Preparation method of nano-hybrid Fe / g-C3N4

Abstract

A kind of preparation method of nano hybrid Fe / g-C3N4 based on spin polarization regulation, 50mg g-C3N4 is dispersed in 50mL 5% polyethylene glycol aqueous solution, ultrasonic dispersion is 10 minutes, 5% polyethylene glycol (PEG) aqueous solution is washed by argon or nitrogen first to remove dissolved oxygen, then g-C3N4 is added to ultrasonic dispersion;FeSO4.7H2O is added again, and magnetic stirring is carried out for 8 hours;Then excess NaBH4 is added in the mixed solution, and stirring is carried out for 30 minutes;Solid sample is washed by deionized water, and centrifuged to collect;The above product is annealed at 300 DEG C in a tube furnace hydrogen argon atmosphere for 2 hours, thereby obtaining nano hybrid Fe / g-C3N4, which is used for photocatalysis and can achieve good effect.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a nanohybrid Fe / g-C3N4 based on spin polarization regulation, and the Fe / g-C3N4 prepared by the method can be used in the field of photocatalysis, for example, photocatalytic reduction of carbon dioxide, and belongs to the technical field of new materials. BACKGROUND

[0002] Solar-driven conversion of CO2 into renewable fuels is an alternative strategy to provide clean and sustainable energy. The conversion of CO2 into value-added chemical fuels, as a kind of artificial photosynthesis, is considered to be one of the solutions to alleviate energy consumption and global warming. Solar-driven CO2 photoreduction into value-added chemical fuels couples the reductive half-reaction of CO2 fixation with a matching oxidative half-reaction (such as water oxidation) to achieve carbon-neutral cycles. Although many semiconductor photocatalysts such as TiO2, ZnIn2S4, and graphite carbon nitride (g-C3N4) have been explored for CO2 photoreduction, the short lifetime (ps-ns) of photoinduced electrons and holes in semiconductors leads to their rapid recombination, which destroys the photocatalytic performance. In particular, in the polymer g-C3N4, the strong Coulomb interaction between photoinduced electrons and holes leads to slow dissociation of excitons and rapid recombination of charges. Traditional methods, such as nanocrystallization, heterostructure construction and coupling of cocatalysts, can accelerate the separation of short-lived photoinduced carriers and migrate to the surface of the photocatalyst to enhance CO2 photoreduction. However, how to effectively promote the dissociation of photoexcited excitons and accelerate the charge transfer in the process of CO2 photoreduction is still a problem to be solved. The electron transfer process is not only dominated by structural and electronic parameters, but also can be manipulated by the spin state of the electron, thereby adjusting the catalytic performance. Spin-selective electron transfer is usually related to magnetic materials or materials with very large spin-orbital coupling. Recent studies have shown that the overpotential required for water oxidation is related to the limitation of electron spin when producing ground-state triplet oxygen molecules, and the spin polarization of magnetic metal oxides is beneficial to the production of paramagnetic triplet oxygen molecules by water oxidation. The improvement of catalytic performance is due to the formation of a conductive path through double exchange interaction, in which process the electrons can be transferred through the oxygen p orbitals between adjacent metal ions. The spin polarization effect is expected to promote the ultrafast charge transfer supporting protons in CO2 photoreduction and the water oxidation process. However, the rapid recombination of photoinduced electron-hole pairs limits its practical application. Here, we use the spin polarization effect in Fe / g-C3N4 nanohybrids as a photocatalyst to improve the efficiency of CO2 photoreduction to CO in the presence of water vapor. The oxidation of Fe nanoparticles on the surface accelerates the dissociation of excitons and spin-selective electron transfer in polymer g-C3N4, and participates in the CO2 photoreduction reaction. In addition, through double exchange, H2O or CO2 on the surface of Fe 2+ / Fe 3+The affinity is also improved, thereby supporting the proton of the CO2 light reduction.

[0003] The inventors of the present application also disclose CN2022115239255 application: a preparation method of g-C3N4 self-assembled nitrogen vacancy powder, comprising the following steps: (1) dissolving dicyandiamide and citric acid in deionized water, then moving the solution into a freeze dryer, and vacuum freeze-drying to remove water to obtain a white powder product; (2) annealing the above product in a muffle furnace at a temperature of 550±25℃ for 2±1 hours, the heating rate is 10±5℃ / min, and after grinding, a graphite phase carbon nitride (g-C3N4) self-assembled nitrogen vacancy powder is obtained. The mass ratio of dicyandiamide and citric acid is 100-300:1, which is used for photocatalysis and can achieve good results, but the material system and application still need to be developed. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of nano-hybrid Fe / g-C3N4 based on spin polarization regulation, which has the advantages of 2+ / Fe 3+ The double exchange effect can provide a superfast charge transfer channel, and the zero-valent Fe can also provide a gathering site for excited electrons to promote the reduction of CO2, and the sample itself has a large specific surface area, so the nano-hybrid Fe / g-C3N4 is a high-performance and low-cost photocatalytic material, and has good effect on reducing carbon dioxide.

