Claims:WE CLAIM:
1. A composition comprising carbon nitride (SG-CN) and nucleophile.
2. The composition as claimed in claim 1, wherein the nucleophile is tetra butyl ammonium bromide (TBAB).
3. The composition as claimed in claim 1, wherein the carbon nitride is in an amount ranging from about 5 mg to 15 mg.
4. The composition as claimed in claim 1, wherein the nucleophile is in an amount ranging from about 0.5 mol% to 1.0 mol%.
5. The composition as claimed in claim 1, wherein the carbon nitride has surface area ranging from about 190 m2/g to 250 m2/g.
6. The composition as claimed in claim 1, wherein the composition provides for about 90% to 100% conversion of carbon dioxide.
7. A method of preparing the composition as claimed in claim 1, said method comprises mixing the carbon nitride and the nucleophile to obtain the composition.
8. A method for conversion of carbon dioxide, said method comprises- mixing carbon dioxide and substrate in presence of the composition as claimed in claim 1, followed by heating to obtain corresponding carbonate.
9. The method as claimed in claim 8, wherein the substrate is selected from a group comprising unsubstituted epoxide, substituted epoxide, alkyl epoxide, aryl epoxide, and combinations thereof.
10. The method as claimed in claim 8, wherein the heating is carried out at a temperature ranging from about 60 ºC to 100 ºC for a duration ranging from about 6 hours to 12 hours under pressure ranging from about 0.6 atm to 1 atm.
11. The method as claimed in claim 8, wherein the method provides for 90% to 100% conversion of the carbon dioxide.
, Description:TECHNICAL FIELD
The present disclosure relates to the field of materials science. The present disclosure particularly relates to a composition comprising carbon nitride (SG-CN) and nucleophile. The disclosure further relates to method of preparing the composition and to a method for carbon dioxide conversion employing the said composition.

BACKGROUND OF THE DISCLOSURE
The concentration of carbon dioxide (CO2) is considered as main causative for global warming. On the other hand, CO2 is a safe, abundant, renewable and inexpensive C1 source, and has the potential of replacing harmful reactants such as CO and phosgene. From the viewpoints of “green chemistry” and “atom economy”, it is attractive to utilize CO2 for the generation of cyclic carbonates. However, CO2 is kinetically and thermodynamically stable, and it is a challenge to bring about its activation. Generally, CO2 is considered as an electrophile since the electrophilicity of the carbon atom is higher than the nucleophilicity of the oxygen atoms. Nucleophilic amine species such as 1,8-Diazabicyclo [5.4.0] undec-7-ene and N-hetero-cyclics are ef?cient for the activation of CO2. However, the processes for the recovery of the homogeneous basic catalysts are known to be complicated.

Carbon nitride has drawn widespread attention as a low-cost alternative to metal-based materials in the field of photocatalysis with applications including photocatalytic water splitting, carbon dioxide reduction, environmental remediation and organic transformations.

Many methods were explored to enhance the activity of carbon nitride, including increase of surface area, improvement of defect sites, and immobilization of functional group for improving the cycloaddition/conversion of CO2 with a substrate. However, the reaction conditions available were harsh and it was noted that there was no efficient cycloaddition/conversion of the CO2 with the substrate.

Thus, there appears a need for effective means for efficient cycloaddition/conversion of CO2 employing the carbon nitride.

STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure relates to an improved catalyst composition comprising carbon nitride (SG-CN) and nucleophile. The catalyst provides for significant carbon dioxide conversion.
The present disclosure further relates to a method of preparation of the catalyst, said method comprising mixing carbon nitride and nucleophile to obtain a homogenous mixture of the composition.

The present disclosure further relates to a method for carbon dioxide conversion employing the said composition, said method comprising- mixing carbon dioxide and substrate in presence of the composition as described above, followed by heating to obtain corresponding carbonate.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:

Figure 1: illustrates schematics of cycloaddition of CO2 with styrene oxide catalysed by the composition.

Figure 2: illustrates plot of time-dependent 1H NMR for the cycloaddition of CO2 with styrene oxide catalysed by the composition, wherein shows increase of peaks at 4.3, 4.8 and 5.6 ppm, due to carbonate formation, and decrease in peaks around 2.7, 3.1 and 3.8 ppm due to decrease substrate, styrene oxide.

DETAILED DESCRIPTION OF THE DISCLOSURE
Definitions:
Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included for better understanding of the present disclosure.

As used herein, the singular forms ‘a’, ‘an’ and ‘the’ include both singular and plural referents unless the context clearly dictates otherwise.

The term ‘comprising’, ‘comprises’ or ‘comprised of’ as used herein are synonymous with ‘including’, ‘includes’, ‘containing’ or ‘contains’ and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

The term ‘about’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less and still more preferably ±0.1% or less of and from the specified value, insofar such variations are appropriate to perform the present disclosure. It is to be understood that the value to which the modifier ‘about’ refers is itself also specifically, and preferably disclosed.

