OMS-2 / g-c3n4 heterojunction material and preparation method and application thereof

Abstract

The application discloses an OMS-2 / g-C3N4 heterojunction material and a preparation method and application thereof, and belongs to the technical field of material preparation and greenhouse gas CO2 photocatalytic reduction fuel preparation technology.The method is characterized in that MnSO4.H2O, (NH4)2S2O8, (NH4)2SO4, KNO3 and g-C3N4 are dissolved in deionized water to perform a hydrothermal reaction, a black product is obtained through filtration, the black product is washed, dried, ground and calcined, and the OMS-2 / g-C3N4 heterojunction material is obtained after cooling.Compared with a mechanically mixed composite material, the OMS-2 / g-C3N4 composite material is constructed, the advantages of the two materials are utilized, the OMS-2 material with excellent redox performance is expanded to the field of photocatalytic CO2 reduction, the natural photosynthesis is simulated, and finally the greenhouse gas CO2 is reduced to high-value-added fuel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material preparation and photocatalytic reduction of greenhouse gas CO2 to prepare fuel, and particularly relates to an OMS-2 / g-C3N4 heterojunction material and a preparation method and application thereof. BACKGROUND

[0002] The combustion of non-renewable fossil fuels produces a large amount of greenhouse gas CO2, making the environmental and energy problems increasingly prominent. Artificial photosynthesis, i.e. converting atmospheric carbon dioxide into renewable energy through photocatalysis, provides a new way to solve environmental and energy problems. However, the conversion efficiency of artificial photosynthesis is still very low at present, and therefore a large number of studies are committed to improving the light response and carrier separation efficiency of traditional photocatalysts to improve the catalytic performance, such as semiconductor compounding, noble metal deposition, element doping, etc. However, recent research reports that improving the CO2 adsorption capacity of photocatalysts provides another possibility for further improving their photocatalytic CO2 reduction capacity. Semiconductor photocatalysis technology, as a green technology, has attracted the attention of many researchers. Using semiconductors as catalysts and utilizing green solar energy to convert CO2 into clean fuels such as CH4 and CH3OH will help to solve the environmental and energy problems at the same time.

[0003] The open tunnel structure in the cryptomelane-type manganese oxide octahedral molecular sieve (OMS-2) material can realize fast electron conduction, and the alkali metal ions doped in the channel can significantly improve the adsorption capacity of acidic gas CO2, so the OMS-2 material has potential application prospects in the photocatalytic reduction of CO2. However, OMS-2 is mostly used in oxidation reactions, and there is no report on its application in photocatalytic CO2 reduction reaction, which may be limited by its relatively narrow band gap and the easy recombination of photo-generated electrons and holes.

[0004] Graphene-like carbon nitride (g-C3N4) has a series of advantages such as simple preparation, suitable energy band structure and fast electron transmission, and is widely used in photocatalytic CO2 reduction reaction. As a carbon-based material, g-C3N4 can realize fast migration of photo-generated electrons and can form a heterojunction with a variety of semiconductor catalysts to improve the photocatalytic reaction activity. Based on the above characteristics, g-C3N4 is used to modify OMS-2 to synthesize a composite material with high catalytic performance. SUMMARY

[0005] In view of the above problems existing in the prior art, a first technical problem to be solved by the present application is to provide a preparation method of OMS-2 / g-C3N4 heterojunction material, to construct OMS-2 / g-C3N4 composite material, and to improve photocatalytic reduction of CO2 to CO. A second technical problem to be solved by the present application is to provide OMS-2 / g-C3N4 heterojunction material, to reduce greenhouse gas CO2 to high-value-added fuel CO. A third technical problem to be solved by the present application is to provide application of OMS-2 / g-C3N4 heterojunction material in photocatalytic reduction of CO2, for treating problems such as current greenhouse gas CO2 emission polluting the environment.

[0006] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of OMS-2 / g-C3N4 heterojunction material, first, MnSO4·H2O, (NH4)2S2O8, (NH4)2SO4, KNO3 and g-C3N4 are dissolved in deionized water for hydrothermal reaction, and a black product is obtained by filtration, the black product is washed, dried, ground and then calcined, and the OMS-2 / g-C3N4 heterojunction material is obtained after cooling.

