CN112774714A

CN112774714A - MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst, preparation method and application

Info

Publication number: CN112774714A
Application number: CN202110108004.1A
Authority: CN
Inventors: 姜德立; 宋奇; 李娣; 周以萌
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2021-01-27
Filing date: 2021-01-27
Publication date: 2021-05-11
Anticipated expiration: 2041-01-27
Also published as: CN112774714B

Abstract

The invention belongs to the field of nano materials, and relates to a MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst, a preparation method and application thereof. The invention prepares carbon nitride (g-C) rich in nitrogen vacancy₃N₄) The nano-sheet is prepared by depositing magnesium-aluminum bimetal layered hydroxide (MgAl LDH) on the surface in situ and continuously calcining the magnesium-aluminum bimetal layered hydroxide (MgAl LDH)/nitrogen vacancy carbon nitride composite photocatalytic CO, which is cheap and easy to obtain, has a stable structure and high catalytic activity₂And (4) reducing the material. The MgAlLDO surface has rich Lewis base/acid site, O^2‑、Mg²⁺‑O^2‑And OH group as Lewis base site for CO enhancement₂Adsorption activation capability of (3), Al³⁺And Al³⁺‑O^2‑Increasing H as a Lewis acid site₂O adsorption/dissociation accelerates H₂The oxidation half reaction of O provides more protons, thereby further improvingHigh content of CO₂Activity of reduction. Meanwhile, surface nitrogen vacancies are beneficial to separation of photo-generated electrons and holes, and Lewis acid/alkali and nitrogen vacancies cooperate to ensure that the composite photocatalytic material has excellent photocatalytic CO₂And (4) performance.

Description

MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst, preparation method and application

Technical Field

The invention belongs to the technical field of nano materials and photocatalysis, and relates to a magnesium-aluminum bimetal layered oxide/nitrogen vacancy carbon nitride nanosheet and a preparation method and application thereof.

Technical Field

In recent years, the photocatalytic technology has been widely noticed by researchers due to its characteristics of low operation cost, mild reaction conditions, small secondary pollution and the like. Photocatalytic reduction of CO₂The technology can utilize abundant solar energy to convert greenhouse gas CO₂Conversion to CO, CH₄The valuable chemical raw materials and energy fuels are an ideal method for solving the energy crisis and relieving the greenhouse effect, and the photocatalytic reduction of CO is realized compared with other conversions₂The method has the advantages of cheap and rich raw materials, high added value of carbon-containing products, high energy density of the products and low operation cost, so that the method has important application value in solving the problems of energy crisis and environmental pollution.

Carbon nitride (g-C)₃N₄) As a widely studied metal-free conjugated semiconductor material, the material has the characteristics of low price, simple and convenient synthesis, stable performance, rich reserves, no toxicity, visible light response and the like, and attracts people's extensive attention. However, in practical applications, due to the fast electron-hole recombination, sufficient CO is not available₂Active sites are adsorbed, so that the solar energy utilization rate is low, and CO is subjected to photocatalytic reduction₂The performance is seriously insufficient.

More recently, nitrogen-vacancy rich g-C₃N₄The photocatalytic system exhibits unique advantages in the field of photocatalysis. The surface nitrogen vacancy can adjust the electronic structure of the catalyst, an intermediate energy gap state is formed at the position edge of a conduction band, and photo-generated electrons are excited to the intermediate energy gap state, so that the response range of incident light is expanded. Meanwhile, nitrogen vacancies capture photo-generated electrons, promote the migration of carriers, greatly limit the recombination of the photo-generated electrons and holes, and further improve the g-C₃N₄Photocatalytic activity of (1). However, a single nitrogen vacancy g-C₃N₄Adsorption of activated CO₂The weak capability greatly limits the photocatalytic reduction of CO₂And (4) activity. Thus, a CO was constructed₂g-C with strong adsorption capacity and high activity₃N₄Photocatalytic systems remain a significant challenge.

