A METHOD OF PREPARATION OF CADMIUM SULPHIDE COLLOIDAL NANOPARTICLES

Abstract

The present disclosure relates to a process of preparing cadmium sulphide colloidal nanoparticles comprising the steps of a) preparing an aqueous Cadmium chloride (CdCl2) solution; b) adding thioglycolic acid (TGA) to the aqueous CdCl2 solution under stirring; c) adding Sodium hydroxide (NaOH) until the pH of solution is 10; d) adding a sodium sulfide to the solution obtained in step (c) and stirring the solution at 300 rpm for a time period of 4 h to obtain cadmium sulphide colloidal nanoparticles.

Specification

Description:FIELD OF THE INVENTION:
[0001] The present disclosure relates to nanoparticles. More particularly, the disclosure relates to a process of preparation of cadmium sulphide colloidal nanoparticles

BACKGROUND OF THE INVENTION
[0002] Cadmium sulphide (CdS) colloidal nanoparticles are emerged as one of key materials in developing miniature devices due to their semiconducting and luminescent properties. Particles size, shape will influence its band gap and emission properties.
[0003] There are some other synthesis processes which are carried at elevated temperature (i.e. thermochemical synthesis) under purging of nitrogen or argon. This requires complex experimental setup.
[0004] M. Molaei, et.al, (AIP ADVANCES 1, 012113 (2011)) have studied the emission properties of CdS nanocrystals that are produced via thermochemical synthesis. The synthesis process carried at elevated temperature (i.e., 80°C for 1.5 hrs). They also investigated the effect of Na2S on photoluminescence properties. A. E. Raevskaya, et.al., (J Nanopart Res (2014) 16:2650) synthesized ultra-small CdS nanoparticles at ambient conditions (temperature, pressure, and atmosphere) stabilized by using the ammonia, and mercaptoacetate complexes. Vidyalakshmi Rajendran et.al. (Journal of Photochemistry and Photobiology B: Biology 78 (2005) 69-75, J. Mater. Chem., 2009, 19, 6348-6353) studied the effect of different capping agents on photoluminescence of CdS nanoparticles. A. Datta et.al. (Journal of Photochemistry and Photobiology B: Biology 78 (2005) 69-75) prepared CdS colloidal nanoparticles. However, the synthesis process involves the gas purging.
[0005] Thus, there is a need for developing simple and cost-effective method for the preparation of CdS colloidal nanoparticles that is cost effective, independent of purging and any gas flow.

OBJECTS OF THE INVENTION
[0006] Some of the objectives of the present disclosure, with at least one embodiment herein satisfied, are listed herein below:
[0007] It is the primary objective of the present disclosure to provide a process for preparing CdS colloidal nanoparticles in a simple way without the use of complex experimental set up.
[0008] It is yet another objective of the present disclosure to provide a cost-effective method for the preparation of CdS colloidal nanoparticles.
[0009] It is further an objective of the present disclosure to provide a process of preparing CdS colloidal nanoparticles of size range of 2nm to 10nm.
[0010] It is yet an objective of the present disclosure to provide a simple process of preparing CdS colloidal nanoparticles without any requirement of heating, gas purging and exhaustive requirement of energy.
[0011] It is further an objective of the present disclosure to provide a method for the synthesis of stable CdS colloidal nanoparticles using Na2S.

SUMMARY OF INVENTION
[0012] The present disclosure relates to a process of preparing cadmium sulphide colloidal nanoparticles comprising the steps of
a) preparing an aqueous cadmium chloride (CdCl2) solution;
b) adding thioglycolic acid (TGA) to the aqueous CdCl2 solution under stirring;
c) adding sodium hydroxide (NaOH) until the pH of solution is in range of 10 to 11;
d) adding a sodium sulfide to the solution obtained in step (c) and stirring the solution at a speed of 200-500 rpm for a time period in the range of 4 h to obtain cadmium sulphide colloidal nanoparticles.
[0013] The present disclosure also relates to cadmium sulphide colloidal nanoparticles.

