GRAPHITIC CARBON NITRIDE MATERIAL, AND ITS SYNTHETIC METHOD AND APPLICATIONS

Abstract

The present invention relates to a synthetic method of graphitic carbon nitride material. The method involves a homogenous mixing of carbon nitride precursor and ammonium salt, and calcining the mixture to obtain a porous graphitic carbon nitride material. Wherein, the ammonium salt is any one or a combination of at least two which could release gaseous NH.sub.3 during thermolysis. The present invention uses thermolabile ammonium salt as a pore former; the thermolysis of ammonium salt could release soft gas bubbles during the calcination; the later burst of bubbles leads to the formation of nanoporous structure. The proposed method is template-free and environmentally-friendly, and the resultant material exhibits high photocatalytic activity in the field of gas and water decontamination.

Claims

1. A synthetic method of graphitic carbon nitride material comprising: homogenous mixing of graphitic carbon nitride precursor and ammonium salt; and calcinating to obtain a porous graphitic carbon nitride material, wherein the ammonium salt is any one or a combination of at least two salts capable of releasing gaseous NH.sub.3 during thermolysis.

2. The method of claim 1, wherein the graphitic carbon nitride precursor is any one or a combination of at least two among cyanamide, dicyandiamide, melamine, thiourea and urea.

3. The method of claim 1, wherein the ammonium salt is any one or a combination of at least two among NH.sub.4F, NH.sub.4Cl, NH.sub.4Br, NH.sub.4I, (NH.sub.4).sub.2CO.sub.3, NH.sub.4HCO.sub.3, NH.sub.4NO.sub.3, (NH.sub.4).sub.2SO.sub.4, NH.sub.4HSO.sub.4, NH.sub.4H.sub.2PO.sub.4, (NH.sub.4).sub.2HPO.sub.4, (NH.sub.4).sub.3PO.sub.4 and (NH.sub.4).sub.2C.sub.2O.sub.4.

4. The method of claim 1, wherein the mass ratio of the g-C.sub.3N.sub.4 precursor to the ammonium salt is 1:10-10:1.

5. The method of claim 1, wherein the calcination temperature is 400-700 C., and the calcination time is 1-6 hours.

6. The method of claim 1, wherein the homogenous mixing of carbon nitride precursor and ammonium salt further comprises: dissolving the carbon nitride precursor and ammonium salt in a solvent, followed by removing the solvent.

7. The method of claim 6, wherein the method of removing the solvent is any one or a combination of at least two among spin evaporation, natural evaporation, heating evaporation, freeze drying and vacuum drying.

8. The method of claim 6, wherein the solvent used for dissolving carbon nitride precursor and ammonium salt is ethanol, water or both.

9. The method of claim 6 further comprising: heating and stirring the solution of carbon nitride precursor and ammonium salt at 30-90 C. for 0.5-6 hours to evaporate most solvent; and further removing it all by freeze drying or vacuum drying for 12-48 hours.

10. The method of claim 9, wherein the freeze drying temperature is from 50 to 10 C., and the vacuum drying temperature is 40-80 C.

11. The method of claim 6, wherein a further washing of the calcined product is requisite to remove the residue from the calcination of the selected ammonium salts; the cleaning agent is water, ethanol or both.

12. The method of claim 1, wherein a temperature programmed process is adopted for the calcination to reach the calcination temperature.

13. The method of claim 12, wherein the temperature programmed rate is 0.5-15 C./min.

14. The method of claim 1 further comprising: (1) mixing the carbon nitride precursor and ammonium salt with a mass ratio of 1:10-10:1 in a solvent to achieve a homogenous mixture; (2) removing the solvent; and (3) heating the resultant product to 400-700 C. at a rate of 0.5-15 C./min and calcining for 1-6 hours.

15. The obtained graphitic carbon nitride material synthesized by the method of claim 1, wherein the graphitic carbon nitride material has a honeycomb-like porous structure with a pore volume of 0.20-0.65 cm.sup.3/g and a pore size of 2-25 nm.

16. The material of claim 15, wherein the specific surface area of the graphitic carbon nitride material is higher than 100 m.sup.2/g.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 shows an X-ray Diffraction (XRD) pattern of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material from Implementation Example 1.

[0042] FIG. 2 shows a field-emission transmission electron microscopy (FETEM) image of the bulk g-C.sub.3N.sub.4-1 from Contrasting Example 1.

[0043] FIG. 3 shows an FETEM image of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material from Implementation Example 1.