Introduction of bimetallic layered oxygen in photocatalytic systemsThe catalyst promoter is used as adsorption site for increasing CO₂Adsorption activation and H₂Adsorption/dissociation of O to improve photocatalytic reduction of CO₂Activity of (R.F.Chong, C.H.Su, Y.Q.Du, Y.Y.Fan, Z.Ling, Z.X.Chang, D.L.Li. Journal of Catalysis,2018,363, 92-101). In particular, CO₂The molecule is a linear molecule (AG) which is relatively thermodynamically stable_f ⁰＝-394.4kJ·mol^-1) In the reduction of CO₂The first step in the process requires the introduction of CO₂The molecules are adsorbed on the surface of the catalyst to continue to react, MgO in the magnesium-aluminum bimetal layered oxide (MgAl LDO) is used as an alkaline oxide, and acidic molecules CO₂Is absorbed by MgO to form magnesium carbonate species with low energy, greatly reduces CO₂The adsorption energy of (1). In addition, magnesium aluminum bi-metal layered hydroxides in the calcination to form MgAl LDO, Al³⁺Diffusing into the MgO lattice, adjacent O to maintain charge balance^2-The ion being changed to coordinatively unsaturated O^2-Ions to generate a large amount of Lewis acid (Al)³⁺And Al³⁺-O^2-) Large amounts of Lewis acids capable of enhancing H₂Adsorption and desorption of O, accelerating H₂By oxidation of O to CO₂The reduction reaction provides more protons, thereby improving the photocatalytic reduction of CO₂Activity of (2). Thus, this patent teaches a method of producing a compound in g-C₃N₄Method for introducing nitrogen vacancy and MgAl LDO (magnesium-doped aluminum) on nano sheet and photo-reduction CO of obtained product₂The performance is good, the stability is good, the preparation process is green and environment-friendly, and the method has potential application prospect in energy problems and nano material synthesis.

Disclosure of Invention

The present invention is directed to g-C₃N₄Photocatalytic reduction of CO₂The problem of low conversion rate, and provides a preparation method of a magnesium-aluminum bimetal layered oxide/nitrogen vacancy carbon nitride nanosheet photocatalytic material. The preparation method synthesizes the magnesium-aluminum bimetal layered oxide/nitrogen vacancy carbon nitride nanosheet through a bimetal deposition method, an in-situ deposition method and a calcination method, and the prepared photocatalyst has good photocatalytic reduction effect on CO₂Efficiency.

The technical scheme of the invention is as follows:

a preparation method of MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst comprises the following steps:

(1) preparation of Nitrogen vacancies g-C₃N₄Nanosheets for use;

in step (1), the nitrogen vacancy is g-C₃N₄The preparation method of the nano sheet comprises the following steps: according to the mass ratio of 1: 4-6 weighing DCDA and NH₄Adding Cl into water, stirring to uniformity, freezing the obtained clear solution in a refrigerator at-4 deg.C for 12h, and vacuum freeze drying to obtain white DCDA and NH₄Mixed crystals of Cl, placing the mixed crystals in a semi-closed crucible, and transferring the crucible to an automatic temperature-programmed, elevated tube furnace in a N₂Calcining at the temperature of 500-600 ℃ for 4-6h under the protection of gas, taking out after naturally cooling to room temperature, grinding into powder by using a mortar to obtain the nitrogen vacancy g-C₃N₄Nanosheets.

(2) Preparing a magnesium-aluminum layered double metal layered hydroxide (MgAl LDH) nanosheet material for later use:

measuring a certain amount of Mg (NO)₃)₂·6H₂O and Al (NO)₃)₃·9H₂Stirring the mixed solution of O in a three-neck flask, simultaneously dripping a glycine solution and a NaOH solution into the mixed solution at a certain speed under the protection of argon, continuously stirring for 6-8h, then aging for 12-18h, finally centrifuging, washing with deionized water, precipitating, and drying in vacuum to obtain glycine intercalation calomel layered double hydroxide Gly-MgAl LDH;

dispersing dried Gly-MgAl LDH into deionized water, then adjusting the pH value by using a hydrochloric acid solution, continuously stirring the mixed solution, and finally obtaining a supernatant, namely the MgAl LDH solution, through centrifugation;

in step (2), Mg (NO)₃)₂·6H₂O and Al (NO)₃)₃·9H₂In a mixed solution of O, Mg²⁺And Al³⁺Has a total concentration of 0.5 mol.L^-1And Mg²⁺And Al³⁺In a molar ratio of 3: 1; the dropping speed is 2 seconds per drop;

glycine dissolutionThe concentration of the solution was 0.5 ml.L^-1The concentration of the NaOH solution is 2 mol. L^-1；

Mg(NO₃)₂·6H₂O and Al (NO)₃)₃·9H₂The volume ratio of the mixed solution of O and glycine is 3: NaOH solution maintained the solution pH at 10.

