Two-dimensional nitrogen-doped carbon-based titanium dioxide composite material, and preparation method and application thereof for degrading and removing organic pollutants in water

Abstract

A preparation method of a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material includes: (1) etching Ti.sub.3AlC.sub.2 with LiF/HCl to prepare two-dimensional transition metal carbide nanosheet; (2) preparing a nanosheet aggregate by electrostatic self-assembly of a two-dimensional transition metal carbide nanosheet and a positively charged nitrogen-containing cationic compound; (3) calcining the nanosheet aggregates to prepare a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material. A method for degrading and removing organic pollutants in water includes (1) etching Ti.sub.3AlC.sub.2 with LiF/HCl to prepare two-dimensional transition metal carbide nanosheet; (2) preparing a nanosheet aggregate by electrostatic self-assembly of a two-dimensional transition metal carbide nanosheet and a positively charged nitrogen-containing cationic compound; (3) calcining the nanosheet aggregates to prepare a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material; (4) placing the two-dimensional nitrogen-doped carbon-based titanium dioxide composite material into water containing organic pollutants to degrade and remove organic pollutants in water.

Claims

1. A preparation method of a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material, comprising the following steps: (1) etching Ti.sub.3AlC.sub.2 with LiF/HCl to prepare a two-dimensional transition metal carbide nanosheet; (2) preparing a nanosheet aggregate by electrostatic self-assembly of the two-dimensional transition metal carbide nanosheet and a positively charged nitrogen-containing cationic compound; (3) calcining the nanosheet aggregate to prepare a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material.

2. The method according to claim 1, wherein in the step (1), the molar ratio of Ti.sub.3AlC.sub.2 to LiF is (7-15):1; the concentration of HCl is 6-9 mol/L; the etching temperature is 20-35° C.; the etching time is 24-48 h; first adding LiF into HCl solution, stirring for 5 minutes to make the solution mix evenly, and then adding Ti.sub.3AlC.sub.2 for etching, the time of adding Ti.sub.3AlC.sub.2 is 5 min.

3. The method according to claim 2, wherein in the step (1), the molar ratio of Ti.sub.3AlC.sub.2 and LiF is 12:1; the concentration of hydrochloric acid is 9 mol/L; the etching temperature is 35° C.; and the etching time is 24 h.

4. The method according to claim 1, wherein in the step (2), the mass ratio of the positively charged nitrogen-containing cationic compound to the two-dimensional transition metal carbide nanosheet is 4:1.

5. The method according to claim 1, wherein the step (2) preparation of the nanosheet further comprises first preparing the nitrogen-containing cationic compound into a homogeneous solution, then mixing it with Ti.sub.3C.sub.2 MXene, stirring, centrifuging to get the precipitate, and freeze-drying to prepare nanosheet aggregate.

6. The method according to claim 1, wherein in the step (3), the nanosheet aggregate is roasted in a high temperature tube furnace, using CO.sub.2 as the roasting atmosphere, the flow rate is 75-90 sccm, the roasting temperature is 550˜700° C., the heating rate is 6-10° C./min, keeping the temperature for 2-4 h, and finally, the two-dimensional nitrogen-doped carbon-based titanium dioxide composite material is prepared by natural cooling.

7. A method for degrading and removing organic pollutants in water, comprising the following steps: (1) etching Ti.sub.3AlC.sub.2 with LiF/HCl to prepare a two-dimensional transition metal carbide nanosheet; (2) preparing a nanosheet aggregate by electrostatic self-assembly of the two-dimensional transition metal carbide nanosheet and a positively charged nitrogen-containing cationic compound; (3) calcining the nanosheet aggregate to prepare a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material; (4) placing the two-dimensional nitrogen-doped carbon-based titanium dioxide composite material into water containing organic pollutants to degrade and remove organic pollutants in water.

8. The method according to claim 7, wherein in the step (4), said organic pollutants comprise phenol.

9. The method according to claim 7, wherein in the step (1), the molar ratio of Ti.sub.3AlC.sub.2 to LiF is (7-15):1; the concentration of HCl is 6-9 mol/L; the etching temperature is 20-35° C.; the etching time is 24-48 h; first adding LiF into HCl solution, stirring for 5 minutes to make the solution mix evenly, and then adding Ti.sub.3AlC.sub.2 for etching, the time of adding Ti.sub.3AlC.sub.2 is 5 min.

