysed using an autocorrelator that determines the autocorrelation function of the signal. This method has its application in the field of life and material sciences, industrial control processes

etc. The speed of Brownian motion is measured and gives the translational diffusion coefficient D, which can be converted to hydrodynamic diameter (DH) using the Stokes-Einstein equation. DH = kT/3πηD Where k is the Boltzmann constant, T is the temperature and η the dispersant viscosity. The hydrodynamic diameter was calculated for the prepared CdZnS nanoparticle as 24.42 nm and Ocimum Tenuiflorum ( 10 ml and 20 ml ) added CdZnS nanoparticles as 13.78 nm and 14.834 nm respectively.

Morphological Studies

The Scanning Electron Micrograph of CdZnS, Ocimum Tenuiflorum added CdZnS nanoparticles are shown in Figures 2a-2c. From the image obtained, it is found that the prepared nanoparticles have tightly packed surface morphology. The particle size of the prepared nanoparticles was also confirmed using IMAGE J software.

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(c) Figure 2: (A) SEM Images for Cdzns, (B) Cdzns Nanoparticles with 10 Ml Of Ocimum Tenuiflorum and (C) Cdzns Nanoparticles with 20 Ml Ocimum Tenuiflorum.

Elemental Studies

The EDAX spectrum was used to confirm the elemental compositions of CdZnS and Ocimum Tenuiflorum added CdZnS nanoparticles. The peaks obtained from the spectrums for CdZnS and Ocimum Tenuiflorum(10 ml,20 ml) added CdZnS nanoparticles are shown in Figures 3a-3c respectively, shows

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(a) (b) the presence of major elements Cadmium, Zinc and Sulphur in the figure and the presence of carbon, nitrogen and oxygen in figures confirms the presence of Ocimum Tenuiflorum with CdZnS nanoparticles. The elemental composition analysis for CdZnS and Ocimum Tenuiflorum 10ml, 20ml added to CdZnS nanoparticles are shown in Tables 1a-1c respectively.

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(c) Figure 3: EDAX Spectrum of (A) CdZns Nanoparticles, (B) Ocimum Tenuiflorum (10 Ml) Added CdZns Nanoparticles; (C) Ocimum Tenuiflorum (20 Ml) Added CdZns Nanoparticles.

(b)

(c) Table 1: EDAX Elemental Analysis for (A) CdZns, EDAX Elemental Analysis for (B) CdZns: Ocimum Tenuiflorum 10 Ml and (C) CdZns: Ocimum Tenuiflorum 20 Ml.

Optical Studies

The absorption spectra of CdZnS and Ocimum Tenuiflorum Added CdZnS nanoparticles were measured in the range of 200-800 nm, based on the spectra the optical band gap was obtained by plotting a graph (αhν)2 versus hν using the equation given below.

α = A(hν – Eg)n ,

Where hν is the photon energy, Eg the optical band gap, A the edge parameter and n = ½ for direct gap material.

The absorption spectra for CdZnS and CdZnS added with the extract of Ocimum Tenuiflorum in different concentration is shown in figure 4. The UV- visible absorption spectra shows that the ultraviolet cut-off absorption of Ocimum Tenuiflorum added CdZnS nanoparticles shifts to lower energy ie longer wavelength when compared to pure CdZnS nanoparticles. The absorption edge is found to shift towards longer wavelength ie red shift which means that the band gap decreases.

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Plot for (αhν) 2 versus hν for CdZnS nanoparticles are shown in Figure 5. The band gap of CdZnS nanoparticles has a band gap of 2.5 eV. The band gap for Ocimum Tenuiflorum added CdZnS nanoparticles found to be decreased by varying concentration. The band gap is found to be 1.5 eV for 10 ml of Ocimum Tenuiflorum and 2 eV for 20 ml of Ocimum Tenuiflorum.