[0044] FIG. 4 shows a comparison curve of the pore size distributions of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material from Implementation Example 1 and the bulk g-C.sub.3N.sub.4-1 from Contrasting Example 1.

EMBODIMENTS

[0045] Herein, Examples are given in order to further outline the technical solution of the present invention.

[0046] The experimental methods of the Examples below are conventional ones, if not otherwise specified.

[0047] The materials, reagents etc. of the Examples below are commercially purchased, if not otherwise specified.

[0048] The reactants of the Examples below are analytically pure thiourea, dicyandiamide, urea, NH.sub.4Cl, (NH.sub.4).sub.2CO.sub.3 and NH.sub.4HCO.sub.3. The targeted pollutant is analytically pure p-hydroxybenzoic acid.

[0049] In the Examples below, the Brunauer-Emmett-Teller (BET) surface areas are measured by an automated gas sorption analyzer (Autosorb-iQ, Quantachrome, USA) at 77K. Pore size distributions are calculated with the non-localized density functional theory method using adsorption data.

[0050] In the Examples below, the morphologies and structures of the prepared samples are investigated by field-emission transmission electron microscopy (FETEM, JEM-2100F, JEOL, Japan).

IMPLEMENTATION EXAMPLE 1

[0051] A synthetic method of honeycomb-like nanoporous g-C.sub.3N.sub.4 material includes the following procedures:

[0052] (1) Adding 10 g of thiourea, 10 g of NH.sub.4Cl and 30 mL of pure water into a beaker (100 mL);

[0053] (2) Placing the beaker in a water bath with stirring at 70 C. for 60 min to evaporate most water and to obtain a homogeneous white paste;

[0054] (3) Placing the white paste in a vacuum drying oven at 60 C. for 16 hours to completely remove water and to obtain a white solid; and

[0055] (4) Putting a crucible with the white solid inside in a muffle furnace, instantly heating the solid to 550 C. with a rate of 15 C./min and maintaining the temperature at 550 C. for 2 hours. The final product, honeycomb-like nanoporous g-C.sub.3N.sub.4 material, can be obtained after naturally cooling to ambient temperature.

CONTRASTING EXAMPLE 1

[0056] The bulk g-C.sub.3N.sub.4 material is prepared by direct heating thiourea without the addition of NH.sub.4Cl as a control, which is termed as the bulk g-C.sub.3N.sub.4-1.

IMPLEMENTATION EXAMPLE 2

[0057] A synthetic method of honeycomb-like nanoporous g-C.sub.3N.sub.4 material includes the following procedures:

[0058] (1) Dispersing 10 g of dicyandiamide, 7.5 g of (NH.sub.4).sub.2CO.sub.3 and 7.5 g of NH.sub.4HCO.sub.3 in 60 mL of ethanol;

[0059] (2) Heating the mixture at 30 C. for 6 hours under stirring to evaporate most ethanol and to obtain a homogeneous white paste;

[0060] (3) Placing the white paste in a vacuum freeze dryer at 50 C. for 48 hours to completely remove ethanol and to obtain a white solid; and

[0061] (4) Putting a crucible with the white solid inside in a tube furnace, instantly heating the solid to 550 C. with a rate of 1 C./min under continuous air purging and maintaining the temperature at 550 C. for 4 hours. The final product, honeycomb-like nanoporous g-C.sub.3N.sub.4 material, can be obtained after naturally cooling to ambient temperature.

CONTRASTING EXAMPLE 2

[0062] The bulk g-C.sub.3N.sub.4 material is prepared by direct calcining dicyandiamide without the addition of (NH.sub.4).sub.2CO.sub.3 and NH.sub.4HCO.sub.3 as a control, which is termed as the bulk g-C.sub.3N.sub.4-2.

IMPLEMENTATION EXAMPLE 3

[0063] A synthetic method of honeycomb-like nanoporous g-C.sub.3N.sub.4 material includes the following procedures:

[0064] (1) Adding 20 g of urea and 8 g of (NH.sub.4).sub.2C.sub.2O.sub.4 into 20 mL of water and 20 mL of ethanol;

[0065] (2) Heating the mixture at 90 C. for 0.5 hours under stirring to evaporate most ethanol and water and to obtain a homogeneous white paste;

[0066] (3) Placing the white paste in a vacuum drying oven at 80 C. for 24 hours to completely remove ethanol and water and to obtain a white solid; and

[0067] (4) Putting a crucible with the white solid inside in a muffle furnace, instantly heating the solid to 700 C. with a rate of 8 C./min and maintaining the temperature at 700 C. for 1.5 hours. The final product, honeycomb-like nanoporous g-C.sub.3N.sub.4 material, can be obtained after naturally cooling to ambient temperature.