The temperature of the vacuum drying is 60 ℃, and the drying time is 12 h;

the concentration of the MgAl LDH solution is 0.005 g/mL; the concentration of the hydrochloric acid solution is 0.1 mol.L^-1The pH was adjusted to 4 and the stirring time was 24 h.

(3) Preparation of magnesium-aluminum bimetal layered oxide/nitrogen vacancy carbon nitride composite nanosheet material (MgAl LDO/N)_v-CN)：

g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nano-sheets into deionized water, stirring and ultrasonically dispersing to obtain uniform and stable g-C₃N₄Adding MgAl LDH solution dropwise under stirring, heating and stirring to evaporate the mixed solution to dryness to obtain MgAl LDH/N_v-CN nanoplatelets;

weighing a certain amount of MgAl LDH/N_vPutting the-CN nano-sheets into a mortar, grinding the nano-sheets, putting the ground nano-sheets into an alumina porcelain boat, transferring the alumina porcelain boat into a temperature rising tube furnace with automatic program temperature control for calcination, naturally cooling the boat to room temperature, taking the boat out, grinding the boat into powder by using the mortar to obtain MgAl LDO/N_v-CN nanosheet composite photocatalytic material.

In step (3), g-C₃N₄The concentration of the yellow suspension is 0.01 g/mL; the concentration of the MgAl LDH solution is 0.005 g/mL; g-C₃N₄The volume ratio of the yellow suspension to the MgAl LDH solution was 5: 1.

In the step (3), the power of an ultrasonic machine used for ultrasonic dispersion is 250W, and the ultrasonic treatment time is 1 h;

the temperature during heating and stirring is 80 ℃;

the calcination temperature is 350-450 ℃, and the calcination time is 2-4 h.

In the magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material, the magnesium-aluminum bimetal oxide accounts for 5-15%, preferably 10% of the mass ratio of the magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material.

The g-C of the LDO rich in nitrogen vacancies/MgAl₃N₄Nanosheet for photocatalytic reduction of CO₂The use of (1).

Performing morphology and structure analysis on the product by using an X-ray diffractometer (XRD), a Transmission Electron Microscope (TEM) and Electron Paramagnetic Resonance (EPR), and measuring the yield of CO and byproducts thereof within a certain time by using a CEAULIFHT GC-7920 gas chromatography to evaluate the yield of CO in photocatalytic reduction₂Activity of (2).

Compared with the prior art, the invention has the beneficial effects that:

the invention successfully prepares the high-activity magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride nanosheet photocatalyst for the first time by adopting a bimetal deposition method, an in-situ deposition method and a calcination method, and the preparation process has the advantages of simple process, low cost, short period, environmental friendliness and the like. The prepared magnalium bimetallic oxide/nitrogen vacancy carbon nitride nanosheet effectively improves photocatalytic reduction of CO₂The activity of the composite photocatalyst is good, the recyclable stability of the composite photocatalyst is good, and the composite photocatalyst has potential application prospects in the field of development of clean energy.

Drawings

FIG. 1 a, b, C are respectively block g-C₃N₄g-C rich in nitrogen vacancies₃N₄Nanosheet, MgAl LDO/N_v-XRD diffractogram of CN nanoplate.

FIG. 2 a, b, C are block g-C₃N₄g-C rich in nitrogen vacancies₃N₄Nanosheet, MgAl LDO/N_v-EPR profile of CN nanoplatelets.

FIG. 3 shows blocks g-C₃N₄g-C rich in nitrogen vacancies₃N₄Nanosheet, MgAl LDO/N_vTEM image of CN nanoplates.