In the description, the term ‘cycloaddition’ and ‘CO2 conversion’ are used interchangeable and it refers to addition of CO2 to a substrate in presence of catalyst to obtain corresponding carbonate.

The present disclosure relates to a composition comprising carbon nitride (SG-CN) and nucleophile. The composition is a catalyst composition.

In some embodiments of the present disclosure, the nucleophile is tetra butyl ammonium bromide (TBAB).

In some embodiments of the present disclosure, the carbon nitride is in an amount ranging from about 5 mg to 15 mg.

In some embodiments of the present disclosure, the carbon nitride is in an amount of about 5 mg, about 6 mg, about 7 mg, about 8 mg, about 9 mg, about 10 mg, about 11 mg, about 12 mg, about 13 mg, about 14 mg or about 15 mg.

In some embodiments of the present disclosure, the nucleophile is in an amount ranging from about 0.5 mol% to 1.0 mol%.

In some embodiments of the present disclosure, the nucleophile in an amount of about 0.5 mol%, about 0.6 mol%, about 0.7 mol%, about 0.8 mol%, about 0.9 mol% or about 1.0 mol%.
In some embodiments of the present disclosure, the carbon nitride has surface area ranging from about 190 m2/g to 250 m2/g.

In some embodiments of the present disclosure, the carbon nitride has surface area of about 190 m2/g, about 192 m2/g, about 194 m2/g, about 196 m2/g, about 198 m2/g, about 200 m2/g, about 202 m2/g, about 204 m2/g, about 206 m2/g, about 208 m2/g, about 210 m2/g, about 212 m2/g, about 214 m2/g, about 216 m2/g, about 218 m2/g, about 220 m2/g, about 222 m2/g, about 224 m2/g, about 226 m2/g, about 228 m2/g, about 230 m2/g, about 232 m2/g, about 234 m2/g, about 236 m2/g, about 238 m2/g, about 240 m2/g, about 242 m2/g, about 244 m2/g, about 246 m2/g, about 248 m2/g or about 250 m2/g.

In some embodiments of the present disclosure, the carbon nitride has surface area of about 242 m2/g.

In some embodiments of the present disclosure, the composition provides for about 90% to 100% conversion of carbon dioxide.

In some embodiments of the present disclosure, the composition provides for about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99% or about 100% conversion of carbon dioxide.

In an exemplary embodiment of the present disclosure, the composition provides for efficient cycloaddition/conversion of CO2 with epoxides resulting in corresponding carbonate with high conversion and selectivity.

In some embodiments, the present disclosure relates to combination of the carbon nitride (SG-CN) and the nucleophile for effective cycloaddition/conversion of CO2.

The present disclosure further relates to a process of preparing the composition.

In some embodiments of the present disclosure, the process of preparing the composition comprises mixing the carbon nitride (SG-CN) and the nucleophile to obtain a homogenous mixture of the composition.

The present disclosure further relates to a method for conversion of carbon dioxide employing the composition described above.

In some embodiments of the present disclosure, the method for conversion of carbon dioxide comprises- mixing the carbon dioxide and substrate in presence of the composition described above, followed by heating to obtain corresponding carbonate.

In some embodiments of the present disclosure, the substrate is selected from a group comprising unsubstituted epoxide, substituted epoxide, alkyl epoxide, aryl epoxide and combinations thereof.

In some embodiments of the present disclosure, the substrate is selected from a group comprising styrene oxide, 1, 2-expoxybutane, epichlorohydrin, 1, 2-epoxyhexane and combinations thereof.

In some embodiments of the present disclosure, the heating is carried out at a temperature ranging from about 60 ºC to 100 ºC, for a duration ranging from about 6 hours to 12 hours under pressure ranging from about 0.6 atm to 1 atm.

In some embodiments of the present disclosure, the heating is carried out at a temperature of about 60 ºC, about 62 ºC, about 64 ºC, about 66 ºC, about 68 ºC, about 70 ºC, about 72 ºC, about 74 ºC, about 76 ºC, about 78 ºC, about 80 ºC, about 82 ºC, about 84 ºC, about 86 ºC, about 88 ºC, about 90 ºC, about 92 ºC, about 94 ºC, about 96 ºC, about 98 ºC or about 100 ºC for a duration of about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours or about 12 hours under pressure of about 0.6 atm, about 0.7 atm, about 0.8 atm, about 0.9 atm or about 1.0 atm.

In an embodiment of the present disclosure, the Figure 1 illustrates schematics of conversion of the carbon dioxide to corresponding carbonate in presence of the composition comprising the carbon nitride and the nucleophile.

In an embodiment of the present disclosure, the Figure 2 illustrates time-dependent 1H NMR for the conversion of CO2 with styrene oxide as substrate into corresponding carbonate, wherein the peaks at 4.3, 4.8 and 5.6 ppm are found to increase due to formation of the product (corresponding carbonate) and decrease in peaks at about 2.7, 3.1 and 3.8 ppm due to decrease in substrate, styrene oxide.