10. The method according to claim 9, wherein in the step (1), the molar ratio of Ti.sub.3AlC.sub.2 and LiF is 12:1; the concentration of hydrochloric acid is 9 mol/L; the etching temperature is 35° C.; and the etching time is 24 h.

11. The method according to claim 7, wherein in the step (2), the mass ratio of the positively charged nitrogen-containing cationic compound to the two-dimensional transition metal carbide nanosheet is 4:1.

12. The method according to claim 7, wherein the step (2) preparation of the nanosheet further comprises first preparing the nitrogen-containing cationic compound into a homogeneous solution, then mixing it with Ti.sub.3C.sub.2 MXene, stirring, centrifuging to get the precipitate, and freeze-drying to prepare nanosheet aggregate.

13. The method according to claim 7, wherein in the step (3), the nanosheet aggregate is roasted in a high temperature tube furnace, using CO.sub.2 as the roasting atmosphere, the flow rate is 75-90 sccm, the roasting temperature is 550˜700° C., the heating rate is 6-10° C./min, keeping the temperature for 2-4 h, and finally, the two-dimensional nitrogen-doped carbon-based titanium dioxide composite material is prepared by natural cooling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a SEM image of Ti.sub.3C.sub.2 MXene nanosheet.

(2) FIG. 2 is a TEM of Ti.sub.3C.sub.2 MXene nanosheet.

(3) FIG. 3 is a SEM image of Ti.sub.3C.sub.2 MXene nanosheet after electrostatic self-assembly.

(4) FIG. 4 is a TEM image of two-dimensional nitrogen-doped carbon-based titanium dioxide composite (2D N—(C/TiO.sub.2)).

(5) FIG. 5 is a SEM image of two-dimensional nitrogen-doped carbon-based titanium dioxide composite (2D N—(C/TiO.sub.2)).

(6) FIG. 6 is the image of the visible photocatalytic degradation of phenol by composite material (2D N—(C/TiO.sub.2)) at room temperature.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

(7) Preparation of two-dimensional Ti.sub.3C.sub.2 MXene nanosheet.

(8) 0.8 g lithium fluoride is added into 10 ml 9 mol/L HCl and stirred for about 5 minutes. Ti.sub.3AlC.sub.2 is added in batches within 5 minutes. Then the reaction is stirred at room temperature for 24 hours to etch. The reaction products are ished by centrifugation with water. When pH is 6 or so, ultra-pure water is added. After 10 minutes of hand shaking, the solution is layered and centrifuged again, the two-dimensional transition metal carbide Ti.sub.3C.sub.2 MXene is obtained. The black colloidal suspension is stored in a refrigerator at 4° C.

(9) FIG. 1 is a SEM image of Ti.sub.3C.sub.2 MXene and FIG. 2 is a TEM image of Ti.sub.3C.sub.2 MXene. From the above figure, it can be seen that Ti.sub.3C.sub.2 MXene is a two-dimensional layered material. The thickness of the nanosheet is in the nanometer scale, the size of the plane is in the micron level, with fewer surface defects and larger specific surface area.

Embodiment 2

(10) Protonation of melamine and its Electrostatic self-assembly with Ti.sub.3C.sub.2 MXene nanosheet.

(11) Add 2 g of melamine to a 50 mL flask, add 30 mL of absolute ethanol, and stir vigorously for 1 h. Then, 3 mL of concentrated hydrochloric acid is added to the above mixed solution. The resulting mixture is further stirred for 1 h, then centrifuged, and transferred to an oven to evaporate the solvent; finally, the dried solid is ground into a powder and centrifuged several times with water and ethanol to obtain a protonated melamine as a nitrogen-containing cationic compound.

(12) The protonated melamine is dissolved in 50 mL 0.1 M dilute hydrochloric acid, and the colloidal suspension 50 mL of Ti.sub.3C.sub.2 MXene nanotablets obtained in embodiment 1 is electrostatically self-assembled with protonated melamine according to the weight ratio of etched Ti.sub.3C.sub.2 MXene to protonated melamine as 1:4. When protonated melamine is added to the etched Ti.sub.3C.sub.2 MXene suspension, the positively charged protonated melamine is adsorbed on the surface of the negatively charged Ti.sub.3C.sub.2 MXene nanosheet, and the dispersed nanosheet precipitated in the aqueous solution. The nanosheet is collected by centrifugation and freeze-drying to obtain nanosheet aggregates.