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Photocatalytic Activity

When a semiconductor material absorbs light with an energy band gap greater than its own, electrons from the valence band are excited into the conduction band. This phenomenon is called photocatalysis, which was defined by Etacheri V, et al. [5]. Thus, the electron–hole pairs formed as a result of a charge separation can cause free radicals to form in the system. Hydroxyl, a powerful organic material oxidizer, reveals the effects of free radicals. Semiconductor (SC) photocatalysts propose a potential for complete removal of toxic chemicals through their effectiveness and potentially wide applicability, as explained by Khatamian M, et al.; Soltani N, et al. [6, 7] described Photocatalysis is a procedure employed by a SC material to absorb energy equal to or greater than the band gap. It leads to the induction of valence band electrons in the conduction band.

To understand the influence of adding leaf extract over photocatalytic ability, the pure CdZnS and Ocimum Tenuiflorum added CdZnS nanoparticles were tested for photo degradation of methylene blue dye in the presence of UV radiation. At first, the pure CdZnS nanoparticles and extract added CdZnS nanoparticles were distributed separately in

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the dye solution and constantly agitated for 1 h in the dark in order to attain the adsorption/desorption equilibrium of dye with the surface of the catalyst. Figure shown below depicts the absorption spectra of methylene blue taken at regular intervals during photocatalysis experiments. Figure 6 is the absorption spectral data presenting photocatalytic degradation of methylene blue by catalysis of a) pure CdZnS, b) 10 ml Ocimum Tenuiflorum added CdZnS nanoparticles and c) 20 ml Ocimum Tenuiflorum added CdZnS nanoparticles.

The complete degradation of methylene blue takes place within 80 minutes for pure CdZnS nanoparticles. Figure 5b shows the photocatalytic degradation of 10 ml Ocimum Tenuiflorum Extract added CdZnS nanoparticles. The photocatalytic activity of 20 ml Ocimum Tenuiflorum added CdZnS nanoparticle is shown in Figure 6c. From the plot it is clear that by adding Ocimum Tenuiflorum the photocatalytic activity of the nanoparticles increased. Also the activity is increased by increasing concentration of extract.

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(c) Figure 6: Absorption Spectral Data Presenting Photocatalytic Degradation of Methylene Blue by Catalysis of (A) Pure CdZns, (B) 10 Ml of Ocimum Tenuiflorum Extract Added CdZns Nanoparticles and (C) 20 Ml of Ocimum Tenuiflorum Extract Added CdZns Nanoparticles.

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(c) Figure 7: The Plot for Time Versus Peak Intensity for (A) Pure CdZns, (B) 10 Ml of Ocimum Tenuiflorum Extract Added CdZns Nanoparticles and (C) 20 Ml of Ocimum Tenuiflorum Extract Added CdZns Nanoparticles.

From the graph it is clear that peak intensity decreases with time ie degradation takes place. The degradation time is varient for the three nanoparticles.

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(a)

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(c) Figure 8: Plot for Percentage of Degradation for (A) Pure CdZns, (B) 10 Ml of Ocimum Tenuiflorum Extract Added CdZns Nanoparticles and (C) 20 Ml of Ocimum Tenuiflorum Extract Added CdZns Nanoparticles.

A graph is drawn between time and rate of degradation shown in Figures 8a-8c for pure CdZnS nanoparticles, 10 ml of Ocimum Tenuiflorum extract added CdZnS nanoparticles and 20 ml of Ocimum Tenuiflorum extract added CdZnS nanoparticles respectively. From the graphs it is clear that the pure CdZnS nanoparticles undergo 94% of degradation in 80 minutes whereas 10 ml thulsi exract added CdZnS nanoparticles undergo 96.4% of degradation in 60 mins and for 20 ml thulsi extract added CdZnS nanoparticles, with in the time of 50 minutes 94.9% of degradation takes place. Thus by adding extract the degradation rate is increased also as the concetration of extract increased the degradation rate is also increased [8, 9, 10, 11, 12, 13, 14].