Method for preparing silicate/carbon composite from attapulgite, and use of silicate/carbon composite

Abstract

A method for preparing a silicate/carbon composite from attapulgite, and use of the silicate/carbon composite are disclosed. The preparation method includes: (1) with attapulgite as a raw material, preparing SiO.sub.2 with a special structure; (2) dispersing the prepared SiO.sub.2 in water to obtain a suspension, and subjecting the suspension to ultrasonic dispersion; dissolving a metal nitrate in the suspension, adding NH.sub.4Cl, and adding ammonia water dropwise to the suspension; and adding sucrose to obtain a suspension; (3) subjecting the suspension to microwave hydrothermal reaction; after the reaction is completed, centrifuging a resulting system; and separating a resulting solid; and (4) subjecting the solid to high-temperature calcination in a muffle furnace, and grinding a resulting product to obtain the silicate/carbon composite, which can be used in photocatalytic ammonia synthesis.

Claims

1. A method for preparing a silicate/carbon composite from attapulgite, wherein the silicate/carbon composite has a general formula: xMSiO.sub.4/C, wherein a molar ratio of MSiO.sub.4 to C is x, and a range of the x is 0.1 to 0.3, and a metal M is one selected from the group consisting of Fe, Co, and Ni; and the method for preparing the silicate/carbon composite comprises the following steps: (1) mixing an attapulgite powder with ammonium sulfate in a ceramic crucible to obtain a first resulting mixture, putting the ceramic crucible in a muffle furnace, and heating and calcining the first resulting mixture to obtain a calcination product; after a calcination, naturally cooling the calcination product to room temperature; dispersing the calcination product in a hydrochloric acid solution to obtain a second resulting mixture, and conducting a water bath heating reaction on the second resulting mixture under a stirring to obtain a first resulting solid; and separating, washing, and drying the first resulting solid to obtain SiO.sub.2 with a special structure; (2) dispersing the SiO.sub.2 prepared in step (1) in water to form a SiO.sub.2 suspension, and subjecting the SiO.sub.2 suspension to an ultrasonic dispersion; dissolving a metal nitrate in the SiO.sub.2 suspension, adding NH.sub.4Cl, and adding ammonia water dropwise to the SiO.sub.2 suspension to obtain a third resulting mixture; and after the third resulting mixture is stirred, adding sucrose to the third resulting mixture to obtain a mixture suspension; (3) transferring the mixture suspension obtained above to a polytetrafluoroethylene (PTFE) hydrothermal reactor, and conducting a microwave reaction on the mixture suspension at 120° C. to 200° C. for 2 h to obtain a fourth resulting mixture; naturally cooling the fourth resulting mixture to room temperature, and centrifuging the fourth resulting mixture to obtain a second resulting solid; and separating, washing, and drying the second resulting solid; and (4) subjecting the second resulting solid obtained from the drying to a thermal treatment at 500° C. in the muffle furnace to obtain a resulting product, and grinding the resulting product into a powder to obtain the silicate/carbon composite (xMSiO.sub.4/C).

2. The method for preparing the silicate/carbon composite from the attapulgite according to claim 1, wherein in step (1), the attapulgite powder and the ammonium sulfate are mixed ata mass ratio of 1:1 to 1:5.

3. The method for preparing the silicate/carbon composite from the attapulgite according to claim 1, wherein the heating and calcining is conducted as follows: heating the first resulting mixture to 500° C. at a rate of 2° C./min and calcining the first resulting mixture at 500° C.; and the water bath heating reaction under the stirring is conducted at 80° C. for 6 h.

4. The method for preparing the silicate/carbon composite from the attapulgite according to claim 1, wherein the water bath heating reaction under the stirring in step (1) is conducted at 80° C. for 6 h.

5. A method of using the silicate/carbon composite prepared by the method according to claim 1, comprising using the silicate/carbon composite in an ammonia synthesis as a photocatalyst.

6. The method of using according to claim 5, wherein in step (1), the attapulgite powder and the ammonium sulfate are mixed at a mass ratio of 1:1 to 1:5.

7. The method of using according to claim 5, wherein the heating and calcining is conducted as follows: heating the first resulting mixture to 500° C. at a rate of 2° C./min and calcining the first resulting mixture at 500° C.; and the water bath heating reaction under the stirring is conducted at 80° C. for 6 h.

8. The method of using according to claim 5, wherein the water bath heating reaction under the stirring in step (1) 1s conducted at 80° C. for 6 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows X-ray diffraction (XRD) patterns of 0.1Co.sub.2SiO.sub.4/C prepared in Example 1 and Co.sub.2SiO.sub.4 prepared in Comparative Example 1; and

(2) FIG. 2 is a transmission electron microscopy (TEM) image of the 0.1Co.sub.2SiO.sub.4/C sample prepared in Example 1 at a scale of 100 nm.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) In the examples, the optimal formula and process are taken as an example to illustrate the content of the present disclosure in further detail. If specific conditions are not indicated therein, conventional conditions should be adopted. All of the used raw materials, reagents, or instruments which are not specified with manufacturers are conventional commercially-available products.