FIG. 4 shows MgAl LDO nanosheets, and bulk g-C₃N₄g-C rich in nitrogen vacancies₃N₄Nanosheet MgAl LDON_v-CN nanosheet, MgAl LDO/g-C₃N₄g-C of nitrogen-rich vacancy/MgAl LDH₃N₄Photocatalytic reduction of CO by nanosheets₂Activity, 10% MgAl LDO/N prepared_vthe-CN nano-sheet has the most excellent photocatalytic activity, and the CO yield of a sample after 5 hours of catalytic reaction reaches 102.35 mu mol g^-1。

Detailed Description

The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.

Example 1

(1) Preparation of Nitrogen vacancies g-C₃N₄Nanosheet, for use:

1g of DCDA and 5g of NH were weighed out₄Cl, the weighed DCDA and NH₄Adding Cl into 50mL of water in sequence, stirring until the solution is transparent and colorless, freezing the clear solution in a refrigerator at-4 ℃ for 12h, and quickly transferring the frozen solution to a vacuum freeze dryer for freeze drying to obtain white DCDA and NH₄Mixed crystals of Cl, placed in a semi-closed crucible, which is subsequently transferred to an automatically programmed temperature-controlled, elevated-temperature tube furnace in N₂Calcining at 550 deg.C under gas protection for 4h, naturally cooling to room temperature, taking out, grinding into powder with mortar to obtain nitrogen vacancy g-C₃N₄Nanosheets.

(2) Preparing a magnesium-aluminum layered double hydroxide (MgAl LDH) nanosheet material for later use:

5.769g of Mg (NO) were weighed out₃)₂·6H₂O and 2.813g of Al (NO)₃)₃·9H₂Dispersing O into 60ml deionized water, and stirring for 30min to obtain uniform and stable transparent solution. 60ml of Mg (NO)₃)₂·6H₂O and Al (NO)₃)₃·9H₂The O mixed solution was transferred to a three-necked flask and stirred, and 100ml of glycine solution (0.5 ml. L.) was added dropwise to the three-necked flask at a rate of 2 sec/drop under an argon shield^-1) Simultaneously dropwise adding 2 mol. L^-1The pH value of the solution is maintained at about 10 by the NaOH solution, and the solution is continuously added after the dripping is finishedStirring for 6h, aging for 12h, centrifuging at 5000rpm, washing with deionized water to obtain glycine intercalation calomel layered double hydroxide (Gly-MgAl LDH) precipitate, and drying in a vacuum oven at 60 deg.C for 12 h. 0.5g of dried Gly-MgAl LDH is taken to be stirred and ultrasonically dispersed into 100ml of deionized water, and 0.1 mol.L is used^-1The pH was adjusted to 4 with a hydrochloric acid solution, and then the mixed solution was continuously stirred for 24 hours and centrifuged at 5000rpm to obtain a MgAl LDH suspension.

(3) Preparation of magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material (MgAl LDO/N)_v-CN)：

g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nanosheets into 10ml of deionized water, stirring and ultrasonically treating to obtain uniform and stable yellow suspension, dropwise adding MgAl LDH solution at the speed of 2 seconds per drop under the stirring condition, stirring and evaporating the mixed solution at 80 ℃ to dryness to obtain MgAl LDH/N_v-CN nanoplatelets. Weighing a certain amount of MgAl LDH/N_vPutting the-CN nano-sheets into a mortar, grinding the nano-sheets, putting the nano-sheets into an alumina porcelain boat, and then transferring the alumina porcelain boat into a temperature rising tube furnace with automatic program temperature control to calcine the nano-sheets for 3 hours at 400 ℃. Naturally cooling to room temperature, taking out, grinding into powder with a mortar to obtain MgAl LDO/N_v-CN nanosheet composite photocatalytic material.

Example 2

Step (1) of this example is the same as step (2) of example 1;

(2) preparing a magnesium aluminum bimetal oxide (MgAl LDO) nanosheet material: taking 20ml of MgAl LDH suspension, stirring and evaporating at 80 ℃, then grinding the evaporated product into powder in a mortar, placing the powder into an alumina porcelain boat, then transferring the alumina porcelain boat into a temperature rising tube furnace with automatic program temperature control, calcining for 3h at 400 ℃, taking out after naturally cooling to room temperature, and grinding into powder by using the mortar to obtain the MgAl LDO nanosheet material.