[0008] The preparation method of g-C3N4 is that urea is placed in a porcelain crucible, then placed in a muffle furnace for calcination, and taken out after cooling to room temperature.

[0009] The calcination temperature is 550 DEG C, the heating rate is 2 DEG C / min, and the time is 4h.

[0010] The molar ratio of the amount of use of MnSO4·H2O, (NH4)2S2O8, (NH4)2SO4 and KNO3 is 1:1:1.875:2.

[0011] The temperature of the hydrothermal reaction is 120 DEG C, and the reaction time is 20h.

[0012] The drying temperature is 110 DEG C, and the time is 12h.

[0013] The calcination temperature is 300 DEG C, the heating rate is 2 DEG C / min, and the time is 4h.

[0014] The OMS-2 / g-C3N4 heterojunction material prepared by the method.

[0015] The application of the OMS-2 / g-C3N4 heterojunction material in photocatalysis.

[0016] The photocatalysis is the application in photocatalytic reduction of CO2.

[0017] Beneficial effects: Compared with the prior art, the advantages of the present application are:

[0018] (1) The application utilizes g-C3N4 to modify OMS-2, and OMS-2 / g-C3N4 heterojunction materials are prepared, and one-step in-situ growth of OMS-2 on g-C3N4 is realized for the first time. OMS-2 is often used for thermal catalytic oxidation, and is less used in the field of photocatalytic reduction. The application introduces OMS-2 into the field of photocatalytic reduction of CO2 for the first time, and the results show that the OMS-2 / g-C3N4 heterojunction materials constructed exhibit excellent performance in photocatalytic reduction of CO2.

[0019] (2) The OMS-2 / g-C3N4 heterojunction materials prepared in the application have a yield of photocatalytic CO2 reduction to fuel CO that is about 4 times higher than that of mechanically mixed composite materials under pure water and full spectrum conditions. The main reason is that the prepared materials have good light absorption performance, due to the rich surface hydroxyl groups, alkali metal ions K + and higher low-valence manganese content, which is beneficial to the adsorption and activation of CO2 molecules. At the same time, the electronic interaction between the interfaces and the formation of built-in electric field promote the formation of Z-type heterojunction under light, so as to realize the efficient separation of photo-generated electrons and holes, improve the defects of easy recombination of photo-generated electrons and holes of OMS-2, realize the efficient separation of photo-generated electrons and holes, and improve the efficiency of photocatalytic CO2 reduction, and generate high-calorific-value fuel.

[0020] (3) The OMS-2 / g-C3N4 heterojunction materials prepared in the application have strong adsorption, activation and conversion capacity for CO2. The unique pore structure of OMS-2 and the incorporation of alkali metal ions are beneficial to the adsorption and activation of CO2 molecules, and the formation of heterojunction under light and the rapid transfer of electrons are beneficial to the conversion of CO2 molecules.

[0021] (4) The process of the application is simple, convenient for mass production, and deionized water is used as a solvent, which reduces the pollution to the environment in the production process. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 XRD spectrum of the sample prepared in the embodiment;

[0023] Figure 2 TEM image of the OMS-2 / g-C3N4 sample prepared in the embodiment;

[0024] Figure 3 FT-IR spectrum of the sample prepared in the embodiment;

[0025] Figure 4 UV-vis DRS spectrum of the sample prepared in the embodiment;

[0026] Figure 5The photocurrent spectrum of the sample prepared in the present embodiment;

[0027] Figure 6 The impedance spectrum of the sample prepared in the present embodiment;

[0028] Figure 7 The comparison chart of the photocatalytic reduction CO2 performance of the OMS-2 / g-C3N4 sample prepared in the present application and the OMS-2, g-C3N4 and Mn-CN-mix materials under full spectrum irradiation;

[0029] Figure 8 The comparison chart of the photocatalytic reduction CO2 performance of the OMS-2 / g-C3N4 sample prepared in the present application and the KMn2 / CN and KMn / CN2 materials under full spectrum irradiation. DETAILED DESCRIPTION

[0030] The present application will be further described below in conjunction with specific embodiments.

