阅读说明：本技术 具有三维疏松结构的分子掺杂改性石墨相氮化碳光催化剂及其制备方法与应用 (Molecular doping modified graphite phase carbon nitride photocatalyst with three-dimensional loose structure and preparation method and application thereof ) 是由 师进文 郑博通 张亚周 关祥久 郭烈锦 于 2019-10-14 设计创作，主要内容包括：本发明公开了一种具有三维疏松结构的分子掺杂改性石墨相氮化碳光催化剂及其制备方法和应用,该方法利用顺丁烯二酸酰肼与三聚氰胺的共聚合反应以及二次热处理得到的三维疏松结构的分子掺杂石墨相氮化碳光催化剂及其制备方法,该方法选择顺丁烯二酸酰肼作为有机单体,三聚氰胺作为石墨相氮化碳前驱体,采用直接煅烧法即得产品。本发明制备的三维疏松结构分子掺杂改性石墨相氮化碳,首次以酰肼类有机化合物作为有机单体,得到三维疏松结构分子掺杂改性的石墨相氮化碳光催化剂。该制备方法有效改善了石墨相氮化碳的可见光催化产氢性能。本发明操作简单,重复性好,扩展了石墨相氮化碳的改性方式以及在光催化和电化学方面的应用。(The invention discloses a molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure, a preparation method and application thereof. The three-dimensional loose structure molecule doped modified graphite phase carbon nitride photocatalyst prepared by the invention is obtained by taking hydrazide organic compounds as organic monomers for the first time. The preparation method effectively improves the visible light catalytic hydrogen production performance of the graphite phase carbon nitride. The method has simple operation and good repeatability, and expands the modification mode of graphite-phase carbon nitride and the application of the graphite-phase carbon nitride in photocatalysis and electrochemistry.)

1. A preparation method of a molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure is characterized by comprising the following steps:

at room temperature, melamine and maleic hydrazide are ground and mixed evenly to obtain mixed powder, and the mixed powder is placed in a furnace body for primary heat treatment at the temperature of 5 ℃ for min^-1The temperature rising rate is raised to 520-550 ℃, and the temperature is preserved to ensure that the mixture fully reacts; then cooling to obtain graphite-phase carbon nitride powder subjected to molecular doping modification;

uniformly spreading the molecular doped modified graphite-phase carbon nitride powder in a ceramic square boat, and carrying out secondary heat treatment: at 5 ℃ min^-1The temperature rising rate is increased to 500-530 ℃, and the temperature is preserved to ensure that the mixture fully reacts; and then cooling to obtain the molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure.

2. The method for preparing the molecular-doped modified graphite-phase carbon nitride photocatalyst with a three-dimensional loose structure as claimed in claim 1, wherein the mixed powder is placed in a crucible during one-time heat treatment and the whole heating process, and the crucible needs to be covered to ensure that the whole calcining process is carried out in static air.

3. The preparation method of the molecular doping modified graphite phase carbon nitride photocatalyst with the three-dimensional loose structure according to claim 1, is characterized in that the mass ratio of melamine to maleic hydrazide is (200-25): 1.

4. The preparation method of the molecular doping modified graphite phase carbon nitride photocatalyst with the three-dimensional loose structure according to claim 1, characterized in that the heat preservation time of one-time heat treatment is 2-6 h.

5. The method for preparing the molecular doping modified graphite phase carbon nitride photocatalyst with the three-dimensional loose structure according to claim 1, characterized in that the cooling is natural cooling.

6. The preparation method of the molecular doping modified graphite phase carbon nitride photocatalyst with the three-dimensional loose structure according to claim 1, characterized in that the heat preservation time of the secondary heat treatment is 3-6 h.

7. The molecular-doped modified graphite-phase carbon nitride photocatalyst prepared by the preparation method of any one of claims 1 to 6, wherein the photocatalyst has a three-dimensional nanosheet structure.