Example 3

Step (1) and step (2) of this example are the same as step (1) and step (2) of example 1;

(3) preparation of MgAl LDH/N_v-CN nanosheet composite photocatalysisMaterials: g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nanosheets into 10ml of deionized water, stirring and ultrasonically dispersing to obtain uniform and stable yellow suspension, dropwise adding the MgAl LDH solution obtained in the step (2) under the stirring condition, and stirring and evaporating the mixed solution at 80 ℃ after dropwise adding.

Example 4

(1) Preparation of blocks g-C₃N₄Nano materials: 1g of DCDA was weighed and placed in a semi-closed crucible, which was subsequently transferred to an automatically temperature-programmed, elevated-temperature tube furnace in an N₂Calcining at 550 ℃ for 4h under the protection of gas, naturally cooling to room temperature, taking out, and grinding into powder by using a mortar.

Example 5

Step (1) of this example is the same as step (1) of example 4, and step (2) of this example is the same as step (2) of example 1;

(3) preparation of MgAl LDO/g-C₃N₄The composite photocatalytic material is as follows: the block g-C obtained in the step (1)₃N₄Dispersing in 10ml deionized water, stirring, ultrasonically treating to obtain uniform and stable yellow suspension, dropwise adding MgAl LDH solution at a speed of 2 s/drop under stirring, stirring and evaporating the mixed solution at 80 ℃ to dryness to obtain MgAl LDH/g-C₃N₄. Weighing a certain amount of MgAl LDH/g-C₃N₄The mixture was ground in a mortar and placed in an alumina porcelain boat, which was then calcined at 400 ℃ for 3h in an auto-programmed temperature-controlled elevated tube furnace. After naturally cooling to room temperature, taking out, and grinding into powder by using a mortar.

Example 6

(1) Preparation of 500 ℃ calcined Nitrogen vacancies g-C₃N₄Nanosheet: 1g of DCDA and 5g of NH were weighed out₄Cl, the weighed DCDA and NH₄Adding Cl into 50mL of water in sequence, stirring until the solution is transparent and colorless, freezing the clear solution in a refrigerator at-4 ℃ for 12h, and quickly transferring the frozen solution to a vacuum freeze dryer for freeze drying to obtain white DCDA and NH₄Mixing crystals of Cl, placing the mixed crystals in a semi-closed crucible, and then heating the crucibleTransferred to an automatic temperature programmed heating tube furnace in N₂Calcining at 500 deg.C for 4h under gas protection, naturally cooling to room temperature, taking out, and grinding into powder with mortar.

Example 7

(1) Preparation of 600 ℃ calcined Nitrogen vacancies g-C₃N₄Nanosheet: 1g of DCDA and 5g of NH were weighed out₄Cl, the weighed DCDA and NH₄Adding Cl into 50mL of water in sequence, stirring until the solution is transparent and colorless, freezing the clear solution in a refrigerator at-4 ℃ for 12h, and quickly transferring the frozen solution to a vacuum freeze dryer for freeze drying to obtain white DCDA and NH₄Mixed crystals of Cl, placed in a semi-closed crucible, which is subsequently transferred to an automatically programmed temperature-controlled, elevated-temperature tube furnace in N₂Calcining at 600 deg.C under gas protection for 4h, naturally cooling to room temperature, taking out, and grinding into powder with mortar.

Example 8

Step (1) of this example is the same as step (1) of example 1, and step (2) of this example is the same as step (2) of example 1;

(3) preparation of 350 ℃ calcined magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material (MgAl LDO/N)_v-CN)：

g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nanosheets into 10ml of deionized water, stirring and ultrasonically treating to obtain uniform and stable yellow suspension, dropwise adding MgAl LDH solution at the speed of 2 seconds per drop under the stirring condition, stirring and evaporating the mixed solution at 80 ℃ to dryness to obtain MgAl LDH/N_v-CN nanoplatelets. Weighing a certain amount of MgAl LDH/N_vPutting the-CN nano-sheets into a mortar, grinding the nano-sheets, putting the nano-sheets into an alumina porcelain boat, and then transferring the alumina porcelain boat into an automatic temperature-controlled heating tube furnace to calcine the nano-sheets for 3 hours at 350 ℃. After naturally cooling to room temperature, taking out, and grinding into powder by using a mortar.