[0031] Embodiment 1:

[0032] Preparation of OMS-2 catalyst: 1.3521 g of MnSO4·H2O, 1.8256 g of (NH4)2S2O8, 1.9821 g of (NH4)2SO4 and 1.6176 g of KNO3 were dissolved in 40 mL of deionized water, and the mixed solution was transferred to a 100 mL hydrothermal kettle, which was placed in an oven and heated to 120℃ for 20 h. After the hydrothermal kettle was cooled to room temperature, the mixture was precipitated and centrifuged, the supernatant was poured off, deionized water was added to wash the precipitate, and the washing was repeated at least three times until the supernatant pH was neutral. After washing, the solid was dried for 12 h, and then ground into powder. The powder was calcined in a muffle furnace at 300℃ for 4 h, and then ground after cooling to obtain powder OMS-2.

[0033] Embodiment 2:

[0034] Preparation of g-C3N4 catalyst: 10 g of urea was placed in a crucible, covered with a crucible cover and placed horizontally in a muffle furnace. The temperature was raised to 550℃ at a rate of 2℃ / min in air, and calcined at this temperature for 4 h. After cooling to room temperature, the g-C3N4 sample was obtained, which was ground and reserved for use.

[0035] Embodiment 3:

[0036] Preparation of OMS-2 / g-C3N4 catalyst: 1.3521 g of MnSO4·H2O and 1.6176 g of KNO3 were dissolved in 20 mL of deionized water, and an appropriate amount of g-C3N4 was ultrasonically dispersed in the above solution. The Mn 2+The molar ratio of g-C3N4 was 1:1, and 1.8256 g (NH4)2S2O8 and 1.9821 g (NH4)2SO4 were dissolved in 20 mL of deionized water, and after complete dissolution, they were added to the previous Mn-containing solution 2+ , K + and g-C3N4 mixed solution, and after ultrasonic dispersion for about 5 min, the mixture was transferred to a 100 mL hydrothermal kettle, placed in an oven, heated to 120°C, and maintained for 20 h. After the hydrothermal kettle was cooled to room temperature, the mixture was precipitated and centrifuged, the supernatant was poured off, deionized water was added to wash the precipitate, and the washing was repeated at least three times until the supernatant pH was neutral. After washing, it was dried for 12 h. The dried solid was ground into powder, calcined at 300°C in a muffle furnace for 4 h, and cooled to obtain OMS-2 / g-C3N4.

[0037] Figure 1 The XRD spectrum of the sample prepared in this example is shown in the figure. Compared with OMS-2 and g-C3N4, the diffraction peak of the (002) crystal plane of g-C3N4 and the diffraction peak of each crystal plane of OMS-2 appeared in OMS-2 / g-C3N4, which indicated that the in-situ growth of OMS-2 on g-C3N4 was successfully realized, and OMS-2 / g-C3N4 composite material was obtained.

[0038] Figure 2 The TEM image of the OMS-2 / g-C3N4 sample prepared in this example is shown in the figure. It can be seen from the figure that the rod-shaped OMS-2 grows on the sheet-shaped g-C3N4 in the TEM image of the OMS-2 / g-C3N4 composite material, which further indicates that the in-situ growth of OMS-2 on g-C3N4 is successfully realized, and the two are in close contact in the OMS-2 / g-C3N4 composite material, and there may be interaction between them at the interface.

[0039] Figure 3 The FT-IR spectrum of the sample prepared in this example is shown in the figure. By comparing the FT-IR spectra of OMS-2, g-C3N4 and OMS-2 / g-C3N4, it was found that OMS-2 / g-C3N4 contained vibration peaks belonging to OMS-2 and g-C3N4, which indicated that OMS-2 and g-C3N4 were successfully combined. Before and after the combination, the vibration peak of the triazine ring of OMS-2 / g-C3N4 at 809 cm -1 was weakened relative to the corresponding peak of g-C3N4, indicating that the vibration intensity of the triazine ring of g-C3N4 in the composite material may have changed, and there may be electronic interaction at the interface.

[0040] Figure 4The UV-vis DRS spectra of the samples prepared in this embodiment are shown in the figure. It can be seen from the figure that OMS-2 and OMS-2 / g-C3N4 have stronger light absorption capacity than g-C3N4, and OMS-2 / g-C3N4 has stronger light absorption capacity than OMS-2 in the ultraviolet-visible light (about 200-650 nm) region.