Example 1

(4) (1) Attapulgite was mixed with ammonium sulfate in a ceramic crucible at a mass ratio of 1:1, and then the crucible was put in a muffle furnace and heated to 500° C. at a rate of 2° C./min, then kept at the temperature for 2 h, and naturally cooled to room temperature; a calcination product was dispersed in a 2 mol/L hydrochloric acid solution at a solid-to-liquid ratio of 1:20, and water bath heating reaction under stirring was conducted at 80° C. for 6 h; and a resulting solid was separated, washed, and dried to obtain white SiO.sub.2.

(5) (2) 0.3 g of the prepared SiO.sub.2 was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 10 mmol of Co(NO.sub.3).sub.2.6H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min; and 1.43 g of sucrose was then added to obtain a mixture suspension.

(6) (3) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 120° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(7) (4) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground to obtain a silicate/carbon composite (0.1Co.sub.2SiO.sub.4/C).

(8) The 0.1Co.sub.2SiO.sub.4/C composite material prepared in this example was subjected to X-ray powder diffraction test, and the morphology and structure of the material were observed under a TEM.

(9) An XRD pattern is shown in FIG. 1. With reference to the PDF card of Co.sub.2SiO.sub.4, it can be known that the unique diffraction peaks of Co.sub.2SiO.sub.4 appear at angles°=31.2°, 36.7°, 59.3°, 65.1°, etc. Because the carbon in the composite material is in an amorphous state, no corresponding characteristic diffraction peak can be seen in the XRD pattern. Moreover, in combination with the TEM image in FIG. 2, it can be proved that the Co.sub.2SiO.sub.4 nanorods are successfully loaded on the surface of the carbon layer.

(10) A TEM image is shown in FIG. 2. It can be seen from the figure that the surface of the carbon layer is uniformly loaded with Co.sub.2SiO.sub.4 nanorods, and the nanorods are uniform in size and have a length of less than 100 nm, which is consistent with the XRD result.

(11) The present disclosure also provides use of the above composite material in photocatalytic ammonia synthesis as a photocatalyst.

(12) A use method was as follows: 0.04 g of the prepared silicate/carbon composite material (Co.sub.2SiO.sub.4/C) was weighed and dissolved in 100 mL of deionized water, and a resulting solution was added to a photocatalytic reaction device; then N.sub.2 was introduced into the reaction device at a flow rate of 60 mL/min; after the N.sub.2 was introduced for 30 min, a 300 W xenon lamp was used as a simulated light source to irradiate; and 10 mL of a sample was collected every 30 min. A Nessler's reagent was added to the sample, and after reaction was completed, a supernatant was collected, and the absorbance was determined with an ultravoilet spectrometer (UVS) at a wavelength of 420 nm.

(13) As measured by the above method, the 0.1Co.sub.2SiO.sub.4/C led to a NH.sub.4.sup.+ concentration of 0.045 g/L at 120 min. When Co.sub.2SiO.sub.4 had a loading ratio of 0.2, the sample led to a NH.sub.4.sup.+ concentration of 0.05 g/L at 120 min, in which case the composite material shows the optimal nitrogen fixation effect. In addition, pure Co.sub.2SiO.sub.4 (Comparative Example 1) is prone to agglomeration in water, and its nitrogen fixation efficiency gradually decreases after a period of reaction. However, the Co.sub.2SiO.sub.4/C loaded with a carbon layer material has excellent dispersibility and can retain a high nitrogen fixation rate within a given period of time.

Example 2

(14) (1) A attapulgite powder was mixed with ammonium sulfate in a ceramic crucible at a mass ratio of 1:2, and then the crucible was put in a muffle furnace and heated to 500° C. at a rate of 2° C./min, then kept at the temperature for 2 h, and naturally cooled to room temperature; a calcination product was dispersed in a 2 mol/L hydrochloric acid solution at a solid-to-liquid ratio of 1:20, and water bath heating reaction under stirring was conducted at 80° C. for 6 h; and a resulting solid was separated, washed, and dried to obtain a white SiO.sub.2 powder.

(15) (2) 0.6 g of the prepared SiO.sub.2 powder was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 20 mmol of Co(NO.sub.3).sub.2.6H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min; and 1.43 g of sucrose was then added to obtain a mixture suspension.

(16) (3) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 140° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(17) (4) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground into powder to obtain a silicate/carbon composite (0.2Co.sub.2SiO.sub.4/C).

(18) Subsequent detection was conducted with reference to Example 1. The NH.sub.4.sup.+ concentration reached 0.05 g/L at 120 min.

Example 3

(19) (1) A attapulgite powder was mixed with ammonium sulfate in a ceramic crucible at a mass ratio of 1:3, and then the crucible was put in a muffle furnace and heated to 500° C. at a rate of 2° C./min, then kept at the temperature for 2 h, and naturally cooled to room temperature; a calcination product was dispersed in a 2 mol/L hydrochloric acid solution at a solid-to-liquid ratio of 1:20, and water bath heating reaction under stirring was conducted at 80° C. for 6 h; and a resulting solid was separated, washed, and dried to obtain a white SiO.sub.2 powder.