BRIEF DESCRIPTION OF DRAWINGS
[0014] The present disclosure contains the following drawings that simply illustrates certain selected embodiments of the CdS colloidal nanoparticles and processes that are consistent with the subject matter as claimed herein, wherein:
[0015] Figure 1 illustrates the protocol used for synthesis of colloidal CdS nanoparticles.
[0016] Figure 2 illustrates. (a) Absorption spectra of colloidal CdS nanoparticles fresh (blue) and aged (red). Photograph of CdS colloidal nanoparticles solution (b) on the day of synthesis and (c) after 4 days.
[0017] Figure 3: depicts characterization of CdS colloidal nanoparticles. (a) Scanning electron microscope (SEM) images of the CdS particles drop casted on silicon wafer. (b) Energy dispersive x-ray spectrum (EDS) collected in SEM, and (c) table shows the elemental composition collected from the particles.
[0018] Figure 4 illustrates Transmission electron microscope (TEM) data of CdS colloidal nanoparticles. (a)&(b) TEM images of the CdS particles drop casted on carbon grid. (c) STEM image of the agglomerate consist of CdS nanoparticles. (d) EDS color maps of Cd ions present in the CdS nanoparticles agglomerate shown in (c). (e) EDS color maps of S ions present in the CdS nanoparticles agglomerate shown in (c).
[0019] Figure 5 illustrates the effect of CdCl2 concentration on optical properties of CdS colloidal particles. (a) Absorption spectra and (b) photoluminescence as a function of wavelength of synthesized CdS colloidal nanoparticles. Samples are excited with laser having the wavelength 400 nm - 450 nm for photoluminescence measurements.
[0020] Figure 6: illustrates the effect of Na2S concentration on absorption of CdS colloidal particles. (a) Photographs of CdS colloidal nanoparticles solutions prepared with different Na2S concentration. (b) Absorption spectra as a function of wavelength of synthesized CdS colloidal nanoparticles.
[0021] Figure 7 illustrates the photoluminescent behaviour of CdS colloidal nanoparticles solutions prepared with different Na2S concentration. (a) Photographs of CdS colloidal particles solutions under laser illumination. (b) Photoluminescence spectra as a function of wavelength of synthesized CdS colloidal nanoparticles. Samples are excited with laser having the wavelength 400 nm - 450 nm for photoluminescence measurements.

DESCRIPTION OF THE INVENTION:
[0022] A detailed description of various exemplary embodiments of the disclosure is described herein. It should be noted that the embodiments are described herein in such detail as to communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.
[0023] The terminology used herein is to describe particular embodiments only and is not intended to be limiting to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising", or "includes" and/or "including" or "has" and/or "having" when used in this specification specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
[0024] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The present disclosure relates to a process of preparing cadmium sulfide colloidal nanoparticles comprising the steps of
a) preparing an aqueous Cadmium chloride (CdCl2) solution;
b) adding thioglycolic acid (TGA) to the aqueous CdCl2 solution under stirring;
c) adding Sodium hydroxide (NaOH) until the pH of solution is in range of 10 to 11;
d) adding a sodium sulfide to the solution obtained in step (c) and stirring the solution at 300 rpm for a time period in the range of 4 h to obtain cadmium sulphide colloidal nanoparticles.
[0025] In another embodiment of the present disclosure, a concentration of the Cadmium chloride (CdCl2) solution is in range of 10 mM to 40 mM.
[0026] In yet another embodiment of the present disclosure, a concentration of the Na2S is in range of. 10 mM-200 mM
[0027] In another embodiment of the present disclosure a concentration of sodium hydroxide is 1M. In another embodiment the volume of NaOH is added to the solution till pH reaches between 10 -11.
[0028] In yet another embodiment of the present disclosure, a volume of TGAis 50 µL.
[0029] In another embodiment of the present disclosure, the cadmium sulfide colloidal nanoparticles is of size range between 2nm to 10nm.
[0030] The present disclosure relates to a cadmium sulfide colloidal nanoparticle obtained from the process as given above
[0031] In an embodiment of present disclosure, CdCl2 is used as a monomer for Cd ions. TGA is used as a capping agent (i.e. stabilizes CdS colloidal particles, and prevent them from agglomerates). NaOH is used as a reducing agent, and to provide the pH for obtaining stable colloidal particles. Na2S is used as a precursor to provide S ions that eventually react with Cd ions and to form CdS particles.
[0032] In another embodiment of present disclosure, TGA addition make CdCl2 to dissociate and precipitates cadmium hydroxide (white color precipitates) in the solution. NaOH addition will help to develop the pH condition required for the production of stable suspension, and dissolves the cadmium hydroxide back into solution. S ion produced from the dissociation of Na2S solution will react with cadmium hydroxide ion to produce CdS particles. TGA acts as a capping agent and stabilizes the resultant CdS colloidal nanoparticles with definite shape and size.
[0033] In an embodiment of the present disclosure, the CdS colloidal nanoparticles have luminescent properites that can be used as a fluorescence based tags in medical imaging, cellular studies, biosensors. In addition, these particles can also ease the substrate making process with good surface coverage area to make devices for fluorescence signal based sensors for the detection of mercury and cadmium.

