CN108579785B

CN108579785B - High-efficiency visible light decomposition aquatic product H2Preparation method of sulfur-doped carbon nitride

Info

Publication number: CN108579785B
Application number: CN201810359238.1A
Authority: CN
Inventors: 邹菁; 曹媛; 毛冬鹏; 江吉周
Original assignee: Wuhan Institute of Technology
Current assignee: Taihe Gas Jingzhou Co ltd
Priority date: 2018-04-20
Filing date: 2018-04-20
Publication date: 2021-10-12
Anticipated expiration: 2038-04-20
Also published as: CN108579785A

Abstract

The invention relates to the technical field of nano photocatalytic materials, and particularly discloses a method for decomposing aquatic product H by visible light₂Sulfur-doped carbon nitride (S-g-C)₃N₄) The preparation method comprises the following steps: 1) weighing a proper amount of ammonium salt, dissolving the ammonium salt in a container by adding diluted acid, adding a certain proportion of melamine into the solution, uniformly mixing, and heating to be nearly dry; 2) calcining the mixture for 3 to 6 hours at the temperature of 500 to 600 ℃ in the air atmosphere, and naturally cooling the mixture to room temperature to obtain the high-efficiency visible light decomposed aquatic product H₂Sulfur doped with carbon nitride. The invention has the advantages that: the one-step thermal polymerization method has the advantages of simple and rapid reaction, easy operation, green and pollution-free reaction process, high yield and suitability for practical application.

Description

High-efficiency visible light decomposition aquatic product H2Preparation method of sulfur-doped carbon nitride

Technical Field

The invention relates to the technical field of nano photocatalytic materials, and particularly discloses a method for decomposing aquatic product H by visible light₂Sulfur-doped carbon nitride (S-g-C)₃N₄) The preparation method of (1).

Background

H₂The fuel is considered as an ideal fuel for the future as a green and renewable clean energy source. Currently over 90% H₂Is obtained by reforming methane steam and shifting water gas, and the preparation process needs a large amount of fossil energy, so that the conversion of solar energy is utilized to produce H₂The significance of (A) is great and is a very challenging research work. Decomposition of water under visible light to produce H₂The method is an important new energy utilization research hotspot at present, and compared with thermocatalysis, photocatalysis has obvious advantages in the aspects of energy conservation, environmental protection and cost reduction, but the photocatalysis efficiency is very low at present. How to improve the photocatalytic decomposition of aquatic product H while reducing the cost₂The activity, stability and selectivity of the system become the photocatalytic decomposition of the aquatic product H₂The key to the research is to find high-efficiency light with high yield, simplicity and economyThe catalyst is urgent. The semiconductor material has wide application in the fields of solar cells, photoelectrochemical catalysis, photocatalysis and the like, and is regarded as an indispensable photocatalytic material of potential green clean energy in the future. Graphite phase carbon nitride (g-C)₃N₄) Self-discovery of H production in visible light₂The performance of the catalyst is used as a non-metal catalyst to quickly become a research hotspot of productivity, and the catalyst has great development potential in solar energy conversion. But its low specific surface area (10 m)²g^-1) The catalytic activity of the photocatalyst is severely restricted by the higher photo-generated electron hole recombination efficiency, so that the photocatalytic performance of the photocatalyst is lower. To solve this problem, g-C can be modified by introducing defects, doping or chemical modification₃N₄The modification is carried out to regulate and control the properties of the composition, the electronic structure, the specific surface area and the like, so that the defects can be effectively improved, and the catalytic activity of the catalyst is improved. Such as by pairing g-C₃N₄When the sulfur atom is doped, the dual effects of sulfur doping and stripping can be achieved by generating gas through reaction, and g-C is regulated and controlled₃N₄To obtain ultra-thin g-C doped with sulfur₃N₄The specific surface area is obviously increased, rich carbon vacancy is generated on the surface, more active sites are exposed, the adsorption of water on the surface of the catalyst is facilitated, and the g-C is enhanced₃N₄Photocatalytic decomposition of aquatic product H₂The method has the advantages of high reactivity, exposure of abundant nitrogen elements on the surface, contribution to adsorption of heavy metals and application to detection of heavy metals in the environment. Lead is an accumulated poison, is easily absorbed by intestines and stomach, and influences enzyme and cell metabolism through blood. Therefore, the content of lead in an environmental water sample is an important index for environmental detection and control. The existing national environmental standard detection method specifies the water quality Pb²⁺The determination of the molecular weight has a dithizone spectrophotometry and an atomic absorption method, the detection limit is 10ug/L, but Pb in an environmental water sample²⁺The content of the lead is low, and the methods can not meet the measurement requirement of trace lead, so that the construction of a rapid and sensitive Pb is very necessary at present²⁺The method of (1).