CONTRASTING EXAMPLE 3

[0068] The bulk g-C.sub.3N.sub.4 material is prepared by direct calcining urea without the addition of (NH.sub.4).sub.2C.sub.2O.sub.4 as a control, which is termed as the bulk g-C.sub.3N.sub.4-3.

IMPLEMENTATION EXAMPLE 4

[0069] A synthetic method of honeycomb-like nanoporous g-C.sub.3N.sub.4 material includes the following procedures:

[0070] (1) Adding 1 g of dicyandiamide and 10 g of (NH.sub.4).sub.2CO.sub.3 into 20 mL of water and 20 mL of ethanol;

[0071] (2) Heating the mixture at 90 C. for 0.5 hours under stirring to evaporate most ethanol and water and to obtain a homogeneous white paste;

[0072] (3) Placing the white paste in a vacuum drying oven at 80 C. for 24 hours to completely remove ethanol and water and to obtain a white solid; and

[0073] (4) Putting a crucible with the white solid inside in a muffle furnace, instantly heating the solid to 400 C. with a rate of 0.5 C./min and maintaining the temperature at 400 C. for 6 hours. The final product, honeycomb-like nanoporous g-C.sub.3N.sub.4 material, can be obtained after naturally cooling to ambient temperature.

CONTRASTING EXAMPLE 4

[0074] The nanoporous g-C.sub.3N.sub.4 from Implementation Example 1 of CN103170358 is selected as a contrasting example, and its specific surface area and photocatalytic activity are tested.

IMPLEMENTATION EXAMPLE 5

[0075] A synthetic method of honeycomb-like nanoporous g-C.sub.3N.sub.4 material includes the following procedures:

[0076] (1) Adding 10 g of urea and 1 g of (NH.sub.4).sub.2C.sub.2O.sub.4 into 20 mL of water and 20 mL of ethanol;

[0077] (2) Heating the mixture at 90 C. for 0.5 hours under stirring to evaporate most ethanol and water and to obtain a homogeneous white paste;

[0078] (3) Placing the white paste in a vacuum drying oven at 80 C. for 24 hours to completely remove ethanol and water and to obtain a white solid; and

[0079] (4) Putting a crucible with the white solid inside in a muffle furnace, instantly heating the solid to 600 C. with a rate of 10 C./min and maintaining the temperature at 600 C. for 1 hours. The final product, honeycomb-like nanoporous g-C.sub.3N.sub.4 material, can be obtained after naturally cooling to ambient temperature.

CONTRASTING EXAMPLE 5

[0080] The nanoporous g-C.sub.3N.sub.4 from Implementation Example 1 of CN103240121 is selected as a contrasting example, and its specific surface area and photocatalytic activity are tested.

[0081] Activity Test and Characterization

[0082] A series of characterizations including XRD, FERTEM, BET surface area and pore size distribution and photocatalytic activity test are adopted on the g-C.sub.3N.sub.4 samples from the implementation and contrasting examples. The detailed methods are presented below:

[0083] XRD:

[0084] The crystal phase is characterized by X-ray Diffraction (XRD) (X PERT-PRO MPD) with a Cu.sub.K irradiation (=0.15406 nm) from Panalytical B. V.

[0085] FIG. 1 shows an XRD pattern of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material in Implementation Example 1. The intensive diffraction peak at 27.4 was an interlayer stacking peak of aromatic systems as indexed as the (0 0 2) plane, and the relatively weak peak at 13.0 labeled as the (1 0 0) plane corresponding to the in-plain structural packing motif of tris-triazine units.

[0086] FETEM:

[0087] The morphologies and structures of the prepared samples are further investigated by field-emission transmission electron microscopy (FETEM, JEM-2100F, JEOL, Japan).

[0088] FIG. 2 shows a field-emission transmission electron microscopy (FETEM) image of the bulk g-C3N4-1. FIG. 3 shows an FETEM image of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material in Implementation Example 1. It can be seen that the g-C.sub.3N.sub.4 sample synthesized by Implementation Example 1 exhibits a honeycomb-like porous structure, while the bulk g-C.sub.3N.sub.4-1 displays dense and thick sheet-structured morphology.