[0005] The purpose of the present application is to provide a use of nano-hybrid Fe / g-C3N4 based on spin polarization regulation, i.e. for photocatalysis. 2+ / Fe 3+ The double exchange effect can provide a superfast charge transfer channel, and the zero-valent Fe can also provide a gathering site for excited electrons to promote the reduction of CO2, and the sample itself has a large specific surface area, so the nano-hybrid Fe / g-C3N4 is a high-performance and low-cost photocatalytic material, and has good effect on reducing carbon dioxide.

[0006] The technical scheme of the present application is: a preparation method of nano-hybrid Fe / g-C3N4 based on spin polarization regulation, comprising the following steps: preparing or preparing a certain amount of g-C3N4, then reducing the iron in ferrous sulfate and compounding with g-C3N4, and annealing treatment under a reducing gas atmosphere at high temperature to obtain Fe / g-C3N4;

[0007] The specific steps are as follows: 50 mg of g-C3N4 is dispersed in 50 mL of a 5% polyethylene glycol (PEG) aqueous solution, ultrasonic dispersion is performed for 10 minutes, the 5% polyethylene glycol (PEG) aqueous solution is washed with argon or nitrogen to remove dissolved oxygen, and then g-C3N4 is added for ultrasonic dispersion; FeSO4.7H2O is added, and magnetic stirring is performed for 8 hours; then excess NaBH4 is added to the mixed solution, stirring is performed for 30 minutes, the solid sample is washed with deionized water, and centrifugal collection is performed; the above product is annealed at 300±30℃ for 3±2 hours in a tube furnace in a hydrogen and argon atmosphere; and nanometer hybrid Fe / g-C3N4 is obtained.

[0008] Fe is reduced by using excess NaBH4, and after washing with deionized water and freeze-drying, annealing reduction is performed at a temperature of about 300℃ to obtain nanometer hybrid Fe / g-C3N4.

[0009] The mass ratio of the graphite phase carbon nitride to the iron element in ferrous sulfate is 20±3:1. For example, 50 mg of graphite phase carbon nitride is added to about 12.4 mg of ferrous sulfate heptahydrate.

[0010] A method for preparing the precursor g-C3N4 is as follows: urea is loaded into an alumina crucible with an aluminum foil cover, and is placed into a muffle furnace to be annealed at 600℃ at a heating rate of 5℃ / min for 2±1 hours to obtain g-C3N4.

[0011] A certain amount of FeSO4·7H2O is added to the g-C3N4 dispersion solution, magnetic stirring is performed for 8 hours, then excess NaBH4 about 1g is added to the mixed solution, stirring is performed, the solid sample is washed with deionized water, and centrifugal collection is performed.

[0012] The product obtained by the present application can be used for photocatalytic reduction of CO2 into value-added chemical fuels, and good effects can be achieved.

[0013] The present application has the following advantages: the raw materials urea and ferrous sulfate are low in cost and easy to obtain, the graphite phase carbon nitride is easy to prepare, the preparation process can be completed by magnetic stirring, drying and annealing, and the steps are simple and convenient. The product obtained by the present application can be used for photocatalytic reduction of CO2 into value-added chemical fuels, and good effects can be achieved. The yield of CO in the first hour of reduction of CO2 into CO is 445 μmol g -1 , which is about 20 times that of graphite phase carbon nitride (g-C3N4). BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The product X-ray diffraction (XRD) pattern of the embodiment of the present application includes characterization of three different samples of g-C3N4, Fe / g-C3N4 and Fe.

[0015] Figure 2(a) (b) (c) (d) are Fe, g-C3N4, and different magnification Fe / g-C3N4 scanning electron microscope (SEM) images of the product of the embodiment of the present application;

[0016] Figure 3 are TEM images of the product of the embodiment of the present application, Figure 3 (a) and (b) are transmission electron microscope (TEM) images of g-C3N4 and nano-hybrid Fe / g-C3N4, respectively;

[0017] Figure 4 are UV-visible absorption spectra of the product of the embodiment of the present application;

[0018] Figure 5 are CO production activities of the product of the embodiment of the present application in photocatalytic reduction of carbon dioxide;

[0019] Figure 6 are g-C3N4 and nano-hybrid Fe / g-C3N4 ferromagnetic characterization of the product of the embodiment of the present application.

[0020] Figure 7 are X-ray photoelectron spectroscopy (XPS) images of the product of the embodiment of the present application. DETAILED DESCRIPTION

[0021] The present application specifically includes the following: nano-hybrid graphite phase Fe / C3N4 preparation and characterization; photocatalytic reduction of CO2 performance.

[0022] (1) 50 of urea was taken into an alumina crucible with an aluminum foil cover, and heated to 600℃ at 5℃ / min in air, and kept for 2h, and naturally cooled to room temperature to obtain g-C3N4.

[0023] (2) 45ml of deionized water and 5ml of PEG solution were measured and mixed. 50mg of g-C3N4 was dispersed in the mixed solution, and argon was introduced to wash away dissolved oxygen. The solution was ultrasonically dispersed for 10min, and 5wt% of ferrous sulfate was added.