But currently the preparation has visible light catalysisDecomposition of aquatic products H₂ g-C₃N₄The method has the defects of low general yield, long preparation time, complex method, high price and the like, and limits the practical application of the method. Thus, a simple and economical modified g-C with high yield was sought₃N₄The preparation method can be applied to the high-efficiency visible light catalytic decomposition of aquatic product H₂And heavy metal Pb in environmental water sample²⁺The determination of (2) has great practical significance.

Disclosure of Invention

The invention aims to solve the technical problem of providing a visible light decomposition water product H₂Sulfur-doped carbon nitride (S-g-C)₃N₄) The preparation method can solve the problem of graphite phase carbon nitride (g-C)₃N₄) Specific surface area (10 m)²g^-1) Low, few surface active sites and few defects, and visible light catalyzed water splitting to H₂The activity is low.

The technical scheme adopted by the invention for solving the technical problems is as follows: for visible light decomposition of water H₂The preparation method of the sulfur-doped carbon nitride comprises the following steps:

1) weighing a proper amount of ammonium salt, dissolving the ammonium salt in a container by adding diluted acid, adding a certain proportion of melamine into the solution, uniformly mixing, and heating to be nearly dry;

2) calcining the mixture for 3 to 6 hours at the temperature of 500 to 600 ℃ in the air atmosphere, and naturally cooling the mixture to room temperature to obtain the high-efficiency visible light decomposed aquatic product H₂Sulfur doped with carbon nitride.

According to the scheme, the ammonium salt in the step 1) is ammonium sulfate, ammonium persulfate or ammonium chloride.

According to the scheme, the dilute acid in the step 1) is dilute sulfuric acid or dilute hydrochloric acid, and the concentration of the dilute sulfuric acid or the dilute hydrochloric acid is 0.1mol L^-1。

According to the scheme, the molar ratio of the ammonium salt to the melamine in the step 1) is 0.5-1.5.

According to the scheme, the temperature rise rate of the calcination in the step 2) is 5-15 ℃/min. The slower the rate, the longer the thermal polymerization time, the lower the yield; the faster the rate, the shorter the thermal polymerization time, but the thicker the sheet layer of the product.

The product obtained by the above method can be used for visible light decomposition of aquatic product H₂Sulfur doped with carbon nitride.

According to the scheme, the sulfur-doped carbon nitride is ultrathin S-g-C with carbon vacancy₃N₄The thickness of the material is 2 to 8nm, and the specific surface area is 90 to 189m²/g。

The sulfur-doped carbon nitride obtained by the invention is used as an electrocatalyst in the determination of lead in an environmental water sample.

The invention adopts a one-step thermal polymerization method of melamine and ammonium sulfate, and generates a large amount of NH by heating and decomposing the ammonium sulfate₃、SO₂And N₂Gas, which is inserted during the thermal polymerization of melamine to control the polymerization degree thereof, and SO produced by the thermal decomposition of ammonium sulfate₂The gas realizes double effects of sulfur doping and stripping, and the ultrathin S-g-C with rich carbon deficiency is prepared₃N₄The thickness is 2.5nm and the specific surface area is as high as 189m²G, photocatalytic decomposition of aquatic product H₂The speed can reach 4923 mu mol.h^-1·g^-1Each is unmodified g-C₃N₄11.8 times and 12.9 times. The invention can also construct Pb in the environmental water sample²⁺The electrochemical determination method has the detection limit of 3nmoL/L and the practical water sample standard recovery rate of 88-103%, and has the characteristics of low sensitivity, good selectivity and high accuracy.

The invention has the advantages that: the one-step thermal polymerization method has the advantages of simple and rapid reaction, easy operation, green and pollution-free reaction process, high yield and suitability for practical application.