[0089] BET Surface Area and Pore Size Distribution:

[0090] The Brunauer-Emmett-Teller (BET) surface areas are measured by an automated gas sorption analyzer (Autosorb-iQ, Quantachrome, USA) at the temperature of liquid nitrogen (77K). Pore size distributions are calculated with the non-localized density functional theory method using adsorption data.

[0091] Photocatalytic Activity Test:

[0092] The photocatalytic degradation is carried out at 25 C. under visible light (420-800 nm) irradiation in a 450 mL cylindrical borosilicate glass reactor with a quartz cap, containing 300 mL of solution with 20 mg/L of p-hydroxybenzoic acid and 0.5 g/L of catalyst. Visible light is provided by a 300 W Xenon lamp (CEL-NP2000, Aulight Co., Ltd., China) with a visible-light reflector and a 420 nm cutoff filter. The average radiant flux is 200 mW/cm.sup.2, measured by a photometer (CEL-NP2000, Aulight Corporation, China). The concentrations of p-hydroxybenzoic acid is analyzed by high performance liquid chromatography (HPLC, Agilent series 1200, USA) equipped with a Zorbax SB-Aq column and a UV-vis detector qualified at 240 nm. The p-hydroxybenzoic acid degradation rate constants are calculated in the presence of the g-C.sub.3N.sub.4 samples from the implementation and contrasting examples to characterize the photocatalytic activities.

[0093] The corresponding results are listed below:

TABLE-US-00001 TABLE 1 The specific surface areas and p-hydroxybenzoic acid degradation rate constants of the g-C.sub.3N.sub.4 samples from the Implementation and Contrasting Examples Item No. S.sub.BET (m.sup.2/g) k.sub.app.sup.a (10.sup.2 mg/L .Math. min) Implementation 1 118.3 6.9 Examples 2 128.7 7.5 3 178.7 8.6 4 110.7 6.0 5 100.8 5.9 Contrasting 1 15.0 3.3 Examples 2 8.9 2.8 3 35.9 3.9 4 29.5 3.8 5 29.6 3.7 .sup.ap-hydroxybenzoic acid degradation rate constant.

[0094] FIG. 4 shows a comparison curve of the pore size distributions of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material from Implementation Example 1 and the bulk g-C.sub.3N.sub.4-1 from Contrasting Example 1. It confirms that the honeycomb-like nanoporous g-C.sub.3N.sub.4 material has both abundant micropores (1.4 nm) and small mesopores (3.0, 4.2, 5.7 and 7.5 nm), while the bulk g-C.sub.3N.sub.4-1 has few nanopores.

[0095] It can be seen from Table 1 that the specific surface area of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material (from Implementation Example 1) is 6.8 times as high as that of the bulk g-C.sub.3N.sub.4-1 (from Contrasting Example 1), and the corresponding p-hydroxybenzoic acid degradation rate is about 2 times as large as that of the bulk g-C.sub.3N.sub.4-1. The specific surface area of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material (from Implementation Example 2) increases 13.4 times compared to that of the bulk g-C.sub.3N.sub.4-2 (from Contrasting Example 2), and a 1.7 times enhancement of p-hydroxybenzoic acid degradation rate occurs on the honeycomb-like nanoporous sample in comparison with the bulk g-C.sub.3N.sub.4-2. A 4 times improvement of the specific surface area can be seen from the honeycomb-like nanoporous g-C.sub.3N.sub.4 material (from Implementation Example 3) compared with the bulk g-C.sub.3N.sub.4-3 (from Contrasting Example 3), and correspondingly, its photocatalytic activity increases 1.2 times in treating p-hydroxybenzoic acid. Compared to the nanoporous sample (from Contrasting Example 4), a 2.7 times improvement of the specific surface area occurs on the honeycomb-like nanoporous g-C.sub.3N.sub.4 material (from Implementation Example 4), and a 70% higher p-hydroxybenzoic acid degradation rate is also observed. The specific surface area of the honeycomb-like nanoporous g-C.sub.3N.sub.4 material (from Implementation Example 5) exhibits a 2.4 times increase compared to that of the nanoporous sample (from Contrasting Example 5), and the p-hydroxybenzoic acid degradation rate increases 50% correspondingly.

[0096] The inventor hereby declares that this invention is not limited to the above implementation examples that are used to specify the technical process and equipment, i.e., that this invention can also be implemented without following the above execution details. Based on this inventive concept, any possible change or replacement of the involved materials, reagents and modes of execution belong to the scope of protection.