8. The use of the molecular-doped modified graphite-phase carbon nitride photocatalyst with a three-dimensional loose structure according to claim 7 in photocatalytic hydrogen production.

Technical Field

The invention belongs to the field of hydrogen energy preparation, and relates to a photocatalytic clean preparation technology of hydrogen energy, namely a photocatalytic hydrogen production technology taking water as a raw material under the condition of simulating sunlight visible light irradiation, in particular to a molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure, and a preparation method and application thereof.

Background

With the gradual depletion of traditional fossil energy such as petroleum, coal and natural gas and the increasing severity of environmental problems, mankind will face an unprecedented energy crisis. Therefore, developing and developing clean and renewable energy sources is an effective way to solve the crisis, and governments around the world also pay great attention to the research direction. The new energy sources with potential at present are solar energy, geothermal energy, wind energy, ocean energy, nuclear energy, biomass energy and the like which exist in nature. The solar energy is an energy which can be inexhaustible in theory and does not pollute the environment, and has great development space. But the utilization of solar energy is also greatly limited due to the characteristics of instability, strong dispersibility, discontinuity, unevenness and the like of the solar energy. Therefore, how to efficiently convert solar energy into chemical energy or electric energy is a difficult problem to overcome at the present stage and is the biggest bottleneck of marketization application. China insists on a sustainable development road, develops new energy according with the sustainable development strategy of China, and if solar energy can be fully utilized, the solar energy can play a great role in promoting future economic development of China.

Because hydrogen gas directly produces water by burning, energy density is high, and a large amount of water resources exist on the earth and can be recycled, and hydrogen has the advantages of storage, transportability, no pollution and the like, and hydrogen energy is considered as an ideal secondary energy source. With the rapid development of various hydrogen energy utilization technologies represented by fuel cells, the demand for hydrogen energy in the future will rise greatly. It is anticipated that the hydrogen economy age may come into the future. However, there are some problems restricting the development of hydrogen energy, such as to really realize the use of hydrogen as energy, and a series of key problems of hydrogen mass production, storage and transportation need to be solved. According to the energy conservation theorem, the hydrogen production process inevitably needs to consume energy, and researches show that substances such as water, biomass, natural gas, coal and the like can be used as hydrogen production raw materials. In consideration of factors such as sustainable development and renewable energy sources, water and biomass are used as raw materials, and hydrogen production by solar energy is a relatively good hydrogen production way. The solar photocatalytic water splitting hydrogen production provides a possible realization way for the hydrogen energy conversion of solar energy, and is a high-salary technology which has the most potential to realize industrial production and obtain cheap hydrogen at present and even in the future.

The principle of photocatalytic water splitting hydrogen production is as follows: under the irradiation of certain energy light, the catalyst is excited to generate electron and hole pairs. The electron and hole pairs migrate to the surface of the catalyst where the electrons and water react to form hydrogen gas and the holes are consumed by the appropriate sacrificial agent added to the system. The key to realize the solar photocatalytic water decomposition is to find a high-efficiency, low-cost and stable visible light photocatalyst. Although a large number of visible light-responsive photocatalysts are reported internationally, the requirements of high efficiency, low cost and the like are still far away.

Organic semiconductor graphite phase carbon nitride (g-C)₃N₄) The photocatalyst has the advantages of low cost, easy preparation, stable structure, proper band edge position, environmental friendliness and the like, and is one of the visible-light-driven photocatalysts with great prospects. However, the absorption and utilization of visible light are quite limited, the recombination of photon-generated carriers is serious, and a small specific surface area cannot provide more photocatalytic reaction sites, so that the photocatalytic hydrogen production performance is poor.

Disclosure of Invention

In order to solve the problem of poor hydrogen production performance of photocatalytic decomposition of water by graphite-phase carbon nitride in the prior art, the invention aims to provide a molecular-doped modified graphite-phase carbon nitride photocatalyst with a three-dimensional loose structure, and a preparation method and application thereof.

In order to achieve the purpose, the invention adopts the following technical means:

a preparation method of a molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure comprises the following steps:

at room temperature, melamine and maleic hydrazide are ground and mixed evenly to obtain mixed powder, and the mixed powder is placed in a furnace body for primary heat treatment at the temperature of 5 ℃ for min^-1The temperature rising rate is raised to 520-550 ℃, and the temperature is preserved to ensure that the mixture fully reacts; then cooling to obtain graphite-phase carbon nitride powder subjected to molecular doping modification;

uniformly spreading the molecular doped modified graphite-phase carbon nitride powder in a ceramic square boat, and carrying out secondary heat treatment: at 5 ℃ min^-1The temperature rising rate is increased to 500-530 ℃, and the temperature is preserved to ensure that the mixture fully reacts; and then cooling to obtain the molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure.

During the whole heating process of one-time heat treatment, the mixed powder is placed in a crucible which needs to be covered so as to ensure that the whole calcining process is carried out in static air.

The mass ratio of the melamine to the maleic hydrazide is (200-25): 1.

The primary heat treatment heat preservation time is 2-6 h.

The cooling is natural cooling.

The heat preservation time of the secondary heat treatment is 3-6 h.

The photocatalyst has a three-dimensional nanosheet structure.

An application of a molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure in photocatalytic hydrogen production.

Compared with the prior art, the invention has the following advantages:

according to the invention, the hydrazide compound is used as an organic monomer to be introduced into the photocatalyst for preparation and modification for the first time, and the prepared catalyst has a special three-dimensional loose nano structure, so that the photocatalytic hydrogen production activity of graphite-phase carbon nitride is greatly improved. On one hand, the introduction of the maleic hydrazide is subjected to copolymerization with melamine to promote charge separation, namely, part of heptazine ring structural units are replaced by organic groups of the maleic hydrazide in the molecular doping process to participate in the construction of valence band tops, so that the band gap is narrowed, the generation of more photogenerated carriers is promoted, the transfer of photogenerated electrons from the organic groups of the maleic hydrazide to adjacent heptazine ring structural units is enhanced, and the effective separation of the photogenerated carriers is realized; on the other hand, the molecular-doped modified graphite-phase carbon nitride nanosheet with the three-dimensional loose structure, which is obtained through secondary heat treatment, has rich pores, is beneficial to light capture, and enhances the light absorption.

The molecular doping modified graphite-phase carbon nitride with the three-dimensional loose structure effectively improves the visible light catalytic hydrogen production performance of the graphite-phase carbon nitride, and the visible light catalytic hydrogen production activity of the molecular doping modified graphite-phase carbon nitride reaches 7689.6 mu mol h^-1g^-1Is 31.5 times of pure graphite phase carbon nitride, and has an apparent quantum efficiency of 8.53% at 425 nm. The method is simple to operate and good in repeatability, and expands the modification mode of graphite-phase carbon nitride and the application of the graphite-phase carbon nitride in photocatalysis.

Drawings

Fig. 1 is (a) (b) SEM images and (c) micro-nano structure schematic diagrams and (d) TEM images of three-dimensional loose-structure molecule-doped modified graphite-phase carbon nitride.

FIG. 2 is (a) (b) SEM and (c) (d) TEM of pure graphite phase carbon nitride and molecular-doped modified graphite phase carbon nitride.

FIG. 3 is N of pure graphite phase carbon nitride, molecular doped graphite phase carbon nitride, and three-dimensional loose structure molecular doped modified graphite phase carbon nitride₂Adsorption and desorption curves.

FIG. 4 shows XRD (a) and FT-IR (850 to 750 cm) of pure graphite-phase carbon nitride, molecularly-doped graphite-phase carbon nitride, and three-dimensional loose-structure molecularly-doped modified graphite-phase carbon nitride^-1) And (c) Uv-vis spectra.

Fig. 5 shows (a) XPS broad spectrum, (b) C1 s spectrum, (C) N1s spectrum, and (d) valence band spectrum of pure graphite-phase carbon nitride and molecular-doped modified graphite-phase carbon nitride.