Drawings

FIG. 1 shows S-g-C obtained by the present invention₃N₄A Transmission Electron Microscope (TEM); (b) atomic Force Microscopy (AFM); c) x-ray diffraction patterns (XRD);

FIG. 2 shows S-g-C obtained by the present invention₃N₄(ii) XPS survey of (a); (b) s_2pA spectrum;

FIG. 3 shows S-g-C obtained by the present invention₃N₄The photo-amperometric pattern of (a); (b) an impedance plot;

FIG. 4 shows S-g-C obtained by the present invention₃N₄A (a) of) A hydrogen production diagram by photocatalytic water decomposition; (b) hydrogen production rate diagram by photocatalytic decomposition.

Detailed Description

In order to better understand the present invention, the following examples are further provided to illustrate the present invention, but the present invention is not limited to the following examples.

Example 1

Ammonium sulfate was added to the solution in a volume of 5mL of 0.1mol L^-1H₂SO₄Dissolving, adding melamine with a molar ratio of 1:1, stirring uniformly, heating to near dryness, calcining in a muffle furnace at 550 ℃ at a heating rate of 7.5 ℃/min for 4h, and naturally cooling to room temperature to obtain S-g-C₃N₄₍₁₎As A, the yield was 30%, while bulk g-C₃N₄The yield is generally only 40%. FIG. 1 is a TEM, AFM and XRD pattern thereof. From the TEM image, S-g-C is clearly seen₃N₄In the form of flakes, a lamella thickness of 2.5nm was clearly seen in the AFM chart, and the specific surface area of the product was 189m as measured by a specific surface area meter²(ii) in terms of/g. From the XRD pattern, S-g-C can be seen₃N₄The characteristic peak of the (100) crystal face formed by the 3-s-triazine structural unit forming the plane at 13.1 degrees disappears, and the characteristic peak of the (002) crystal face caused by the layered accumulation of graphite at 27.5 degrees and a pi conjugated plane obviously reduces, which indicates that the sheet layer is obviously thinned. As can be seen from FIG. 2 (a), the product contains C, N and S, and FIG. 2(b) clearly analyzes that the binding energy of S is 168.1 eV, which is consistent with the reference, and indicates that S is successfully incorporated into carbon nitride, and the C/N ratio is changed from 0.75 to 0.64 of bulk, indicating that S occupies carbon sites and the surface has obvious carbon vacancy.

Example 2

The procedure of example 1 was followed except that the ratio of ammonium sulfate to melamine was changed to 1:1.5 and 0.5: 1. To obtain S-g-C₃N_4(1.5)And S-g-C₃N_4(0.5)And are denoted as B and C, respectively.

Example 3

The temperature rise rate is only changed to 15 ℃/min, and the rest steps are the same as the example 1, so that 15 ℃ -S-g-C is obtained₃N₄₍₁₎H produced after being illuminated by 420nm visible light for three hours₂Volume and yield H₂The rates are: 726 mu mol and 4841 mu mol & h^-1·g^-1。

Example 4

And (3) testing photocurrent:

mixing the photocatalyst (A, B, C) with bulk-g-C₃N₄Each of the solutions was prepared as 1.0mg/L aqueous dispersion, and 5. mu.L of the aqueous dispersion was applied onto a glassy carbon electrode surface having a diameter of 3mm by pipetting. Under the illumination condition with the wavelength of 420nm, 1mol/L Na₂SO₄The measured photocurrent ratio of the catalyst in the solution is A, B, C, bulk-g-C₃N₄Approximately equal to 8:6:3:1, as shown in fig. 3(a), where the photocurrent at a is the greatest, indicates the best visible-photocatalytic performance.

Example 5

Electrochemical impedance spectroscopy test:

mixing the photocatalyst A and bulk-g-C₃N₄Prepared into 1.0mg/L aqueous dispersion, 5. mu.L of the aqueous dispersion was applied by pipetting onto a surface of a glassy carbon electrode having a diameter of 3mm, and the solution was mixed in an amount of 0.005mol/L K₃[Fe(CN)₆]/K₄[Fe(CN)₆]And 0.1mol/L KCl solution, and the impedance of the photocatalyst A is obviously lower than bulk-g-C₃N₄The impedance values are 53.9 Ω and 240.6 Ω, respectively, which shows that the faster the charge transport rate of the photocatalyst a surface, the higher the efficiency of separating electrons from holes, and the better the electrocatalytic performance, and the results are shown in fig. 3 (b).