(13) FIG. 3 is a SEM image of nanosheet aggregates obtained by electrostatic self-assembly of Ti.sub.3C.sub.2 MXene and protonated melamine. It can be found that after self-assembly, due to the insertion of the nitrogen-containing cationic compound; it becomes wrinkled, effectively reducing the stack between the Ti.sub.3C.sub.2 MXene nanosheet.

Embodiment 3

(14) Preparation of two-dimensional nitrogen-doped carbon-based titanium dioxide composites (2D N—(C/TiO.sub.2)).

(15) Two-dimensional nitrogen-doped carbon-based titanium dioxide composites are synthesized by placing the above-mentioned freeze-dried nanosheet aggregates in a high temperature tubular furnace in a CO.sub.2 atmosphere with the flow rate of 75 sccm, at a heating rate of 6° C./min to 550° C. for 4 h and cooling naturally.

(16) FIGS. 4 and 5 are TEM and SEM diagrams of two-dimensional nitrogen-doped carbon-based titanium dioxide composites, respectively. It can be seen from the figure that the calcination process does not break the layered skeleton of Ti.sub.3C.sub.2 nanosheet, the composite material maintains a two-dimensional layered morphology, and the two-dimensional carbon-based surface has obvious TiO.sub.2 nanocrystal particles, uniform disperse on the surface. This indicates the successful preparation of a two-dimensional nitrogen-doped carbon-based titanium dioxide composite.

Embodiment 4

(17) The two-dimensional nitrogen-doped carbon-based titanium dioxide composite is placed in simulated wastewater containing phenol, and the Xenon lamp is used as a light source for illumination for a certain period of time, and the curve of phenol concentration in water according to the illumination time is measured to evaluate the photocatalytic degradation effect for organic pollutants in water of the composite under visible light:

(18) Adding the above prepared 50 mg two-dimensional nitrogen-doped carbon-based titanium dioxide composite 2D N—(C/TiO.sub.2) to 50 mL of 20 ppm phenol in water, and stir for 1 h in the dark to achieve adsorption equilibrium. Then, the xenon light source is turned on to perform visible light catalytic degradation of phenol in water.

(19) The specific phenol degradation effect is determined by an ultraviolet-visible spectrophotometer and calculated from the phenol concentration-absorbance operating curve. That is, the absorbance is measured by adding a coloring agent, the degradation efficiency is calculated from the absorbance, and the initial concentration of phenol is recorded as 100%, and then the concentration gradually decreases as the photocatalysis progresses, thereby obtaining a specific phenol degradation curve; After treating the 50 ppm phenol in water for 180 minutes, the phenol residual ratio is also less than 12%.

(20) FIG. 6 shows the degradation curve of 2D N—(C/TiO.sub.2) on phenol in water. The first 60 minutes is the equilibrium adsorption time. The calculation method of phenol degradation rate is as follows:

(21) $D\%=\frac{A_0-A}{A_0}\times 100\%$

(22) A.sub.0 and A are the initial phenol absorbance and test absorbance in the experiment (tested every 30 minutes).

(23) The invention adopts a surface electrostatic assembly of a two-dimensional layered crystalline compound (MXene) titanium carbide (Ti.sub.3C.sub.2) nanosheet containing a nitrogen-containing cationic compound as a raw material, and in situ constructs a two-dimensional nitrogen-doped carbon-based titanium dioxide composite material by a calcination method. Simultaneously achieving nitrogen doping of TiO.sub.2 and its uniform loading on the surface of the carbon material, thereby increasing the absorption of TiO.sub.2 in the visible range and its photo-quantum efficiency (the residual ratio of Ti.sub.3C.sub.2 MXene at 180 minutes is 88%), and overcoming the two major drawbacks of the TiO.sub.2 photocatalyst at one time. It is possible to make TiO.sub.2 photocatalysts more widely used in environmental purification.