Example 9

(3) preparation 450 deg.CCalcined magnesium aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material (MgAl LDO/N)_v-CN)：

g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nanosheets into 10ml of deionized water, stirring and ultrasonically treating to obtain uniform and stable yellow suspension, dropwise adding MgAl LDH solution at the speed of 2 seconds per drop under the stirring condition, stirring and evaporating the mixed solution at 80 ℃ to dryness to obtain MgAl LDH/N_v-CN nanoplatelets. Weighing a certain amount of MgAl LDH/N_vPutting the-CN nano-sheets into a mortar, grinding the nano-sheets, putting the nano-sheets into an alumina porcelain boat, and then transferring the alumina porcelain boat into a temperature rising tube furnace with automatic program temperature control to calcine the nano-sheets for 3 hours at 450 ℃. After naturally cooling to room temperature, taking out, and grinding into powder by using a mortar.

Example 10

(3) preparing a magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material (MgAl LDO/N) with the calcination time of 2h_v-CN)：

g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nanosheets into 10ml of deionized water, stirring and ultrasonically treating to obtain uniform and stable yellow suspension, dropwise adding MgAl LDH solution at the speed of 2 seconds per drop under the stirring condition, stirring and evaporating the mixed solution at 80 ℃ to dryness to obtain MgAl LDH/N_v-CN nanoplatelets. Weighing a certain amount of MgAl LDH/N_vPutting the-CN nano-sheets into a mortar, grinding the nano-sheets, putting the nano-sheets into an alumina porcelain boat, and then transferring the alumina porcelain boat into a temperature rising tube furnace with automatic program temperature control to calcine the nano-sheets for 2 hours at 400 ℃. After naturally cooling to room temperature, taking out, and grinding into powder by using a mortar.

Example 11

(3) preparing a magnesium-aluminum bimetal oxide/nitrogen vacancy carbon nitride composite nanosheet material (MgAl LDO/N) with the calcination time of 4 hours_v-CN)：

g-C of nitrogen vacancy obtained in step (1)₃N₄Dispersing the nanosheets into 10ml of deionized water, stirring and ultrasonically treating to obtain uniform and stable yellow suspension, dropwise adding MgAl LDH solution at the speed of 2 seconds per drop under the stirring condition, stirring and evaporating the mixed solution at 80 ℃ to dryness to obtain MgAl LDH/N_v-CN nanoplatelets. Weighing a certain amount of MgAl LDH/N_vPutting the-CN nano-sheets into a mortar, grinding the nano-sheets, putting the nano-sheets into an alumina porcelain boat, and then transferring the alumina porcelain boat into a temperature rising tube furnace with automatic program temperature control to calcine for 4 hours at 400 ℃. Naturally cooling to room temperature, taking out, grinding into powder with a mortar to obtain MgAl LDO/N_v-CN nanosheet composite photocatalytic material.

Example characterization analysis of Mg-Al layered bimetallic oxide/N-vacancy carbon nitride composite nanoplatelets photocatalyst

FIG. 1 a, b, C are respectively block g-C₃N₄g-C rich in nitrogen vacancies₃N₄g-C of nanosheet and MgAl LDO rich in nitrogen vacancies₃N₄XRD diffraction pattern of the nano-sheet. As can be seen, g-C rich in nitrogen vacancies₃N₄Nanosheets, nitrogen vacancy-rich/MgAl LDO nanosheet composites have been successfully prepared, and the composite samples have high crystallinity and are free of impurities.

From the figure, it can be seen that the maps all belong to g-C₃N₄Diffraction peaks of typical triazine ring planar structure and interlayer structure, and no other phases and impurities were found, indicating that introduction of nitrogen vacancies and MgAl LDO did not affect g-C₃N₄The main body structure of (1). And no MgO or Al is observed₂O₃The diffraction peak of (a) indicates that the MgAl LDO exists in a highly dispersed form.