In some embodiments of the present disclosure, the method provides for about 90% to 100% conversion of carbon dioxide.

In some embodiments of the present disclosure, the method provides for about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99% or about 100% conversion of the carbon dioxide.

It is to be understood that the foregoing description is illustrative not a limitation. While considerable emphasis has been placed herein on particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure, certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLE

Example 1: Preparation of Carbon nitride (SG-CN)
Cyanamide (CA) was used as carbon nitride precursor and tetraethylorthosilicate (TEOS) was used for template synthesis to get high surface area carbon nitride. CA and TEOS were taken in 6:1 molar ratio. The mixture was dissolved in 0.01 M aqueous HCl (4 g) and ethanol (4 g). The pH of the resultant mixture was adjusted to 2 by addition of HCl dropwise. After stirring the mixture for 30 minutes, the solvent was evaporated and subsequently dried at 80 °C for 24 hours. Later, the obtained solid was further calcined at 550 °C in a muffle furnace under argon atmosphere with a ramping rate of 5 °C/min for 4 hours to get the mesoporous carbon nitride-silica composite. After being cooled to room temperature naturally, the obtained light yellow-brownish product was ground into powder using mortar and pestle. The composite was washed with 4 M ammonium hydrogen difluoride (NH4HF2) solution for 48 hours to remove the silica followed by washing with water and ethanol several times to obtain pure mesoporous carbon nitride (SG-CN). The obtained SG-CN was dried in normal oven for overnight at 120 °C followed by drying in the vacuum oven at 150 °C overnight.

Example 2: Conversion of CO2 with styrene oxide as substrate
This experiment was conducted to test the conversion/cycloaddition of CO2 with styrene oxide as substrate at various conditions of CO2 pressure.
About 10 mmol of styrene oxide was mixed with CO2 in presence of the composition comprising carbon nitride (SG-CN) about 10 mg and about 1 mole% of tetra-butyl ammonium bromide (TBAB). The catalytic results showed the formation of the corresponding cyclic carbonate with about 73% conversion in about 12 hours at a temperature of about 60 ºC. However, the conversion was increased to about 95% with increase in temperature to about 100 ºC.
Data in Table 1 demonstrates that the effective conversion of at least 95% is achieved with the composition comprising carbon nitride (SG-CN) and TBAB. From the data in Table 1 it was noted that the conversion was negligible or was about 14% when only SG-CN and TBAB are employed individually.
The data in Table 1 also demonstrates that the carbon nitride other than SG-CN in combination with TBAB leads to conversion of only about 63% CO2.
Thus, the composition comprising carbon nitride (SG-CN) and TBAB provides for effective conversion of at least 99%.
Entry No. Catalyst [mol%] Co-catalyst [mol%] Pressure [MPa] Time [h] Temp. [° C] Conversion [%][a]
1 None None 0.6 12 r.t. NIL
2 None None 0.6 12 60 NIL
3 None None 0.6 12 100 NIL
4 SG-CN None 1atm/0.6 12 r.t. NIL/~2
5 SG-CN None 1atm/0.6 12 60 ~2/~8
6 SG-CN None 1atm/0.6 12 100 ~3/~14
7 None TBAB 0.6 12 r.t. < 3
8 None TBAB 0.6 12 60 12
9 None TBAB 0.6 12 100 14
10 SG-CN TBAB 0.6 12 60 73
11 SG-CN TBAB 0.6 12 100 95
12 G-CN TBAB 0.6 12 100 ~63
13 SG-CN TBAB 0.6 15 100 99
Table 1:

1H NMR analysis of the product obtained during conversion revealed that product formed was only cyclic carbonates and that there were no other by-products. Figure 2 demonstrates time dependent 1H NMR for the cycloaddition/conversion of CO2 with styrene oxide catalysed by the carbon nitride (SG-CN) and TBAB, wherein increase in peaks at about 4.3, about 4.8 and about 5.6 ppm were observed due to formation of the product (cyclic carbonate) and decrease in peaks at about 2.7, about 3.1 and about 3.8 ppm were observed due to decrease in substrate (styrene oxide).

Example 3: Conversion of CO2 with alkyl epoxides as substrate
About 10 mmol of substrate such as 1, 2-epoxybutane, epichlorohydrin and 1, 2-epoxyhexane were independently mixed with CO2 in presence of the composition comprising carbon nitride (SG-CN) and TBAB. The mixture was heated to a temperature of about 100 ºC for about 12 hours.
Data in Table 2 describes conversion of the CO2 to corresponding carbonate. It was observed that the catalytic conversion of substrates such as 1, 2-epoxybutane, epichlorohydrin and 1, 2-epoxyhexane, respectively were found to be equivalent with the conversion of styrene oxide.

Entry No. Substrate
[R] Pressure [MPa] Conversion[b] [%]

1
0.6 >95

2

3

0.6

0.6 99

96

4
0.6 91
Table 2: