NOVEL COMPOSITE OF SILICA AND GRAPHENE QUANTUM DOTS AND PREPARATION THEREOF

Abstract

The present invention relates to a novel composite of graphene quantum dot and silica. The present invention further relates to a novel one step process for the synthesis of composite of GQD and silica from paper. The composite is useful for biological applications such as bioimaging, drug delivery etc.

Claims

1. A novel composite of graphene quantum dot and silica in the weight ratio gqd and silica is in the range of 1-5: 1-2 and depend upon source of paper.

2. The composite as claimed in claim 1, wherein said composite is obtained from paper, wood pulp, leaves, bananas, coconut peel, coal or cotton.

3. The composite as claimed in claim 1, wherein said gqd is luminescent and size is in the range of 4-6 nm.

4. The composite as claimed in claim 1, wherein size of said silica is in the range of 40-50 nm.

5. The composite as claimed in claim 1, wherein the main chemical component of said paper is silicate of magnesia wherein the amount of silica is 62-70%.

6. A novel one step process for the synthesis of said composite of gqd and silica as claimed in claim 1 comprising the steps of: a) burning the paper to afford ash; b) suspending the ash of step (a) in water by sonicating and adding oxidizing agent followed by heating in a microwave for 2-4 minutes and repeating the microwave heating for six to seven times at 750 watts to afford a black residue of GQDs silica composite, with green fluorescence.

7. The process as claimed in claim 6, wherein said oxidizing agent is selected from glycolic acid, citric acid or ascorbic acid.

8. The process as claimed in claim 6, wherein said paper is silicate of magnesia wherein the amount of silica is 62-70%.

9. The process as claimed in claim 6, wherein said water is de-ionised water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 depicts TGA of GQD-SiO.sub.2 composite

[0041] FIG. 2 depict (A) and (B) the TEM images of GQDs which are well dispersed in the size range of 4-6 nm. The GQDs are uniformly distributed without agglomeration and are circular. Figure (C) and (D) shows the TEM images of well discrete silica particles within the size range 40-60 nm.

[0042] FIG. 3 depicts UV-visible spectra of the as-synthesized GQD-SiO.sub.2 composite. Inset shows the photograph of green luminescent GQDs observed under UV lamp

DETAILED DESCRIPTION OF THE INVENTION

[0043] The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

[0044] The present invention provides a novel composite of Graphene Quantum Dot and silica, wherein the weight ratio of Graphene Quantum Dots: Silica in the said composite is 1-5: 1-2.

[0045] In an embodiment the present invention provides a novel composite, wherein said composite is from paper, wood pulp, leaves, bananas, coconut peel, coal or cotton.

[0046] In another embodiment, said GQD is luminescent and size is in the range of 4-6 nm; size of silica is in the range of 40-50 nm.

[0047] In yet another embodiment, the present invention provides a novel one step process for the synthesis of composite of GQD and silica from paper comprising the steps of: [0048] a) Burning the paper to afford ash; [0049] b) Suspending the ash of step (a) in water by sonicating and adding oxidizing agent followed by heating in a microwave for 2-4 minutes and repeating the microwave heating for six to seven times at 750 watts to afford a black residue of GQDs silica composite, with green fluorescence.

[0050] In still another embodiment, said oxidizing agent is selected from glycolic acid, citric acid and ascorbic acid.

[0051] In still yet another embodiment, the main chemical component of said paper is Silicate of magnesia wherein the amount of silica is 62-70%.

[0052] In still yet another embodiment, said water is de-ionized water.

[0053] The as-synthesized GQD-SiO.sub.2 composite exhibited green fluorescence when illuminated under UV lamp.

[0054] To synthesize gqd-silica composite paper was used as a precursor material for the source of carbon and silica. The highly carbon and silica contain material such as leaf; wood pulp etc. can also be used as the precursor material to prepare the composite material. In our experiment, we have only used paper as precursor but the above mentioned precursors also be used as potential material for the biocompatible synthesis.

[0055] In the synthesis procedure glycolic acid is used as an oxidizing agent. The main function of the oxidizing agent is to cut off the carbon chain in smaller pieces. Well-controlled oxidation provide break down of graphene to more smooth edges compared to heat or sonic treatment. Thus, similar biocompatible oxidizing agent like ascorbic and citric acid having comparable oxidizing power also work well for the synthesis.

[0056] From the TGA data it can be seen that oxidation of grapheme quantum dots take place between 200 C.-600 C. After 750 C. burned out of the entire graphitic carbon take place and after that a linear pattern can be observed which confirms the presence of silica due to its stability in high temperature.

[0057] Figure (A) and (B) shows the TEM images of GQDs which are well dispersed in the size range of 4-6 nm. The GQDs are uniformly distributed without agglomeration and are circular. Figure (A) and (B) shows the TEM images of well discrete silica particles within the size range 40-50 nm.

[0058] The absorption peak at 238 nm can be assigned to the -* transition of aromatic graphitic sp.sup.2 domains and the strong absorption band appeared 327 nm is due to the n-* transitions of CO bonds. The GQDs exhibit green fluorescence under UV illumination and also exhibit excellent water dispersibility. (Refer FIG. 3)

[0059] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Examples

Example 1: Synthesis of GQD-SiO.SUB.2 .Composite Material

[0060] First the paper was burnt down to ashes in a controlled environment. Then the black ash was crushed well in a mortar pestle. After that, 100 mg ash was weighed and mixed in 50 ml de-ionized water. The solution was sonicated in bath sonicator for 30 minutes. 50 ml solution of 1 g glycolic acid was added drop wise in the sonicated solution. After addition of glycolic acid, the solution was further sonicated for 30 minutes. Then the solution was heated in a microwave at 500 watt for 20 minutes through 10 microwave cycles for 2 minutes. The viscous solution was collected and mixed with 50 ml de-ionized water. The pH of the solution was made 7 by mixing NaOH and the solution was ultra-sonicated for 15 minutes and filtrate to obtain a clear bright yellow solution. Further the solution was heated in the microwave at 500 watt for 10 minutes and then diluted in de-ionized water.

[0061] Advantages of Invention: [0062] 1. Biocompatible, green fluorescent graphene quantum dot-silica composite have been prepared without using any harsh chemical. [0063] 2. The preparation method is very cheap and the product can be synthesized in a very short time i.e. less than one hour. [0064] 3. The bright photoluminescence and low cytotoxicity render the material for biological applications such as bioimaging, drug delivery etc. [0065] 4. Different sensors can be fabricated with GQD-silica composite either signal-off or signal-on processes. Such photoluminescence sensors have been used for metal ion detection like Fe.sup.3+ etc. [0066] 5. The GQD-silica composite material can also be used in photocatalysis and photovoltaic devices.