ADVANTAGES OF THE PRESENT INVENTION
[0034] In accordance with the present disclosure the method of preparation of cadmium sulphide colloidal nanoparticles by using CdCl2 and Na2S has the following advantages:
• Simple experimental setup with no requirement of heating mantle, gas purging and no exhaustive requirement of energy.
• No requirement of resuspension of cadmium sulfide colloidal nanoparticles.
• Less production cost
• Stable CdS colloidal nanoparticles are obtained.
[0035] The present disclosure will be explained using the following examples:

EXAMPLE
Example 1
Preparation of cadmium sulfide colloidal nanoparticles
[0036] As depicted in Figure 1 process involves the addition of 50 µL of thioglycolic acid (TGA) to 10 mL of aqueous CdCl2 (10 mM) solution (under stirring at 300 rpm using magnetic stirrer) that was taken in 25 mL conical flask. Solution turned into white turbid color. TGA's amphiphilic nature makes it an effective capping agent for nanoparticles. Then, aqueous NaOH (1M) is added until the solution pH becomes 10. The addition of NaOH resulted the transparent solution. Then, 1mL of aqueous solution of Na2S (100 mM) is added. The reaction mixture then stirred for 4 hours at 300 rpm. Light yellow color solution was obtained after 4 hrs of reaction. The finally obtained TGA-capped CdS colloidal nanoparticles diluted with same volume of HPLC water. This is referred as stock solution. The stock solution is stored in a refrigerator at 4°C for future use.
However, the effect of precursor's (both CdCl2 and Na2S) concentration on CdS colloidal particles is conducted in a reduced volume (volume of all the solutions scaled down to 5 times), stirring free ambient condition (no gas purging, at room temperature, atmosphere). These batches of solutions characterized without dilution further.

Example 2:
Stability of cadmium sulphide colloidal nanoparticles:
[0037] Absorption spectra of synthesized CdS colloidal nanoparticles (after 4 hrs and after 4 days) are measured using the commercial ultraviolet-visible (UV-Visible) spectrometer (Model: UV-Vis Lambda 365, Company: PerkinElmer).
[0038] Figure 2(a) showed absorption spectrum of the aqueous CdS colloidal nanoparticles solution. The absorption spectrum shows a broad hump in the wavelength range between 350 nm and 420 nm. The absorption spectra (measured on the day of synthesis, and after 4 days) show the similar profile. This confirms that the CdS colloidal particles are stable even after 4 days. Spectrum is compared with the absorption spectrum of HPLC water (black line) in the same wavelength range, and that shows flat line. Figure 2(b)&(c) shows the photographs of the CdS colloidal nanoparticles on the day of synthesis and after 4 days respectively.

Example 3:
Characterization of cadmium sulphide colloidal nanoparticles
A. Scanning Electron microscopy
[0039] Morphology of synthesized CdS colloidal nanoparticles is analysed using focused ion beam scanning electron microscope (FIBSEM, Model: JEOL FIB-4700F) using secondary electron imaging mode. The accelerating voltage of 15 kV is used.
[0040] Figure 3 (a) shows that Scanning electron microscope (SEM) images of the CdS particles drop casted on silicon wafer.