Example 6

Hydrogen test of visible light catalytic decomposition water:

1) 50mg of photocatalyst (A, B, C) was mixed with bulk-g-C₃N₄Respectively adding into 90mL deionized water, adding 10mL triethanolamine and 1 wt% Pt, and irradiating in photoreactor (Labsolalar III (AG) with light source of 300W xenon lamp inserted into 420nm filter) for three hours to obtain H₂The amounts are respectively: a-739. mu. mol, B-530. mu. mol, C-147. mu. mol, bulk-57. mu. mol. Produce H₂The rates are: a-4923. mu. mol. h^-1·g^-1，B-3530μmol·h^-1·g^-1，C-980μmol·h^-1·g^-1，bulk-382 μmol·h^-1·g^-1Wherein A is bulk-g-C₃N₄12.9 times of the total amount of the active hydrogen, has the highest hydrogen decomposition efficiency of water by photocatalysis, and is higher than the g-C reported by general documents₃N₄Both high and the results are shown in figure 4.

2) According to the method 1), 25mg and 100mg of photocatalyst are respectively added, and H is produced after the photocatalyst is irradiated by visible light with the wavelength of 420nm for three hours₂The amounts are respectively: 245 mu mol and 904 mu mol, which produce H₂The rates were 3273. mu. mol g, respectively^-1h^-1And 3012. mu. mol g^-1h^-1。

Example 7

Determination of lead in an environmental water sample:

weighing S-g-C₃N₄Dispersing the modifier in water solution, dripping on a glassy carbon electrode, and performing L-Cysteine electropolymerization to obtain a modified electrode; irradiating with 410nm visible light for 2min, adding 0.4 mLSDS and Pb with different concentrations into pH 4.4NaAc-HAc buffer solution²⁺Solution, potential enrichment at 1.4v for 100s followed by differential pulse scanning according to Pb² ⁺Linear equation of oxidation peak current intensity and its concentration: i is_Pb2+(μA)＝＝0.078C_Pb2+(μ M) +0.31(R ═ 0.988); linear range of 2.5 x 10^-6mol/L-7.5*10^-8mol/L, Pb can be measured²⁺The content and the detection limit are 3nmoL/L, and the standard adding recovery rate applied to an actual water sample is 88-103% (RSD is 1.05%). 100 times Pb²⁺Concentration: k⁺、Na⁺、Zn²⁺、Ca²⁺、Mg²⁺、Fe³⁺、 Hg²⁺、Cl^-、Ac^-、NO^3-No interference occurs; 50 times Pb²⁺Concentration: cr (chromium) component³⁺、Co³⁺No interference occurs; 10 times Pb²⁺Concentration: cd [ Cd ]²⁺Without interference. The constructed method has higher sensitivity and selectivity.

Claims

1. For visible light decomposition of water H₂The preparation method of the sulfur-doped carbon nitride comprises the following steps:

1) weighing a proper amount of ammonium salt, dissolving the ammonium salt in a container by adding diluted acid, adding a certain proportion of melamine into the container, uniformly mixing, heating to be nearly dry, wherein the ammonium salt is ammonium sulfate or ammonium persulfate, and the diluted acid is dilutedThe acid is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 0.1mol L^-1(ii) a The molar ratio of the ammonium salt to the melamine is 0.5-1.5;

2) calcining for 3-6 hours at the temperature of 500-600 ℃ in an air atmosphere, wherein the temperature rise rate of the calcining is 5-15 ℃/min; naturally cooling to room temperature to obtain high-efficiency visible light decomposed aquatic product H₂Sulfur doped with carbon nitride.

2. The method of claim 1, wherein the product H is produced by decomposing visible light₂Sulfur doped with carbon nitride.

3. Use according to claim 2 for decomposing water H with visible light₂The sulfur-doped carbon nitride is characterized in that the sulfur-doped carbon nitride is ultrathin S-g-C with carbon vacancy₃N₄The thickness of the material is 2 to 8nm, and the specific surface area is 90 to 189m²/g。

4. Use of the sulfur-doped carbon nitride of claim 2 as an electrocatalyst in the determination of lead in an ambient water sample.