Fig. 6 is a super cell model of (a) graphite phase carbon nitride and (b) molecular doped graphite phase carbon nitride for DFT calculations.

Fig. 7(a) is a graph of calculated band structure curve and density of states for graphite phase carbon nitride, fig. 7(b) is a graph of calculated band structure curve and density of states for molecular-doped graphite phase carbon nitride, and MH represents a curve of density of states for the introduced maleic hydrazide organic group.

Fig. 8 is (a) a steady state PL spectrum and (b) a time resolved transient PL spectrum of pure graphite phase carbon nitride, molecular doped graphite phase carbon nitride, and three-dimensional loose structure molecular doped modified graphite phase carbon nitride.

FIG. 9 shows (a) the curves of photocurrent density with time (scan bias: 0.62V vs Ag/AgCl) and (b) the electrochemical impedance spectroscopy (scan bias: 0.15V vs Ag/AgCl, 100 kHz-0.1 Hz) for pure graphite-phase carbon nitride, molecularly-doped graphite-phase carbon nitride, and three-dimensional loose-structured molecularly-doped modified graphite-phase carbon nitride.

Fig. 10 shows (a) hydrogen production activity curves of pure graphite phase carbon nitride, molecular-doped graphite phase carbon nitride, and three-dimensional loose-structure molecular-doped modified graphite phase carbon nitride, and (b) photocatalytic hydrogen production stability test results of three-dimensional loose-structure molecular-doped modified graphite phase carbon nitride.

Fig. 11 is a schematic diagram of hydrogen production activity columns, (a) is a schematic diagram of hydrogen production activity columns of pure graphite phase carbon nitride, molecular-doped graphite phase carbon nitride, and three-dimensional loose-structure molecular-doped modified graphite phase carbon nitride, and (b) is a schematic diagram of quantum efficiency columns of three-dimensional loose-structure molecular-doped modified graphite phase carbon nitride at different excitation wavelengths.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The invention relates to a preparation method of a molecular doping modified graphite phase carbon nitride photocatalyst with a three-dimensional loose structure, which comprises the following steps:

the method comprises the following steps: grinding and uniformly mixing 200-25 parts of melamine and 1 part of maleic hydrazide at room temperature, transferring the mixture into a crucible, putting the crucible into a high-temperature furnace body, and performing grinding and mixing at the temperature of 5 ℃ for min^-1The temperature rising rate is increased to 520-550 ℃, and the temperature is kept for 2-6 h. During the entire heating process, the crucible needs to be covered to ensure that the entire calcination process is carried out in still air. And naturally cooling to room temperature to obtain the molecular doped modified graphite phase carbon nitride.

Step two: 1.0g of prepared molecule is taken to be doped and modified g-C₃N₄Spreading the powder in ceramic square boat at 5 deg.C/min^-1The temperature rise rate is increased to 500-530 ℃, and the temperature is kept for 3-6 h. After naturally cooling to room temperature, the three-dimensional loose structure molecule doped modified graphite phase carbon nitride can be obtained.

The principle is as follows: the method comprises the steps of carrying out copolymerization reaction on maleic hydrazide and melamine and carrying out secondary heat treatment to obtain the three-dimensional loose structure molecule doped modified graphite phase carbon nitride photocatalyst, wherein maleic hydrazide is selected as an organic monomer, melamine is selected as a graphite phase carbon nitride precursor, and a direct calcination method is adopted to obtain the product. Firstly, hydrazide organic compounds are used as organic monomers to obtain the three-dimensional loose structure molecule doped modified graphite-phase carbon nitride photocatalyst, and the visible light catalytic hydrogen production activity of the photocatalyst reaches 7689.6 mu mol h^-1g^-131.5 times that of pure graphite phase carbon nitride, and a table at 425nmThe quantum efficiency can reach 8.53%, and the preparation method effectively improves the visible light catalytic hydrogen production performance of the graphite phase carbon nitride.