B. Energy Dispersive X- Ray Spectroscopy (EDS)
[0041] Elemental composition of synthesized CdS colloidal nanoparticles is analysed using focused ion beam scanning electron microscope (FESEM, Model: JEOL FIB-4700F) using energy dispersive x-ray spectroscopy (EDS) method. The accelerating voltage of 15 kV is used.
[0042] Figure 3(b)&(c) Energy dispersive x-ray spectrum collected in SEM, and table shows the elemental composition collected from the particles.

C. Transmission electron microscope (TEM)
[0043] Morphology and elemental mapping (to identify the presence and distribution of Cd and S ions) of synthesized CdS colloidal nanoparticles are analysed using the transmission electron microscope (TEM, JEOL JEM F200).
[0044] Images of CdS nanoparticles (Figure 4(a)&(b)) are captured in transmission bright field mode at 200 kV accelerating voltage. Elemental mapping (Figure 4 (d)&(e)) is captured in scanning transmission electron microscopy mode using the same instrument (TEM, JEOL JEM F200).

Example 5:
Effect of CdCl2 concentration on optical properties of CdS colloidal particles.
[0045] Absorption spectra (shown in Figure 5(a)) of synthesized CdS colloidal nanoparticles are measured using the commercial ultraviolet-visible (UV-Visible) spectrometer (Model: UV-Vis Lambda 365, Company: PerkinElmer). Photoluminescence property of the synthesized CdS colloidal nanoparticles are evaluated using the homemade setup. Samples (0.5 mL taken in plastic disposable cuvette) are excited using laser having the wavelength between 400 nm and 450 nm. Laser is operated using external the power supply, and voltage of 5 V is used to pump the laser. Photoluminescence from the sample collected using 60X objective lens (installed in the commercial Nikon microscope), and analysed using spectrometer (Andor Kymera 328i with Newton 920 CCD camera, Oxford Instruments).
[0046] Figure 5 conveys that the synthesized CdS colloidal nanoparticles are stable, and absorbing the light in the wavelength between 350 nm and 450 nm (indication that particle are having interaction with the light). In addition, synthesized CdS colloidal nanoparticles are having luminescent in nature. These findings reveals that optical properties (both absorption and photoluminescence) of colloidal CdS nanoparticles can be tuned noticeably by changing the CdCl2 concentration used during the synthesis for a desired laser excitation source and emission required for the application of choice.
[0047] Figure 5 shows the optical properties of the CdS colloidal nanoparticles as a function of wavelength that are synthesized with different concentration of the CdCl2 under same experimental conditions. Absorption spectra shows a broad hump between 350 nm and 450 nm (Figure 5(a)).
Figure 5(b) shows the photoluminescence spectra of CdS colloidal solution. It is observed that peak wavelength at which maximum emission occurs shifted to lower wavelength with an increase in CdCl2 concentration. Pure water spectrum shows flat profile indicates that there no emission from the solvent (CdS nanoparticles are suspended in aqueous medium).

Example 6:
Effect of Na2S concentration on absorption of CdS colloidal particles
[0048] Absorption spectra (shown in Figure 5(a)) of synthesized CdS colloidal nanoparticles are measured using the commercial ultraviolet-visible (UV-Visible) spectrometer (Model: UV-Vis Lambda 365, Company: PerkinElmer).
[0049] . From figure 6(a), it is observed that particles synthesized with 10 mM, 20 mM, 30 mM, and 40 mM shows very pale color within an hour and even after 12 hrs. CdS paprticles synthesized with 500 mM Na2S concentration showed precipitation within one hour. Similarly, 300 mM also shows precipitation in 12 hours. Na2S concentration between 60 - 150 mM shows pale yellow color, and particles are stable. Figure 6(b) shows the absorption spectrum of the CdS colloidal particles as a function of wavelength. Peak absorption wavelength shifted to higher wavelength with increase in Na2S concentration. It is demonstrated that absorption of CdS colloidal particles can be tuned be between 360 nm and 450 nm wavelength by changing the Na2S concentration.