[0041] Figure 5 The photocurrent spectra of the samples prepared in this embodiment are shown in the figure. Figure 6 The impedance spectra of the samples prepared in this embodiment are shown in the figure. It can be seen from the figure that the OMS-2 / g-C3N4 composite material has stronger photocurrent intensity than OMS-2 and g-C3N4, indicating that the composite material has more excellent separation efficiency of photo-generated electrons and holes and faster light-induced charge transfer capacity. In addition, the OMS-2 / g-C3N4 composite material has a smaller circular arc radius in the EIS test. Generally, a smaller circular arc radius corresponds to smaller resistance in the charge transfer process, indicating that the composite material has higher charge transfer capacity.

[0042] Example 4:

[0043] The photocatalysts prepared in Examples 1-3 were applied to reduce CO2. The experimental steps were as follows:

[0044] The photocatalytic reduction of CO2 was carried out in a 100 mL high-pressure reactor using a 300 W xenon lamp as the light source. 25 mg of catalyst powder was uniformly dispersed in 1.5 mL of deionized water, transferred to a quartz sand plate to disperse the catalyst on the surface, and 0.4 MPa of high-purity CO2 gas was added. Full-spectrum irradiation was carried out for 5 hours. The CO and CH4 products were monitored every 1 hour using an online gas chromatograph. Circulating cooling water was used to maintain the temperature in the device at 25°C during the entire reaction process. The CO2 reduction activity was measured by the amount of CO and CH4 produced per gram of catalyst. The amount of CO and CH4 was obtained by the following formula:

[0045]

[0046]

[0047] where N CO , are the amounts of CO and CH4, respectively; A CO , are the peak areas of gas products CO and CH4 in the gas chromatograph, respectively; C1 and C2 are the standard concentrations of CO and CH4 in the standard gas bottle, respectively; A1 and A2 are the peak areas of CO and CH4 in the gas chromatograph in the standard gas bottle, respectively; P is the pressure of the gas in the reactor; V rV is the volume of the reactor; R is the molar gas constant, R = 8.314 J / (mol·K); T is the reaction temperature, T = 298.15 K; m is the mass of the catalyst cat V is the volume of the reactor; R is the molar gas constant, R = 8.314 J / (mol·K); T is the reaction temperature, T = 298.15 K; m is the mass of the catalyst

[0048] Figure 7 The figure is a comparison of the photocatalytic reduction of CO2 performance of the OMS-2 / g-C3N4 sample prepared in this embodiment with OMS-2, g-C3N4 and Mn-CN-mix material under full spectrum irradiation. As can be seen from the figure, compared with OMS-2 and g-C3N4, the OMS-2 / g-C3N4 composite material has more excellent photocatalytic reduction performance, not only can produce more CO, but also can produce more fuel CH4 with higher heat value, and improve the photocatalytic resource utilization of CO2. Among them, the Mn-CN-mix material in the figure is a mixed material obtained by mechanically grinding OMS-2 and g-C3N4. Compared with the mechanically mixed Mn-CN-mix material, the yield of OMS-2 / g-C3N4 heterojunction material photocatalytic CO2 reduction to fuel CO is increased by about 4 times under pure water and full spectrum conditions. It shows that the synthesis method used in the present application can realize the strong electronic interaction between the interface of OMS-2 and g-C3N4, promote the formation of heterojunction under light, and show better activity in the photocatalytic CO2 reduction reaction. There is no strong interface interaction in the mechanically mixed sample, so the photocatalytic CO2 reduction reaction performance is poor.

[0049] Comparative Example 1

[0050] Preparation of KMn2 / CN material: 1.3521 g of MnSO4·H2O and 1.6176 g of KNO3 were dissolved in 20 mL of deionized water, and a proper amount of g-C3N4 was ultrasonically dispersed in the above solution, wherein the molar ratio of Mn 2+ to g-C3N4 was 2:1, and 1.8256 g of (NH4)2S2O8 and 1.9821 g of (NH4)2SO4 were dissolved in 20 mL of deionized water. After complete dissolution, it was added to the above solution containing Mn 2+ , K + and g-C3N4, and ultrasonic dispersion was performed for about 5 min. Then the mixture was transferred to a 100 mL hydrothermal kettle, placed in an oven, heated to 120°C, and maintained for 20 h. After the hydrothermal kettle was cooled to room temperature, the mixture was precipitated and centrifuged, and the supernatant was poured off. Deionized water was added to wash the precipitate, and the washing was repeated at least three times until the supernatant was neutral. After washing, the precipitate was dried for 12 h. The dried solid was ground into powder, calcined at 300°C in a muffle furnace for 4 h, and then ground to obtain the KMn2 / CN material.