(20) (2) 0.9 g of the prepared SiO.sub.2 powder was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 30 mmol of Co(NO.sub.3).sub.2.6H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min; and 1.43 g of sucrose was then added to obtain a mixture suspension.

(21) (3) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 160° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(22) (4) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground into powder to obtain a silicate/carbon composite (0.3Co.sub.2SiO.sub.4/C).

(23) Subsequent detection was conducted with reference to Example 1. The NH.sub.4.sup.+ concentration reached 0.042 g/L at 120 min.

Example 4

(24) (1) A attapulgite powder was mixed with ammonium sulfate in a ceramic crucible at a mass ratio of 1:4, and then the crucible was put in a muffle furnace and heated to 500° C. at a rate of 2° C./min, then kept at the temperature for 2 h, and naturally cooled to room temperature; a calcination product was dispersed in a 2 mol/L hydrochloric acid solution at a solid-to-liquid ratio of 1:20, and water bath heating reaction under stirring was conducted at 80° C. for 6 h; and a resulting solid was separated, washed, and dried to obtain a white SiO.sub.2 powder.

(25) (2) 0.6 g of the prepared SiO.sub.2 powder was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 10 mmol of Fe(NO.sub.3).sub.3.9H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min; and 1.43 g of sucrose was then added to obtain a mixture suspension.

(26) (3) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 180° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(27) (4) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground into powder to obtain a silicate/carbon composite (0.1FeSiO.sub.3/C).

(28) Subsequent detection was conducted with reference to Example 1. The NH.sub.4.sup.+ concentration reached 0.036 g/L at 20 min.

Example 5

(29) (1) A attapulgite powder was mixed with ammonium sulfate in a ceramic crucible at a mass ratio of 1:5, and then the crucible was put in a muffle furnace and heated to 500° C. at a rate of 2° C./min, then kept at the temperature for 2 h, and naturally cooled to room temperature; a calcination product was dispersed in a 2 mol/L hydrochloric acid solution at a solid-to-liquid ratio of 1:20, and water bath heating reaction under stirring was conducted at 80° C. for 6 h; and a resulting solid was separated, washed, and dried to obtain a white SiO.sub.2 powder.

(30) (2) 0.3 g of the prepared SiO.sub.2 powder was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 10 mmol of Ni(NO.sub.3).sub.2.6H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min; and 1.43 g of sucrose was then added to obtain a mixture suspension.

(31) (3) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 200° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(32) (4) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground into powder to obtain a silicate/carbon composite (0.1Ni.sub.2SiO.sub.4/C).

(33) Subsequent detection was conducted with reference to Example 1. The NH.sub.4.sup.+ concentration reached 0.03 g/L at 120 min.

Comparative Example 1

(34) The operations in Comparative Example 1 were the same as that in Example 1 except that no sucrose was added in step (2), so a product did not include a carbon carrier.

(35) (1) Attapulgite was mixed with ammonium sulfate in a ceramic crucible at a mass ratio of 1:1, and then the crucible was put in a muffle furnace and heated to 500° C. at a rate of 2° C./min, then kept at the temperature for 2 h, and naturally cooled to room temperature; a calcination product was dispersed in a 2 mol/L hydrochloric acid solution at a solid-to-liquid ratio of 1:20, and water bath heating reaction under stirring was conducted at 80° C. for 6 h; and a resulting solid was separated, washed, and dried to obtain white SiO.sub.2.

(36) (2) 0.3 g of the prepared SiO.sub.2 was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 10 mmol of Co(NO.sub.3).sub.2.6H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min to obtain a mixture suspension.

(37) (3) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 120° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(38) (4) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground into powder to obtain a silicate material (Co.sub.2SiO.sub.4).

(39) Subsequent detection was conducted with reference to Example 1. The NH.sub.4 concentration only reached 0.015 g/L at 120 min.

Comparative Example 2

(40) The operations in Comparative Example 2 were the same as that in Example 1 except that a conventional commercially-available SiO.sub.2 powder was used.

(41) (1) 0.3 g of the commercially-available SiO.sub.2 powder was dispersed in water to obtain a SiO.sub.2 suspension, and the suspension was subjected to ultrasonic dispersion for 30 min; then 10 mmol of Co(NO.sub.3).sub.2.6H.sub.2O was dissolved in the above suspension, 20 mmol of NH.sub.4Cl was added to the suspension, 1 mL of 28% ammonia water was added dropwise to the suspension, and a resulting mixture was stirred for 10 min; and 1.43 g of sucrose was then added to obtain a mixture suspension.

(42) (2) The suspension obtained above was transferred to a 100 mL PTFE hydrothermal reactor, and microwave reaction was conducted at 120° C. for 2 h; a resulting mixture was naturally cooled to room temperature and centrifuged; and a resulting solid was separated, washed, and dried.

(43) (3) The solid obtained above was subjected to thermal treatment at 500° C. for 2 h in a muffle furnace, and a resulting product was ground into powder to obtain a silicate/carbon composite (0.1Co.sub.2SiO.sub.4/C).

(44) Subsequent detection was conducted with reference to Example 1. The NH.sub.4.sup.+ concentration only reached 0.005 g/L at 120 min.