FIG. 2 a, b, C are block g-C₃N₄g-C rich in nitrogen vacancies₃N₄g-C of nanosheet and MgAl LDO rich in nitrogen vacancies₃N₄EPR spectrum of the nanosheet. Block g-C₃N₄There was a weak EPR peak. And g-C rich in nitrogen vacancies₃N₄g-C of nanosheet and MgAl LDO rich in nitrogen vacancies₃N₄The nano-sheet has obvious EPR peak at g-2.0021, which indicates that at g-C₃N₄Oxygen vacancies are successfully introduced into the nano-chip, and the introduction of the MgAl LDO does not influence the existence of nitrogen vacancies.

FIG. 3 shows blocks g-C₃N₄g-C rich in nitrogen vacancies₃N₄Nanosheets, MgAl LDO nanosheets, and g-C rich in nitrogen vacancies/MgAl LDO₃N₄TEM images of the nanoplates. From FIG. b it can be seen that g-C of nitrogen vacancies was successfully prepared₃N₄Nanosheets. From FIG. d, successful g-C at nitrogen vacancies can be seen₃N₄MgAl LDO nanosheets are introduced into the nanosheets.

FIG. 4 shows MgAl LDO nanosheets, and bulk g-C₃N₄g-C rich in nitrogen vacancies₃N₄Nanosheet, MgAl LDO/N_v-CN nanosheet, MgAl LDO/g-C₃N₄MgAl LDH/nitrogen-rich vacancy g-C₃N₄Photocatalytic reduction of CO by nanosheets₂Active, can show blocky g-C₃N₄Photocatalytic reduction of CO without suitable adsorption sites and electron donors₂The activity of (a) is poor. And g-C rich in nitrogen vacancies₃N₄Nano-sheet photocatalytic reduction of CO₂The activity of (2) is improved because nitrogen vacancies can promote the separation of photogenerated electron holes and accelerate the migration of carriers. MgAl LDO/N obtained after MgAl LDO is introduced_vthe-CN nano-sheet realizes the synergy of MgAl LDO and nitrogen vacancy, and the yield of CO reaches 102.35 mu mol g^-1。

Claims

1. A preparation method of MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst is characterized by comprising the following steps:

(1) preparation of Nitrogen vacancies g-C₃N₄Nanosheets for use;

measuring a certain amount of Mg (NO)₃)₂·6H₂O and Al (NO)₃)₃·9H₂Mixed solution of OStirring in a three-neck flask, simultaneously dropwise adding a glycine solution and a NaOH solution into the mixed solution at a certain speed under the protection of argon, continuously stirring for 6-8h, aging for 12-18h, finally centrifuging, washing with deionized water, precipitating, and vacuum drying to obtain a glycine intercalation calomel layered double hydroxide Gly-MgAl LDH;

2. The process according to claim 1, wherein in step (1), the nitrogen vacancy is g-C₃N₄The preparation method of the nano sheet comprises the following steps: according to the mass ratio of 1: 4-6 weighing DCDA and NH₄Adding Cl into water, stirring to uniformity, freezing the obtained clear solution in a refrigerator at-4 deg.C for 12h, and vacuum freeze drying to obtain white DCDA and NH₄Mixed crystals of Cl, placing the mixed crystals in a semi-closed crucible, and transferring the crucible to an automatic temperature-programmed, elevated tube furnace in a N₂Calcining at 600 deg.C for 4-6h under gas protection, naturally cooling to room temperature, taking out, and grinding into powder with mortar to obtainTo nitrogen vacancy g-C₃N₄Nanosheets.

3. The method according to claim 1, wherein the reaction mixture,

the concentration of glycine solution was 0.5 ml. L^-1The concentration of the NaOH solution is 2 mol. L^-1；

4. The method according to claim 1, wherein, in the step (2),

the temperature of the vacuum drying is 60 ℃, and the drying time is 12 h;

5. The method according to claim 1, wherein the reaction mixture,

6. The method according to claim 1, wherein the reaction mixture,

the temperature during heating and stirring is 80 ℃;

the calcination temperature is 350-450 ℃, and the calcination time is 2-4 h.

7. The MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst is characterized by being prepared by the preparation method of any one of claims 1-6, wherein the mass ratio of the magnesium-aluminum bimetallic oxide to the nitrogen vacancy carbon nitride based composite nanosheet material is 5-15%.

8. Use of the MgAl LDO/nitrogen vacancy carbon nitride based photocatalyst of claim 7 for photocatalytic reduction of CO₂The use of (1).