[0051] Comparative Example 2

[0052] Preparation of KMn / CN2 material: 1.3521 g of MnSO4·H2O and 1.6176 g of KNO3 were dissolved in 20 mL of deionized water, and an appropriate amount of g-C3N4 was ultrasonically dispersed in the above solution, wherein the molar ratio of Mn 2+ to g-C3N4 was 1:2, and 1.8256 g of (NH4)2S2O8 and 1.9821 g of (NH4)2SO4 were dissolved in 20 mL of deionized water. After complete dissolution, the solution was added to the above solution containing Mn 2+ , K + , and g-C3N4, and ultrasonic dispersion was performed for about 5 min. Then, the mixture was transferred to a 100 mL hydrothermal kettle, placed in an oven, heated to 120°C, and maintained for 20 h. After the hydrothermal kettle was cooled to room temperature, the mixture was precipitated and centrifuged, the supernatant was poured out, deionized water was added to wash the precipitate, and the washing was repeated at least three times until the pH of the supernatant was neutral. After washing, the solid was dried for 12 h. The dried solid was ground into powder, calcined at 300°C in a muffle furnace for 4 h, cooled, and ground to obtain the KMn / CN2 material.

[0053] The KMn2 / CN and KMn / CN2 materials were subjected to photocatalytic reduction of CO2 performance test under full spectrum irradiation, Figure 8 The OMS-2 / g-C3N4 sample prepared in this example was compared with the KMn2 / CN and KMn / CN2 materials in terms of photocatalytic reduction of CO2 performance under full spectrum irradiation. As can be seen from the graph, the OMS-2 / g-C3N4 composite material has more excellent photocatalytic reduction performance, indicating that controlling the molar ratio of Mn 2+ to g-C3N4 to 1:1 can obtain a composite material with more excellent photocatalytic reduction performance. The reason for the difference in activity may be that a lower proportion of g-C3N4 in the composite material is not conducive to the rapid conduction of electrons, showing poorer photocatalytic reduction of CO2 performance; while a higher proportion of g-C3N4 may excessively wrap OMS-2, affecting the adsorption of CO2 by OMS-2, so that the adsorption capacity of the material for CO2 is weakened, showing poorer photocatalytic reduction of CO2 performance.

Claims

1. A method for preparing an OMS-2 / g-C3N4 heterojunction material, characterized in that, MnSO4·H2O, (NH4)2S2O8, (NH4)2SO4, KNO3 and g-C3N4 are dissolved in deionized water to carry out a hydrothermal reaction, a black product is obtained by filtration, the black product is washed, dried, ground and calcined, and the OMS-2 / g-C3N4 heterojunction material is obtained after cooling; the preparation method of the g-C3N4 is that: urea is placed in a porcelain crucible, and then placed in a muffle furnace for calcination, and taken out after cooling to room temperature; the calcination temperature is 550 DEG C, the heating rate is 2 DEG C / min, and the time is 4 h; the molar ratio of the amounts of the MnSO4·H2O, (NH4)2S2O8, (NH4)2SO4 and KNO3 is 1:1:1.875:2; the hydrothermal reaction temperature is 120 DEG C, and the reaction time is 20 h; the drying temperature is 110 DEG C, and the time is 12 h; the calcination temperature is 300 DEG C, the heating rate is 2 DEG C / min, and the time is 4 h.

2. The OMS-2 / g-C3N4 heterojunction material prepared by the method of claim 1.

3. The application of the OMS-2 / g-C3N4 heterojunction material of claim 2 in photocatalysis.

4. The application of the OMS-2 / g-C3N4 heterojunction material of claim 3 in photocatalysis, which is the application in photocatalytic reduction of CO2.

Images