[0024] (3) The solution was magnetically stirred for 8 hours, and excess sodium borohydride was used to reduce Fe. The solution was collected by centrifugal freeze-drying. In a tube furnace, the final sample was obtained by annealing at 300℃ in a hydrogen-argon atmosphere for 2h, and can be used for photocatalytic reduction of CO2.

[0025] (4) The product was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible absorption spectrum (UV), X-ray photoelectron spectroscopy (XPS) spectrum, and superconducting quantum magnetic measurement system (SQUID).

[0026] Figure 1is the XRD pattern of the product of the embodiment of the present application, containing pure phase g-C3N4, nano-hybrid Fe / g-C3N4 after loading Fe, and Fe obtained by reducing pure ferrous sulfate, the characterization of three different samples. It can be seen that after loading Fe, the Fe signal in the XRD is not obvious, indicating that the content of Fe element is very low.

[0027] Figure 2 (a) (b) (c) (d) are the Fe, g-C3N4, and different magnification Fe / g-C3N4 scanning electron microscope images (SEM) of the product of the embodiment of the present application, g-C3N4 is a two-dimensional flexible nanosheet, and Fe is a nanocube of about 80 nm.

[0028] Figure 3 is a TEM image, Figure 3 (a) and (b) correspond to the transmission electron microscope images (TEM) of g-C3N4 and nano-hybrid Fe / g-C3N4, and the lattice fringes of Fe can be seen at high resolution.

[0029] Figure 4 is the ultraviolet-visible absorption spectrum of the product of the embodiment of the present application, and it can be seen that the light absorption rate is higher after loading Fe.

[0030] Figure 5 is the CO production activity of the product of the embodiment of the present application for photocatalytic reduction of carbon dioxide, which is a sample of g-C3N4 loaded with 5wt% Fe.

[0031] Figure 6 is the ferromagnetic characterization of g-C3N4 and nano-hybrid Fe / g-C3N4, the product of the embodiment of the present application. It can be seen that the sample becomes ferromagnetic after loading Fe.

[0032] Figure 7 is the X-ray photoelectron spectroscopy (XPS) pattern of the product of the embodiment of the present application. Fe 2+ and Fe 3+ form a charge superfast transfer channel.

[0033] Application example

[0034] The photocatalyst prepared in the embodiment is used for photocatalytic reduction of CO2, specifically: first, 0.1g of the photocatalyst is uniformly dispersed in 4.2cm 2The glass reactor was placed on a hole glass sheet, and the volume of the whole reaction system was 230 ml, and the light source was a 300 W xenon lamp; then the reaction system was vacuumed, and high-purity CO2 gas was introduced, so that the pressure in the reaction system was standard atmospheric pressure; then, 0.4 ml of double-distilled water was injected into the system as a reducing agent, and after dark adsorption for several hours, the light was turned on for irradiation, and 1 ml of gas was taken out from the system at intervals and injected into a gas chromatograph to analyze the amount of generated CO.

[0035] The relationship between the amount of CO and time is shown in Figure 5 The results show that the nano hybrid catalyst has the activity of photocatalytic reduction of CO2.

[0036] The above only describes the preferred embodiments of the present application and is not used to limit the present application, although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacement for part of the technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An application of spin-polarized regulated nano-hybrid Fe / g-C3N4 in the photocatalytic reduction of carbon dioxide to carbon monoxide, characterized in that, The preparation method of the nano-hybrid Fe / g-C3N4 includes the following steps: preparing a certain amount of g-C3N4, then reducing the iron in ferrous sulfate and combining it with g-C3N4, and annealing it at high temperature in a reducing gas atmosphere to obtain Fe / g-C3N4; The specific steps for preparing nano-hybrid Fe / g-C3N4 are as follows: 50 mg of g-C3N4 is dispersed in 50 mL of an aqueous solution containing 5% polyethylene glycol (PEG), and ultrasonically dispersed for 10 minutes. The 5% PEG aqueous solution is first flushed with argon gas to remove dissolved oxygen before adding g-C3N4 for ultrasonic dispersion. FeSO4·7H2O is then added, and the mixture is magnetically stirred for 8 hours. Excess NaBH4 is then added to the mixed solution, and the mixture is stirred for 30 minutes. The solid sample is washed with deionized water, centrifuged, freeze-dried, and collected. The product was annealed in a tube furnace under a hydrogen-argon atmosphere at 300±30℃ for 3±2 hours to obtain nano-hybridized Fe / g-C3N4.

2. The application according to claim 1, characterized in that, The preparation method of g-C3N4 is as follows: urea is placed in an alumina crucible with an aluminum foil cover, and then placed in a muffle furnace and annealed at 600℃ for 2±1 hours at a heating rate of 5℃ / min to obtain g-C3N4.

3. The application according to claim 1, characterized in that, The mass ratio of iron in g-C3N4 and ferrous sulfate is 20±3:1.

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