Example 7:
Photoluminescence behaviour of CdS colloidal nanoparticles solutions prepared with different Na2S concentration
[0050] Photoluminescence properties of synthesized CdS colloidal nanoparticles are evaluated using the homemade setup. Samples (0.5 mL taken in plastic disposable cuvette) are excited using laser having the wavelength between 400 nm and 450 nm. Laser is operated using external the power supply, and the voltage of 5 V is used to pump the laser. Photoluminescence from the sample collected using 60X objective lens (installed in the commercial Nikon microscope), and analysed using spectrometer (Andor Kymera 328i with Newton 920 CCD camera, Oxford Instruments).
[0051] . Photographs shows the emission color is changed from pale yellow to pink color with increase in Na2S concentration (Figure 7(a)). Figure 7(b) shows photoluminescence spectra of CdS colloidal solution measured. It is observed the CdS colloidal particles synthesized with 10 mM Na2S show no noticeable profile, though there is a clear emission (yellow color) in the photograph (see Figure 7(a)). CdS colloidal particles produced at all the other experimental conditions shows a clear profile in photoluminescence spectra in the wavelength range between 500 nm and 600 nm. Photoluminescence intensity increases with increase in Na2S concentration. However, the CdS particles produced with 200 mM Na2S shows peak around 610 nm and 150 mM case shows narrow spectrum with two peaks in the wavelength range 480 nm and 600 nm. Findings in this section demonstrates that particles synthesized with 10 mM shows weak emission, and high Na2S concentration (150 mM and 200 mM) shows shift in the emission spectrum, while the other conditions do not shows a shift. Na2S concentration lies in the 20 mM till 150 mM are suitable for the production of stable CdS colloidal particles with a clear signature or profile in the photoluminescence spectra.

 

SPECIFIC EMBODIMENTS OF THE INVENTION
[0052] In an embodiment, the present disclosure relates to a process of preparing cadmium sulphide colloidal nanoparticles comprising the steps of
a) preparing an aqueous Cadmium chloride (CdCl2) solution;
b) adding thioglycolic acid (TGA) to the aqueous CdCl2 solution;
c) adding Sodium hydroxide (NaOH) until the pH of solution is in range of 10 to 11.
d) adding a sodium sulfide to the solution obtained in step (c) and stirring to obtain cadmium sulphide colloidal nanoparticles.
[0053] Such a process, wherein a concentration of the Cadmium chloride (CdCl2) solution is in range of 10 mM to 40 mM
[0054] Such a process wherein a concentration of the Na2S is in range of 20 mM to 150mM.
[0055] Such a process, wherein a concentration of sodium hydroxide is in range of 1 M
[0056] Such a process, wherein a volume of TGA is 50 µL
[0057] Such a process, wherein the cadmium sulphide colloidal nanoparticles is of size range between 2nm to 10nm.
[0058] Such a process, wherein the solution in step (d) is stirred at a speed of 200-500 rpm for a time period of 4 h.
[0059] The present disclosure also relates to a cadmium sulphide colloidal nanoparticle.

, Claims:WE CLAIM

1.A process of preparing cadmium sulphide colloidal nanoparticles comprising the steps of
a) preparing an aqueous Cadmium chloride (CdCl2) solution;
b) adding thioglycolic acid (TGA) to the aqueous CdCl2 solution;
c) adding Sodium hydroxide (NaOH) until the pH of solution is in range of 10 to 11.
d) adding a sodium sulfide to the solution obtained in step (c) and stirring to obtain cadmium sulphide colloidal nanoparticles.
2. The process as claimed in claim 1, wherein a concentration of the Cadmium chloride (CdCl2) solution is in range of 10 mM to 40 mM
3. The process as claimed in claim 1, wherein a concentration of the Na2S is in range of 20 mM to 150mM.
4. The process as claimed in claim 1, wherein a concentration of sodium hydroxide is in range of 1 M
5. The process as claimed in claim 1, wherein a volume of TGA is 50 µL
6. The process as claimed in claim 1, wherein the cadmium sulphide colloidal nanoparticles is of size range between 2nm to 10nm.
7. The process as claimed in claim 1, wherein the solution in step (d) is stirred at a speed of 200-500 rpm for a time period of 4 h.
8. A cadmium sulphide colloidal nanoparticle obtained from the process as claimed in claim 1.

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